Radiation Chemistry and its Applications · RADIATION CHEMISTRY AND ITS APPLICATIONS (Technical Reports Series, No. 84) ABSTRACT. The report of a panel convened by the IAEA and held

TECHNICAL REPORTS SERIES No. 84

Radiation Chemistry

and its Applications

?J INTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1968

RADIATION CHEMISTRY AND ITS APPLICATIONS

T h e fo l lowing States a re Member s of the In t e rna t iona l A t o m i c Energy Agency :

AFGHANISTAN GERMANY, FEDERAL NORWAY ALBANIA REPUBLIC OF PAKISTAN ALGERIA GHANA PANAMA ARGENTINA GREECE PARAGUAY AUSTRALIA GUATEMALA PERU AUSTRIA HAITI PHILIPPINES BELGIUM HOLY SEE POLAND BOLIVIA HUNGARY PORTUGAL BRAZIL ICELAND ROMANIA BULGARIA INDIA SAUDI ARABIA BURMA INDONESIA SENEGAL BYELORUSSIAN SOVIET IRAN SIERRA LEONE

SOCIALIST REPUBLIC IRAQ SINGAPORE CAMBODIA ISRAEL SOUTH AFRICA CAMEROON ITALY SPAIN CANADA IVORY COAST SUDAN CEYLON JAMAICA SWEDEN CHILE JAPAN SWITZERLAND CHINA JORDAN SYRIAN ARAB REPUBLIC COLOMBIA KENYA THAILAND CONGO, DEMOCRATIC KOREA, REPUBLIC OF TUNISIA

REPUBLIC OF KUWAIT TURKEY COSTA RICA LEBANON UGANDA CUBA LIBERIA UKRAINIAN SOVIET SOCIALIST CYPRUS LIBYA REPUBLIC CZECHOSLOVAK SOCIALIST LUXEMBOURG UNION OF SOVIET SOCIALIST

REPUBLIC MADAGASCAR REPUBLICS DENMARK MALI UNITED ARAB REPUBLIC DOMINICAN REPUBLIC MEXICO UNITED KINGDOM OF GREAT ECUADOR MONACO BRITAIN AND NORTHERN EL SALVADOR MOROCCO IRELAND ETHIOPIA NETHERLANDS UNITED STATES OF AMERICA FINLAND NEW ZEALAND URUGUAY FRANCE NICARAGUA VENEZUELA GABON NIGERIA VIET-NAM

YUGOSLAVIA

T h e A g e n c y ' s S t a t u t e was approved on 23 October 1956 by the C o n f e r e n c e on the S ta tu te of the IAEA held a t Uni ted Nat ions Headquar te r s , New York; i t en te red in to fo rce on 29 July 1957. T h e H e a d q u a r t e r s of t h e Agency a r e s i tuated in V i e n n a . I ts p r inc ipa l o b j e c t i v e is " to a c c e l e r a t e and en la rge t h e con t r ibu t ion of a t o m i c energy to p e a c e , h e a l t h and prosperi ty throughout t he w o r l d " .

Pr inted by t h e IAEA in Austria April 1968

TECHNICAL REPORTS SERIES No. 84

RADIATION CHEMISTRY AND ITS APPLICATIONS

R E P O R T OF A P A N E L ON RADIATION CHEMISTRY: RECENT D E V E L O P M E N T AND REVIEW OF RANGE

OF A P P L I C A B I L I T Y OF EXISTING SOURCES, HELD IN VIENNA, 17 -21 A P R I L 1967

INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 1968

RADIATION CHEMISTRY AND ITS APPLICATIONS (Techn ica l Reports Series, No . 84)

ABSTRACT. The report of a panel convened by the IAEA and held in Vienna, 1 7 - 2 1 April 1967. The meet ing was attended by 15 specialists from ten countr ies .

Contents: Introduction: Summary of discussions; General observations and recommendat ions; Reports; Communicat ions and comments .

T h e ten reports cover such subjec ts as app l i c a t i on of i on iz ing rad ia t ion t o po lymer c h e m i s t r y , t h e status of chemonuclear reactors and radiation c h e m i c a l processing, synthesis and decomposi t ion induced by ioniz ing radiat ion, and the use of low-energy electron acce le ra to r s for the curing of paints and thin f i l m s . Each report is in its original language (9 English and 1 French) and is preceded by an abstract in English with a second o n e in t h e o r ig ina l l a n g u a g e if th is is not Engl i sh . T h e rest of t h e p u b l i c a t i o n is in Eng l i sh .

(182 p p . , 16 X 24 c m , p a p e r - b o u n d , 2 3 f igures) (1968) Price: US S4.00; £ 1 . 1 3 . 4

RADIATION CHEMISTRY AND ITS APPLICATIONS IAEA, VIENNA, 1968

S T I / D O C / 1 0 / 8 4

F O R E W O R D

In recent y e a r s cons iderab le p r o g r e s s has been made in understanding the fundamental chemica l react ions that occur when mater ia l s are irradiated. This has followed f r o m the development of new techniques for studying these r e a c t i o n s . There have a l s o been s igni f icant advances in s o u r c e technology and in the des ign of a c c e l e r a t o r s for c a r r y i n g out i rradiat ions .

P a r a l l e l to these deve lopments there has been an increas ing in teres t in the industr ial application of c h e m i c a l e f f ec t s of radiation, part icularly in work on p o l y m e r s .

The Internat ional A t o m i c E n e r g y A g e n c y held a P a n e l on R a d i a t i o n C h e m i s t r y in Vienna on 17 - 21 Apr i l 1967 to r e v i e w the current s ta tus of v a r i o u s s o u r c e s , new t e c h n i q u e s in radiat ion c h e m i s t r y , and the i r app l i -c a t i o n s . F i f t e e n s p e c i a l i s t s attended f r o m 10 c o u n t r i e s .

The main sources mentioned by the Panel were isotope sources , electron a c c e l e r a t o r s , and chemonuclear r e a c t o r s . Among the bas i c techniques d i s -c u s s e d w e r e pulsed r a d i o l y s i s , f l a sh photolys i s , fas t ESR methods, i r r a d i -at ion at l iquid h e l i u m t e m p e r a t u r e s , e l e c t r i c d i s c h a r g e m e t h o d s and f a r u l t r a - v i o l e t m e t h o d s . I n t e r e s t i n g indus tr ia l app l i ca t ions w e r e d i s c u s s e d , such as the development of wood-p las t i c combinat ions , and a paper was given on the curing of paints and thin f i l m s .

S u m m a r i e s of the presenta t ions and d i s c u s s i o n s , together with the r e -c o m m e n d a t i o n s and the wr i t ten contr ibut ions , are g iven in th i s report . It i s hoped that the publication wi l l be useful to radiation c h e m i s t s and to those r e s p o n s i b l e for e s tab l i sh ing and operat ing p r o g r a m m e s based on radiat ion c h e m i c a l p r o c e s s e s .

CONTENTS

I . INTRODUCTION 1 II. SUMMARY OF DISCUSSIONS 1 III. GENERAL OBSERVATIONS AND RECOMMENDATIONS 17 IV. R E P O R T S 23

App l i ca t ion of ioniz ing r a d i a t i o n to p o l y m e r c h e m i s t r y ( P L - 236/1) 23 A . Danno

C h a r a c t e r i s t i c s and r a n g e of app l i cab i l i ty of a c c e l e r a t o r s f o r r a d i a t i o n c h e m i c a l p r o c e s s e s ( P L - 2 3 6 / 1 0 ) 43 N. W. Holm

Sta tus r e p o r t on c h e m o n u c l e a r r e a c t o r s and r a d i a t i o n c h e m i c a l p r o c e s s i n g ( P L - 2 3 6 / 4 ) : 53 M. Steinberg

Safe ty f o r l a r g e i r r a d i a t i o n f a c i l i t i e s ( P L - 2 3 6 / 2 ) 63 A. Danno

L o w - t e m p e r a t u r e i r r a d i a t i o n s ( P L - 2 3 6 / 5 ) 67 Z. P. Zagorski and S. Mine

P u l s e r a d i o l y s i s ( P L - 2 3 6 / 6 ) 89 D. F. Sangster

L e déve loppemen t de la r a d i o c h i m i e : que lques a s p e c t s de la c o n j o n c t u r e ( P L - 2 3 6 / 8 ) 93 P. Lévêque et J.R. Puig

Syn thes i s and d e c o m p o s i t i o n induced by ionizing r a d i a t i o n ( P L - 2 3 6 / 7 ) 97 Silvia Ionescu

Rad ia t ion - induced p o l y m e r i z a t i o n : m e c h a n i s m s and i n d u s t r i a l a s p e c t s ( P L - 2 3 6 / 9 ) 125 D. O. Hummel, Christel Schneider, R. C. Potter, G. Ley, J. Denaxas, D. Widdershoven and M. Ryska

T h e use of l o w - e n e r g y e l e c t r o n a c c e l e r a t o r s f o r the c u r i n g of pa in t s and th in f i l m s ( P L - 2 3 6 / 3 ) 165 F.L. Dalton

V. COMMUNICATIONS AND COMMENTS 171 L i s t of p a r t i c i p a n t s 181

I. INTRODUCTION

The u s e of radiat ion in industry has i n c r e a s e d grea t ly during the l a s t f e w y e a r s . Of i m p o r t a n c e h a s been the u s e of rad ia t ion to m o d i f y p o l y m e r s g iv ing c r o s s - l i n k e d and shr inkable p l a s t i c f i l m and tubing. It h a s a l s o b e e n d e m o n s t r a t e d that c h e m i c a l s can be manufac tured by rad ia t ion c h e m i c a l p r o c e s s e s . M o r e r e c e n t l y radiat ion graf t ing of p o l y m e r s on to v a r i o u s s u b s t r a t e s and the manufac ture of c o p o l y m e r s have both b e e n under inves t iga t ion . In t h e s e c a s e s , to obtain opt imum condi t ions , r e s e a r c h i s d i r e c t e d to m a x i m i z e y i e l d s .

In any a tomic e n e r g y p r o g r a m m e t h e r e wi l l be many e x a m p l e s of m a t e r i a l s e x p o s e d to i o n i z i n g radiat ion. R e a c t o r m o d e r a t o r , coolant , c h e m i c a l r e p r o c e s s i n g so lut ions and r a d i o i s o t o p e s m a y be ins tanced . In t h e s e c a s e s it i s n e c e s s a r y to m i n i m i z e the d e l e t e r i o u s e f f e c t s of radiat ion .

Fundamenta l i n v e s t i g a t i o n s in the f i e l d of rad ia t ion c h e m i s t r y have b e e n d i r e c t e d t o w a r d s e luc idat ing the r e a c t i o n m e c h a n i s m s obtained in s y s t e m s subjec ted to radiat ion , and m e a s u r e m e n t s of the r e a c t i o n p a r a m e t e r s . T h i s h a s l e d to a be t t er unders tanding of c h e m i c a l r e a c t i o n s , in g e n e r a l , a s w e l l a s of t h o s e par t i cu lar ly a s s o c i a t e d with r a d i o l y s i s .

The f i e l d c o v e r e d by the P a n e l w a s broad in i t s s c o p e ranging f r o m fundamenta l s t u d i e s through r e s e a r c h and d e v e l o p m e n t of p r o c e s s e s of potent ia l indus tr ia l i m p o r t a n c e to c o m m e r c i a l e n t e r p r i s e s . B e c a u s e of th i s wide s c o p e , th i s r e p o r t cannot c l a i m to have c o v e r e d each a r e a e x h a u s t i v e l y . Rather , an at tempt h a s been made to def ine the f i e l d and to put e a c h part into p e r s p e c t i v e in re la t i on to e a c h other part . At the s a m e t i m e it h a s b e e n p o s s i b l e on s o m e s u b j e c t s to c o m m e n t in s o m e deta i l w h e r e the e x p e r t knowledge of P a n e l m e m b e r s m a d e th i s p o s s i b l e .

The r e p o r t of the P a n e l c o m p r i s e s four p a r t s : s u m m a r y of p r e s e n t a t i o n s and d i s c u s s i o n s on e a c h topic d i s c u s s e d at the Pane l ; g e n e r a l o b s e r v a t i o n s that r e f l e c t the v i e w of the part i c ipants on each top ic , and r e c o m m e n d a t i o n s r e g a r d i n g the Agency 1 s a c t i v i t i e s ; the ten wr i t ten contr ibut ions to the P a n e l ; f ina l ly , c o m m e n t s on v a r i o u s s e l e c t e d t o p i c s .

I I . S U M M A R Y O F D I S C U S S I O N S

1. S o u r c e s

1 . 1 . V a r i o u s e x i s t i n g s o u r c e s

Ste inberg (United States of A m e r i c a ) r e v i e w e d c h e m o n u c l e a r f i s s i o n -f r a g m e n t e n e r g y s o u r c e s 1 . Uranium containing g l a s s f i b r e and U 0 2 - c o a t e d plat inum s o u r c e s has the d i sadvantages of low mel t ing point and radiat ion d a m a g e . Uran ium-pa l lad ium so l id so lut ions have been deve loped to the point w h e r e r e l i a b l e f i s s i o n - f r a g m e n t radiat ion c h e m i s t r y e x p e r i m e n t s

1 STEINBERG, M . , "Status report on c h e m o n u c l e a r reactors and rad ia t ion c h e m i c a l process ing" , this Report, P L - 2 3 6 / 4 .

1

2 D I S C U S S I O N S

can be p e r f o r m e d . P l a t i n u m - c o a t e d U - P d i m p r o v e s the r e s i s t a n c e to rad ia t ion d a m a g e and should p r e v e n t s p a l l a t i o n of uran ium a t o m s . N i t r o u s o x i d e and c a r b o n dioxide g a s d o s i m e t r y a l l o w s the d e t e r m i n a t i o n of f i s s i o n -f r a g m e n t e n e r g y d e p o s i t i o n e f f i c i e n c y wh ich i s in c o n f o r m i t y wi th a n a l y t i c a l r a n g e - g e o m e t r i c a l c a l c u l a t i o n s . The 0.1 m i l (2 .5 /urn) fo i l has b e e n f a b r i c a t e d into h o n e y c o m b a r r a y s for i n s e r t i o n into the i n - p i l e c h e m o -n u c l e a r loop.

B r o o k h a v e n i s cont inuing to d e v e l o p bonded c o e x t r u d e d 6 0 Co s o u r c e s . 1 3 7 C s s o u r c e s of c a e s i u m c h l o r i d e in s t a i n l e s s - s t e e l e n v e l o p e s a r e be ing t e s t e d . 90Sr s o u r c e s of m i c r o s p h e r e s in s t a i n l e s s - s t e e l n e e d l e s a r e be ing u s e d in s m a l l - s c a l e e x p e r i m e n t s . L a r g e r m u l t i c u r i e s o u r c e s of 9 0 Sr w h i c h would have h igh in tegr i ty have ye t to be deve loped . 1 3 7 Cs has the advantage of long h a l f - l i f e and a v a i l a b i l i t y , but l a r g e - s c a l e app l i ca t ion depends p r i m a r i l y on the d e v e l o p m e n t of a high i n t e g r i t y s o u r c e .

H o l m (Denmark) r e v i e w e d h i s work on d. c . and l i n e a r a c c e l e r a t o r s 2 . The m a i n po in t s inc luded i n c r e a s e d t e c h n o l o g i c a l d e v e l o p m e n t of m a c h i n e rad ia t ion s o u r c e s b a s e d on cont inued d e v e l o p m e n t of a c c e l e r a t o r s for r e s e a r c h p u r p o s e s . The e c o n o m i c s of the v a r i o u s a c c e l e r a t o r s , b e a m c h a r a c t e r i s t i c s , p e n e t r a t i o n c h a r a c t e r i s t i c s , , rout ine p r o c e s s c o n t r o l and e n e r g y c o n v e r s i o n e f f i c i e n c i e s of e l e c t r o n b e a m to X - r a y rad ia t ion w e r e s t r e s s e d . He e s p e c i a l l y po inted out the b e n e f i t s of P V C f i l m d o s i m e t r y and a s p e c i a l c a l o r i m e t e r c o n s i s t i n g of a t h e r m i s t o r bur ied in s t y r o f o a m ( f o a m e d p o l y s t y r e n e ) i n s e r t e d in a p e t r i d i s h f i l l e d wi th w a t e r . In the d i s c u s s i o n the i m p o r t a n c e w a s pointed out of current dens i ty and p o w e r in the rad ia t ion i n t e n s i t y f a c t o r a v a i l a b l e f r o m e l e c t r o n m a c h i n e rad ia t ion s o u r c e s .

H u m m e l ( F e d e r a l Republ ic of G e r m a n y ) r e v i e w e d the rad ia t ion s o u r c e s and pi lot plant f a c i l i t i e s be ing d e s i g n e d and d e v e l o p e d at the U n i v e r s i t y of Cologne? S o m e of the m a i n d e s i g n f e a t u r e s inc lude a c o r o n o i d s o u r c e wi th an a c t i v i t y of not m o r e than 10 5 Ci, a v a r i a b l e but u n i f o r m d o s e d i s t r ibut ion , a r e a c t i o n v o l u m e of not m o r e than 100 l i t r e s , f a c i l i t i e s f o r t r a n s p o r t of heavy equ ipment and i n s t a l l a t i o n of s a f e t y d e v i c e s . S e v e r a l d e s i g n s s u b m i t t e d by d i f f e r e n t m a n u f a c t u r e s w e r e shown. C o s t s of US $125 000 to US $200 000 for t y p i c a l f a c i l i t i e s w e r e m e n t i o n e d .

M r s . I o n e s c u (Romania ) r e v i e w e d the a lpha rad ia t ion s o u r c e f a c i l i t y d e v e l o p e d in her l a b o r a t o r y 4 . The (n, a) r e a c t i o n on l i th ium i s u s e d . F o i l s of L i i n s e r t e d in a r e a c t i o n v e s s e l of about 1 l i t r e c a p a c i t y a r e p l a c e d i n -s i d e n u c l e a r r e a c t o r s wi th a m a x i m u m f lux of 1 0 1 3 n / c m 2 s . G a s e s a r e p a s s e d o v e r t h i s f o i l and the p r o d u c t s a n a l y s e d . When m e t h a n e g a s w a s p a s s e d o v e r the i r r a d i a t e d l i t h i u m fo i l , a d e c o m p o s i t i o n of 40% of the m e t h a n e w a s e x p e r i e n c e d . T h i s should be c o m p a r e d with a c o n v e r s i o n of 3% when no l i th ium w a s p r e s e n t , and s e e m s to indicate a L E T e f f e c t .

Danno (Japan) r e v i e w e d the d e s i g n f e a t u r e s and d e v e l o p m e n t of l a r g e -s c a l e 6 0 Co s o u r c e s 5 . S o m e of the c h a r a c t e r i s t i c s of m a c h i n e and rod,

2 HOLM, N. W . , "Cha rac t e r i s t i c s and r ange of app l i cab i l i t y of acce le ra to r s for r a d i a t i o n - c h e m i c a l

processes", this Report, P L - 2 3 6 / 1 0 .

3 HUMMEL, D. O . , SCHNEIDER, C . , POTTER, R. C . , LEY, G . , DENAXAS, J . , WIDDERSHOVEN, D . , RYSKA, M . , "Rad ia t ion - induced p o l y m e r i z a t i o n : m e c h a n i s m s and industr ia l aspects" , this Report, P L - 2 3 6 / 9 .

4 IONESCU, S . , "Synthesis and decompos i t i on induced by ion i z ing rad ia t ion" , this Report , P L - 2 3 6 / 7 .

5 DANNO, A . , "App l i ca t i on of ion iz ing rad ia t ion to po lymer chemis t ry " , this Report, P L - 2 3 6 / 1 .


pla te , c y l i n d r i c a l and h o n e y c o m b r a d i o i s o t o p e type s o u r c e s w e r e m e n t i o n e d . A m a j o r d e s i g n c o n s i d e r a t i o n i s heat g e n e r a t i o n f r o m the i n t e n s i t y of the s o u r c e and the e x o t h e r m i c heat of p o l y m e r i z a t i o n of m o n o m e r . In the c a s e of a c c e l e r a t o r s , the b e a m i s u s e d in a s c a n n i n g m o d e . T h u s p o w e r only i s an ind icat ion of output, not e n e r g y d i s s i p a t i o n r a t e . Danno po inted out that if it w e r e p o s s i b l e to i n c r e a s e the d o s e - r a t e of g a m m a s o u r c e s to 10 M r a d / h , p r o c e s s i n g of a l l p o l y m e r i c s y s t e m s would be m a d e p o s s i b l e wi th r a d i o i s o t o p e s o u r c e s . 8 5 K r i s be ing s tud ied a s a p o s s i b l e h o m o -g e n e o u s rad ia t ion s o u r c e for l iqu id - and g a s - p h a s e r e a c t i o n s . Conta -m i n a t i o n of s a m p l e s and l e a k a g e into f a c i l i t i e s a r e two important p r o b l e m s e n c o u n t e r e d in u s i n g 8 5 Kr.

P u i g ( F r a n c e ) r e v i e w e d the m a i n radiat ion s o u r c e s and f a c i l i t i e s o p e r a t i n g in F r a n c e 6 . A to ta l of 700 000 Ci of 6 0Co are be ing u s e d in indus try , g o v e r n -m e n t and u n i v e r s i t y l a b o r a t o r i e s and p lants , and the m o b i l e i r r a d i a t o r IRMA u s e s 400 000 Ci 1 3 7 Cs . A l i n e a r e l e c t r o n b e a m a c c e l e r a t o r (7 M e V - 1 0 kW) i s o p e r a t e d at the SRTI i r r a d i a t i o n plant . A p a n o r a m i c -type f a c i l i t y at S a c l a y p r o v i d e s e x t r e m e l y f l e x i b l e a r r a n g e m e n t s for e x -p e r i m e n t a l i r r a d i a t i o n . The N u c l e a r Centre at G r e n o b l e i s be ing u s e d to s tudy the t e c h n o l o g y of i r r a d i a t i o n both on an e x p e r i m e n t a l and a t h e o -r e t i c a l b a s i s . The c o m m e r c i a l f a c i l i t i e s a r e u s e d p r i m a r i l y for s t e r i l i z a t i o n .

Dalton (United Kingdom) l i s t e d the i n d u s t r i a l and d e v e l o p m e n t s o u r c e s in the United K i n g d o m 7 . T h e s e inc lude 6 0 C o s o u r c e s of Johnson , G i l l e t t e , E t h i c o n , S w a n - M o r e t o n and an a c c e l e r a t o r of S m i t h and N e p h e w . Two l a r g e p i l o t - s c a l e p l a n t s u s i n g 6 0 C o and a 4 - M e V a c c e l e r a t o r a r e a v a i l a b l e in Wantage , and at H a r w e l l t h e r e i s a spent f u e l a s s e m b l y us ing e l e m e n t s f r o m the DIDO r e a c t o r . A 5 - 1 5 MeV a c c e l e r a t o r and a 3 0 0 - k V , 1 0 0 - m A a c c e l e r a t o r a r e under c o n s t r u c t i o n at Wantage. It w a s po in ted out that during pi lot and d e v e l o p m e n t work e a c h p r o c e s s m u s t b e t r e a t e d in a s p e c i f i c m a n n e r . Wantage has t ended to u s e l a r g e c o n c r e t e - s h i e l d e d c a v e s with s i m p l e rad ia t ion s o u r c e s and bui ld the n e c e s s a r y equ ipment round the s o u r c e even if th i s i n v o l v e s a low e f f i c i e n c y of s o u r c e u t i l i za t ion .

S a n g s t e r (Aus tra l ia ) m e n t i o n e d that in addit ion to the W e s t m i n s t e r C a r p e t s S o u r c e w h i c h i s u s e d for s t e r i l i z a t i o n of goat ha ir and p h a r m a -c e u t i c a l s and s o m e r e s e a r c h work in Melbourne , a spent fue l pond i s a v a i l a b l e at L u c a s He ight s . A l a r g e range of d o s e - r a t e s i s p o s s i b l e ; h o w e v e r , the fue l e l e m e n t f a c i l i t y i s not a c o m m e r c i a l p r o p o s i t i o n b e c a u s e the need to r e s h u f f l e fue l e l e m e n t s r e q u i r e s r e p e a t e d d o s i m e t r y m e a s u r e -m e n t s .

Getoff (Aus tr ia ) m e n t i o n e d the u s e of radon a s an alpha s o u r c e and s o m e i n t e r e s t i n g enhancing e f f e c t s of LET in o r g a n i c ac id r e a c t i o n . He s t r e s s e d the appl i ca t ion of X - r a y and v a c u u m u. v . s o u r c e s for r e s e a r c h work , p i l o t -p lant e x p e r i m e n t s and p u l s e d r a d i o l y s i s .

S i l v e r m a n (United S t a t e s of A m e r i c a ) m e n t i o n e d two t y p e s of m a c h i n e s o u r c e s . One i s the v a r i a b l e - e n e r g y p o s i t i v e l y c h a r g e d p a r t i c l e a c c e l e -r a t o r for s tudying L E T e f f e c t s in s o l i d and l iquid s y s t e m s , and the o ther i s the h i g h - i n t e n s i t y e l e c t r o n b e a m a c c e l e r a t o r that i s be ing i n c r e a s i n g l y

6 LEVEQUE, P . , PUIG, J. R . , "Le d e v e l o p p e m e n t de l a r a d i o c h i m i e : quelques aspects d e l a c o n j o n c t u r e " , this Report , P L - 2 3 6 / 8 .

' DALTON, F. L . , " T h e use of l o w - e n e r g y e l ec t ron acce l e r a to r s for t h e cur ing of pa in ts and thin f i l m s " , this Report, P L - 2 3 6 / 3 .


appl i ed in rad ia t ion c h e m i c a l s y s t e m s . The l a t t e r can be r e l a t i v e l y l o w -e n e r g y e l e c t r o n m a c h i n e s . R e l a t i v e l y l o w - c o s t e l e c t r o n gun a c c e l e r a t o r s a r e b e c o m i n g a v a i l a b l e , b o r r o w i n g t e c h n o l o g y f r o m e l e c t r o n e v a p o r a t o r , e l e c t r o n - b e a m - w e l d i n g and T V - t u b e - m a n u f a c t u r i n g t e c h n i q u e s . L E T and h i g h - e n e r g y b a s i c rad ia t ion c h e m i s t r y r e q u i r e m u c h f u r t h e r s tudy for e l u c i d a t i n g e f f e c t s p r e v i o u s l y noted.

1. 2. Other r e m a r k s

F i s s i o n - c h e m o n u c l e a r p r o c e s s e s look e c o n o m i c a l l y m o s t a t t r a c t i v e on the b a s i s of US $ / k W h of rad ia t ion e n e r g y but p o s e l a r g e p r o b l e m s in, f o r e x a m p l e , contaminat ion . R e s e a r c h i s s t i l l in the e a r l y s t a g e s s o that c o s t s cannot be r e a l i s t i c . The q u e s t i o n i s w h e t h e r c o u n t r i e s wi th r e a c t o r s can c a r r y out c a p s u l e e x p e r i m e n t s to advance the n e c e s s a r y r e s e a r c h and d e v e l o p m e n t work .

Along t h e s e l i n e s S t e i n b e r g m e n t i o n e d that the B r o o k h a v e n c h e m o -n u c l e a r i n - p i l e r e s e a r c h loop, wh ich i s a h ighly v e r s a t i l e , unique r e s e a r c h f a c i l i t y , c o u l d p o s s i b l y be m a d e a v a i l a b l e f o r an in ternat iona l e f f o r t w h e r e s c i e n t i s t s f r o m a l l p a r t s of the w o r l d cou ld go to B r o o k h a v e n to e x p e r i m e n t w i t h t h i s f a c i l i t y .

The c r i t e r i o n of a rad ia t ion p r o c e s s m u s t be the c o s t of product in US $ / k g and what it can be s o l d f o r . T h e r e i s no c l e a r ind icat ion of what s o u r c e should be u s e d u n l e s s p r o c e s s in c o n s i d e r e d a s a w h o l e and s p e c i f i -c a l l y . In the c a s e of l o w - e n e r g y a c c e l e r a t o r s window t e c h n o l o g y m u s t b e a d v a n c e d .

C o n s i d e r a b l e d i s c u s s i o n took p l a c e on the u s e of 1 3 7 C s a s a g a m m a s o u r c e . H u m m e l m e n t i o n e d the drawback of the s o f t e r g a m m a r e g a r d i n g p e n e t r a t i o n and c o s t . S t e i n b e r g po inted out the advantage of h a l f - l i f e and low m a i n t e n a n c e c o s t for a f r a c t i o n a l p o w e r i n t e n s i t y d e p e n d e n c e of ra te . A s o u r c e of high in tegr i ty m u s t be d e v e l o p e d . Dalton and S i l v e r m a n quoted c o s t s of A m e r i c a n 1 3 7 C s rang ing f r o m 10 to 15 £ / C i of 1 3 7 Cs un-e n c a p s u l a t e d . P u i g m e n t i o n e d a c o s t of 1.2 F. F r . / C i e n c a p s u l a t e d for F r e n c h m a t e r i a l .

The d u a l - p u r p o s e e l e c t r o c h e m o n u c l e a r s y s t e m u s i n g p o w e r f o r e l e c t r o l y t i c c e l l s w a s m e n t i o n e d by S t e i n b e r g a s n o m i n a l l y c o m p e t i t i v e wi th c h e m o n u c l e a r r e a c t o r s . The B r o o k h a v e n c h e m o n u c l e a r i n - p i l e loop f a c i l i t y and the J a p a n e s e JAERI c h e m o n u c l e a r loop f a c i l i t y now under c o n s t r u c t i o n m a y be c o n s i d e r e d unique, and IAEA could act a s a c l e a r i n g h o u s e f o r the p o s s i b l e u s e of t h e s e f a c i l i t i e s by v a r i o u s r e s e a r c h and d e v e l o p m e n t g r o u p s .

S i n g e r (Denmark) spoke of the p o s s i b i l i t y of u s ing m i x e d p i l e r a d i a -t ion for w o o d - p l a s t i c r e s e a r c h and d e v e l o p m e n t s i m i l a r to what i s be ing done by L o c k h e e d - G e o r g i a in the United S ta tes of A m e r i c a .

S t e i n b e r g m e n t i o n e d that 2 5 2Cf spontaneous f i s s i o n s o u r c e s that a re b e c o m i n g m o r e r e a d i l y a v a i l a b l e in the United S t a t e s of A m e r i c a can be a u s e f u l too l for i n v e s t i g a t i n g high L E T radiat ion c h e m i s t r y .

A q u e s t i o n w a s r a i s e d c o n c e r n i n g the u s e and s t a t u s of l iquid m e t a l c i r c u l a t i n g l o o p s in r e a c t o r s a s h i g h - i n t e n s i t y s h o r t - l i v e d g a m m a i r r a -d i a t o r s , for e x a m p l e , the g a m m a - e m i t t i n g i n d i u m - g a l l i u m l o o p s , a s m e n t i o n e d by the R u s s i a n s in S a l z b u r g in 1963 at the C o n f e r e n c e on the Appl i ca t ion of L a r g e Radiat ion S o u r c e s in Industry, but no rep ly w a s f o r t h c o m i n g .


2. D o s i m e t r y

2 . 1 . E l e c t r o n and g a m m a d o s i m e t r y

A s u b s t a n t i a l part of the p a p e r s and d i s c u s s i o n s w a s devoted to the d o s i m e t r y of g a m m a s and fas t e l e c t r o n s . H o l m (Denmark) g a v e an out -l i n e of the P V C f i l m d o s i m e t e r u s e d at R i s ^ for fa s t e l e c t r o n d o s i m e t r y , and exp la ined how s u c h a f i l m s y s t e m could be c a l i b r a t e d by m e a n s of a c h e a p and s i m p l e w a t e r c a l o r i m e t e r . The a c c u r a c y of the c a l o r i m e t e r w a s r e p o r t e d to be ± 1-2%. The a c c u r a c y of the P V C f i l m u s e d w a s about ± 3-5% for a c a l i b r a t e d s h e e t and ± 10% when the ba tch on ly w a s c a l i b r a t e d . The P V C u s e d w a s a 0 . 2 5 - m m "GENOTHERM" f i l m f r o m Kal l e , F e d e r a l Republ i c of G e r m a n y . P u i g ( F r a n c e ) r e v i e w e d the m e t h o d s u s e d f o r e l e c t r o n d o s i m e t r y in F r a n c e . At S a c l a y an a l u m i n i u m c a l o r i m e t e r and at SRTI a w a t e r - f l o w c a l o r i m e t e r for tota l p o w e r m e a s u r e m e n t a r e be ing u s e d . F o r rout ine u s e at the CIRCE a c c e l e r a t o r , PVC w a s u s e d a f t e r c a l i b r a t i o n a g a i n s t an a l u m i n i u m - p l a t e c a l o r i m e t e r . C o r r e c t i o n s had to b e m a d e f o r b a c k - s c a t t e r i n g and b r e m s s t r a h l u n g product ion . The r e p r o -duc ib i l i ty of the P V C d o s i m e t e r w a s r e p o r t e d to be p o o r and t h e r e w a s an ind ica t ion of an e n e r g y - d e p e n d e n c e . P u i g s ta ted that in g e n e r a l one should a l w a y s a t t empt to u s e d o s i m e t e r s of the s a m e a t o m i c c o m p o s i t i o n a s that of the m a t e r i a l s to be i r r a d i a t e d , and that p h y s i c a l c o n d i t i o n s should be c a r e f u l l y s i m u l a t e d when d o s i m e t r y s u r v e y s w e r e m a d e . S i l v e r m a n (United S t a t e s of A m e r i c a ) po inted out that v e r y l i t t l e w a s known c o n c e r n i n g ab-s o r p t i o n of e l e c t r o n s in c o m p l e x t a r g e t s . S o m e work had b e e n done at R i s ^ [1] and in Japan [2], and s o m e c a l c u l a t i o n s had been done by B e r g e r [ 3 ] and S p e n c e r [4], S i l v e r m a n had r e c e n t l y m a d e s o m e s u c h c a l c u l a t i o n s and p r e s e n t e d t h e m at m e e t i n g s of the A m e r i c a n P h y s i c a l S o c i e t y and in Japan [5], It w a s s t r e s s e d that m o r e e f f o r t s shou ld be devoted to t h i s subjec t . H o l m r e m a r k e d that s o m e m o r e i n f o r m a t i o n on d o s e d i s t r i b u t i o n s w a s g i v e n at the Internat iona l C o n f e r e n c e on Radiat ion R e s e a r c h , Nat ick , M a s s . , United S t a t e s of A m e r i c a , in January 1963.

A d i s c u s s i o n f o l l o w e d on the b e h a v i o u r of P V C and o t h e r f i l m s y s t e m s , p a r t i c u l a r l y wi th r e g a r d to t h e i r r e s p o n s e to g a m m a and e l e c t r o n rad ia t ion . It w a s conc luded that t h e s e s y s t e m s had to be c a l i b r a t e d under the condi t ions w h e r e they w e r e to be u s e d , and that i n c o n v e n i e n c e s s u c h a s heat t r e a t m e n t (PVC) o r humidi ty c o n t r o l (Red P e r s p e x ) had to be t o l e r a t e d . Much m o r e , h o w e v e r , should be known about the r e a c t i o n m e c h a n i s m s of t h e s e s y s t e m s . F o r e x a m p l e , for P V C the m e a s u r e d e f f e c t w a s m o s t probably due to i m -p u r i t i e s and t h i s e x p l a i n e d why d i f f erent b r a n d s d i f f e r e d in t h e i r r e p r o -duc ib i l i ty and s e n s i t i v i t y . It w a s g e n e r a l l y a g r e e d that s e v e r a l s y s t e m s , s u c h a s P V C , B lue Ce l lophane , Red P e r s p e x and C l e a r P e r s p e x w e r e e q u a l l y u s a b l e . When dea l ing wi th thin c o a t i n g s o r f i l m s , c a l c u l a t i o n s c o u l d support or be a subs t i tu te for the m e a s u r e m e n t s .

S a n g s t e r (Aus tra l ia ) e x p r e s s e d the n e e d for r e l i a b l e c h e m i c a l d o s i -m e t e r s u s a b l e at high d o s e s . H o l m d e s c r i b e d a number of d o s i m e t e r s u s e a b l e beyond the upper l i m i t of the F r i c k e d o s i m e t e r , s u c h a s o x a l i c ac id , f e r r o u s - c u p r i c - s u l p h a t e , d e - a e r a t e d f e r r o u s su lphate , M c L a u g h l i n ' s Dye s y s t e m , and the w a t e r d o s i m e t e r d e v e l o p e d at Argonne . The l a t t er should be e s p e c i a l l y w e l l s u i t e d to high d o s e - r a t e s . It w a s e m p h a s i z e d that d o s i m e t e r s in g e n e r a l n e e d not be " s i m p l e and e a s y to o p e r a t e " but t h e y should be a c c u r a t e . T h e r e should a l w a y s be t i m e to dea l in depth


with th i s important p r o b l e m by doing a c c u r a t e m e a s u r e m e n t s and then subst i tu t ing the rout ine d o s i m e t r y wi th a good p r o c e s s contro l . The d i s c u s s i o n w a s fur ther d e v e l o p e d on the F e - C u s y s t e m , and S i l v e r m a n and Dalton (United Kingdom) r e p o r t e d v e r y s a t i s f a c t o r y r e s u l t s with th i s s y s t e m . H o l m m e n t i o n e d that they u s e d the s y s t e m a s d e s c r i b e d by Hart in 1954 but r e d e t e r m i n e d the G - v a l u e to be 0 .70 [6]. U n l e s s f r e s h l y p r e -p a r e d s o l u t i o n s w e r e m a d e e v e r y day, it w a s r e c o m m e n d e d to p r e - i r r a d i a t e the s t o c k so lu t ion to 300 krad, thus s t a b i l i z i n g the so lu t ion for s e v e r a l d a y s .

. 2 .2 . I n - p i l e d o s i m e t r y

I n - p i l e d o s i m e t r y w a s c o v e r e d in a p r e s e n t a t i o n g iven by P u i g . In F r a n c e , t h r e e d i f f erent t y p e s of c a l o r i m e t e r s have b e e n d e v e l o p e d for d o s i m e t r y in high d o s e - r a t e f i e l d s . The i s o t h e r m a l c a l o r i m e t e r s a r e o p e r a t e d s u b m e r g e d in w a t e r p o o l s . The u s e of the c o n d u c t i o n - t y p e c a l o r i -m e t e r s d o e s nor r e l y on the knowledge of the s p e c i f i c heat of the c a l o r i -m e t r i c b o d i e s . T h e y g ive a cont inuous indicat ion of the in s tantaneous d o s e - r a t e , and they are a b s o l u t e (in the s e n s e of b u i l t - i n c a l i b r a t i o n f a c i l i t i e s ) , f a s t and s e n s i t i v e .

2 . 3 . F i s s i o n - p r o d u c t p a r t i c l e d o s i m e t r y

The d o s i m e t r y of f i s s i o n - p r o d u c t p a r t i c l e radiat ion , a s u s e d in r e a c t o r l o o p s to i r r a d i a t e g a s e s , w a s deal t wi th in the p a p e r g i v e n by S te inberg (United S t a t e s of A m e r i c a ) . He u s e d the N 2 0 - s y s t e m , a s d e s c r i b e d in the l i t e r a t u r e [7], m e a s u r i n g by g a s c h r o m a t o g r a p h y the N 2 produced . The upper t e m p e r a t u r e l imi t of that s y s t e m i s 150°C; t h e r e s e e m to be ne i ther L E T nor s u r f a c e e f f e c t s , a s shown by the good a g r e e m e n t wi th c a l c u l a t e d d o s e v a l u e s . A s m a l l contr ibut ion f r o m (n, p) r e a c t i o n s m a y be s u p p r e s s e d ( a c c o r d i n g to a r e c e n t publ i ca t ion by H a r t e c k and D o n d e s ) by us ing 1 5 N 2 0 [ 8 ] , T h i s i s , h o w e v e r , a r a t h e r c o s t l y p r o c e d u r e .

2. 4. G e n e r a l r e m a r k s

S o m e contr ibut ions w e r e m a d e c o n c e r n i n g c o - o p e r a t i o n and exchange of i n f o r m a t i o n on d o s i m e t r y . H a r a (IAEA) d e s c r i b e d the a c t i v i t i e s of the IAEA, wh ich had s p o n s o r e d t h r e e s y m p o s i a and t h r e e p a n e l s on th i s subjec t . A handbook on f l u e n c e m e a s u r e m e n t s and one on a b s o r b e d d o s e m e a s u r e -m e n t s a r e be ing p r e p a r e d under the a u s p i c e s of the IAEA, and a P a n e l he ld in 1966 r e c o m m e n d e d that the A g e n c y should s p o n s o r an i n t e r c o m p a r i -s o n p r o g r a m m e for i n - p i l e c a l o r i m e t e r s and should s e t up a w o r k i n g group on d o s i m e t r y . S t e i n b e r g r e p o r t e d on the B N L d o s i m e t r y w o r k s h o p and the a c t i v i t i e s in the United S t a t e s of A m e r i c a with r e g a r d to p r o c u r i n g s t a n d a r d m e t h o d s . He r e c o m m e n d e d the IAEA to e x c h a n g e i n f o r m a t i o n wi th o r g a n i z a t i o n s l ike NBS, ASTM and the B N L w o r k s h o p m e n t i o n e d a b o v e . S a n g s t e r m e n t i o n e d that the t e c h n i q u e s u s e d by h o s p i t a l r a d i o -l o g i s t s in m e a s u r i n g d o s e s a c c u r a t e l y might be he lpfu l to rad ia t ion c h e m i s t s . T h e r e p o r t s i s s u e d by the ICRU should be looked into. P u i g r e c o m m e n d e d that the p h y s i c s of a b s o r p t i o n of h i g h - e n e r g y e l e c t r o n s should be s tudied m o r e e x t e n s i v e l y , and that the c h e m i s t r y of thin f i l m d o s i m e t e r s should be l o o k e d at m o r e s y s t e m a t i c a l l y wi th s p e c i a l r e f e r e n c e to d y e - s t u f f s .


C o - o p e r a t i o n b e t w e e n g r o u p s work ing on d o s i m e t r y w a s a l s o r e c o m m e n d e d . H o l m o b s e r v e d that s e v e r a l g r o u p s within the IAEA a l r e a d y dea l t w i th d o s i m e t r y , and that it should not be the t a s k of the P a n e l to s t i m u l a t e the f o r m a t i o n of another s u c h group but r a t h e r to b r i n g to the at tent ion of the e x i s t i n g g r o u p s p r o b l e m s that w e r e of p a r t i c u l a r i n t e r e s t to t h i s P a n e l .

3. F u n d a m e n t a l s

3 . 1 . P u l s e d r a d i o l y s i s

S a n g s t e r (Aus tra l ia ) d e s c r i b e d the v a l u e of p u l s e d r a d i o l y s i s in the d i r e c t o b s e r v a t i o n of the k i n e t i c s of s p e c i e s p r o d u c e d s h o r t l y a f t e r the a b s o r p t i o n of i o n i z i n g r a d i a t i o n 8 . Whi le m o s t of the work r e p o r t e d to date i s in the m i c r o s e c o n d reg ion , s o m e r e s u l t s have a l r e a d y b e e n obta ined in the n a n o s e c o n d r e g i o n at Argonne Nat iona l L a b o r a t o r y . Much of the r e s e a r c h e f f o r t has b e e n in a q u e o u s s y s t e m s ; h o w e v e r , t h e r e i s a s i g n i f i -cant body of i n f o r m a t i o n on o r g a n i c l i q u i d s and s o m e work in g a s e o u s s y s t e m s . The r e s u l t s not only y i e l d the d e c a y t i m e s of t r a n s i e n t s p e c i e s p r o d u c e d s h o r t l y a f t e r the rad ia t ion event but a l s o , in the c a s e of n a n o -s e c o n d s t u d i e s , m a y show the e x i s t e n c e of s p u r s .

D i s c u s s i o n r e v e a l e d that work on i c e s y s t e m s has b e e n p u b l i s h e d by Sov ie t s c i e n t i s t s . S i m i l a r s t u d i e s a r e in p r o g r e s s in D e n m a r k . S a n g s t e r added i n f o r m a t i o n r e g a r d i n g work in the g a s p h a s e on N H 3 and on CO2. Imthe l a t t e r s y s t e m , e v i d e n c e of the c a r b o n a t o m has b e e n o b s e r v e d . S i l v e r m a n (United S t a t e s of A m e r i c a ) r e m a r k e d that p u l s e d r a d i o l y s i s c a n be u s e d to o b s e r v e prompt p r o d u c t i o n of unusua l s t a b l e s p e c i e s (as o p p o s e d to t r a n s i e n t o n e s ) s u c h a s d iene f o r m a t i o n in a l k a n e s ; the p r o m p t product ion of t h i s s p e c i e s would i n v o l v e the a l m o s t s i m u l t a n e o u s r e m o v a l of four h y d r o g e n a t o m s . H u m m e l ( F e d e r a l Republ ic of G e r m a n y ) r e f e r r e d to s t u d i e s on s t y r e n e and s t y r e n e - w a t e r s y s t e m s p e r f o r m e d by S c h n e i d e r and S w a l l o w . In addit ion to the f r e e r a d i c a l s p e c i e s r e p o r t e d by t h e m e a r l i e r , t h e y now f i n d - t r a n s i e n t s t h e y a t tr ibute to r a d i c a l a n i o n s . T h e y found u s i n g r e p e t i t i o n p u l s i n g (50 p / s ) that s o m e of the p o l y m e r i z i n g r a d i c a l s c a n s u r v i v e 1 0 2 - 1 0 3 p u l s e s . A l s o the cha in l e n g t h of the p o l y m e r s p r o d u c e d in the m i c r o s e c o n d p u l s e s i s far g r e a t e r than one c a n account for by f r e e r a d i c a l k i n e t i c s . Dal ton (United Kingdom) m a d e the s a m e o b s e r -v a t i o n r e g a r d i n g chain l ength in s t u d i e s at Wantage of the p o l y m e r i z a t i o n of s t y r e n e (and o ther m o n o m e r s ) by m e a n s of a pu l s ing l i n e a r a c c e l e r a t o r . S i l v e r m a n obta ined s i m i l a r r e s u l t s at Ris^ . It w a s o b s e r v e d that o ther m e t h o d s and i n s t r u m e n t s can be u s e d for the d e t e c t i o n and m e a s u r e m e n t s of s h o r t - l i v e d i n t e r m e d i a t e s .

3 . 2 . Low t e m p e r a t u r e t e c h n i q u e s

Z a g o r s k i and Mine (Poland) p r e s e n t e d a c o m p r e h e n s i v e r e v i e w of l o w - t e m p e r a t u r e radiat ion c h e m i s t r y 9 , and s u m m a r i z e d the p r e s e n t s i tuat ion in rad ia t ion c h e m i s t r y . S t r e s s i n g the p r e s e n t a c h i e v e m e n t s in d i f f e r e n t b r a n c h e s of radiat ion c h e m i s t r y , it w a s a l s o po inted out that

8 SANGSTER, D . F . , "Pulse radiolysis" , this Report, P L - 2 3 6 / 6 . 9 ZAGORSKI, Z . P . , MINC, S . , " L o w - t e m p e r a t u r e i r rad ia t ions" , this Report, P L - 2 3 6 / 5 .


both the technique of l o w - t e m p e r a t u r e i r r a d i a t i o n s and t h e i r i n t e r p r e t a t i o n a r e in n e e d of s u p p l e m e n t a r y i n v e s t i g a t i o n s . The m o s t important a r e a l l m e a s u r e m e n t s c h a r a c t e r i z i n g the f r o z e n s a m p l e : d e n s i t i e s , s o l u b i l i t i e s of g a s e s , h o m o g e n e i t y e v e n of o n e - c o m p o n e n t s y s t e m s , c r y s t a l s i z e , s t r u c t u r e of g l a s s e s , p r e s e n c e , ident i ty and c o n c e n t r a t i o n of d e f e c t s of d i f f e r e n t k inds .

The addi t ional m e a s u r e m e n t s a r e in m a n y i n s t a n c e s m o r e c o m p l i c a t e d than the r a d i a t i o n - c h e m i c a l part of the i n v e s t i g a t i o n . N e v e r t h e l e s s , t h e s e m e a s u r e m e n t s have to be done to j u s t i f y the c o n c l u s i o n s drawn, and m u s t be i n t e g r a t e d into the whole p i c ture of r a d i a t i o n - i n d u c e d p h e n o m e n a in c o n d e n s e d p h a s e s .

One c a n c o n s i d e r l o w - t e m p e r a t u r e radiat ion c h e m i s t r y a s the s o u r c e of a p p l i c a t i o n s f o r the r a t h e r distant future . One of the n e g a t i v e f a c t o r s i s of an e c o n o m i c nature: br ing ing the s a m p l e into low t e m p e r a t u r e m e a n s an addi t ional c o s t . T h i s s i tuat ion m a y not be a s d i s a d v a n t a g e o u s if the p r o c e s s i n g d e m a n d s the appl icat ion of low t e m p e r a t u r e , f o r i n s t a n c e in s o m e m e t h o d s of food i r r a d i a t i o n .

Another n e g a t i v e f a c t o r i s c o n n e c t e d with d iminut ion of rad ia t ion y i e l d s due to the enhanced e m i s s i o n of l ight in the c o u r s e of i r r a d i a t i o n and thawing. N e v e r t h e l e s s , t h e r e i s j u s t i f i e d o p t i m i s m a s to the p o s s i -b i l i t y of obtaining quite unusual p o l y m e r s of v e r y high v a l ue and s p e c i f i c p r o p e r t i e s in the p r o c e s s of l o w - t e m p e r a t u r e i r rad ia t ion .

H u m m e l ( F e d e r a l Republ ic of G e r m a n y ) po inted out the advantage of p e r f o r m i n g c a t i o n i c p o l y m e r i z a t i o n s in s u c h s y s t e m s , e s p e c i a l l y in c o m -m e r c i a l l y a t t r a c t i v e a l t ernat ing c o p o l y m e r s ( s e e Footnote 3). T h i s s p a r k e d off c o n s i d e r a b l e d i s c u s s i o n of the potent ia l p r a c t i c a l v a l u e of l o w -t e m p e r a t u r e p r o c e s s e s . The P o l i s h contr ibut ion s t r e s s e d the l a r g e e n e r g y l o s s e s in f r o z e n s y s t e m s due to l u m i n e s c e n c e and a l s o pointed out the c o s t of f r e e z i n g . H u m m e l m e n t i o n e d that e n e r g y l o s s e s in long chain p o l y m e r i z a t i o n s a r e not a s e r i o u s c o s t e l e m e n t in the ionic c o p o l y -m e r i z a t i o n s of po tent ia l p r a c t i c a l v a l u e . Danno (Japan) o b s e r v e d that s o m e of the s o l i d - s t a t e p r o c e s s e s w e r e r e g a r d e d with g r e a t i n t e r e s t at the Japan A t o m i c E n e r g y R e s e a r c h Inst i tute . Z a g o r s k i po inted out that t h e r e a r e m a r k e d d i f f e r e n c e s b e t w e e n s o l i d - s t a t e p o l y m e r i z a t i o n p r o c e s s e s n e a r r o o m t e m p e r a t u r e and d e e p - f r o z e n s y s t e m s . The guarded p e s s i m i s m e x p r e s s e d in the paper r e f e r r e d to the l a t t e r .

S o m e r e m a r k s w e r e m a d e r e g a r d i n g the d i f f i c u l t i e s in obta in ing r e -l i a b l e k i n e t i c s of s o l i d - s t a t e p o l y m e r i z a t i o n b e c a u s e of p o s t - e f f e c t s . S i l v e r m a n (United S ta tes of A m e r i c a ) r e p o r t e d on h i s and o t h e r pub l i shed work wi th f r o z e n s t y r e n e under cond i t ions w h e r e p o s t - e f f e c t s w e r e r ig id ly e x c l u d e d . He m a d e two o b s e r v a t i o n s : the e x i s t i n g data do not fit any p u b l i s h e d t h e o r y , and the nature of the s o l i d can be adjus ted to g i v e a wide v a r i e t y of r e s u l t s . The c o m p l e x , d i s c o n t i n u o u s pa t tern of the p o s t -i r r a d i a t i o n of a c r y l a m i d e c r y s t a l s o b s e r v e d by A d l e r at B r o o k h a v e n w a s a d v a n c e d to show that h o m o g e n e o u s p o l y m e r i z a t i o n k i n e t i c s should not be app l i ed to s o l i d s . Dalton (United Kingdom) r e p o r t e d s i m i l a r o b s e r v a t i o n s in e x p e r i m e n t s at Wantage wi th so l id a c r y l o n i t r i l e . He conc luded that s o l i d - s t a t e p o l y m e r i z a t i o n s t u d i e s should be done only on t h o s e s y s t e m s w h e r e the nature of the s o l i d can be s h a r p l y def ined .

In r e s p o n s e to a ques t ion by S te inberg (United S t a t e s of A m e r i c a ) about the rad ia t ion c h e m i s t r y of m u l t i p h a s e l iqu ids at l ow t e m p e r a t u r e s , Z a g o r s k i m e n t i o n e d that nothing unusual w a s o b s e r v e d in s i n g l e - p h a s e l iquid s y s t e m s


at low t e m p e r a t u r e s e x c e p t in cha in r e a c t i o n s w h e r e v i s c o s i t y e f f e c t s o c c u r ; when a s e c o n d phase i s in t roduced ( so l id or l iquid) , l ight e m i s s i o n and s e c o n d a r y p h o t o c h e m i c a l p r o c e s s e s a r e f r e q u e n t l y o b s e r v e d ; f u r t h e r -m o r e , in addi t ion to the c o m p l i c a t i o n s , i n t e r e s t i n g ca ta ly t i c e f f e c t s f r e -quent ly of a p r o m i s i n g nature a r i s e f r o m the introduct ion of s o l i d s .

Mine and Z a g o r s k i m e n t i o n e d that the r a d i a t i o n - i n d u c e d or m o d i f i e d c a t a l y s i s w a s not deal t with. In c o n n e c t i o n wi th the d i s c u s s i o n on the t w o -p h a s e s y s t e m s at l ow t e m p e r a t u r e , it h a s to be s t r e s s e d that f u r t h e r in -v e s t i g a t i o n on s u r f a c e p h e n o m e n a in the rad ia t ion f i e ld has to be m a d e . T h i s m a y he lp to enhance the r e a c t i v i t y of b o u n d a r i e s b e t w e e n p h a s e s and s e e m s to be important a l s o to the s o - c a l l e d radiat ion c a t a l y s i s .

3. L E T

P u i g ( F r a n c e ) r e p o r t e d on r e c e n t r e s u l t s on the L E T d e p e n d e n c e of the d e c o m p o s i t i o n of t e r p h e n y l by m i x e d g a m m a r a y and f a s t neutron f l u x e s . T h e d e p e n d e n c e of the d e g r e e of c o n v e r s i o n on the c o n c e n t r a t i o n of t e r -p l i eny l s w a s d e t e r m i n e d and found to be p r o p o r t i o n a l to a p o w e r of the c o n c e n t r a t i o n of about 3 / 2 . Init ia l G - v a l u e s for the d i s a p p e a r a n c e of t e r p h e n y l s a s a funct ion of LET can then be c a l c u l a t e d for a l l a v a i l a b l e data: 0 .2 for pure g a m m a r a y s and about 0 .9 for pure fa s t neutron f l u x e s .

S i l v e r m a n d e s c r i b e d the l a r g e v a r i a t i o n in r e p o r t e d n e u t r o n - t o - g a m m a G - v a l u e r a t i o s f o r t h i s s y s t e m ranging f r o m 2 to 20. T h i s a r i s e s f r o m the t r e a t m e n t of the heat , g a m m a and neutron e f f e c t s in a l i n e a r m a n n e r . It s e e m e d to h i m h igh ly un l ike ly that a s y s t e m of s u c h c o m p l e x i t y could b e l i n e a r . He d e s c r i b e d open d i s c u s s i o n s with MIT and O R G E L s c i e n t i s t s and r e f e r r e d to h i s p a p e r on addi t iv i ty of rad ia t ion e f f e c t s c h a l l e n g i n g the e a r l i e r work of t h e s e g r o u p s [9]. The m a i n point w a s that apparent o v e r -a l l G - v a l u e s in a c o m p l e x s e q u e n c e of r e a c t i o n s a r e u s e f u l f o r e n g i n e e r i n g p u r p o s e s but it i s d i f f i cu l t to d e r i v e a -mechan i s t i c m e a n i n g f r o m s u c h data and d a n g e r o u s to e x t r a p o l a t e f r o m t h e m . T h u s the high ra t io ( ~ 4 ) r e p o r t e d by P u i g , wh i l e d e r i v e d f r o m u s e f u l e n g i n e e r i n g data, i s s t i l l too high than one might e x p e c t f r o m o ther s y s t e m s , and i t s b a s i c c h e m i c a l s i g n i f i c a n c e i s s t i l l u n c e r t a i n .

S i l v e r m a n a l s o r a i s e d the q u e s t i o n of e q u i v a l e n c e of e l e c t r o n b e a m r e s u l t s c o m p a r e d wi th g a m m a e f f e c t s p r o d u c e d by the s a m e d o s e at the s a m e d o s e r a t e . R e v i e w s by Motz , O l s e n and Koch of the US Nat iona l B u r e a u of S tandards s u g g e s t t h i s a s an important a r e a of r e s e a r c h [10].

3 . 4 . u. v. t e c h n i q u e s

Getoff (Austr ia ) g a v e a shor t p r e s e n t a t i o n on the v a c u u m u. v . rad ia t ion (X < 2000 A ) a s a l ink b e t w e e n u. v. l ight in i t s u s u a l s e n s e (X > 2000 A) and i o n i z i n g rad ia t ion . In addit ion to a g e n e r a l d e s c r i p t i o n of v a c u u m u. v . rad ia t ion s o u r c e s and t h e i r o p e r a t i o n , data c o n c e r n i n g r e s o n a n c e e m i s s i o n s f o r a n u m b e r of g a s e s and s p e c i f i c a t i o n s of v a c u u m u. v . t r a n s m i t t i n g m a t e r i a l s w e r e r e p o r t e d .

The v a c u u m u. v . radiat ion i s e n e r g e t i c enough to e f f e c t p h o t o d i s s o c i a -t ion, and in s o m e c a s e s a l s o photo ion iza t ion of m o l e c u l e s . T h e s e two p r o c e s s e s l e a d to the f o r m a t i o n of f r e e r a d i c a l s , r a d i c a l ions and i o n s in e x a c t l y the s a m e way a s they a r e p r o d u c e d by ion iz ing rad ia t ion . F r o m

1 0 D I S C U S S I O N S

t h i s point of v i e w the v a c u u m u. v . rad ia t ion r e p r e s e n t s a p o w e r f u l too l for i n v e s t i g a t i n g r e a c t i o n m e c h a n i s m s c a u s e d by radiat ion .

It w a s m a d e c l e a r that v a c u u m u . v . l ight , whi l e capab le of ion iz ing and e x c i t i n g a wide v a r i e t y of s u b s t a n c e s , i s d i f f erent f r o m g a m m a s in that the f o r m e r i s a m u c h m o r e s e l e c t i v e t o o l f o r r e s e a r c h p u r p o s e s , e . g . in the produc t ion of s p e c i f i c ion m o l e c u l e s .

S i l v e r m a n (United S t a t e s of A m e r i c a ) added that Sch lag [11] u s e d far u . v . and an e l e c t r i c f i e l d to d e m o n s t r a t e c o n c l u s i v e l y that i s o b u t e n e c a t i o n s in i t ia te the p o l y m e r i z a t i o n of the m o n o m e r but that n e g a t i v e and neutra l s p e c i e s p r o d u c e d in the e n e r g y a b s o r p t i o n p r o c e s s do not.

3. 5. Other t e c h n i q u e s

Mine m e n t i o n e d that a m o n g new s o u r c e s of high e n e r g y for c h e m i c a l p u r p o s e s , l o w - t e m p e r a t u r e p l a s m a (about 20 000°C) i s ga in ing i m p o r t a n c e . At the s a m e t i m e the rad ia t ion c h e m i s t r y of g a s e s i s m o r e and m o r e p r o m i s i n g , and c o n n e c t i o n b e t w e e n t h e s e two b r a n c h e s of high e n e r g y c h e m i s t r y m a y r e s u l t in the d e v e l o p m e n t of p r o c e s s e s for , for e x a m p l e , a c e t y l e n e , e thy l ene and o ther p r o d u c t s of i n d u s t r i a l i m p o r t a n c e . On the o t h e r hand, in both c a s e s , i n t e r e s t i n g i n t e r m e d i a t e s a r e f o r m e d , and any d i f f e r e n c e s or s i m i l a r i t i e s m a y l e a d to the b e t t e r unders tanding of the m e c h a n i s m s .

S i l v e r m a n e m p h a s i z e d the va lue of a t o m i c b o m b a r d m e n t t e c h n i q u e s , p a r t i c u l a r l y t h o s e invo lv ing h i g h - f r e q u e n c y d i s c h a r g e , in d i s t ingu i sh ing b e t w e e n ionic and f r e e r a d i c a l e f f e c t s . B r o i d a ' s c l a s s i c a l work [12] on the g a s d i s c h a r g e w a s c i t e d a s the b a s i s for obtaining a t o m s in good y i e l d without d e t e c t a b l e c o n t a m i n a t i o n by e x c i t i n g an i o n i z e d E P R s p e c i e s . S i l v e r m a n d e s c r i b e d r e s u l t s on p o l y e t h y l e n e f i l m with hydrogen a t o m s s h o w i n g i t s s i m i l a r i t i e s wi th g a m m a - i r r a d i a t e d p o l y e t h y l e n e and s o m e d i f f e r e n c e s .

S t e i n b e r g s u g g e s t e d that i r r a d i a t e d g a s e s m a y p r o d u c e h igher c o n c e n -t r a t i o n s of a t o m s than g a s d i s c h a r g e t e c h n i q u e s .

3 . 6 . G e n e r a l fundamenta l c o n s i d e r a t i o n s

U s i n g p o l y o l e f i n s a s an e x a m p l e , S i l v e r m a n i l l u s t r a t e d the a d v a n c e s and f a i l u r e s in unders tand ing and e x p l o i t i n g radiat ion e f f e c t s : the f r e e r a d i c a l s have b e e n c o n s i d e r e d in t e r m s of po tent ia l ly p r a c t i c a l gra f t ing p r o c e s s e s , the c r o s s - l i n k i n g of p o l y e t h y l e n e i s a l r e a d y an important p r a c t i c a l p r o c e s s , unsa tura t ion (which i s a s abundant in y i e l d a s c r o s s -l inking) has not found a p r a c t i c a l v a l u e , and n e i t h e r have the ions .

S t e i n b e r g e x p r e s s e d c o n c e r n o v e r the inabi l i ty to obtain m o r e than a half of the t h e o r e t i c a l m a x i m u m G - v a l u e for n i t rogen f ixa t ion in N2-O2 s y s t e m s . He fe l t that e n e r g y t r a n s f e r s t u d i e s in s o l i d - g a s s y s t e m s might hold the c lue to the so lu t ion of th i s p r o b l e m .

Cit ing f u r t h e r potent ia l a d v a n t a g e s in h e t e r o g e n e o u s s y s t e m s , S i l v e r m a n d e s c r i b e d the r e s u l t s of Snow at the S i n c l a i r Oi l Co. in the rad ia t ion p o l y m e r i z a t i o n of e t h y l e n e - c a t a l y s t s y s t e m s [13], and the work of L a m p e and Johnston on d i m e t h y l a m i n e g a s with c o p p e r [14],


3. 7. D r y n e s s and puri ty

H u m m e l ( F e d e r a l Republ ic of G e r m a n y ) m a d e a s u r v e y of the a d v a n c e s and p r o b l e m s in e m u l s i o n p o l y m e r i z a t i o n and s u s p e n s i o n p o l y m e r i z a t i o n ( s e e Footnote 3). He d e s c r i b e d the breakdown of the S m i t h - E w a r t t h e o r y , p a r t i c u l a r l y in s y s t e m s o ther than s t y r e n e . Dalton r e p o r t e d on an e a r l i e r s tudy of the e m u l s i o n p o l y m e r i z a t i o n of s t y r e n e in which the d o s e - r a t e d e p e n d e n c e on m o n o m e r c o n c e n t r a t i o n s h o w e d an apparent deviat ion f r o m the S m i t h - E w a r t t h e o r y . The unusual b e h a v i o u r he a s c r i b e d to two d i f f erent r e d u c i n g r a d i c a l s , the hydrogen a tom and the s o l v a t e d e l e c t r o n .

P u i g c i t e d the work of Magat on p r e s s u r e e f f e c t s on p o l y m e r i z i n g s y s t e m s and de ta i l ed p h y s i c a l c h a r a c t e r i z a t i o n of g r a f t s . T h i s i s an a r e a of p r a c t i c a l i m p o r t a n c e that has r e c e i v e d too l i t t l e at tent ion.

H u m m e l s t r e s s e d the i m p o r t a n c e of pur i ty and d r y n e s s , e s p e c i a l l y in v i n y l p o l y m e r i z a t i o n s and c o p o l y m e r i z a t i o n s . L a r g e i n c r e a s e s in y i e l d a r i s e f r o m r i g o r o u s p u r i f i c a t i o n of the s t y r e n e (as shown by the work at Wantage , United Kingdom, B r o o k h a v e n , United S t a t e s of A m e r i c a , and Kyoto U n i v e r s i t y , Japan) . The r e s u l t s ind ica te the n e e d for fur ther e x -t e n s i v e s t u d i e s in the above and r e l a t e d s y s t e m s .

4. A p p l i c a t i o n s

4. 1. P o l y m e r i z a t i o n and o ther r e a c t i o n s

Work c a r r i e d out at B N L w a s r e p o r t e d by S t e i n b e r g (United S t a t e s of A m e r i c a ) ( s e e Footnote 1). The f o r m a t i o n of n i t r o g e n c o m p o u n d s , o z o n e , hydrogen , hydrogen p e r o x i d e and hydraz ine w a s i n v e s t i g a t e d in a m p o u l e i r r a d i a t i o n by r e c o i l f i s s i o n f r a g e m e n t s f r o m uran ium. A s a r e s u l t of a s tudy of the e c o n o m i c s of n u c l e a r r e a c t o r s us ing d i r e c t l y the r e c o i l f i s s i o n e n e r g y for c h e m i c a l c o n v e r s i o n , the n i t r o g e n f ixa t ion would be e c o n o m i c a l p r o v i d e d that a G - v a l u e of 6 i s r e a c h e d for c o n v e r s i o n . T h i s has not yet b e e n obta ined . A loop i s be ing c o n s t r u c t e d to eva lua te the p r o c e s s fur ther .

P o l y m e r i z a t i o n r e a c t i o n s of g a s e s w e r e a l s o s tudied us ing 6 0 Co g a m m a i rrad ia t ion . The e thy lene r e a c t i o n w a s s tudied in s ta t ic and dy-n a m i c d e v i c e s with t e m p e r a t u r e s up to 200°C and p r e s s u r e s r e a c h i n g 2000 k g / c m 2 . S te inberg s t r e s s e d the s a f e t y p r o b l e m s r a i s e d by t h e s e e x p e r i m e n t s during which e x p l o s i o n s o c c u r r e d a s s o c i a t e d with fas t r ea c t i o n r a t e s ( G ( - C 2 H 4 ) ~ 10®). E x o t h e r m i c r e a c t i o n s l ike C 2 H 4 p o l y m e r i z a t i o n r e q u i r e t h e r e f o r e c a r e f u l c h e m i c a l e n g i n e e r i n g d e s i g n to tack le the heat g e n e r a t i o n .

The e c o n o m i c s of the radiat ion product ion of l o w - d e n s i t y p o l y e t h y l e n e w a s s tudied , and it w a s shown that the m o s t favourab le c o s t of c o n v e r s i o n of e thy lene into p o l y e t h y l e n e w a s about 1 <?/lb, b a s e d on an annual output of 50 m i l l i o n lb.

The work on e thy lene i s be ing cont inued us ing a f low s y s t e m which i s d e s i g n e d to produce about 500 g of p o l y e t h y l e n e p e r hour ( t e m p e r a t u r e above m e l t i n g point of p o l y e t h y l e n e , p r e s s u r e s up to 30 000 l b / i n 2 gauge ) .

E x p e r i m e n t s on the c o p o l y m e r i z a t i o n of e t h y l e n e wi th carbon m o n -ox ide and sulphur d ioxide g a v e i n t e r e s t i n g p l a s t i c m a t e r i a l s .

S t e i n b e r g a l s o r e f e r r e d to a p l a s t i c - i m p r e g n a t e d c o n c r e t e that has i m p r o v e d c o m p r e s s i o n s t r e n g t h by a f a c t o r of 2 .4 and r e d u c e d p e r m e a -b i l i t y by 98%. C r y o g e n i c i r r a d i a t o r s and rad ia t ion t r e a t m e n t of w a s t e


w a t e r f o r po l lut ion c o n t r o l w e r e a l s o m e n t i o n e d a s be ing i n v e s t i g a t e d at B r o o k h a v e n .

Danno (Japan) r e v i e w e d the important pi lot s c a l e work c a r r i e d out at the T a k a s a k i R e s e a r c h E s t a b l i s h m e n t of the Japan A t o m i c E n e r g y R e s e a r c h Inst i tute ( s e e Footnote 5). T h e s e s t u d i e s c o m p r i s e d p o l y m e r i z a t i o n of e t h y l e n e b e l o w 500 k g / c m 2 p r e s s u r e and 150°C in a f low s y s t e m , p o l y -m e r i z a t i o n of t r i o x a n e , the g r a f t i n g of c e l l u l o s i c f i b r e s ( s t y r e n e ) , the g r a f t i n g of p o l y v i n y l c h l o r i d e (butadiene) , a n d t h e c h l o r i n a t i o n of h y d r o c a r b o n s .

Danno e x p l a i n e d that the p u r p o s e of t h e s e s t u d i e s i s to i n v e s t i g a t e the t e c h n o l o g y of i r r a d i a t i o n on r e p r e s e n t a t i v e m o d e l s y s t e m s and to supply l a r g e quant i t i e s of t e s t i n g m a t e r i a l s .

A s r e g a r d s p o l y e t h y l e n e f o r m a t i o n , data a re p r e s e n t e d on the e f f e c t of the f l o w - r a t e and the d e g r e e of p o l y m e r i z a t i o n , both be ing d e c r e a s i n g f u n c t i o n s of the f l o w - r a t e .

Q u e s t i o n s w e r e r a i s e d whether any c r o s s - l i n k i n g o c c u r r e d during the p o l y m e r i z a t i o n of e t h y l e n e , and why CO2 w a s u s e d a s a s o l v e n t in s o m e c a s e s . Danno r e p l i e d that he could not at p r e s e n t d i s c u s s the f i r s t , but that CO2 w a s u s e d to enab le a cont inuous s l u r r y of p o w d e r e d p o l y m e r to be obta ined s i n c e it w a s a conven ient iner t s o l v e n t .

Dalton (United Kingdom) d i s c u s s e d the r e c e n t d e v e l o p m e n t of t r a n s -f o r m e r - r e c t i f i e r s e t s in the 1 5 0 - 3 0 0 kV range for the t r e a t m e n t of c o a t i n g s and thin f i l m s ( s e e Footnote 7). He out l ined the p r e s e n t s t a t e of d e v e l o p -m e n t of the a c c e l e r a t o r s and e n u m e r a t e d the type of c o a t i n g s that could b e s u c c e s s f u l l y c u r e d by rad ia t ion and t h o s e that r e q u i r e d m o d i f i c a t i o n o r d e v e l o p m e n t .

A f t e r d i s c u s s i n g the a d v a n t a g e s of radiat ion cur ing and g i v i n g an out -l ine of the c o s t s invo lved , he e m p h a s i z e d t h o s e a r e a s in wh ich he c o n s i d e r e d f u r t h e r d e v e l o p m e n t work w a s urgent ly n e e d e d of m a x i m u m u s e w a s to be m a d e of the t echn ique ( a c c e l e r a t o r s and point s y s t e m s ) .

In r e p l y to a r e q u e s t f r o m S i l v e r m a n (United S t a t e s of A m e r i c a ) for an ind ica t ion of the i n d u s t r i a l po tent ia l of g a m m a - i n i t i a t e d e m u l s i o n p o l y -m e r i z a t i o n , Dalton m e n t i o n e d that he did not think that t h e r e would be any p l a n t s c o n s t r u c t e d in the n e a r future , but that when new plant w a s be ing i n s t a l l e d the e c o n o m i c s of g a m m a - i n d u c e d s y n t h e s i s should be c l o s e l y s t u d i e d . He doubted w h e t h e r s u c h a d v a n t a g e s a s f r e e d o m f r o m c a t a l y s t c o u l d be u s e d to o f f s e t d i r e c t c o s t c o m p a r i s o n s . In the c a s e of v i n y l -c h l o r i d e , w h e r e wor ld produc t ion w a s b e i n g expanded, the p o s s i b i l i t y of r e p l a c i n g c o n v e n t i o n a l i n i t i a t o r s by s o u r c e s both in bulk and e m u l s i o n shou ld b e e x a m i n e d a s the high G - v a l u e s might l e a d to s i g n i f i c a n t r e -d u c t i o n s in c o s t s .

H u m m e l ( F e d e r a l Republ ic of G e r m a n y ) m e n t i o n e d that a c c o r d i n g to h i s own c a l c u l a t i o n s , 6 0 C o , o r p o s s i b l y 1 3 7 C s , c o u l d b e a s c h e a p a s c o n -v e n t i o n a l c a t a l y s t s . The m a i n r e a s o n s f o r th i s a r e the l ow d o s e - r a t e s n e e d e d (i. e . in the range of 10 3 - 104 r a d / h ) , and the f a l l in the p r i c e of g a m m a s o u r c e s during the l a s t few y e a r s . F u r t h e r m o r e , the r a d i a t i o n -in i t ia ted p r o c e s s h a s a n u m b e r of a d v a n t a g e s o v e r the c o n v e n t i o n a l one: v a r i a b i l i t y of in i t ia t ion ra te during the r e a c t i o n , c o n t r o l of the m o l e c u l a r we ight by the in i t iat ion rate and not by r e g u l a t o r s , thus avo id ing e n d - g r o u p s of r e g u l a t o r m o l e c u l e s , and f ina l ly the p o s s i b i l i t y of r a d i a t i o n - g r a f t i n g of the l a t e x .

M r s . I o n e s c u (Romania) r e m a r k e d that the g a m m a - i n i t i a t e d c h l o r i -nat ion of b e n z e n e p r o c e e d s wi th G - v a l u e s up to about 1 0 5 ( s e e Footnote 4).


C o n t r a r y to the f ind ings of o t h e r a u t h o r s , no r e m a r k a b l e d i f f e r e n c e s w e r e found in the i s o m a r c o m p o s i t i o n of the h e x a c h l o r o c y c l o h e x a n e c o m p a r e d wi th the r e a c t i o n product of the u . v . - i n i t i a t e d ch lor ina t ion .

S t e i n b e r g a s k e d if M r s . I o n e s c u cou ld expand h e r r e f e r e n c e to the ox idat ion of s u l p h i d e s . H e r r e p l y w a s that the work had b e e n pub l i shed in de ta i l , but that the p r o c e s s w a s not be ing u s e d i n d u s t r i a l l y .

H u m m e l r e m a r k e d that t h i s r e s u l t s h o w s o n c e m o r e that , in the c a s e of l o n g - c h a i n r e a c t i o n s , the kind of in i t ia t ion d o e s not a f f e c t the c o m p o -s i t i o n of the r e a c t i o n p r o d u c t s . Only with s h o r t - c h a i n r e a c t i o n s , b e c a u s e of the d i f f e r e n t s p e c i e s p r o d u c e d by the in i t ia t ion r e a c t i o n , s l ight d i f f e r e n c e s in the c o m p o s i t i o n of the r e a c t i o n p r o d u c t s might be o b s e r v e d .

R e f e r r i n g to D a l t o n ' s o p t i m i s t i c p i c t u r e of the u s e of ion iz ing rad ia t ion f o r the cur ing ( p o l y m e r i z a t i o n o r c r o s s - l i n k i n g ) of l a c q u e r s for c u r v e d (uneven) s u r f a c e s . H u m m e l r e m a r k e d that one of the b i g g e s t m a r k e t s in t h i s f i e l d i s that of c a r e n a m e l s . T h e r e , h o w e v e r , the hydrophi l i c baking e n a m e l s (pheno l i c s , a c r y l i c c o p o l y m e r s , u r e a and m e l a m i n e c o m b i n a t i o n s ) with t h e i r e a s y appl i ca t ion ( e l e c t r o p h o r e t i c coat ing) and good q u a l i t i e s might b e v e r y s t r o n g c o m p e t i t o r s . Dal ton r e p l i e d that the t echn ique appl ied only to i n d u s t r i a l f i n i s h i n g and that t h e r e w e r e l a r g e a r e a s w h e r e the r e s i n s m e n t i o n e d by H u m m e l w e r e not a p p r o p r i a t e .

P u i g g a v e an in troduct ion to the p r e s e n t m a i n d e v e l o p m e n t s in rad ia t ion p r o c e s s i n g in F r a n c e : (a) G a m m a - r a y - c r o s s l i n k e d p o l y e t h y l e n e f i l m i s r e a d y f o r c o m m e r c i a l i -

zat ion . (b) Wood p l a s t i c c o m p o u n d s have b e e n taken up by a p r i v a t e c o m p a n y with

i n t e r e s t i n g p r o s p e c t s f o r the i m m e d i a t e fu ture . (c) P r e - c u r i n g of na tura l rubber l a t e x by e l e c t r o n b e a m i r r a d i a t i o n i s

b e i n g a c t i v e l y i n v e s t i g a t e d in c o - o p e r a t i o n wi th p r i v a t e indus try . (d) P o l y m e r i z a t i o n of t r i o x a n e in the s o l i d s t a t e i s a l s o be ing i n v e s t i g a t e d .

Other i t e m s a r e r e f e r r e d to in the p a p e r p r e s e n t e d by Puig1 0 . S t e i n b e r g u n d e r l i n e d H u m m e l ' s r e m a r k s on the i m p o r t a n c e of m a k i n g

c o p o l y m e r s of m a t e r i a l s that would not h o m o p o l y m e r i z e . He then a s k e d P u i g why c r o s s - l i n k i n g of p o l y e t h y l e n e f i l m w a s b e c o m i n g a 6 0 C o r a t h e r than a m a c h i n e p r o c e s s in F r a n c e . P u i g m e n t i o n e d that t h i s w a s a d e c i s i o n of the p r o d u c e r s on w h i c h he cou ld not c o m m e n t .

He s u g g e s t e d that it would be u s e f u l to p e r s u a d e e l e c t r i c i t y c o m p a n i e s to s e l l high v o l t a g e d. c . Dal ton m e n t i o n e d that w h i l e t h i s p o s s i b i l i t y w a s n a t u r a l l y be ing c o n s i d e r e d , it w a s at p r e s e n t not f e a s i b l e in the United K i n g d o m .

4. 2. W o o d - p l a s t i c s

S i n g e r (Denmark) p r e s e n t e d a s t a t e m e n t c o n c e r n i n g the ac tua l s t a t u s of the i r r a d i a t e d w o o d - p o l y m e r c o m b i n a t i o n s , and po inted out that t h e r e s t i l l r e m a i n u n s o l v e d p r o b l e m s , in i m p r e g n a t i o n t e c h n o l o g y such a s the eva luat ion of t y p e s of p o l y m e r s and in radiat ion t e c h n o l o g y such a s the type of radiat ion s o u r c e . He c l a i m e d that the appl i ca t ion of e l e c t r o n a c c e l e r a t o r s for t h i s p r o c e s s h a s not b e e n s u f f i c i e n t l y i n v e s t i g a t e d .

10 LEVEQUE, P . , PUIG, J . R . , "Le d e v e l o p p e m e n t de l a r a d i o c h i m i e : quelques aspects d e la c o n j u n c t u r e " , this Report, P L - 2 3 6 / 8 .


P u i g m e n t i o n e d that one F r e n c h c o m p a n y i s now o f f e r i n g i r r a d i a t e d c o m -b inat ions of b e e c h and m e t h y l - m e t h a c r y l a t e on a c o m m e r c i a l s c a l e , and that t h i s c o m p a n y has b a s e d i t s product ion on an e x t e n s i v e m a r k e t a n a l y s i s c o v e r i n g m o r e than 100 wood m a n u f a c t u r e r s and c o n s u m e r s . S te inberg a g r e e d wi th the v i e w s e x p r e s s e d by S inger and added that he had b e e n able to load pine with p o l y e t h y l e n e to 100% by weight . Dalton pointed out that c o m m e r c i a l 6 0Co plants for fabr ica t ing w o o d - p l a s t i c have to be ra ther l a r g e to be e c o n o m i c a l l y a t t r a c t i v e , and th i s puts a l i m i t on p o s s i b l e i n t e r e s t i n g p r o d u c t s . S i l v e r m a n r e f e r r e d to the s t a r t i n g - u p of o ther r a d i a t i o n - t e c h n i c a l p r o c e s s e s s u c h a s m e d i c a l s t e r i l i z a t i o n and p o l y -e t h y l e n e c r o s s - l i n k i n g , wh ich f r o m v e r y s m a l l b e g i n n i n g s have i n c r e a s e d to v e r y important product ion . W o o d - p l a s t i c p r o d u c t s could probab ly in the beg inning f ind appl i ca t ion in h i g h - c o s t s p e c i a l i z e d a r t i c l e s for a n u m b e r of s m a l l e r e n t e r p r i s e s . Such e n t e r p r i s e s could v e r y w e l l be s t a r t e d in d i f f e r e n t c o u n t r i e s u s i n g the i n c r e a s i n g n u m b e r of product ion and p i lo t -p lant i r r a d i a t i o n i n s t a l l a t i o n s o f f e r i n g t h e s e s e r v i c e s to i n t e r e s t e d w o o d -m a n u f a c t u r e r s .

In th i s c o n n e c t i o n S inger r e f e r r e d to s o m e e x p e r i e n c e r e g a r d i n g spor t ing a r t i c l e s , w h e r e the product ion p r i c e would have no p r a c t i c a l i n f l u e n c e on the f ina l p r i c e of the product , and w h e r e t r a n s p o r t of the p r e f a b r i c a t e d p r o d u c t s to a s e r v i c e i r r a d i a t i o n plant and back i s no m a j o r p r o b l e m .

5. In format ion

It w a s g e n e r a l l y a g r e e d that t h e r e i s a need for fur ther e x c h a n g e of i n f o r m a t i o n . W h e r e a s m e e t i n g s on fundamenta l a s p e c t s a r e he ld ra ther f r e q u e n t l y , m e e t i n g s on app l i ca t ions a r e m o r e r e g i o n a l and r e s t r i c t e d . T h e r e f o r e f u r t h e r m e e t i n g s of a c l e a r i n g - h o u s e type a r e r e q u i r e d .

Hara (IAEA) d e s c r i b e d the two funct ions of the IAEA a s r e g u l a t o r y func t ions , s u c h a s s a f e g u a r d s and s a f e t y , and p r o m o t i n g func t ions , such a s t e c h n i c a l a s s i s t a n c e , s c i e n t i f i c i n f o r m a t i o n and p r o m o t i o n of p a r t i c u l a r r e s e a r c h .

To i m p l e m e n t t h e s e func t ions , the o r g a n i z a t i o n of s y m p o s i a , p a n e l s , e t c . ,. w a s m e n t i o n e d .

B e s w i c k (IAEA) pointed out that the IAEA w a s c o m p i l i n g a w o r l d l i s t of l a r g e rad ia t ion s o u r c e f a c i l i t i e s , and that th i s would inc lude a l l f a c i l i t i e s with m o r e than 20 000 Ci of ac t iv i ty . It w a s hoped that a l l M e m b e r S ta tes w o u l d c o - o p e r a t e in supply ing i n f o r m a t i o n so that the d e t a i l s in the l i s t would b e a s c o m p l e t e a s p o s s i b l e . A C o n s u l t a n t s ' M e e t i n g on B i b l i o g r a p h i e s on Industr ia l A p p l i c a t i o n s of R a d i o i s o t o p e s in Apr i l 1966 had r e s u l t e d in t e n t a t i v e a g r e e m e n t f r o m s o m e M e m b e r S t a t e s to supply r e g u l a r l y to the A g e n c y , on p u n c h e d - c a r d s o r tape , r e f e r e n c e s f r o m l i t e r a t u r e p u b l i s h e d in e a c h country . It w a s hoped to s tar t publ icat ion of a q u a r t e r l y b i b l i o -g r a p h y l a t e r t h i s y e a r , and t h i s would conta in r e f e r e n c e s on radiat ion c h e m i s t r y , inc luding p a t e n t s .

A Study Group on I rrad ia ted Wood P l a s t i c C o m b i n a t i o n s w a s to be c o n v e n e d in Bangkok in N o v e m b e r 1967 to d i s c u s s the e c o n o m i c and t e c h n i c a l s i g n i f i c a n c e of t h i s m a t e r i a l in A s i a and the F a r E a s t . A l a r g e n u m b e r of c o u n t r i e s in t h i s r e g i o n w e r e c a r r y i n g out r e s e a r c h on th i s m a t e r i a l , and it w a s hoped that th i s r e s e a r c h could be c o - o r d i n a t e d .


S e v e r a l P a n e l m e m b e r s po inted out that p s e u d o - t e c h n i c a l i n f o r m a t i o n r e l e a s e d to the p r e s s o f t en c r e a t e d a b e t t e r r e s p o n s e f r o m i n d u s t r y than a r t i c l e s in the s c i e n t i f i c l i t e r a t u r e .

P u i g d e s c r i b e d the i n f o r m a t i o n w o r k that had a r i s e n f r o m c o - o p e r a t i o n b e t w e e n the E u r o p e a n C o m m o n Marke t c o u n t r i e s during the p a s t t h r e e y e a r s : (a) I n v e s t i g a t i o n of the s i tuat ion in the t e x t i l e indus try in the s i x c o u n t r i e s by v i s i t s of n u c l e a r e x p e r t s . The r e s u l t w a s to be m a d e publ ic at the b e -g inning of Ju ly 1967 in an in ternat iona l s y m p o s i u m . (b) The g a t h e r i n g of i n f o r m a t i o n r e l a t i n g to the v a r i o u s t e c h n i q u e s of i r r a d i a t i o n . (c) The g a t h e r i n g of i n f o r m a t i o n r e l a t i n g to wood t e c h n o l o g y . (d) The c e n t r a l i z a t i o n of s c i e n t i f i c , t e c h n i c a l and patent l i t e r a t u r e u s i n g c o m p u t e r s t o r a g e .

The CEA in F r a n c e i s d e v e l o p i n g m e c h a n o g r a p h i c c e n t r a l i z a t i o n of r e f e r e n c e s inc luding p a t e n t s . M o r e g e n e r a l i n f o r m a t i o n i s d i s s e m i n a t e d by o r g a n i z i n g a o n e - y e a r c o u r s e on "preparat ion and m o d i f i c a t i o n of p o l y m e r s " f o r i n d u s t r i a l i s t s and r e s e a r c h e r s at the U n i v e r s i t y of P a r i s .

A c o m p i l a t i o n of p a p e r s dea l ing wi th a p p l i c a t i o n s c a r r i e d out in F r a n c e t o g e t h e r wi th a l i s t of m a i n i r r a d i a t i o n f a c i l i t i e s i s i s s u e d annual ly .

6. N o n - t e c h n i c a l p r o b l e m s inc luding s a f e t y

Danno s t r e s s e d that wi th i n c r e a s i n g s o u r c e d i m e n s i o n s the p o t e n t i a l h a z a r d i s g r e a t l y i n c r e a s e d . The i n s t a l l a t i o n s have to be s a f e a g a i n s t rad ia t ion , p r e s s u r e , f i r e or e x p l o s i o n and c o r r o s i o n . W h e r e a s the p r o b l e m of h a z a r d s of n u c l e a r r e a c t o r s i s w e l l taken c a r e of , s i m i l a r a c t i v i t i e s should be p r o m o t e d in rad ia t ion c h e m i s t r y .

S t e i n b e r g m e n t i o n e d a n u m b e r of s a f e t y p r o b l e m s r e l a t i n g to the u s e of e x p e r i m e n t a l and d e v e l o p m e n t rad ia t ion f a c i l i t i e s for woTking wi th c o m b u s t i b l e and e x p l o s i b l e m a t e r i a l s . Radiat ion b i o l o g i c a l h a z a r d s a r e f a i r l y c o v e r e d , but the addi t ional load f r o m c o m b u s t i o n , e x p l o s i o n and c h e m i c a l h a z a r d s shou ld be t r e a t e d on a b r o a d e r b a s i s . E x c h a n g e of i n f o r m a t i o n c o n c e r n i n g the e x p e r i e n c e s of v a r i o u s g r o u p s and t h e i r d e s i g n s t a n d a r d s would be v e r y v a l u a b l e . U n d e r w a t e r f a c i l i t i e s a r e v e r y s a f e f o r u s e w h e n d e a l i n g wi th e x p l o s i v e s in v e s s e l s ; h o w e v e r , they p r e s e n t g r e a t p r o b l e m s in bui ld ing and o p e r a t i n g f l o w equ ipment . C l o s e d c a v e f a c i l i t i e s m a k e e x p e r i m e n t a l and d e v e l o p m e n t o p e r a t i o n s m u c h m o r e conven ien t but they p r e s e n t g r e a t e r h a z a r d p r o b l e m s .

H u m m e l s t a t e d that s o u r c e s should b e d e s i g n e d to w i ths tand p r e s s u r e and s h o c k w a v e s . He p r e f e r r e d c o r o n a - t y p e s o u r c e a r r a n g e m e n t s doubly conta ined in s t a i n l e s s s t e e l and c e l l s of "open roof" d e s i g n .

P u i g d e s c r i b e d s o m e a c c i d e n t s o c c u r r i n g during m e a s u r e m e n t of s o u r c e in dry i r r a d i a t i o n c e l l s , and m e c h a n i c a l f a i l u r e s in s w i m m i n g -poo l i r r a d i a t i o n u n i t s .

S i l v e r m a n s u g g e s t e d that the s a f e t y p r o b l e m s should be t r e a t e d s e p a -r a t e l y f o r r e s e a r c h l a b o r a t o r i e s , t e s t i n g and pi lot p l a n t s un i t s , and i n -d u s t r i a l p lan t s . Dal ton suppor ted t h i s with the addi t iona l r e m a r k that h a z a r d s can be r e d u c e d on the l a b o r a t o r y s c a l e by a r e d u c t i o n of the quantity of m a t e r i a l , and in i n d u s t r i a l plant u s e should be m a d e of b a c k -ground knowledge of e x p e r t s f o r c o n v e n t i o n a l c h e m i c a l p l a n t s . To a r e m a r k f r o m Getoff c o n c e r n i n g the e x p l o s i o n h a z a r d i n v o l v e d in i r r a d i a t i o n s


of l iquid n i t r o g e n , Z a g o r s k i s t a t e d that n e i t h e r in P o l a n d nor in the USSR had th i s p r o b l e m o c c u r r e d during t h e i r e x p e r i m e n t s .

P u i g m e n t i o n e d that s o m e of the p r o b l e m s , and in p a r t i c u l a r i r r a d i a -t i o n s at a g o g e n i c t e m p e r a t u r e s , have a l r e a d y b e e n e x p e r i e n c e d and s o l v e d in r e s e a r c h r e a c t o r l o o p s .

Dalton po inted out that b e s i d e s the s a f e t y a s p e c t s t h r e e o t h e r p r o b l e m s a r i s e during the t r a n s f e r s t e p s f r o m l a b o r a t o r y s c a l e to i n d u s t r i a l d i -m e n s i o n s : r e l i a b i l i t y ( 6 0 0 - 8 0 0 h / a wi th p r e d i c t e d shutdowns) , g u a r a n t e e d supp ly of s o u r c e s , and e c o n o m i c a s s e s s m e n t b a s e d on i n d u s t r i a l s tandard m e t h o d s .

Hahn d e s c r i b e d in de ta i l s a f e t y a s p e c t s of rad ia t ion t e c h n o l o g y u s i n g m a c h i n e s w h e r e the product ion of the m a c h i n e , p e r s o n n e l and p r e c a u t i o n s a g a i n s t r e a c t i o n a c c i d e n t s have to be c o n s i d e r e d . P r o p e r i n t e r l o c k i n g s y s t e m s can b e p r o v i d e d but s p e c i a l a s p e c t s have to b e c o n s i d e r e d a l s o , s u c h a s r e s i d u a l c h a n g e s in c a p a c i t o r s f o r l i n e a r s .

C o n c e r n i n g the t e r m s of r e f e r e n c e of th i s P a n e l , P u i g s t r e s s e d that m a r k e t i n g w a s o u t s i d e i t s s c o p e and that in F r a n c e th i s ac t iv i ty i s c o n f i n e d to i n d u s t r y . S t e i n b e r g a g r e e d in p r i n c i p l e , s ta t ing that r e c o m m e n d a t i o n s shou ld n e v e r t h e l e s s be m a d e , and he p r o p o s e d that i n d u s t r i a l i s t s shou ld b e inv i t ed to future m e e t i n g s .

R E F E R E N C E S

[1] BRYNJOLFSON, A . , THAARUP, B . , Ristf Rep. No. 53, Danish A. E. K. (1963). [2] NAKAI, Y . , Jap . J. Phys. 2 (1963) 743. [3] BERGER, M . J . , " M o n t e Car lo c a l c u l a t i o n of t he pene t ra t ion and d i f fus ion of f as t charged pa r t i c l e s " ,

Methods in C o m p u t a t i o n a l Physics 1 (ALDER, B. , FERNBACH, S . , ROTENBERG, M . , Eds), A c a d e m i c Press, New York (1963); BERGER, M . J . , " T a b l e s of energy losses and range of e lec t rons and posi t ions" . Paper 10, Pub l i ca t ion 1133, US Na t iona l A c a d e m y of Sciences , N a t i o n a l Research Counc i l (1964).

[4] SPENCER, L. V . , Energy Dissipat ion by Fast Electrons, NBS Monograph No. 1, Na t iona l Bureau of Standards, Washington (1959).

[5] KNIEDLER, M . , SILVERMAN, J . , Paper A / M - Z , Seventh Japan C o n f e r e n c e on Radioisotopes, 1966 (in press).

[6] HART, E . J . , Radia t . Res. 1 (1954) 342. [7] DONDES, S . , Int . Conf . p e a c e f u l Uses a t o m . Energy (Proc. Conf. Geneva , 1955) 14 UN, New York

(1956) 176; HEARNE, J . A . , Radiat . Res. 15 (1961) 254; STEINBERG, M . , Radiat ion Processing Report No. 1, G a m m a I r rad ia t ion Exper iments in t he N 2 - O z Sys tem, BNL Rep. 612, Brookhaven Na t iona l Laboratory (1960).

[81 BROWN, R . D . , DONDES, S . , HARTECK, P . , S o m e Studies of t h e Ion iz ing Radiat ion Induced Isotopic Exchange in Gaseous Ni t rogen, Progress Rep. USAEC RPI 321 -9 , Rensselaer Po ly techn ic Ins t i tu te , T roy , N. Y. (1966).

[9] SILVERMAN, J . , Trans . A m . nucl . Soc. 7 (1964) 442. [10] M O T Z , J . W . , OLSEN, H . , KOCH, A . W . , Rev. m o d . Phys. 36 (1964) 881. [11] SCHLAG, E . W . , SPARAPANY, J . J . , J . A m . c h e m . Soc. 86 (1964) 1875. [12] BROIDA, H . P . , MOYER, J . W . , J. opt . Soc. Am. 42 (1952) 37 ; BASS, A . M . , BROIDA. H . P . (Eds).

Fo rma t ion and Trapp ing of F ree Radicals , A c a d e m i c Press, New York (1960); FEHSENFELD, F . C . , EVENSON, K. M . , BROIDA, H . P . , Rev. sc ient . Ins t rum. 36 (1965) 294.

[13] SNOW, A . , P r i v a t e c o m m u n i c a t i o n . [14] LAMPE, F. W . , JOHNSTON, W. H . , Paper B /3 -2 , Seventh Japan C o n f e r e n c e on Radioisotopes,

1966 (in press).

OBSERVATIONS A N D RECOMMENDATIONS 1 7

III. GENERAL OBSERVATIONS AND RECOMMENDATIONS 1. S o u r c e s

S o u r c e s f o r u s e in c o m m e r c i a l radiat ion c h e m i c a l p r o c e s s i n g m i g h t c o m p r i s e : 1. I sotope s o u r c e s , e . g . g a m m a - e m i t t i n g s o u r c e s l ike 6 0Co and 1 3 7Cs o r beta e m i t t e r s s u c h as 9 0Sr. 2. E l e c t r o n a c c e l e r a t o r s , such a s d. c . - m a c h i n e s , and l i n e a r a c c e l e r a t o r s with or without X - r a y c o n v e r s i o n d e v i c e s . 3. C h e m o n u c l e a r r e a c t o r s u t i l i z ing , f o r e x a m p l e , f i s s i o n f r a g m e n t s or i on i za t ion radiat ion f r o m l o o p s . 4 . Spent f u e l e l e m e n t f a c i l i t i e s .

The d e l i b e r a t i o n s of the P a n e l c o n c e n t r a t e d on the s o u r c e t y p e s w h e r e an e a r l y i n d u s t r i a l appl icat ion could be f o r e s e e n , and the P a n e l did not d i s c u s s in depth a l l the p o s s i b i l i t i e s m e n t i o n e d above .

1 . 1 . I so tope s o u r c e s

With r e g a r d to i s o t o p e s o u r c e s it w a s o b s e r v e d that abundant i n f o r m a t i o n w a s ava i lab le on the c o n s t r u c t i o n and opera t ion of 6 0Co p lant s . The m o s t i m p o r t a n t d e v e l o p m e n t s e e m s to be the c o n s t r u c t i o n of the bonded s o u r c e s , which o f f e r an i m p r o v e d s o u r c e i n t e g r i t y .

Much i n t e r e s t w a s shown in the appl icat ion of 1 3 7Cs in rad ia t ion c h e m i c a l p r o c e s s i n g . The advantages inc lude l i gh ter s h i e l d i n g ( m o b i l e i r r a d i a t o r s ) , p o s s i b l e h i g h e r s o u r c e u t i l i za t ion e f f i c i e n c y , c h e a p e r s o u r c e m a t e r i a l a s 1 3 7 Cs i s produced f r o m r e a c t o r w a s t e product s , and a l o n g e r h a l f - l i f e . P r i c e s f o r u n e n c a p s u l a t e d 1 3 7 Cs m i g h t be e x p e c t e d to be about 10 - 15 ^ / C i , when l a r g e s e p a r a t i o n plants a r e b e c o m i n g o p e r a t i o n a l . P r o b l e m s inc lude i m p r o v e d e n c a p s u l a t i o n t e c h n i q u e s as t h e s e s o u r c e s m u s t have a i o n g e r l i f e t i m e , and su i tab le i r r a d i a t i o n t e c h n i q u e s n e e d to b e d e v e l o p e d .

1 . 2 . E l e c t r o n a c c e l e r a t o r s

With r e g a r d to e l e c t r o n a c c e l e r a t o r s the P a n e l o b s e r v e d that a s p e c i a l s i tuat ion a r o s e b e c a u s e such m a c h i n e s had to be d e s i g n e d f o r a c e r t a i n , quite high p o w e r output in o r d e r to be e c o n o m i c a l . In addit ion, a s s e m b l y l i n e product ion w a s n e c e s s a r y f o r obtaining low p r i c e s on s u c h e q u i p m e n t . It w a s t h e r e f o r e s u g g e s t e d that nat ional l a b o r a t o r i e s or s e r v i c e f a c i l i t i e s m a d e i r r a d i a t i o n s e r v i c e s ava i lab le , s o that e n t e r p r i s e s that could not j u s t i f y a l a r g e plant on t h e i r own could be in troduced on a s h a r e b a s i s . It w a s e m p h a s i z e d that s u c h equipment m u s t m e e t the s a m e r e l i a b i l i t y r e q u i r e m e n t s a s convent iona l p r o c e s s equipment , and that f u r t h e r d e v e l o p m e n t work n e e d s to be done in th i s r e s p e c t . The P a n e l o b s e r v e d that v e r y l o w - e n e r g y a c c e l e r a t o r s (20 keV) m i g h t be appl i cab le to c e r t a i n p r o c e s s e s , if a su i tab le i r r a d i a t i o n technique can be w o r k e d out.

1 . 3 . C h e m o n u c l e a r r e a c t o r s

The appl icat ion of c h e m o n u c l e a r r e a c t o r s i s s t i l l at the e a r l y e x p e r i -m e n t a l s t a g e . The cont inuat ion of s u c h work i s j u s t i f i e d as c h e m o n u c l e a r

2

1 8 OBSERVATIONS A N D RECOMMENDATIONS

r e a c t o r s could prov ide the c h e a p e s t i o n i z i n g e n e r g y f o r e s e e a b l e . It should be e m p h a s i z e d , h o w e v e r , that such plants n e e d to be v e r y l a r g e to be e c o n o m i c a l , s o that only product s f o r which t h e r e i s a l a r g e demand ( s u c h a s n i t r o g e n f e r t i l i z e r s ) should be c o n s i d e r e d . With r e g a r d to the appl i ca t ion of r e a c t o r l o o p s , it w a s o b s e r v e d that t h e s e could m a i n l y be c o n s i d e r e d i n t e r e s t i n g when it w a s conven ient to in tegra te the c h e m i c a l f a c t o r y with a m u l t i p u r p o s e n u c l e a r p o w e r plant . To p e r f o r m e x p e r i m e n t a l work on th i s subjec t , it was s u g g e s t e d that i n - p i l e r e s e a r c h loop f a c i l i t i e s , s u c h as the B r o o k h a v e n c h e m o n u c l e a r i n - p i l e loop, should be m a d e ava i lab le to i n v e s t i g a t o r s f r o m al l c o u n t r i e s .

1 . 4 . Spent f u e l s

In g e n e r a l , spent fue l e l e m e n t s w e r e c o n s i d e r e d i m p r a c t i c a l f o r rad ia t ion c h e m i c a l p r o c e s s i n g at p r e s e n t .

1 . 5 . Safe ty

The s a f e t y of l a r g e i r r a d i a t i o n f a c i l i t i e s m a y be div ided into the s a f e t y a s p e c t s of d e s i g n and the s a f e t y of c h e m i c a l r e a c t i o n s under i r r a d i a t i o n s , and it w a s o b s e r v e d that i n f o r m a t i o n on the s a f e t y of both l a b o r a t o r y -s c a l e e x p e r i m e n t s and that of p l a n t - s c a l e d e v e l o p m e n t i s not w i d e l y ava i lab l e . It w a s pointed out that appropr iate m e a s u r e s for guidance m u s t be e s t a b l i s h e d on the s a f e t y of l a r g e i r r a d i a t i o n f a c i l i t i e s , and m o r e e f f o r t s are needed to d i s s e m i n a t e i n f o r m a t i o n on th i s subjec t .

2 . D o s i m e t r y

It w a s o b s e r v e d that v e r y m a n y o r g a n i z a t i o n s w e r e dea l ing a l r e a d y with d o s i m e t r y p r o b l e m s , and that e f f o r t s should be d i r e c t e d to c o -ord inate t h e s e e x i s t i n g a c t i v i t i e s r a t h e r than to c r e a t e new o n e s .

In g e n e r a l , it w a s pointed out that work should be pursued on d o s e d i s t r i b u t i o n s in c o m p l e x t a r g e t s , and that fundamenta l i n f o r m a t i o n should be obtained on the reac t ion m e c h a n i s m s of p l a s t i c f i l m d o s i m e t e r s .

The P a n e l a g r e e d that it w a s v e r y important , when e s t a b l i s h i n g a rad ia t ion p r o c e s s , to c a r r y out an a c c u r a t e d o s i m e t r y s u r v e y , but w h e n e v e r p o s s i b l e to subst i tute f o r t h i s a rout ine d o s i m e t r y p r o g r a m m e with an e x t e n s i v e p r o c e s s c o n t r o l .

3. F u n d a m e n t a l s

The ta sk of de f in ing s u b j e c t s of r e s e a r c h f o r p r a c t i c a l p u r p o s e s i s a l w a y s d i f f i cu l t . The t o p i c s c i t ed are of much w i d e r i n t e r e s t than the p r a c t i c a l end to which th i s P a n e l w a s m a i n l y devoted . N e v e r t h e l e s s , the P a n e l found s o m e t o p i c s of p a r t i c u l a r r e l e v a n c e and it d i r e c t s the attent ion of radiat ion s c i e n t i s t s t o w a r d s t h e m .

The fundamenta l t a s k s w e r e d iv ided into three c a t e g o r i e s : r e s e a r c h p r o b l e m s , t e c h n i q u e s , and r e a c t i o n s of potent ia l p r a c t i c a l i n t e r e s t .

19 OBSERVATIONS A N D RECOMMENDATIONS

3 . 1 . R e s e a r c h p r o b l e m s

T h e p h e n o m e n a that s t i m u l a t e d the e x t e n s i v e d i s c u s s i o n w e r e as f o l l o w s :

(1) L E T e f f e c t s ( inc luding f i s s i o n f r a g m e n t c h e m i s t r y ) (2) High d o s e - r a t e e f f e c t s (3) L o w - t e m p e r a t u r e e f f e c t s (4) High pur i ty (5) H e t e r o g e n e o u s r e a c t i o n s (6) C o r r e l a t i o n of the e f f e c t s of rad ia t ion c h e m i s t r y and of l o w -

t e m p e r a t u r e g a s d i s c h a r g e (7) E f f e c t s of t r a n s i e n t s p e c i e s o ther than f r e e r a d i c a l s in the

ground s t a t e . The f i r s t f o u r are p a r a m e t e r s of n o r m a l i n t e r e s t to the rad ia t ion

c h e m i s t . The P a n e l m e n t i o n e d t h e m e x p l i c i t l y f o r the f o l l o w i n g r e a s o n s . In the c a s e of L E T , it i s i n c r e a s i n g l y apparent that s t u d i e s i n v o l v i n g t h i s p a r a m e t e r a r e o f ten i n c o m p l e t e and a m b i g u o u s . Knowledge on f i s s i o n f r a g m e n t c h e m i s t r y i s inadequate . F u r t h e r m o r e , t h e r e i s s o m e i n f o r m a t i o n to s u g g e s t that e l e c t r o n and g a m m a - r a y e f f e c t s m a y not, a s i s o f ten a s s u m e d , be e q u i v a l e n t . S i m i l a r l y , e f f e c t s at v e r y h igh d o s e -r a t e s h a v e b e e n quite u n e x p e c t e d on the b a s i s of l o w d o s e - r a t e r e s u l t s ; they m e r i t f u r t h e r s tudy. R e s u l t s at low t e m p e r a t u r e h a v e been u s e d to advance m e c h a n i s m t h e o r i e s . The d i s c u s s i o n s s h o w e d that m a n y of t h e s e s t u d i e s w e r e b a s e d on s y s t e m s in which the na ture of the s o l i d w a s too p o o r l y d e f i n e d . The q u e s t i o n of pur i ty i s a l w a y s of c o n c e r n but the v a s t l y d i f f e r e n t r e s u l t s obta ined in the rad ia t ion c h e m i s t r y of u l t r a - d r y and u l t r a - p u r e s y s t e m s now o b l i g e s rad ia t ion s c i e n t i s t s to r e - e x a m i n e s e v e r a l s y s t e m s that had b e e n c o n s i d e r e d w e l l - k n o w n , p a r t i c u l a r l y s i n c e s o m e of the n e w e s t r e s u l t s point to h ighly i n c r e a s e d y i e l d s in p o l y m e r i -zat ion p r o c e s s e s of c o m m e r c i a l i n t e r e s t . Jus t a s t r a c e h o m o g e n e o u s c o n t a m i n a n t s s o m e t i m e s p o i s o n i m p o r t a n t and i n t e r e s t i n g r e a c t i o n s , h e t e r o g e n e o u s a d d i t i v e s s o m e t i m e s s t r o n g l y enhance s u c h r e a c t i o n s . Appl ied r e s e a r c h in h e t e r o g e n e o u s s y s t e m s i s s t i l l too m e a g r e and should be e n c o u r a g e d .

The P a n e l a l s o took n o t i c e of the a d v a n c e s in gas d i s c h a r g e t e c h n i q u e s and r e c o m m e n d s cont inuing and i n c r e a s e d at tent ion to t h i s s u b j e c t . G a s d i s c h a r g e m a y turn out to be a s t r o n g c o m p e t i t o r of rad ia t ion in c o m m e r c i a l a p p l i c a t i o n s , and a c o m p a r i s o n of the e f f e c t s should be m a d e in the s y n t h e s i s of c h e m i c a l s that can be m a d e by both t e c h n i q u e s . T h e l a s t i t e m on the l i s t of r e c o m m e n d e d t o p i c s f o r r e s e a r c h r e f l e c t s the P a n e l ' s o b s e r v a t i o n that m o s t of the p r a c t i c a l app l i ca t ions u n d e r c o n s i d e r a t i o n i n v o l v e the u s e of rad ia t ion a s a g e n e r a t o r of f r e e r a d i c a l s in the ground s ta te a l l through a t a r g e t . T h i s i s f a r too l i m i t e d , and the P a n e l e n c o u r a g e s m o r e r e s e a r c h into app l i ca t ions of the o t h e r s p e c i e s produced by rad ia t ion .

3 . 2 . B a s i c t e c h n i q u e s

T h e b a s i c t e c h n i q u e s d i s c u s s e d w e r e a s f o l l o w s : (1) P u l s e d r a d i o l y s i s (2) F l a s h p h o t o l y s i s ( inc lud ing p u l s e d l a s e r b e a m s )

2 0 OBSERVATIONS A N D R E C O M M E N D A T I O N S

(3) F a s t ESR m e t h o d s (4) I rrad ia t ion at l iquid h e l i u m t e m p e r a t u r e s (5) E l e c t r i c d i s c h a r g e m e t h o d s (6) F a r u. v. m e t h o d s . The f i r s t t h r e e t e c h n i q u e s r e f l e c t the P a n e l ' s v i e w that i n f o r m a t i o n on

prompt e f f e c t s a r e u s e f u l not only in pure r e s e a r c h but a l s o in the unders tand ing of such d i v e r s e appl ied p r o b l e m s a s h igh ly i n c r e a s e d p o l y m e r i z a t i o n r a t e s of u l t r a - p u r e v iny l m o n o m e r s , d a m a g e to r e a c t o r c o o l a n t s and m o d e r a t o r s , and the bu i ld -up of u n s a t u r a t i o n of p o l y o l e f i n s .

Liquid h e l i u m f r e e z e s a l m o s t a l l m o l e c u l a r mot ion , and can be u s e d to p r e s e r v e m a n y e a r l y radiat ion e f f e c t s without m o r e e x p e n s i v e p u l s i n g equ ipment .

The g a s d i s c h a r g e method i s of i n t e r e s t not only a s a t echnique that i s potent ia l ly c o m p e t i t i v e with radiat ion , but a l s o as a g e n e r a t o r of g a s e o u s a t o m s f o r r e s e a r c h p r o b l e m s that d i s t i n g u i s h b e t w e e n f r e e r a d i c a l and o t h e r e f f e c t s in rad ia t ion c h e m i s t r y . F a r u. v. t e c h n i q u e s can be u s e d to g e n e r a t e a s h a r p l y def ined r a n g e of a t o m i c , m o l e c u l a r and ion ic s p e c i e s in s e l e c t e d s t a t e s of e x c i t a t i o n and thus s e r v e a s i m i l a r end.

3 . 3 . R e a c t i o n s of potent ia l p r a c t i c a l i n t e r e s t

The l i s t that f o l l o w s i s not in tended to c o v e r p r o m i s i n g p r o c e s s app l i ca t ions but i t r e f l e c t s the P a n e l ' s v i e w that t h e s e t o p i c s d e s e r v e i n c r e a s e d i n d u s t r i a l i n t e r e s t :

(1) P o l y m e r i z a t i o n and c o p o l y m e r i z a t i o n of u l t r a - p u r e s y s t e m s (2) H e t e r o g e n e o u s p o l y m e r i z a t i o n and t e l o m e r i z a t i o n r e a c t i o n s (3) Chain c u r i n g r e a c t i o n s at high d o s e - r a t e s .

4 . A p p l i c a t i o n s

The P a n e l c o n s i d e r e d that the p r e s e n t p o s i t i o n r e g a r d i n g rad ia t ion c h e m i c a l p r o c e s s i n g could be d iv ided into t h r e e c a t e g o r i e s :

(1) Industr ia l radiat ion c h e m i c a l p r o c e s s e s now in e x i s t e n c e , an e x a m p l e of which i s c r o s s l i n k i n g of po lye thy l ene ;

(2) P r o c e s s e s c u r r e n t l y in advanced s t a g e s of d e v e l o p m e n t , s u c h a s w o o d - p l a s t i c combinat ion;

(3) Subjects w h e r e f u r t h e r s tudy m a y l ead to e c o n o m i c a l p r o c e s s e s and p r o d u c t s .

4 . 1 . Industr ia l rad ia t ion c h e m i c a l p r o c e s s e s in o p e r a t i o n

The P a n e l a g r e e d that t h e r e w a s no point in e x t e n s i v e l y d i s c u s s i n g p r o c e s s e s in t h i s c a t e g o r y .

4 . 2 . P r o c e s s e s in advanced d e v e l o p m e n t a l s t a g e

In th i s c a t e g o r y a n u m b e r of t h e s e p r o c e s s e s a r e be ing s tud ied in de ta i l by g r o u p s invo lv ing c o m m e r c i a l a s p e c t s inc lud ing patents and p r o p r i e t o r y k n o w - h o w . In m a n y i n s t a n c e s t h e r e i s i n s u f f i c i e n t background knowledge to support t h e s e p r o g r a m m e s . In p a r t i c u l a r i t w a s f e l t that k i n e t i c s of r e a c t i o n in high i n t e n s i t y e l e c t r o n b e a m s and in d y n a m i c s y s t e m s could u s e f u l l y be the s u b j e c t of m o r e i n t e n s i v e s t u d i e s . A l s o

21 OBSERVATIONS A N D R E C O M M E N D A T I O N S

the k i n e t i c s and m e c h a n i s m of cha in r e a c t i o n s with r e s p e c t to h igh pur i ty s y s t e m s should be c o n s i d e r e d . The e f f e c t of L E T i s a l s o f a r f r o m c l e a r in m a n y c a s e s of p r a c t i c a l i n t e r e s t .

4 . 3 . F u t u r e potent ia l p r o c e s s e s

The P a n e l r e c o g n i z e d that the c h o i c e of s u b j e c t depends to a l a r g e extent on p e r s o n a l opinion and l o c a l c o n d i t i o n s . It may , h o w e v e r , be r e l e v a n t to point out that there i s r e l a t i v e l y l i t t l e e x p e r i m e n t a l data on i n - p i l e r e a c t o r and h e a v y - c h a r g e d p a r t i c l e s radiat ion c h e m i s t r y . A l s o , in chain r e a c t i o n s that do not l e a d to p o l y m e r s there have been f e w s y s t e m a t i c s t u d i e s . In p o l y m e r i z a t i o n f u r t h e r ac t iv i ty m a y be c o n s i d e r e d such a s e m u l s i o n and s u s p e n s i o n p o l y m e r i z a t i o n s .

The P a n e l a g r e e d that in g e n e r a l t h e r e i s i n c r e a s i n g e m p h a s i s on t e c h n o l o g y and e n g i n e e r i n g , inc luding s a f e t y , and that th i s should be f o s t e r e d .

5. R e c o m m e n d a t i o n s to the IAEA

Radiat ion c h e m i s t r y and rad ia t ion c h e m i c a l p r o c e s s e s c o v e r a wide area , and a l r e a d y a n u m b e r of o r g a n i z a t i o n s h a v e been m a k i n g an e x t e n s i v e e f f o r t . In c a r r y i n g out any p r o g r a m m e , the IAEA should pay at tent ion to the a c t i v i t i e s of o ther o r g a n i z a t i o n s to avo id u n n e c e s s a r y over lapp ing , and a l s o to the c o m m e r c i a l a s p e c t s of any p r o p o s e d a c t i v i t i e s .

5 . 1 . S o u r c e s

The P a n e l e n c o u r a g e s the IAEA in i t s e f f o r t s to c o m p i l e a l i s t of rad ia t ion s o u r c e s in m e m b e r c o u n t r i e s , and s u g g e s t s that the IAEA i n v e s t i g a t e which of t h e s e s o u r c e s are ava i lab le f o r s e r v i c e i r r a d i a t i o n s f o r o t h e r m e m b e r c o u n t r i e s . T h i s l i s t should ind ica te which s o u r c e s a r e a v a i l a b l e f o r n o n - p r o f i t a n d / o r c o m m e r c i a l o r g a n i z a t i o n s .

5 . 2 . D o s i m e t r y

The P a n e l r e c o m m e n d s that the IAEA should draft p r o c e d u r e s f o r s e l e c t e d d o s i m e t e r s , and a r r a n g e f o r t e s t i n g t h e s e at a n u m b e r of l a b o r a t o r i e s in m e m b e r c o u n t r i e s .

It f u r t h e r r e c o m m e n d s that the IAEA should c o n s i d e r the a c t i v i t i e s of v a r i o u s o r g a n i z a t i o n s in t h i s s u b j e c t with the a i m of i n t e g r a t i n g i t s a c t i v i t i e s a c c o r d i n g l y .

5 . 3 . F u n d a m e n t a l s

The P a n e l r e c o m m e n d s that the IAEA should v i e w with f a v o u r p r o p o s a l s m a d e r e g a r d i n g the t o p i c s of r e s e a r c h c i t ed in S e c t i o n III. 3. 1, p a r t i c u l a r l y the e f f e c t s of L E T ( inc luding f i s s i o n f r a g m e n t c h e m i s t r y ) , high d o s e - r a t e , pur i ty and h e t e r o g e n e o u s s y s t e m s .

The IAEA should avoid c o m m i t t i n g funds to bui ld ing n e w p u l s e d r a d i o l y s i s f a c i l i t i e s e x c e p t w h e r e it i s d e m o n s t r a t e d that r e a d y a c c e s s to s u c h f a c i l i t i e s i s g e n e r a l l y not p o s s i b l e f o r qua l i f i ed s c i e n t i s t s .

2 2 OBSERVATIONS A N D RECOMMENDATIONS

H o w e v e r , IAEA p r o v i s i o n of funds to support t r a v e l to, and work at, e x i s t i n g f a c i l i t i e s i s e n c o u r a g e d by the P a n e l .

The IAEA should s e t up advanced c o u r s e s and s e m i n a r s in rad ia t ion c h e m i s t r y , and d e v e l o p appropr ia te c o u r s e s and educa t iona l m a t e r i a l s .

5 . 4 . Appl ic a t ions

The P a n e l r e c o m m e n d s to the IAEA that i t should undertake to r e v i e w and eva luate any and al l radiat ion c h e m i c a l p r o c e s s e s and produc t s that a r e l i k e l y to be of potent ia l i m p o r t a n c e . F o r i n s t a n c e , the IAEA should under take the publ icat ion of m o n o g r a p h s dea l ing with s o m e advanced a s p e c t s of appl ied radiat ion c h e m i s t r y and t e c h n o l o g y . T h e s e eva lua t ing m o n o g r a p h s should inc lude s a f e t y a s p e c t s .

The IAEA might a r r a n g e f o r s p e c i a l i z e d e x i s t i n g r e s e a r c h and d e v e l o p m e n t f a c i l i t i e s to be m a d e avai lable to s c i e n t i s t s f r o m o ther c o u n t r i e s , in p a r t i c u l a r a c c e s s to c h e m o n u c l e a r l o o p s and l a r g e a c c e l e r -a t o r s could be of g r e a t i n t e r e s t .

5. 5. A d v i s o r y s e r v i c e to d e v e l o p i n g c o u n t r i e s

The P a n e l f e e l s that it i s d e s i r a b l e to p r o m o t e radiat ion c h e m i c a l work w h e r e s u c h work i s r e l a t e d to l o c a l n e e d s . H o w e v e r , in p r o m o t i n g such work, at tent ion m u s t be paid to the e c o n o m i c a s p e c t s . Patent a s p e c t s of work a l r e a d y c a r r i e d out in advanced c o u n t r i e s , e s p e c i a l l y t h o s e he ld by c o m m e r c i a l f i r m s , m u s t a l s o be c o n s i d e r e d . When e x p e r t s a re s e n t to c o u n t r i e s n e e d i n g them, e . g . a d e v e l o p i n g country , to m a k e an o n - t h e - s p o t a s s e s s m e n t , c o n s i d e r a t i o n should be g iven to c a r r y i n g out any n e c e s s a r y r e s e a r c h and d e v e l o p m e n t in another country with m o r e appropr ia te r e s o u r c e s of s c i e n t i s t s and f a c i l i t i e s .

5 . 6 . C o - o r d i n a t i o n of a c t i v i t i e s

With r e g a r d to c h e m o n u c l e a r p r o c e s s f l o w s y s t e m s , there w i l l be two l o o p s ava i lab le , and the e s t a b l i s h m e n t of c o - o r d i n a t e d e f f o r t on t h e s e l o o p s would contr ibute to p r o g r e s s in th i s s p h e r e .

5 . 7 . Safety

In format ion on the s a f e t y of l a b o r a t o r y - s c a l e and p l a n t - s c a l e e x p e r i -m e n t s i s l i m i t e d in i t s ava i lab i l i ty . The P a n e l f e l t that appropr ia te guiding p r i n c i p l e s should be e s t a b l i s h e d on s a f e t y in i r r a d i a t i o n s with l a r g e s o u r c e s .

5 . 8 . P a n e l

The IAEA should o r g a n i z e a P a n e l m e e t i n g of s c i e n t i s t s a c t i v e l y engaged in d e v e l o p i n g radiat ion c h e m i c a l p r o c e s s e s with m o r e r e s t r i c t e d t e r m s of r e f e r e n c e than the p r e s e n t P a n e l , n a m e l y , to eva luate s u c h p r o c e s s e s .

IV. REPORTS

APPLICATION OF IONIZING RADIATION TO POLYMER CHEMISTRY

A. DANNO TAKASAKI-SHI RADIATION CHEMISTRY RESEARCH ESTABLISHMENT, JAPAN ATOMIC ENERGY RESEARCH INSTITUTE, TAKASAKI-SHI, JAPAN

Abstract

APPLICATION OF IONIZING RADIATION TO POLYMER CHEMISTRY. Promising f i e lds for r ad ia t ion c h e m i c a l processes in po lymer chemis t ry a re m o d i f i c a t i o n of po lymer , r ad ia t ion- induced gra f t copo ly -m e r i z a t i o n , r ad ia t ion - induced po lymer i za t ion , and radia t ion-synthes is of chemica l s . T h e r e a re m a n y spec ia l and d i f f i cu l t problems in t he p rac t i ca l app l i ca t ion of radia t ion chemis t ry . Some t e c h n o l o g i c a l problems are discussed based on the radia t ion c h e m i c a l processes now be ing invest igated at t he Takasak i Radiat ion Chemis t ry Research Establ ishment . Examples a r e product ion of f oamed po lye thy lene , g ra f t ing of s tyrene on to ce l lu los ic f ib re , po lymer i za t i on of e thy lene in the gas phase, so l id - s t a te p o l y m e r i z a t i o n of t r ioxane and r ad i a t i on - in i t i a t ed ch lor ina t ion of hydrocarbons. T h e fo l lowing points on t echno log ica l problems regarding Ihe use of radia t ion sources a re discussed: compar ison be tween radio iso tope sources and e lec t ron b e a m acce le ra to r s , radioisotope sources used on a l a r g e sca le , and the dose and d o s e - r a t e required for radia t ion t r e a t m e n t .

1. I N T R O D U C T I O N

T h e p r a c t i c a l a p p l i c a t i o n of r a d i a t i o n c h e m i s t r y in i n d u s t r y h a s p r o -g r e s s e d r a t h e r s l o w l y . T o d a y , h o w e v e r , w e h a v e a c c u m u l a t e d m u c h b a s i c i n f o r m a t i o n in p o l y m e r c h e m i s t r y , and i n d u s t r i a l a p p l i c a t i o n s of r a d i a t i o n c h e m i s t r y h a v e c o m e to l ook m o r e p r o m i s i n g . T h e s e a r e r a d i a t i o n m o d i -f i c a t i o n of p l a s t i c s [1] , r a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n and g r a f t c o p o l y -m e r i z a t i o n [2] , G r e a t a t t e n t i o n h a s b e e n g i v e n to the a p p l i c a t i o n of i r r a -d i a t e d p o l y e t h y l e n e , w h i c h w a s o n e of the f i r s t c o m m e r c i a l p r o d u c t s and had the q u a l i t i e s of hea t r e s i s t a n c e and heat s h r i n k a b i l i t y . U n f o r t u n a t e l y n e w a p p l i c a t i o n s of r a d i a t i o n c h e m i s t r y in the p o l y m e r i n d u s t r y h a v e not p r o g r e s s e d a s r a p i d l y a s w a s o r i g i n a l l y e x p e c t e d . R e c e n t l y , h o w e v e r , the a p p l i c a t i o n s h a v e b e e n r e - e x a m i n e d at m a n y l a b o r a t o r i e s w h e r e e x -p e r i m e n t s on a p i l o t s c a l e o r at a d v a n c e d s t a g e s a r e b e i n g c a r r i e d out .

P r o m i s i n g f i e l d s in w h i c h r a d i a t i o n c h e m i c a l p r o c e s s e s in p o l y m e r c h e m i s t r y a r e a l r e a d y in u s e o r a p p e a r to b e p r o m i s i n g a r e l i s t e d in T a b l e I [3] . N e w a p p l i c a t i o n s of r a d i a t i o n c h e m i s t r y in i n d u s t r y m a y b e e x p e c t e d b e c a u s e of the d e v e l o p m e n t of r a d i a t i o n e n g i n e e r i n g , w h i c h h a s n e v e r b e e n e x p e r i e n c e d in the c o n v e n t i o n a l c h e m i c a l p r o c e s s e s , a s w e l l a s the a c c u m u l a t i o n of b a s i c i n f o r m a t i o n on r a d i a t i o n c h e m i s t r y . T h e r e a r e m a n y s p e c i a l and d i f f i c u l t p r o b l e m s in the p r a c t i c a l a p p l i c a t i o n of r a d i a t i o n c h e m i s t r y . In t h i s r e v i e w p a p e r , s o m e t e c h n o l o g i c a l p r o b l e m s a r e d i s c u s s e d b a s e d on the r a d i a t i o n c h e m i c a l p r o c e s s e s now b e i n g i n v e s t i g a t e d .

2 3

2 4 D A N N O

T A B L E I. I N D U S T R I A L C H E M I C A L P R O C E S S E S USING R A D I A T I O N

Chemical process Location Status Source

Modification of polymer

Polyethylene tape General Electric (U. S. A . ) Sumitomo Electric (Japan) and several others

Commerc ia l

Commerc ia l

Accelerator

Accelerator

Polyethylene f i lm W.R. Grace (U.S. A.) and several others

Commercia l Accelerator

Polyethylene oxide Union Carbide (U .S .A . )

Design plant

Co-60, 100 kCi

Plastic moulded parts Raychem ( U . S . A . )

Commerc ia l Accelerator

Polyethylene foam Toyo Rayon (Japan) Sekisui Chemica l (Japan)

Commerc ia l

Commerc ia l

Accelerator

Accelerator

Polyethylene wire covering

Several (U. S. A . , France, Japan, e t c . )


Natural rubber latex Saclay (France)

Pilot Accelerator

Graft copolymerization

Polyethylene with acrylic acid

Dow Chemical ( U . S . A . )

Pilot Electron, 2 MeV

Polyethylene with butadiene

Electrical Communicat ion Lab. (Japan)

Pilot Co-60

Polyethylene with butadiene and styrene

Takasaki Research Establishment (Japan)

Pilot Co-60

Poly v in ylchloride with butadiene


Pilot Co-60, 36 kCi

Polyvinylchloride with styrene

Dow Chemica l (U.S. A.)

Pilot Co-60, 18 kCi

Polyester and cotton blend fabric with vinyl monomer

Deer ing-Mil l iken (U.S. A . )


Cellulosic fibre with styrene



Polyethylene f i lms with vinyl monomers

Sekisui Chemica l (Japan)

Pilot Accelerator

Polymerizat ion

Ethylene Brookhaven (U.S. A.) Takasaki Research Establishment (Japan) and several others (USSR, France, Italy)

Pilot

Pilot

Co-60, 10 kCi

Co-60, 108 kCi

P L - 2 3 6 / 1 2 5

T A B L E I ( c o n t )

Chemica l process Location Status Source

Ethylene, vinyl compounds

Farbwerke Hoechst (Fed.Rep. Germany)

Experim ental Co-60 , 11 kCi

Trioxane H. B.N.P. C. (France) Takasaki Research Establishment (Japan)

Pilot

Pilot

X -rays

Electron, 3 MeV

Coating, polyesters with styrene and acrylics

Radiation Dynamics ( U . S . A . )

Commerc ia l Electron, 0.3 MeV

Polyestere in glass-fibre l amina te

Ford Motor ( U . S . A . )

Commerc ia l Electron, 0.3 MeV

Wood-plastics combinat ion

American Novawood ( U . S . A . ) Lockheed-Georgia ( U . S . A . ) West Virginia University ( U . S . A . )

Commerc ia l

Pilot

Experimental

Co-60

Co-60

Co-60

Chemicals

Bromination of hydro-carbons (ethyl bromide)

Dow Chemical ( U . S . A . )

Commercia l Co-60, 3 kCi

Sulphoxidation of hydro-carbons (SAS)

Esso Research (U. S . A . )

Pilot plant Co-60

Chlorination of hydro-carbons


Pilot Co-60

Chlorination of benzene (BHC)

Wantage Research Lab-oratory (United Kingdom)

Experimental Co-60

Oxidation of paraff in (Romania) Industrial Gamma rays

Oxidation of benzene in aqueous solution


Experimental Co-60

Cracking of hydrocarbons Institute of Petroleum and Chemical Synthesis (USSR)


2 . A P P L I C A T I O N O F R A D I A T I O N C H E M I S T R Y

I o n i z i n g r a d i a t i o n h a s not y e t found a c o m m e r c i a l l y i m p o r t a n t i n d u s -t r i a l a p p l i c a t i o n . H o w e v e r , the a p p l i c a t i o n of r a d i a t i o n i s a l r e a d y b e i n g u s e d in s o m e i n d u s t r i a l p r o c e s s e s , w h i c h m a y b e d i v i d e d into f o u r s e c t i o n s , a s s e e n in T a b l e I.

T h e u s e of h i g h - e n e r g y r a d i a t i o n f o r the m o d i f i c a t i o n of p o l y m e r s i s a v e r y i n t e r e s t i n g a p p l i c a t i o n . T h i s i s i l l u s t r a t e d by the p r o d u c t i o n of r a d i a t i o n c r o s s - l i n k i n g p o l y e t h y l e n e on an i n d u s t r i a l s c a l e . R a d i a t i o n -i n d u c e d g r a f t c o p o l y m e r i z a t i o n i s a n o t h e r e x a m p l e in w h i c h s u p e r i o r p o l y -m e r i c m a t e r i a l s c a n be p r o d u c e d . One of the e x a m p l e s i s a c o m m e r c i a l p r o d u c t , a n e w f a b r i c in w h i c h h e a t - s e t and s o i l - r e l e a s e p r o p e r t i e s a r e i m p a r t e d to a p o l y e s t e r - c o t t o n - b l e n d f a b r i c . R a d i a t i o n - i n d u c e d p o l y -m e r i z a t i o n i s a l s o a d i r e c t a p p l i c a t i o n of r a d i a t i o n . U n f o r t u n a t e l y , c o m -

2 6 D A N N O

m e r c i a l appl icat ion of t h i s p r o c e s s h a s not y e t b e e n r e p o r t e d , but p i l o t -s c a l e e x p e r i m e n t s a r e be ing c a r r i e d out at s e v e r a l l a b o r a t o r i e s . Radiat ion s y n t h e s i s of c h e m i c a l s i s a t e c h n o l o g i c a l l y i n t e r e s t i n g f ie ld . The p r o d u c -t ion of e thy l b r o m i d e by m e a n s of radiat ion w a s an in i t ia l p r o c e s s that d e m o n s t r a t e d how radiat ion c h e m i s t r y could be appl ied in industry , u s i n g r e l a t i v e l y s m a l l a m o u n t s of r a d i o i s o t o p e s .

2. 1. Radiat ion m o d i f i c a t i o n of p l a s t i c s

The f o r m a t i o n of c r o s s - l i n k i n g i s one of the m o s t important c h e m i c a l c h a n g e s brought about by radiat ion on p o l y m e r s . S ince c r o s s - l i n k e d p o l y m e r s l ead to b e n e f i c i a l c h a n g e s in s o m e of t h e i r p r o p e r t i e s , s u c h a s heat r e s i s t a n c e , t e n s i l e s trength , co ld f low, e t c . , the p o s s i b i l i t y of r a -diat ion e f f e c t s on p o l y m e r s has a t t rac ted a n u m b e r of app l i ca t ions .

P o l y e t h y l e n e c o n v e r t e d by i r r a d i a t i o n of h i g h - e n e r g y radiat ion into c r o s s - l i n k e d p o l y e t h y l e n e can be c o n s i d e r e d a new kind of p l a s t i c e x h i -b i t ing a n u m b e r of m o d i f i e d p r o p e r t i e s . At p r e s e n t , s e v e r a l k inds of i r -r a d i a t e d p o l y e t h y l e n e a r e c o m m e r c i a l l y a v a i l a b l e - t a p e s and f i l m s of v a r i o u s s i z e s , wrapping f o i l s and insu la t ion tubing a s w e l l a s mould ing p r o d u c t s .

R e c e n t l y , f o a m e d p o l y e t h y l e n e s h e e t s w e r e p r o d u c e d c o m m e r c i a l l y in Japan. The m e t h o d of produc ing f o a m e d p o l y e t h y l e n e i s a s f o l l o w s . A b lowing agent m i x e d with p o l y e t h y l e n e i s d e c o m p o s e d under the ac t i on of radiat ion , thus br ing ing about f o a m i n g and c r o s s - l i n k i n g of the p o l y m e r at the s a m e t i m e . P o l y e t h y l e n e f o a m s a r e p r o d u c e d by expanding the i r r a d i a t e d m a t e r i a l to 10 to 40 t i m e s the o r i g i n a l d i m e n s i o n s under r a i s e d t e m p e r a t u r e s . The product has e x c e l l e n t c h a r a c t e r i s t i c s , a s shown in T a b l e II. T h e s e r e s u l t s indicate that p o l y e t h y l e n e f o a m i s su i tab le f o r a l a r g e v a r i e t y of u s e s s u c h a s in c u s h i o n s , s h o c k a b s o r b e r s , heat i n s u l a -t o r s , f l o a t s and d e c o r a t i o n s .

The radiat ion d o s e u s e d for the c r o s s - l i n k i n g of p l a s t i c s i s in the range of 4 - 4 0 Mrad, b e c a u s e the G - v a l u e of the c r o s s - l i n k i n g for p o l y e t h y l e n e i s about 3. T h i s m e a n s that h i g h - d o s e i r rad ia t ion i s n e c e s s a r y to produce the i r r a d i a t e d m a t e r i a l s . E l e c t r o n s f r o m a c c e l e r a t o r s a re t h e r e f o r e m o s t o f t en u s e d to p r o d u c e t h e s e m a t e r i a l s . M o r e o v e r , the s a m p l e s to be i r -r a d i a t e d a r e u s u a l l y in the f o r m of f i l m s , t a p e s and s h e e t s that a r e s u i t -ab le for cont inuous t r e a t m e n t by e l e c t r o n b e a m i r r a d i a t i o n .

To r e d u c e the o p t i m u m d o s a g e , the addit ion of a s e n s i t i z e r has b e e n i n v e s t i g a t e d . F o r e x a m p l e , natural rubber l a t e x [4] h a s b e e n c o n v e r t e d by i r r a d i a t i o n into a c r o s s - l i n k e d m a t e r i a l . Rubber f i l m s obta ined f r o m pure l a t e x i r r a d i a t e d with 13 Mrad had e x c e l l e n t m e c h a n i c a l p r o p e r t i e s . The o p t i m u m d o s e can be r e d u c e d by a f a c t o r of about ten when c h l o r o -f o r m s o l u t i o n s a r e u s e d a s the s e n s i t i z e r .

2 . 2 . R a d i a t i o n - i n d u c e d graf t c o p o l y m e r i z a t i o n

A n u m b e r of s t u d i e s on the p r e p a r a t i o n of g ra f t c o p o l y m e r s have b e e n p u b l i s h e d . T h e r e s u l t s a l r e a d y a v a i l a b l e have a t t r a c t e d c o n s i d e r a b l e i n t e r e s t in p o l y m e r c h e m i s t r y , b e c a u s e it has b e e n found that rad ia t ion c h e m i c a l m e t h o d s for the p r e p a r a t i o n of gra f t c o p o l y m e r s a re o f t en e a s i e r in p r a c t i c e than convent iona l c h e m i c a l m e t h o d s . M o r e o v e r , t h e s e m e t h o d s

P L - 2 3 6 / 1 2 7

T A B L E II. P R O P E R T I E S O F P O L Y E T H Y L E N E F O A M P R O D U C E D B Y T H E R A D I A T I O N P R O C E S S

A p p a r e n t d e n s i t y ( g / c r a 3 )

P r o p e r t i e s

0 . 0 3 5 0. 070 0 . 1 1

M e c h a n i c a l p r o p e r t i e s

T e n s i l e s t r e n g t h ( g / c m 2 ) 4 . 7 1 7 . 5 1 1 0 . 2 1

T e n s i l e e l o n g a t i o n (%) 167 2 8 9 2 9 0

T e n s i l e m o d u l u s ( k g / c m 2 ) 9 . 5 27 36

C o m p r e s s i o n m o d u l u s ( k g / c m ! ) 0 . 8 1 . 0 1 . 5

C o m p r e s s i o n p e r m a n e n t s t r a i n ("7°) 22 1 4 11

R e s i l i a n c e (%) 53 3 8 19

T h e r m a l p r o p e r t i e s

T o l e r a b l e t e m p e r a t u r e f o r

c o n t i n u o u s use ( ° C ) 80 80 80

M a x i m u m t e m p e r a t u r e f o r use C) 100 100 100

M i n i m u m t e m p e r a t u r e f o r use (°C) - 7 0 - 7 0 - 7 0

T h e r m a l c o n d u c t i v i t y ( k c a l / m l d e g C) 0 . 0 3 8 - -

I g n i t i o n t e m p e r a t u r e ( ° Q 4 7 0 4 7 0 4 7 0

F l a s h p o i n t ( " q 3 6 0 3 6 0 360

E l e c t r i c a l p r o p e r t i e s

D i e l e c t r i c s t r e n g t h ( k V / m m ) 4 - -

D i e l e c t r i c c o n s t a n t 1 . 0 5 - -

P o w e r f a c t o r 0 . 0 0 0 2 - -

V o l u m e r e s i s t i v i t y ( o h m c m ) 1. 5 X 1 0 "

a r e v e r y g e n e r a l , in p r i n c i p l e , and c a n b e u s e d to p r e p a r e a n y d e s i r e d c o m b i n a t i o n of p o l y m e r s .

T h e p o s s i b i l i t y of u s i n g r a d i a t i o n - g r a f t i n g to m o d i f y p o l y m e r s i s a v e r y i n t e r e s t i n g a p p l i c a t i o n . T h e g r a f t c a n e i t h e r be m a d e h o m o g e n e o u s l y t h r o u g h o u t the p o l y m e r m a t e r i a l , o r b e l i m i t e d to a l a y e r of any d e s i r e d

2 8 D A N N O

t h i c k n e s s at the s u r f a c e . The advantages and p o s s i b i l i t i e s of g ra f t p o l y -m e r i z a t i o n point t o w a r d s the e c o n o m i c ut i l i ty of radiat ion gra f t ing .

Ioniz ing radiat ion , s u c h a s g a m m a r a d i a t i o n s o r h i g h - e n e r g y e l e c t r o n s , m a y be u s e d to p r e p a r e gra f t c o p o l y m e r s . S e v e r a l m e t h o d s for the p r e -p a r a t i o n have b e e n d e v e l o p e d and can be div ided into four m a i n m e t h o d s :

(a) D i r e c t gra f t ing of v i n y l m o n o m e r on to a p o l y m e r by i r r a d i a t i n g the p o l y m e r in the p r e s e n c e of a m o n o m e r ;

(b) Graft ing on r a d i a t i o n - p r e o x i d i z e d p o l y m e r s ; (c) Graft ing in i t ia ted by trapped r a d i c a l s ; (d) Combinat ion of two d i f ferent p o l y m e r i c r a d i c a l s . In the c a s e of (b) and (c), p r e - i r r a d i a t i o n of the p o l y m e r i s f i r s t

m a d e and then graf t ing of the m o n o m e r f o l l o w s . The c h o i c e of t h e s e m e t h o d s i s dependent on the c h a r a c t e r of the p o l y m e r s , the r e a c t i v i t y of m o n o m e r s and the p r o p e r t i e s of graf t c o p o l y m e r s .

Graf t ing of v i n y l m o n o m e r s on to p o l y e t h y l e n e i s a good e x a m p l e . A p i l o t - s c a l e e x p e r i m e n t for graf t ing of a c r y l i c ac id on to p o l y e t h y l e n e [5] h a s b e e n s tud ied in the United S ta tes of A m e r i c a . The g r a f t c o p o l y m e r i s g r e a t l y i m p r o v e d in a d h e s i o n p r o p e r t i e s . Graf t ing of butadiene on to p o l y e t h y l e n e [6] h a s been i n v e s t i g a t e d in Japan. In the f o r m e r c a s e , the p r e - i r r a d i a t i o n m e t h o d w a s u s e d and the p o l y m e r w a s i r r a d i a t e d to 0 . 8 - 2 . 0 Mrad of to ta l i r r a d i a t i o n dose us ing e l e c t r o n b e a m s f r o m the a c c e l e r a t o r . In the l a t t er c a s e , the d i r e c t - i r r a d i a t i o n m e t h o d w a s u s e d in the g a s p h a s e , and p o l y e t h y l e n e w a s i r r a d i a t e d to 0 . 2 - 1 . 0 Mrad by g a m m a r a y s f r o m a 60Co s o u r c e .

T h e r e i s no d i s t inc t ru le f o r taking e i t h e r e l e c t r o n b e a m s or g a m m a r a y s a s the rad ia t ion s o u r c e . Some idea of what type of rad ia t ion can be u s e d for gra f t ing i s d e t e r m i n e d by s e v e r a l f a c t o r s , s u c h a s inhibit ion of the h o m o p o l y m e r in graf t ing m a t e r i a l and the p r o c e s s of g r a f t i n g on a l a r g e s c a l e . In the p r e - i r r a d i a t i o n m e t h o d e l e c t r o n - b e a m i r r a d i a t i o n i s appropr ia te f o r p o l y e t h y l e n e - a c r y l i c ac id , c e l l u l o s e - s t y r e n e and p o l y e s t e r cot ton f a b r i c - a c r y l i c ac id s y s t e m s . In t h e s e s y s t e m s , r e l a t i v e l y l a r g e d o s e s a r e n e c e s s a r y to produce a su f f i c i en t amount of r e a c t i v e s i t e s in the p o l y m e r s . A f t e r i rrad ia t ion , the p o l y m e r r e a c t s wi th the m o n o m e r in a su i tab le so lut ion to m a k e graf t c o p o l y m e r s . On the o t h e r hand, in the d i r e c t i r rad ia t ion m e t h o d , g a m m a - r a y i r r a d i a t i o n i s appropr ia te for the p o l y e t h y l e n e - b u t a d i e n e and p o l y v i n y l c h l o r i d e - b u t a d i e n e s y s t e m s . In t h e s e s y s t e m s , the m o n o m e r i s g r a f t e d in the g a s p h a s e o r the l iquid p h a s e and the f o r m a t i o n of h o m o p o l y m e r i s v e r y s l i ght . Low d o s e - r a t e i r r a d i a t i o n i s m o r e su i tab le b e c a u s e of the d i f fus ion of the m o n o m e r into the p o l y m e r . M o r e o v e r , s i n c e s a m p l e s a r e usua l ly in the shape of p o w d e r s , g r a i n s o r bu lks , a high pene tra t ing p o w e r of rad ia t ion i s r e q u i r e d .

Many w o r k s on p r e - i r r a d i a t i o n g r a f t i n g on to f ibre have b e e n r e p o r t e d , but l i t t l e s e e m s to have b e e n done on p r e p a r a t i o n on a l a r g e s c a l e . At the T a k a s a k i Radiat ion C h e m i s t r y R e s e a r c h E s t a b l i s h m e n t , g r a f t i n g of s t y r e n e on to p r e - i r r a d i a t e d c e l l u l o s i c f i b r e s [7] h a s b e e n s tudied to obtain the b a s i c data for s c a l i n g up the p r o c e s s . The f i b r e u s e d w a s s t a p l e f i b r e , m o s t l y p o l y n o s i c rayon , in the f o r m of w e b s . P r e - i r r a d i a t i o n w a s c a r r i e d out in a i r by m e a n s of 2 MeV e l e c t r o n s ( f r o m EBG) to d o s e s of b e t w e e n 0 .3 and 7 Mrad. The m o n o m e r was e m u l s i f i e d in d i s t i l l e d w a t e r wi th e m u l s i f i e r s .

The s tandard c o n d i t i o n s c h o s e n f o r s t y r e n e w e r e : 2 Mard p r e -i r r a d i a t i o n of p o l y n o s i c f i b r e , 10% m o n o m e r c o n c e n t r a t i o n in e m u l s i o n ,

P L - 2 3 6 / 1 2 9

p o l y e t h y l e n e - s o r b i t a n - m o n o l a u r a t e a s e m u l s i f i e r , 200 m l e m u l s i o n / 1 g of f i b r e , 2 0 0 p p m o x y g e n c o n t e n t in the r e a c t i o n a t m o s p h e r e , a r e a c t i o n t e m p e r a t u r e of 50°C, and a r e a c t i o n t i m e of 1 h. T h e g r a f t i n g r e a c t i o n o c c u r r e d in t w o s t a g e s , i . e . the r e a c t i o n f i r s t p r o c e e d e d v e r y r a p i d l y , and w a s f o l l o w e d by a r a t h e r s l o w s t a g e . A s e x p e c t e d , the r e a c t i o n r a t e w a s i n c r e a s e d by i n c r e a s i n g the t o t a l a b s o r b e d d o s e a s s h o w n in F i g . 1, but no e f f e c t of the m o n o m e r c o n c e n t r a t i o n w a s s e e n a b o v e a c r i t i c a l v a l u e . T h e e f f e c t of the o x y g e n c o n t e n t in the m o n o m e r e m u l s i o n a t m o s -p h e r e w a s r a t h e r s m a l l c o m p a r e d w i t h g r a f t p o l y m e r i z a t i o n c a r r i e d out in a s o l u t i o n of m o n o m e r .

2. 3 . R a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n

T h e r a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n of v i n y l m o n o m e r s i s a d i r e c t a p p l i c a t i o n of r a d i a t i o n . In g e n e r a l , i o n i z i n g r a d i a t i o n c a n i n i t i a t e r a d i c a l p o l y m e r i z a t i o n . T h e a c t i v a t i o n e n e r g y f o r the i n i t i a t i o n i s s u p p l i e d o n l y b y i o n i z i n g r a d i a t i o n s . O n c e the i n i t i a t i o n r a d i c a l s a r e f o r m e d , the p r o -p a g a t i o n r e a c t i o n p r o c e e d s in a s i m i l a r w a y to the f r e e r a d i c a l c h a i n r e a c t i o n . In c e r t a i n s p e c i f i c c a s e s , r a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n a l s o i n i t i a t e s i o n i c p o l y m e r i z a t i o n .

100

UJ o <

LU o 0C Lli 50

o z I— U. < o: O

0

FIG. 1. Ef fec t of reac t ion t i m e on g ra f t ing of ce l lu los ic f ib re ; 10% s tyrene e m u l s i o n , 200 ppm oxygen , 50"C reac t ion t e m p e r a t u r e . A = polynosic rayon; 0 = co t ton ; • = ref ined f aced rayon .

I o n i z i n g r a d i a t i o n i s f ind ing a v a l u a b l e u s e in the s p e c i a l s y s t e m of p o l y m e r i z a t i o n . R a d i c a l s a r e g e n e r a t e d at a w i d e r a n g e of r a t e s in any c h e m i c a l s y s t e m a t -any t e m p e r a t u r e and in any p h a s e . T h e r e f o r e , c o m p a r e d w i t h the c o n v e n t i o n a l p o l y m e r i z a t i o n , no r e s t r i c t i o n s on t e m -p e r a t u r e s , p r e s s u r e s and p h a s e s a r e o b s e r v e d in r a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n . B a s i c r e s e a r c h on r a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n h a s i n d i c a t e d that e t h y l e n e w a s p o l y m e r i z e d by r a d i a t i o n at l o w e r t e m -p e r a t u r e s and at r e l a t i v e l y l o w e r p r e s s u r e s . T h e p r o d u c t s o b t a i n e d i n c l u d e o i l y l iquid , w a x - l i k e m a t e r i a l s and tough , s o l i d p l a s t i c s , d e -p e n d i n g on the o p e r a t i n g c o n d i t i o n s . T h e h i g h - m o l e c u l a r w e i g h t p r o -d u c t s a r e p r o d u c e d at h i g h e r p r e s s u r e s and at t e m p e r a t u r e s s l i g h t l y a b o v e r o o m t e m p e r a t u r e .

REACTION TIME ( m i n )

3 0 D A N N O

A p i l o t - s c a l e e x p e r i m e n t i s be ing c a r r i e d out at s e v e r a l l a b o r a t o r i e s . At the B r o o k h a v e n Nat ional L a b o r a t o r y in the United S ta tes of A m e r i c a a d v a n c e d s t a g e e x p e r i m e n t s on p o l y m e r i z a t i o n of e thy lene [8] at constant cond i t ions in a n o n - f l o w s y s t e m have b e e n s tudied. At the T a k a s a k i Radiat ion C h e m i s t r y R e s e a r c h E s t a b l i s h m e n t in Japan, p i l o t - s c a l e e x -p e r i m e n t s [9] in a f low s y s t e m are be ing c a r r i e d out under h igher p r e s -s u r e s and at t e m p e r a t u r e s b e l o w the m e l t i n g point of p o l y e t h y l e n e . F i g u r e 2 s h o w s the f low s h e e t of th i s p r o c e s s .

VACUUM PUMP

COOLER

FIG. 2 . Flow sheet of e thy lene po lymer iza t ion pilot p lan t .

The o p e r a t i n g condi t ions w e r e d e t e r m i n e d to obtain a p o w d e r - l i k e p o l y e t h y l e n e . The r e a c t i o n v e s s e l w a s a s t a i n l e s s - s t e e l (SUS-32) c y l i n d e r wi th a c a p a c i t y of 10 l i t r e s . The v e s s e l w a s d e s i g n e d to o p e r a t e at a m a x i m u m p r e s s u r e and a m a x i m u m t e m p e r a t u r e of 440 a tm and 150°C r e s p e c t i v e l y . I rrad ia t ion w a s c a r r i e d out us ing a c y l i n d r i c a l 6 0 C o s o u r c e of 108 000 Ci l o c a t e d outs ide the v e s s e l . The rad ia t ion in tens i ty i n s i d e the v e s s e l w a s 3 . 7 X 1 0 5 r a d / h .

The p o l y e t h y l e n e p r o d u c e d in th i s pi lot plant has a dens i ty and a c r y s t a l l i n i t y i n t e r m e d i a t e b e t w e e n t h o s e of convent iona l " l o w - d e n s i t y " and "h igh-dens i ty" p o l y e t h y l e n e . The m o l e c u l a r weight of the p o l y m e r s v a r i e d in a wide range f r o m 20 000 to 300 000 depending on the r e a c t i o n cond i t i ons . F i g u r e 3 s h o w s the r e l a t i o n b e t w e e n the m o l e c u l a r weight and the r e a c t i o n t i m e a s a funct ion of the r e a c t i o n t e m p e r a t u r e [9], It i s c l e a r l y s e e n how at l o w e r t e m p e r a t u r e s the m o l e c u l a r weight i n c r e a s e s wi th reac t ion t i m e , and t e n d s to sa tura te i n c r e a s i n g l y e a r l i e r a s the r e a c t i o n t e m p e r a t u r e i s r a i s e d . The d i s t i n c t i v e nature of the p o l y e t h y l e n e p r o d u c e d by radiat ion c o n s i s t s of v e r y low m e t h y l branching and of v e r y low un-s a t u r a t i o n s p r o v i d i n g good p r o p e r t i e s f o r e l e c t r i c a l m a t e r i a l s .

P L - 2 3 6 / 1 3 1

3

0 2 3 5

REACTION TIME ( h )

FIG. 3. Relat ionship be tween m o l e c u l a r weight and reac t ion t i m e at various r eac t ion t empe ra tu r e s ; pressure 400 k g / c m ! , dose - r a t e 2 . 5 x 1 0 4 r a d / h .

T h e s e r e s u l t s i n d i c a t e that the r a d i a t i o n p r o c e s s h a s m a n y a d v a n t a g e s in the p r o d u c t i o n of p o l y e t h y l e n e s u c h a s : (a) T h e m o l e c u l a r w e i g h t of the p o l y m e r c a n b e c o n t r o l l e d by s e l e c t i n g the r a d i a t i o n i n t e n s i t y , r e a c t i o n p r e s s u r e , r e a c t i o n t e m p e r a t u r e and r e a c t i o n t i m e ; (b) T h e c r y s t a l l i n i t y and m e l t - i n d e x of the p o l y m e r c a n be c h a n g e d in a w i d e r a n g e u s i n g the s a m e p lant .

A n o t h e r a d v a n t a g e of r a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n i s the p o s s i -b i l i t y of i n i t i a t i n g p o l y m e r i z a t i o n in the s o l i d s t a t e at l o w e r t e m p e r a t u r e s of v i n y l m o n o m e r s and c y c l i c c o m p o u n d s . A n u m b e r of s t u d i e s o n s o l i d -s t a t e p o l y m e r i z a t i o n h a v e b e e n p u b l i s h e d . T h e s e r e s u l t s h a v e i n d i c a t e d a c o n s i d e r a b l e i n t e r e s t in p o l y m e r c h e m i s t r y b e c a u s e it w a s found that i o n i c p o l y m e r i z a t i o n t o o k p l a c e in s o m e s p e c i f i c s y s t e m .

S o l i d - s t a t e p o l y m e r i z a t i o n of t r i o x a n e h a s b e e n s t u d i e d f r o m the p o i n t s of v i e w of b o t h r e s e a r c h and a p p l i c a t i o n . S c a l e - u p e x p e r i m e n t s of t h i s p r o c e s s h a v e b e e n c a r r i e d out in F r a n c e and J a p a n , but d e t a i l s h a v e not b e e n p u b l i s h e d . S o m e p r e l i m i n a r y w o r k [10 ] c a r r i e d out at the T a k a s a k i R a d i a t i o n C h e m i s t r y R e s e a r c h E s t a b l i s h m e n t i s d e s c r i b e d a s f o l l o w s : T r i o x a n e u s e d in the e x p e r i m e n t i s p u r i f i e d b y d i s t i l l a t i o n o v e r c a l c i u m h y d r i d e in a f l o w of n i t r o g e n f o l l o w e d by c r y s t a l l i z a t i o n and i s t h e n c r u s h e d to a c e r t a i n s i z e . I r r a d i a t i o n s a r e c a r r i e d out in a i r u s i n g e l e c t r o n s f r o m a C o c k c r o f t - W a l t o n - t y p e a c c e l e r a t o r of 3 M e V . A f t e r i r r a d i a t i o n , p o l y -m e r i z a t i o n i s c a r r i e d out in a p r e s s u r i z e d v e s s e l at t e m p e r a t u r e s b e l o w 50°C, the m e l t i n g po in t of t r i o x a n e . T h e p o l y m e r y i e l d i s d e p e n d e n t on t h e p r e - i r r a d i a t i o n d o s e , p o s t - p o l y m e r i z a t i o n t e m p e r a t u r e and r e a c t i o n t i m e . W h e n s a m p l e s w e r e i r r a d i a t e d w i t h 1.3 X 1 0 6 r a d in a i r , and w e r e a f t e r -w a r d s p o l y m e r i z e d in a i r at d i f f e r e n t t e m p e r a t u r e s , p o l y m e r y i e l d s f i n a l l y r e a c h e d a c o n v e r s i o n of about 80%, e x c e p t in the c a s e of the 58°C t e m -p e r a t u r e . T h e s a t u r a t i o n c o n v e r s i o n y i e l d d e p e n d s on the p r e - i r r a d i a t i o n d o s a g e , a s s h o w n in F i g . 4 . In the r a n g e b e t w e e n 0 . 0 5 and 0 . 1 4 M r a d , the

3 2 D A N N O

100

a 55 °C 96 h

• 50 °C 96 h

O 45 °C 96 h

X 55°C 3 h

IxlO5 Jx106 1x10

P R E - I R R A D I A T I O N DOSE ( M r a d )

FIG. 4 . Effect of t o t a l dose on conversion of pos t -po lymer iza t ion of t r ioxane at various t empe ra tu r e s .

sa tura t ion y i e l d i s p r o p o r t i o n a l to the i r r a d i a t i o n d o s a g e , and above 0 . 2 0 Mrad the y i e l d r e a c h e s about 80% c o n v e r s i o n .

The a d v a n t a g e s of r a d i a t i o n - i n d u c e d s o l i d - s t a t e p o l y m e r i z a t i o n a r e that pure t r i o x a n e i s e a s i l y obta ined and the heat of r e a c t i o n in the p o l y -m e r i z a t i o n p r o c e s s i s s m a l l e r c o m p a r e d with p o l y m e r i z a t i o n of f o r m a l -dehyde . The d i s t i n c t i v e nature of p o l y o x y m e t h y l e n e p r o d u c e d by r a d i a t i o n -induced p o l y m e r i z a t i o n of t r i o x a n e m e a n s that the p o l y m e r c o n s i s t s of h igh ly t h r e e - d i m e n s i o n a l l y o r d e r e d c r y s t a l s and h a s twin conf igura t ion .

2 . 4 . R a d i a t i o n - s y n t h e s i s of c h e m i c a l s

T h e r e has b e e n a g r o w i n g i n t e r e s t in the r a d i a t i o n - s y n t h e s i s of c h e m i c a l s . T h e r e a r e m a n y f i e l d s in which r e s e a r c h h a s b e e n c a r r i e d out wi th s o m e s u c c e s s . T h e s e a r e the product ion of c h e m i c a l s by h a l o -g e n a t i o n , ox idat ion , su lphoxidat ion , and m a n y e f f e c t s in c a t a l y t i c a l r e -a c t i o n s . The appl i ca t ion of radiat ion to produce e t h y l b r o m i d e [11] w a s a beg inn ing in d e m o n s t r a t i n g what kind of a p p l i c a t i o n s can be m a d e by a rad ia t ion c h e m i c a l industry , and how a r e l a t i v e l y s m a l l rad ia t ion s o u r c e can in i t ia te a r e a c t i o n .

Ioniz ing rad ia t ion i s g e n e r a l l y u s e f u l for in i t iat ing f r e e r a d i c a l r e a c -t i o n s . Dur ing the l i f e t i m e of the f r e e r a d i c a l s , t h e y can undergo a n u m b e r of t y p e s of r e a c t i o n s , s u c h a s a b s t r a c t i o n , addit ion and r e c o m b i n a t i o n r e a c t i o n s . T h e r e a r e m a n y e x a m p l e s of f r e e r a d i c a l chain r e a c t i o n s . In the c a s e of f r e e r a d i c a l p o l y m e r i z a t i o n , s i n c e the product r a d i c a l s a r e s i m i l a r to the r e a c t a n t , on ly one type of propagat ion i s needed .

T h e r e a r e m a n y f r e e r a d i c a l cha in r e a c t i o n s in wh ich addi t ion-a b s t r a c t i o n c o m b i n a t i o n s r e g e n e r a t e the o r i g i n a l r a d i c a l that p r o v i d e s c y c l i c paths to long c h a i n s . T h e s e e x a m p l e s a r e b r o m i n a t i o n of e thy l ene

P L - 2 3 6 / 1 3 3

( D o w - p r o c e s s ) , c h l o r i n a t i o n of h y d r o c a r b o n s (in Japan) , s u l p h o x i d a t i o n of h y d r o c a r b o n s ( E s s o - p r o c e s s ) and o x i d a t i o n of p a r a f f i n (in R o m a n i a ) .

R a d i a t i o n - i n i t i a t e d c h l o r i n a t i o n of h y d r o c a r b o n s [12] h a s b e e n s t u d i e d at the T a k a s a k i R a d i a t i o n C h e m i s t r y R e s e a r c h E s t a b l i s h m e n t . D i r e c t c h l o r i n a t i o n by g a m m a r a d i a t i o n i s o n e of the o u t s t a n d i n g e x a m p l e s of r a d i a t i o n - i n i t i a t e d f r e e r a d i c a l r e a c t i o n . It w a s found that the c h a i n r e -a c t i o n can be i n i t i a t e d and m a i n t a i n e d if c h l o r i n e i s f e d c o n t i n u o u s l y . T h e f o l l o w i n g r e a c t i o n s a r e thought to o c c u r in the r e a c t i o n of a c o m p o u n d of C n H m C l p , w h e r e n, m , and p a r e i n t e g e r s and m + p = 2n + 2:

C n H m C l p - — > " C n H m Clp-i + • CI

' C n H m - l C l p + - H

• C n H m - i Clp + C l 2 C n H m - i Clp + 1 + • CI

T h e a b o v e r e a c t i o n s o c c u r o n l y u n d e r i r r a d i a t i o n and a r e not a f f e c t e d b y t e m p e r a t u r e o r p r e s s u r e . A s s o o n a s the c h l o r i n e r a d i c a l s a r e f o r m e d the c h l o r i n a t i o n p r o c e e d s by the f o l l o w i n g c h a i n r e a c t i o n s :

• CI + C n H m C l p -» • C n H m _ ! C l p + HC1

" C n H m - i C l p + C I 2 - C n H m - i C l p + i + - CI

H y d r o c a r b o n s a r e t h u s c h l o r i n a t e d s u c c e s s i v e l y to m o r e h igh ly c h l o r i n a t e d h y d r o c a r b o n s and wi th e x t r e m e l y h i g h y i e l d s .

T h e G - v a l u e s f o r the r a d i a t i o n - i n i t i a t e d c h l o r i n a t i o n of 1, 2 - d i c h l o r o -e t h a n e (DCE) w e r e m e a s u r e d a s f u n c t i o n s of r a d i a t i o n i n t e n s i t y , f l o w - r a t e of c h l o r i n e g a s and r e a c t i o n t e m p e r a t u r e . T h e e f f e c t s of the d o s e - r a t e and the f l o w - r a t e of c h l o r i n e g a s on the G - v a l u e of c o n v e r s i o n of 1 , 2 -d i c h l o r o e t h a n e a r e s h o w n in T a b l e III. It i s s e e n that G ( - D C E ) d e c r e a s e s wi th i n c r e a s i n g d o s e - r a t e and i n c r e a s e s w i t h i n c r e a s i n g f l o w - r a t e of C l 2 .

T A B L E III. E F F E C T S O F D O S E - R A T E A N D F L O W - R A T E O F C l 2 O N C H L O R I N A T I O N Y I E L D

D o s e - r a t e 3

CIO3 r a d / h ) G ( - D C E )

CI,, f l o w - r a t e ^ ( m l / m i n )

G( -DCE)

2 5 0 4 . 9 X 10 3 3 0 0 6 . 7 X 10 3

120 8 . 6 X 10 3 500 8. 9 X 103

22 4 . 5 X 10* 700 1 2 . 4 X 10 3

8 , 6 1 1 . 4 X 104 • 1200 1 6 . 0 X 10 3

a T e m p e r a t u r e , 2 0 ° C ; C l 2 f l o w - r a t e , 5 0 0 m l / m i n .

b T e m p e r a t u r e , 2 0 ° C ; d o s e - r a t e , 1 . 2 x 1 0 5 r a d / h .

3 4 D A N N O

o 2.2 S

li. 2.0 °

0 20 AO 60 eo

REACTION TIME ( m i n )

0 100 120

FIG. 5 . Changes of product components f rom the chlor ina t ion of d ich lo roe thane (EDC) as a func t ion of r eac t ion t i m e at 1 . 2 X 10 5 r a d / h , 500 m l of C l 2 / m i n , and 2 0 ° C .

A p o s i t i v e t e m p e r a t u r e c o e f f i c i e n t w a s o b s e r v e d , dependent on the d e g r e e of ch lor ina t ion .

F i g u r e 5 s h o w s c h a n g e s in the component of c h l o r i n a t e d c o m p o u n d s in the c h l o r i n a t i o n of 1 , 2 - d i c h l o r o e t h a n e a s a funct ion of i r rad ia t ion t i m e . At the beg inn ing of the r e a c t i o n t r i c h l o r o e t h a n e w a s f i r s t produced , then i t s c o n c e n t r a t i o n r e a c h e d about 40 m o l e %, and product ion of t e t r a c h l o r o -e thane began . Two i s o m e r s of t e t r a c h l o r o e t h a n e w e r e f o r m e d . The m a x i -m u m y ie ld of t r i c h l o r o e t h a n e w a s obta ined at about 70 m o l e %. The amount of c h l o r i n e r e a c t i n g at th i s y i e l d w a s 1 . 0 - 1 . 1 m o l e / 1 . 0 m o l e of 1 , 2 - d i c h l o r o -ethane. B y i n c r e a s i n g the r e a c t i o n t i m e , c o n c e n t r a t i o n of h igher c h l o r i -nated e thane i n c r e a s e d , a s shown in F i g . 5.

3. RADIATION SOURCES USED IN RADIATION PROCESSES

The p o s s i b i l i t y of rad ia t ion c h e m i c a l p r o c e s s e s b e c o m i n g c o m p e t i t i v e wi th convent iona l p r o c e s s e s w i l l l a r g e l y depend on the rad ia t ion s o u r c e s in e c o n o m i c a l u s e . The rad ia t ion s o u r c e s now w i d e l y u s e d a r e r a d i o i s o t o p e s and p a r t i c l e a c c e l e r a t o r s . R a d i o i s o t o p e s e m p l o y e d in indus tr ia l i r r a d i a t i o n plant are m a i n l y 6 0 Co with s o m e 1 3 7 C s . On the o ther hand, a c c e l e r a t o r s u s e d in rad ia t ion c h e m i c a l p r o c e s s e s a r e m a i n l y e l e c t r o n b e a m a c c e l e r a t o r s of 0 . 5 - 3 MeV and of s e v e r a l k i lowat t s , with s o m e X - r a y g e n e r a t o r s of 0 . 2 - 0 . 5 MeV and a few k i lowat t s . It i s d i f f i cu l t to c h o o s e the m o s t u s e f u l t y p e s of rad ia t ion s o u r c e s in indus tr ia l plant, b e c a u s e the c h o i c e depends on the nature of e a c h c h e m i c a l p r o c e s s .

O = d ich loroe thane A = t r i ch lo roe thane O = t e t r ach lo roe thane

V = pen tach lo roe thane • hexach lo roe thane

ch lor ine

= 1 , 1 , 1 , 2 - i s o m e r = 1 , 1 , 2 , 2 - i s o m e r

3'

P L - 2 3 6 / 1 3 5

F o r i n d u s t r i a l t r e a t m e n t , a 8 0 Co s o u r c e s e e m s to b e m o s t appropr ia te f o r l a r g e o b j e c t s , s u c h a s packaged g o o d s , and f o r p r o c e s s e s s u c h a s p o l y m e r i z a t i o n w h e r e low d o s e - r a t e i r rad ia t ion i s important . T h e s e s o u r c e s can be e x t r e m e l y r e l i a b l e , and once i n s t a l l e d r e q u i r e l i t t l e s p e c i a l i s t s u p e r v i s i o n . F o r a s p e c i a l c a s e , a 1 3 7Cs s o u r c e (0.67 MeV) a p p e a r s to be su i tab le b e c a u s e it r e q u i r e s l e s s sh ie ld ing for the radiat ion .

The a d v a n t a g e s and d i s a d v a n t a g e s of u s ing r a d i o i s o t o p e s in i n d u s t r i a l product ion a r e a s f o l l o w s :

(1) A d v a n t a g e s

(a) Ratio of output e n e r g y to the weight of s o u r c e i s v e r y l a r g e , s o that an i r r a d i a t i o n fac i l i t y can be of a c o m p a c t s i z e .

(b) The h a l f - l i f e of r a d i o i s o t o p e s i s l o n g e r for 6 0Co and 1 3 7 C s , s o that the m a i n t e n a n c e of an i rrad ia t ion f a c i l i t y i s e a s y .

(c) In g e n e r a l , the induced ac t iv i ty of a product by g a m m a r a y s d o e s not o c c u r b e l o w 2 MeV of g a m m a radiat ion .

(d) L o w e r d o s e - r a t e i r rad ia t ion i s p o s s i b l e , and d o s e - r a t e d e p e n d e n c e on c h e m i c a l r e a c t i o n can be reduced .

(e) Var ia t ion of d o s e - r a t e i s s m a l l , so that opera t ion of f a c i l i t i e s i s e x t r e m e l y r e l i a b l e .

(f) Radiat ion i s e m i t t e d in a l l d i r e c t i o n s f r o m the s o u r c e , and i r r a d i a -t ion can be m a d e at any p o s i t i o n .

(2) D i s a d v a n t a g e s

(a) In the c a s e of g a m m a r a y s , the amount of sh i e ld ing i s l a r g e s o that the c o s t of sh i e ld ing p e r output e n e r g y of radiat ion i s high.

(b) Radiat ion cannot s top when the s o u r c e i s not in u s e . (c) C a r e m u s t be taken to p r e v e n t contaminat ion of product and

f a c i l i t y f r o m the l e a k a g e of r a d i o i s o t o p e s . (d) H i g h e r d o s e - r a t e i r rad ia t ion i s not p o s s i b l e . (e) The d o s e - r a t e d e c r e a s e s o v e r a long p e r i o d , s o that a c e r t a i n

amount of r a d i o i s o t o p e m u s t be c h a r g e d e a c h y e a r . (f) Shie ld ing of the radiat ion i s n e c e s s a r y in a l l d i r e c t i o n s so that

the c o s t of s h i e l d i n g i n c r e a s e s .

The n u m b e r of e l e c t r o n b e a m a c c e l e r a t o r s h a s g r e a t l y i n c r e a s e d in the paist f ew y e a r s . T h e y include e l e c t r o s t a t i c g e n e r a t o r s (Van de Graaff type) , p u l s e d g e n e r a t o r s ( l inear a c c e l e r a t o r type) , t r a n s f o r m e r s y s t e m s ( r e s o -nant t r a n s f o r m e r type and ICT type) and c a p a c i t y d e v i c e s ( C o c k c r o f t -Walton type and D y n a m i t r o n type) . At p r e s e n t the h ighes t p o w e r output, of about 10 kW o r m o r e , i s ava i lab le f r o m t r a n s f o r m e r d e v i c e s , o p e r a t i n g at s o m e w h a t l o w e r v o l t a g e s and p a r t i c u l a r l y su i tab le for thin m a t e r i a l s . A s d e s i g n p r o g r e s s e s , the p o w e r f r o m t h e s e m a c h i n e s has b e e n g r o w i n g v e r y rap id ly . E l e c t r o n - b e a m a c c e l e r a t o r s can prov ide high d o s e - r a t e i r -rad ia t ion in a r e l a t i v e l y s m a l l v o l u m e and for p r o c e s s e s s u c h a s c r o s s -l inking w h e r e a high d o s e i s n e c e s s a r y .

3 . 1 . L a r g e - s c a l e r a d i o i s o t o p e s o u r c e s

F o r indus tr ia l t r e a t m e n t l a r g e s o u r c e s c o m p r i s i n g m a n y thousands of c u r i e s of r a d i o a c t i v e e l e m e n t a r e u s e d . A 6 0 C o s o u r c e i s at p r e s e n t

3 6 D A N N O

a v a i l a b l e f o r indus tr ia l p u r p o s e s , and i s p r e f e r r e d for a number of indus tr ia l app l i ca t ions w h e r e cont inuous working and high penetrat ion a r e important f e a t u r e s . To r e d u c e the s h i e l d i n g r e q u i r e m e n t , a ^ C s s o u r c e i s u s e d in s p e c i a l c a s e s s u c h a s m o v a b l e i r rad ia t ion equipment .

T h e r e are s e v e r a l t y p e s of l a r g e radiat ion s o u r c e s for indus tr ia l u s e . T h e y a r e , for c o n v e n i e n c e , d iv ided into the rod type , p la te type, c y l i n d r i c a l type and h o n e y c o m b type s o u r c e s . C h a r a c t e r i s t i c s of t h e s e s o u r c e s a r e d e s c r i b e d b e l o w .

3. 1. 1. Rod- type s o u r c e

T h i s type i s u s u a l l y c o n s t r u c t e d in a s t a i n l e s s - s t e e l tube in which the p e l l e t s , c o i n s or rods s o u r c e s are e n c a p s u l e d . To obtain u n i f o r m r a d i a -t ion in tens i ty a long the a x i s of the rod, two s m a l l p i e c e s of rod wi th high ac t iv i ty a r e a r r a n g e d on both ends . The r o d - t y p e s o u r c e m a k e s handling s i m p l e and e a s y .

M a x i m u m r a d i o a c t i v i t y of the s i n g l e r o d - t y p e s o u r c e i s l i m i t e d by heat g e n e r a t i o n and s e l f - a b s o r p t i o n , wh ich are due to absorpt ion of rad ia t ion in the rod. At p r e s e n t , s e v e r a l thousand c u r i e s of 6 0 Co s o u r c e s a r e a v a i l a b l e .

3. 1. 2. P l a t e - t y p e s o u r c e

P la te - type s o u r c e s a r e c o m p o s e d of a number of r o d - t y p e s o u r c e s a s s e m b l e d in p a r a l l e l with e a c h o ther to f o r m a p la te . The p l a t e - t y p e s o u r c e i s m o s t appropr ia te for indus tr ia l t r e a t m e n t b e c a u s e there i s no l i m i t a t i o n on s a m p l e s a s r e g a r d s shape and v o l u m e . S a m p l e s to be i r -rad ia ted a r e m o v e d in p a r a l l e l along the s u r f a c e of the p late . A l a r g e n u m b e r of s a m p l e s can be t r e a t e d by m o v i n g them s u c c e s s i v e l y . To m a k e i rrad ia t ion un i form, s a m p l e s a r e m o v e d b e t w e e n a pa ir of p l a t e s , o r on both s i d e s of the s u r f a c e of a p la te . In the la t ter c a s e , the i r r a d i a -t i on e f f i c i e n c y of the p la te s o u r c e i n c r e a s e s r e m a r k a b l y .

3. 1. 3. C y l i n d r i c a l - t y p e s o u r c e

T h i s type has b e e n w i d e l y u s e d a s an e x p e r i m e n t a l s o u r c e . A c y -l i n d r i c a l - t y p e s o u r c e i s c o m p o s e d of a n u m b e r of r o d - t y p e s o u r c e s a s -s e m b l e d in a c i r c l e to f o r m a c y l i n d e r . T h i s s o u r c e a p p e a r s to be s u i t -ab le not only for r e s e a r c h but a l s o for product ion . The m a x i m u m radiat-ion i n t e n s i t y i s a v a i l a b l e in the c e n t r e of the c y l i n d e r w h e r e high d o s e - r a t e i r r a d i a t i o n e x p e r i m e n t s are p o s s i b l e . The l o w e r rad ia t ion f i e ld ou t s ide the c y l i n d e r i s a l s o u s e d for i rrad ia t ion of m a t e r i a l s in l a r g e v o l u m e . At p r e s e n t , about a hundred thousand c u r i e s of 6 0 Co s o u r c e i s be ing u s e d in a p i l o t - s c a l e e x p e r i m e n t .

3. 1 . 4 . Hor ieycomb- type s o u r c e

A h o n e y c o m b - t y p e s o u r c e i s c o m p o s e d of a n u m b e r of r o d - t y p e s o u r c e s a s s e m b l e d in a hexagona l to f o r m a h o n e y c o m b s t r u c t u r e . B e c a u s e of the s p e c i a l c h a r a c t e r of t h i s s o u r c e it i s p o s s i b l e to obtain an a l m o s t u n i f o r m radiat ion f i e l d in the c e n t r e of e a c h hexagona l . T h i s s o u r c e m a y be u s e d for i r rad ia t ion of g a s e o u s o r l iquid s a m p l e s in a f low s y s t e m .

P L - 2 3 6 / 1 3 7

2.725 x 10* ' < z > 4.304 x 1 0 ! — 5.1B9x'l0J '|

7.610x10*

w x io;| ^T3.787x 102

8.767 x lO2

6.598 x I0 !

C Y L I N D R I C A L TYPE P L A T E TYPE HONEYCOMB TYPE

FIG. 6. Radiat ion intensi ty distr ibution of p l a t e , cy l ind r i ca l and h o n e y c o m b type sources. Each source is composed of 42 rods hav ing the s a m e amount of ac t i v i t y .

F i g u r e 6 s h o w s a c o m p a r i s o n b e t w e e n r a d i a t i o n f i e l d s in the p l a t e - , c y l i n d r i c a l - and h o n e y c o m b - t y p e s o u r c e s [13] . E a c h s o u r c e i s c o m p o s e d of 42 r o d - t y p e s o u r c e s h a v i n g the s a m e a m o u n t of a c t i v i t y , and h a s n e a r l y t h e s a m e v o l u m e i n s i d e the s o u r c e . It i s s h o w n that the r a d i a t i o n f i e l d o b t a i n e d f r o m the p a i r of p l a t e s i s l o w e s t and the f i e l d o b t a i n e d f r o m the h o n e y c o m b - t y p e s o u r c e i s h i g h e s t w h e n the s a m e a m o u n t of r a d i o i s o t o p e s i s i n s t a l l e d . M o r e o v e r , the u n i f o r m i t y of r a d i a t i o n f i e l d i n s i d e the s o u r c e i s in the o r d e r h o n e y c o m b , c y l i n d r i c a l ^ p l a t e s .

3. 2. D o s e and d o s e - r a t e r e q u i r e d f o r r a d i a t i o n t r e a t m e n t

T h e d o s e and d o s e - r a t e r e q u i r e d f o r r a d i a t i o n c h e m i c a l p r o c e s s e s a r e s u m m a r i z e d in T a b l e IV. R a d i a t i o n d o s e s r e q u i r e d f o r c h e m i c a l p r o c e s s e s a r e d e p e n d e n t on i r r a d i a t i o n c o n d i t i o n s , s u c h a s kind of r a d i a -t i o n s , d o s e - r a t e s , r e a c t i o n t e m p e r a t u r e s , r e a c t i o n p r e s s u r e s and a d d i -t i o n of s e n s i t i z e r s . In the c a s e of c r o s s - l i n k i n g of p l a s t i c s and r a d i a t i o n -i n d u c e d g r a f t i n g , t h e y a r e a l s o d e p e n d e n t o n the p r o p e r t i e s of the p r o d u c t to be p r o d u c e d . M o r e o v e r , the d o s e - r a t e h a s an i n f l u e n c e o n the r a t e of r e a c t i o n and the G - v a l u e of the p r o d u c t . T h e r e f o r e , v e r y c l o s e a t t e n t i o n m u s t be pa id to the u s e of r a d i a t i o n s o u r c e s .

3. 2. 1. I n f l u e n c e on r a t e of r e a c t i o n and G - v a l u e

T h e f o l l o w i n g r e l a t i o n s h i p s a r e o b t a i n e d f o r r a d i a t i o n c h e m i c a l r e a c t i o n s :

Rate of r e a c t i o n x I n

G - v a l u e I""1

w h e r e I d e n o t e s d o s e - r a t e and n i s a c e r t a i n c o n s t a n t d e t e r m i n e d by the r e a c t i o n k i n e t i c s of the c h e m i c a l p r o c e s s . In g e n e r a l , the v a l u e of n i s in the r a n g e of 0 . 5 - 1 . 0 .

3 8 D A N N O

T A B L E IV. T H E D O S E A N D D O S E - R A T E R E Q U I R E D F O R R A D I A T I O N C H E M I C A L P R O C E S S E S

C h e m i c a l p rocess Dose (Mrad)

D o s e - r a t e

( r a d / h ) R a d i a t i o n 3

N i t r o g e n f i x a t i o n (N2 + o 2 = N O z )

5 5 0 - 1 0 " F . S .

C r o s s - l i n k i n g of p o l y e t h y l e n e

4 - 40 1 0 s - 101 0 e

V u l c a n i z a t i o n of n e u t r a l r u b b e r (w i th s e n s i t i z e r )

10 - 50

3 - 5

10 6 - 101 0 X , e

C u r i n g of p o l y e s t e r 0 . 1 - 5 105 - 10 1 0 X, e

G r a f t c o p o l y m e r i z a t i o n ( in g e n e r a l )

0 . 1 - 5 10 4 - 10 9 X , e

P o l y m e r i z a t i o n ( in g e n e r a l )

0 . 1 - 10 10 4 - 10® X, e

P o l y m e r i z a t i o n of t r i o x a n e

0. 05 - 2 . 0 10 4 - 10 8 X, e

E thy l b r o m i d e ( C 2 H 4 + HBr = C 2 H 5 Br)

0 . 2 4 - 105 X

S u l p h o x i d a t i o n of h y d r o c a r b o n s

0 . 2 - 10 5 X

O x i d a t i o n of p a r a f f i n

0 . 2 5 - 10 4 X

a F . S . = f i s s ion f r a g m e n t , e = e l e c t r o n s , X = g a m m a rays o r X - r a y s .

No p r o b l e m on the d o s e - r a t e e f f e c t i s o b s e r v e d when n = 1. H o w e v e r , when n i s s m a l l e r than unity, with i n c r e a s i n g d o s e - r a t e the G - v a l u e d e -c r e a s e s and the rad ia t ion d o s e r e q u i r e d for the p r o c e s s i n c r e a s e s . On the o ther hand, with d e c r e a s i n g d o s e - r a t e , the ra te of r e a c t i o n d e c r e a s e s and the v o l u m e of the r e a c t i o n v e s s e l m u s t be e n l a r g e d to keep a cons tant ra te of product ion . T h e r e f o r e , an o p t i m u m e c o n o m i c d o s e - r a t e can be d e t e r m i n e d f o r the g i v e n p r o c e s s .

In the c a s e of g r a f t c o p o l y m e r i z a t i o n by the d i r e c t method , when the d o s e - r a t e i s g r e a t e r than the c e r t a i n l i m i t i n g v a l u e , the v a l ue of n m a y s o m e t i m e s be s m a l l e r than 0 .5 b e c a u s e of the d i f f u s i o n of the m o n o m e r f r o m the s u r f a c e to the i n t e r i o r of the m a t e r i a l .

P L - 2 3 6 / 1 3 9

3. 2. 2. I n f l u e n c e on the m o l e c u l a r w e i g h t

T h e m o l e c u l a r w e i g h t of the p o l y m e r o b t a i n e d f r o m the r a d i a t i o n -i n d u c e d p o l y m e r i z a t i o n i s i n v e r s e l y p r o p o r t i o n a l to I n . F o r e x a m p l e , in the c a s e of r a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n , the e f f e c t of the d o s e -r a t e on the m o l e c u l a r w e i g h t [14 ] i s s h o w n in F i g . 7, w h i c h s h o w s the e f f e c t of the d o s e - r a t e in the r a n g e f r o m 5 . 8 X 1 0 4 to 4 . 7 X 1 0 5 r a d / h on the i n t r i n s i c v i s c o s i t y , rj< at p r e s s u r e s of 6 8 0 and 3 4 0 a t m r e s p e c t i v e l y . E a c h e x p e r i m e n t w a s i r r a d i a t e d f o r a t o t a l d o s e of l'.OX 1 0 5 r a d at a t e m p e r a t u r e of about 20°C. At the c o n d i t i o n s i n d i c a t e d the i n t r i n s i c v i s -c o s i t y i s i n v e r s e l y p r o p o r t i o n a l to the i n t e n s i t y .

FIG. 7 . Effec t of dose - r a t e on intr insic viscosity of po lye thy lene produced by r ad i a t i on .

T h e s a m e e f f e c t m a y be o b s e r v e d in the c a s e of g r a f t c o p o l y m e r i z a t i o n in the d i r e c t m e t h o d . T h e n u m b e r of g r a f t i n g s i t e s and l e n g t h of g r a f t e d p o l y m e r (or m o l e c u l a r w e i g h t ) m a y b e dependent on the d o s e - r a t e . T h e r e -f o r e , to p r o d u c e a g i v e n m o l e c u l a r w e i g h t of g r a f t e d p o l y m e r o r the a p -p r o p r i a t e p r o p e r t i e s of g r a f t c o p o l y m e r , the c h o i c e of d o s e - r a t e i s a v e r y i m p o r t a n t f a c t o r .

10

TOTAL DOSE 1x 105 rad REACTION TEMPERATURE 20 °C

0 2 3 4 5 6

D O S E - R A T E ( 1 0 5 r a d / h )

4 0 D A N N O

3. 2. 3. Generat ion of heat and a c c u m u l a t i o n of c h a r g e s

When m a t e r i a l s a r e i r r a d i a t e d wi th high d o s e - r a t e us ing e l e c t r o n s f r o m a c c e l e r a t o r s , g e n e r a t i o n of heat and a c c u m u l a t i o n of c h a r g e in the i r r a d i a t e d m a t e r i a l s br ing about s e r i o u s d a m a g e . Mel t ing of the ex i t window on the a c c e l e r a t i n g tube and d i s c h a r g e of e l e c t r o n s a c c u m u l a t e d in the i r r a d i a t e d m a t e r i a l a r e reported .

G e n e r a t i o n of heat , Q ( c a l / g min) , a b s o r b e d by radiat ion in the i r r r a -d iated m a t e r i a l s , i s c a l c u l a t e d by the fo l lowing equation:

Q = 2 .4 I

and t e m p e r a t u r e r i s e , T (deg C / g min) , of the i r r a d i a t e d m a t e r i a l i s g iven by

T = 2 .4 I / C

w h e r e I i s the d o s e - r a t e in M r a d / m i n and C ( c a l / g deg C) i s the heat c a p a c i t y of the m a t e r i a l .

F i g u r e 8 s h o w s the r e l a t i o n s h i p b e t w e e n the d o s e - r a t e and heat g e n e r a t e d in the i r r a d i a t e d m a t e r i a l . In the c a s e of p o l y m e r s , s i n c e the upper l i m i t of heat g e n e r a t e d m a y be d e t e r m i n e d f r o m the m e l t i n g point of the p o l y m e r , the l i m i t i s r e a s o n a b l y to s e t t l e the v a l u e of 10 c a l / g m i n . The heat g e n e r a t e d by g a m m a r a y s i s v e r y low b e c a u s e the m a x i m u m radiat ion i n t e n s i t y by g a m m a - r a y s o u r c e s i s l o w e r than 10® r a d / m i n (6 M r a d / h ) . On the other hand, the heat g e n e r a t e d by e l e c -

D O S E - R A T E ( r a d / h g )

FIG. 8. Heat generat ion from absorption of rad ia t ion .

P L - 2 3 6 / 1 4 1

t r o n i r r a d i a t i o n i s s o h igh that the b e a m s m u s t b e s p r e a d o v e r a l a r g e a r e a by the s c a n n i n g t e c h n i q u e .

A n o t h e r s o u r c e of hea t g e n e r a t i o n i n d u c e d b y c h e m i c a l r e a c t i o n m u s t b e t a k e n into c o n s i d e r a t i o n . In p i l o t - s c a l e e x p e r i m e n t s , it i s a s e r i o u s p r o b l e m to e l i m i n a t e h e a t p r o d u c e d b y r a d i a t i o n and b y c h e m i c a l r e a c t i o n f r o m the i r r a d i a t e d m a t e r i a l s . T h e r e f o r e , i r r a d i a t i o n w i t h a h i g h d o s e -r a t e i s not a p p r o p r i a t e in l a r g e - s c a l e e x p e r i m e n t s . F o r e x a m p l e , when m a t e r i a l s a r e i r r a d i a t e d by s c a n n i n g w i t h an e l e c t r o n a c c e l e r a t o r at 10 kW, the b e a m s b e i n g 50 c m w i d e and the s a m p l e m o v i n g at a s p e e d of 10 c m / m i n , t h e a b s o r b e d d o s e d e p o s i t e d in the m a t e r i a l i s

D ( r a d / m i n ) = 1 .2 X 1 0 5 ( r a d / m i n c m 2 )

and h e a t g e n e r a t i o n b y a b s o r p t i o n of r a d i a t i o n , a s s u m i n g the t h i c k n e s s of s a m p l e i s 0 . 5 c m and the d e n s i t y i s 1 . 0 g / c m 3 , i s

Q ( c a l / m i n ) = 6 . 4 X 10" 1 ( c a l / m i n g )

On the o t h e r hand, the heat of r e a c t i o n in the c a s e of r a d i a t i o n - i n d u c e d g r a f t c o p o l y m e r i z a t i o n i s c o n s i d e r a b l e , p r o v i d e d that the G - v a l u e of p o l y -m e r i z a t i o n i s 1 0 4 and the h e a t of p o l y m e r i z a t i o n 15 k c a l / m o l e ,

Q1 ( c a l / m i n ) = 3 7 . 4 ( c a l / m i n g)

C o m p a r i s o n of the heat g e n e r a t i o n of Q and w i t h that of Q' s h o w s that h e a t g e n e r a t e d f r o m the c h e m i c a l r e a c t i o n i s s e v e r a l t i m e s g r e a t e r than that f r o m r a d i a t i o n .

R E F E R E N C E S

[1] CHARLESBY, A . , A t o m i c Radiat ion and Polymers , Pe rgamon , Oxford (1960). [2] CHAPIRO, A . , Radiat ion Chemistry of Po lymer i c Systems, In te r sc ience Publishers, Chiches ter (1962). [3] CHEMICAL WEEK, 17 D e c . (1966) 84. [4] LAMM, A . , LAMM, G . , Appl ica t ion des Rayonnements en F rance 1 (1965) 139. [5] RIEKE, J. K . , HART, G. M . , SAUNDER, F. L . , J. Po lym. Sci. C_4 (1963) 589. [6] FURUHASHI, A . , KADONAGA, M . , Rev. e l e c t . C o m m u n . Lab. , Tokyo 12 (1964) 775. [7] GOTODA, M . , KAGEYAMA, E . , NOZAKI, F . , UENO, T . , MATSUDA, O . , UDAGAWA, A . ,

Int . Symp. Mac romolecu l a r Chemis t ry , Paper 5 / 2 / 0 6 , Tokyo Kyoto, 1966. [8] STEINBERG, M . , COLOMBO, P . , EL KUKACKA, L . , CHAPMAN, R . N . , ADLER, G . , Rep.

BNL-740 (T-238) (1963), [9] MACHI, S . , HAGIWARA, M . , MITSUI, M . , KAGIYA, T . , Int. Symp. M a c r o m o l e c u l a r Chemis t ry ,

Paper 4 / 2 / 0 8 , Tokyo Kyoto, 1966. [10] SAKAMOTO, M . , ISHIGAKI, I . , SHIMIZU, A . , KUMAKURA, K . , NISHI, M . , YAMASHINA, H . ,

IWAI, T . , ITO, A . , Int . Symp. M a c r o m o l e c u l a r Chemis t ry , Paper 4 / 2 / 1 6 , Tokyo Kyoto, 1966. [11] HARMER, D . E . , BEALE, J. S . , PUMPELLY, C. T . , WILKINSON, B . W . , in Industr ia l Uses of Large

Radiat ion Sources (Proc. Conf . Salzburg, 1963) 2, IAEA, Vienna (1963) 205. [12] DANNO, A . , TSUCHIHASI, G . , SODA, T . , 18th Annual Mee t ing of C h e m . Soc. of Japan (1965). [13] DANNO, A . , J. a t o m . Energy Soc. Japan 2 (1960) 554. [14] COLOMBO, P . , FONTANA, J . , KUKACKA, L. E . , STEINBERG, M . , Rep. BNL-9043 (1965).

CHARACTERISTICS AND RANGE O F A P P L I C A B I L I T Y O F A C C E L E R A T O R S F O R RADIATION CHEMICAL PROCESSES

N . W . H O L M

A C C E L E R A T O R D E P A R T M E N T ,

R E S E A R C H E S T A B L I S H M E N T R I S Ø ,

R O S K I L D E , D E N M A R K

Abstract

CHARACTERISTICS AND RANGE OF APPLICABILITY OF ACCELERATORS FOR RADIATION

CHEMICAL PROCESSES. A general description of the characteristics of d. c. -accelerators and linear

accelerators is given. Some comments are made on the economics of radiation processing, beam

characteristics, penetration characteristics, process control and conversion efficiency.

GENERAL REMARKS ON ACCELERATORS

As l i t t le p rac t i ca l p r o c e s s informat ion is available at p resen t on the c h a r a c t e r i s t i c s and range of applicabil i ty of a c c e l e r a t o r s for radiat ion chemica l p rocess ing , the subject has to be dealt with in ve ry genera l t e r m s .

Two bas ic types of e lec t ron a c c e l e r a t o r a r e capable of radiat ion chemica l p rocess ing : d. c . - a c c e l e r a t o r s and l i nea r a c c e l e r a t o r s .

Most of the d. c . - m a c h i n e s opera te in a compara t ive ly low energy range , 0 . 3 - 4 . 0 MeV. When the e lec t rons a r e applied di rect ly , the penet ra t ing ability s e t s na r row l imi t s to the applicabili ty, the usefu l range being about 1 -15 m m of water -equiva len t m a t e r i a l . These machines a r e t h e r e f o r e p r i m a r i l y useful fo r i r r ad ia t ion of thin m a t e r i a l s like p las t ic tubes and f i lms , tex t i les , f i b r e s and coatings, o r fo r o ther su r f ace t r e a t m e n t s , pa r t i cu la r ly in s t e r i l i za t ion . The chemis t ry behind these appl icat ions will not be d i scussed h e r e .

L inea r a c c e l e r a t o r s have la te ly gained in populari ty a f t e r a some-what slow s t a r t as f a r as indus t r i a l application i s concerned. Manufactured fo r use at h igher par t ic le energ ies , they can handle much bulkier m a t e r i a l s and have been used pa r t i cu la r ly fo r r ad io - s t e r i l i za t ion of medica l p roduc t s . The re is at p resen t no l inea r a c c e l e r a t o r (except those at mul t i -purpose o r s e rv i ce instal lat ions) in opera t ion on a s t r i c t ly radia t ion chemical p r o c e s s . It is l ikely that this s i tuat ion will change for s e v e r a l r e a s o n s . One is the construct ion of the two-mi le l inear a c c e l e r a t o r at Stanford, Cal i forn ia . At a l a t e r s tage th is a c c e l e r a t o r will supposedly be fed by approximate ly 1000 k lys t rons ; about 300 a r e used at p r e s e n t . Such a plant b r ings with it m o r e powerful and much cheaper power sources , i . e . k lys t rons , and it also in t roduces vi tal pa r t s such as a cce l e r a to r wave guides on a t r u e fac tory assembly l ine . It is c l ea r that this event could mean an economic breakthrough for p r o c e s s l inear a c c e l e r a t o r s . Another r ea son is tö be found in the neat and tidy di rec t ional emiss ion of radia t ion energy f r o m the l inac compared with isotope s o u r c e s . It is s imply e a s i e r to obtain a good uti l izat ion of the radia t ion .

43

T A B L E I. CHARACTERISTICS OF VARIOUS T Y P E S OF E L E C T R O N A C C E L E R A T O R S [ 1]

Approx ima te number Energy Current Power

Purchase cost

($/kW)

M a i n t e n a n c e cost

($/kWh) ins ta l led or on order

(MeV) (MA) (kW)

Purchase cost

($/kW)

M a i n t e n a n c e cost

($/kWh)

0 . 3 a 25 7 . 5 6 . 7 0 0 1 . 5 10 15 6 . 0 0 0 0 . 3 0

Dynamit ron 15 (RDI) 3 . 0 10 30 4 . 4 0 0 0 . 2 5

Insulat ing 0 . 5 20 10 1 0 . 0 0 0 0 . 3 0 - 0 . 6 0

core 44 t ransformer ( 3 . 0 ) (20) (60) ( 6 . 2 0 0 ) 0 . 0 8 - 0 . 1 5

(HVEC)

5 . 0 6 . 0 30 8 . 0 0 0 ( 5 . 0 ) (50 .0 ) (250) (2. 000)

Linac 63 (severa l 1 0 . 0 0 . 5 5 5 0 . 0 0 0 6 . 0 0 companies ) ( 1 0 . 0 ) (2. 5) (25) (22 .000 ) (2 . 00)

Resonance 200

1 . 0 ( p e a k ) 5 . 0 - 4 17 .750 1 . 0 0 t ransformer

200

(GE) 2 . 0 (peak) 6 . 0 10 13 .100 0 . 5 0

1 . 5 1 . 6 2 . 5 2 4 . 0 0 0 2 . 0 0 - 3 . 0 0

Van de Graaff 200 (ma in ly HVEC) 4 . 0 1 . 0 4 . 0 3 9 . 0 0 0 3 . 0 0 - 4 . 0 0

BBCa 2 0 . 6 3 . 0

10 10

6 30

- -

a In format ion inset ted by N . W . H o l m .

P L - 2 3 6 / 1 0 4 5

The a p p l i c a b i l i t y of both t y p e s of m a c h i n e can be v a s t l y expanded by c o n v e r s i o n of the e l e c t r o n s into the m o r e pene tra t ing b r e m s s t r a h l u n g . T h i s m e t h o d of i r r a d i a t i o n of v e r y bulky i t e m s , h o w e v e r , d o e s not s e e m t o o f f e r s e r i o u s c o m p e t i t i o n to g a m m a - e m i t t i n g i s o t o p e s o u r c e s , at l e a s t not at p r e s e n t .

A f t e r t r e a t i n g the subjec t in the m o s t g e n e r a l t e r m s , it m a y be of i n t e r e s t to c o m m e n t in m o r e de ta i l o n s o m e s e l e c t e d a c c e l e r a t o r c h a r a c t e r i s t i c s a s t h e s e m a y r e f l e c t o t h e r a s p e c t s of the a p p l i c a b i l i t y . The s u b j e c t s d e a l t with a r e the e c o n o m i c s of rad ia t ion p r o c e s s i n g , b e a m c h a r a c t e r i s t i c s , p e n e t r a t i o n c h a r a c t e r i s t i c s , p r o c e s s c o n t r o l and c o n -v e r s i o n e f f i c i e n c y .

ECONOMICS OF VARIOUS T Y P E S OF A C C E L E R A T O R S

A s the e c o n o m i c f a c t o r s a r e o f t e n g i v e n top p r i o r i t y , t h e y w i l l be c o v e r e d f i r s t . T h i s i s a s o m e w h a t d e l i c a t e s u b j e c t a s m o s t a v a i l a b l e i n f o r m a t i o n i s obta inable only f r o m the m a n u f a c t u r e r s b e c a u s e m a n y of the u s e r s c o n s i d e r t h e i r o p e r a t i o n a l e x p e r i e n c e s a s p r o p r i e t a r y i n f o r -m a t i o n . To e x p l a i n t h i s , l e t us take a t y p i c a l " c a s e s t o r y " a s e v a l u a t e d by the s a l e s d i v i s i o n of a c o m p a n y . T h e s e p e o p l e wi l l m o s t o f t en a m o r t i z e the equ ipment o v e r a t e n - y e a r p e r i o d . E v e r y c u s t o m e r wi th w h o m the subjec t w a s d i s c u s s e d s ta ted u n h e s i t a t i n g l y that with the f a s t d e v e l o p m e n t in th i s f i e l d they would not e v e n c o n s i d e r an a m o r t i z a t i o n p e r i o d l o n g e r than f i v e y e a r s . An a s s u m p t i o n a l s o f r e q u e n t l y m a d e in t h e s e budge t s i s that you can run on ful l load - and p r o c e e d on th i s load - f r o m the v e r y minute you push the g r e e n button the f i r s t t i m e , an a s s u m p t i o n that i s not a l w a y s c o r r e c t . A d i l e m m a i s found in the e s t i m a t e d c o s t c o m p a r e d wi th t h e g u a r a n t e e d l i f e t i m e of c o s t l y v i t a l s p a r e p a r t s such a s k l y s t r o n s , e l e c t r o n guns , a c c e l e r a t o r t u b e s and the l i k e . On the one hand the c o m p a n y h a s to be c o n s e r v a t i v e in i t s g u a r a n t e e s , on the o t h e r hand, to d e m o n s t r a t e the good e c o n o m i c a s p e c t s , it w i l l have to point out that such c o m p o n e n t s l a s t m u c h l o n g e r than the guaranteed p e r i o d . T h e s e r e m a r k s a r e not intended to be pure ly c r i t i c a l , but m e r e l y e m p h a s i z e that s u c h budgets can be m i s l e a d i n g when appl ied to o t h e r s i t u a t i o n s than t h o s e o r i g i n a l l y a s s u m e d . T a b l e I i s b a s e d on a m a n u f a c t u r e r ' s i n f o r -m a t i o n and c o m p i l e d by Koch and E i s e n h o w e r [ 1 ] , to which a f ew data have b e e n added.

It i s r e g r e t t a b l e that a m o r e u p - t o - d a t e c o m p i l a t i o n cannot be p r e s e n t e d . It i s n o t i c e a b l e that the p r i c e s p e r ki lowatt d e c r e a s e d r a s t i -c a l l y with i n c r e a s i n g t o t a l p o w e r . The m a j o r i t y of the m a c h i n e s r e f e r r e d to in the tab le a r e u s e d in r e s e a r c h . Indus tr ia l a c c e l e r a t o r s accounted f o r about 150 kW at that t i m e (1964) , and m a c h i n e s good f o r a to ta l about 4 5 0 - 5 0 0 kW a r e u s e d in rad ia t ion p r o c e s s i n g today; t h i s n u m b e r a s w e l l a s the n u m b e r of a p p l i c a t i o n s i s rap id ly i n c r e a s i n g .

It should be added that s e v e r a l o t h e r c o m p a n i e s produce a c c e l e r a t o r s , d. c . - m a c h i n e s a r e , f o r e x a m p l e , m a d e a l s o by H a e f e l y (Swi tzer land) and S a m e s ( F r a n c e ) ; l i n e a r a c c e l e r a t o r s a r e produced by, f o r e x a m p l e , ARCO (United S t a t e s of A m e r i c a ) , CSF ( F r a n c e ) , Mul lard (United Kingdom), V a r i a n (United S t a t e s of A m e r i c a ) and V i c k e r s (United K i n g d o m ) . It i s p o s s i b l e that s u c h m a c h i n e s a r e a l s o m a d e in Japan and the USSR.

4 6 HOLM

B E A M CHARACTERISTICS

The b e a m c h a r a c t e r i s t i c s a r e , of c o u r s e , m a i n l y d e t e r m i n e d by the d e s i g n p r i n c i p l e s of the p a r t i c u l a r type of m a c h i n e . The d . c . - m a c h i n e s g e n e r a t e the fu l l potent ia l r e q u i r e d to a c c e l e r a t e the e l e c t r o n s to t h e i r f ina l e n e r g y , and a r e t h e r e f o r e in p r a c t i c e l i m i t e d to e n e r g i e s about 4 M e V . The p r a c t i c a l l o w e r l i m i t i s to s o m e extent d e t e r m i n e d by the a b s o r p t i o n in the b e a m ex i t window. T h i s window, o f t e n m a d e of a lumin ium o r t i tan ium, s e p a r a t e s the v a c u u m in the a c c e l e r a t o r tube f r o m the a t m o s p h e r e . F o r an e n e r g y of , e . g . 0 . 3 MeV, about 15% of the b e a m p o w e r i s l o s t a s heat in the window. T h i s a l s o puts a l i m i t on the b e a m c u r r e n t and t h e r e b y on the to ta l power output. The l o w e r the e l e c t r o n e n e r g y and the h i g h e r the current , the m o r e heat i s g e n e r a t e d by b e a m a b s o r p t i o n in the window. T h i s heat p r o b l e m i s n o r m a l l y accounted f o r by f o r c e d a i r c o o l i n g and by scanning and/or d e f o c u s i n g the beam b e f o r e it h i t s the window. It i s thought that the b e a m c h a r a c t e r i s t i c s shown in T a b l e I do not r e p r e s e n t the p o w e r l i m i t of such m a c h i n e s . The s c a n width m a y be f u r t h e r i n c r e a s e d , coo l ing s y s t e m s m a y be i m p r o v e d , or s e v e r a l h e a d s m a y be adapted to e a c h g e n e r a t o r unit .

Turning o u r at tent ion to l i n e a r a c c e l e r a t o r s , we m a y s a y that the a v a i l a b l e e n e r g y range i s , in pr inc ip l e , u n l i m i t e d . At the l o w e r end the l i m i t i s s e t by e c o n o m i c s , a s e l e c t r o n s a c c e l e r a t e d by m i c r o w a v e s a r e s u b s t a n t i a l l y m o r e e x p e n s i v e than e l e c t r o n s a c c e l e r a t e d in d . c . - m a c h i n e s . One t h e r e f o r e s e l d o m f inds l i n a c s for o p e r a t i o n b e l o w 4 - 6 MeV. The u p p e r l i m i t h a s in p r a c t i c e b e e n s e t by the induced a c t i v i t y in the product . It i s , f o r e x a m p l e , not l i k e l y that i r r a d i a t i o n of f o o d s w i l l be c l e a r e d f o r e n e r g i e s above 10 MeV in the n e a r fu ture . Depending on the s y s t e m t o be i r r a d i a t e d , h o w e v e r , m u c h h i g h e r e n e r g i e s could s a f e l y be appl ied to n o n - c o n s u m a b l e product s , which would i n c r e a s e the u s e f u l p e n e t r a t i o n range and the a p p l i c a b i l i t y . The b e a m c u r r e n t i s a funct ion of the k l y s t r o n p o w e r , the c o n v e r s i o n e f f i c i e n c y of the wave g u i d e s and the e n e r g y at which the m a c h i n e i s to o p e r a t e . With a k l y s t r o n g iv ing an a v e r a g e output p o w e r of , f o r e x a m p l e , 25 kW, a b e a m p o w e r of 1 0 - 1 3 kW m a y b e obta ined . It i s o b v i o u s that t h e r e i s no d i r e c t c o n s t r u c t i o n a l l i m i t a t i o n to p e r f o r m a n c e , and the windpw p r o b l e m i s m u c h l e s s s i g n i f i c a n t for the h i g h e r e n e r g i e s at wh ich the l i n a c s o p e r a t e , a s m u c h l e s s of the b e a m e n e r g y i s a b s o r b e d in the window.

Another r e s p e c t in which the l inac i s d i s t i n g u i s h e d f r o m the d. c . -' a c c e l e r a t o r i s the p u l s e d m o d e in which it o p e r a t e s . The pulse c h a r a c t e r -

i s t i c s a r e m a i n l y d e t e r m i n e d by the type of k ly s t ron; t y p i c a l f i g u r e s a r e p u l s e l e n g t h s of 3 - 7 /us and r e p e t i t i o n r a t e s of 2 0 0 - 6 0 0 p / s . Al l t h e s e p a r a m e t e r s a r e i m p o r t a n t f o r the match ing of equipment and p r o c e s s . A n o t h e r f a c t o r d e s e r v e s at tent ion: the d o s e - r a t e . In pu l sed m a c h i n e s , w h e r e the b e a m i s "on" p e r h a p s only 0 . 1 % of the t i m e , the peak d o s e -ra te - in the p u l s e - i s e v i d e n t l y v e r y high c o m p a r e d with the a v e r a g e d o s e - r a t e , and thus with the d o s e - r a t e of a d. c . - m a c h i n e of the s a m e output and about the s a m e e n e r g y . T h i s f a c t o r m a y have a v e r y s ub-s t a n t i a l i n f l u e n c e on the y i e l d f o r a n u m b e r of rad ia t ion c h e m i c a l p r o c e s s e s , and should t h e r e f o r e b e c a r e f u l l y c o n s i d e r e d . It should b e noted, how-e v e r , that f o r d. c . - m a c h i n e s in the l o w e r part of the e n e r g y range , e . g . 0 . 3. MeV, the m a j o r part of the b e a m p o w e r m a y be a b s o r b e d in a 1 - m m

PL-236/10 4 7

l a y e r c o m p a r e d wi th a 3 5 - m m l a y e r f o r a 1 0 - M e V l i n a c , i . e . t h e d o s e -r a t e of s u c h a m a c h i n e m a y a l s o b e h i g h .

P E N E T R A T I O N C H A R A C T E R I S T I C S

T h e p e n e t r a t i o n c h a r a c t e r i s t i c s of r a d i a t i o n at a g i v e n e n e r g y h a v e t o be e x a m i n e d w h e n an i r r a d i a t i o n p r o c e s s i s p lanned , to e v a l u a t e a good c o m b i n a t i o n of d o s e h o m o g e n e i t y and r a d i a t i o n e c o n o m y . T h i s r e q u i r e m e n t i s n o r m a l l y b e s t m e t w h e n the e x i t d o s e e q u a l s the e n t r a n c e d o s e .

S o m e d o s e d i s t r i b u t i o n c u r v e s f o r b r o a d e l e c t r o n b e a m s of v a r i o u s e n e r g i e s i m p i n g i n g o n a unit d e n s i t y t a r g e t ( w a t e r ) a r e s h o w n in F i g . 1 . T h e s e c u r v e s c a n p r o v i d e a rough e s t i m a t e of t h e o p t i m u m m a t e r i a l t h i c k n e s s to be i r r a d i a t e d at a g i v e n e n e r g y . F o r i r r a d i a t i o n o f h o m o -g e n e o u s m a t e r i a l s in l o w - e n e r g y m a c h i n e s t h e i n f o r m a t i o n m a y i n m a n y c a s e s b e m o s t e a s i l y o b t a i n e d by c a l c u l a t i v e m e t h o d s a s d o s e d i s t r i b u t i o n m e a s u r e m e n t s i n t h i n s a m p l e s r e q u i r e qu i te s o p h i s t i c a t e d d o s i m e t r y t e c h n i q u e s . A s i m p l e m e t h o d of c a l c u l a t i n g the c o n d i t i o n s u n d e r w h i c h t h e e x i t d o s e e q u a l s the e n t r a n c e d o s e f o r v a r i o u s e n e r g i e s and v a r i o u s l o w - Z m a t e r i a l s h a s b e e n d e v e l o p e d b y C h e e k and L i n n e n b o m [2] . At h i g h e r e n e r g i e s it i s p r o b a b l y p r e f e r a b l e t o run a d o s i m e t r y s u r v e y f o r

FIG. 1. Dose distr ibution in water at d i f fe ren t e l ec t ron energ ies .

It s h o u l d be kept in m i n d that t h e s e d o s e d i s t r i b u t i o n c u r v e s do not n e c e s s a r i l y r e p r e s e n t a c o m p l e t e l y u n c h a n g e a b l e s i t u a t i o n . T h e d o s e d i s t r i b u t i o n m a y be i n f l u e n c e d b y v a r i o u s t r i c k s . F i g u r e 2 [3] d e m o n -s t r a t e s h o w the a p p l i c a t i o n of a r e f l e c t o r p l a t e c a n i m p r o v e t h e d o s e d i s t r i b u t i o n in a m a t e r i a l of a g i v e n t h i c k n e s s . F i g u r e 3 [4] s h o w s how the m a x i m u m o n the d o s e d i s t r i b u t i o n c u r v e c a n be f l a t t e n e d by u s i n g

4 8 HOLM

FIG. 2 . Dose distr ibution in water at d i f fe ren t depths.

FIG. 3 . Effec t on dose distribution curve caused by a sca t ter p l a t e .

a s c a t t e r plate b e t w e e n the b e a m exi t window and the s a m p l e . A c o m b i -nat ion of s u c h d e v i c e s can c e r t a i n l y l ead to both b e t t e r d o s e h o m o g e n e i t y and b e t t e r b e a m ut i l i za t ion .

ROUTINE PROCESS CONTROL

When a l l e v a l u a t i o n s a r e m a d e of b e a m and pene tra t ion c h a r a c t e r -i s t i c s with r e g a r d to the p r o c e s s to be c a r r i e d out, the rout ine p r o c e s s

PL-236/10 4 9

F I G . 4 . System for cont ro l l ing m a c h i n e pa ramete r s .

c o n t r o l m u s t be c o n s i d e r e d . T h e i n f o r m a t i o n w e want i s h o w to m a i n t a i n and r e c o r d the i r r a d i a t i o n p a r a m e t e r s c h o s e n f o r the p r o c e s s in the m i n u t e - t o - m i n u t e and d a y - t o - d a y o p e r a t i o n . T h i s p r o b l e m h a s b e e n d e a l t w i th i n a c h a p t e r o n d o s i m e t r y in i n d u s t r i a l r a d i a t i o n p r o c e s s i n g i n a f o r t h c o m i n g n e w e d i t i o n of Hine and B r o w n e l l ' s R a d i a t i o n D o s i m e t r y . T h e r o u t i n e at t h e l i n e a r a c c e l e r a t o r f a c i l i t y at R i s ^ h a s b e e n d e s c r i b e d b y B r y n j o l f s s o n e t a l . ( 1 9 6 3 ) . F i g u r e 4 g i v e s an i d e a of h o w t h e m a c h i n e p a r a m e t e r s a r e at p r e s e n t c o n t r o l l e d . Two s e c o n d a r y e m i s s i o n c o l l e c t o r s a r e l o c a t e d in the s c a n n e r h o u s i n g . T h e b e a m e n e r g y i s d e r i v e d f r o m t h e c u r r e n t t o the b e n d i n g m a g n e t n e c e s s a r y t o bend the b e a m t o p a s s s y m m e t r i c a l l y b e t w e e n the two c o l l e c t o r s . When it d o e s s o , the e l e c t r o n s r e f l e c t e d f r o m t h e e x i t w i n d o w w i l l c a u s e i d e n t i c a l s i g n a l s f r o m t h e t w o c o l l e c t o r s . O t h e r w i s e o n e of the c o l l e c t o r s w i l l p ick up m o r e c u r r e n t t h a n the o t h e r , and t h i s c a n be m a d e t o t r i g g e r a n a l a r m o r an e n e r g y -r e g u l a t i n g c i r c u i t . T h e s a m e s e t - u p p r o v i d e s a m e a n s of c u r r e n t c o n t r o l a s the n u m b e r of r e f l e c t e d e l e c t r o n s p i c k e d up by the c o l l e c t o r s i s p r o -p o r t i o n a l t o the c u r r e n t of the p r i m a r y b e a m . At R i s ^ t h i s s i g n a l i s f e d b a c k t o the c o n v e y o r d r i v e s o that a d e c r e a s e i n c u r r e n t i s c o m p e n s a t e d b y a s i m u l t a n e o u s d e c r e a s e in c o n v e y o r s p e e d ; t h u s a c o n s t a n t s u r f a c e d o s e i s m a i n t a i n e d . T h e s c a n n i n g o p e r a t i o n i s a l s o c o n t r o l l e d by a f e e d -b a c k s y s t e m f r o m a p i c k - u p c o i l at t h e m a g n e t b a c k to the p o w e r s u p p l y . When c o m b i n e d into a s i n g l e s i g n a l , t h e s e f e a t u r e s shou ld t a k e c a r e of t h e n e c e s s a r y p r o c e s s c o n t r o l i n a c o n s t a n t i r r a d i a t i o n g e o m e t r y . T h e g e n e r a l p r i n c i p l e s of t h i s s y s t e m s h o u l d b e a p p l i c a b l e to any kind of i r r a d i a t i o n p r o c e s s .

C O N V E R S I O N E F F I C I E N C I E S

It w a s s t a t e d e a r l i e r that c o n v e r s i o n of the e l e c t r o n b e a m into b r e m s s t r a h l u n g b y l e t t i n g the b e a m i m p i n g e o n a h e a v y m e t a l t a r g e t w o u l d l e a d to m u c h m o r e p e n e t r a t i n g r a d i a t i o n . T h i s m e t h o d h a s b e e n a d v o c a t e d b y s e v e r a l p e o p l e a s a v e r y t e m p t i n g i d e a . A s it m i g h t be of

4

T A B L E II. C A L C U L A T E D E F F I C I E N C E S FOR X - R A Y PRODUCTION [1] Ol o

Alumin ium target Tungsten ta rge t

E (MeV)

• Range ( g / c m 2 )

T o t a l e f f i c i ency

Forward e f f i c i ency

C7°)

Range,

( g / c m 2 )

T o t a l e f f i c i e n c y

m

Forward e f f i c i ency

(7»)

1 0 . 0 5 . 8 7 . 7 6 . 3 6 . 1 30 19

5 . 0 3 . 1 4 . 0 3 . 1 3 . 6 19 11

3 . 0 1 . 9 2 . 5 1 . 9 2 . 3 14 6 . 2

2 . 0 1 . 2 1 . 8 1 . 3 1 . 6 10 4 . 1

1 . 0 0 . 5 5 0 . 9 0 . 7 0 . 7 6 6 2 . 0

0 . 5 0 . 2 3 0 . 4 0 . 3 0 . 3 3 3 0 . 9

P L - 2 3 6 / 1 0 5 1

i n t e r e s t f o r s o m e s p e c i a l a p p l i c a t i o n s , and, at a l a t e r s t a g e , when e l e c t r o n s m a y be e v e n c h e a p e r than today, f o r a m u c h b r o a d e r u s e , s o m e c o n v e r s i o n e f f i c i e n c y data r e p o r t e d by Koch and E i s e n h o w e r (1965) a r e g i v e n in T a b l e II. It should be noted that on ly X - r a y s in the f o r w a r d d i r e c t i o n can be u t i l i z e d and that on ly s o m e f r a c t i o n of t h e s e can be a b s o r b e d in the p r o d u c t . The c o m p l e x e n e r g y s p e c t r u m of the b r e m s -s t r a h l u n g wi l l m a k e it d i f f i cu l t to obtain a good d o s e h o m o g e n e i t y in the product u n l e s s m u l t i p a s s c o n v e y o r s y s t e m s (or , in the c a s e of a l iquid, m u l t i p a s s f low s y s t e m s ) are p r o v i d e d . It i s a l m o s t c e r t a i n that th i s m e t h o d w i l l c o m e into u s e s o m e day, but it i s at p r e s e n t not l i k e l y to be c h o s e n f o r a g i v e n p r o c e s s .

B e c a u s e of l a c k of su i tab le i n f o r m a t i o n , p r a c t i c a l rad ia t ion c h e m i c a l p r o c e s s e s have not b e e n c o v e r e d h e r e . L i t t l e m a t e r i a l h a s b e e n r e l e a s e d on s u c h p r o c e s s e s , but the whole f i e ld i s in a s t a t e of v e r y rapid d e v e l o p -m e n t , and two m a j o r b r e a k t h r o u g h s w e r e r e p o r t e d during 1966 (the D e e r i n g - M i l l i k a n t e x t i l e p r o c e s s and the F o r d coat ing t e c h n i q u e ) .

R E F E R E N C E S

[ 1 ] KOCH, H . W . , EISENHOWER, E . H . , Accelera tors for Food Processing, N. A . S . - N . R . C . Rep. 1273 . (1965) .

[ 2 ] CHEEK, C . H . , LINNENBOM, V . J . , Ca lcu la t ions of Absorbed Dose, NRLRep.5448 (1960) . [ 3 ] BRYNjdLFSSON, A . , HOLM, N . W . , THARUP. G . , SEHESTED, K . , "Industrial s te r i l iza t ion at the

e l ec t ron l i n e a r - a c c e l e r a t o r fac i l i ty a t Ris^", Industrial Uses of Large Radiat ion Sources (Proc. Conf . Salzburg, 1963) 2, IAEA, Vienna (1963) 281.

[ 4 ] BRYNjdLFSSON, A . , THARUP, G . , D e t e r m i n a t i o n of Beam Parameters and Measurements of Dose Distr ibution in Mate r i a l s I r radiated by Electrons in the Range of 6 MeV to 14 MeV, Rise! Rep. No. 53 ( 1 9 6 3 ) .

S T A T U S R E P O R T O N C H E M O N U C L E A R R E A C T O R S A N D R A D I A T I O N C H E M I C A L P R O C E S S I N G

M. STEINBERG BROOKHAVEN NATIONAL LABORATORY, UPTON, N . Y . , UNITED STATES OF AMERICA

Abstract

STATUS REPORT ON CHEMONUCLEAR REACTORS AND RADIATION CHEMICAL PROCESSING. T h e use of nuc l ea r energy for the synthesis and product ion of industrial c h e m i c a l s is r ev iewed . F iss ion- f ragment c h e m o n u c l e a r reactors a r e used for bas ic endo the rmic reactors in la rge c a p a c i t i e s . These a r e a p p l i c a b l e to t he f ixat ions of ni t rogen, synthesis of ozone and synthesis of carbon m o n o x i d e from low-cos t , r ead i ly ava i l ab l e , raw m a t e r i a l s . T h e d e v e l o p m e n t of f i s s iochemonuclear fue l e l em en t s , f iss iochemistry, the c o n t a m i n a t i o n prob lem, t he i n - p i l e loop exper iments and the economics of c h e m o n u c l e a r reactors a r e rev iewed. T h e use of isotopic and m a c h i n e sources is ma in ly reserved for e x o t h e r m i c c h a i n - t y p e reac t ions . These sources range f rom 6°Co, 1 3 ,Cs, 9°Sr to l iquid 24Na and In-Ga loops to 0 . 3 to 20 MeV acce le ra to r s . Po lymer iza t ion , pa r t i a l oxidat ion and ha logena t ion h a v e par t i a l ly reached c o m m e r c i a l s ta tus . New areas for research inc lude he terogeneous radia t ion chemis t ry , c ryogenic rad ia t ion chemis t ry , e l e c t rode reac t ions , p las t ic m a t e r i a l combinat ions , copo lymer i za t ion and ionic p o l y m e r i z a t i o n .

INTRODUCTION

The p o s s i b i l i t i e s of the u s e of h i g h - e n e r g y radiat ion for the s y n t h e s i s and product ion of industr ia l c h e m i c a l s and c h e m i c a l p r o c e s s i n g p u r p o s e s w e r e f i r s t c o n s i d e r e d in the l a t e r 1 9 4 0 s . S e r i o u s r e s e a r c h and deve lop-ment work began in the e a r l y 1950s and has grown through s e v e r a l c y c l e s and d e g r e e s of i n t e r e s t and support to the p r e s e n t day. H i g h - e n e r g y radiat ion c h e m i c a l p r o c e s s i n g has at tracted c o n s i d e r a b l e r e s e a r c h expend i -ture; h o w e v e r , the p r a c t i c a l appl icat ion to operat ing p r o c e s s e s has b e e n r e l a t i v e l y s low in developing, and r e l a t i v e l y few l a r g e - s c a l e radiat ion-induced p r o c e s s e s e x i s t today . The potential , h o w e v e r , s t i l l e x i s t s , and c o n s i d e r i n g that the subject i s c o m p a r a t i v e l y new, it appears to m a n y to be worth much further exp lorat ion .

R e s e a r c h and deve lopment in the e a r l y days, w e r e based on a t r i a l -a n d - e r r o r b a s i s in a wide v a r i e t y of s y s t e m s . Th i s w a s m a i n l y c a r r i e d out in the United States of A m e r i c a by pr ivate co rpo ra t io ns who quickly b e c a m e d i s i l lu s ioned b e c a u s e they found that radiat ion was not the panacea for al l t h e i r ex i s t ing convent ional c h e m i c a l p r o c e s s i n g p r o b l e m s . The r e s e a r c h then r e v e r t e d to m o r e fundamental s tud ie s on the e f f e c t s of the in terac t ion of h i g h - e n e r g y radiat ion with m a t t e r . During th is t i m e the USAEC began to support an expanding p r o g r a m m e f o r applying radiat ion to industr ia l p r o c e s s e s and th i s has continued to the p r e s e n t day. The USAEC has a l s o s t rong ly supported a v e r y fundamental r e s e a r c h pro-g r a m m e in b a s i c radiat ion c h e m i s t r y . In addit ion to the s tud ie s and p r o g r a m m e s in the United States of A m e r i c a , work has been going on in maijy c o u n t r i e s throughout the world and c o m p r e h e n s i v e p r o g r a m m e s have

5 3

5 4 STEINBERG

b e e n p a r t i c u l a r l y d e v e l o p e d in F r a n c e , Japan and the S o v i e t Union. I b e l i e v e that today we h a v e a b e t t e r unders tand ing as to w h e r e and how the v a r i o u s k inds of h i g h - e n e r g y radiat ion could apply, and b e c a u s e of t h i s c e r t a i n p a t t e r n s of d e v e l o p m e n t can be t r a c e d .

In r e v i e w i n g the s t a t u s of radiat ion c h e m i c a l p r o c e s s i n g , a d i s c u s s i o n i s p r e s e n t e d , s t a r t i n g f i r s t with a m a j o r c l a s s i f i c a t i o n of rad ia t ion s o u r c e s . Then, under e a c h c a t e g o r y , the type of p r o c e s s that b e s t f i t s the s o u r c e i s r e v i e w e d . T h i s i s f o l l o w e d by a d i s c u s s i o n of the d e v e l o p m e n t of the d e s i g n and f a b r i c a t i o n of the s o u r c e . F i n a l l y , the p r o c e s s e s that e i t h e r h a v e b e e n d e v e l o p e d , are in advanced s t a g e s of d e v e l o p m e n t , o r a r e in the e a r l y s t a g e s of r e s e a r c h and d e v e l o p m e n t , a re d i s c u s s e d .

I. F I S S I O N - F R A G M E N T AND REACTOR RADIATION PROCESS D E V E L O P M E N T

The u s e of f i s s i o n - f r a g m e n t r e c o i l e n e r g y for inducing c h e m i c a l c h a n g e s in m a t t e r i s a d i r e c t c o n v e r s i o n of n u c l e a r to c h e m i c a l e n e r g y . T h i s type of e n e r g y i s p r i m a r i l y m a d e a v a i l a b l e in a uran ium f i s s i o n

FIG. 1. C h e m o n u c l e a r reactors : power requ i rement versus G - v a l u e for ave rage product MW = 50.

r e a c t o r . F o r l a r g e c a p a c i t i e s , it a p p e a r s to be the l o w e s t c o s t f o r m of h i g h - e n e r g y rad ia t ion . B e c a u s e of the l a r g e capac i ty , the appl icat ion of t h i s type of rad ia t ion i s u s u a l l y r e s e r v e d f o r e n d o t h e r m i c , non-cha in , l o w y ie ld , l o w G - v a l u e r e a c t i o n s , as shown in F i g . 1.

I . l . F i s s i o n - f r a g m e n t s o u r c e and fuel d e v e l o p m e n t

B e c a u s e of the low range of f i s s i o n f r a g m e n t s in s o l i d s , u s u a l l y < 1 0 jum, it b e c o m e s n e c e s s a r y to d e s i g n f i s s i o n - f r a g m e n t so l id s o u r c e s with at l e a s t one d i m e n s i o n l e s s than t h i s r a n g e . T h i s i s b e c a u s e a s i g n i f i c a n t f r a c t i o n of the e n e r g y of the f i s s i o n f r a g m e n t c a n be r e l e a s e d

o NONCHAIN REACTIONS £ ENOOTHERMIC . , CHAIN REACTIONS-EXOTHERMIC—^ z>

O.I1 L. 0.1 1.0

_l I I I 1 \ 1 0.1 * 10 100 1000 10 000 100000 1000 000

G - V A L U E - M O L E C U L E S / l O O e V

P L - 2 3 6 / 1 5 5

in the c h e m i c a l r e a c t a n t . In i t i a l l y u r a n i u m conta in ing g l a s s f i b r e of 3 and 6 jum in d i a m e t e r w a s d e v e l o p e d . E n e r g y d e p o s i t i o n e f f i c i e n c y of about 50% w a s a v a i l a b l e . The s t a b i l i t y of t h i s m a t e r i a l to t h e r m a l and r a d i a t i o n d a m a g e , h o w e v e r , i s l i m i t e d . Work h a s b e e n p e r f o r m e d by s e v e r a l i n v e s t i g a t o r s on d e v e l o p m e n t of m e t a l and c e r m e t f i b r e f u e l in m i c r o n d i a m e t e r s i z e s . The m o s t advanced f o r m of f i s s i o n - f r a g m e n t c h e m o -n u c l e a r fue l , d e v e l o p e d at B r o o k h a v e n Nat iona l L a b o r a t o r y (BNL) , i s a 2 . 5-/um thin fo i l of an a l l o y of u r a n i u m in p a l l a d i u m and c o a t e d with p l a t i n u m . T h i s s h o w s good c h a r a c t e r i s t i c s f o r m e c h a n i c a l , t h e r m a l , c h e m i c a l and r a d i a t i o n s t a b i l i t y . A f i s s i o n - f r a g m e n t e n e r g y d e p o s i t i o n e f f i c i e n c y of 35% h a s b e e n obta ined with t h i s e l e m e n t . A m u l t i p l e a r r a y h o n e y c o m b f u e l e l e m e n t of t h i s m a t e r i a l w a s f a b r i c a t e d . The f o i l h a s b e e n u s e d in m a n y i n - p i l e c a p s u l e i r r a d i a t i o n e x p e r i m e n t s .

1 . 2 . F i s s i o n - f r a g m e n t r a d i a t i o n c h e m i s t r y and y i e l d v a l u e s

The m a i n c h e m i c a l r e a c t i o n s that have b e e n i n v e s t i g a t e d u s i n g f i s s i o n - f r a g m e n t e n e r g y in c a p s u l e e x p e r i m e n t s a r e a s f o l l o w s : (1) F o r m a t i o n of n i t r o g e n o x i d e s ( f i xed n i t r o g e n a s N 0 2 and NzO) f r o m n i t r o g e n and o x y g e n . (2) The s y n t h e s i s of c a r b o n m o n o x i d e (CO) by the d e c o m p o s i t i o n of c a r b o n d i o x i d e . (3) The s y n t h e s i s of o z o n e ( 0 3 ) f r o m o x y g e n . (4) The f o r m a t i o n of h y d r o g e n (H 2 ) and h y d r o g e n p e r o x i d e (H2O2) by d e c o m p o s i t i o n of w a t e r . (5) The s y n t h e s i s of h y d r a z i n e f r o m l iquid a m m o n i a . (6) The s y n t h e s i s of h y d r o c y a n i c ac id (HCN) f r o m n i t r o g e n and m e t h a n e . (7) The s y n t h e s i s of e t h y l e n e g l y c o l (CH2OH)2 f r o m m e t h a n o l .

The m o s t e x t e n s i v e w o r k with f i s s i o n - f r a g m e n t e n e r g y h a s b e e n done in the h o m o g e n e o u s i r r a d i a t i o n of g a s - p h a s e n i t r o g e n and o x y g e n f o r the f i x a t i o n of n i t r o g e n in s t a t i c c a p s u l e e x p e r i m e n t s . One c a n c o n v e r t a l a r g e f r a c t i o n of the n i t r o g e n and o x y g e n , f o r m i n g h igh c o n c e n t r a t i o n s of o x i d e s of n i t r o g e n . The p r o b l e m h a s b e e n in obta in ing y i e l d s that would be e c o n o m i c a l l y a t t r a c t i v e . F o r e x a m p l e , a G - v a l u e of 2 f o r N 0 2 f o r -m a t i o n can be r e a d i l y obta ined; h o w e v e r , i t i s n e c e s s a r y to obta in a G - v a l u e of 6 to c o m p e t e e c o n o m i c a l l y with c o m p e t i t i v e n i t r o g e n f i x a t i o n p r o c e s s e s . R e c e n t w o r k at B N L h a s ind ica ted that t h e r e i s a p o s s i b i l i t y that a t w o - p h a s e g a s - l i q u i d a q u e o u s s y s t e m m a y b r i n g i m p r o v e m e n t in the y i e l d s . B e c a u s e of the huge f e r t i l i z e r m a r k e t , t h i s s y s t e m c o n t i n u e s t o a t t rac t cont inual r e s e a r c h s t u d i e s .

The y i e l d s of c a r b o n m o n o x i d e and the f o r m a t i o n of o z o n e a p p e a r to be , f o r the m o m e n t , e c o n o m i c a l l y m o r e a t t r a c t i v e . The c a r b o n m o n o x i d e s y s t e m i s of g r e a t i n t e r e s t f o r c h e m i c a l s y n t h e s i s g a s and p i p e l i n e g a s product ion , w h e r e a s t h e o z o n e s y s t e m i s of i n t e r e s t f o r p o s s i b l e w a t e r p u r i f i c a t i o n and c h e m i c a l o x y g e n a t i o n p r o c e s s e s .

The o t h e r s y s t e m s m e n t i o n e d above s u f f e r e i t h e r f r o m s m a l l e r m a r k e t d e m a n d o r v a l u e s that do not p r o v i d e the i n c e n t i v e f o r cont inued r e s e a r c h and d e v e l o p m e n t e x p e n d i t u r e s to br ing the p r o c e s s e s to an e c o n o m i c a l l y c o m p e t i t i v e s t a t u s . In the c a s e of h y d r a z i n e , s o m e c a p s u l e f i s s i o n -f r a g m e n t c h e m i s t r y w a s p e r f o r m e d and a l iquid a m m o n i a i n - p i l e l o o p w a s built; h o w e v e r , s i n c e the m a r k e t demand f o r h y d r a z i n e i s l o w , the

5 6 STEINBERG

work was d i s c o n t i n u e d . In the c a s e of h y d r o c y a n i c ac id , the y i e l d s o b -ta ined did not appear to be of s u f f i c i e n t va lue to cont inue the d e v e l o p m e n t .

An i n t e r e s t i n g point c o n c e r n i n g the fundamenta l rad ia t ion c h e m i s t r y of f i s s i o n - f r a g m e n t rad ia t ion i s that in v e r y f ew i n s t a n c e s has it b e e n found that the high l i n e a r e n e r g y t r a n s f e r (LET) radiat ion f r o m the h e a v y f i s s i o n f r a g m e n t s y i e l d s r e s u l t s that a r e d i f f erent f r o m the low L E T g a m m a - and b e t a - t y p e rad ia t ion . Th i s m e a n s that the radiat ion c h e m i s t r y of f i s s i o n f r a g m e n t s can be c a r r i e d on m o r e e c o n o m i c a l l y and c o n v e n i e n t l y with n o n - r e a c t o r radiat ion, and t h e s e r e s u l t s can then l a t e r be v e r i f i e d by r e a c t o r e x p e r i m e n t s .

1 . 3 . Contaminat ion p r o b l e m

The p r i c e o n e pays f o r obtaining l a r g e quant i t i e s of l o w - c o s t h igh -e n e r g y rad ia t ion i s the p o s s i b i l i t y of contaminat ing the product with r a d i o -a c t i v e f i s s i o n p r o d u c t s . Work to date in c a p s u l e s i n d i c a t e s that the g a s e o u s p r o d u c t s are contaminated with h a l o g e n and noble g a s f i s s i o n f r a g m e n t s . T h i s contaminat ion can be e l i m i n a t e d by s tandard c h e m i c a l e n g i n e e r i n g o p e r a t i o n s . H o w e v e r , t h i s h a s ye t to b e d e m o n s t r a t e d on l a r g e r quant i t i e s of m a t e r i a l produced with f i s s i o n - f r a g m e n t e n e r g y . T h e d e t e r m i n a t i o n of y i e l d s f r o m radiat ion c h e m i s t r y s t u d i e s s t i l l r e m a i n s the m a i n a r e a f o r i n v e s t i g a t i n g the d e v e l o p m e n t of c h e m o n u c l e a r p r o c e s s e s . U n l e s s s u f f i c i e n t l y high y i e l d s a r e obta ined, a l a r g e e f f o r t in d e v e l o p i n g d e c o n t a m i n a t i o n s t u d i e s i s not w a r r a n t e d .

1 . 4 . I n - p i l e l o o p s

A s l u r r y l o o p of uran ium oxide in l iquid a m m o n i a w a s o p e r a t e d by the A e r o j e t - G e n e r a l Corpora t ion in the M a t e r i a l s T e s t i n g R e a c t o r at Idaho F a l l s at v a r i o u s t i m e s in 1965 . The l o o p w a s c o n s t r u c t e d to s y n t h e s i z e h y d r a z i n e , and s o m e y i e l d and c o n c e n t r a t i o n data w e r e obta ined . The l o o p has s i n c e b e e n r e m o v e d and d i s m a n t l e d .

A c h e m o n u c l e a r i n - p i l e l o o p or s m a l l c i r c u l a t i n g r e a c t o r rad ia t ion pi lot plant i s n e a r i n g c o m p l e t i o n at the s i t e of the B r o o k h a v e n Graphi te R e s e a r c h R e a c t o r . With th i s l o o p it should be p o s s i b l e to i n v e s t i g a t e a l l the c h e m i c a l s y s t e m s s o f a r c o n s i d e r e d f o r c h e m o n u c l e a r p r o c e s s e s . P r e s s u r e cond i t ions up to 68 atm, t e m p e r a t u r e s up to 540°C, and f i s s i o n -f r a g m e n t e n e r g i e s up to 5000 W are the d e s i g n c a p a b i l i t i e s of t h i s l o o p . C h e m i c a l a n a l y s i s can be m a d e with a s o p h i s t i c a t e d cont inuous i n - l i n e c h e m i c a l i n s t r u m e n t a t i o n s y s t e m .

1 . 5 . Status of c h e m o n u c l e a r r e a c t o r s

No f i s s i o n - f r a g m e n t r e a c t o r has b e e n built to date . R e s e a r c h and d e v e l o p m e n t h a s ind icated that th i s f o r m of h i g h - e n e r g y radiat ion i s m o s t app l i cab le to the product ion of l a r g e - c a p a c i t y l o w - c o s t c h e m i c a l s that f e e d on l o w - c o s t raw m a t e r i a l s . The potent ia l s e e m s at p r e s e n t to be m a i n l y l i m i t e d to the f o l l o w i n g p r o c e s s e s : (1) The f i x a t i o n of n i t r o g e n f r o m air for f e r t i l i z e r product ion . (2) The product ion of carbon m o n o x i d e f r o m carbon d iox ide for s y n t h e s i s and p ipe l ine g a s product ion . (3) The s y n t h e s i s of o z o n e f r o m oxygen and a i r for w a t e r pur i f i ca t ion and c h e m i c a l oxygenat ion p r o c e s s e s .

P L - 2 3 6 / 1 5 7

Other s y s t e m s that have potent ia l but are of l e s s i m m e d i a t e i n t e r e s t a r e t h o s e that y i e ld hydrogen p e r o x i d e f r o m w a t e r and h y d r a z i n e f r o m a m m o n i a . Tab le I i n d i c a t e s s o m e of the c a p a c i t i e s that a r e needed to m a k e t h e s e s y s t e m s e c o n o m i c a l l y c o m p e t i t i v e under US c o n d i t i o n s . F i s s i o n - f r a g m e n t c h e m o n u c l e a r r e a c t o r s e s s e n t i a l l y c o m p e t e with e l e c t r o -c h e m i c a l p r o c e s s e s . The e n e r g y required f o r t h e s e p r o c e s s e s can be d e r i v e d e i t h e r f r o m convent iona l f o s s i l fuel p lants o r f r o m n u c l e a r p o w e r r e a c t o r s o u r c e s . In fac t , in s o m e of the s y s t e m s c o n s i d e r e d above a r e dual c y c l e p r o c e s s e s w h e r e b y both d i r e c t n u c l e a r - t o - c h e m i c a l and i n d i r e c t n u c l e a r - t o - p o w e r - t o - c h e m i c a l product ion s c h e m e s a r e c o m b i n e d to obta in an e c o n o m i c a l l y o p t i m u m s y s t e m .

The d e v e l o p m e n t of the rad ia t ion c h e m i s t r y and the d e t e r m i n a t i o n of rad ia t ion c h e m i c a l y i e l d s in both s t a t i c and f low s y s t e m s r e m a i n the g r e a t e s t and m o s t f e r t i l e r e s e a r c h a r e a for d e v e l o p i n g r e a c t o r rad ia t ion f o r product ion p u r p o s e s . A s the m e a n s for obtaining i n c r e a s e d y i e l d s a r e d e v e l o p e d , the l e s s t h e r e i s a need f o r high e f f i c i e n c y f i s s i o n - f r a g m e n t fue l , and the c l o s e r one g e t s to a convent ional p o w e r r e a c t o r type fue l with i n c r e a s e d t h i c k n e s s . A g r e a t e r u t i l i za t ion i s thus m a d e of the r e a c t o r neutron and g a m m a e n e r g y .

In the United S t a t e s of A m e r i c a , r e s e a r c h and d e v e l o p m e n t e f f o r t in c h e m o n u c l e a r p r o c e s s e s i s m a i n l y supported by the USAEC in u n i v e r s i t i e s and nat ional l a b o r a t o r i e s .

II. ISOTOPIC AND MACHINE RADIATION PROCESS D E V E L O P M E N T

A s can be s e e n in F i g . l , i s o t o p i c and m a c h i n e - p r o d u c e d rad ia t ion s o u r c e s a r e m a i n l y su i table f o r e x o t h e r m i c , c h a i n - t y p e , h i g h - y i e l d , high G - v a l u e r e a c t i o n s . T h e s e r e a c t i o n s u s u a l l y i n v o l v e s u c h p r o c e s s e s a s p o l y m e r i z a t i o n , ox idat ion and ha logenat ion .

II. 1 . S o u r c e s

The m o s t h igh ly d e v e l o p e d g a m m a s o u r c e i s 6 0Co. Bonded, doubly e n c a p s u l a t e d , s t a i n l e s s - s t e e l s t r i p s o u r c e s of 6 0 Co have been d e v e l o p e d at BNL, and can be m a d e a v a i l a b l e c o m m e r c i a l l y . C y l i n d r i c a l p e l l e t s , w i r e and o t h e r shaped 60CQ s o u r c e s a r e a v a i l a b l e in v a r i o u s c o u n t r i e s throughout the w o r l d . S o u r c e s of 1 3 7Cs in s t a i n l e s s - s t e e l s l a b s have b e e n d e v e l o p e d at B N L and a r e under t e s t . Other f o r m s of 1 3 7 Cs s o u r c e s of i n t e g r i t y a r e ava i lab le in F r a n c e . Smal l 9 c 5 r be ta n e e d l e s o u r c e s a r e a l s o c o m m e r c i a l l y a v a i l a b l e . The l a r g e r 9 0 S r c lad s o u r c e s h a v e ye t t o be d e v e l o p e d f o r c o m m e r c i a l u s e . S h o r t e r - l i v e d l iquid m e t a l l o o p s coupled to r e a c t o r s f o r supp ly ing g a m m a e n e r g y have had l e s s a p p l i c a t i o n in the United S t a t e s of A m e r i c a than in the S o v i e t Union. The 2 4 N a s y s t e m in the H a l l a m , N e b r a s k a , r e a c t o r did not m a t e r i a l i z e b e c a u s e the r e a c t o r w a s shut down. H o w e v e r , s e v e r a l l i q u i d - m e t a l l o o p s ( i . e . In-Ga) h a v e b e e n r e p o r t e d to have b e e n o p e r a t e d in the S o v i e t Union.

E l e c t r o n a c c e l e r a t o r s f o r beta e n e r g y h a v e b e e n m a i n l y popular in the 2 - to 3 - M e V e n e r g y r a n g e . The bulk of the rad ia t ion e n e r g y u s e d in i n d u s t r y today, m a i n l y f o r s t e r i l i z a t i o n and c r o s s - l i n k i n g p u r p o s e s , i s d e r i v e d f r o m e l e c t r o n a c c e l e r a t o r s . A new g e n e r a t i o n of m a c h i n e s p r o -v id ing e n e r g i e s in the 0 . 3 - M e V r a n g e , m a i n l y f o r t r e a t i n g thin c o a t i n g s ,

T A B L E I . C H E M O N U C L E A R P R O D U C T I O N C O S T E S T I M A T E S 01 CO

Product 3 System G-value'5 Energy0

(kWh(th)/lb)

Fixed charge

rate f

Production cost

V

Reactor power

P(MW(th))

To ta l plant cost ($ mi l l ion)

Plant capaci ty T (tons/d)

1. Fixed nitrogen as N in (NH3+ N 0 2 ) with O j by-product

Dual cycle

6 1 1 . 1 0 . 0 7 $30/eq ton NH3

$4/ton O j

2000 128 2150 N

5750 0 2

2. Fixed nitrogen as N in (NH3 + NO z)

Dual cycle

11 8 . 5 0 . 1 4 330/eq ton NH3

3300 220 4650 N

3 . Fixed nitrogen as N in ( N 0 2 ) and e lec t r ica l power by-product

Dual purpose

6 29.0 0 . 0 7 $25/eq ton NH3

4 . 0 mils/ kWh(e)

1300 98 540 N

400 MW(e)

4 . Synthesis gas (CO + H; ) with O j by-product

Dual cyc le

20 2 .9 0 . 0 7 $ 0 . 3 0 / 1 0 s f t 3

( H j t C O )

$4/ton O ;

1250 98 5900 (160 X 1012 f t 3 )

(CO + H j ) 5000 0 2

5. Synthesis gas (CO + H2) with O z by-product

Dual cycle

10 4 .0 0 .07 $ 0 . 6 0 / 1 0 6 f t 3

(H2+ CO)

$4Aon O ,

1890 135 6300 (171 X 1 0 " f t 3 )

( C O + H j ) 8000 Oj

6. Ozone, 0 3 Single purpose

6 8 . 5 0 . 1 4 $47/ton 423 38 600

7. Hydrogen peroxide, HjOj Single purpose

1 . 7 42 .0 0. 25 $ 0 . 1 5 / l b 700 51 200

8. Hydrazine, N2H., Single purpose

2 .0 38 .0 0 . 2 5 $0 .25 / lb (excludes NH3 cost)

100 16 30

cn - 3 ra t—t Z t i l

o

® Raw mate r ia l for all products are air and water. b G-va lue for f ission-fragment energy. c Energy requirement is total for product and by-products, includes f ission-fragment and e lec t r i ca l energy.

Basis: tj0 - fission-fragment energy deposition ef f ic iency = 0 . 5 0 . ijp = t he rma l - to -e l ec t r i ca l power eff ic iency = 0 . 3 1 1 . Energy for H2 e lec t rolyt ic cells = 140 kWh(e) 106 f t3 H2

PL-236/1 5 9

h a s r e c e n t l y b e e n r e c e i v i n g c o n s i d e r a b l e a t t e n t i o n in t h e U n i t e d S t a t e s of A m e r i c a .

II . 2 . C h e m i c a l p r o c e s s i n g

T h e p r o c e s s e s that e i t h e r h a v e g a i n e d c o m m e r c i a l s t a t u s o r h a v e b e e n n e a r c o m m e r c i a l i z a t i o n u s i n g i s o t o p i c s o u r c e s a r e a s f o l l o w s : (1) T h e D o w P r o c e s s f o r p r o d u c i n g e t h y l b r o m i d e by t h e h y d r o b r o m i n a t i o n of e t h y l e n e . T h i s p r o c e s s r e m a i n s o n e of the f e w o u t s t a n d i n g c o m m e r c i a l r a d i a t i o n c h e m i c a l p r o c e s s s u c c e s s e s i n e x i s t e n c e t o d a y . (2) T h e s u l p h o x i d a t i o n of h y d r o c a r b o n s f o r t h e p r o d u c t i o n of b i o d e g r a d a b l e d e t e r g e n t s a l k a n e s u l p h o n a t e s . A l t h o u g h r e p o r t e d to b e i n a d v a n c e d s t a g e s of d e v e l o p m e n t , bo th b y E s s o R e s e a r c h and F a r b w e r k e H o e c h s t , i t i s doubt fu l w h e t h e r t h e p r o c e s s i s now c o m m e r c i a l l y p r a c t i s e d . (3) T h e o x i d a t i o n of p a r a f f i n s h a s b e e n r e p o r t e d t o b e p r a c t i s e d o n an i n d u s t r i a l s c a l e in R o m a n i a .

II. 3 . P o l y m e r i z a t i o n

R a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n c o n t i n u e s t o be o n e of t h e m o s t a c t i v e a r e a s f o r p o s s i b l e l a r g e - s c a l e r a d i a t i o n p r o c e s s i n g .

II. 3 . 1 . P o l y m e r i z a t i o n of e t h y l e n e

W o r k at B N L h a s i n d i c a t e d that t h e 6 0 C o g a m m a - r a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n of e t h y l e n e c a n b e c o m p e t i t i v e w i t h the h i g h - p r e s s u r e t h e r m o c a t a l y t i c p r o c e s s . A s m a l l - s c a l e , 1 0 0 - c m 3 p i l o t f l o w plant i s i n the p r o c e s s of b e i n g o p e r a t e d u n d e r c o n d i t i o n s a b o v e the m e l t i n g point of the p o l y m e r w h e r e f i l m - g r a d e - t y p e m a t e r i a l i s p r o d u c e d . T h e T a k a s a k i R a d i a t i o n R e s e a r c h E s t a b l i s h m e n t i s o p e r a t i n g a p i l o t p lant u n d e r c o n d i t i o n s b e l o w t h e m e l t i n g point of p o l y e t h y l e n e w h e r e a l o w m e l t i n d e x p o w d e r i s f o r m e d . T h e S o v i e t R a d i a t i o n P r o c e s s i n g L a b o r a t o r y at Obninsk i s r e p o r t e d to be i n v e s t i g a t i n g t h e r a d i a t i o n p o l y m e r i z a t i o n of e t h y l e n e . A F a r b w e r k e H o e c h s t g r o u p i n t h e F e d e r a l R e p u b l i c of G e r m a n y i s a l s o i n v o l v e d i n t h i s kind o f i n v e s t i g a t i o n .

II . 3 . 2 . S o l i d - s t a t e p o l y m e r i z a t i o n

An e x p e r i m e n t a l p i l o t p lant h a s b e e n b u i l t and o p e r a t e d b y t h e T a k a s a k i L a b o r a t o r y f o r the p o l y m e r i z a t i o n of c r y s t a l l i n e t r i o x a n e wi th m a c h i n e r a d i a t i o n .

II. 3. 3. C u r i n g of c o a t i n g s

T h e r e h a s b e e n a r e c e n t i n t e n s e i n t e r e s t in the Uni ted S t a t e s of A m e r i c a i n the u s e of m a c h i n e r a d i a t i o n f o r the c u r i n g of p o l y e s t e r and o t h e r m o n o m e r c o a t i n g s o n v a r i o u s m a t e r i a l s . T h e a d v a n t a g e s of m a c h i n e s o v e r o t h e r t y p e s of r a d i a t i o n and o v e r c u r i n g b y c o n v e n t i o n a l t h e r m a l m e a n s a r e t h e r e l a t i v e l y l o w i n v e s t m e n t c o s t of t h e s y s t e m and t h e h igh r a t e of p r o d u c t i o n . The F o r d M o t o r C o m p a n y , T h e B o i s e C a s c a d e C o m p a n y , and the R a d i a t i o n D y n a m i c s C o m p a n y a r e l e a d e r s in t h i s f i e l d i n the Un i t ed S t a t e s of A m e r i c a .

6 0 STEINBERG

II. 3 . 4 . W o o d - p l a s t i c c o m b i n a t i o n s

The W e s t V i r g i n i a U n i v e r s i t y , with support f r o m the USAEC, has p i o n e e r e d in deve lop ing p l a s t i c - i m p r e g n a t e d w o o d . The A m e r i c a n Novawood Company and the L o c k h e e d G e o r g i a Company have s i n c e a c q u i r e d the capab i l i ty of turning out r e l a t i v e l y l a r g e quant i t i e s of wood-p l a s t i c c o m b i n a t i o n s f o r t e s t and c o m m e r c i a l p u r p o s e s . Advantages of the rad ia t ion p r o c e s s o v e r t h e r m o c a t a l y t i c p r o c e s s e s r e l a t e to the p o o r t h e r m a l conduct iv i ty of wood and the abi l i ty of g a m m a radia t ion to p o l y m e r i z e and o p e r a t e at low enough t e m p e r a t u r e s to prevent v a p o r i -za t ion of the m o n o m e r , thus provid ing a m o r e u n i f o r m i m p r e g n a t i o n .

II. 3. 5 . Graft c o p o l y m e r i z a t i o n

The g r a f t i n g of m o n o m e r s to v a r i o u s f i b r e s has a t t rac ted c o n s i d e r a b l e ' i n t e r e s t in the United S t a t e s of A m e r i c a . T h e s e p r o c e s s e s a l low i m p r o v e d q u a l i t i e s of "permanent p r e s s " , e a s y removed of s o i l by wash ing ( r e f e r r e d to a s " s o i l r e l e a s e " ) , and i m p r o v e m e n t s in d y e a b i l i t y and i m p r o v e d " w a s h -a n d - w e a r " p r o p e r t i e s to be built into t e x t i l e s and c lothing m a d e of r a d i a t i o n - i n d u c e d g r a f t - c o p o l y m e r i z e d f i b r e s . The f i r m s of Dow, D e e r i n g - M i l l i k e n , Bur l ing ton I n d u s t r i e s and T a k a s a k i L a b o r a t o r i e s a r e a c t i v e l y working in t h i s f i e l d .

II. 3. 6. P o l y m e r i r r a d i a t i o n

The i r r a d i a t i o n c r o s s - l i n k i n g of p o l y e t h y l e n e f o r produc ing i m p r o v e d e l e c t r i c a l in su la t ing tape and food wrapping f i l m has b e e n a s u c c e s s f u l c o m m e r c i a l v e n t u r e . The foaming of p o l y e t h y l e n e has b e e n r e p o r t e d to be c o m m e r c i a l i z e d in Japan. The c r o s s - l i n k i n g of natura l rubber l a t e x h a s b e e n r e p o r t e d in the pi lot plant s t a g e at S a c l a y in F r a n c e . A rad ia t ion p r o c e s s f o r c r o s s - l i n k i n g of po lye thy lene ox ide to i n c r e a s e i t s v i s c o s i t y and i m p r o v e o t h e r p r o p e r t i e s h a s b e e n r e p o r t e d by the Union Carbide Company .

III. NEW AREAS FOR RESEARCH

I n v e s t i g a t i o n s of new radiat ion p r o c e s s e s a r e undoubtedly cont inuing in m a n y pr iva te l a b o r a t o r i e s . S o m e of t h e s e could have s i g n i f i c a n t appl ied va lue in the not too d is tant fu ture . T h e fo l l owing a re a r e a s of r e s e a r c h c u r r e n t l y be ing i n v e s t i g a t e d , m a i n l y at B N L .

I I I . l . H e t e r o g e n e o u s rad ia t ion c h e m i s t r y

C h e m i c a l s y s t e m s a r e be ing i n v e s t i g a t e d to d e t e r m i n e i m p r o v e d rad ia t ion u t i l i z a t i o n e f f i c i e n c i e s and e n e r g y t r a n s f e r e f f e c t s . S tud ie s on the h e t e r o g e n e o u s r a d i a t i o n - i n d u c e d d e c o m p o s i t i o n of CO2 and f o r m a t i o n of o x i d e s of n i t r o g e n o v e r so l id ox ide s u b s t r a t e s o v e r a range of p r e s s u r e s and t e m p e r a t u r e s are being i n v e s t i g a t e d . T h e s e could have appl i ca t ion to r e a c t o r i r r a d i a t i o n p r o c e s s e s , p a r t i c u l a r l y in an at tempt t o obtain e n e r g y t r a n s f e r f r o m f i s s i o n - f r a g m e n t s o u r c e s .

P L - 2 3 6 / 1 6 1

A s tudy on the e f f e c t of 6<>Co g a m m a rad ia t ion on the h i g h - p r e s s u r e t h e r m o c a t a l y t i c s y n t h e s i s of a m m o n i a ind ica ted that t h e r e w e r e e i t h e r no i m p r o v e d y i e l d e f f e c t s o r e v e n s l i g h t l y n e g a t i v e e f f e c t s on the y i e l d of a m m o n i a .

III. 2. E f f e c t s of rad ia t ion on e l e c t r o d e r e a c t i o n s

T h e r e have b e e n ind ica t ions f r o m v a r i o u s s o u r c e s that h i g h e r L E T rad ia t ion r e d u c e s the o x y g e n o v e r - v o l t a g e in e l e c t r o l y t i c c e l l s . T h i s could be of s o m e s i g n i f i c a n c e in reduc ing e n e r g y r e q u i r e m e n t s in s u c h l a r g e e l e c t r o c h e m i c a l p r o c e s s e s a s t h o s e f o r the product ion of c a u s t i c and c h l o r i n e . A s tudy i s being p e r f o r m e d at B N L on the e f f e c t of 60Co g a m m a and o t h e r p a r t i c l e radiat ion on the o x y g e n o v e r - v o l t a g e at o x y g e n e l e c t r o d e s .

III. 3. C r y o g e n i c r a d i o l y s i s

T h e ab i l i ty to produce a r e a c t i v e r a d i c a l o r ion ic s p e c i e s under a l m o s t any cond i t ions by m e a n s of h i g h - e n e r g y radiat ion has p r o m p t e d an i n v e s t i g a t i o n at B N L on the p o s s i b i l i t y of producing t h e r m a l l y uns tab le m a t e r i a l s by e x o t h e r m i c r e a c t i o n s . F o r e x a m p l e , the r e a c t i o n of h y d r o g e n and o x y g e n at l iquid o x y g e n t e m p e r a t u r e s m a y produce s i g n i f i c a n t y i e l d s of h y d r o g e n p e r o x i d e . Another e x a m p l e i s that of the i r r a d i a t i o n of h y d r o g e n in l iquid n i t r o g e n f o r the s y n t h e s i s of e x o t h e r m i c a m m o n i a . It i s the in s i tu product ion , quenching and s t a b i l i z a t i o n of r e a c t i v e f r e e r a d i c a l s that one i s s e e k i n g in t h e s e s y s t e m s . Chain r e a c t i o n s would be n e e d e d to m a k e the t echnique e c o n o m i c a l l y a t t r a c t i v e .

III. 4 . R a d i a t i o n - i n d u c e d ox idat ion p r o c e s s f o r w a t e r p u r i f i c a t i o n

A m i n e d r a i n a g e w a s t e p r o b l e m i s be ing i n v e s t i g a t e d c o n c e r n i n g the p o s s i b i l i t y of the cha in ox idat ion of f e r r o u s to f e r r i c i r o n in the p r e s e n c e of an o r g a n i c i m p u r i t y f o r e v e n t u a l l y r e m o v i n g i r o n f r o m the m i n e d r a i n a g e w a s t e f o r d i s p o s a l to ground. The product ion and u t i l i z a t i o n of o z o n e by a l o w - c o s t rad ia t ion p r o c e s s could a l s o be of i n t e r e s t in w a t e r p u r i f i c a t i o n t r e a t m e n t s . It i s f e l t that o t h e r p o s s i b i l i t i e s f o r w a t e r p u r i f i c a t i o n u s i n g r a d i a t i o n - i n d u c e d ox idat ion and s t e r i l i z a t i o n r e a c t i o n s e x i s t , but have h i ther to r e m a i n e d e s s e n t i a l l y u n e x p l o r e d . T h e r e h a s b e e n r e l a t i v e l y l i t t l e r e s e a r c h p e r f o r m e d on t h i s subjec t .

I I L 5 . P l a s t i c - i m p r e g n a t e d c o n c r e t e

It h a s b e e n d e m o n s t r a t e d at B N L that c o n c r e t e can be fu l ly i m p r e g n a t e d with p o l y m e r by i r r a d i a t i n g with 60Co g a m m a radiat ion a p i e c e of c o n c r e t e s o a k e d with m o n o m e r . The c o m p r e s s i v e s t r e n g t h has b e e n i n c r e a s e d by m o r e than a f a c t o r of two and the p e r m e a b i l i t y h a s been a l m o s t c o m p l e t e l y e l i m i n a t e d . T h e r e are m a n y p o s s i b l e app l i ca t ions of th i s new m a t e r i a l . P l a s t i c - i m p r e g n a t e d c o n c r e t e would prevent the " f r e e z e - t h a w " c r a c k i n g of c o n c r e t e . It could i m p r o v e the c o r r o s i o n r e s i s t a n c e of c o n c r e t e t o w a r d s c h e m i c a l s and b r i n e s f o r d e s a l i n a t i o n and c h e m i c a l equipment m a n u f a c t u r e . The ful l potent ia l of th i s m a t e r i a l has yet to be e x p l o r e d .

It has a l s o b e e n p r e l i m i n a r i l y d e m o n s t r a t e d that l e a t h e r s c a n be i m p r e g n a t e d with p o l y m e r us ing in s i tu rad ia t ion p o l y m e r i z a t i o n t e c h n i q u e s .

6 2 STEINBERG

III. 6. P o l y m e r i z a t i o n

It has been found that radiat ion- induced po lymer iza t ion of ul trapure m o n o m e r s such as s t y r e n e probably p r o c e e d s by m e a n s of an ionic m e c h a n i s m . The ra te s of po lymer iza t ion may be as much as two to three o r d e r s of magnitude higher than those of conventional f r e e - r a d i c a l p o l y m e r i z a t i o n . Radiat ion- induced ionic p o l y m e r i z a t i o n thus m a y bring e c o n o m i c b e n e f i t s in the form of l o w e r cos t p r o c e s s e s for the manufacture of a number of l arge market conventional p l a s t i c s . Pur i ty of th is m o n o m e r raw m a t e r i a l , e s p e c i a l l y with r e s p e c t to oxygen and water , i s of p r i m e c o n s i d e r a t i o n in th i s c a s e . Deve lopment work in this f i e ld could be expanded.

I I I .7 . Copo lymer iza t ion

New h i g h - p o l y m e r c o m p o s i t i o n s have been f o r m e d f r o m v e r y inexpens ive m o n o m e r s by using 60Co g a m m a - i n i t i a t e d p o l y m e r i z a t i o n t e c h n i q u e s . Ethylene has been c o p o l y m e r i z e d with carbon monoxide f o r m i n g s table h i g h - m o l e c u l a r weight po lyketones . Ethylene has been c o p o l y m e r i z e d with sulphur dioxide, f o r m i n g h i g h - m o l e c u l a r weight po lysu lphones . F u r t h e r inves t igat ion of the p r o p e r t i e s and p r o c e s s i n g c h a r a c t e r i s t i c s i s required to find proper appl icat ions for t h e s e m a t e r i a l s . The f i e ld of radiat ion- induced c o p o l y m e r i z a t i o n of two and m o r e c o m -ponent s y s t e m s i s a f e r t i l e f i e ld for inves t igat ion .

III. 8. Mater ia l pur i f icat ion

A r e l a t i v e l y untouched area i s the poss ib i l i t y of radiat ion- induced pur i f i cat ion of g a s e s , l iquids and s o l i d s . F o r example , if it i s n e c e s s a r y to r e m o v e s m a l l t r a c e s of oxygen f r o m organic s t r e a m s such as e thylene , it i s p o s s i b l e to i rrad ia te the s t r e a m , thus forming h i g h - m o l e c u l a r weight oxygenated compounds that can be condensed and m o r e e a s i l y r e m o v e d f r o m the s y s t e m . The radiat ion- induced desulphurizat ion and dehydro-su lphurizat ion of pe tro leum raw m a t e r i a l s have been ment ioned as p o s s i b l e r e s e a r c h a r e a s in the Soviet l i t e r a t u r e .

III. 9. Radiat ion c h e m i c a l r e a c t o r and p r o c e s s d e s i g n s t u d i e s

Both conceptual d e s i g n s and exper imenta l work on radiat ion c h e m i c a l p r o c e s s e s are being c a r r i e d out at BNL f o r developing g e n e r a l des ign c r i t e r i a and p r i n c i p l e s f o r making radiat ion p r o c e s s i n g a standard c h e m i c a l eng ineer ing unit operat ion.

B I B L I O G R A P H Y

STEINBERG, M . , C h e m . Engng Prog. 62 (1966) 105. STEINBERG, M . , C h e m o n u c l e a r and Radiation C h e m i c a l Process Research and Deve lopmen t , Brookhaven Nat ional Laboratory, Informal Rep. BNL-10020 (1966). HARMER, D. E . , Symposium on Radiat ion Processing, A m e r i c a n Inst i tu te of C h e m i c a l Engineers Nat ional Mee t ing , Detroi t , November 1966 (in press). LAWRENCE, I . H . , MANOWITZ, B. , LOEB, B . S . , Radioisotopes and Radiat ion, McGraw-Hi l l , New York (1964) 103-29 . Annual and Bimonthly Reports of the Nuclear Engineering Depa r tmen t , Brookhaven Nat iona l Laboratory, Upton, N . Y . 1 9 6 6 - 6 7 .

SAFETY FOR LARGE IRRADIATION FACILITIES

A. DANNO TAKASAKI-SHI RADIATION CHEMISTRY RESEARCH ESTABLISHMENT, JAPAN ATOMIC ENERGY RESEARCH INSTITUTE, TAKASAKI-SHI, JAPAN

Abstract

SAFETY FOR LARGE IRRADIATION FACILITIES. Safe ty for l a rge i r radia t ion f ac i l i t i e s on a p i lo t s ca le or in industr ia l use is very impor tan t not only f rom the point of view of rad ia t ion , but also f r o m the s tandpoint of rad ia t ion c h e m i c a l processing. The regulat ions cover safe ty for rad ia t ion , safe ty for f i re and explosion, sa fe ty for high pressure and sa fe ty for corrosion by c h e m i c a l s . An e x a m p l e is g iven of t he p o l y m e r i z a t i o n of e thy lene on a pi lot s ca le at the T a k a s a k i Radiat ion Chemis t ry Research Establ ishment .

INTRODUCTION

L a r g e i r r a d i a t i o n f a c i l i t i e s on a pi lot s c a l e or in i n d u s t r i a l u s e m u s t n a t u r a l l y c o m p l y wi th a l l the s a f e t y r e g u l a t i o n s c o v e r i n g c o n v e n t i o n a l i n d u s t r i a l i n s t a l l a t i o n s and m u s t be s a f e f r o m the point of v i e w of rad ia t ion . T h e s e r e g u l a t i o n s c o v e r s a f e t y f o r rad ia t ion , s a f e t y f o r f i r e and e x p l o s i o n , s a f e t y f o r high p r e s s u r e and s a f e t y f o r c o r r o s i o n by c h e m i c a l s . T h e s e c o n s i d e r a t i o n s f u n d a m e n t a l l y a f f e c t the d e s i g n of an i r r a d i a t i o n plant and r e a c t i o n v e s s e l [1]. An a p p r e c i a t i o n of t h e s e w i l l a s s i s t in unders tand ing the r e a s o n s behind the d e s i g n .

1. S A F E T Y FOR RADIATION

M a x i m u m a c c e p t a b l e l e v e l s of radiat ion have been a g r e e d i n t e r n a -t i o n a l l y f o r d i f f e r e n t c a t e g o r i e s of p e r s o n s . T h e s e a r e :

G e n e r a l publ ic 0. 25 m r a d / h N o n - c l a s s i f i e d w o r k e r s 0. 7 5 m r a d / h C l a s s i f i e d w o r k e r s 2. 5 m r a d / h The plant d e s i g n e r w i l l have to d e s i g n the plant for a m a x i m u m d o s e -

ra te of l e s s than 0. 7 5 m r a d / h in any a r e a to wh ich plant o p e r a t i o n o r m a i n t e n a n c e m e n can ga in a c c e s s .

A s i s o b v i o u s to any p e r s o n work ing in rad ia t ion c h e m i s t r y , no induced r a d i a t i o n i s c r e a t e d by t r e a t m e n t of m a t e r i a l s in g a m m a rad ia t ion . P r o v i s i o n f o r the r e m o t e p o s s i b i l i t y that c o n t a m i n a t i o n f r o m the s o u r c e m i g h t be s p r e a d has , h o w e v e r , b e e n taken, A n i t r o g e n purge s t r e a m i s u t i l i z e d to w a r n of equ ipment f a i l u r e that could r e s u l t in product c o n t a -m i n a t i o n and a rad ia t ion h a z a r d [2], The n i t r o g e n purge s t r e a m s p a s s through v e r y r e t e n t i v e f i l t e r s to c o n c e n t r a t e any p o s s i b l e r a d i o a c t i v e c o n t a m i n a t i o n . The tube of a s e n s i t i v e G e i g e r c o u n t e r i s l o c a t e d in the o p e r a t i o n bui ld ing n e a r the product r e t u r n l ine and the f i l t e r s .

6 3

6 4 D A N N O

2. S A F E T Y FOR F I R E AND EXPLOSION

F i r e p r e c a u t i o n s m a y have to be taken when i n f l a m m a b l e m a t e r i a l s a r e be ing i r r a d i a t e d , s u c h a s e thy lene in r a d i a t i o n - i n d u c e d p o l y m e r i z a -t ion o r i s o p r o p y l a l c o h o l in the packing of s o u r c e s . T h e n an automat i c C.O2 f i r e - e x t i n g u i s h i n g s y s t e m i s needed in the i r r a d i a t i o n c e l l , labyr inth and c o n v e y o r - l o a d i n g r o o m . T h i s s y s t e m m u s t be i n t e r l o c k e d with the d e t e c t o r of i n f l a m m a b l e g a s s o that the s y s t e m c a n o p e r a t e a s soon a s the g a s l e a k s into the c e l l . T h e s e n s i t i v i t y of the d e t e c t o r i s ad jus ted to o p e r a t e when the c o n c e n t r a t i o n of g a s r e a c h e s above o n e - t h i r d of the l i m i t i n g c o n c e n t r a t i o n of e x p l o s i o n .

A l l e l e c t r i c equ ipment u s e d in the c e l l o r n e a r g a s s t r e a m l i n e s m u s t be prov ided wi th e x p l o s i o n - p r o t e c t i o n d e v i c e s . T h e s e a r e e l e c t r i c m o t o r s , c o m p r e s s o r s , m a g n e t i c s w i t c h e s , e t c .

3. S A F E T Y FOR P R E S S U R E [3] ,

P r e s s u r e v e s s e l s inc luding r e a c t i o n v e s s e l s , p r e s s u r e r e l i e f tanks, product r e c e i v e r s , f i l t e r s and heat e x c h a n g e r s m u s t be d e s i g n e d with a m i n i m u m s a f e t y f a c t o r of t h r e e b a s e d on u l t i m a t e t e n s i l e s t rength . P ip ing , v a l v e s and c o m p r e s s o r s are d e s i g n e d in a c c o r d a n c e wi th r u l e s such a s the ASME p r e s s u r e v e s s e l r u l e s and s o have a m i n i m u m s a f e t y f a c t o r of four .

The rupture d i s c on the r e a c t i o n v e s s e l i s s e t to vent to the p r e s s u r e r e l i e f tank at a p r e s s u r e of 10% i n c r e a s e in o p e r a t i n g p r e s s u r e . The s y s t e m p r e s s u r e would, t h e r e f o r e , at a l l t i m e s be kept be low the equip-m e n t d e s i g n p r e s s u r e e v e n in the event of d e c o m p o s i t i o n o r e x p l o s i o n of reac tant g a s e s .

The p r e s s u r e r e l i e f tank i s a l w a y s f i l l e d with i ner t g a s b e f o r e plant s t a r t - u p . E s c a p e of c o m b u s t i b l e g a s through a rupture d i s c o r b r e a k in the p r o c e s s equ ipment would t h e r e f o r e not l ead to c o m b u s t i o n and d e -c o m p o s i t i o n .

A t h e r m a l - c o n d u c t i v i t y - t y p e gas a n a l y s e r should be l o c a t e d within the c e l l to c o n t i n u o u s l y m o n i t o r the l eakage of i n f l a m m a b l e g a s into the i ner t a t m o s p h e r e . The m o n i t o r , w h o s e s e n s i t i v i t y i s about 500 ppm e thy lene by v o l u m e , w i l l r e q u i r e about 200 c m 3 / m i n of g a s s a m p l e . An e thy lene c o n c e n t r a t i o n s i g n a l w i l l be r e t r a n s m i t t e d to a c o n t r o l r o o m m e t e r and a l a r m .

4. A N E X A M P L E FOR POLYMERIZATION OF E T H Y L E N E ON A PILOT S C A L E [4]

R a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n of e thy l ene in a p i l o t - s c a l e e x p e r i -m e n t a l f a c i l i t y at the T a k a s a k i Radiat ion C h e m i s t r y R e s e a r c h E s t a b l i s h -m e n t p a s s e d a v e r y s t r i c t i n s p e c t i o n conducted by G o v e r n m e n t o f f i c i a l s wi th r e g a r d to c o n t r o l r e g u l a t i o n s b e f o r e the s t a r t - u p of the f a c i l i t y in S e p t e m b e r 1965. T h e s e r e g u l a t i o n s r e l a t e d to i n f l a m m a b l e g a s e s , h igh-p r e s s u r e g a s e s and r a d i a t i o n s .

I r r a d i a t i o n w a s c a r r i e d out in a c o n c r e t e - s h i e l d e d c e l l . A 6 0 Co s o u r c e wi th 108 000 Ci w a s s t o r e d at the bot tom of a, pool of w a t e r about

P L - 2 3 6 / 2 6 5

6 m d e e p . A r e a c t i o n v e s s e l of 10 l i t r e s c a p a c i t y and two s t a i n l e s s - s t e e l r e s e r v o i r s wi th a c a p a c i t y of 45 l i t r e s a r e l o c a t e d in the c e n t r e of the c e l l . B e f o r e the s t a r t - u p , the s o u r c e i s l i f t ed above the w a t e r l e v e l and i s then p l a c e d o u t s i d e the r e a c t i o n v e s s e l . E x p e r i m e n t a l c o n d i t i o n s a r e : m a x i m u m p r e s s u r e , 410 k g / c m 2 , n o r m a l t e m p e r a t u r e , about 150° C, c u r r e n t v e l o c i t y , 5 - 1 5 kg C 2 H 4 / h .

To i m p l e m e n t the above s a f e t y f e a t u r e s , and to prov ide p r o t e c t i o n a g a i n s t o ther f o r e s e e a b l e h a z a r d s , the fo l l owing equ ipment i s prov ided:

(a) Rupture d i s c s o r s a f e t y r e l i e f v a l v e s a r e a t tached to a l l v e s s e l s and p r o c e s s e q u i p m e n t .

(b) Safe ty r e l i e f v a l v e s l oca ted on h i g h - p r e s s u r e s y s t e m s a r e d e s i g n e d in a c c o r d a n c e wi th the c o n t r o l r e g u l a t i o n s on h i g h - p r e s s u r e g a s e s .

(c) The rupture d i s c on the r e a c t i o n v e s s e l i s s e t to vent at 440 k g / c m 2

s o that the s y s t e m p r e s s u r e can be kept be low the o p e r a t i n g p r e s s u r e of 410 k g / c m 2 e v e n in the e v e n t s . The rupture d i s c i s m a d e of a l u m i n i u m fo i l s o that it can be e a s i l y ruptured.

(d) I n t e r l o c k s and r e l a y s a r e i n s t a l l e d to a u t o m a t i c a l l y shut off the e t h y l e n e supply and D o w t h e r m h e a t e r in the event of e i t h e r an i n c r e a s e in s y s t e m p r e s s u r e o r a sudden i n c r e a s e in t e m p e r a t u r e .

(e) E t h y l e n e p r e s s u r e in the h i g h - p r e s s u r e l ine i s m e a s u r e d at e a c h c h e c k i n g point and i s r e c o r d e d , and an a l a r m i s g i v e n when the p r e s s u r e l i m i t i s e x c e e d e d .

(f) A n a l y s i s of e thy l ene g a s can be prov ided to m o n i t o r e t h y l e n e d e c o m p o s i t i o n s by a b a t c h - t y p e s a m p l i n g s y s t e m .

(g) A c a r b o n - d i o x i d e f i r e - e x t i n g u i s h i n g s y s t e m i s l o c a t e d in the c e l l s o that f i r e s of any or ig in can be e x t i n g u i s h e d .

(h) Two t y p e s of g a s m o n i t o r s a r e l oca ted i n s i d e and out s ide the c e l l to c o n t i n u o u s l y moni tor the l e a k a g e of e thy lene g a s .

(i ) The i n s i d e and the outs ide of the c e l l a r e vent i la ted during o p e r a t i o n . (j ) A l l e l e c t r i c equipment i s prov ided with e x p l o s i o n - p r o t e c t i o n d e -

v i c e s . (k) In the e x t e r n a l s o u r c e r e a c t i o n v e s s e l , the s o u r c e would not be

d a m a g e d in the event of an a c c i d e n t , a s it i s doubly e n c a p s u l a t e d in s t a i n l e s s - s t e e l .

(1) The c e l l i s m a d e of h i g h - d e n s i t y c o n c r e t e provid ing both radiat ion s h i e l d i n g and p r o t e c t i o n in the event of an explos ion . ,

R E F E R E N C E S

[1] BAINES, B. D . , Appl ica t ion of Large Radiation Sources in Industry, Elsevier, Ams te rdam, (1964) 119. [2] • HARMER, D. E . , BEALE, J. S . , PUMPELLY, C. T . , WILKINSON, B. W . , in Industr ial Uses of Large

Radiation Sources (Proc. Conf. Salzburg, 1963) 2, IAEA, Vienna (1963) 205. [3] STEINBERG, M . , e t a l . , Rep. BNL-796 (T-305) (1963) [4] Cited f r o m the Government o f f i c i a l inspect ion for the safety of an e t h y l e n e pi lo t p lan t (1965)

5

L O W - T E M P E R A T U R E IRRADIATIONS

Z. P. ZAGÓRSKI AND S. MINC DEPARTMENT OF RADIATION CHEMISTRY, INSTITUTE OF NUCLEAR RESEARCH, WARSAW, POLAND

Abstract

LOW-TEMPERATURE IRRADIATIONS. Radiation chemistry of deep frozen materials is reviewed from the point of view of phenomena characteristic of this particular form of radiolysis. Differences of chemical end-points in the liquid and frozen state are stressed. Special attention is paid to the identity and migration of intermediate species at the temperature of irradiation and at higher temperatures (thawing). The importance of luminescent phenomena is shown by examples. Low-temperature radiation chemistry of particular systems (from water to those occurring in outer space chemistry) is reviewed. In experimental considerations the role of the structure of frozen solids is discussed and the need for additional investigations put forward.

1. INTRODUCTION

Look ing b a c k on the p a p e r s devo t ed to l o w - t e m p e r a t u r e i r r a d i a t i o n s one i s i m p r e s s e d by the v a r i e t y of r e a s o n s t ha t l e d the i n v e s t i g a t o r to t h a t p a r t i c u l a r and d i f f i c u l t cond i t i on of e x p e r i m e n t . At the s a m e t i m e one m a y e a s i l y be a s t o n i s h e d by the r e c k l e s s c o n c l u s i o n s d r a w n f r o m s o m e e x p e r i m e n t s on f r o z e n s y s t e m s w h o s e s t r u c t u r e s a r e p r a c t i c a l l y u n k n o w n .

U n f o r t u n a t e l y , s o m e p a p e r s do not t r e a t t he i n v e s t i g a t i o n of t h e d e e p - f r o z e n s t a t e a s the " r a d i a t i o n c h e m i s t r y of d e e p - f r o z e n m a t e r i a l s " bu t a s a s u p p l e m e n t a r y e x p e r i m e n t c a r r i e d out in ad d i t i o n to the " r a d i a t i o n c h e m i s t r y of l i q u i d s " .

We s h a l l t r y to show t h a t t h e r a d i a t i o n c h e m i s t r y of d e e p - f r o z e n s u b -s t a n c e s i s a s e p a r a t e b r a n c h of r a d i a t i o n c h e m i s t r y , and tha t t r e a t i n g t h i s t e c h n i q u e a s a s u p p l e m e n t a r y one m a y l e a d to e r r o n e o u s r e s u l t s . We s h o u l d l i ke a l s o to s t r e s s t h e n e e d f o r b a s i c r e s e a r c h on the f r o z e n s t a t e , on b a s i c p h y s i c a l and p h y s i c o c h e m i c a l d a t a s u c h a s d e n s i t i e s , s o l u b i l i t i e s of g a s e s , c r y s t a l l i n e s t r u c t u r e s a n d s i z e of c r y s t a l s .

It i s obv ious t ha t we c a n n o t r e v i e w a l l t h e p u b l i s h e d l i t e r a t u r e on l o w -t e m p e r a t u r e i r r a d i a t i o n s . We s h a l l o m i t , f o r e x a m p l e , E . S. R. m e a s u r e -m e n t s p e r f o r m e d a f t e r l o w - t e m p e r a t u r e i r r a d i a t i o n , quo t ing s o m e p a p e r s on ly when t h e y c o n t r i b u t e to t h e q u e s t i o n of t r u e " f r o z e n - s t a t e r a d i a t i o n c h e m i s t r y " and a r e not r e s t r i c t e d to the i d e n t i f i c a t i o n of t h e f r e e r a d i c a l f r o m i t s s i g n a l s .

It i s w o r t h e m p h a s i z i n g t h a t n o w a d a y s E . S. R . i n t e r p r e t a t i o n s t e n d t o t r e a t t he f r e e r a d i c a l not a s an e n t i t y i s o l a t e d f r o m the m a t r i x , bu t a s an i n t e g r a l c o n s t i t u e n t of t h e s y s t e m . D u r i n g t h e p a s t f ew y e a r s a l a r g e n u m b e r of i n o r g a n i c r a d i c a l s h a v e b e e n i d e n t i f i e d by the E . S . R. t e c h n i q u e in i r r a d i a t e d , u s u a l l y f r o z e n , s o l i d s . Many u n s t a b l e s p e c i e s a r e s a t i s -f a c t o r i l y d e s c r i b e d a s s m a l l m o l e c u l e s and t h e e l e c t r o n s p i n r e s o n a n c e r e s u l t s a r e we l l i n t e r p r e t e d by s i m p l e m o l e c u l a r o r b i t a l t h e o r y f o r s u c h m o l e c u l e s . In o t h e r i n s t a n c e s , t he m a g n e t i c c e n t r e c a n n o t b e d e s c r i b e d

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6 8 ZAGORSKI and M I N C

a s a s m a l l m o l e c u l e s i n c e it r e m a i n s part of the bulk m a t e r i a l . In ye t o t h e r i n s t a n c e s p o s i t i v e h o l e s o r e l e c t r o n s a r e t rapped in the l a t t i c e . It i s a s s o c i a t e d with a p a r t i c u l a r p r o p e r t y of the c r y s t a l and b e a r s no r e -s e m b l a n c e to an o r d i n a r y m o l e c u l a r f r a g m e n t [1]. The l a t t er c a s e s b e l o n g c l e a r l y to the f i e l d of " l o w - t e m p e r a t u r e rad ia t ion c h e m i s t r y " .

We s h a l l not dea l s e p a r a t e l y with o p t i c a l a b s o r p t i o n m e t h o d s , b e -c a u s e they a r e u s e d a s an a n a l y t i c a l t o o l . A s in the c a s e of E . S . R . , the m e t h o d has s p e c i a l f e a t u r e s d i s t i n g u i s h i n g it f r o m s p e c t r o p h o t o m e t r y in l iquid , but t h e s e w i l l b e m e n t i o n e d o n l y in the f ina l s e c t i o n devoted to e x -p e r i m e n t a l d e t a i l s . T h e r e s u l t s obta ined by m e a s u r e m e n t of u l t r a - v i o l e t , v i s i b l e and i n f r a - r e d a b s o r p t i o n a r e v e r y important for l o w - t e m p e r a t u r e rad ia t ion c h e m i s t r y , and wi l l b e quoted in a p p r o p r i a t e p l a c e s in t h i s r e v i e w .

The m e a s u r e m e n t of l ight e m i s s i o n i s m o r e c l o s e l y bound to the l o w -t e m p e r a t u r e rad ia t ion c h e m i s t r y and radiat ion c h e m i s t r y of the s o l i d s t a t e s o that a s p e c i a l s e c t i o n i s devoted to t h e s e p r o b l e m s .

The n u m b e r of pub l i ca t ions on l o w - t e m p e r a t u r e i r r a d i a t i o n s i s in -c r e a s i n g at p r e s e n t m o r e rapidly than in o ther b r a n c h e s of radiat ion c h e m i s t r y . The p r o g r e s s may be e s t i m a t e d by a c o m p a r i s o n of annual r e p o r t s w h e r e l o w - t e m p e r a t u r e p r o b l e m s a r e t r e a t e d in s e p a r a t e s e c t i o n s o r in s p e c i a l s u r v e y s ( e . g . Re f s [ 2 , 3 ] ) .

2. RADIATION CHEMISTRY O F D E E P - F R O Z E N SUBSTANCES AS A S E P A R A T E BRANCH OF RADIATION CHEMISTRY

2 . 1 . G e n e r a l c o n s i d e r a t i o n s

A s u r v e y of the s i tuat ion w i l l f i r s t be p r e s e n t e d , b a s e d on p a p e r s in wh ich l o w - t e m p e r a t u r e i rrad ia t ion i s t r e a t e d not a s a s u p p l e m e n t a r y t e c h -nique but a s a s e p a r a t e branch of radiat ion c h e m i s t r y .

T h e r e i s a m a r k e d d i f f e r e n c e in the e f f e c t s if we c o n s i d e r the m o d e of br ing ing the s a m p l e into the s o l i d s t a t e . T h e f i r s t group c o n s i s t s of s a m p l e s that a r e s o l i d at r o o m t e m p e r a t u r e b e f o r e low t e m p e r a t u r e i s appl ied , n a m e l y s o l i d s a m p l e s obtained by c r y s t a l l i z a t i o n f r o m the m e l t o r f r o m the so lu t ion , then s u b s t a n c e s n o r m a l l y s o l i d b e c a u s e of high m o -l e c u l a r weight . The s e c o n d group c o n s i s t s of l iquid or e v e n g a s e o u s s a m p l e s s h o c k - f r o z e n to the s o l i d s t a t e . We e n c o u n t e r h e r e the kind of s o l i d s ta te hard ly c o m p a r a b l e with the s ta te we u s u a l l y dea l with at r o o m t e m p e r a t u r e and h igher . S h o c k - f r e e z i n g r e s u l t s v e r y o f ten in g l a s s y s t a t e f o r m a t i o n on which there i s not m u c h in format ion . The s a m e a p p l i e s to the ques t ion of d e f e c t s in the d e e p - f r o z e n s t a t e , an important p r o b l e m e v e n in r e s p e c t to the f r o z e n s a m p l e s , s o l i d even at r o o m t e m p e r a t u r e . T h e ques t ion of d e f e c t s has to b e unders tood in a b r o a d s e n s e , e . g . in t e r m s of s u s c e p t i b i l i t y of the s t r u c t u r e f r o m potent ia l w e l l s ( l o w - e n e r g y e l e c t r o n s m a y dig t r a p s in the m a t r i x ) .

The u n i q u e n e s s of l o w - t e m p e r a t u r e radiat ion c h e m i s t r y i s v e r y o f t e n due to the u n i q u e n e s s of f r o z e n and deep c o o l e d - d o w n s t r u c t u r e s . We shou ld have l iked to m a k e the s e c t i o n on the r o l e p l a y e d by s t r u c t u r e the l a r g e s t one , but unfortunate ly at the p r e s e n t t i m e t h e r e i s not enough i n f o r m a t i o n .

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2. 2. The c h e m i c a l end-po int of r a d i o l y s i s in the l iquid and f r o z e n s t a t e

A l l i r r a d i a t e d s y s t e m s , g a s e o u s , l iquid o r s o l i d , r e a c h a c e r t a i n c h e m i c a l c o m p o s i t i o n a f t e r i r r a d i a t i o n . T h i s c h e m i c a l end-po int i s the s t a t e of e q u i l i b r i u m of s tab le c o m p o u n d s and a p p e a r s s o m e t i m e a f t e r the f lux of i o n i z i n g radiat ion c e a s e s . The p e r i o d of t i m e v a r i e s c o n s i d e r -ably , f r o m m i c r o s e c o n d s to w e e k s . The t i m e of attaining the e q u i l i b r i u m i s dependent on the v i s c o s i t y of the m e d i u m if the r e a c t i o n s demand t r a n s p o r t of r e a c t i n g s p e c i e s , or a r e t o t a l l y independent of the s t a t e of the s a m p l e if the r e a c t i o n c o n s i s t s in i n t r a m o l e c u l a r change , e . g . in the d e c a y of a t r i p l e t s t a t e .

In rad ia t ion c h e m i s t r y we dea l with a v e r y wide s p e c t r u m of r e a c t i v i -t i e s and m o b i l i t i e s of i n t e r m e d i a t e s p e c i e s , and t h e r e f o r e the t i m e of a t -ta in ing e q u i l i b r i u m i s h ighly dependent on the p h a s e and the t e m p e r a t u r e of the s a m p l e . E v e n in the l iquid s t a t e we e n c o u n t e r the r e a c t i o n s e i t h e r o c c u r r i n g with m a x i m u m s p e e d c a u s e d by r e a c t i o n s at e v e r y c o l l i s i o n , or , on the o t h e r hand, o c c u r r i n g s l o w l y , e . g . b e t w e e n the m o l e c u l a r product of r a d i o l y s i s of w a t e r - h y d r o g e n p e r o x i d e and i ron (II) ions p r e s e n t in the s y s t e m .

In the f r o z e n s ta te the s i tuat ion i s m o r e c o m p l i c a t e d . We n o t i c e r e a c t i o n s which s t i l l take p l a c e at the low t e m p e r a t u r e long a f t e r the rad ia t ion h a s b e e n s topped , then we o b s e r v e the nebula of r e a c t i o n s in the c o u r s e of heat ing and thawing. E v e n a f t e r r e a c h i n g the l iquid s t a t e the r e a c t i o n s m a y p r o c e e d fur ther .

T h e r e i s nothing r e m a r k a b l e in the fact that the r e s u l t s of i r r a d i a t i o n of the s a m e compound in the l iquid and s o l i d s t a t e d i f f er . A f t e r a l l we a r e c o n v e r s a n t with the phenomenon c a l l e d the p h a s e e f f e c t , o c c u r r i n g in i r r a d i a -t ion of s a m p l e s just b e l o w and just above the m e l t i n g point . H o w e v e r , in l o w - t e m p e r a t u r e c h e m i s t r y the d i f f e r e n c e s a r e b i g g e r than in the s o - c a l l e d p h a s e e f f e c t [4], b e c a u s e the f ina l e f f e c t i s in f luenced not only by the p h a s e of the s a m p l e but a l s o by the wide range of t e m p e r a t u r e s .

The d i f f e r e n c e s a r e of a quant i tat ive or e v e n of a qua l i ta t ive nature . The f i r s t group (d i f ferent G - v a l u e s ) i s , of c o u r s e , l a r g e r , b e c a u s e f r o m the point of v i e w of t h e r m o d y n a m i c s the p r o b a b i l i t y of f o r m a t i o n of quite d i f f erent c o m p o u n d s , due only to the changed m o d e of degradat ion of suppl i ed e n e r g y , i s h ighly i m p r o b a b l e in the g i v e n s y s t e m . T h e r e f o r e in the m a j o r i t y of s y s t e m s only the y i e l d s of p a r t i c u l a r p r o d u c t s a r e changed, not the qua l i ta t ive c o u r s e of r e a c t i o n s . Thus the f r o z e n F r i c k e s y s t e m g i v e s iron (III), a l though the s m a l l e r the y i e l d , the l o w e r the t e m p e r a t u r e [5, 6], The p h e n o m e n o n i s so c l o s e l y c o n n e c t e d to the l o c a l t e m p e r a t u r e that the t r i t i a t e d s y s t e m c o o l e d down to a t e m p e r a t u r e of 77°K g i v e s i ron (III) with a G - v a l u e c h a r a c t e r i s t i c r a t h e r for a h igher t e m p e r a t u r e , due to l o c a l t h e r m a l s p i k e s .

The s e c o n d group, of qua l i ta t ive ly d i f f erent r e s u l t s in c o m p a r i s o n with l iquid i r r a d i a t i o n , i s a s m a l l e r one , e v e n if s y s t e m s a r e i n c o r p o -r a t e d wh ich at low t e m p e r a t u r e s g i v e s u b s t a n t i a l amounts of a compound but at r o o m t e m p e r a t u r e in l iquid s t a t e n i l , o r v i c e v e r s a . Although the d i f f e r e n c e s e e m s to be qual i ta t ive , the c o n t r a s t b e t w e e n high y i e l d to G - v a l u e equal z e r o h a s the c h a r a c t e r of a quant i tat ive d i f f e r e n c e .

T h i s w a s d i s c o v e r e d by Z a g o r s k i and Weimann [7] in the s i m p l e a l k a -l ine s y s t e m . P o l a r o g r a p h y appl ied to the m o l t e n s a m p l e s he lped to r e v e a l the b a s i c d i f f e r e n c e b e t w e e n the r a d i o l y s i s of the l iquid aqueous s o d i u m


h y d r o x i d e so lu t ion and the s o l i d i f i e d one; in the l iqu id-s ta te i r rad ia t ion , no hydrogen p e r o x i d e m a y be de tec ted , in addit ion to t h e r e be ing no hydrogen . The s i tuat ion r e s e m b l e s one of pure w a t e r r a d i o l y s i s . Only a f t e r adding an appropr ia te s c a v e n g e r (in our c a s e su lphi te , SO|", w a s i n v e s t i g a t e d ) , m o l e c u l a r hydrogen i s obtained in the b a s i c y i e l d , g e n e r a l l y a c c e p t e d , of 0 .45 [8]. In s o l i d i f i e d a lka l ine so lu t ion i r r a d i a t e d at a t e m p e r a t u r e of 77°K, we have found a p p r e c i a b l e a m o u n t s of hydrogen p e r o x i d e with a radiat ion y i e l d of about 0.1 for the d o s e 5X 101 8 e V / m l , a l r e a d y without s c a v e n g e r s .

T h e f ina l r e s u l t of r a d i o l y s i s ( c h e m i c a l end-po int ) , both in the l iquid o r in the f r o z e n s t a t e , m a y be n i l , which m e a n s that the s y s t e m i s c o m i n g back to the o r i g i n a l c o m p o s i t i o n and s t r u c t u r e but only at a s l i g h t l y in -c r e a s e d t e m p e r a t u r e , equiva lent to the e n e r g y of a b s o r b e d radiat ion . That m a y be the c a s e e i ther when there i s no p o s s i b i l i t y of the f o r m a t i o n of a s t a b l e compound ( e . g . i r rad ia t ion of g a s e o u s hydrogen , g a m m a i r -rad ia t ion of m e t a l s ) , or if one group of p r o d u c t s of r a d i o l y s i s i s d e s t r o y i n g another ( e . g . r a d i o l y s i s of pure water ) . Sol id s y s t e m s a r e i n t e r e s t i n g in th i s r e s p e c t : quite a number of t h e m , on the way f r o m the t e m p e r a t u r e of i r rad ia t ion to the me l t ing point , l o s e the d e p o s i t e d e n e r g y , p a r t i a l l y a s l ight , and they r e a c h the m e l t i n g point in an annea led s ta te . A s e x a m p l e s m a y s e r v e a l l s y s t e m s u s e d for t h e r m o l u m i n e s c e n t d o s i m e t r y or a lka l i h a l i d e s . The l a t t er , h o w e v e r , m a y be d i s s o l v e d b e f o r e t h e r m a l o r photo-c h e m i c a l annea l ing ( i rrad ia ted NaCl p r o d u c e s c h l o r i n e , hydroxy l ions [9]), o f f e r i n g ins ight into the nature of f r o z e n i n t e r m e d i a t e s .

Unfortunate ly , a s i m i l a r e x p e r i m e n t in the c a s e of d e e p - f r o z e n s y s -t e m s s e e m s to be d i f f icu l t if not i m p o s s i b l e . A s far a s we know such an idea has not b e e n r e a l i z e d ye t b e c a u s e of the lack of the appropr ia te s o l -vent , l iquid and able to d i s s o l v e at l iquid n i t rogen t e m p e r a t u r e .

The concept of d i s s o l v i n g the i r rad ia ted s a m p l e at p o s s i b l y low t e m p e r a t u r e s without r e a c h i n g the m e l t i n g point w a s r e a l i z e d by F a l c o n e r and Sa lovey [10]. T h e y have o b s e r v e d p o s t - i r r a d i a t i o n s u p p r e s s i o n of the d i m e r ; when i r r a d i a t e d (at the s o l i d CO2 t e m p e r a t u r e ) so l id n - h e x a d e c a n e w a s d i s s o l v e d at t e m p e r a t u r e s be low i ts me l t ing point in s o l v e n t s s u c h a s 2 - m e t h y l p e n t a n e containing d i s s o l v e d iodine . In e a c h c a s e G (d imer) w a s r e d u c e d to v i r t u a l l y the s a m e l e v e l a s when d i s p e r s e d iodine w a s p r e s e n t during i rrad ia t ion .

2 . 3 . Ionic s p e c i e s in the i r r a d i a t e d f r o z e n s y s t e m s

Most p a p e r s deal ing with c h a r g e d s p e c i e s in f r o z e n s a m p l e s a r e c o n -c e r n e d with e l e c t r o n s , the ir trapping and r e a c t i o n s . The f o r m a t i o n of e l e c t r o n s is obv ious : the f i r s t act of ion izat ion i s a l m o s t independent of the s a m p l e ' s t e m p e r a t u r e and p h a s e . C o m p a r a t i v e l y l i t t l e at tent ion i s paid to c h a r g e d s p e c i e s of oppos i t e p o s i t i v e c h a r g e . Although p o s i t i v e s p e c i e s o r h o l e s a r e not a s m o b i l e a s e l e c t r o n s , t h e i r r o l e i s equa l ly important .

The q u e s t i o n of p o s i t i v e c h a r g e d s p e c i e s w a s c o n s i d e r e d r e c e n t l y in the c a s e of f r o z e n w a t e r and aqueous so lu t ions by Moorthy and W e i s s [11]. T h e s e authors c l a i m to p r o v i d e e v i d e n c e that the r e a c t i o n s of the rad ia t ion p r o d u c e d p o s i t i v e h o l e s apart f r o m the r e a c t i o n s of the e l e c t r o n s . E . S . R. m e a s u r e m e n t s show that r a d i a t i o n - p r o d u c e d e l e c t r o n s r e a c t with a c i d i c s o l u t e s to f o r m H - a t o m s and with group l ib m e t a l ions to g ive c o r r e s p o n d i n g

P L - 2 3 6 / 1 7 1

univalent r a d i c a l i o n s , whi le the h o l e s can r e a c t with an ions such a s SO4" and H2PO4, g iv ing the r a d i c a l ions SO4 and HPO4. Continuing the concept of p o l a r o n s d e v e l o p e d by W e i s s et a l . , the authors think that e l e c t r o n s and h o l e s a r e coup led with each o ther and m a y e x i s t in i r r a d i a t e d pure i c e p r i m a r i l y in an e x c i t o n - l i k e bound s t a t e . The e l e c t r o n s a r e d i s t r i -buted a m o n g a n u m b e r of exc i ton l e v e l s c o v e r i n g a wide e n e r g y r a n g e . The e l e c t r o n s bound in l e v e l s that a r e s e p a r a t e d f r o m the conduct ion band by e n e r g i e s l e s s than the t h e r m a l e n e r g y can be t h e r m a l l y e x c i t e d into the conduct ion band. F o l l o w i n g s u c h an e x c i t a t i o n the e l e c t r o n s and h o l e s can undergo r a d i a t i v e r e - c o m b i n a t i o n , thus c a u s i n g the o b s e r v e d t h e r m o l u m i -n e s c e n c e of i r r a d i a t e d f r o z e n i c e ( s e e Sec t ion 2. 5).

The s e p a r a t i o n of e l e c t r o n s and p o s i t i v e ions has f a r - r e a c h i n g c o n s e -q u e n c e s . It i s c l e a r f r o m i n v e s t i g a t i o n s on m i g r a t i o n of e l e c t r o n s ( s e e Sec t ion 2.4) that in f r o z e n g l a s s t h e r e m a y be enough t i m e , e v e n in the r e g i o n of the spur , for the p o s i t i v e ion to r e a c t with ne ighbour ing m o l e -c u l e s b e f o r e n e u t r a l i z a t i o n o c c u r s .

P o s i t i v e i o n s m a y be f o r m e d in s e c o n d a r y p r o c e s s e s . Dainton, S a l m o n and T e p l y [12] d e m o n s t r a t e d that in the r a d i o l y s i s of m e t h a n o l i c g l a s s e s at 77°K, the CH3OH2 ion i s f o r m e d by a proton t r a n s f e r p r o c e s s , and that th i s ion, upon n e u t r a l i z a t i o n , y i e l d s a hot hydrogen a t o m that r e a c t s with m e t h a n o l to produce CH2OH.

2. 4. M i g r a t i o n of i n t e r m e d i a t e s p e c i e s in l o w - t e m p e r a t u r e r a d i o l y s i s

2 . 4 . 1 . G e n e r a l

The ques t ion what i s d i f fus ing , o r m o r e g e n e r a l l y , m i g r a t i n g , how far and with what c o n s e q u e n c e , r e m a i n s the c e n t r e of a t tent ion in e x p e r i -m e n t s and t h e o r e t i c a l c o n s i d e r a t i o n s on rad ia t ion c h e m i s t r y in the l iquid s t a t e . The s a m e q u e s t i o n s a r e s t i l l wor th a n s w e r i n g in l o w - t e m p e r a t u r e rad ia t ion c h e m i s t r y al though it i s o b v i o u s that m i g r a t i o n of i n t e r m e d i a t e s p e c i e s cannot r e s e m b l e the s i tuat ion in the l iquid s t a t e , both in r e s p e c t to the ident i ty of s p e c i e s and to the m o d e and d i s t a n c e of m i g r a t i o n .

M i g r a t i o n in f r o z e n s y s t e m s m a y be roughly d iv ided into the p h e n o -m e n o n taking p l a c e during, or v e r y s h o r t l y a f t e r , i r r a d i a t i o n , then into the m i g r a t i o n that p r o c e e d s without the i n c r e a s e of the t e m p e r a t u r e of the s a m p l e , and, f ina l ly , into the l a r g e and c o m p l i c a t e d group of p h e n o m e n a during w a r m i n g and thawing of the i r r a d i a t e d s a m p l e .

The s e c o n d group i n c l u d e s p h e n o m e n a g e n e r a l l y c a l l e d "bleaching". If the i r r a d i a t e d s a m p l e i s t r e a t e d a f t e r w a r d s with u l t r a - v i o l e t ( s o m e t i m e s even v i s i b l e l ight i s s u f f i c i e n t ) , E . S . R. and o p t i c a l s p e c t r u m m a y b e changed . Apparent ly the trapped, but u n s t a b l e , s p e c i e s obtain e n e r g y of a b s o r b e d l ight quanta and m a y t h e r e f o r e t r a v e l to another trap o r a c c e p t o r , o r even to the s i t e of o r i g i n . The c l a s s i c a l e x a m p l e h e r e i s the o p t i c a l b l e a c h i n g of F - c e n t r e s in i r r a d i a t e d c r y s t a l s of a lka l i h a l i d e s (v io le t KCI, y e l l o w NaCl , e t c . , b e c o m e c o l o u r l e s s again) .

In s o m e c a s e s , induced p h e n o m e n a of m i g r a t i o n s t i l l take p l a c e at the low t e m p e r a t u r e of i r r a d i a t i o n , but be long c l e a r l y to the th ird group. T h e s e a r e a l l c a s e s in which l o c a l i n c r e a s e of the t e m p e r a t u r e t a k e s p l a c e , e . g. due to i n f r a - r e d i r r a d i a t i o n o r to the i n t e r n a l s o u r c e of h igh L E T i r r a d i a t i o n . The l a s t - m e n t i o n e d c a s e i s r e p r e s e n t e d by i n t e r n a l t r i t i u m i r r a d i a t i o n in which l o c a l t h e r m a l s p i k e s c a u s e the i r r a d i a t i o n to take


p l a c e a l w a y s at a h i g h e r t e m p e r a t u r e than the a v e r a g e , m e a s u r e d t e m -p e r a t u r e of the s a m p l e .

Contrary to the l iquid s t a t e , the d i f f e r e n c e s b e t w e e n the d i f fus ion cons tant of p a r t i c u l a r s p e c i e s a r e l a r g e r than in the l iquid s t a t e . At t e m p e r a t u r e s of 77°K and l o w e r , p r a c t i c a l l y on ly e l e c t r o n s and hydrogen a t o m s m a y d i f fuse , a l l o ther s p e c i e s be ing l a r g e enough to r e n d e r d i f fus ion in the r i g i d m a t r i x i m p o s s i b l e . In th i s s e c t i o n we r e f e r to f r e e d i f fus ion and do not take into c o n s i d e r a t i o n the m i g r a t i o n of e x c i t a t i o n s which m a y s i m u l a t e the t r a n s p o r t of a t o m s or m o l e c u l e s . A l s o we a r e not c o n s i d e r i n g h e r e s h o r t - r a n g e d e r e a l i z a t i o n s .

2. 4. 2. Migrat ion of i n t e r m e d i a t e s in f r o z e n s o l i d s at low t e m p e r a t u r e s

Most of the p a p e r s that dea l with the m i g r a t i o n of i n t e r m e d i a t e s during i r r a d i a t i o n are c o n c e r n e d wi th e l e c t r o n s , h y d r o g e n a t o m s and s o m e p o s i t i v e i o n s . A s w a s e x p e c t e d , e l e c t r o n s w e r e shown to be ab le to m i g r a t e for f a i r l y long d i s t a n c e s in f r o z e n s y s t e m s , if no m o l e c u l e s of an a p p r o p r i a t e a c c e p t o r a r e in t h e i r way . H a m i l l and h i s c o - w o r k e r s [13] d e m o n s t r a t e d that in l o w - t e m p e r a t u r e g l a s s y s o l i d s , e l e c t r o n s can m i g r a t e d i s t a n c e s of s e v e r a l t e n s of a n g s t r o m s f r o m the s i t e of the i on i za t ion p r o c e s s , and c a n then e i t h e r be trapped p h y s i c a l l y in the m a t r i x , f o r m i n g a t rapped e l e c t r o n ( e x - ) o r b e c o m e a t tached to a m o l e c u l e of a su i table e l e c t r o n a c c e p t o r . H a m i l l ' s work w a s p e r f o r m e d on s y s t e m s c o n s i s t i n g of 2 - m e t h y l t e t r a h y d r o f u r a n , 3 - m e t h y l p e n t a n e , m e t h y l c y c l o h e x a n e e thano l and i s o p e n t a n e a s s o l v e n t s , and biphenyl , naphthalene , n i t r o b e n z e n e , benzophenone , t e t r a c y a n o e t h y l e n e , s t y r e n e and carbon t e t r a c h l o r i d e a s s o l u t e s w h o s e anion absorpt ion s p e c t r a a r e r e c o r d e d . The s o l v e n t s p e c -t r u m can be s e l e c t i v e l y b l e a c h e d , with a c o n c o m i t a n t i n c r e a s e in the s o l u t e an ion a b s o r p t i o n bands . Inves t iga t ion of the in f luence of the a c -c e p t o r concentra t ion m a y m a k e it p o s s i b l e to c a l c u l a t e the r a n g e .

Dainton and Sa lmon [14] a l s o u s e d 2 - m e t h y l t e t r a h y d r o f u r a n (MTHF) to i n v e s t i g a t e the range of m i g r a t i o n of e l e c t r o n s . T h i s h a s e x c e l l e n t c o m p a t i b i l i t y with g l a s s , m e t h a n o l and c o n c e n t r a t e d g l a s s y s o l u t i o n s of NaOH and KOH. The addi t ion of s o l u t e s (capable of captur ing e l e c t r o n s ) to any of t h e s e s y s t e m s , r e d u c e s the extent of e l e c t r o n trapping in the m a t r i x and in s o m e c a s e s an ident i f iab le product of e l e c t r o n capture i s p r o d u c e d . E l e c t r o n capture can re su l t e i t h e r in the f o r m a t i o n of a s tab le an ion or in d i s s o c i a t i o n of the capturing m o l e c u l e . The produc t s of t h e s e r e a c t i o n s a r e i m m o b i l i z e d in g l a s s y m a t e r i a l s at 77°K and can t h e r e f o r e be e x a m i n e d by E . S . R. and opt i ca l s p e c t r o s c o p y . At the s a m e t i m e , t h e r m a l i z e d e l e c t r o n s that e s c a p e d the r e a c t i o n with a c c e p t o r s a r e a l s o f r o z e n and show t h e i r p r e s e n c e in the E . S . R. s p e c t r u m . In the c a s e of m e t h a n o l , Dainton u s e d a s a c c e p t o r s c a r b o n t e t r a c h l o r i d e , s u l p h u r i c a c i d , naphthalene and b e n z y l ch lor ide ; e l e c t r o n capture e f f i c i e n c i e s w e r e in the ra t io 2 . 2 : 1 . 7 : 1 . 2 : 1 . 0 . The t h e r m a l i z i n g e l e c t r o n e n c o u n t e r s on the a v e r a g e 450 m e t h a n o l m o l e c u l e s b e f o r e r e a c t i n g with a c a r b o n t e t r a -c h l o r i d e m o l e c u l e or about 1000 b e f o r e r e a c t i n g with a m o l e c u l e of b e n z y l c h l o r i d e . S i m i l a r r e s u l t s have b e e n obta ined with anhydrous f e r r i c c h l o r i d e a s the e l e c t r o n a c c e p t o r in M T H F , which s u g g e s t s that e l e c t r o n s a r e d i s p l a c e d through an a v e r a g e l inear d i s t a n c e of about 35 A in t h i s s y s t e m b e f o r e r e a c t i n g with F e C l 3 .

P L - 2 3 6 / 1 73

The e x p e r i m e n t a l approach d e s c r i b e d i s g e n e r a l l y of no u s e , b e c a u s e m a n y g l a s s y s y s t e m s do not t rap e l e c t r o n s a s s u c h b e c a u s e e i t h e r t h e r e i s no s i g n i f i c a n t n u m b e r of trapping s i t e s a v a i l a b l e , a s in the c a s e of a lkane g l a s s e s ( e . g . 3 - m e t h y l p e n t a n e ) , o r e l e c t r o n s a r e able to r e a c t wi th a component of the g l a s s y m a t e r i a l i t s e l f , a s in the case , of the a c i d a q u e o u s g l a s s e s . N e v e r t h e l e s s , u s i n g s p e c i f i c e l e c t r o n a c c e p t o r s , Da in ton ' s r e s e a r c h e r s w e r e ab le to e s t i m a t e the d i s t a n c e s of m i g r a t i o n of e l e c t r o n s a s about 50 A in 5 M g l a s s y su lphur ic a c i d at 77°K.

The next s t e p i n v o l v e s the i n v e s t i g a t i o n of m i g r a t i o n a s a funct ion of the e n e r g y of e l e c t r o n s . In t h e s e e x p e r i m e n t s the r e l e a s e of d i f f e r e n t e n e r g y e l e c t r o n s i s he lpful ; th i s m a y be a c h i e v e d by t h e r m a l o r o p t i c a l b l e a c h i n g . In M T H F g l a s s , f or e x a m p l e , t h e r m a l l y r e l e a s e d e l e c t r o n s do not r e a c t wi th F e C l 3 w h e r e a s th i s s o l u t e d o e s r e d u c e the f o r m a t i o n of trapped e l e c t r o n s and hence m u s t capture e l e c t r o n s l i b e r a t e d by g a m m a i r r a d i a t i o n . It s e e m s probable that in M T H F e l e c t r o n s t r a v e l a p p r o x i -m a t e l y 150 A b e f o r e b e i n g t h e r m a l i z e d and trapped . H o w e v e r , an e l e c t r o n cannot r e a c t with a F e C l 3 m o l e c u l e if it h a s l e s s e n e r g y than it p o s s e s s e s a f t e r m i g r a t i n g 35 A f r o m i ts parent p o s i t i v e ion.

The d i s t a n c e s of e l e c t r o n m i g r a t i o n found by Dyne and M i l l e r [15] a l s o in m e t h y l t e t r a h y d r o f u r a n g l a s s a r e e v e n l o n g e r . T h e y noted that the quantum y i e l d of b l e a c h i n g e l e c t r o n s depends on the f r a c t i o n of e l e c t r o n s b l e a c h e d and not on t h e i r c o n c e n t r a t i o n . The authors c i t e d c o n c l u d e that O • about half the e l e c t r o n s a r e t rapped c l o s e to the p o s i t i v e ion ( 1 0 - 8 0 A), w h e r e a s the o t h e r half a r e trapped h o m o g e n e o u s l y a f t e r t r a v e l l i n g up to 1000 A.

A r e m a r k a b l e fact w a s a l s o d e m o n s t r a t e d by Dainton who s t a t e d that in s o m e s y s t e m s e l e c t r o n s a r e m o r e m o b i l e in the g l a s s y p h a s e than in e i t h e r the l iquid o r c r y s t a l l i n e p h a s e s . In the c a s e of su lphur ic a c i d , the f o r -mat ion of a c i d g l a s s e s i s thought to be due to the c o n d e n s a t i o n of the a c i d into long chain p o l y m e r s , and it m a y be that e l e c t r o n s a r e ab le to m i g r a t e p r e f e r e n t i a l l y a long t h e s e c h a i n s .

Apart f r o m c o n c l u s i o n s c o n c e r n i n g the fate of e l e c t r o n s , the c o n s e -quence of l o n g - r a n g e m i g r a t i o n of e l e c t r o n s a f f e c t s a l s o s p e c u l a t i o n s on the fate of p o s i t i v e i o n s , which m a y not be n e u t r a l i z e d f o r a r e l a t i v e l y long t i m e and a r e ab le to r e a c h the ne ighbour ing m o l e c u l e s . M o r e d e -t a i l s about p o s i t i v e i o n s m a y be found in S e c t i o n 3. 3.

2. 4. 3. Migrat ion of i n t e r m e d i a t e s at t e m p e r a t u r e s h igher than the t e m p e r a t u r e of i r rad ia t ion

In l o w - t e m p e r a t u r e radiat ion c h e m i s t r y we encounter two p e r i o d s of enhanced c h e m i c a l c h a n g e s : the f i r s t , during the i rrad ia t ion , w h e r e the m i g r a t i o n of s m a l l and m o b i l e i n t e r m e d i a t e s f o l l o w s the p r i m a r y e f f e c t s , and the s e c o n d , during w a r m i n g up, when f r o z e n i n t e r m e d i a t e s a r e m o -b i l i z e d and r e a c t , r e a c h i n g the c h e m i c a l end-po in t with a ra te r e l a t e d to the ra te of heat ing . In b e t w e e n t h e r e i s a p e r i o d w h e r e s o m e s l o w p r o -c e s s e s take p l a c e , in s p i t e of keep ing the t e m p e r a t u r e at the low l e v e l , the s a m e o r l o w e r than at the i r rad ia t ion . The p e r i o d b e t w e e n the i r r a d i a -t ion and thawing m a y be p r a c t i c a l l y i n d e f i n i t e l y long, p r o v i d i n g t h e r e i s no i n c r e a s e in t e m p e r a t u r e and no absorpt ion of e n e r g y (u. v . , v i s i b l e l ight , i . r . ) by the s a m p l e .


The s t o r m y and e x t r e m e l y c o m p l i c a t e d s t a g e of w a r m i n g up i s not quite c l e a r a s far a s the m e c h a n i s m s invo lved a r e c o n c e r n e d , b e c a u s e s e v e r a l c h a n g e s a r e taking p l a c e in p a r a l l e l : s t r u c t u r a l c h a n g e s of the m a t r i x , and v i b r a t i o n s of the e l e m e n t s of the s t r u c t u r e , which m a y p r o -v i d e the ac t iva t ion e n e r g y for the trapped s p e c i e s , then d i f fus ion of i n t e r -m e d i a t e s to the s i t e s of r e a c t i o n and s e v e r a l p h e n o m e n a of l e s s i m p o r t a n c e . S o m e of t h e s e e f f e c t s a r e connec ted with the evo lut ion or consumpt ion of t h e r m a l e n e r g y that contr ibutes to the h e t e r o g e n e i t y of the s y s t e m , c o m p l i -ca t ing the in t erpre ta t ion .

It i s obv ious that a p r o p e r a n a l y t i c a l method i s the b e s t t oo l f o r the ident i f i ca t ion of c h a n g e s in the s a m p l e during m e l t i n g and l o c a l i z a t i o n of p r o d u c t s on the t e m p e r a t u r e a x i s .

The m o s t important method i s E. S. R . , prov id ing in format ion about c h a n g e s of f r e e r a d i c a l both qua l i ta t ive ly and quant i tat ive ly . T h i s m e t h o d d o e s not c o v e r the to ta l c h e m i c a l c o m p o s i t i o n and i s supported by a b -s o r p t i o n s p e c t r o p h o t o m e t r y in d i f f erent p a r t s of the s p e c t r u m . S o m e e x a m p l e s w i l l i l l u s t r a t e the e x p e r i m e n t a l approach .

The appl icat ion of i . r . s p e c t r o s c o p y o f f e r s i n t e r e s t i n g p o s s i b i l i t i e s . The paper of Sukhov et a l . [16] m a y s e r v e a s an e x a m p l e . They dea l with d i f f e r e n t c a o u t c h o u c s , i r r a d i a t e d in v a c u u m , with 1 - 2 MeV e l e c t r o n s , at a t e m p e r a t u r e b e t w e e n 85-90°K, then a n a l y s e d by i . r . in the range 7 0 0 - 1 7 0 0 c m - 1 and 1 6 0 0 - 3 0 0 0 c m - 1 c o n s e c u t i v e l y at t e m p e r a t u r e s of , f o r i n s t a n c e , 90, 120, 250, 310°K. A s the i . r . s p e c t r o s c o p y i s not v e r y s e n s i t i v e , the d o s e app l i ed had to be ra ther h igh - up to 600 Mrad. R e -s u l t s show that m o s t important r e a c t i o n s p r o c e e d at the t e m p e r a t u r e of i r r a d i a t i o n : 48% of the i s o p r e n e double bonds in natura l caoutchouc d i s a p p e a r e d at 120°K. About 2% turned into t r a n s v i n y l double bonds through m i -g r a t i o n . The r e s t (46%) of the i s o p r e n e double bonds f o r m e d c r o s s -l i n k i n g s . During fur ther heat ing to 2 50°K t r a n s v i n y l unsaturat ion doubles b e c a u s e of the e f f e c t of the s e c o n d a r y t r a n s f e r of the f r e e r a d i c a l c e n t r e on the chain and the r e s u l t i n g m i g r a t i o n of the double bond. Other s e c o n -dary p r o c e s s e s i n c r e a s e the d e g r e e of a m o r p h i s m . The c h e m i c a l end-po int d i f f e r s f r o m that in r o o m t e m p e r a t u r e i r rad ia t ion .

2. 5. L u m i n e s c e n c e , p h o s p h o r e s c e n c e and t h e r m o l u m i n e s c e n c e in i r r a d i a t e d f r o z e n s y s t e m s

The r o l e p l a y e d in rad ia t ion c h e m i s t r y by r a d i a t i o n - i n d u c e d l u m i n e s -c e n c e and p h o s p h o r e s c e n c e i n c r e a s e d and widened a f t e r i r r a d i a t i o n s at l ow t e m p e r a t u r e s had b e e n extended.

R a d i a t i o n - i n d u c e d l u m i n e s c e n c e of l iquids i s v e r y weak and u s u a l l y a m o u n t s to about 3% of total e m i s s i o n of g a m m a - i r r a d i a t e d aqueous s o -l u t i o n s . The r e m a i n d e r i s Cherenkov radiat ion , which i s e a s y to d i s t i n -g u i s h f r o m l u m i n e s c e n t l ight . Only in the c a s e of s p e c i f i c compounds p r e s e n t in the s y s t e m i s the a b s o r b e d e n e r g y of ion iz ing radiat ion e m i t -t ed a s l ight . T h i s e f f e c t r e a c h e s i t s m a x i m u m in the c a s e of d e l i b e r a t e l y c h o s e n l iquid s c i n t i l l a t o r s .

V e r y weak l u m i n e s c e n c e e m i t t e d by m o s t s o l u t i o n s w a s s e l d o m i n t e r -p r e t e d b e c a u s e of the i n t e n s i v e Cherenkov background, but both s o u r c e s of l ight had to be taken into account [17] in o p t i c a l m e a s u r e m e n t s [18] p e r f o r m e d in the rad ia t ion f i e l d .

P L - 2 3 6 / 1 7 5

The e f f e c t of e m i s s i o n of l ight both a s l u m i n e s c e n c e and p h o s p h o r e s -c e n c e i s m o r e c o m m o n in the c a s e of s o l i d s . Most i n t e n s i v e l u m i n e s c e n c e i s g i v e n by s c i n t i l l a t o r s , o r g a n i c and i n o r g a n i c . C o m p a r a t i v e l y high c o n -v e r s i o n i s r e a c h e d a l s o in the c a s e of o r d i n a r y f u s e d s i l i c a . A s far a s we know, no u s e i s m a d e of it; on the c o n t r a r y , i n t e n s i v e l ight e m i t t e d i s a c o m p l i c a t i n g f a c t o r in op t i ca l m e a s u r e m e n t s . Dondes [19] .who had e x -p e r i e n c e of t h i s , e s t i m a t e d the rad ia t ion y i e l d of l ight quanta to have a G - v a l u e of about 1 (1 quantum of v i s i b l e or u. v . l ight p e r 100 eV of a b -s o r b e d e n e r g y of ion iz ing radiat ion) . The g lowing of o r d i n a r y quartz i s v e r y i n t e n s i v e , which l e d us in o u r e a r l i e r work to abandon th i s m a t e r i a l t o ta l l y , and to u s e c e l l s and o t h e r equipment only of v e r y pure S iOj that d o e s not darken nor e m i t l ight in the i on iz ing radiat ion f i e l d [17].

O r d i n a r y s i l i c a a l s o e m i t s l ight a s p h o s p h o r e s c e n c e of long durat ion. Both r a d i o l u m i n e s c e n c e and p h o s p h o r e s c e n c e of s i l i c a depend on the qual i ty and quantity of i m p u r i t i e s a s w e l l a s on the s t r u c t u r e of the s a m p l e .

The th ird phenomenon c o n n e c t e d wi th the e m i s s i o n of l ight , n a m e l y t h e r m o l u m i n e s c e n c e , w a s i n v e s t i g a t e d m a i n l y f r o m the point of v i e w of d o s i m e t r y . S u b s t a n c e s l i k e C a F 2 , L i F , C a S 0 4 doped with Mn or Sm, and SrS doped wi th Sm, p r o v e d to be e x c e l l e n t a c c u m u l a t o r s of a b s o r b e d i o n i z i n g e n e r g y , r e l e a s i n g c o m p a r a t i v e l y l a r g e p o r t i o n s of it a s v i s i b l e l ight when heated ( for a r e c e n t r e v i e w of t h e r m o l u m i n e s c e n t d o s i m e t r y s e e Ref . [20]) . Mos t work in th i s f i e l d has b e e n p e r f o r m e d with s a m p l e s i r r a d i a t e d at r o o m t e m p e r a t u r e s , and d o e s not be long to l o w - t e m p e r a t u r e rad ia t ion c h e m i s t r y (but s e e Sec t ion 3 . 6 ) .

One c a n s a y g e n e r a l l y that m o v i n g t o w a r d s l o w e r t e m p e r a t u r e s of the s a m p l e s the c o n v e r s i o n to l ight i s enhanced . F r o z e n l iqu ids that w e r e not emi t t ing in the l iquid s ta te , now show the phenomenon of r a d i o l u m i n e s -c e n c e and v e r y o f t en a l s o p h o s p h o r e s c e n c e l a s t i n g for h o u r s , b e c a u s e of the s l o w i n t r a m o l e c u l a r t r a n s f o r m a t i o n s .

F o r i n s t a n c e , B r o c k l e h u r s t , P o r t e r and Y a t e s [21] took s p e c t r a of the l ight e m i t t e d during the w a r m - u p of a g a m m a - i r r a d i a t e d s o l u t i o n of naphthalene in an a lkane m i x t u r e at 77°K. The p h o s p h o r e s c e n c e e m i t t e d by naphthalene w a s about s i x t i m e s m o r e i n t e n s e than the f l u o r e s c e n c e . It w a s t h e r e f o r e conc luded that a t r i p l e t e x c i t e d s ta te of naphthalene w a s p r o d u c e d by ion r e c o m b i n a t i o n .

Most of the p a p e r s in this s e c t i o n d e a l with p h o s p h o r e s c e n c e s t i m u l a t e d by u. v . , v i s i b l e or i . r . radiat ion app l i ed to the f r o z e n s a m p l e a f t e r h igh -e n e r g y (usua l ly g a m m a o r e~) i r r a d i a t i o n .

The e f f e c t s of i . r . i l luminat ion a r e u s u a l l y s i m i l a r to t h o s e obta ined in w a r m i n g up, wh ich r e s u l t s in t h e r m o l u m i n e s c e n c e . U s u a l l y not on ly f r o z e n s p e c i e s that a r e a b s o r b i n g in th i s s p e c t r a l r e g i o n a r e m o b i l i z e d , but a l s o the m a t r i x m a y be l e s s r ig id in the e f f e c t of l o c a l heat ing .

The t echnique of the r e c o m b i n a t i o n - l u m i n e s c e n c e s t i m u l a t i o n by i l l u -minat ion of f r o z e n i r r a d i a t e d s o l u t i o n s p r o v e d u s e f u l , e s p e c i a l l y in in -v e s t i g a t i o n s on ionic p r o c e s s e s in g a m m a - i r r a d i a t e d o r g a n i c s o l i d s .

T h u s Ske l ly and H a m i l l [22] m e a s u r e d the p h o s p h o r e s c e n c e e m i t t e d when a g a m m a - i r r a d i a t e d dilute so lu t ion of t r i p h e n y l a m i n e (TPA) in 3 - m e t h y l - p e n t a n e i s b l e a c h e d with i. r . l ight (0.8 - 2 nm) at 77°K. O p t i c a l absorpt ion s p e c t r o s c o p y p r o v i d e s e v i d e n c e for c o l o u r c e n t r e s t e n t a t i v e l y ident i f i ed a s T P A + , T P A " a s w e l l a s s o l v e n t - t r a p p e d e l e c t r o n s (e"). i . r . b l e a c h i n g of e" and T P A " induces p h o s p h o r e s c e n c e of T P A with c o r r e -

76 ZAGORSKI and M I N C

sponding d e c r e a s e of T P A + . Addit ion of o r g a n i c ha l ide (e~ trap) d e c r e a s e s T P A ~ and e", and ethanol (hole trap) d e c r e a s e s T P A + , whi le both d e -c r e a s e p h o s p h o r e s c e n c e which i s a t tr ibuted to ion r e c o m b i n a t i o n .

In the USSR ) T o c h i n et a l . [23] have w o r k e d on a r o m a t i c c o m p o u n d s i r -r a d i a t e d by 1.6 MeV e l e c t r o n s at 77°K and then i l l u m i n a t e d by m o n o -c h r o m a t i c l ight of constant f lux , but changing cont inuous ly f r o m 350 n m to 2.3 /um. L u m i n e s c e n c e p e a k s appear , be ing i n t e r p r e t e d by n e u t r a l i z a -t ion of both n e g a t i v e and p o s i t i v e ions . B e f o r e the i l luminat ion t h e s e i o n s a r e s t a b i l i z e d in the p r o c e s s of i r r a d i a t i o n . A c c o r d i n g to the a u t h o r s c i t e d , p o s i t i v e c h a r g e i s s t a b i l i z e d in m o l e c u l e s of the m a i n cons t i tuent of the s y s t e m . To p r o v e th i s , s y s t e m s with low y i e l d of r a d i c a l s w e r e c h o s e n ( c r y s t a l l i n e b e n z e n e , d ipheny lamine , g l a s s y c u m e n e , and both g l a s s y and c r y s t a l l i n e to luene , e t h y l b e n z e n e and t r i p h e n y l m e t h a n e ) . The d o s e appl ied w a s u s u a l l y about 0.3 Mrad. S p e c t r a l c o m p o s i t i o n of the e m i t t e d l ight d o e s not depend on the w a v e - l e n g t h of the e x c i t i n g i l l u m i n a -t ion . A l l i n v e s t i g a t e d h y d r o c a r b o n s s h o w e d a m a x i m u m at 1 /um of s t i m u -la t ing l ight , and one about 450 nm. In addit ion, t h e r e w e r e s o m e p e a k s c h a r a c t e r i s t i c for p a r t i c u l a r c o m p o u n d s . The l u m i n e s c e n c e o c c u r r i n g at the l a s t - m e n t i o n e d w a v e - l e n g t h w a s i n t e r p r e t e d a s the r e l e a s e of e l e c t r o n s t rapped by r a d i c a l s . The l o n g - w a v e e x c i t a t i o n s e e m s to be c o n n e c t e d with the r e l e a s e of p o s i t i v e ions s t a b i l i z e d on a c l u s t e r of n o n - i o n i z e d m o l e c u l e s , s i m i l a r to the m e c h a n i s m p r o p o s e d by Shida and H a m i l l [24] in the c a s e of CCI4 s t a b i l i z a t i o n on CCI4 m o l e c u l e s .

S o m e p a p e r s h a v e dealt with the ques t ion of the m e c h a n i s m of l u m i n o -s i t y i t s e l f r a t h e r than us ing it on ly a s a s i gn of r e a c t i o n s taking p l a c e .

The e x i s t e n c e of t h e r m o l u m i n o s i t y of s u b s t a n c e s i r r a d i a t e d at l ow t e m p e r a t u r e b e c o m e s a g e n e r a l ru le . A f t e r i n v e s t i g a t i n g s e v e r a l , m o s t l y d i f f e r e n t , g r o u p s of c o m p o u n d s we m a y s a y that if on ly the n a r r o w e s t s p e c t r a l window ( t r a n s m i t t e n c e in the u. v. o r v i s i b l e r e g i o n ) e x i s t s in the i n v e s t i g a t e d s a m p l e , it w i l l e m i t l ight a f t e r i r r a d i a t i o n at at l e a s t l iqu id n i t r o g e n t e m p e r a t u r e . A c c o r d i n g to the r e g u l a t i o n s of an IAEA P a n e l we cannot g i v e o u r unpubl ished data c o n c e r n i n g the u n i v e r s a l i t y of p h e n o m e n a and t h e i r i m p o r t a n c e to the r e a c t i o n s in the f r o z e n s t a t e . F o r t h e s e r e a s o n s we sha l l not d i s c u s s p a p e r s dea l ing with r a d i o l y s i s of c o m p o u n d s a d s o r b e d on the s u r f a c e of s i l i c a n e o u s m a t e r i a l s , i r r a d i a t e d at the t e m p e r a t u r e of l iquid n i t r o g e n (e. g. Ref . [25]) .

We a r e a l s o c o n s c i o u s of the fact that v i r t u a l l y a l l s o l i d s o c c u r r i n g in n a t u r e , e x c e p t t h o s e f r e s h l y f o r m e d , inher i t s o m e radiat ion c h a n g e s in t h e i r s t r u c t u r e s . T h i s a p p l i e s e s p e c i a l l y to o ld m i n e r a l d e p o s i t s that f r o m the c o o l i n g - d o w n s t a g e to the p r e s e n t t i m e w e r e absorb ing e n e r g y of ion iz ing radiat ion (mainly pro tons f r o m o u t e r s p a c e and radiat ion f r o m e n v i r o n m e n t a l rad ioac t iv i ty ) . The e n e r g y s t o r e d in t h i s way m a y b e m o s t e a s i l y r e l e a s e d a s t h e r m o l u m i n e s c e n c e . It i s u n n e c e s s a r y to e m p h a s i z e how important t h i s phenomenon i s for g e o l o g y (cf . S e c t i o n 3 .6) .

The i n v e s t i g a t i o n of t h e r m o l u m i n e s c e n c e a l o n g w i t h E . S . R. and opt i ca l s p e c t r a , and g e n e r a l confrontat ion with the c h e m i s t r y of the i n v e s t i g a t e d s y s t e m , h a s h e l p e d t o e n r i c h rad ia t ion c h e m i s t r y wi th f a c t s f o r m e r l y b e -long ing to radiat ion p h y s i c s . F o r e x a m p l e , t h e r e i s a t endency to c o n -s i d e r r a d i a t i o n - i n d u c e d c h a n g e s in ionic s o l i d s a s p u r e p h y s i c a l p h e n o -m e n a . The b e s t proof that they a r e not i s d e m o n s t r a t e d in v a r i o u s e x -p e r i m e n t s invo lv ing the d i s s o l u t i o n of i r r a d i a t e d a lka l i h a l i d e s . If the d i s s o l u t i o n in w a t e r of i r r a d i a t e d s o d i u m c h l o r i d e t a k e s p l a c e in the d a r k -

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n e s s , products of reac t ion between e l e c t r o n s and of f r e e ch lor ine a t o m s with water may be e a s i l y found [9]. What i s m o r e , during d i s so lut ion l u m i n e s c e n c e appears , an in t ere s t ing phenomenon p r e s e n t e d in the s e r i e s of p a p e r s by Ahns trom.

2. 6. The s t ruc ture of f r o z e n s a m p l e and l o w - t e m p e r a t u r e radiat ion c h e m i s t r y

It i s s u r p r i s i n g that such l i t t le in format ion i s ava i lab le on the s t r u c -ture of f r o z e n l iquids or even d e e p - f r o z e n c r y s t a l l i n e s u b s t a n c e s ob-tained at h igher t e m p e r a t u r e s . The s e c o n d group may be only appar-ently l e s s c o m p l i c a t e d .

Inves t iga tors of l o w - t e m p e r a t u r e radiat ion c h e m i s t r y usua l ly divide rapidly f r o z e n s t r u c t u r e s into c r y s t a l l i n e and g l a s s y s t r u c t u r e s on the b a s i s of v i s u a l inspect ion . In s o m e s y s t e m s it i s p o s s i b l e , e i ther by changing the rate of the t e m p e r a t u r e drop, or by condit ioning or p r e s s u r e t rea tment , to p a s s f r o m the g l a s s y to the c r y s t a l l i n e s ta te , and to c o m p a r e the radia t ion- induced e f f e c t s in both s t a t e s . For such c a s e s there i s s o m e in format ion ava i lab le in the l i t e ra ture .

The inf luence of the s t ruc ture of f r o z e n g l a s s e s and, m o r e o v e r , of c h a n g e s that take p l a c e in the s ta te was shown, among o t h e r s , by Burton and c o - w o r k e r s . Th i s author [26] has shown that g a m m a - i r r a d i a t e d , pure 3 -methy lpentane g l a s s at 77°K e m i t s a c h a r a c t e r i s t i c p h o s p h o r e s c e n c e of s e v e r a l hours duration, and that i t s in tens i ty i s d e c r e a s e d [27] by p e r -mit t ing the s a m p l e to r e l a x at 77°K between v i t r i f i ca t ion (complete a f t e r 3 min) and g a m m a irrad ia t ion (up to s e v e r a l hours) . The o c c u r r e n c e of s o m e c r a c k s in the annealed g l a s s indicated that the g l a s s re laxat ion or s t r u c t u r a l r e a r r a n g e m e n t had taken p l a c e .

J a n s s e n [28] has shown that c r a c k s in the annealed g l a s s e s are not n e c e s s a r i l y required for the anneal ing e f f e c t to be o b s e r v e d , although they apparent ly a c c e l e r a t e the g l a s s re laxat ion marked ly . It was a l s o shown that the l u m i n e s c e n c e s p e c t r a of i sopentane d i f f er for the g l a s s y and poly c r y s t a l l i n e s t a t e s .

Voevodsk i i et a l . [29] have tr ied to inves t igate the inf luence of the p h y s i c a l s ta te on the r e s u l t of radiat ion- induced r e a c t i o n s . They have inves t iga ted a l c o h o l s and hydrocarbons , and obtained r e s u l t s indicating that the f r e e radica l y i e l d s (determined by the E. S. R. method) in the s a m e compound are a lways h igher in the amorphous (g lassy) s a m p l e than in the c r y s t a l l i n e . A l s o d i f f e r e n c e s in the re la t ive concentrat ions of the d i f ferent r a d i c a l s have been o b s e r v e d . Accord ing to Voevodski i th is e f f ec t s e e m s to be connected with the inf luence of s t ruc tura l de f ec t s on the p r i m a r y p r o c e s s e s of r a d i o l y s i s .

It i s evident f r o m the lengthy paper by Teply [30] that it i s diff icult to g e n e r a l i z e on the ro l e played by the crys ta l l in i ty of the s a m p l e .

Looking m o r e c l o s e l y at the p r o b l e m of s tructure we may e a s i l y c o m e to the conc lus ion that s i m p l e d iv is ion into c r y s t a l l i n e and amorphous s a m p l e s produces an i m p r e c i s e s i m p l i f i c a t i o n of the s i tuat ion. If there i s a d i f f erence in behaviour between c r y s t a l l i n e and g l a s s y s a m p l e s , the s i z e of the c r y s t a l s as w e l l a s the s i z e of the a g g r e g a t e s or m i c e l l e s in a g l a s s y s a m p l e must be dif ferent too. Henriksen [31] has written on the e f f e c t of c r y s t a l d imens ions on the y ie ld of radiat ion- induced rad ica l s in organic s u b s t a n c e s .


It i s important to r e a l i z e that c o m p l i c a t i o n s i m p l i e d by the s t r u c t u r e a r e not r e s t r i c t e d to those s a m p l e s which are l iquids at r o o m t e m p e r a t u r e and s h o c k - f r o z e n to the t e m p e r a t u r e of i rrad ia t ion . L o w - t e m p e r a t u r e rad ia t ion c h e m i s t r y i s a l s o c o m p l i c a t e d in s a m p l e s that a re s o l i d at r o o m t e m p e r a t u r e and m e r e l y coo led . In th i s c a s e a l s o p h a s e c h a n g e s a r e p o s s i b l e , and the f o r c e s deve loped between c r y s t a l s m a y r e a c h v a l u e s s o high that on w a r m i n g a t r i b o t h e r m o l u m i n e s c e n t peak i s deve loped , s i m u l a t i n g r a d i a t i o n - i n d u c e d t h e r m o l u m i n e s c e n c e . T h e r e f o r e , e s p e c i a l l y in the c a s e of o p t i c a l m e a s u r e m e n t s on d e e p - f r o z e n c r y s t a l s involv ing thawing , a blank e x p e r i m e n t without i r r a d i a t i o n m u s t be p e r f o r m e d . T r i -b o l u m i n e s c e n t p e a k s a r e known in t h e r m o l u m i n e s c e n t d o s i m e t r y [32],

The ques t ion of " c r y s t a l l i n e or g l a s s y " i s important in a o n e -component s y s t e m , but i s even m o r e c o m p l i c a t e d in t w o - and m o r e component s y s t e m s . Most i n v e s t i g a t o r s hope that f r o z e n s a m p l e s that a re apparent ly g l a s s y are to ta l ly u n i f o r m in sp i t e of t h e i r m u l t i c o m p o n e n t c o m p o s i t i o n . If the s a m p l e i s c r y s t a l l i n e , t h e r e i s no such guarantee at a l l . In s o m e c a s e s t h e r e i s to ta l s e p a r a t i o n into individual c r y s t a l s that exhibit t h e i r own radiat ion c h e m i s t r y ; in o t h e r s the s a m p l e s a r e p e r f e c t l y h o m o g e n e o u s , wh ich m e a n s e v e r y part of the s y s t e m on the m o l e c u l a r l e v e l has the s a m e c o m p o s i t i o n a s the a v e r a g e of the s y s t e m s .

A paper by Dyne and Denhartog [33] p r o v i d e s a s t r ik ing e x a m p l e . T h e y i n v e s t i g a t e d a c l a s s i c a l c y c l o h e x a n e - b e n z e n e s y s t e m known for i t s c h a r a c t e r i s t i c c u r v e of hydrogen y i e ld , deviat ing f r o m the addi t iv i ty law b e c a u s e of the p r o t e c t i v e act ion of b e n z e n e . The i n v e s t i g a t i o n w a s p e r -f o r m e d at a t e m p e r a t u r e of 77°K. If s o l i d m i x t u r e s w e r e p r e p a r e d s i m p l y by plunging l iquid s a m p l e s into l iquid n i t rogen the e f f e c t of the p r o t e c t i v e ac t ion of b e n z e n e would be hard ly v i s i b l e : hydrogen y i e l d w a s a l m o s t l i n e a r - c y c l o h e x a n e s e e m e d to be di luted with a d i f f e r e n t s u b s t a n c e (cf. Ref . [-34]). T h e r e w a s , h o w e v e r , a s u s p i c i o n that t h e r e had been s o m e s e g r e g a t i o n of the l iquid m i x t u r e into two p h a s e s , s o l i d b e n z e n e and s o l i d c y c l o h e x a n e . T h i s s e g r e g a t i o n would e l i m i n a t e the i n t e r a c t i o n s that o c c u r in the r a d i o l y s i s of the l iquid m i x t u r e s , and the y i e l d s would l i e c l o s e to the m i x t u r e l i n e .

To t e s t t h i s . Dyne p r e p a r e d o ther s a m p l e s by the s low c o n d e n s a t i o n of a s t r e a m of the p r e m i x e d v a p o u r s on to a s u r f a c e c o o l e d by l iquid n i t r o g e n . S e g r e g a t i o n into two p h a s e s w a s inhibi ted at t h e s e t e m p e r a -t u r e s , the s a m p l e s w e r e h o m o g e n e o u s , and the y i e l d s w e r e m u c h l o w e r than f r o m the f r o z e n l iquid s a m p l e s and did not d i f f e r qual i ta t ive ly f r o m t h o s e found in the l iquid, and did not o b e y the m i x t u r e law but d e m o n s t r a -t e d the p r o t e c t i o n e f f e c t .

2. 7. L o w - t e m p e r a t u r e radiat ion c h e m i s t r y and s o l i d - s t a t e c o n c e p t s

It i s obv ious that s e v e r a l authors have t r i e d to approach the i n t e r -p r e t a t i o n of l o w - t e m p e r a t u r e r a d i o l y s i s f r o m the point of v i ew of s o l i d -s t a t e c o n c e p t s , e s p e c i a l l y in v i e w of the s u c c e s s of radiat ion p h y s i c s with ion ic c r y s t a l s and s e m i c o n d u c t o r s , s o l i d at r o o m t e m p e r a t u r e s . Rad io -l y s i s of f r o z e n l iqu ids m a y be a l s o t r e a t e d in t e r m s of s o l i d - s t a t e c o n -c e p t s . A c c o r d i n g to t h e s e , the ion izat ion p r o c e s s i s equiva lent to the e x c i t a t i o n of an e l e c t r o n into the conduct ion band cont inuum l eav ing behind a p o s i t i v e ho le in the v a l e n c e band. In the band p i c t u r e ne i ther the e l e c -t r o n nor the ho le i s l o c a l i z e d on any s p e c i f i c m o l e c u l e . F u r t h e r , they

PL-236/1 7 9

c a n b r i n g about e l e c t r o n i c p o l a r i z a t i o n of the s u r r o u n d i n g m e d i u m and c a n e x i s t in the p o l a r o n s t a t e [11] . T h e a t t r a c t i v e p o t e n t i a l b e t w e e n s u c h e l e c t r o n and h o l e p o l a r o n s d e t e r m i n e s a s e r i e s of s t a b l e bound s t a t e s in the e n e r g y gap b e t w e e n the v a l e n c e and c o n d u c t i o n b a n d s . In the a b s e n c e of r e a c t i v e s o l u t e s in the s y s t e m , the e l e c t r o n s s u b s e q u e n t l y drop into o n e o f t h e s t a b l e e x c i t o n s t a t e s , and t h i s p r o c e s s r a t h e r than the a n n i h i -l a t i o n of e l e c t r o n s and h o l e s i s c o n s i d e r e d to b e the f i r s t - o r d e r r e c o m b i -n a t i o n p r o c e s s d i s c u s s e d by the c i t e d a u t h o r s .

T h e s o l i d - s t a t e a p p r o a c h would be a f r u i t f u l o n e in the f i e l d d i s c u s s e d , if m o r e e x p e r i m e n t a l data on f r o z e n i r r a d i a t e d s y s t e m s c o u l d be found. E . S . R. , l ight a b s o r p t i o n and e m i s s i o n g i v e i n s u f f i c i e n t data f r o m the point of v i e w of s o l i d - s t a t e c h e m i s t r y and p h y s i c s . M o r e e x p e r i m e n t s c o n n e c t e d w i t h e l e c t r i c a l p r o p e r t i e s of f r o z e n i r r a d i a t e d s y s t e m s a r e n e e d e d . T h e f a c t that t h e y a r e not p e r f o r m e d in the r a n g e n e e d e d m a y be e x p l a i n e d by e x p e r i m e n t a l d i f f i c u l t i e s c o n n e c t e d wi th e l e c t r i c a l m e a s u r e m e n t s at l o w t e m p e r a t u r e s and d i f f e r e n t p a r a m e t e r s of the e x p e r i m e n t in c o m p a r i s o n wi th r o o m t e m p e r a t u r e m e a s u r e m e n t s , due to the d i f f e r e n t e n e r g y l e v e l s , m o b i l i t i e s , e t c . , i n v o l v e d .

2 . 8 . I n v e s t i g a t i o n s r e l a t e d to the l o w - t e m p e r a t u r e r a d i a t i o n c h e m i s t r y

C o n s i d e r i n g the b a s i c r a d i a t i o n c h e m i s t r y of f r o z e n s a m p l e s one c a n n o t c o n f i n e o n e ' s a t t en t ion o n l y to i n v e s t i g a t i o n s i n v o l v i n g i o n i z i n g r a d i a t i o n . I n v e s t i g a t i o n s c a r r i e d on f r o m o t h e r p o i n t s of v i e w and u s i n g d i f f e r e n t t e c h n i q u e s m a y p r o d u c e a v a l u a b l e n e w out look , e s p e c i a l l y in the c a s e of d i f f i c u l t i e s in i n t e r p r e t a t i o n . T h u s the p a p e r s and c o n c e p t s of R i e h l [35] p r e s e n t e d at the E n e r g y T r a n s f e r S y m p o s i u m a r e w o r t h m e n t i o n i n g . T h i s author i s i n t e r e s t e d in p r o t o n i c c o n d u c t i v i t y in i c e o r o t h e r c o m p o u n d s f o r m i n g h y d r o g e n b r i d g e s . At t e m p e r a t u r e s s u f -f i c i e n t l y l o w to p r e c l u d e t h e r m a l d i s s o c i a t i o n , he w a s a b l e to e s t a b l i s h s p a c e - c h a r g e d l i m i t e d p r o t o n c u r r e n t s u s i n g p r o t o n - i n j e c t i n g c o n t a c t s and h igh e l e c t r i c a l f i e l d s . P u r e i c e s i n g l e c r y s t a l s w e r e c o o l e d to 77°K, and f i e l d s b e t w e e n p o w d e r e d P d e l e c t r o d e s s a t u r a t e d wi th h y d r o g e n w e r e a p p l i e d up to 450 k V / c m . L e a v i n g a s i d e t h e q u e s t i o n of p r o t o n t r a p s , a m o u n t i n g r o u g h l y to 3 . 5 X 1 0 1 2 / c m 3 d e n s i t y , R i e h l c a m e to an i n t e r e s t i n g c o n c l u s i o n : the pro ton m o b i l i t y i n c r e a s e s wi th d e c r e a s i n g t e m p e r a t u r e . T h i s i n d i c a t e s that the m o b i l i t y of p r o t o n s in i c e m u s t b e c o n s i d e r e d a s a p r o c e s s s i m i l a r to the m o t i o n o f e l e c t r o n s in a c o n d u c t i o n band and not a s a "hopping" m e c h a n i s m .

A l t h o u g h t h i s f ind ing m a y not b e qui te r e a d y f o r g e n e r a l i z a t i o n , it i s w o r t h c o n s i d e r i n g and, w e b e l i e v e , d o e s not c o n t r a d i c t the r e s u l t s f r o m the r a d i a t i o n c h e m i s t r y o f i c e .

3. S U R V E Y O F L O W - T E M P E R A T U R E RADIATION C H E M I S T R Y O F P A R T I C U L A R S Y S T E M S

3 . 1 . G e n e r a l

Unt i l now, p r a c t i c a l l y a l l the m o s t i m p o r t a n t l i q u i d s y s t e m s h a v e b e e n i n v e s t i g a t e d in the f r o z e n s t a t e a l s o . T h e r e s u l t s undoubted ly e n -


r i c h e d l iquid rad ia t ion c h e m i s t r y , contr ibut ing to a m o r e c o m p l e t e p i c t u r e of rad ia t ion c h e m i s t r y .

The i m p o r t a n c e of l o w - t e m p e r a t u r e rad ia t ion c h e m i s t r y d o e s not f i n i s h with a s u p p l e m e n t a r y r o l e for l iqu ids . The i m p l i c a t i o n s of t h i s t e c h n i q u e and g e n e r a l i z e d f a c t s s t r e t c h f r o m b a s i c r e s e a r c h on the a t o m i c l e v e l through m o l e c u l a r b io logy to the new c o n c e p t s of c h e m i c a l e f f e c t s in o u t e r s p a c e . T h u s l o w - t e m p e r a t u r e c h e m i s t r y has i n c r e a s e d the c o n -t r i b u t i o n s to o ther b r a n c h e s of s c i e n c e .

It i s v e r y d i f f i cu l t to gain a whole p i c t u r e of p h e n o m e n a in rad ia t ion c h e m i s t r y of p a r t i c u l a r i m p o r t a n c e today , b e c a u s e , a s a r u l e , e v e r y author g i v e s a s o m e w h a t b i a s e d p i c ture of p h e n o m e n a , s t r e s s i n g one p a r t i c u l a r a s p e c t and n e g l e c t i n g o t h e r s . A s s t r e s s e d f requent ly in t h i s s u r v e y , the f r o z e n s t a t e o f f e r s s o m a n y s t r u c t u r a l and e n e r g e t i c p o s s i -b i l i t i e s that a l l p h e n o m e n a o b s e r v e d a r e u n d e r s t a n d a b l e . The r e l a t i v e i m p o r t a n c e of p h e n o m e n a and m e c h a n i s m s r e m a i n s to be i n v e s t i g a t e d , a s i s a l r e a d y done in o ther b r a n c h e s of rad ia t ion c h e m i s t r y of s o l i d s , n a m e l y those that a r e s o l i d at r o o m t e m p e r a t u r e , e . g . in the c a s e of a l k a l i h a l i d e s .

3. 2. Water and a q u e o u s s y s t e m s

In the f i r s t p l a c e , the s tudy of the r a d i o l y s i s of i c e and f r o z e n aqueous s o l u t i o n s he lped to e l u c i d a t e the v i e w s put f o r w a r d to expla in the r a d i a t i o n -induced c h e m i c a l c h a n g e s in w a t e r and aqueous s o l u t i o n s . E a r l y , but m o s t important , p a p e r s [ 3 6 - 4 1 ] p r e s e n t e d p r o o f s for the p r e s e n c e of H and OH r a d i c a l s in d e e p - f r o z e n i r r a d i a t e d i c e by E . S . R . and o p t i c a l s p e c t r o s c o p y . B a s i c radiat ion y i e l d s e s t a b l i s h e d then by S i e g e l , G / H / = G / O H / = 0.8 - 0 .9 at 4°K or G / H / = 0 and G / O H / = 0.6 at 77°K, n e e d now to be c o r r e c t e d , and a c c o r d i n g to Moorthy and W e i s s [11] a r e too high by a f a c t o r of about two .

If the b a s i c y i e l d s m a y be the s o u r c e of s o m e c o n t r o v e r s y , e s p e c i a l l y in c a s e s c o n c e r n i n g v e r y low t e m p e r a t u r e and pure w a t e r , s o the r e g i s t r a -t ion of p h e n o m e n a in f r o z e n aqueous s o l u t i o n s s e e m s to a g r e e within s a t i s -f a c t o r y l i m i t s . T h u s e a r l y m e a s u r e m e n t s by S c h u l t e - F r o h l i n d e [42] of a b s o r p t i o n s p e c t r a of g a m m a - i r r a d i a t e d a lka l ine i c e (which i s deep blue) w e r e m a n y t i m e s c o n f i r m e d , f o r e x a m p l e , r e c e n t l y by E r s h o v £Lnd P i k a e v [43] . A l s o m a n y p a p e r s on E . S . R . s p e c t r a of d i f f erent f r o z e n s o l u t i o n s , for e x a m p l e , H e n r i k s e n [44] in the c a s e of a lka l ine s o l u t i o n s , s e e m to a g r e e .

N e v e r t h e l e s s , the c o n t r o v e r s y b e g i n s u s u a l l y at the s t a g e of i n t e r -p r e t a t i o n . E v e r y new e x p e r i m e n t a l fac t , p e r h a p s the convent iona l a n a -l y s i s of the m o l t e n s a m p l e , o r the introduct ion of the new p a r a m e t e r of the s a m p l e m e a s u r e d (cf. R e f s [7, 45] in the c a s e of a lka l ine s o l u t i o n s ) , c a u s e s a change in the in t erpre ta t ion .

3 . 3 . S i m p l e o r g a n i c c o m p o u n d s

L o w - t e m p e r a t u r e radiat ion c h e m i s t r y of s i m p l e o r g a n i c c o m p o u n d s i s a l r e a d y v e r y r i c h . In th i s s h o r t s e c t i o n we s h a l l s t r e s s only the ques t ion of p o s i t i v e i ons . E x p e r i m e n t a l d e m o n s t r a t i o n of i t s p r e s e n c e and behav iour in the f r o z e n s a m p l e d i s t i n g u i s h e s the s i tua t ion c l e a r l y f r o m rad ia t ion c h e m i s t r y of the s a m e compounds in the l iquid s t a t e .

P L - 2 3 6 / 1 8 1

The s e r i e s of p a p e r s by H a m i l l [24, 46, 47] i s devoted to m o l e c u l a r i o n s and ion ic p r o c e s s e s in o r g a n i c g l a s s e s . G a m m a - i r r a d i a t e d (at 77°K) p o l y c r y s t a l l i n e CCI4 s h o w s the p r e s e n c e of p o s i t i v e h o l e s a b s o r b i n g at about 400 nm. The s o l v e n t band i s d e p r e s s e d by a r o m a t i c a m i n e s o r o ther a d d i t i v e s that act a s hole t r a p s with the a p p e a r a n c e of the c o r r e -sponding a m i n e ca t ion absorpt ion . P h o t o - b l e a c h i n g or b r i e f heat ing to 143°K r e d u c e s the 400 nm band with an i n c r e a s e in so lu te ca t ion a b s o r p -t ion . A kinet ic t r e a t m e n t that a s s u m e s that the only l ab i l e s p e c i e s in the s y s t e m i s a m i g r a t i n g p o s i t i v e c h a r g e can exp la in the e x p e r i m e n t a l r e -s u l t s in a s a t i s f a c t o r y w a y . A rough e s t i m a t e of the t o t a l a v a i l a b l e p o s i t i v e c h a r g e i s 1 . 9 / 1 0 0 e V of a b s o r b e d e n e r g y .

The addi t ion of a r o m a t i c h y d r o c a r b o n s to the p o l y c r y s t a l l i n e m a t r i x of CCI4 l e a d s to the f o r m a t i o n of m o l e c u l a r m o n o p o s i t i v e ions o f , f or e x a m p l e , b e n z e n e , t o luene , b iphenyl , t e r p h e n y l , naphthalene and s t i l b e n e . T h e authors i n t e r p r e t t h e s e r e s u l t s a s r e s o n a n c e c h a r g e t r a n s f e r f r o m CCI4 to CCI4, t e r m i n a t e d by t r a n s f e r f r o m CCI4 to the s o l u t e .

P o s i t i v e - h o l e m i g r a t i o n has a l s o b e e n found in 3 - m e t h y l p e n t a n e (a l so by H a m i l l ) . In the s y s t e m c o n s i s t i n g of th i s h y d r o c a r b o n and a s m a l l addit ion of compounds undergo ing c h a r g e t r a n s f e r o r pro ton t r a n s f e r r e a c t i o n s , the m o b i l e p o s i t i v e ho le i s t r a n s f e r r e d f r o m 3 - m e t h y l p e n t a n e to the add i t ive , and t rapped .

Although we s t r e s s the i m p o r t a n c e of p o s i t i v e ions in the r a d i o l y s i s of organ ic c o m p o u n d s , which i s shown c l e a r l y in l o w - t e m p e r a t u r e r a d i a -t ion c h e m i s t r y , we do not c l a i m that it i s the s o l e m e c h a n i s m . P a r a l l e l o r l a t e r p r o c e s s e s a r e go ing on in which f r e e r a d i c a l s o c c u r (cf. Ref . [48] for the c a s e of 3 - m e t h y l p e n t a n e ) . The l o w - t e m p e r a t u r e rad ia t ion c h e m i s t r y of the s a m e c o m p o u n d has been m e n t i o n e d a l s o e l s e w h e r e in t h i s r e v i e w .

The fu l l p i c t u r e of the r a d i o l y s i s of o r g a n i c compounds i s f a r f r o m c o m p l e t e , if we take a l l e x p e r i m e n t a l f a c t s and a l l r a n g e s of t i m e into c o n s i d e r a t i o n .

3 . 4 . O r g a n i c p o l y m e r s

The p r o b l e m s of l o w - t e m p e r a t u r e rad ia t ion c h e m i s t r y c o n n e c t e d wi th p o l y m e r s a r e aga in too w i d e l y r e p r e s e n t e d in the l i t e r a t u r e to be c o v e r e d fu l ly in th i s r e v i e w . T h i s f i e l d m a y be d iv ided into t h r e e g r o u p s : r a d i a t i o n -induced p o l y m e r i z a t i o n , w h e r e the s t a r t i n g point i s the m o n o m e r , the s e c o n d group of r a d i a t i o n - i n d u c e d degradat ion and c r o s s - l i n k i n g of i r r a d i a t e d p o l y m e r s , and the th ird i n t e r m e d i a t e group w h e r e both p o l y m e r and m o n o m e r a r e i r r a d i a t e d , r e s u l t i n g in r a d i a t i o n - i n d u c e d g r a f t i n g .

The f i r s t group, r a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n , h a s v e r y m u c h in c o m m o n with the rad ia t ion c h e m i s t r y of s i m p l e o r g a n i c m o l e c u l e s , which in p r a c t i c a l l y a l l c a s e s p r o d u c e s p o l y m e r s in i t s wide s p e c t r u m of p r o d u c t s , in s p i t e of the fact that no typ i ca l m o n o m e r w a s u s e d a s an i r r a d i a t e d s a m p l e . In the c a s e of a typ i ca l m o n o m e r the y i e l d s a r e u s u a l -l y m u c h l a r g e r . R a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n p r o c e e d s in 3. f r o z e n s t a t e that i s d i f f erent in c o m p a r i s o n with the l iquid s ta te . In p a r t i c u l a r , r e a c t i o n s p r o c e e d i n g with v e r y high radiat ion y i e l d s of ev ident cha in m e c h a n i s m s c o n n e c t e d with the d i f fus ion of i n t e r m e d i a t e s , p r o c e e d at a d i f f erent low t e m p e r a t u r e .

Up to now m o s t i n t e r e s t has b e e n paid to t h o s e c a s e s of r a d i a t i o n -induced p o l y m e r i z a t i o n in the f r o z e n s ta te in which the ionic m e c h a n i s m


of r e a c t i o n w a s s u s p e c t e d . Convinc ing proof for the ionic m e c h a n i s m in the f r o z e n s t a t e could be an a r g u m e n t for a s i m i l a r explanat ion for p o l y m e r i z a t i o n in the l iquid s t a t e , c o m p e t i n g with a g e n e r a l l y a c c e p t e d r a d i c a l m e c h a n i s m . The t h e o r y of t h e s e r e a c t i o n s i s not ye t fu l ly a g r e e d . Many i n t e r v e n i n g s t e p s a r e invo lved b e t w e e n in i t ia l e n e r g y absorpt ion and f i n a l e n d - p o i n t s [49],

T h e r e i s s o m e hope that p o l y m e r s m a y be obtained, c h a r a c t e r i z e d by unusua l p r o p e r t i e s , wh ich m a y be of i n d u s t r i a l i m p o r t a n c e .

In the s e c o n d group - l o w - t e m p e r a t u r e radiat ion c h e m i s t r y of p o l y m e r s -the i n t e r m e d i a t e e f f e c t s a r e m o r e s i m i l a r to the e f f e c t s at the r o o m t e m p e r a t u r e than w a s the c a s e with l iquid m o n o m e r s i r r a d i a t e d at r o o m t e m p e r a t u r e and in the f r o z e n s ta te . In p o l y m e r s the m o b i l i t y i s r e -s t r i c t e d e v e n at r o o m t e m p e r a t u r e if not s o s e v e r e l y a s in l iquid n i t rogen .

The m o s t i n t e r e s t i n g p o s s i b i l i t i e s o f f e r e d by l o w - t e m p e r a t u r e r a d i a -t ion c h e m i s t r y in the f i e l d of radiat ion in terac t ion on p o l y m e r s c o n s i s t in l o c a l i z a t i o n of p a r t i c u l a r e f f e c t s on the t e m p e r a t u r e a x i s . T h e s e m e a s u r e m e n t s a r e p e r f o r m e d with the he lp of E. S. R. s p e c t r o s c o p y , and a l s o with i . r . [16] and u. v . a b s o r p t i o m e t r y (e. g. Ref . [50]), conduct iv i ty and t h e r m o l u m i n e s c e n c e .

The l a s t m e n t i o n e d f i e l d i s at the s t a g e of in tense d e v e l o p m e n t . P o l y -m e r s i r r a d i a t e d at l iquid n i t rogen t e m p e r a t u r e s e m i t c o m p a r a t i v e l y in -t e n s e l ight when w a r m e d . Glow c u r v e s , e a s y to obtain e v e n without a p h o t o m u l t i p l i e r , m a y be u s e d for the in terpre ta t ion of phenomena o c c u r r i n g , and a r e a l s o p r o p o s e d for ident i f i ca t ion p u r p o s e s and qual i ty contro l . Thus M o z i s e k [51] found the p e a k s on the g low c u r v e to be d i r e c t l y c o n n e c t e d wi th the m o b i l i t y v a r i a t i o n s of the m o l e c u l e s or t h e i r s e g m e n t s , and c o r -r e s p o n d to the s t r u c t u r a l t r a n s i t i o n t e m p e r a t u r e s . T h i s technique i s t h e r e -f o r e p r o p o s e d to i n v e s t i g a t e p o l y m e r s t r u c t u r e .

3. 5. Compounds of b i o l o g i c a l i m p o r t a n c e

A s in o ther s u b - s e c t i o n s of Sec t ion 3, it i s i m p o s s i b l e to g i v e a ful l account of the r o l e p layed by l o w - t e m p e r a t u r e i r r a d i a t i o n s . We s h a l l t h e r e f o r e c o n f i n e o u r s e l v e s to one p r o b l e m only c o n n e c t e d with r a d i o -p r o t e c t i v e a g e n t s .

An important r o l e i s p l a y e d by l o w - t e m p e r a t u r e i r rad ia t ion in the f i e l d of the c h e m i s t r y of r a d i o - p r o t e c t i v e a g e n t s , which i s a s e p a r a t e b r a n c h of the e n e r g y t r a n s f e r group of p r o b l e m s . F o r e x a m p l e , c y s t e a m i n e (NH2 . (CH2)2> SH, c a l l e d MEA) i s a w e l l - k n o w n r a d i o - p r o t e c t i v e agent at a l l l e v e l s , f r o m the who le a n i m a l to individual c h e m i c a l s . A s the m e c h a n i s m s invo lved a r e not c l e a r , s e v e r a l a t t e m p t s w e r e made to i n v e s t i g a t e it , inc luding i r r a d i a t i o n s and E . S. R. m e a s u r e m e n t s at 77°K. C o n c l u s i o n s f r o m l o w - t e m p e r a t u r e i r r a d i a t i o n of p r o t e i n s with c y s t e a m i n e ( R e f s [ 5 2 - 5 8 ] ) m a y be s u m m a r i z e d in an important s t a t e m e n t , that MEA h a s l i t t l e o r no e f f e c t on the E . S . R . s p e c t r u m at th i s t e m p e r a t u r e , and t h e r e f o r e th i s compound d o e s not in f luence f r e e r a d i c a l f o r m a t i o n . At h i g h e r t e m p e r a t u r e s it w a s found that the p r o t e i n or nuc l eopro te in r a d i -c a l s m i g r a t e d to the su lphydry l group of the MEA to g i v e the r a d i c a l -CH2-S" . The p r o p o s e d m e c h a n i s m i s d a m a g e to the pro te in m o l e c u l e RH:

RH/WWV^R-

6*

P L - 2 3 6 / 1 8 3

and the r e a c t i o n R- + -SH -» RH + - S ' , c a l l e d "repair" . T h i s r e p a i r r e a c t i o n could account for the p r o t e c t i v e act ion of MEA. In the p r e s e n c e of oxygen , MEA and o x y g e n c o m p e t e for the f r e e r a d i c a l s , g i v i n g p r o t e c -t ion and s e n s i t i z a t i o n r e s p e c t i v e l y . Oxygen r e a c t s with the su lphur r a d i -c a l s f o r m e d by the r e p a i r r e a c t i o n , thus p r e v e n t i n g the damaging back r e a c t i o n .

3. 6. Outer s p a c e c h e m i s t r y

A s w a s a l r e a d y m e n t i o n e d in S e c t i o n s 2 .2 and 2 .5 , r a d i a t i o n - i n d u c e d c h a n g e s m a y be f r o z e n in d i f ferent d e p o s i t s and m i n e r a l s o c c u r r i n g in the e a r t h c r u s t . The t e m p e r a t u r e of the d e p o s i t s found d o e s not go down to the t e m p e r a t u r e s c o m m o n in l o w - t e m p e r a t u r e radiat ion c h e m i s t r y . E v e n r o c k s f r o m A n t a r c t i c a would be too "warm" to s t o r e i n t e r m e d i a t e s p e c i e s u s u a l l y f r o z e n at l iquid n i t rogen t e m p e r a t u r e .

O u t s i d e the ear th , h o w e v e r , t h e r e a r e condi t ions of e x t r e m e co ld , e x t r e m e heat , v a r i o u s kinds of rad ia t ion and s u f f i c i e n t t i m e that m a k e the r e a c t i o n s of co ld radiat ion c h e m i s t r y p o s s i b l e . Sun [59] b e l i e v e d that ion iz ing rad ia t ion r e a c h i n g the s u r f a c e of the m o o n and lunar t e m p e r a t u r e c h a n g e s p r o v i d e idea l condi t ions for t h e r m o l u m i n e s c e n c e , the r e l e a s e of s t o r e d - u p e n e r g y in the f o r m of v i s i b l e l ight during a rapid t e m p e r a t u r e r i s e . The dark s i d e of the moon , at a t e m p e r a t u r e of ~ - 1 5 0 ° C , and which i s b o m b a r d e d by p r o t o n s , s t o r e s e n e r g y a l m o s t l ike s a m p l e s of s i l i c o u s m a t e r i a l s , g a m m a - i r r a d i a t e d under l iquid n i t r o g e n in the l a b o r a t o r y . The r e v o l v i n g moon b r i n g s dawn a f t e r a t w o - w e e k lunar night and the s t o r e d e n e r g y i s r e l e a s e d in the f o r m of v i s i b l e l ight . Thus , in a s t r ip l e s s than 100 m i l e s wide a l o n g s i d e the lunar t e r m i n a t o r the m o o n e m i t s l ight of i t s own, wh ich m a y be a l m o s t a s i n t e n s e a s i t s r e f l e c t e d sunl ight , if we take into account that the "day" t e m p e r a t u r e of the s u r f a c e of the m o o n r e a c h e s about +120°C, and that the radiat ion y i e l d s of t h e r m o l u m i n e s -c e n c e m a y be v e r y high (cf . S e c t i o n 2 .5) . One h a s to keep in mind that the lunar s u r f a c e h a s no p r o t e c t i v e a t m o s p h e r e , s o that in v a c u o e v e n 1 keV pro tons r e a c h the m o o n . The f l u o r e s c e n t m a t e r i a l s m a y r e c e i v e a d o s e of about 10 3 Mrad during the dark p e r i o d , at about 200 A . The ra te of t e m p e r a t u r e r i s e i s about 4 .5 d e g C / m i n , which m e a n s an i n c r e a s e f r o m - 1 5 0 to +120°C in about 1 h. Sun's theory s e e m s to be a r e a s o n a b l e e x -planat ion for the fact that the band of moonl ight n e a r the t e r m i n a t o r i s b r i g h t e r than the r e s t of the m o o n ' s dayt ime s u r f a c e .

A s we s e e , the m o o n ' s s u r f a c e i s p o s s i b l y a s i t e w h e r e p e r i o d i c a l l y r e a c t i o n induced by radiat ion at l ow t e m p e r a t u r e happens . Outer s p a c e m a y in g e n e r a l be c o n s i d e r e d a s a g igant ic "cold radiat ion c h e m i s t r y " l a b o r a t o r y . The m e t e o r i t e s a r e v e r y probably a s o u r c e of f o r m a t i o n of f r e e r a d i c a l s , e s p e c i a l l y when they c o l l i d e wi th a planet not l a r g e enough to hold an a t m o s p h e r e and far away f r o m the sun, s o that it i s at the t e m p e r a t u r e of o u t e r s p a c e (about 2°K) [60]. C o l l i s i o n p r o d u c e s a l o c a l i z e d t e m p e r a t u r e s u f f i c i e n t l y high to v a p o r i z e m a n y s u b s t a n c e s and d i srupt c h e m i c a l bonds wi th subsequent s t a b i l i z a t i o n of f r e e r a d i c a l s , i o n s and e l e c t r o n s . No work h a s b e e n done in the l a b o r a t o r y at t h i s t e m p e r a t u r e , but e x p e r i e n c e f r o m l o w - t e m p e r a t u r e i r rad ia t ion at a s l i g h t l y h i g h e r t e m -p e r a t u r e of 4°K (boi l ing point of h e l i u m ) s h o w s the p o s s i b i l i t y of m a n i f o l d r e a c t i o n s with important c o n s e q u e n c e s for c o s m i c c h e m i s t r y .


4. E X P E R I M E N T A L CONSIDERATIONS

4. 1. P r e p a r a t i o n and handling of f r o z e n s a m p l e s

It i s w e l l known that the p r e p a r a t i o n of d e e p - f r o z e n s a m p l e s ( e . g . in l iquid n i t rogen) for g a m m a i rrad ia t ion and subsequent i n v e s t i g a t i o n by the E . S . R. m e t h o d (for the p r e s e n c e of s p e c i e s wi th unpa ired e l e c t r o n s ) for a b s o r p t i o n and e m i s s i o n of l ight , s t r u c t u r a l i n v e s t i g a t i o n , e t c . , i s not an e a s y p r o c e d u r e . The technique e m p l o y e d m u s t a l low a conven ient t r a n s f e r of s a m p l e s f r o m the i r r a d i a t i o n v e s s e l into the s a m p l e h o l d e r . The m o s t s i m p l e way, i . e . the i r r a d i a t i o n in t h i n - w a l l t u b e s , has m a n y d i s a d v a n t a g e s :

(i) Mos t m a t e r i a l s ( e .g . g l a s s ) e m i t rad ia t ion in the E . S . R. s p e c t r u m o r in o t h e r m e t h o d s (absorpt ion and e m i s s i o n of l ight and o t h e r s ) b e c a u s e of the f o r m a t i o n of i n t e r m e d i a t e o r s e m i - s t a b l e produc t s of r a d i o l y s i s .

(i i) S o m e m a t e r i a l s do not g i v e s i g n a l s in the s a m e r e g i o n a s the s a m p l e . H o w e v e r , e v e n in favourab le c a s e s ( e . g . s p e c i a l g l a s s that d o e s not g ive the s i g n a l s a f t e r i rrad ia t ion) the p r e s e n c e of addi t ional s u b s t a n c e s surround ing the s a m p l e in the m a g n e t i c c a v i t y o r o ther d e v i c e l o w e r s the s e n s i t i v i t y of m e a s u r e m e n t .

( i i i) Mos t m a t e r i a l s for tub ings , e s p e c i a l l y organ ic o n e s , m a y c o n -t a m i n a t e s a m p l e s during pour ing and f r e e z i n g . V e r y o f t e n the i n v e s t i g a -t ion of the addi t ion of an ac t ive so lu t ion is needed .

S e v e r a l t e c h n i q u e s have b e e n p r o p o s e d to o v e r c o m e t h e s e d i f f i c u l t i e s . The m o s t important a r e :

(i) I rrad ia t ion of r o d - s h a p e d s a m p l e s in s e a l e d g l a s s tubings s e v e r a l t i m e s l o n g e r than the s a m p l e

A f t e r the i r r a d i a t i o n , the l o w e r part of the tubing, with the s a m p l e , i s kept in l iquid n i t rogen , whi le the upper end i s heated to annea l the rad ia t ion c h a n g e s . A f t e r w a r d s the en t i re tube i s c o o l e d aga in , turned round and the s a m p l e pushed into the r e g e n e r a t e d part .

(i i) I rrad ia t ion , o r shaping in a t h i n - w a l l tubing m a d e of o r g a n i c m a t e r i a l , r e s i s t a n t to l ow t e m p e r a t u r e

P l a s t i c m a t e r i a l m a y be d e s t r o y e d and d i s c a r d e d b e f o r e or a f t e r the i r r a d i a t i o n . T h i s t echnique e n t a i l s the danger of contaminat ion of the s a m p l e with o r g a n i c m a t e r i a l b e c a u s e the i n v e s t i g a t e d s o l u t i o n s a r e u s u a l -l y a c t i v e [61].

( i i i) A p p l i c a t i o n of i n t e r n a l s o u r c e s of l o w - r a n g e radiat ion that a r e unable to p e n e t r a t e c o n s i d e r a b l y the m a t e r i a l of the v e s s e l o r tubing

T h i s t echnique i n t r o d u c e s s i g n i f i c a n t c h a n g e s into the r a d i a t i o n -induced p r o c e s s , b e c a u s e the rad ia t ion f r o m the i n t erna l s o u r c e has , a s a ru le , an L E T va lue h igher than the L E T of g a m m a rad ia t ion and c a u s e s . t h e r m a l s p i k e s in the s y s t e m [62].

(iv) D i r e c t i r r a d i a t i o n of the s a m p l e in l iquid n i t r o g e n B e c a u s e of t r o u b l e s c a u s e d b y the c o n s t r u c t i o n m a t e r i a l s of the v e s s e l , the

d i r e c t i r rad ia t ion of the s a m p l e in l iquid n i t rogen i s s o m e t i m e s appl ied . F o r e x a m p l e , in the c a s e of aqueous s o l u t i o n s (Ref.[63]), the s o l u t i o n s w e r e rapid ly f r o z e n in 2 m m i. d. P y r e x tubes in l iquid n i t r o g e n to g ive opaque c r y -

P L - 2 3 6 / 1 8 5

s t a l l i n e s o l i d s . The r e q u i r e d l engths w e r e cut off f r o m t h e s e , and the i c e c y l i n d e r s w e r e pushed out into 4 m m i. d. P y r e x tubes for i r r a d i a t i o n . The s p e c i m e n s w e r e in contact with l iquid n i t rogen during i r r a d i a t i o n . Rods of the s a m p l e m a y be p r e p a r e d a l s o in a d i f f erent way: Cas t ing of the s a m p l e of the d e s i r e d shape in the mould , m a d e f r o m s o l i d i f i e d m e r c u r y , i s p o s s i b l e . T h i s o p e r a t i o n m a y be p e r f o r m e d in a s i m p l e d e v i c e [64], The s t e e l c y l i n d e r i s f i l l e d to the a p p r o p r i a t e l e v e l wi th m e r c u r y , and a s t e e l rod i n s e r t e d and pos i t i oned . The rod i s shaped a c c o r d i n g to a s t r i c t pa t t ern a c c o r d i n g to the shape and d i m e n s i o n s of the d e s i r e d f r o z e n s a m p l e to be obta ined . The f i l l e d d e v i c e i s l o w e r e d into l iquid n i t rogen and kept t h e r e unti l the m e r c u r y i s s o l i d i f i e d . B e c a u s e of the shr inkab i l i t y of m e r c u r y , the rod i s e a s i l y r e m o v e d and the whole d e v i c e thoroughly f r o z e n with l iquid n i t r o g e n . The r o o m p r e v i o u s l y o c c u p i e d by the s t i c k i s then f i l l e d with the i n v e s t i g a t e d l iquid in which, at the f ina l p h a s e of o p e r a t i o n , the p la t inum e y e i s f ixed .

F u r t h e r e x p e r i m e n t a l p r o b l e m s c o n c e r n the p u r i f i c a t i o n of s a m p l e s . L o w - t e m p e r a t u r e rad ia t ion c h e m i s t r y has r e v e a l e d new kinds of i m -p u r i t i e s . Johnson and A l b r e c h t [65], f or i n s t a n c e , r e p o r t that CO2 i s an e f f i c i e n t e l e c t r o n trap in 3 - m e t h y l p e n t a n e at 7 7°K. U s u a l l y the p r e s e n c e of CO2 i s not p r e v e n t e d by convent iona l v a c u u m d e g a s s i n g t e c h n i q u e s .

4. 2. Addi t ional data n e e d e d for e x p e r i m e n t a l work and in terpre ta t ion in the f i e l d of l o w - t e m p e r a t u r e radiat ion c h e m i s t r y

In th i s s u r v e y the point has been f requent ly s t r e s s e d that the r e -s e a r c h e r in th i s f i e l d i s l ack ing m a n y data. T h e s e m a y be div ided into two g r o u p s : the f i r s t i s c o n n e c t e d with the technique of i r r a d i a t i o n , the s e c o n d with in terpre ta t ion .

In the f i r s t group we s h a l l put data c o n n e c t e d with the p h y s i c p c h e m i c a l p r o p e r t i e s of f r o z e n l i q u i d s . T h e r e a r e p r a c t i c a l l y no data on d e n s i t i e s of s a m p l e s . F o r i n s t a n c e , it i s known that aqueous s o l u t i o n s of s o d i u m h y d r o x i d e behave l i k e w a t e r up to the c o n c e n t r a t i o n of about 6N, n a m e l y the d e n s i t y of a lka l ine i c e i s l o w e r than the l iquid p h a s e . At h igher c o n -c e n t r a t i o n s the d e n s i t y i s h igher , which m e a n s that the l iquid i s shr ink ing at f r e e z i n g . S i m i l a r p h e n o m e n a o c c u r in o t h e r l iqu ids ; th i s c o m p l i c a t e s the p r e p a r a t i o n of s a m p l e s and m a k e s the exac t c a l c u l a t i o n of d o s e s i m p o s s i b l e .

T h e r e a r e a l s o no data on the b e h a v i o u r of d i s s o l v e d g a s e s in the p r o -c e s s of f r e e z i n g , both with r e s p e c t to the h o m o g e n e i t y of the f r o z e n s a m p l e and to the f o r m a t i o n of p o r o s i t y (vo ids ) .

In the s e c o n d group w e e n c o u n t e r a l l the i n f o r m a t i o n on the f r o z e n s t a t e c o n n e c t e d with the i n t e r p r e t a t i o n of r e s u l t s . A s w a s s t r e s s e d in p r e v i o u s s e c t i o n s one e n c o u n t e r s a s e r i o u s lack of i n f o r m a t i o n on the s t r u c t u r e , both on the m o l e c u l a r and the m a c r o s c o p i c l e v e l , h o m o g e n e i t y and p h a s e c h a n g e s during w a r m i n g . T h e equ i l ibr ia at l ow t e m p e r a t u r e s and how f a r our s y s t e m i s f r o m the e q u i l i b r i u m , what f o r c e s a r e a c t i v e in the f r o z e n s y s t e m , a r e a l s o unknown. C o n s e q u e n t l y , the k i n e t i c s of r e a c h i n g the e q u i l i b r i u m a r e u s u a l l y not known, in addit ion to the r o l e of d e f e c t s of d i f f erent k inds , the p o s s i b i l i t i e s of f o r m a t i o n and anneal ing of d e -f e c t s c a u s e d by i r r a d i a t i o n , e t c .

The lack of m e a s u r e m e n t s i s not c a u s e d by lack of appropr ia te e x -p e r i m e n t a l m e t h o d s . The e x i s t i n g t e c h n i q u e s m a y b e adapted, and in


m a n y c a s e s a r e a l r e a d y adapted, for m e a s u r e m e n t s at low t e m p e r a t u r e s , and a r e wai t ing for e x p e r i m e n t a l r e a l i z a t i o n . We a r e inc l ined to put f i r s t e l e c t r o n m i c r o s c o p y , X - r a y s t r u c t u r a l a n a l y s i s , neutron d i f f rac t ion , d i f -f e r e n t i a l t h e r m a l a n a l y s i s , o p t i c a l m i c r o s c o p y , autoradiography , a l l of w h i c h a r e c o n n e c t e d wi th m e t h o d s of making d e f e c t s and m a c r o s c o p i c s t r u c t u r a l d e t a i l s v i s i b l e .

T h e r e i s no doubt that s t r u c t u r a l i n v e s t i g a t i o n at l ow t e m p e r a t u r e i s not s i m p l e , and in future w i l l demand c o n s i d e r a b l e e x p e r i m e n t a l s k i l l and the d e v e l o p m e n t of to ta l ly new a p p r o a c h e s . Unfortunate ly they a r e on ly addi t ional to the m a i n p r o b l e m s of l o w - t e m p e r a t u r e rad ia t ion c h e m i s t r y and t h e r e f o r e not v e r y a t t r a c t i v e . N e v e r t h e l e s s , if l o w - t e m p e r a t u r e r a d i a -t i on c h e m i s t r y i s to be deve loped they have to be t a c k l e d .

R E F E R E N C E S

SYMONS, M. C. R . , Symposium II, Paper No. 8, 3rd Int. Congress on Radiation Research, Cort ina d ' A m p e z z o , 1966. MATHESON, M. S . , Nucleonics 19 10 (1961) 57. SHARPATYI, W . A . , U s p . K h i m . 32 (1963) 737. BURR, I. G . , Nucleonics 19. 10 (1961) 49. KROH, J . , SPINKS, J . , Roczn. C h e m . 36 (1962) 563. KROH, J . , CZERWIK, Z . , Bull. Acad . pol . Sci. S6r. Sci . c h i m . 14 (1966) 245. ZAG6RSKI, Z . P . , WEIMANN, L . , IBJ Rep. 549/XVII (1964). ZAGORSKI, Z . P . , P r o c . S y m p . R a d i a t i o n Chemis t ry , T ihany , Hungary (1962) 405. TAYLOR,, E. H . , J. c h e m . Educ. 36 (1959) 396. FALCONER, W. E. , SALOVEY, R. , J. c h e m . Phys. 46 (1967) 387. MOORTHY, P . N . , WEISS, J . J . , in Solvated Electrons (HART, E . J . , Ed.) , Amer ican C h e m i c a l Soc. Publ icat ions , Washington, D. C. (1965) 180. DAINTON, F . S . , SALMON, G. A . , TEPLY, J . , Proc. R. Soc. A 286 (1965) 27. RONAYNE, M . R . , GUARINO, J . P . , HAMILL, W. H. , J. Am. c h e m . Soc. 8 4 ( 1 9 6 2 ) 4230. DAINTON, F. S . , SALMON, G. A . , in Energy Transfer in Radiat ion Processes (PHILLIPS, G. O . , Ed.) , Elsevier, Ams te rdam (1966) 85. DYNE, P . J . , MILLER, O. A . , C a n . J . C h e m . 43 (1965) 2696.

SUKHOV, F . F . , IL'ICHEVA, Z . F . , SLOVOKHOTOVA, N . A . , MARGOLIN, D . M . , TEREKHOV, V. D . , Kh imiya vys. Energii 1 (1967) 58. ZAGORSKI, Z . P . , KOSEK, S . , IBJ Rep. 431/XVII (1963). MINC, S . , ZAG6RSKI, Z . P . , Nature,Lond. 193 (1962) 1290. DONDES, S . , HARTECK, P . , KUNZ, C . , Radiat. Res. 27 (1966) 174. SPURNY, Z . , A tom. Energy Rev. 3 2 (1965) 61. BROCKLEHURST, B . , PORTER, G . , YATES, J. M . , J .phys. C h e m . 68 (1964) 203 . SKELLY, P . W . , HAMILL, W. H . , J. c h e m . Phys. 43 (1965) 3497. TOCHIN, V. A . , NIKOL'SKH, V. G . , BUBEN, N. Y a . , Kh imiya vys. Energii 1 (1967) 71. SHIDA, T . , HAMILL, W. H . , J . c h e m . Phys. 44 (1966) 2369. SOROKIN, Y u . A . , KOTOV, A. G . , PSHEZHETSKII, S . Y a . , Z h . f i z . k h i m . 40 (1966) 2277. BURTON, M . , DILLON, M . , REIN, R. , J . c h e m . Phys. 41 (1964) 2228. FUNABASHI, K . , HARLEY, P . J . , BURTON, M . , J . c h e m . P h y s . 43 (1965) 3939. JANSSEN, O . , FUNABASHI, K . , J . c h e m . Phys. 46 (1967) 101. VOEVODSKII, V. V . , ERMOLAEV, V. K . , SOLOVYCH, N. A . , in Radiat ion Chemis t ry 2 (DODO, J . , HEDVIG, P . , Eds), A k a d e m i a i K iado , Budapest (1967). T E P L f , J . , JANOWSKY, Rep. UJV-1739 (1967). HENRIKSEN, T . , Acta c h e m . scand. 20 (1966) 2898. KARZMARK, C . J . , FOWLER, J . F . , WHITE, J. T . , Int . J. appl . Radiat . Isotopes 17 (1966) 161. DYNE, P . J . , t lENHARTOG, J . , Nature , Lond. 202 (1964) 1105. KROH, J . , KAROLCZAK, S . , Nature, Lond. 201 (1964) 66. RIEHL, N . , in Energy Transfer in Radiat ion Processes (PHILLIPS, G . O . , Ed.) , Elsevier, Amste rdam (1966) 95.

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[36] SMALLER, B. , MATHESON, M . S . , YASAITIS, E. L., Phys. Rev. 94 (1954) 202. [31] LIVINGSTON, R. , ZELDES, H. , TAYLOR, E. H . , Phys. Rev. 94 (1954) 725. [38] LIVINGSTON, R. , ZELDES, H. , TAYLOR, E.'H. , Discuss. Faraday Soc. 19 (1955) 166. [39] GHORMLEY, J. A . , STEWART, A. C. , J. Am. chem. Soc. 78 (1956) 2934. [40] SIEGEL, S . , BAUM, L. H . , SKOLNIK, S . , FLOURNOY, J. M . , J. chem. Phys. 32 (1960) 1249. [43] SIEGEL, S. , FLOURNOY, J. M . , BAUM, L. H . , J. chem. Phys. 34 (1961) 1782. [42] SCHULTE-FROHLINDE, D . , EIBEN, K. , Z.Naturf. 17A (1962) 445. [43] ERSHOV, B. G. , PKAEV, A. K. , Khimiya vys. Energii 1 (1967) 29. [44] HENRIKSEN, T . , Radiat. Res. 23 (1964) 63. [45] ZAG6RSKI, Z . P . , MINC, S . , Paper No. 950 , 3rd Int. Congress on Radiation Research,

Cortina d 'Ampezzo , 1966. [46] SHIDA, T . , HAMILL, W. H . , J. chem. Phys. 44 (1966) 2375. [47] GALLIVAN, J. B. , HAMILL, W. H . , J. chem. Phys. 44 (1966) 2378. [48] TSUJI, K . , YOSHIDA, H. . HAYASHI, K . , J. chem. Phys. 46 (1967) 810. [49] CHARLESBY, A . , Paper No. 49, 3rd Int. Congress on Radiation Research, Cortina d 'Ampezzo ,

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[50] DOLE, M . , BODILY, D. M . , Paper No. 50, 3rd Int. Congress on Radiation Research, Cortina d'Ampez^o, 1966.

[51] MOZISEK, M . , in Radiation Chemistry 2 (DOD6, J. , HEDVIG, P . , Eds), Akademiai Kiad<5, Budapest (1967).

[52] ORMEROD, M. G . , ALEXANDER, P . , Nature, Lond. 193 (1962) 290. [53] ORMEROD, M. G . , ALEXANDER, P . , Radiat. Res. 18 (1963) 495. [54] HENRIKSEN, T . , SAUNER, T . , PIHL, A . , Radiat. Res. 18 (1963) 163. [55] ALEXANDER, P . , ORMEROD, M. G . , "Repair of the primary chemica l lesion: a unitary hypothesis

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PULSE RADIOLYSIS

D.F. SANGSTER AUSTRALIAN ATOMIC ENERGY RESEARCH ESTABLISHMENT, LUCAS HEIGHTS, N S . W . , AUSTRALIA

Abstract

PULSE RADIOLYSIS. The technique of pulse radiolysis enables one to examine the early species formed in radiolysis and to study their reactions. There remains much work to be done in the microsecond to mil l isecond region. Recent advances include techniques with a t ime resolution of less than one nano-second. This enables one to study the "primary species" present in the so-cal led spur region. These reactions could be important in the concentrated solutions that are l ikely to be encountered in practical applications.

P u l s e r a d i o l y s i s i s the technique w h e r e b y a s y s t e m i s subjec ted to an in tense p u l s e of ioniz ing radiat ion, u sua l l y an e l e c t r o n beam, for a v e r y shor t t i m e - m i c r o s e c o n d s or n a n o s e c o n d s . The ensuing c h e m i c a l r e a c t i o n s can then be fo l lowed during the pu l se or over a further in terva l of t i m e with d e t e c t o r s capable of v e r y rapid r e s p o n s e t i m e s . Since the c h e m i c a l s p e c i e s p r e s e n t during the v e r y e a r l i e s t s t a g e s of the r e a c t i o n can thus of ten be ident i f ied , m e a s u r e d and fo l lowed, this has proved a m o s t va luable method of de termin ing the m e c h a n i s m of rad io ly t i c r e a c t i o n s .

R e v i e w a r t i c l e s [1, 2] a r e ava i lab le on the subject , and two r e c e n t c o n f e r e n c e p r o c e e d i n g s have been publ i shed in book f o r m [3, 4] . The k ine t i c s of the r e a c t i o n s of the hydrated e l e c t r o n have been studied e x -t e n s i v e l y , and a number of r e a c t i o n - r a t e cons tants have been m e a s u r e d . T h e s e have been tabulated by Anbar and Neta [5] . A number of other t rans ient s p e c i e s , u sua l l y radica l s p e c i e s or exc i ted s t a t e s , have been ident i f ied and c h a r a c t e r i z e d .

PRINCIPLES

E s s e n t i a l l y , a shor t pulse of ioniz ing radiat ion i s d e l i v e r e d to the s y s t e m being inves t iga ted , and the appearance and d i sappearance of c h e m i c a l s p e c i e s s tudied over the ensuing t i m e in terva l . U s u a l l y the radiat ion s o u r c e i s an e l e c t r o n a c c e l e r a t o r of energy 1 - 1 6 m i l l i o n v o l t s and a current of 1 - 2 0 0 mA. The pu l se duration i s 0.1-10/LIS. The s y s t e m can be so l id , l iquid or g a s e o u s , or a so lut ion . Of c o u r s e , the e x p e r i m e n t a l a r r a n g e m e n t s m a y be d i f ferent in each c a s e .

Any m e a n s can be used to detect the s p e c i e s formed , prov ided it i s s e n s i t i v e to s m a l l concentrat ions or s m a l l changes in concentrat ion , and i t s t i m e of r e s p o n s e short enough to fo l low the changes . Optical absorpt ion , conduct iv i ty and, r e c e n t l y , po larography have been u s e d . E l e c t r o n sp in r e s o n a n c e has a l i m i t e d applicat ion, but the s c a n t i m e i s ra ther long for convenience ; h o w e v e r , it can g ive va luable in format ion on the s t r u c t u r e of the rad ica l s p e c i e s f o r m e d . Conductivity i s not v e r y s e l e c t i v e b e c a u s e any ionic s p e c i e s wi l l g i v e a s i gna l . U l t r a - v i o l e t and v i s i b l e a b s o r t i o m e t r y

8 9

90 SANGSTER

has been the most widely used technique, and it can g ive some information on the probable structure of the s p e c i e s formed. A great number of the s p e c i e s formed show absorption bands.

RECENT DEVELOPMENTS

An idea of the variety of problems and s y s t e m s that have already been studied can be obtained from the r e f e r e n c e s and f rom the chemical l i t erature .

The number and nature of the anci l lary techniques that can be used with pulse rad io lys i s are constantly being extended. Under a high p r e s s u r e of hydrogen gas (100 atm) all the oxidizing rad ica l s in aqueous solution are converted to reducing radica l s , and this s i m p l i f i e s the problems considerably .

Gaseous s y s t e m s have a l s o been studied. A start has been made on studying the photochemistry of the short - l ived transient s p e c i e s - a combination of pulse rad io lys i s with f lash photo lys i s .

Over the past few months measurement t i m e s have become increas ing ly shorter as machines have been commiss ioned giving intense e lec tron p u l s e s last ing about 1 ns . One of the most recent u t i l i ze s the f ie ld e m i s s i o n principle as a source of e lec trons . The importance of this short t ime interval i s that one can now study "spur" react ions - the react ions that are l ikely to predominate in the more concentrated "practical" s y s t e m s that would be expected in industrial applications.

We can expect to s e e further extensions of the techniques in the near future. Perhaps l a s e r s will find an application here in following s o m e of the s p e c i e s . F a s t e r i . r . detectors are being developed. The kinet ics of var ious f r e e radical and ion-molecu le react ions wil l be worked out, and their transit ion complexes pos i t ive ly identif ied. We can expect to have spectra l tables to a s s i s t in identifying all manner of shor t - l ived s p e c i e s .

ACCESS

P u l s e rad io ly s i s fac i l i t i e s are expensive both in capital cost and operation, although s o m e exist ing acce lerat ing machines have been m o d i -f ied at reasonable cos t . Custodians of these fac i l i t i e s have been e x t r e m e -ly generous in allowing other groups to use them. The use fu lnes s of pulse rad io lys i s i s such that all invest igators should cons ider whether it can a s s i s t in solv ing their prob lems .

INSTALLATIONS

In s o m e centres there are pulse rad io lys i s fac i l i t i e s that have been operating for s o m e y e a r s : Argonne National Laboratory; Mount Vernon Hospital, London; Paterson Laboratory, Manchester Hospital; Univers i ty of Notre Dame, United States of America; Brookhaven National Laboratory; Du Pont R e s e a r c h Laboratory; Mellon Institute; CEN, Saclay.

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Others c o m m i s s i o n e d m o r e r e c e n t l y a r e : Cookridge Radiat ion Centre , L e e d s ; Oak Ridge National Laboratory; Ohio State Univers i ty ; Ri s^ , Denmark; Hahn-Mei tner Institut, Ber l in ; Genera l A t o m i c s , San Diego; and Nat ick R e s e a r c h Center .

VALUE OF P U L S E RADIOLYSIS

The va lue of the technique l i e s in the fact that one i s able to obtain an understanding of the ear ly , and p r e v i o u s l y i n a c c e s s i b l e , r e a c t i o n s . F o r m e r l y , induct ive reason ing had to be u s e d . The radiat ion c h e m i s t , knowing how the f inal products a l t e r e d a s condi t ions w e r e changed, argued back to the i n t e r m e d i a t e and p r i m a r y s p e c i e s . Now it i s p o s s i b l e to ident i fy and m e a s u r e many of the t rans i en t s p e c i e s p r e s e n t during the f i r s t few mi l l i on ths of a s econd of r e a c t i o n when radiat ion i n t e r a c t s with m a t t e r . Even l e s s i s unders tood about what happens in n o n - p o l a r l iqu ids .

B io log i ca l and b i o c h e m i c a l

E x p e r i m e n t s in radiat ion b io logy show the s o r t of p r o b l e m involved , but the s i m p l e s t b io log ica l s y s t e m i s s o c o m p l e x that even a part ia l s o l u -t ion i s m o s t unl ike ly to be found. An unders tanding of the rad ia t ion c h e m i s t r y of s i m p l e r c h e m i c a l s (model compounds) i s b e c o m i n g p o s s i b l e . This understanding can be expected to be extrapolated to s i m p l e b i o l o g i c a l c e l l s along such paths as that through p r o t e i n s and nuc le i c a c i d s .

Aqueous and po lar s o l v e n t s

D e s p i t e the g r e a t amount of work that has been done on aqueous s y s t e m s , the nature , y i e ld and spat ia l d i s tr ibut ion of the e a r l i e s t p h y s i c o -c h e m i c a l s p e c i e s i s not cer ta in . Rather m o r e i s known about the l a t e r c h e m i c a l en t i t i e s ( s o - c a l l e d " p r i m a r y s p e c i e s " ) but e v e n h e r e t h e r e a r e d i s c r e p a n c i e s . V e r y l i t t l e i s known about y i e l d s and r e a c t i o n s in a lkal ine so lut ions (pH13) , and independent i n v e s t i g a t o r s have a r r i v e d at s o m e w h a t d i f ferent v a l u e s . T h i s r e f l e c t s the inadequacy of our knowledge of the ear ly e v e n t s . The e a r l y work w a s done on di lute so lu t ions b e c a u s e t h e s e a r e s o m e w h a t s i m p l e r but r e c e n t l y the work on m o r e concentra ted so lu t ions has i n c r e a s e d . It i s expec ted that many i n t e r e s t i n g phenomena wi l l be found. Concentrated so lut ions a r e c l o s e r to what can be expec ted in industr ia l p r a c t i c e .

Of the po lar so lvent s y s t e m s other than aqueous s y s t e m s , the m o r e i n t e n s i v e l y i n v e s t i g a t e d ones a r e methano l i c and ethanol ic s o l u t i o n s . The o lder data on y i e l d s , e t c . , are being r e - i n v e s t i g a t e d at p r e s e n t .

P o l y m e r s

P o l y m e r s have been dealt with in detai l during th is Pane l m e e t i n g . It i s s t i l l debatable whether ionic or rad ica l m e c h a n i s m s operate in the v a r i o u s p o l y m e r i z a t i o n r e a c t i o n s . S o l i d - s t a t e p o l y m e r i z a t i o n induced by radiat ion i s an in t ere s t ing f i e ld .

92 SANGSTER

C O N C L U S I O N

The full impact of the technique of pulse rad io ly s i s i s only now b e -ginning to be fe l t . At las t we have a method of determining what i s happening at the very beginning of the radiation chemical reac t ions , and of studying the react ions of the transient s p e c i e s . This opens up what i s v irtual ly a new world of chemis try that wil l go far beyond the bounds of present -day radiation chemis try .

R E F E R E N C E S

[ 1 ] DORFMAN. L . M . , MATHESON, M . S . , in Progress in Reaction Kinetics 3 (PORTER, G . . Ed.) Pergamon, Oxford (1965) 237 .

[ 2 ] SANGSTER, D . F . , Atomic Energy in Australia 8 3 (1965) 13. [31 The Solvated Electron, Advances in Chemistry Series, N o . 5 0 , American Chemical Society (1965) . [ 4 ] EBERT, M . , KEENE, J . P . , SWALLOW, A . J . , BAXENDALE, I . H . (Eds), Pulse Radiolysis, Academic

Press, London (1965) . [ 5 ] ANBAR, M . , NETA, P . , Int. J. appl. Radiat. Isotopes 16 (1965) 227; Israel Atomic Energy Commission,

Rep. I . A . 1079 (1966) .

L E D E V E L O P P E M E N T DE LA RADIOCHIMIE Q u e l q u e s a s p e c t s de l a c o n j o n c t u r e

P. LEVEQUE ET J. R. PUIG

CENTRE D'ETUDES NUCLEAIRES DE SACLAY,

FRANCE

Abstract — Résumé

DEVELOPMENTS IN RADIOCHEMISTRY: SOME ASPECTS OF THE PRESENT SITUATION. The situation in radiochemistry during 1966-67 in France is described. The principal features are the appearance and ecorfomic exploitation of powerful irradiation facilities, and the increased emphasis being placed on the industrial nature of development studies. Basic research is being maintained, particularly in macromolecular chemistry.

LE DEVELOPPEMENT DE LA RADIOCHIMIE; QUELQUES ASPECTS DE LA CONJONCTURE. Les auteurs présentent une analyse de la conjoncture française en 1966-1967 dans le domaine de la radio-chimie. Cette conjoncture se caractérise par l 'apparition et l 'utilisation économique de puissantes installations d'irradiation, ainsi que par des études techniques dont le caractère industriel est de plus en plus accusé. La recherche fondamentale est toujours soutenue, notamment dans le domaine de la chimie macromoléculaire .

Depuis quelques années la physionomie de la situation en m a t i è r e de chimie des radia t ions subit une évolution profonde. Une p r i s e de conscience semble se f a i r e dans l ' i ndus t r i e . Des s ec t eu r s nouveaux voient dans cet te technique un moyen de production et d ' innovation à ne pas négl iger . Des procédés nouveaux sont développés. Sur le plan internat ional la coopérat ion s ' i n s t au re , soit de façon b i la té ra le , soit pa r le t ruchement d ' o rgan i smes internationaiux.

Dans quelles conditions cette évolution se f a i t - e l l e? C 'es t ce que nous e s s a i e r o n s d ' ana lyse r . Il nous para î t que, si des réalisations à une échelle beaucoup plus grande que par le pas sé sont m i s e s en oeuvre, l e s succès e n r e g i s t r é s sont autant de cas pa r t i cu l i e r s qui rendent difficile tout pronost ic d ' o r d r e généra l au t re que celui d 'une accé lé ra t ion des r e c h e r c h e s au cours des années à ven i r .

L 'appar i t ion d ' ins ta l la t ions d ' i r r ad ia t ion à grande échelle au cours des d e r n i è r e s années es t un phénomène remarquab le qui se fait s en t i r auss i bien dans la r eche rche que dans l ' i ndus t r i e de l ' i r r ad i a t i on . Nous énumére rons c i -des sous les pr inc ipa les instal la t ions f r a n ç a i s e s .

1) L ' ins ta l la t ion du Centre lyonnais d 'applicat ion atomique. Cette instal la t ion déjà ancienne a été rénovée en 1966 et dotée de deux sys t èmes de convoyeurs: un sys t ème à balancel les permet tan t le chargement continu depuis une zone externe et un convoyeur semi-cont inu dit convoyeur c a r r é , semblable à celui d'IRMA. La source de cobal t -60 atteint actuel lement environ 100 000 Ci.

2) L ' i r r a d i a t e u r mobile autonome (IRMA). Cet appare i l a déjà, été décr i t . L 'exploi tat ion s ' en poursui t de façon sa t i s fa i san te avec la source de 170 000 Ci de cés ium-137 dont il es t pourvu.

93

94 LEVEQUE e t PUIG

Ces deux ins ta l la t ions sont gé rées pa r la socié té Conservatome Indus t r ie . Deux t r a i t emen t s radiochimiques y sont r éa l i s é s en plus des t r a i t emen t s de radio pas teur isa t ion, rad ios té r i l i sa t ion et rad io-inhibition; ce sont la fabr ica t ion d'un film de polyethylene ré t iculé , le «Giro lène» , dont le m a r c h é se développe, et la fabr ica t ion de « b o i s -plast ique» pour lequel cette société a fait une enquête de marché appro-fondie et qui l a i s s e en t revoi r des débouchés sé r ieux .

3) Le CARIC (Centre d 'application des radia t ions ionisantes de Corbevil le) . Ce cent re est gé ré pa r une en t r ep r i se pr ivée (SRTI) et

mobi l i se l ' a c c é l é r a t e u r l inéa i re CIRCE., Cette instal la t ion fonctionne depuis l ' é t é 1966 et donne toute sa t i s fac t ion . CIRCE fournit un fa i sceau de 8 à 10 kW d ' é l ec t rons de 7 MeV et es t ut i l isé pr incipalement pour la s t é r i l i sa t ion méd ica le . De nombreuses i r r ad ia t ions de r eche rche y sont e f fec tuées sous contra t , notamment une étude de développement de la radiovulcanisat ion du la tex.

4) Le C o m m i s s a r i a t à l ' éne rg ie atomique est en t r a i n de s ' équ ipe r de nouveaux moyens puissants qui viendront p rendre la suite de l 'uni té re la t ivement modes te qui fonctionne à Saclay depuis 1960 ( accé lé ra t eu r l i néa i r e Mévadyne de 4 MeV et 0, 2 kW, i r r a d i a t e u r panoramique de 10 kCi PAGURE). Les p r o g r a m m e s d 'extension concernent :

a) Un l abora to i r e de technologie de l ' i r r ad ia t ion , qui a commencé à fonctionner au Centre de Grenoble . Il comprend une casemate s u r p isc ine d'une capaci té de 100 000 Ci de cobal t -60. Ce l abora to i r e étudie expér imenta lement l e s p rob lèmes de configurat ion et de fabr ica t ion des sou rces ; il a m i s au point des méthodes de calcul FORTRAN donnant l e s solutions d 'une v a r i é t é de p rob lèmes de configurat ion et d ' au toabsorp -t ion. Cette ins ta l la t ion abr i te auss i des expér iences de génie radiochimique, notamment une boucle dest inée à la polymér isa t ion en phase liquide à 300°C et une boucle dest inée à la polymér isa t ion en phase gazeuse à p r e s s ion élevée.

b) Un cen t re d 'appl icat ion des rayonnements ionisants , qui s e r a implanté au Centre de Saclay et pos séde ra essen t ie l lement deux c a s e m a t e s su r piscine d 'une capaci té de 106 Ci de cobalt-60, un a c c é l é r a t e u r d ' é l ec t rons de 3 MeV et 3 kW et un a c c é l é r a t e u r fournissant des impul-s ions uniques de quelques nanosecondes .

P a r a i l l eu r s , PAGURE s e r a renforcé , l ' ac t iv i t é de sa sou rce passan t à 20 kCi au cours du p r e m i e r s e m e s t r e de 1967. Un cer ta in nombre de p r o j e t s qui, il y a seulement cinq ans, aura ient paru ex t r êmement ambit ieux sont donc en cours de réa l i sa t ion et m ê m e d 'exploi tat ion. Ceci n ' a évidemment é té poss ib le que g râce à ce r t a ins succès de la r e c h e r c h e qui ont coïncidé avec une si tuation commerc i a l e f avorab le .

Dans ce qui suit , nous décr ivons succinctement l es act ivi tés déployées en F r a n c e dans l e s d i f fé ren t s s e c t e u r s de la r e c h e r c h e ou de l ' explo i ta -t ion en rad ioch imie .

La r eche rche radiochimique en F r a n c e remonte , on le sa i t , au début des années 50. On peut cons ta te r aujourd 'hui que, insens ib les aux en thous iasmes ou aux scep t i c i smes i r r a i s o n n é s , des c h e r c h e u r s ont accumulé , en dépit des nombreux a léas auxquels i ls ont dû f a i r e f ace .

P L - 2 3 6 / 8 95

une quanti té de r é s u l t a t s dont c e r t a i n s p r é s e n t e n t d e s a t t r a i t s c o m m e r c i a u x e t cons t i tuent donc d e s d o m a i n e s de v a l o r i s a t i o n é c o n o m i q u e de l a r a d i o -c h i m i e . D i v e r s d e g r é s d ' a v a n c e m e n t d e s t r a v a u x ont t o u t e f o i s é t é a t t e in t s :

C o m m e r c i a l i s a t i o n

- G i r o l è n e

D é v e l o p p e m ent

- B o i s - p l a s t i q u e - L a t e x r a d i o v u l c a n i s é - P o l y m é r i s a t i o n ( t r i o x a n e , o l é f i n e s )

R e c h e r c h e appl iquée

- R a d i o s y n t h è s e de l ' h y d r a z i n e - G r e f f a g e s d i v e r s , t e x t i l e s ou a u t r e s p o l y m é r i s a t i o n s - S y n t h è s e s d i v e r s e s - R e t i c u l a t i o n d e s p o l y m è r e s

R e c h e r c h e de b a s e

- P o l y m é r i s a t i o n en p h a s e s o l i d e c r i s t a l l i n e ou v i t r e u s e ( l a b o r a t o i r e du D r Chapiro)

- G r e f f a g e ( l a b o r a t o i r e du P r Magat - l a b o r a t o i r e dû D r Chapiro)

C o n s t r u c t i o n d ' i n s t a l l a t i o n d ' i r r a d i a t i o n

- C o n s e r v a t o m e Industr ie ( C o - 6 0 , C s - 1 3 7 ) - C o m p a g n i e de t é l é g r a p h i e s a n s f i l ( C S F ) , a c c é l é r a t e u r l i n é a i r e du

type CIRCE - SAMES ( a c c é l é r a t e u r é l e c t r o s t a t i q u e )

L a s i tua t ion a c t u e l l e o f f r e donc aux r a d i o c h i m i s t e s q u e l q u e s m o t i f s de s a t i s f a c t i o n , m a i s s i l ' on c o n s i d è r e que nous v o y o n s l à l ' a b o u t i s s e -ment d'une quinza ine d ' a n n é e s d ' e f f o r t s , i l apparaî t que l e d é v e l o p p e m e n t de l a r a d i o c h i m i e a é té r e l a t i v e m e n t l ent , et c e l a en r a i s o n de d i f f i c u l t é s de t o u s o r d r e s .

L a p r i n c i p a l e d i f f i c u l t é que r e n c o n t r e n t e n F r a n c e l e s p r o m o t e u r s de l a c h i m i e d e s r a d i a t i o n s t ient ci l ' i g n o r a n c e ou au s c e p t i c i s m e de l ' i n d u s t r i e jo in t s au r e f l e x e de cra in te que provoque t o u j o u r s l ' é v o c a t i o n d e s r a y o n n e -m e n t s i o n i s a n t s . Il faut b ien l e d i r e a u s s i , de n o m b r e u s e s t â c h e s p r i o r i -t a i r e s ont e m p ê c h é pendant l o n g t e m p s l e s e n t r e p r i s e s publ iques et p r i v é e s et l e s c e n t r e s de r e c h e r c h e s p u b l i c s e u x - m ê m e s de c o n s a c r e r d e s m o y e n s i m p o r t a n t s e n p e r s o n n e l e t en capi taux à un d o m a i n e de l a r e c h e r c h e où l e s p o s s i b i l i t é s d ' innovat ion demandent un e f f o r t d ' i m a g i n a -t ion que ne v i e n t a i g u i l l o n n e r aucune c o n c u r r e n c e é t r a n g è r e .

Aujourd'hui , c e s f a c t e u r s tendent à d i s p a r a î t r e . En o u t r e , depuis deux ans l e s a c t i o n s s t i m u l a n t e s s e font p lus e f f i c a c e s .

En F r a n c e , l e C o m m i s s a r i a t à l ' é n e r g i e a tomique s ' e s t appl iqué à d é f i n i r une pol i t ique d ' a s s o c i a t i o n a v e c l ' i n d u s t r i e e n prenant à s a c h a r g e l a p lus grande par t i e d e s r i s q u e s et d e s c h a r g e s f i n a n c i è r e s . P a r a i l l e u r s , i l a m u l t i p l i é l e s c o l l a b o r a t i o n s p a r d e s c o n t r a t s b i l a t é r a u x

9 6 LEVEQUE e t PUIG

a v e c d e s f i r m e s i n t é r e s s é e s . L ' A s s o c i a t i o n t echnique pour l ' é n e r g i e n u c l é a i r e a c o n s t i t u é , s o u s l ' i m p u l s i o n du CEA, une c o m m i s s i o n où s e r é u n i s s e n t d e s i n d u s t r i e l s et d e s c h e r c h e u r s qui par t i c ipent au d é v e l o p p e -m e n t de la r a d i o c h i m i e , au n o m b r e d'une t r e n t a i n e e n v i r o n . Le CEA c o l l a b o r e , par d e s é c h a n g e s de p e r s o n n e l et d ' i n f o r m a t i o n s et par une c o o r d i n a t i o n d e s e f f o r t s , a v e c l e Japan A t o m i c E n e r g y R e s e a r c h Ins t i tu te . Il a m i s s u r pied au début de l ' année un c o u r s s u r l a p r é p a r a t i o n et l a m o d i f i c a t i o n d e s p o l y m è r e s par l ' i r r a d i a t i o n qui e s t d i s p e n s é à d e s r e s p o n s a b l e s de l ' i n d u s t r i e e t à d e s u n i v e r s i t a i r e s par l e D r Chapiro et l e P r Hayash i ( U n i v e r s i t é de Kyoto) . Enf in , l e CEA p a r t i c i p e a c t i v e -m e n t aux a c t i o n s e n t r e p r i s e s à l ' é c h e l l e e u r o p é e n n e par l e b u r e a u E u r i s o t o p de l ' E u r a t o m pour l a d i f fus ion d e s c o n n a i s s a n c e s et d e s t e c h n i q u e s r a d i o c h i m i q u e s .

A c t u e l l e m e n t c e s a c t i o n s c o m m e n c e n t à p o r t e r l e u r s f r u i t s , n o t a m -m e n t dans l e d o m a i n e d e s t e x t i l e s et du b o i s .

C o m m e on l e vo i t , i l s e m b l e b ien que l e s condi t ions s o i en t maintenant r é u n i e s pour un e s s o r rapide m a i s r a i s o n n é d e s appl i ca t ions r a d i o c h i m i q u e s . Cependant , i l e x i s t e e n c o r e de n o m b r e u x o b s t a c l e s , qui, en tout é tat de c a u s e , gênent un d é v e l o p p e m e n t que d e s i n s t a n c e s i n t e r n a t i o n a l e s souhai tent e n c o u r a g e r ; e l l e s pourra ient l e f a i r e en contribuant

- ci l a d i f fus ion d e s c o n n a i s s a n c e s et d e s t e c h n i q u e s dans l ' i n d u s t r i e ( enquê te s , sondage) ,

- au sout i en , en capi taux et surtout en p e r s o n n e l , d e s p r o j e t s à l ' é tude dans l e s c e n t r e s b ien é q u i p é s ,

- à l a c e n t r a l i s a t i o n d e s r e n s e i g n e m e n t s et k l e u r d i f f u s i o n par d e s m é t h o d e s r a p i d e s et e f f i c a c e s ( l i t t é r a t u r e , b r e v e t s , t raduc t ions ) ,

- à l ' o r g a n i s a t i o n et au sout ien de l ' e n s e i g n e m e n t d e s d i s c i p l i n e s r a d i o c h i m i q u e s ,

- ^ l a r é d a c t i o n de m o n o g r a p h i e s couvrant d e s d o m a i n e s a v a n c é s de l a t echn ique rad ioch imique ,

- à l a c o o p é r a t i o n i n t e r n a t i o n a l e .

Il ne s ' a g i t l à que de s u g g e s t i o n s qui ne s e veu lent pas l i m i t a t i v e s et dont nous e s p é r o n s q u ' e l l e s apporteront une contr ibut ion p o s i t i v e aux t r a v a u x du Groupe d ' é t u d e .

SYNTHESIS AND DECOMPOSITION INDUCED BY IONIZING RADIATION

SILVIA IONESCU INSTITUTE OF ATOMIC PHYSICS, BUCHAREST, ROMANIA

Abstract

SYNTHESIS AND DECOMPOSITION INDUCED BY IONIZING RADIATION. Syntheses and decompo-sitions that have been studied most are shortly reviewed. Ozone formation and decomposit ion, hydrazine synthesis of ammonia , nitrogen f ixat ion, hydrocyanic acid formation, radiosynthesis with sulphur, products obtained from the radiolysis of COZ l products from radiolysis of hydrocarbons, chlorination reactions, radiochemical oxidations, radiolytic carboxidation, ethylene g lyco l synthesis and nitration of aromatic compounds are described simply.

The methods employed to increase the G-va lue of methane transformation in unsaturated hydrocarbons are discussed.

INTRODUCTION

Ionizing radiat ion o f f e r s a new f o r m of e n e r g y for c h e m i c a l t echno logy . At p r e s e n t the d e v e l o p m e n t of a t echno logy based on the u s e of ioniz ing radiat ion i s e x p e n s i v e and r e q u i r e s s p e c i a l s t u d i e s . Whether such an industry wi l l in fact deve lop i s a p r o b l e m of e c o n o m i c s . A c o m p a r i s o n be tween c h e m i c a l p r o c e s s e s induced by radiat ion and t h o s e a c c o m p l i s h e d by t h e r m a l and e l e c t r i c a l methods s h o w s many p o s s i b i l i t i e s of explo i t ing any advantages inherent in the use of radiat ion. F o r th i s c o m p a r i s o n the c o n s u m e d e n e r g y i s e x p r e s s e d in wat t s . We can r e p r e s e n t the c o n v e r s i o n of wat ts into c u r i e s for g a m m a radiat ion of d i f ferent i n t e n s i t i e s . In th i s c a s e the s o u r c e power i s e x p r e s s e d in watts too .

The n u m b e r of t r a n s f o r m e d m o l e c u l e s for a watt i s

2 - 2 5 I O O ° 2 2 G = 2 - 2 5 X 1 O 2 0 G

The number of k i l o g r a m s for a watt i s

2 . 2 5 X 1 0 2 0 G . M Q 3 7 3 X 1 0 - 6 Q M 6 .02X1023 X 1000 ° - d 7 d X 1 0 G - M

2 . 7 8 X 1 0 6 w h e r e M i s the m o l e c u l a r weight and 1 W / k g = ^

and the s a m e value f o r 1 kW/t . We can expec t that in the n e a r future n u c l e a r e n e r g y w i l l be ava i lab le

f o r c h e m i c a l p r o c e s s e s . F o r such an event we have to c a l c u l a t e the l i m i t s of i t s appl i cab i l i ty . If G = 10 m o l e c u l e s / 1 0 0 eV and the m o l e c u l a r weight

7

9 7

9 8 IONEISCU

M = 100, the energy n e c e s s a r y for the production of 1 kg of this mater ia l

will be 2 ' 7 ° ^ 1 0 6 = 2700 (or 0 . 0 4 4 $ / k g ) . 103 kg 6 '

F o r G = 105 and M = 100, the irradiation cos t wil l be 0. 27 W/kg or 0. 27 kW/t, which makes it very attract ive .

F o r G - v a l u e s of 10 or higher, or for very high molecu lar weight m a t e r i a l s , industrial application i s a poss ib i l i ty . In this c a s e we require a chain react ion to g ive a high G, or a p r o c e s s in which a smal l p e r -centage of chemica l change brings the des ired l arge molecu lar weight change in the product.

F o r an industry to be based on radiation c h e m i s t r y the synthes i s of expens ive m a t e r i a l s , or those which could not be prepared by any other method and where radiation r e p l a c e s the catalyst , would be needed. The penetrating power of ionizing radiation a l lows m o r e uniform r e -act ions in large v o l u m e s of reactants , and makes it poss ib le to carry out the react ions at re la t ive ly low temperatures and at high p r e s s u r e s . The radiation-induced react ions may el iminate s o m e s t a g e s of a synthes i s , and give r i s e to products of very great purity.

Unfortunately, the ionizing radiation i s not usual ly absorbed in a s e l e c t i v e manner; in the irradiated s y s t e m a variety of products appear. Their determination often requ ires difficult ana lyse s . On the other hand, the result ing products react t h e m s e l v e s or with initial mo lecu le s , hindering the pr imary react ions . One may achieve a steady state , where the concen-tration of the products does not vary. It is an equil ibrium state character-ized by an equality of the formation and the decomposi t ion rate of the product. In this steady state the increase in the G-va lue c e a s e s .

F r o m the great number of react ions that have been c lose ly studied only a few will be se l ec ted of part icular interest to industry.

The most thoroughly studied syntheses and decompos i t ions induced by ionizing radiation will be rev iewed here .

OZONE FORMATION IN THE RADIOLYSES OF OXYGEN

The radiolyt ic synthes i s of ozone by alpha par t i c l e s begun by Lind [1] and continued by var ious r e s e a r c h e r s [2-4] has reso lved the mechan i sm of the formation and decomposi t ion of ozone in this c a s e .

In a more recent work, Buneev et al. [5] irradiated liquid and gaseous oxygen with e l ec trons of 200 keV and with 6 0 C o gamma rays . The quantity of ozone formed i s proportional to the total dose and to the e lectron energy . Plott ing the ozone concentration [ 0 3 ] / t a s function of the contact t ime with the v e s s e l , the curve shows the d e c r e a s e of ozone concentration, which tends to a s teady-s ta te concentration of 0. 18%. The s a m e exper i -ments , repeated with liquid oxygen in static condit ions, g ive a s t eady-s ta te value of 0. 8% of ozone.

In gaseous oxygen irradiated by e lec trons of 200 keV by a f low of seven minutes contact, a G-va lue of 1. 5 m o l e c u l e s / 1 0 0 eV i s obtained. F o r the steady state of gaseous oxygen, [ 0 3 ] / [ 0 2 ] = IX 10"3-^ 2X10" 3 , and for the liquid state , th is ratio i s 8 X 1 0 - 3 . T h e s e va lues show that in the g a s e o u s oxygen the react ion rate of ozone decompos i t ion i s 5 0 0 - 1000 t i m e s greater than the format ion rate , and in liquid 125 t i m e s g r e a t e r .

T

P L - 2 3 6 / 7 9 9

B e c a u s e the ra t io of y i e l d s of ozone in the l iquid and the g a s e o u s s ta te i s 6, one may deduce that th i s n u m b e r r e p r e s e n t s the ra t io of the two rate cons tant s of the r e a c t i o n s in both media .

The g r e a t e r ra te of the ozone format ion in l iquid oxygen i s to be ex-plained b e c a u s e at the low t e m p e r a t u r e of l iquid n i trogen the e x c i t e d m o l e c u l e s cannot e a s i l y d i s a c t i v a t e . The c o l l i s i o n number be tween m o l e c u l e s i s s m a l l e r and the ozone f o r m e d d e c o m p o s e s e x t e n s i v e l y . The in f luence of the v e s s e l wal l on the recombinat ion of oxygen a t o m s i s g r e a t e r in the g a s e o u s s ta t e .

The e x p e r i m e n t a l v a l u e s of G obtained by v a r i o u s w o r k e r s a r e l i s t e d in Tab le I.

T A B L E I. E X P E R I M E N T A L V A L U E S O F G .

Type of G(Oa) Date Ref.

radiation G(Oa) Date Ref.

Alpha 1 .5 1911 [ 1 ]

Alpha 3 . 1 - 3 . 8 1925 [ 2 ]

Alpha 3 . 1 1926 [ 3 ]

Alpha 3 . 1 - 5 . 2 1927 [ 4 ]

Electrons 62 - 124 1925 [ 6 ]

Electrons 6 . 2 - 9 . 3 1928 [ 7 ]

Electrons 3 . 1 1936 [81

Gamma 9 1960 [ 9 ]

Gamma 12.8 1963 [10]

Taking th i s and other l a t e r r e s u l t s a s a b a s i s , F . W. L a m p e et a l . [11] ca l cu la ted G ( 0 3 ) v a l u e s and s t e a d y - s t a t e c o n c e n t r a t i o n s us ing a m e c h a -n i s m that i n c l u d e s the part ic ipat ion of ions and exc i t ed m o l e c u l e s . Omitt ing the two e x t r e m e c a s e s [1] and [5], the authors conc luded that G ( 0 3 ) for p a r t i c l e s i s 3 - 5 , for fas t e l e c t r o n s 3 - 9 and for g a m m a r a y s 9-13.

The p r i m a r y ion izat ion r e a c t i o n s of oxygen r a d i o l y s e s a r e O2-JW—•0++ e" (1) or 0 2 - jmr—»0 2

+ + e" (2) (pos i t ive ions) 0 2 + e " ->nAr—"O^" >0" + 0 (3). Only if c o l l i d e s with 0 2 b e f o r e d i s s o c i a t i o n could s tab le O2 be

found. H o w e v e r C^* d i s s o c i a t e s in 10_ 13s, and c o l l i s i o n t i m e at the p r e s s u r e of 1 atm i s 10"10 s . Neutra l i za t ion r e a c t i o n s a r e

0 2 + e " — . O + O (4) or O 2 + O " — + 0 (5)

1 0 0 IONEISCU

Ozone i s formed by

0 + 02 + 02 >03+02 (6) or

° 2 + ° 2 > 0 3 + 0

If ozone i s formed by methods (3) (5) and (7), four ozone m o l e c u l e s per ion pair are formed. W(02 ) = 32. 5 eV g ives 3. 08 ion pairs , 3. 08X4 = 12. 3 m o l e c u l e s of o z o n e / 1 0 0 eV and G(0 3 ) ~ 12. If the ozone format ion takes place via (4) and (7), only two ozone taolecules per ion pair are formed, and G ( 0 3 ) = 6; G(Oa) would i n c r e a s e a s LET d e c r e a s e s .

F o r the steady state of ozone formation, the decomposit ion of ozone after a s ignif icant ozone concentration must be taken into account:

O + Og » 2 0 1

0 + surface > | 0 2

03—ilWC—'dissociation

Taking the rate of ozone formation and decomposi t ion that are equal at the steady state , and the rate va lues from experimental work [12], Lampe and c o - w o r k e r s calculated s teady-s ta te ozone formation for dif-ferent p r e s s u r e s at different t emperatures . At low temperatures and high p r e s s u r e s the convers ion of 0 2 to 0 3 i s great (Fig. 1). Taking into account the coef f ic ient of the surface destruct ion of ozone convers ion, the convers ion of ozone, at the steady state , i s very smal l , in fact many o r d e r s of magnitude s m a l l e r than that calculated without surface destruct ion (Fig . 2). The ozone i s decomposed by t rans fer of energy stored in the sur face .

To test these calculat ions F . W. Lampe and c o - w o r k e r s have con-structed a beta irradiator , a 600-Ci 9 0 S r source .

HYDRAZINE SYNTHESIS FROM AMMONIA

Various papers [13-16] have been concerned with rad io lys i s of ammonia which d e c o m p o s e s by irradiation according to

..NH' + H" NH 3-rfinr—>

NH' +H2

The radica l s act between t h e m s e l v e s leading to hydrazine: N H s + N H j >N2H4 and NH' + NH3 >N2H4

At the same t ime , hydrazine decomposes :

H- + N 2 H 4 > N 2 H 3 + H 2

2 N 2 H j — ~ N 2 + 2 N H 3

H' + N 2 H 4 — > NH3 +NH 2

P L - 2 3 6 / 7 1 0 1

0.7 100 •/. YIELD CONVERSION OF 0 2 TO 0 3

0 100 200 300

TEMPERATURE (°K) FIG. 1. Effect of temperature on conversion of 0 2 to 0 3 .

Shortly after the irradiation of ammonia a steady state i s reached where the hydrazine concentration i s very smal l .

The ammonia was irradiated with alpha part ic les [13], fast e l ec trons [14], dark d i s charges [15] and with 200-keV e lec trons [16], In all these exper iments , the G-va lue for the formation of hydrazine i s between 1. 27 and 2. 5 m o l e c u l e s for 100 eV. The d e c r e a s e of temperature does not i n c r e a s e the hydrazine yield; greater dens i t i es do not permit long radical l i v e s .

In more recent works [17-19] the ammonia i s irradiated with gamma r a y s . Reported G - v a l u e s are very smal l , 0 . 5 - 0 . 9 m o l e c u l e s for 100 eV absorbed.

White [20] has studied the hydrazine formation in the f i s s i o n - f r a g m e n t rad io lys i s of liquid ammonia, and obtained a G-value of 1 . 5 . This value d e c r e a s e s rapidly with increas ing dose and approaches a G-va lue of approximately 0. 1 at high d o s e s .

A recent work of Sorokin et al . [21] studied the hydrazine synthes i s from ammonia absorbed on synthetic zeo l i te . Exper iments were per -formed at 0 and -196°C using a 1017 e V / g s d o s e - r a t e . Table II shows the different y i e lds of hydrazine and G - v a l u e s that reach 38 m o l e c u l e s / 1 0 0 eV but this large value corresponds to a very smal l quantity of ammonia

T A B L E I I . E N E R G E T I C Y I E L D V A L U E S O F T H E A M M O N I U M R A D I O L Y S I S P R O D U C T S

Dose-rate 1.35X 1 0 " eV/g s Dose = 4 . 8 5 x 10 ! 0 eV/fc

Irradiation temper aiure <"C)

NH, (wt.%)

Product radiolysis quantities

<10"19 moleculcs/g NH3)

Gads = moleculesAOO eV adsorbed by NH,

^heterogeneous = m ° l e c u l i

adsorbed (adsorbed by NH,}

M O O eV Conversion

% NHS into N sH (

N,H4 N.H, " A N>

0 0.33 18.5 14.3 38.1 29.6 - 0.14 0.11 1.056

0 0.65 9.2 10. 0 - 19.0 20.6 - 0.14 0.15 - 0.520

0 1.12 7.7 8.0 - 15.9 16.5 - 0.21 0.21 - 0.436

0 4.95 1.95 2.3 0.5 4.05 4 . 8 0.97 0.23 0.27 0.05 O.UO

0 11.9 1.96 1.62 1.0 4.05 3.3 2.06 0.50 0.41 0.25 0.112

0 100.0 0.03 0.32 0.08 0.07 0.65 0.17 0.07 0.65 0.17 0.0019

-106 0.31 9.2 12.4 0 19.0 25.5 0 0.07 0.09 0 0.52

-196 1.05 6.5 5.2 0 13.4 10.7 0 o . i e 0.13 0 0.368

-196 1.42 5.7 11.8 - 0.19 - - 0.324

-196 1.76 4.8 9.8 " - 0.20 - - 0.264

-196 11.90 0.8 1.5 0.3 1.7 3.1 0.6 0.20 0.37 0.07 0.046

-196 14.00 0.9 0.8 1.9 1.6 - 0.27 0.22 - 0.053

-196 100.0 0.04 0.15 0.03 0.08 0.32 0.07 0.08 0.32 0.07 0.002

P L - 2 3 6 / 7 1 0 3

absorbed by zeolite , namely 0. 33%. This makes the method very unattractive.

F r o m these different resu l t s , it may be concluded that the best method of obtaining hydrazine from ammonia i s offered by dark d i scharges and not by ionizing radiation.

NITROGEN FIXATION

The well-known exper iments of Harteck and Dondes [22] show that along a f i s s i o n fragment track concentrations of ions and radicals i s so great that their recombination takes place before these entit ies can leave the track by diffusion. The facts are more evident at great pres sure .

Exper iments carr ied out in a nuclear reactor with N2 + 0 2 mixtures of different percentages s o m e t i m e s yield large concentrations of N 0 2 exceeding the saturation p r e s s u r e and N 2 0 4 condensed during the irradiation.

The most important mechanism proposed involves the following react ions;

N2-dW—>N2 + e" (1)

N 2 + 0 2 • NO + NO+ (2)

N 2 + N 2 ' N 4 I3)

N | + N2 » N+4+e" (4)

(N2+f + N 2 ' N 3 + N (5)

N 3+ + 0 2 > N 0 2 + N 2

+ (6)

Ng + 0 2 • N 2 0* + NO+ (7)

N 3 + ° 2 >N0 + N 2 0 (8)

In pract ice , radiation does not decompose N02(GNC,2= 075) (2) but

nitrogen atoms react with NOZ forming

—> NO + NO+ (9)

N O Z + N 2 > N 2 0 + N 0 (10)

N G 2 + N ^ 2 + 0 2 (11)

N20'" result ing f rom (7) i s transformed:

N 2 0* • N + NO

N2O • N2+O

N 2 0 * + M • N P + M*

1 0 4 IONEISCU

and the neutral izat ion of

NO+ + e" > N + O

The G - v a l u e s of N 2 0 , NO and N 0 2 are strong, depending on the proportion of the initial mixtures , p r e s s u r e and temperature . G ( - N 2 ) ~ 7 in the reac tor by f r a g m e n t - f i s s i o n irradiation [22],

Later exper iments by Dmitr iev and P s h e z h e t s k i i [23] started f rom the fact that the excitat ion and ionization of nitrogen a toms l eads to the formation of a toms which then react further with oxygen. They studied the mechan i sm of the nitrogen oxidation by e l ec trons of e n e r g i e s f r o m 15 to 400 eV and by smal l p r e s s u r e s . Later [24] the s a m e authors, working with mixtures of 0 2 : N 2 as 1:1, by atmospher ic p r e s s u r e and irradiating with e l ec trons of 200 eV, found a G( -N 2 ) of 2 m o l e c u l e s / 1 0 0 eV and for air G = l . 3 m o l e c u l e s / 1 0 0 eV.

The s a m e authors [25] studied these reac t ions under the action of the e l ec t rons of 9 0 Sr beta rays . The pr imary ions are identif ied a s N 2 , 0 2 , N and O . The y i e lds depend on nitrogen molar fraction; the grea ter the mo lar fract ion, the s m a l l e r the y i e lds . The nitrogen ions resul t f rom the radiolyt ic oxidation of N.

The latest work of Dmitr iev and- Sorokin [26] studied these react ions at high t emperatures between 0 and 1000°C and p r e s s u r e s from 1 atm to 150 atm. The determinat ions were made in a glow discharge for vol tages <15 kV. A s the temperature i n c r e a s e s from 0 to 200°C, the rate and energy yield of the react ion increase owing to a d e c r e a s e in the r e c o m -bination coeff ic ient of the ions. The e f fect ive energy of activation v a r i e s with p r e s s u r e from 1. 5 to 2 k c a l / m o l . F r o m 200°C the rate of the react ion d e c r e a s e s because a r e v e r s e react ion takes place . A s the temperature i s increased from 200 to 700°C the energy yield d e c r e a s e s f rom 3. 3 m o l e c u l e s / 1 0 0 eV at 200°C to 1. 1 m o l e c u l e s / 1 0 0 eV at 600°C because of the thermal decomposi t ion of NOz . At t emperatures between 700-1000°C, the react ion rate i n c r e a s e s because of the additional factor of the thermal oxidation of nitrogen.

RADIATION SYNTHESIS OF HYDROCYNANIC ACID

Hydrocynanic acid re su l t s f rom mixtures of unsaturated hydrocarbons with nitrogen or ammonia [27-29] , The mechan i sm proposed by Dzantiev and Trubnikov i s the following:

N|-JWP—»N' + N"

C ^ a + N' >HCN + CH'

CH' + N 2 > HCN + N"

The mixtures irradiated with 600 keV e l ec trons show large G - v a l u e s , between 300-900, depending on composit ion, p r e s s u r e and addit ives (Ar or He) where growth i n c r e a s e s the y i e lds .

Var ious mix tures of C2H4, C 2 H 2 , CH 4 , C2Hg, C3H8 and C4H10, and NH3 were sea led in quartz tubes and irradiated with neutrons in a nuclear

PL-236/7 105

reactor at integral d o s e s of 0. 35 -2 . 7 X 1 0 1 2 n / c m 2 s . The quanti t ies of HCN_, spec trophotometr i ca l ly determined , G(HCN). are proport ional to the d o s e - r a t e , hydrocarbon-ammonia rat io , and p r e s s u r e s (in the range 1 -5 atm). G^CN)517 5 0 0 f o r 35% C2H4, 65% NH3 and a l s o for the mixture 30% C 2 H 6 , 70%"NH3 at a total dose of 5 X 1 0 1 5 e V / g .

F u r t h e r m o r e , the rad iochemica l convers ion of thiocyanate in a c e t i c acid was a l s o studied [30], Solutions of KCNS and NH4 CNS in water with 6 0 C o g a m m a rays at d o s e - r a t e s of 1 0 1 4 - 1 0 1 6 e V / m l s in the p r e s e n c e of He and O2 w e r e irradiated . Among the r a d i o l y s i s products a r e SO2*, CN and K + . The rad iochemica l y ie ld G, in a 0. 1 M solution of KNCN, irradiated with 10 1 8 e V / m l , i s approximate ly 360. It d e c r e a s e s with i n c r e a s e in the dose . The G-dependence of the d o s e - r a t e shows chain reac t ions .

RADIOSYNTHESIS WITH SULPHUR

R a d i o s y n t h e s i s of sulphuric acid i s one of the e a r l i e s t s tudies in th i s f ie ld [31], L a t e r the r a d i o l y s i s of S 0 2 + 0 2 + H 2 0 was taken up in different var iants .

One sugges t ion [31] was to i rradiate a saturated sulphur dioxide solut ion with 6 0 C o g a m m a rays . The non- irradiated part of the solution contained m o r e sulphuric acid than the irradiated one. A g a s e o u s mixture of S 0 2 + 0 2 was irradiated at higher t e m p e r a t u r e s up to 115°C. A few p e r c e n t s of SOa w e r e formed, b e c a u s e S 0 3 d e c o m p o s e s during the i rrad i -ation [32], F ina l ly S 0 2 was prev ious ly irradiated at 260°C and a f ter -wards was introduced into a c h e m i c a l reac tor that contained oxygen at a high p r e s s u r e . Ne i ther of these methods can g ive substantial y i e lds of sulphuric acid.

Careful quantitative s tudies on th is subject were carr i ed out by Schrader and Sch&nherr [33-36] on the radiolyt ic oxidation of sulphurous acid. Aqueous so lut ions saturated with S 0 2 and 0 2 w e r e irradiated with X - r a y s f r o m RCntgen tubes of 180 kW and 15 mA and with gamma radiation f rom a 0. 8 -C i 6 0Co s o u r c e . In all t h e s e c a s e s the d o s e - r a t e was about 3. 1016 e V / m l min. The G - v a l u e s depend on the d o s e - r a t e , dose and t e m p e r a t u r e s . The highest value of G, at the beginning of the react ion , was 5 1 0 + 3 0 . The d o s e - r a t e dependence i s re lated to G(H2so4) = 3.1 X 1010 XD"0-47 where D i s the d o s e - r a t e . 2

In our laboratory a mixture of SO2+O2 + H2O vapour was subjected to the g a m m a r a y s of a 800-Ci 6 0Co s o u r c e [37], Static e x p e r i m e n t s were carr i ed out. The composi t ion , p r e s s u r e , t emperature , d o s e - r a t e and d o s e w e r e var ied . Sto ich iometr ic compos i t ion of the mixture S 0 2 + 0 2

gave higher y i e l d s . Water was a lways in e x c e s s . Although g r e a t e r p r e s s u r e s fac i l i tated the react ion the e x p e r i m e n t s were c a r r i e d out at two a t m o s p h e r e s in the t emperature ranges 6 0 - 1 5 0 ° C and for 6 atm at 26 - 74°C. The G - v a l u e s showed a l inear dependence on the i n v e r s e square root of the d o s e - r a t e , showing that the react ion i s a chain react ion . The extrapolat ion of G at zero t i m e gave a max imum value of ~ 8 0 0 m o l e c u l e s / 1 0 0 eV.

Hirakadze et al . [38] irradiated with X- and gamma r a y s s o m e solut ions of sulphides , th iocyanates , mercaptans , thiophenols and thiourea.

106 IONEISCU

Aqueous solutions of 0. 005 to 0 . 5 M of Na 2S, KHS, and Na HS were oxidized to the corresponding sulphates with G = 60. In these cyanate solutions the convers ion was only 30 to 40% with a G-value of 20 to 30 that decreased with the temperature . The sulphur f rom butyl, amyl and hexyl mercaptans was oxidized to S and S02~ in non-aqueous and aqueous solutions respect ive ly . Thiophenols produced the corresponding disulphides with a G-value of 20. An oxidation-decomposit ion occurred in thiourea with a G-value of 180 and a 15-20% conversion. It was observed that irradiation of sulphur compounds produces directed changes in their state of oxidation.

The same authors [39-42] studied a l so radiolytic oxidation of other sulphur organic compounds such as aliphatic mercaptans, aliphatic mercapt ides , thiophenols in alkaline media and thiourea solutions. They obtained radiation chemical y ie lds reaching 600-700 m o l e c u l e s / 1 0 0 eV. The p r o c e s s e s involved are considered to be of a chain character .

PRODUCTS OBTAINED FROM THE RADIOLYSIS OF C 0 2 AND VARIOUS MIXTURES CONTAINING C 0 2

The stability of pure gaseous carbon dioxide to ionizing radiation i s well known. In the presence of additives that can react with oxygen atoms, C 0 2 decomposes with G-va lues in the range of 9 [43] to 3. 5 [44], The CC^ i s more stable to radiation in the gas than in the liquid phase.

The products of gamma rad io lyses of liquid C 0 2 are CO, 0 2 and 0 3

with G-va lues G^coj= 5 - 3 . 5, 0 - 0. 6 and 0. 7 in the presence of such additives as C2H2 , C 2H 4 , C 4H 1 0 , N 0 2 , N 2 0 and H2 , at -42°C [45], In gaseous C 0 2 these values are smal l er .

Since the carbon dioxide i s a favourable coolant in the reactor, i ts decomposit ion in carbon monoxide and oxygen was achieved by introducing smal l amounts of nitrogen dioxide [4 3],

Recently, the radiolytic behaviour of C 0 2 by pursuing an isotopic exchange reaction between C 0 2 - 0 2 - C O , using labelled 13 C and l s O , has been studied [46], CO i s formed as a primary product with a G-value of 11. C^ resulted as secondary product from the decomposit ion of COj. The f i rs t step in the radio lys i s of C 0 2 may be 2 CO2-JUIP—>2 C 0 + 0 2 .

The radio lys i s of C 0 / C 0 2 mixtures was studied in the reactor [47] at 130-150°C. A solid of approximately the formula C^gO was found. The CO i s destroyed with a G-va lue of about 5. A simultaneous reaction takes place to r e - f o r m CO.

Radio lys i s of a mixture of C 0 2 and H2 [48, 49] forms initially CO and water vapour in equal quantities together with smal l t races of methane. A s the react ion p r o g r e s s e s , the rate of CO formation d e c r e a s e s rapidly and an orange solid, with the empir ica l formula C 2 H 3 0 1 - 1 , i s formed in the react ion. Variation in re lat ive concentrations of the reactants shows that the activated s p e c i e s from H 2 (H 2 or H) contributed only to CH4 formation (GCH4

= 0. 3) with little or no effect on the formation of CO and H 2 0 . (G(CO) = G ( H 2 0 ) = 1 7 . 3 e"1700 /RT m o l e c u l e s / 1 0 0 eV.)

The reduction of C 0 2 by H2 , initiated by 115 keV electrons,gave-CO, glyoxal and organic ac ids [50],

PL-236/7 107

Carbon dioxide r e s u l t s in many chemica l industr ies as an unusual product. A rational use was d i s c u s s e d by Harteck and Dondes [51], They irradiated in the reac tor with f i s s i o n f ragments the mixture

c o 2 + | N2 +O 2 >NO2 + N2O +CO

If C 0 2 i s irradiated, one obtains CO and 0 2 . The ionizing radiation t r a n s f o r m s CO in suboxide with G = 2. 5. Th i s po lymer ize s ; the po lymer can react with water or a lcohols to g ive anhydride or other organic function which can s e r v e in a different synthes i s . Harteck and Dondes calculated that 1 g of 3 3 5 U, in the reac tor , in favourable condit ions, could generate a tonne of suboxides from CO.

PRODUCTS RESULTING FROM ALCAN RADIOLYSES

Gamma r a d i o l y s i s of a lcans does not yie ld chain reac t ions . F o r this reason the energet ic balance i s bad. Thus, the radiolyt ic yie ld i s 7 - 1 0 m o l e c u l e s / 1 0 0 eV for radica l ic products and ~ 3 for unsaturated products . Cons ider ing an average value of 3 eV per chemica l bond, it fo l lows that only 30% of the absorbed energy i s used to produce chemica l r eac t ions , 70% being los t in co l l i s i ons and energy t r a n s f e r . Considering the s e l e c t i v i t y of bond breaking, 80% of products resu l t f r o m breaking of C-H bonds and 20% f r o m C - C bonds, giving r i s e to saturated and non-saturated hydrocarbons [5 2],

In the r a d i o l y s i s of a l cans , the main products are H 2 and CH4-CH4 percentage i n c r e a s e s with CH3/CH2 rat io [53]. F o r instance , GCH4

- 2 in n -hexadecane r a d i o l y s i s and 3 . 2 in i s o - h e x a n e rad io ly s i s r e s p e c t i v e l y . Cyclopentane does not f o r m methane a s an irradiat ion product, but i zo -octane y i e lds = 37% of CH4.

The product -y ie ld dependence on dose i s l inear in the range of s m a l l d o s e s (3. 10 1 8 - 20. 1018 e V / m l ) for n -hexane and s i m i l a r hydrocarbons . The deviat ion f rom l inear i ty at high d o s e s (1 -30 . 102 1 eV) i s caused by secondary reac t ions .

The hexane r a d i o l y s i s in the s m a l l dose range [54-58] g i v e s the fol lowing products: hydrogen with a G - v a l u e of 5. 1, methane , 0 . 4 1 , ethane, 0 . 8 2 , ethylene, 0 . 6 2 , propane, 0 . 6 8 , butane, 0 . 6 5 , 1-butene, 0 . 2 4 , 1 -hexane , 0 . 2 5 , vinyl idene s t ruc tures , 0 . 2 9 , hexadienes , 0 . 0 0 8 , pentanes , heptanes and heptanes non-de termined , nonanes , 0. 17, decanes , 0 . 1 9 , undecanes , 0 . 0 3 , including 4. 5 diethyloctane, 0 . 3 9 , 4 e thy l -5 -methy lnonane , 0 . 8 5 , d imethyldecane , 0 . 5 2 , 5 -methy lundecane + n -e thy l decane, 0. 4, n -dodecane , 0. 03. In the high dose range up to ~ 1 0 . 10 2 1 e V / m l was found: H2 4 . 5 , CH 4 , 0 . 2 , C 2 -C5 saturated hydro-carbons , 1 . 6 , C 2 - C 5 unsaturated hydrocarbons , 0 . 4 , l iquid unsaturated compounds, ~ 2 . 0 .

F r o m i n f r a - r e d spec tra , even at d o s e s of 1. 10 2 1 eV, approximate ly 20% of the liquid compounds are non-sa turated hydrocarbons containing m o r e than ten carbon a t o m s per m o l e c u l e . The m a s s s p e c t r o m e t r i c ana-l y s i s of t h e s e compounds shows a l s o a number of saturated hydrocarbons (Cg -C28 )• However , the major i ty are non-saturated compounds.

1 0 8 IONEISCU

The pract ica l u s e s of t h e s e radiolyt ic p r o c e s s e s are unimportant. Even hydrogen production does not e x c e e d a G - v a l u e of 5 m o l e c u l e s / 1 0 0 eV.

Alcan r a d i o l y s i s in the p r e s e n c e of oxidic c a t a l y s t s

In s e v e r a l s tudies [59] a l inear re lat ionship was es tabl i shed between the radio lyt ic rate of the react ion and the number of e l e c t r o n s contained in a monolayer of the cata lyst surface and the absorbed hydrocarbon. The constant rat io of t h e s e two quantit ies shows that the energy t r a n s f e r i s p o s s i b l e only in the adsorbing monolayer . In the bulk, the reac t ion i s cons idered to be homogeneous .

A relat ion between cata lys t compos i t ion and this catalyt ic e f fect has been demonstrated by E . S . R . spectra . It i s p r e s u m e d that during the irradiat ion excitat ion or charge accep tors a r e formed on the cata lys t s u r f a c e . The sudden d e c r e a s e of the react ion rate in the he terogeneous r a d i o l y s i s at high d o s e s i s a scr ibed to a rapid po lymer izat ion p r o c e s s of the unsaturated compounds on the cata lys t sur face . In this c a s e , the cata-lys t e f f i c i e n c y i s very great , because the po lymer iza t ions are chain r e a c t i o n s . T h e r e f o r e we be l i eve that po lymer izat ion reac t ions on ca ta ly s t s have the mos t promis ing future in the radiation c h e m i s t r y of he terogeneous s y s t e m s .

T e m p e r a t u r e inf luence on alcan rad io ly s i s

Alcan r a d i o l y s i s at higher t e m p e r a t u r e s does not g ive a much g r e a t e r number of products than at ordinary t e m p e r a t u r e s , but the radio lyt ic y i e lds are percept ib ly i n c r e a s e d . High t e m p e r a t u r e s , together with radiation, r a i s e the number of ini t iat ions and of chain propagation c e n t r e s . This fact led to the study of radiation thermal cracking of hydrocarbons [60-62] in v iew of i t s industrial application.

T h e r m a l cracking of a l cans usually takes p lace at t e m p e r a t u r e s of 500-600°C and c o n s i s t s of two steps: init iation of the react ion , i . e . the creat ion of rad ica l s f r o m the molecu le d i s s o c i a t i o n , which need an act i -vation energy of 80 k c a l / m o l [53], and the chain propagation whose ac t i -vation energy i s ~ 2 0 k c a l / m o l . The average energy of 60 k c a l / m o l i s the r e a s o n for the high temperature of the thermal cracking. The u s e of the irradiat ion together with the heating d e c r e a s e s t e m p e r a t u r e s by 150-200 deg C to obtain the s a m e ef fect , b e c a u s e the irradiat ion in f luences only the init iation step that c o n s u m e s the g r e a t e r part of the energy .

The e f f i c i ency of the thermo-rad io ly t i c cracking was studied in stat ic and continuous e x p e r i m e n t s . Both t e s t s gave s i m i l a r r e s u l t s . Up to 550°C the thermal component i s very s m a l l and the radiation inf luence gave an important initiation to the p r o c e s s . Even over 550°C, when an intens ive thermal cracking takes p lace , the radio lyt ic component i s four t i m e s g r e a t e r than the t h e r m a l one at a cer ta in d o s e - r a t e . In this way, the use of i rradiat ion with the thermal cracking p r o c e s s has a favourable e f fec t on the d e c r e a s e of cracking temperature and i n c r e a s e s apprec iably the quantity of products .

The promis ing r e s u l t s obtained by radiothermal cracking represent an init ial s tep in the invest igat ion. To comple te the work r e q u i r e s supple-mentary s tudies on p r e s s u r e influence on cata lys t p r e s e n c e and on the best dynamic fac tors .

PL-236/7 109

THE RADIOLYSIS OF UNSATURATED HYDROCARBONS

Studies on the rad io lys i s of unsaturated hydrocarbons s e e m to indicate some poss ib l e d irect ions . The s imples t compounds represent the most suitable s y s t e m s for s tudies of fundamental p r o c e s s e s . F o r this reason , ethylene, the f i r s t representat ive of unsaturated hydrocarbons, was most ly studied [63-71] , On this substance , photochemical [72-75] , f r e e rad ica l s [76] and m a s s - s p e c t r o m e t r i c [77-83] s tudies w e r e made.

Sauer and Dorfman [74], Okabe and McNesby, as wel l a s Dzantiev and c o - w o r k e r s [75], carr ied out photolitic reac t ions on ethylene with hydrogen and methyl addition to form ethane and butane. Yang and Manno [66] d i sagreed with radical ic formation of butane. M e i s e l s and Sworski [69 ,71] , af ter detailed studies made to e lucidate the ro le of hydrogen a toms and of in termediates in ethylene rad io lys i s , came to the conclus ion that the ethyl radical was yielded in ethylene rad io ly s i s with a G-va lue of 6 .7 r a d i c a l s / 1 0 0 eV. M e i s e l s cons idered that higher hydrocarbons are formed by i o n - m o l e c u l e react ions , and it i s not n e c e s s a r y to cons ider rad ica l s as p r e c u r s o r s in the formation of the se compounds. N-propyl , sec -propyl , s ec -buty l are formed in smal l quantit ies by ion molecu le reac t ions .

The kinetic treatment of this problem i s based on three hypotheses . The s t eady- s ta te concentration of rad ica l s i s determined by the hydrogen and by rad ica l s formed out of it. The initial quantity of rad ica l s i s constant, and all rad ica l s are added to ethylene or combine with ethyl radica l s . The experimental data agree with the radical m e c h a n i s m of the formation of higher homologues .

At s m a l l d o s e - r a t e s and high p r e s s u r e s , ethylene p o l y m e r i z e s . M e i s e l s es tabl i shed for the G-va lue of acety lene po lymer izat ion a re lat ion-ship based on a radical ic mechan i sm that coincided per fec t ly with the empir ica l re lat ionship of Hayward and Bretton [84],

The ro le of methyl rad ica l s , obtained in the r a d i o l y s i s of unsaturated hydrocarbons, was determined by label l ing them with 1 4 C [85, 86]. Un-saturated hydrocarbons, label led with 2 H , showed that a l ly l ic hydrogen i s l o s t e l even t i m e s m o r e readily than a pr imary hydrogen.

The irradiat ion of butadyene, i soprene , p iperi lene di isopropenyl and cyclopropenyl [64] gave r i s e to products such as H 2 , CH 4 , C3H6 , C2H2 . The r e s u l t s of butene irradiation are C 2 H 4 , 03!% , C 2 H 2 , CH4 and H2 and saturated hydrocarbons with long chains [87], S imi lar products are ob-tained by the rad io ly s i s of c i s - 2 - b u t e n e . In p r e s e n c e of Ar or Xe the main product i s C2H4 , and others are H2 and CH4 .

The radiolyt ic i somer iza t ion of st i lbene [88, 89] was performed in a solution of saturated hydrocarbons and in benzene. In irradiated solut ions of saturated hydrocarbons decomposi t ion products were found, whereas in benzene solutions an i somer iza t ion takes place [88 ,89] , Irradiation of binary solut ions, such a s cyclopentane with cyclohexane, or cyclopentane and cyclohexane, gave decomposi t ion products a l so [90],

Ace ty lene was irradiated a s a gas and in aqueous solut ions . The chief product obtained in the gaseous phase was benzene [91, 92], Its yie ld was a p r e s s u r e function; at 20-30 Torr , it pas sed through a maximum that r o s e with the temperature increase . In this c a s e , the G - v a l u e s were 5. 1 - 1 3 . 0 . The quantity of benzene did not depend on d o s e - r a t e , but at

1 1 0 IONEISCU

6X 12-42X 10 1 2 eV/cm 3 s f e l l suddenly [91, 93]. The irradiated solut ions of acety lene gave p o l y m e r s in the presence of N 2 and H2 . In the presence of 0 2 the polymerizat ion was inhibited and high y ie lds of glyoxal were found.

Aromat ic hydrocarbons are res i s t ent to irradiation. F a s t neutrons decompose them more rapidly than gamma radiations [94, 95]. Alpha p a r t i c l e s , resul t ing from a 1 0 B ( n , a ) 7 L i react ion, cause higher G - v a l u e s [96], A variat ion of G(H2) in this rad io lys i s caused by protons, deuterons and alpha par t i c l e s i s a function of L E T [97, 98], Orthoterphenyl and di-phenyl in this c a s e showed a variation of G(H2) and G(-MJ on LET a l so [94], Burns and Jones [99] d i s c u s s e d these re su l t s for benzene.

The rad ica l s formed in the rad io lys i s of benzene [100] and the format ion of cyclohexadyene [101] have been studied. The hydrogen yield obtained by the irradiation in the cyclotron i s grea ter than that obtained by fast e lec tron irradiat ions [102], The irradiated mix tures of benzene and methyl and ethyl cyclohexane [103] show a lower hydrogen yie ld. Much work has been devoted to the mixtures of aromatic and saturated hydro-carbons [103-105] ,

Solutions of benzylchloride or benzalchloride in saturated hydrocarbons by irradiat ion g ive up their radica l s and e l iminate the chlorine atoms [106, 107], The rad io lys i s of antracene o i l s has been studied by Proksch and Bi lds te in [108],

CHLORINATION REACTIONS

At an IAEA Conference in 1959 in Warsaw, an economic evaluation by I . R o s e n [109] concluded that in chlorination a s in sulphochlorination reac t ions , gamma radiation ac t s as a f r e e radical initiator, and the same products as in photochemical react ions are obtained. The energy cost of the photochemical initiation i s negl ig ible , and cannot be reduced by the use of high energy radiation s o u r c e s .

The chlorination rate, for large d o s e - r a t e s , depends only on the rapidity of d i sso lut ion and the quantity of chlorine . This rate i s l i t t le changed by changing the temperature . It i s there fore more suitable to work at room temperature .

FIG. 3. Radiation plant for ethyl bromide synthesis.

PL-236/7 111

It i s general ly considered that the se lec t ive preparation of n-alkyl chlor ides by the chlorination of o lef f ins i s difficult; recent Japanese work [2] found that both n-butyl chloride and ethyl-chloride were ef f ic ient ly (G = 35 000) formed by a gamma-ray- induced reaction of ethylene and hydrogen chloride. The G-va lues depend on both the dose and the dose-rate. The reaction i s presumed to be a vapour phase radical chain reaction; and the proposed mechanism agrees with experimental resu l t s .

Initiation HCHUT—H' + Cl'

c 2 H 4 + c r > c 2 H 4 c r

C2H4C1" + H C 1 — > C2H5C1 + C1' chain

c 2 H 4 c r +C2H4 > c 4 H 8 c r

c 4 H 8 c r + HCI < c 4 H 9 c i + c r

c i ' + c r >ci 2

F r o m the gamma radio lys i s of mixtures of CC14, CHC13 , CH2C12 and cycloalkene one obtains a synthes i s of intricate compounds [2] as tr ichloromethyl cycloalkanes and others. These are used to obtain t r a c e r s containing 14C in the molecule .

The gamma radio lys i s of o- and m-dichlorbenzene [3] y ie lds benzene substitution der ivat ives from C6H4Cl2 to C6H2C14 and o l igomers . The G-values are between 0. 9 and 7 . 1 . For this purpose acce lerated e lectrons from a Van de Graaf generator (1 .5 MeV) were a l so employed.

The chlorination of kerosene by gamma 6 0 Co-irradiat ion [5] takes place rapidly (15 t i m e s more rapidly than that effected by u. v. irradiation), G = 20X105 and the product includes 60% chlorine.

Hydrogen bromide addition to ethylene

Ethyl bromide preparation i s the f irs t industrial application of a radiolyt ic synthes i s (Dow Chemical Company). The gaseous ethylene and hydrogen bromides are introduced in a chemical reactor through g (Fig.3). The 6 C t o - s o u r c e (1800 Ci) i s in d. The reaction is presumed to be a chain react ion with the following mechanism;

HBr-dW—'H' + Br'

B r ' + CH2 = CH2 •BrCH2 - CH£

Br CH2 - CHj + HBr >BrCH2 -CH3 + B r '

These react ions take place at -2°C and at 0. 15X106 rad/h . The G-value i s 3X9X104 m o l e c u l e s / 1 0 0 eV. The mixture f lows with a speed that permits a great transformation of the g a s e s . The remaining g a s e s are conducted again into the c ircuit . The hydrogen bromide formed i s e l i -minated, cooled, dist i l led, neutralized and dried. The chemical reactor

112 IONESCU

i s built of nickel . Seventy per cent of the g a m m a - s o u r c e radiation is used. The method requires clean and dried HBr for radiolytic synthes i s . The radiation i s cheap ( < $ l / d ) . The Dow Chemical Company synthesized 500 t o n s / y r . It s e r v e s as an anaesthetic and as an intermediate in organic synthes i s .

RADIOCHEMICAL OXIDATIONS OF ORGANIC SYSTEMS

Radiation may be used to acce l era te normal thermal oxidations, a l -though it i s difficult in such s y s t e m s to gain any understanding of the fundamental radiolyt ic p r o c e s s e s .

If it i s a s s u m e d that the initial radiolytic decomposit ion of the hydro-carbon i s pr imari ly to give radica ls , then from the knowledge of the e lementary p r o c e s s e s occurring in thermal oxidations the following sequence of react ions may be proposed [112]:

RH-IAJIP—>R ' + H'

RH-rfinr—>R i+ R2 H + O 2 *HO2

R- + O2 -RO2

H' + RH - H 2 + R '

HOJ + RH — — H 2 0 2 + R'

ROG + RH — —'ROOH + R'

H 0 2 + H 0 2 -— • H2O2 + o 2

R 0 2 + R 0 2 - >ROOR + 0 2

RO2 + HO2 - >ROOH + OJ

RO2+RO2- > ketone + alcohol + O;

Saturated hydrocarbons

The radiolytic oxidation of methane was original ly studied in the Wantage Research Laboratory for poss ib le industrial application. An attempt was made to induce thermal oxidation (which occurs via a chain react ion at about 350°C) to occur at lower temperatures by gamma irradi -ation. Fa i lure to obtain a chain react ion led to a study of radiolyt ic oxi-dation at room temperature , and a note was published [113] on the var i -ation in methyl hydroperoxide yield on 6 0 Co gamma rad io lys i s of 0 . 1 , 1. 0 and 10% O2-CH4 mixtures . The y ie lds of methyl hydroperoxide and formaldehyde f rom the 4 -MeV e lec tron and 6 0 Co gamma r a d i o l y s e s of 10% 0 2 - C H 4 mixture at 25°C have been studied [114] in the f i r s t part of

PL-236/7 113

the work over p r e s s u r e and d o s e - r a t e ranges of 1 -76 cm Hg, and 1. 82X10 1 4 - 9. 62 X 1017 e V / m l min, normal ized to 20°C and 76 c m Hg. G(CH3OOH) i n c r e a s e d f r o m 0. 9 to 6. 0 with increas ing d o s e - r a t e (at a tmospher ic p r e s s u r e ) , and i n c r e a s e s f rom 1. 7 to 6 . 0 with increas ing p r e s s u r e (at the highest d o s e - r a t e ) . G(CH20) i s about half G(CH3OOH), and behaves s i m i l a r l y with respect to d o s e - r a t e and p r e s s u r e .

In the second part [115] of the report the formation of the a lcohols , e s t e r s , a ldehydes , ketones , e thers and hydrocarbons i s descr ibed . A study of the react ion m e c h a n i s m based on rad ica l - rad ica l and a tom-rad ica l r e -act ions was carr ied out. The product formation G - v a l u e s w e r e unimportant and the G-va lue for the methane disappearance was G(-CH 4 ) = 14.

Of all the radiation-induced hydrocarbon oxidation s y s t e m s , the cyc lo -hexane-oxygen s y s t e m has been the most widely invest igated.

By using both paper and gas chromatography it has been es tabl i shed [116] that the organic products of the oxidation of cyclohexane are cyc lo -hexyl hydroperoxide, dicyclohexyl peroxide , cyclohexanone and cyc lo -hexanol. The product y ie lds obtained in Ref . [116] are compared in Table III with those of Bakh [117] , Dewhurst [118] and McCarthy and MacLachlan [119],

The absolute y ie lds of these products are st i l l not def inite ly es tab-l i shed . The carbonyl y ie ld in pure chlorocyclohexane i s cons iderably greater than in cyc lohexane, and this i s cons is tent with the higher radical yield observed in chlorocyclohexane.

Unsaturated hydrocarbons

The d i f ference in behaviour of unsaturated hydrocarbons compared with saturated hydrocarbons in irradiat ion- induced oxidation may be partly attributed to the weaker alpha C-H bond so that the react ion

R 0 2 + RH > R0 2H + R'

may take place readi ly at room temperature , and thus give r i s e to chain-induced oxidation, and partly to the poss ib i l i ty of the addition of rad ica l s to the double bond.

When induced-radiat ion oxidation of acety lene is carr ied out, a ye l low polymer r e s e m b l i n g cuprene i s obtained, with - M / N = 19 .8 .

The m e c h a n i s m of these reac t ions has not yet been elucidated [119], In the p r e s e n c e of s ignif icant concentrat ions of oxygen, the oxidation

of the ethylene takes place [120], The product y ie lds obtained for carbon dioxide, organic ac ids , formaldehyde, perox ides , glycolaldehyde and butene are not grea ter than 3 . 5 .

F o r the induced-radiat ion oxidations of other unsaturated hydrocarbons a s propylene, cyc lohexane, di isobutylene, the product y i e lds w e r e a l s o unimportant.

Oxidation of other organic compounds

Formaldehyde and hydrogen w e r e proved to be major products of the oxidation of m ethanol. 60 Co - g a m m a r a d i o l y s i s of aerated methanol was invest igated by Hayon and W e i s s [121] and Lichtin et al . [122], Hayon and W e i s s obtained G(CH20) = 4. 28 and G(H 2 0 2 ) = 2. 89 at a d o s e - r a t e of

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T A B L E III. P R O D U C T Y I E L D S FOR C Y C L O H E X A N E OXIDATION T E M P E R A T U R E : 2 5 ° C

Product G - v a l u e

Ref. [ 1 1 6 ] Ref. [ 1 1 9 ] Ref. [ 1 1 8 ] Ref. [ 1 1 7 ]

C y c l o h e x a n o n e 2 . 0 2 2 . 2 8 3 . 5 0 . 6

C y c l o h e x a n o l 1 . 5 5 2 . 4 0 3 . 7 -

Cyc lohexy lhydroperox ide 1 . 0 5 1 . 1 0 1 . 0

D i c y c l o h e x y l p e r o x i d e 0 . 3 1 - - 0 . 2

Hydrogen perox ide 0 . 1 0 - - 0

A c i d - 0 - 0 . 2

Irradiation source 1 3fcs 6 - M e V 0 . 8 - M e V 7 0 - k V

rays e lec trons e lectrons X-rays

D o s e - r a t e 1 . 6 X 10" e V / g " 1

s"1

Pulsed irradiation

1. 6 x 101 9 e V / g" 1

s"1

1 0 n eV g" 1

s-1

T o t a l dose 2XlO2 0 e V / g"1

2 x l 0 2 1 e V / g" 1

6 x l 0 2 1 eV

g" 1

102 1 eV G"1

1 .6X1016 e V / m l min , and a tota l d o s e of ( 1 - 2 ) X 101 8 e V / m l . On the other hand, Licht in et a l . found that aera ted methanol y i e l d s f o r m a l d e h y d e and p e r o x i d e with G = 1 0 + 1 and 2. 8, at a d o s e - r a t e o f 2 X 1 0 1 7 e V / m l min , and a total d o s e of the s a m e order a s g iven by Hayon and W e i s s . I m a m u r a and Seki [123] in a m o r e r e c e n t work r e i n v e s t i g a t e d t h i s s y s t e m exten-s i v e l y , and r e v e a l e d the pronounced e f f e c t s of d o s e and oxygen c o n c e n -tra t ion upon the y i e l d of f o r m a l d e h y d e .

F r o m a study of the e f f e c t of 6 0 Co g a m m a radiat ion on benzy l a l c o h o l - 0 2 so lu t ions , it was shown that a high y i e ld of p e r o x i d e s (G = 50) w a s obtained [124], T h i s c l e a r l y indicated the e x i s t e n c e of a chain m e c h a n i s m , p r e s u m a b l y b e c a u s e p e r o x y r a d i c a l s can abs trac t a hydrogen a tom f r o m benzy l a lcohol .

Pheno l f r o m b e n z e n e

Many r e s e a r c h e r s have t r i ed to obtain phenol f r o m a b e n z e n e - w a t e r m i x t u r e in the p r e s e n c e and in the a b s e n c e of a i r ' [125] .

PL-236/7 115

In O2-saturated solut ions and at 220°C the G-va lue for the phenol formation was 50 m o l e c u l e s / 1 0 0 eV; this method of obtaining phenol may there fore be cons idered convenient for industrial application.

P r o s k u r n i n e t a l . [ 1 2 6 ] studied the e f f ec t s of t emperature , total dose , d o s e - r a t e and 0 2 - p r e s s u r e on the radiochemical oxidation of benzene in aqueous solut ions . Chr i s t ensen [127] carried out the rad io lys i s of aqueous 0 . 1 N alkaline solut ions of benzene with 6 0 C o - g a m m a rays in the p r e s e n c e of var ious inorganic oxides such as CuO, C r 2 0 3 , ZnO, T i 0 2 , Th0 2 , U 0 2 . When C 2 0 3 ge l , ZnO or T i 0 2 were added, a 9-13% i n c r e a s e in the y ie ld of phenol was obtained, and the addition of U 0 2 and ThO z caused a 31 and 39% i n c r e a s e .

P - xylene oxidation

A p -xy lene solution containing 1% Co naphthenate was irradiated [128] with fast neutrons and gamma rays in the p r e s e n c e of oxygen. After 8 h we obtained a yield of 12-22% p-toluic acid. The dose rate was: 1 . 2 5 X 1 0 1 3 e V / g s; the fast neutron beam was 107 n / c m 2 s; temperature was 60-130°C.

The oxidation of p -xy lene at 25°C induced by 6 0 C o - g a m m a radiation [129] i s acce lera ted by the addition of organic bromine compounds. C B r 4 i s the most eff ic ient s e n s i t i z e r and the rate of absorption of oxygen a c c e l e r a t e s to a maximum at about 2% oxidation and then d e c r e a s e s . The observed kinet ics are cons is tent with a mechani sm in which the auto-retardation and the pos t - i rradiat ion oxidation resul t f rom the react ion ROOH + HBr •RO' + HsO+Br between the hydroperoxide and hydrogen bromide formed as in termedia tes .

Oxidation of paraffin

The authors [130] used the f i s s i o n products in a pilot se t -up to initiate the oxidation of paraff in. They descr ibed the se t -up for the irradiat ion of paraffin without a ir bubbling, the r e s u l t s relat ing to the oxidation of pre - i rrad ia ted paraffin, the optimum work conditions for the source used and data on the d o s e s absorbed in the course of the exper iments .

Oxidation was carr ied out in the p r e s e n c e of a ir and at 135°C, F r o m 300g oxidized products , 87. 5g fatty ac ids were obtained. Af ter a vacuum dist i l lat ion at 1 m m Hg three charac ter i s t i c f ract ions were obtained.

Ethers

Irradiation of pure disopropyl ether [131] by 200-kV X - r a y s in the absence of oxygen g ives G(carbonyl) = 10 and Glalcohol )^ 0 . 7 . The carbonyl compounds are acetaldehyde, acetone and a long chain of methyl-ketone. In the presence of oxygen, the carbonyl yield i s = 25 and formalde-hyde i s formed in addition to acetaldehyde. New products include ac ids (G = 1. 5) and peroxides (G = 20).

S imi lar resu l t s were obtained using diethyl ether, G(carbonyl) = 20 and G(peroxide)= 15.

1 1 6 IONEISCU

Halogen compounds

The d i f f i cu l ty of obtaining pure compounds a p p e a r s to be one of the p r o b l e m s in th is f i e ld .

The oxidat ion of c h l o r o f o r m has been shown [132] to p r o c e e d via a chain m e c h a n i s m with G ( - C H C l 3 > - 100 for a d o s e - r a t e of 10 1 5 e V / g s us ing 6 0 C o g a m m a r a y s at r o o m t e m p e r a t u r e .

T e t r a f l u o r e t h y l e n e when i rrad ia ted in an equimolar m i x t u r e with 0 2 , at 1 atm total p r e s s u r e , with 50-kV X - r a y s at r o o m t e m p e r a t u r e , i s ox id ized by a chain p r o c e s s [133], The fo l lowing y i e l d s w e r e found: G(COF 2 ) = 3300 and G ( C F 2 ) p = 1090.

RADIOLYTIC CARBOXILATION

S imple organic s u b s t a n c e s can be ca'rboxilated by carbon dioxide under the in f luence of ioniz ing radiat ion [134-136] , In the i rrad ia ted C 0 2 aqueous so lu t ions formaldehyde , f o r m i c acid and oxal ic acid a r e f o r m e d by g a m m a -and a l p h a - p a r t i c l e i rradiat ion . The p r o c e s s i s s trongly dependent on the pH of the solut ion, d o s e - r a t e and d o s e . In a f o r m i c ac id aqueous solut ion, oxa l ic ac id i s produced with a G - v a l u e of 1. 8 at a d o s e of 2 X 1 0 1 8 e V / m l . At i n c r e a s i n g pH v a l u e s up to 1 0 . 8 the c h e m i c a l y i e ld (9. 1 m o l e c u l e s / 1 0 0 eV) i s i n c r e a s e d too. The quant i t ies of oxa l ic acid a r e s t rong ly dependent on the d o s e ra te . At 140 k r a d / h the curve p a s s e s through a m a x i m u m . T h i s m e a n s that for the format ion of oxa l ic acid many r e a c t i o n s take p lace , i . e . it i s a chain reac t ion .

The iron-II ions r e a c t a s s c a v e n g e r s for in termedia te rad io l i t i c product s of water , and reduce the y i e ld of f o r m i c acid in C 0 2 aqueous so lu t ions .

In methanol so lut ions saturated with C 0 2 , under the in f luence of g a m m a r a y s , g l y c o l i c ac id i s produced. The proposed m e c h a n i s m i s :

CH3OH + H' 'CH2OH + H 2

CH3OH + OH' >' CH2OH + I^O

COOH ' CH2OH + ' COOH » in ac id ic so lu t ions

CH2OH

CH2OH 'CH2OH + CO2 in neutral and a lkal ine so lu t ions

COO"

In di lute aqueous so lut ions the r a d i c a l s ' CH2OH and 'COOH a r e f o r m e d (G = 2. 95).

PL-236/7 1 1 7

By the combination of two rad ica l s , tartar ic acid was formed according to:

CH2OH | + H • COOH

' CHOH + H r

COOH

CH2OH + OH'

COOH

'CHOH + H2O

COOH

'CHOH

COOH

COOH (CHOH)2 COOH

At high concentrat ions of methanol no more oxal ic acid e x i s t s , and only ethylene g lycol i s formed [137],

FISSION FRAGMENTS INITIATE ETHYLENE GLYCOL SYNTHESIS

The react ion of methanol to produce ethylene g lyco l apparently in-v o l v e s pr imar i ly the combining of 'CH2OH radica l s that a r i s e e i ther when H' i s e jected from a neutral ized parent ion CH3OH+ or when a f r e e radical (H' , CHj, CH 2 , e t c . ) ex trac t s hydrogen f rom methanol:

H'

CH2OH+ -

CH,

Ho

->'CH2OH+ -

CH,

2 CH2OH' >(CH2OH)2

In the irradiated mater ia l , hydrogen extract ion must compete with recombinat ion of rad ica l s such as H' , CHg and CH 2 , which reduces the ethylene glycol y ie ld . '

F i s s i o n f ragments , each having about 20-22 unit charges at the moment of f i s s i o n , produce short but dense ionization t racks . The m o l e -cu le s within this track are ionized or broken into ionized fragments , which react d irect ly or combine with e l ec t rons to form neutral but e x t r e m e l y react ive f ragments . T h e s e f ragments then react by typical f r e e - r a d i c a l mechan i sm, a s we have descr ibed above.

Irradiation of methanol by f i s s i o n f ragments [138] g i v e s 0. 1 lb of ethylene g lycol per kilo'watt hour with 65% chemica l convers ion (plus an additional 10% convers ion to formaldehyde) . T h e s e r e s u l t s represent the irradiat ions c a r r i e d out in two different types of react ion v e s s e l s in two nuclear r e a c t o r s . Although these y i e l d s are high, they can probably be i n c r e a s e d by further r e s e a r c h on the use of di luents (such as water or H2) and chain t rans fer agents in irradiat ions above 150°C [139],

1 1 8 IONEISCU

Methanol irradiat ion exper iments w e r e des igned to show the e f f ec t s of t emperature , dilution with water and addition of carbon te trachlor ide .

RADIATION-INDUCED NITRATION OF AROMATIC COMPOUNDS

The nitration of aromat ic compounds induced by radiation has already been studied for neutral [140] or acidic [141] solutions of e ither benzene [140-142] or benzoic and sa l i cy l i c ac ids [141], In these invest igat ions the observed products were those of nitration (as nitrobenzene) or nitration and oxidation (as the corresponding nitrophenols) . In a recent work [143] the radiation-induced nitration of benzene and phenol in ac idic , neutral and alkaline aqueous solutions has been invest igated. A "Gammacel l 220" 6 0 C o - s o u r c e was used, giving a d o s e - r a t e of 2 .96X10 1 7 e V / m l min. Solutions were irradiated at natural pH or in the p r e s e n c e of sulphuric acid or sodium hydroxide up to concentrat ions of 0. 05 N and 0. 5 N r e s p e c t i v e l y . The corresponding G - v a l u e s of the o-nitrophenol formation under the conditions mentioned above were G = 0 .41; 0 .68; 0 . 3 8 , NO nitrobenzene or p icr ic acid was formed.

Referr ing to the mechanism, it s e e m s probable that this p r o c e s s may proceed s imultaneously by oxidation of the pr imary formed ni tro-compounds as wel l a s by a direct radical react ion.

DYES

The dyes undergo colour changes under the radiation, e i ther by oxi-dation or by reduction reac t ions . They there fore may be used in chemica l dos imetry . Interest in the behaviour of dyes under radiation began in 1931 [144],

Disco lourat ion of dyes i s not a sens i t ive enough react ion to be used for l o w - d o s e determinat ions .

Methylene blue, which i s eas i ly reduced by ionizing radiations to the c o l o u r l e s s form, i s the dye most studied [145, 146],

Methylene blue d i sco lours in the absence of oxygen and in the p r e s e n c e of s o m e organic substances such as albumin, ethanol and g lucose . The colour r e c o v e r s ent irely in the p r e s e n c e of an appreciable amount of oxygen, proving that the discolourat ion i s due to a reduction react ion . This react ion may be employed in the chemica l dos imetry by using a i r - f r e e so lut ions .

A large number of dyes behave l ike methylene blue under irradiation. The radiochemical discolourat ion of seven dyes in the p r e s e n c e and

absence of 2. 5-dichlorohydroquinone was examined in the p r e s e n c e of air [147], In the p r e s e n c e of the hydroquinone discolourat ion occurs because of the action of HO2 radica l s . H0 2 radica l s do not attack safranine T and neutral red, whereas methylene blue, acridine orange NO and the indigo dyes are d i sco loured . The G-va lue of discolourat ion by HO2 rad ica l s depends strongly on the dye concentration.

Some dye syntheses were performed exper imental ly under radiation, in part icular that of thionine [148], A hydrochloric solution of p-phenylene diamine was irradiated with a 6 0Co source in the p r e s e n c e of CUSO4 and

PL-236/7 119

"S(NH 4 ) 2 with d i f ferent pH v a l u e s . Most i r r a d i a t i o n s w e r e c a r r i e d out at 20°C, at d o s e - r a t e s f r o m 14 000 to 150 000 r a d / h . It s e e m s that the r e a c t i o n y i e l d m a y r e a c h 2.

DISCUSSION

E n d o t h e r m i c c h e m i c a l r e a c t i o n s o c c u r by the radio ly t ic p r o c e s s w h e r e the rad ia t ive e n e r g y i s par t ia l ly t r a n s f o r m e d into c h e m i c a l energy . Many s y n t h e s e s have been produced in d i f ferent l a b o r a t o r i e s in the hope that they can be appl ied in industry . F r o m the l a r g e number of r a d i o c h e m i c a l r e a c t i o n s p r o p o s e d (apart f r o m the p o l y m e r s ) , only the e thy lene b r o m i d e s y n t h e s i s h a s been u s e d in industry . A deta i l ed a n a l y s i s of rad io ly t i c p r o c e s s e s i s t h e r e f o r e needed.

The c h e m i c a l r e a c t i o n s induced by ioniz ing radiat ion g ive r i s e to a l a r g e number of product s , s o m e of t h e m in quant i t i es c o m p a r a b l e with those obtained by n o r m a l methods . A f t e r a c e r t a i n t i m e , the d e s i r e d product r e a c h e s a s t eady s tate , the product d e c o m p o s i n g at the s a m e rate a s it i s f o r m e d . If the s e c o n d a r y produc t s can be r e m o v e d , the r e v e r s e r e a c t i o n wi l l be d e c r e a s e d and thus the p o s s i b i l i t y of a g r e a t e r c o n v e r s i o n wi l l be c r e a t e d .

The g r e a t e r part of the radiat ion e n e r g y i s c o n s u m e d in p r i m a r y p r o c e s s e s to f o r m ions and exc i ted m o l e c u l e s . The ac t ivat ion e n e r g y for ion or rad ica l recombinat ion i s neg l ig ib le c o m p a r e d with that con-s u m e d for the p r i m a r y p r o c e s s e s . F r o m th i s a r i s e s the d i f f i cu l ty of d irec t ing the subsequent p r o c e s s e s t o w a r d s forming the d e s i r e d product .

In the r a d i o l y s i s of oxygen to obtain ozone , the wal l e f f ec t c a u s e s the r e c o m b i n a t i o n of a tomic oxygen with i t se l f or with ozone m o l e c u l e s producing a c o n s i d e r a b l e d e c r e a s e of the ozone y ie ld . L i n d e ' s c a l c u l a t i o n s show that the d e c r e a s e of th is e f f ec t p r o d u c e s a c o n s i d e r a b l e i n c r e a s e in ozone c o n v e r s i o n . If in the hydraz ine r a d i o s y n t h e s i s the hydrogen could be r e m o v e d by d i f fus ion , the h y d r a z i n e c o n v e r s i o n would be much g r e a t e r .

The r a d i o l y s i s of methane o f f e r s an even c l e a r e r e x a m p l e . The methane being i r r a d i a t e d with alpha p a r t i c l e s [63], with 2 MeV e l e c t r o n s [149], deu terons . X - r a y s or g a m m a r a y s [150], with s l o w e l e c t r o n s [151], with f i s s i o n r e c o i l f r a g m e n t s [152], with e l e c t r i c d i s c h a r g e s [153], with fas t e l e c t r o n s f r o m a l i n e a r a c c e l e r a t o r [154] or with 6 0 C o - g a m m a r a d i -ation, g i v e s r i s e to the s a m e products : g a s e o u s and saturated hydrocarbons of C1-C6 , and an o i ly l iquid c o m p o s e d of both unsaturated and saturated hydrocarbons , of C 1 6 - C 2 8 [150], B e c a u s e the condensat ion i s r e l a t e d to the p r i m a r y a c t s of r a d i o l y s i s , the ra t io C / H g i v e s 72% CnH 2 n and 28% C n H 2 n + 2. The nature of the products i s independent of the in i t ia l g a s p r e s s u r e , the d o s e - r a t e and t e m p e r a t u r e up to 100°C. But the methane c o n v e r s i o n v a r i e s f r o m 10 to 100%. The G - v a l u e s d e c r e a s e at high d o s e s , beyond 50 Mrad.

A c c o r d i n g to L a m p e , the p o l y m e r quantity i n c r e a s e s proport iona l ly to the d o s e . M o r e o v e r , the identity G(H2) = G(.C H 4J is found.

W e x l e r and Y e s s e [155] gave a m e c h a n i s m f o r the f o r m a t i o n of d i f ferent ions by i o n - m o l e c u l e r e a c t i o n s , and showed that the p a s s a g e to

1 2 0 IONEISCU

higher homologues , and the concomitant formation of ethylene and acety lene , occur as fol lows:

CH4+ CH4 »CH5 + CH3

CH*+e' » CHj +H 2 »CH2+H2 + H

CH3++CH4 ' (C2H7V » C 2 H 5 + H 2

C2H7+e" » C2Hg + H 2 »C2H4 + H2 + H'

C2H5+ + e — ^ C2H * • C2H4 + H •

The formation of ethylene a lso takes place by radical recombination in the c a s e of excited molecules:

CH4 -TWT- CH^ »CHG + H' ; 2CH3 »C2H6

CH3 «— ' C H 2 + H 2CH2 »C2H4

CH3 + CH2 C2H5

C2H,- < 1 CH - CHG + HG

CH2 - C H ' i = ? C H = CH + H' nCH = CH vpolymer

The condensed fraction, which i s not yet well known, constitutes the only interest ing product result ing from all the numerous works concerning methane radio lys i s . It might be avoided if the condensation or the poly-merizat ion of unsaturated hydrocarbons could be hindered.

F a r l e y and Lloyd [152] and Miguel and Chirol [153], who worked by means of dark d i scharges , showed the initial formation of smal l quanti-t i e s of ethylene and t races of acetylene, which disappeared after a short t ime of irradiation.

In recent work by Hummel [115, 156], smal l quantities of oxygen were added to methane. In this case , the ethylene appeared with a G-value of 0. 65 oxygen, probably inhibiting partially the condensation or the poly-merizat ion. When the static experiments were replaced with dynamic ones, and the rad io lys i s products passed through a trap cooled with liquid nitrogen, the G-value of ethylene was high.

Hummel showed that the p r o c e s s e s invoked for C H 4 - r a d i o l y s i s had to explain the ethylene and acetylene formation, and many of the products, previous ly ascr ibed to the ion-molecule p r o c e s s e s , resulted from ethylene and acetylene react ions taking place in the primary step. The energy content of an excited molecule i s so great that it decomposes to give a methylene radical and reacts with other CH 4 molecu les to give ethylene and acetylene direct ly .

A comparison with conventional c la s s i ca l methods of acetylene for-mation from methane, taking into consideration that the ionizing radiation rep laces thermal or e lec tr ic energ ies , g ives some interest ing conclusions.

PL-236/7 1 2 1

In the e l ec tr i c d i scharge the methane r e m a i n s only 1 / 1 0 0 0 - 1 / 1 0 0 s for the radical format ion and af terwards the mixture i s soon cooled for the recombination of rad ica l s . Perhaps if methane p a s s e s rapidly through a strong radiation f ie ld that o f fers a certa in dose-rate , and the final mixture can be c irculated to condense the unsaturated hydrocarbons, it wil l be poss ib l e to obtain great quantities of ethylene and acety lene f rom methane.

Another problem i s to remove the hydrogen formed (contributing to the r e v e r s e react ions) by diffusion.

T h e s e examples show that this new form of energy i s not used wel l . The bas ic invest igat ions with ionizing radiat ions have given us an under-standing of the natural phenomena (the ro le of the solvated e lec tron in solutions, charge , energy and proton t rans fer , the type of ions and ex-cited m o l e c u l e s , e t c . ) . The application of this knowledge to economic use needs much m o r e work.

R E F E R E N C E S

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FIELD, F . H . , FRANKLIN, I. L . , LAMPE, F . W . , J. Am. c h e m . Soc. 79 (1957) 2419. MELTON, C . E . , RUDOLPH, P. S . , I. c h e m . Phys. 32 (1960) 1128. FIELD, F . H . , J. Am. c h e m . Soc. 83 (1961) 1523. FUCHS, R . , Z. Naturf. 16A (1961) 1026. HARRISON, A . G . , Can. J. Chem. 41 (1963) 236 . KEBARLE, P . , GODBOLE, E. W . , J. c h e m . Phys. 39 (1963) 1131. WEXLER, S . , MARSHALL, R . , J. Am. chem. Soc. 86 (1964) 781. HAYWARD, J . C . , BRETTON, R . H . , Chem. Engng Prog. Symp. Ser. No. 13 (1954) 73. HOLROYD, R . A . , KLEIN, G . W . , USAEC Rep. RRL-143 (1964). HOLROYD, R . A . , KLEIN, G . W . , Int. J. appl. Radiat. Isotopes 15 (1964) 633. CROSS, D . A . , USAEC TID-22232 (1965). LEHMANN, H. P . , STEIN, G . , FISCHER, E . , Chem. Commun. No. 22 (1965) 583. SRIVASTAVA, S . B . , in Pioc. Symposium on Nuclear Radiation Chemistry, Waltair, India, 1966, 134-40 . YANG, J. Y . , MARCUS, 1. , J. chem. Phys. 42 (1965) 3315. FIELD, F . H . , I. phys. Chem. 68 (1964) 1039. RANSSEAN, Y . , MAINS, G . , J. phys. Chem. 68 (1964) 3081. COCHRAN, T. B . , USAEC Rep. TID-22231 (1965). BATES, T . H . , BURNS, W . G . , EAST, M . J . , MORRIS, B . , REED, C.R. V . , WILKINSON, R. W. , WINTER, J . A . , Rep. AERE-R-3743 (1962). BURNS, W . G . , WILD, W . , WILLIAMS, T . F . , in Int. Conf. peaceful Uses atom. Energy (Proc. Conf. Geneva, 1958) 2 9 , UN, Geneva (1958) 266. BURNS, W . G . , REED, C . R . V . , Trans. Faraday Soc. 59 (1963) 101.

BURNS, W . , Trans. Faraday Soc. 59 (1963) 101. GAEUMANN, T . , SCHULER, R. H . , J. phys. Chem. 65 (1961) 703. BURNS, W . G . , JONES, J . D . , Trans. Faraday Soc. 60 (1964) 2022. TROFIMOV, V . I . , CHKHEIDZE, I . I . , BUBEN, N . Y a . , Kinet. Katal. 5 (1964) 736. EBERHARDT, M . , J. phys. Chem. 67 (1963) 2856. SCHULER, R . H . . Trans. Faraday Soc. 61 (1965) 100. MERKLIN, J . F . , LIPSKY, S . , J. phys. Chem. 68 (1964) 3297. GAEUMANN, T . , Helv. ch im. Acta 46 (1963) 2873. BURR, J . G . , GOODSPEED, F . , J. chem. Phys. 40 (1964) 1433. CHILTON, H . T . J . , PORTER, G . , J. phys. Chem. 63 (1959) 904. BROCKLEHURST, B . , PORTER. G . , SAVADATTI, M . , Trans. Faraday Soc. 60 ( 1 9 6 4 ) 2 0 1 7 . PROKSCH, E . , BILDSTE1N, H . , Atompraxis 10 (1964) 105. ROSEN, I . , "Some industrial aspects of radiat ion-induced chlorination reactions", Large Radiation Sources in Industry (Proc. Conf. Warsaw, 1959) 2 , IAEA, Vienna (1960) 97. Commercial radiation synthesis of ethyl bromide, Nucleonics 21 1 (1963) 74. ROSINGER, S . , C h e m i e - I n g r - T e c h . 3 7 N o . 2 (1965) 128. HUGHES, G . , in Oxidation and Combustion Reviews 1 , (TIPPER, C . F . H . , Ed.) Elsevier, Amsterdam (1965) 47. JOHNSON, G.R. A . , SALMON, G. A . , J. phys. Chem. 65 (1961) 177. HEARNE, J. A . , HUMMEL, R . W . , Rep. AERE-R-4581 (1964). HEARNE, J. A . , HUMMEL, R . W . , Rep. AERE-R-4871 (1965). DOBSON, G . , HUGHES, G . , J. phys. Chem. 69_(1965) 1814. BAKH, N. A . , Symposium on Radiation Chemistry, Academy of Sciences of the USSR, Moscow, 1965, English translation, p. 145, 156. DEWHURST, H. A. , J. phys. Chem. 63 (1959) 813. MCCARTHY, R. L. , MACLACHLAN, A . , Trans. Faraday Soc. 57 (1961) 1107. MIKHA1LOV, B . M . , KISELEV, V. G . , Bull. Acad. Sci . USSR Div. chem. Sci . (1960) 1504. HAYON, E. , WEISS, J . J . , J. c h e m . Soc. (1961) 3970. LICHTIN, N . N . , ROSENBERG. L. A . , IMAMURA, M . , J. Am. chem. Soc. 8 4 ( 1 9 6 2 ) 3587. 1MAMURA, M . , SEKI, H . , Sci . Pap. Inst. phys. chem. Res . , Tokyo 59_ (1965) 146. PROSKURNIN, M. A . , BARELKO, E . V . , in Int. Conf. peaceful Uses atom. Energy (Proc. Conf. Geneva, 1955) 7, UN, New York (1956) 542. Int. Conf. peaceful Uses atom. Energy (Proc. Conf. Geneva, 1 9 5 8 i U N , Geneva (1958). PROSKURNIN, M. A . , BARELKO, E . V . , KARTASHEVA, L. I . , Problemy f i z . khim. (1959) 177. CHRISTENSEN, H. C . , Aktiebolaget Atomenergi, Stockholm, Rep. AE-192 (1965). COSTEA, T . , MANTESCU, NEGOESCU, I . , Int. J. appl. Radiat. Isotopes 13 (1962) 1 - 6 , 306.

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[131] BAKH, N . A . , MEDVEDOVSKY, V . I . , SARAEVA, V . V . , in Int. Conf. peaceful Uses atom. Energy (Proc. Conf. Geneva, 1958) 29, UN, Geneva (1958) 128.

[132] SCHULTE, I . W . , SUTTLE, J . F . , WILHELM, R., J. Am. c h e m . Soc. 75 (1953) 2222. [ 133 ] CAGLIOTI, V . , LENZI, M. , MELE, A . , Nature, Lond. 201 (1964) 610. [ 134 ] GETOFF, N . , Discuss. Faraday Soc. 36 (1963) 314. [ 135 ] GUTLBAUER, F . , GETOFF, N . , Radiochim. Acta 3 (1964) 1. [ 136 ] GUTLBAUER, F . , GETOFF, N . , Int. I. appl. Radiat. Isotopes 16 (1965) 199. [ 137 ] GETOFF, N . , GUTLBAUER, F . , SCHENK, G . O . , Int. ] . appl. Radiat. Isotopes 1]_ (1966) 341. [138] WIEBE, A . K . , CONNER, W. P. , KINZER, G . W . , Nucleonics (Feb. 1961) 50. [ 139 ] CONNER, W. P . , DAVIS, W . E . , Canadian Patent No. 576 979, 2 lune , 1959; German Patent

No. 1045 , 403, 27 May, 1959; U . K . Patent 770. 594, 20 March, 1957. [ 1 4 0 ] BROSZKIEWICZ, R . , MINC, S . , ZAGORSKI, Z. P., Institute of Nuclear Research, Warsaw, Rep.

123/ChR (1959); BROSZKIEWICZ, R. , MINC, S . , ZAGC5RSKI, Z. P . , Bull. Acad. pol. Sc i . Sgr. Sci. ch im. 8 (1960) 103.

[ 141 ] CHERNOVA, A. L . OREKHOV, V. D . , PROSKURNIN, M . A . , in Tr. 2 - 9 0 (Vtorogo) Vses. Soveshch. po Radiats. K h i m . , 1960, Akad. Nauk SSSR, Otd. Khim. Nauk, Moscow ( 1 9 6 2 ) 2 3 3 .

[142] SUGIMOTO, K . , ANDO, W . , OAE, S . , Bull. c h e m . Soc. lapan 36 (1963) 124. [ 143 ] BROSZKIEWICZ, R . , Nature, Lond. 209 (1966) 1235. [ 144 ] CLARK, G . L . , FITCH, K .R . , Radiology r7 (1931) 285. [ 145 ] DAY, M . J . , STEIN, G . , Radiat. Res. 6 (1957) 666. [146] HA YON, E . , SCHOLES, G . , WEISS, I . , I. c h e m . Soc. (1957) 301. [ 147 ] BALES TIC, F . , MAGAT, M . , in Large Radiation Sourcesin Industry (Proc. Conf. Warsaw, 1959) 2,

IAEA, Vienna (1960) 149. [148] RAKINTZIS, N . , PAPACONSTANT1NOU, E . , Z. phys. C h e m . 4 4 ( 1 9 6 5 ) 257 . [149] LAMPE, F . W . , J. Am. chem. Soc. 79 (1959) 1055. [150] MAURIN, ] . , I. Ch im. phys. 59 (1962) 15. [151] WILLIAMS, R. , J. phys. Chem. 63 (1959) 776. [152] FARLEY, C. W. , LLOYD, W . A . , Trans. Am. nucl. Soc. 5 (1962) 1. [153] MIGUEL, R . , CHIROL, M . , Bull. Soc. chim. Fr. 8 ^ 9 ( 1 9 6 2 ) 1677. [154] HUMMEL, R. W . , Nature, Lond. 192 (1961) 1178. [155] WEXLER, S . , IESSE, N . , I. Am. c h e m . Soc. 84 (1962) 3425. [156] HEARNE, J. A . , HUMMEL, R. W. , Rep. AERE-R-4581 (1964).

RADIATION-INDUCED POLYMERIZATION: MECHANISMS AND INDUSTRIAL ASPECTS

D . O . HUMMEL. CHRISTEL SCHNEIDER, R . C . POTTER,

G . LEY, J . DENAXAS, D . WIDDERSHOVEN I N S T I T U T FÜR PHYSIKALISCHE CHEMIE UND KOLLOIDCHEMIE, ABTEILUNG FÜR STRAHLENCHEMIE, UNIVERSITY OF COLOGNE, COLOGNE, FEDERAL REPUBLIC OF GERMANY AND M . RYSKA INSTITUTE FOR MACROMOLECULAR CHEMISTRY, ACADEMY OF SCIENCES, PRAGUE, CSSR

Abstract

RADIATION-INDUCED POLYMERIZATION: MECHANISMS AND INDUSTRIAL ASPECTS. Rad ia t i on -induced p o l y m e r i z a t i o n is one of the ma in f ie lds in r ad i a t ion chemis t ry that has an impor t an t p r a c t i c a l v a l u e . This paper is in tended to g i v e a cu r ren t p ic ture of r a d i a t i o n - i n d u c e d p o l y m e r i z a t i o n in both f u n d a m e n t a l and app l i ed research and d e v e l o p m e n t . T h e subjec ts cove red i nc lude suspension p o l y m e r i z a t i o n , emul s ion p o l y m e r i z a t i o n , c o p o l y m e r i z a t i o n , g r a f t c o p o l y m e r i z a t i o n , ionic p o l y m e r i z a t i o n of l iquid m o n o m e r s , and so l id - s t a t e p o l y m e r i z a t i o n . A descr ipt ion is g iven a lso of a p i l o t - p l a n t inves t iga t ion in to c e r t a i n r a d i a t i o n c h e m i c a l processes .

INTRODUCTION

T h e r e i s no doubt that the study of radia t ion- induced polymer iza t ion reac t ions has en la rged our knowledge of the mechanism of this type of reac t ion to a cons iderab le degree . Well-known sys t ems have been r e -invest igated, and completely new aspec t s have been revea led of the kinet ics of emuls ion polymeriza t ion , ionic polymer iza t ion and so l id - s t a t e po lymer iza t ion . F u r t h e r m o r e , polymer iza t ion reac t ions have been init iated under condit ions where " c l a s s i c a l " in i t i a to rs have previously fa i led. Final ly , quite a number of po lymers have been synthesized, which cannot, o rd ina r i ly , be p r e p a r e d by conventional p r o c e s s e s .

T h e r e has been, and the re s t i l l i s , much scept ic i sm on the indus t r i a l applicabili ty of rad ia t ion- in i t ia ted polymer iza t ion . Undoubtedly the idea of la rge r a d i a t i o n - s o u r c e s - not to speak of nuc lear r e a c t o r s - as vi ta l components of indus t r i a l syntheses i s ana thema to many chemis t s . The main r e a s o n s fo r this atti tude may be the uncer ta in t i es in the calculat ion of the p r i ce of the f inal product , f e a r f o r the potential haza rds when rad i -ation i s involved, o r me re ly the cons iderab le r ed - t ape that has to be ove r -come be fo re an i r r ad ia t ion unit can be ins ta l led . Never the less , it i s un-rea l i s t i c to bel ieve that radiat ion chemica l p r o c e s s e s have no indus t r i a l fu tu re ; and th i s i s especia l ly t r u e f o r radia t ion- in i t ia ted po lymer iza t ions o r o ther rad ia t ion- in i t i a ted chain reac t ions .

125

1 2 6 HUMMEL e t a l .

One of the m a i n p r o b l e m s i s l ack of f a c i l i t i e s on a p i l o t - p l a n t s c a l e . T h i s s i t u a t i o n h a s l ed a group of rad ia t ion c h e m i s t s in t h i s l a b o r a t o r y to p lan s u c h , a p i lot plant to s tudy cont inuous o r d i s c o n t i n u o u s p o l y m e r i z a t i o n r e a c t i o n s u n d e r a l a r g e v a r i e t y of f a c t o r s s u c h a s d o s e - r a t e , | t e m p e r a t u r e and p r e s s u r e . This , i s not y e t an i d e a l plan, h o w e v e r .

W e a l s o know of a s m a l l n u m b e r of s i m i l a r f a c i l i t i e s b e i n g p lanned or a l r e a d y in o p e r a t i o n ; f o r i n s t a n c e , i n the B r o o k h a v e n Nat iona l L a b o r a t o r y , in Wantage ( U . K . A . E . A . ) and in S a c l a y ( F r a n c e ) .

E s s e n t i a l l y , then, the m a i n c o n c e r n of th i s r e v i e w i s to r e v i t a l i z e the d i s c u s s i o n on i n d u s t r i a l a p p l i c a t i o n s of r a d i a t i o n - i n i t i a t e d p o l y m e r i z a t i o n . The d e s c r i p t i o n of r a d i a t i o n - i n i t i a t e d p o l y m e r i z a t i o n r e a c t i o n s be ing i n v e s t i g a t e d in l a b o r a t o r i e s throughout the w o r l d i s not by any m e a n s e x h a u s t i v e . In fact , s u c h a d i s c u s s i o n would f i l l a l a r g e v o l u m e , and s o we d e c i d e d to m a k e a j u d i c i o u s and, it i s hoped, a p r a g m a t i c s e l e c t i o n .

I. SUSPENSION AND EMULSION POLYMERIZATION

Two t y p e s of r e a c t i o n s are w e l l d i f f e r e n t i a t e d by t h e i r p h y s i c s and k i n e t i c s : h o m o g e n e o u s and h e t e r o g e n e o u s p o l y m e r i z a t i o n . The l a t t e r can be d iv ided into two f u r t h e r g r o u p s : (1) S y s t e m s that are in i t ia l ly h o m o g e n e o u s and that b e c o m e h e t e r o g e n e o u s

during the p o l y m e r i z a t i o n r e a c t i o n . (2) S y s t e m s that c o n s i s t in i t i a l l y of two or m o r e d i f f e r e n t p h a s e s .

T h e f i r s t group i s r e p r e s e n t e d by p o l y m e r i z a t i o n s in the g a s p h a s e , p r e c i p i t a t i o n p o l y m e r i z a t i o n s and s o l i d - s t a t e p o l y m e r i z a t i o n s . S u s p e n s i o n and e m u l s i o n s y s t e m s be long to the s e c o n d group. H o m o g e n e o u s s y s t e m s are c o m p a r a t i v e l y s i m p l e in t h e i r k i n e t i c s . On the o t h e r hand, rap id ly p o l y m e r i z i n g m o n o m e r s in h o m o g e n e o u s s y s t e m s m a y c a u s e s e v e r e p r o b l e m s of heat t r a n s f e r and m o l e c u l a r we ight c o n t r o l . In s u c h c a s e s , the u s e of p r o p e r s o l v e n t s m a y he lp to o v e r c o m e t h e s e p r o b l e m s . S tr i c t ly speak ing , no p o l y m e r i z a t i o n c a n be c o n s i d e r e d a s h o m o g e n e o u s in a k ine t i c s e n s e s i n c e the p o l y m e r i t s e l f c a n be c o n s i d e r e d a s a new p h a s e , e v e n though p h a s e s e p a r a t i o n i s not o b s e r v a b l e . T h i s i s e s p e c i a l l y t rue in the p r e s e n c e of p o o r s o l v e n t s .

By de f in i t ion , in a s u s p e n s i o n p o l y m e r i z a t i o n the m o n o m e r i s d i s -p e r s e d in a n o n - s o l v e n t by the u s e of a d i s p e r s i n g agent that d o e s not f o r m m i c e l l e s in the s o l v e n t p h a s e ; in t h e s e c a s e s , the in i t i a tor i s u s u a l l y s o l u b l e in the m o n o m e r but r e l a t i v e l y i n s o l u b l e in the s e c o n d p h a s e (usua l ly w a t e r ) . E m u l s i o n s a r e f o r m e d when the e m u l s i f i e r m o l e c u l e s a g g r e g a t e and the m o n o m e r i s part ly o c c l u d e d in t h e s e m i c e l l e s ; h e r e the i n i t i a t o r i s s o l u b l e in the cont inuous p h a s e (usua l l y w a t e r ) and c o m p a r a t i v e l y i n s o l u b l e in the m o n o m e r . A th ird p h a s e m a y be f o r m e d by the m o n o m e r d r o p l e t s , wh ich a r e o r d e r s of magni tude l a r g e r than the m o n o m e r - s w o l l e n m i c e l l e s . The p r e f e r r e d loc i f o r the p o l y m e r i z a t i o n r e a c t i o n , in th i s c a s e , are the m i c e l l e s , and not the m o n o m e r d r o p l e t s .

T h e c r i t i c a l f a c t o r d e t e r m i n i n g the p h y s i c s and k i n e t i c s of the s y s t e m i s , in both c a s e s , the type of d i s p e r s i n g agent ( p r o t e c t i v e co l lo id ) o r e m u l s i -f i e r that i s e m p l o y e d . ( W a t e r - s o l u b l e m o n o m e r s cannot be c o n s i d e r e d in t h i s r e s p e c t . ) Thus , in the c a s e of rad ia t ion in i t ia t ion w e c a n o b s e r v e the a n a l o g o u s f o r m a t i o n of k i n e t i c a l l y " r e a l " e m u l s i o n o r d i s p e r s i o n s y s t e m s , depending on the kind of p r o t e c t i v e c o l l o i d o r e m u l s i f i e r , a l though the

P L - 2 3 6 / 9 1 2 7

formation of rad ica l s i s not re s t r i c t ed to one of the phases as in the c a s e of chemica l in i t iators .

E m u l s i o n s or suspens ions may be of the types "o i l - in -water" or "water - in -o i l" . Usual ly the monomer i s the d i s p e r s e d phase; however , during the last few y e a r s inverse s y s t e m s have been invest igated in which the m o n o m e r i s the continuous phase [1] .

1. Radiation-init iated suspens ion polymerizat ion

The f i r s t and, up to now, the last study on suspens ion po lymerizat ion in the aqueous phase was published in 1959 by Chapiro and Maeda [2] . F o r each exper iment , 5.5 ml of s tyrene was d i s p e r s e d in 45 ml of water with 0.09 g of polyvinyl alcohol as a protect ive col loid. Each batch was de-gassed , agitated and po lymerized under the inf luence of gamma radiation. The react ion rate was proportional to l<>-65, a n ( j ^he m o l e c u l a r weight was proportional to I"0-5; Up to 60% of the convers ion was proportional to the react ion t ime . Comparing the condit ions, the o v e r - a l l react ion rate of the suspension po lymerizat ion was four t i m e s the rate of the bulk polymerizat ion, probably because a large fraction of the initiating radica l s i s formed in the aqueous phase and, from there, enters the d i spersed monomer drople t s . In this way the radiation-init iated suspens ion polymerizat ion d i f f er s remarkably from the conventional suspens ion polymerizat ion, which i s initiated by radica l s of an oleophil ic init iator d i sso lved in the monomer . This react ion can therefore be regarded as a water -coo led bulk polymerizat ion.

Chapiro and Maeda observed an o v e r - a l l react ion rate of 0.007% min"1

(or 6.7 X 10"6 mo le kg"1 min"1) at a d o s e - r a t e of 8.7 X 1015 eV g"1 min"1 . The ( v i s c o s i m e t r i c ) molecu lar weight of the po lymer was 2 X 104 under the above conditions, and the polymer was only partial ly soluble in benzene. Very l ikely the benzene- inso luble fract ion (20%) was grafted by polyvinyl alcohol, which, in aqueous solution, i s readi ly degraded by gamma radiation.

Nakashio et al. [3] were the f i rs t the invest igate a radiat ion-init iated suspens ion polymerizat ion in a non-aqueous s y s t e m . They d i spersed liquid formaldehyde at -80°C in n-heptane or methylcyclohexane (28% HCHO in the hydrocarbon), in the p r e s e n c e of sorbitane sesquio leate as a d i s -pers ing agent. The solubility of formaldehyde in n-heptane at -80° C i s l e s s than 2%. The polymerizat ion was initiated by g a m m a radiation, and the suspens ion in the evacuated v e s s e l was agitated during the subsequent react ion. The o v e r - a l l react ion rate i s , init ial ly, a lmost independent of the concentrat ion of the d i spers ing agent, and a l so of the s i z e and number of monomer di'oplets. On the other hand, the react ion rate i n c r e a s e d a lmost proportionally with the d o s e - r a t e (I0-9) and also showed a dependency on the m o n o m e r concentration in the s y s t e m . The average molecu lar weight of the po lymer was about 105 and was nearly independent of the d o s e - r a t e . The init ial react ion rate, with a monomer concentration of 28% and a d o s e - r a t e of 5.5 X 1016 eV g"1 min"1 , was 0.35% min"1 (or 3.27 X 10"2 mole kg"1 ( suspension) min The result ing polyoxymethylene i s pear l - shaped and has an average part ic le d iameter of 50-100 /Lim.

The s a m e authors a lso invest igated the radiat ion-init iated po lymer i -zation of formaldehyde in toluene or ethyl bromide solution [4] . F r o m their r e s u l t s the authors conclude that the polymerizat ion fo l lows an ionic


mechani sm, with the molecu lar weight of the po lymer pr imari ly determined by chain t rans fer to the monomer .

Final ly, Chapiro and Jendrychowska-Bonamour [5] invest igated a suspens ion polymerizat ion at low temperatures in a sol id medium. Their resu l t s are d i s c u s s e d below.

Although not much i s known concerning radiation-init iated suspens ion polymerizat ion, this technique i s undoubtedly of cons iderable industrial in teres t . B e c a u s e of the high fraction of initiation from the aqueous phase, the rates should be higher than in homogeneous po lymerizat ions . If d i spers ing agents with a good radiation res i s tance are used, the result ing po lymers .should contain fewer impuri t ies than conventional suspension po lymers .

2. Radiation-init iated emuls ion polymerizat ion

Most of the work concerned with this type of polymerizat ion react ion was carr ied out by the following seven groups of radiation chemis t s : (1) D .S . Ballantine e t a l . (Brookhaven National Laboratory). (2) S .S . Medvedev e t a l . (Karpov Institute, Moscow). (3) P . E . M . Allen e t a l . (University of Birmingham, United Kingdom). (4) J .W. Vanderhoff at al. (Dow Chemical Company). (5) G . J . K . A c r e s and F . L. Dalton ( U . K . A . E . A . , Wantage Laboratory). (6) . V . T . Stannett et al. (Research Triangle Institute, Durham, N. C. ). (7) D .O. Hummel e t a l . (University of Cologne, F e d e r a l Republic of

Germany). Since radiation-init iated emuls ion polymerizat ion (EP) i s industrial ly

promis ing we shall cons ider this subject in some detai l .

2 . 1 . D .S . Ballantine et al. [6] were the f i r s t to study gamma-radiat ion-initiated EP. The monomer (styrene) was emuls i f i ed in 1 and 3% aqueous solutions of Duponol G (probably an amine salt of a fatty alcohol sulphate), and was irradiated at a d o s e - r a t e of 6 X 1016 eV g"1 min"1 . The authors observed o v e r - a l l reaction rates 10 to 100 t i m e s higher and molecu lar weights approximately 10 t i m e s higher than those obtainable by bulk poly-merizat ion under comparable conditions. With a monomer concentration of 1 mole kg"1 (emulsion), at 25°C an o v e r - a l l reaction rate of 5.7 X 10~3 mole kg"1 (emulsion) min"1 and molecular weights of approxi-mately 1 X 10® were observed. The react ion rate appeared to be dependent on the temperature of the s y s t e m , and an o v e r - a l l activation energy for the react ion of 3.7 kcal mole"1 was calculated.

2 . 2 . L. P . Mezhirova et al. [7] have studied the E P of s tyrene and methyl methacrylate in the presence of sodium laurate, "MK" (Ci5H31SOsNa), Nekal (alkyl naphthalene sulphonate) and cetylpyridinium bromide as e m u l s i f i e r s (3% aqueous solutions). The m o n o m e r - w a t e r ratio was about 1 : 3, the t emperatures var ied between 25 and 87°C, and the d o s e - r a t e was kept constant at about 2.4 X 1017 eV g ^ m i n " 1 . The o v e r - a l l react ion rate was 100-300 t i m e s higher than for a bulk polymerizat ion under comparable conditions; it was approximately independent of temperature , but depended on the type of e m u l s i f i e r . The highest ra tes were obtained with sodium laurate, the lowest ones with the cationic emuls i f i er , ce ty l -pyridinium bromide. The absolute o v e r - a l l react ion rate for an emuls ion

P L - 2 3 6 /9 1 2 9

with 3% "MK" was 7.7 X 10"4 mole kg (emulsion)"1 min"1 . The average molecu lar weight of the po lymer was about 1.6 X 106, which i s roughly 10 t imes higher than the molecu lar weight obtained by a bulk polymerizat ion under comparable conditions. The authors observed a cons iderable "after-effect": af ter the interruption of the radiation, the polymerizat ion continued for about 60 - 65 min and the convers ion during this period was approxi-mately 15 - 20% of the total monomer . This a f t er - e f f ec t s e e m e d to in-c r e a s e with d e c r e a s i n g temperature . The authors as sume that the a f ter -effect can be explained by long- l ived radica l s in emuls ion s y s t e m s , or by the presence of H^D2 formed during the rad io lys i s of water . The rate constant for the terminat ion react ion was es t imated to be 10 -10 3 l i t r e s / mole"1 s"1 .

The o v e r - a l l react ion rate during the E P of methyl methacrylate was much higher than for the E P of s tyrene: at 25°C, and under the condit ions given above, a convers ion of 63% was obtained in 12 min. The maximum o v e r - a l l react ion rate under the descr ibed conditions was 13.8% min"1 , i . e . 3.4 X 10"1 mo le kg (emulsion)"1 min"1 . The molecu lar weight of the po lymer was 1.3 X 106.

2 . 3 . P . E . M . Al len et al. [8] have invest igated the radiat ion-induced grafting of s tyrene and methyl methacrylate on polyvinyl acetate ( f i l m s , la texes , and f inely divided sol id polymer) . In this connection the authors a l so studied the radiat ion-induced E P of vinyl acetate and methyl metha-cry late . An emuls ion of 1.25 m l monomer and 10 ml of 3.75% aqueous sodium dioctyl sulphosuccinate was irradiated with a d o s e - r a t e of 6 X 1016 eV g"1 min"1 . The resu l t s of these authors are shown in Table I.

T A B L E I. EMULSION POLYMERIZATION OF VINYL A C E T A T E (VAc) AND M E T H Y L M E T H A C R Y L A T E (MMA) [8]

M o n o m e r Temperature

r c > Part ic les

(ml" 1 l a tex) React ion rate ( m o l e l ' V )

kp

(1 mole" 1 s" 1 )

V A c 15 4 . 8 5 X 1 0 1 5 5 . 7 7 2 3 0

V A c 1 4 8 . 4 4 X 1 0 1 5 9 . 8 2 3 0

V A c 2 8 9 . 3 2 X 1 0 1 5 1 0 . 1 2 2 0

MMA 5 1 0 . 4 X 1 0 1 5 4 . 2 9 2

2 . 4 . J . W . Vanderhoff et al. [9] have compared the E P of s tyrene init iated by potass ium persulphate with that by gamma radiation. They u s e d e m u l -s ions with two m o n o m e r concentrat ions (20% and 40%) and four e m u l s i f i e r concentrat ions (1.5, 1.75, 2.0 and 2.25% of sodium dihexyl sulphosuccinate) . The d o s e - r a t e (gammaradiat ion) was 4.42 X 1 0 1 6 e V g"1 min"1 and the t emperatures w e r e 30, 50 and 70°C.

It was found that the number of part i c l e s N increased with the square of the e m u l s i f i e r concentration, w h e r e a s according to the theory of Smith and Ewart, N should i n c r e a s e with the 0.6th power of (E). This deviation from the theory and from the r e s u l t s of Gerrens et al. i s , according to the

10


authors, a consequence of the different e m u l s i f i e r s . The va lues for the propagation and terminat ion constants (kp and k t) w e r e calculated to be 41 l i t r e s / m o l e " 1 s'Mkp, 30°C), and 1 0 4 - 1 0 5 l i t r e s / m o l e ' 1 s ' 1 ^ , 50°C).

Final ly , the authors invest igated the "competi t ive growth" of la texes of known part ic le s i z e , and determined the corresponding re su l t s for radiation-induced and catalyt ical ly induced E P ,

The only s ignif icant d i f ference between the two types of init iation became obvious in the temperature dependence of part ic le formation. F o r persulphate- in i t iated s y s t e m s , the part ic le number N i n c r e a s e s with in-c r e a s i n g temperature; radiat ion-init iated s y s t e m s , on the other hand, show the opposite e f fect . This i s explained as fo l lows .

The rate of radical format ion (p) for radiation-init iated p r o c e s s e s i s , within certa in l imi t s , independent of the temperature , w h e r e a s kp in-c r e a s e s with the temperature . The rate of decomposi t ion of persulphate i n c r e a s e s with the temperature and, therefore , has a pos i t ive temperature coe f f i c i ent . Since a m o n o m e r - p o l y m e r part ic le would grow fas ter at higher t emperatures , more e m u l s i f i e r i s used for i ts s tabi l izat ion. Consequently, m o r e m i c e l l e s have to be broken up for this p r o c e s s , and are thus unable to form new m o n o m e r - p o l y m e r par t i c l e s .

2 . 5 . G . J . K . A c r e s and F . L. Dalton [10] studied the E P of s tyrene and methyl methacrylate , us ing a d i latometr ic method. Sodium dioctyl sulphosuccinate was used as an e m u l s i f i e r ; the d o s e - r a t e was 3.8 X 1016 eV g"1 min"1 , and the temperature 21.5°C. The authors found inhibition periods of from 1 to 8 min, depending on the d o s e - r a t e and the m o n o m e r concentration. They c la im that these inhibition per iods are charac ter i s t i c for emuls ion po lymerizat ions and cannot be o v e r c o m e "by the most exhaust ive purif icat ion techniques which have been employed". This conclus ion does not agree with the re su l t s of Ley et a l . , who did not find any inhibition per iods when the s y s t e m was careful ly f reed from oxygen and other radical s c a v e n g e r s .

A c r e s and Dalton found a d o s e - r a t e dependency for the over - all react ion rate, which was considerably lower than those previously observed. Ac-cording to these authors, the d o s e - r a t e exponent "a" has va lues between 0.2 and 0.35, depending mainly upon the monomer concentration. Only with very smal l monomer concentrat ions i s the value of "a" said to approach the theoret ica l value of 0.4 (according to Smith and Ewart) . This i s explained by the role of H - a t o m s formed during the rad io lys i s of water . These H-atoms , according to A c r e s and Dalton, have two pos s ib i l i t i e s of react ion: (1) To initiate a po lymerizat ion by entering a m i c e l l e or a monomer-

po lymer part ic le , or (2) To react with d i s so lved s tyrene m o l e c u l e s in the aqueous phase "to

produce a somewhat unreact ive radical whose nature remains unspeci f ied". The unusually low values of the exponent "a" are thus explained by

the inactivation of pr imary radica l s . It i s doubtful, however, whether such a s tr ic t dif ferentiat ion between H and OH radicals for the initiation react ion i s reasonable .

F o r a monomer concentration of 1.525 m o l e s of s tyrene per l i tre of emuls ion and 2.78% sodium dioctyl sulphosuccinate in the aqueous phase, an o v e r - a l l react ion rate of 1.5 X 10~3 mole kg"1 (emulsion) min"i was

P L - 2 3 6/9 1 3 1

found. For a monomer concentrat ion of 2.77 m o l e s of MMA per l i tre emuls ion and 1.39% e m u l s i f i e r in the aqueous phase, an o v e r - a l l react ion rate of 7.2 X 10"2 mole kg"1 (emulsion) min"1 was found.

2 . 6 . V . T . Stannett [11] invest igated the E P of s tyrene and vinyl acetate with lauryl sulphate as an e m u l s i f i e r and gamma-radia t ion as an init iator. Each batch contained 75 g of water, 25 g of monomer, and 0.5 g of e m u l s i f i e r . The d o s e - r a t e was 4.5 X 1016 eV g"1 min"1 at t emperatures of 0 and 60°C, re spec t ive ly . F o r s tyrene the authors observed a con-s iderable d i f f erence in the pH va lues of the f inal l a texes , depending upon the type of initiation (by radiation or by potass ium persulphate):

Radiation Persulphate Styrene 7 . 9 . - 9 . 2 3 . 8 Vinyl acetate 3 . 1 . - 3 . 8 3 . 1 . - 3 . 8

The la texes obtained by radiation-init iat ion showed a s m a l l e r d i s tr i -bution of part ic le s i z e s than the la texes obtained by persulphate initiation. The v i s c o s i m e t r i c molecu lar weight of the polys tyrene obtained by radiat ion-init iat ion was measured and found to be 4.13 X 105 (0°C) and 1.66 X 106 (60°C). Under comparable conditions, persu lphate -cata lyzed polystyrene exhibited a m o l e c u l a r weight of 2.7 X 106. The molecu lar weight distribution was about the s a m e for all po lymer s a m p l e s . The v i s c o s i m e t r i c m o l e c u l a r weights of the polyvinyl acetate s a m p l e s w e r e as fo l lows:

M v initiation Temperature (°C)

Persulphate 60 4,9 X lO 5

.Radiation 60 1.06 XlO 6

Radiation 0 1.9 X l O 6

The o v e r - a l l react ion ra te s (vbr) w e r e measured by a di latometr ic method. F o r s tyrene with radiation initiation, the fol lowing va lues were determined:

v br

% min"1 mole kg"1 min"1

1 .85 1. 5 X 10"2

1 .01 8 . 6 XlO"3

0 .231 3 . 2 X 10"3

F r o m the temperature dependence vbr , an o v e r - a l l activation energy of 3 . 2 kcal mole"1 was calculated.

The E P of i soprene and MMA was studied only with respect to poss ib le changes in the micros truc ture of the po lymers . Unfortunately, i soprene p o l y m e r i z e s only very s lowly in emulsion; react ion rates w e r e not given

Temperature ( ° C )

60 40

0. 7

T A B L E II. MAXIMUM REACTION R A T E S OF VARIOUS MONOMERS, T O G E T H E R WITH E X P E R I M E N T A L P A R A M E T E R S

Monomer Temp.

C O

Dose (eV g"

-rate m i n - 1 )

Monomer concentration (moles kg"1

(emulsion))

Concentration of sodium dodecyl

sulphate (moles kg 1

(water))

Absolute react ion

rate (g min"1 kg"1

(emulsion))

Relative reaction

rate (styrene = 1)

Methacrylonitri le 25 17 . 5 X 1014 2 . 2 2 9 1 8 . 7 5 0 0127 0 0404

45 17 . 5 X 1014 2 . 2 2 9 1 8 . 7 5 0 . 1 3 8 4 0 234

D e c y l methacrylate 25 17 5 X 1014 0 . 6 6 2 1 7 . 5 0 281 0 310

Styrene 25 17 5 X 1014 1 . 2 8 8 5 0 . 7 6 0 963 1 000

Acrylonitri le 25 17 5 X 1014 2 . 8 9 0 1 7 . 8 0 287 1 335

Vinyl idene chloride 5 17 5 x i o 1 4 2 . 4 4 1 1 8 . 3 0 3565 1 833

5 17 5 X 1014 2 . 4 3 6 5 4 . 5 0 8476 1 829

Methyl methacrylate 25 8 75 X 1014 1 . 4 4 9 5 3 . 4 1 8i92 2 316

Butyl methacrylate 25 8 75 X 1014 1 . 0 9 5 5 3 . 1 6 2 655 2 475

25 8 75 X 101 4 1 . 0 3 9 6 1 7 . 8 1 652 4 464

Chloroprene 5 17 5 x i o 1 4 2 . 1 3 5 4 . 8 1 267 2 67

Butyl acrylate 25 4 4 X 10' 4 1 . 5 7 8 1 8 . 7 5 5 749 11 20

Ethyl acrylate 25 4 4 X 101 4 2 . 0 3 2 1 8 . 7 2 6. 769 16 . 90

Methyl acrylate 25 4 4 X 10 14 2 . 2 2 8 1 8 . 7 5 7 . 944 23. 06

P L - 2 3 6 / 7 1 3 3

by the authors. The tact ic i ty of the PMMA s a m p l e s was studied by a NMR method:

Po lymer iza t ion Syndiotactic Heterotactic temperature

°C)

Syndiotactic (%) (%)

60 5 9 . 4 4 0 . 6 0 6 7 . 2 3 1 . 8

The i n c r e a s e in syndiotactic s tructures with decreas ing polymerizat ion t emperatures f i ts in we l l with the known behaviour of polymeriz ing MMA.

2. 7. D .O . Hummel et al. [12] invest igated the kinet ics of the E P of a s e r i e s of vinyl m o n o m e r s . Sodium lauryl sulphate, ce ty l pyridinium bromide and cetyl tr imethyl ammonium chloride w e r e used as e m u l s i f i e r s . Table II shows the maximum react ion rates with different monomers , together with exper imenta l p a r a m e t e r s .

F o r an e a s i e r comparison, the react ion rates for different m o n o m e r s w e r e a l so related to the maximum react ion rate of a s tyrene emuls ion s y s t e m under s i m i l a r condit ions.

All rate m e a s u r e m e n t s w e r e per formed by an automatic recording di latometr ic apparatus of e x t r e m e sens i t iv i ty ( 1 - m m pen def lect ion c o r -responding to 0 . 1 - m g polystyrene g"1 (emuls ion)) . Inhibition periods w e r e e l iminated by a carefu l purif icat ion of all substances , and by a virtual ly comple te exc lus ion of oxygen. The la texes obtained by radiation-init iated po lymerizat ion were rather stable . The part ic le concentration in the la texes was found in the usual range: 10 1 4 - 1016 par t i c l e s per ml latex. B e c a u s e of the re lat ive ly low d o s e - r a t e s (between 500 and 2000 rad/h) , the molecu lar weights of the p o l y m e r s were rather high, being in the range of 106 (provided that no regulators w e r e added).

The r a t e - t i m e functions obtained for the different monomers had the "c las s i ca l" form (Gerrens) only in a very few c a s e s . Generally, the kinetic behaviour of the m o n o m e r s i s much more complicated than that predicted by the theory of Smith and Ewart . Measurements during the non-stat ionary state of the s y s t e m s led to the conclus ion that radicals are able to e scape the m o n o m e r - p o l y m e r part ic l e s , even in the c l a s s i c a l s tyrene s y s t e m .

H a l f - l i v e s for radica ls , and rate constants for the termination react ion between growing chains ("interparticle" termination), have been deter -mined for a s e r i e s of s y s t e m s . The termination constants in emuls ion s y s t e m s are lower by two to four orders of magnitude than the c o r r e s -ponding termination constants in homogeneous s y s t e m s . This explains the high react ion rates in emuls ion s y s t e m s and, a lso , the high molecu lar weights of the po lymers .

A complete kinetic descr ipt ion and a plausible quantitative inter-pretation of the behaviour of these complicated s y s t e m s i s not poss ib le according to the exis t ing theor i e s .

3. Conclusions

This short review of our present knowledge on the behaviour of emuls ion and suspension s y s t e m s , under the inf luence of ionizing radiation, has


perhaps conveyed s o m e of the theoret ical and industrial potential in this f ield of r e s e a r c h . Up to the present t ime a considerable fraction, if not the majority , of industrial po lymers are produced by suspension and emuls ion p r o c e s s e s . Perhaps the day i s not far off when radiation-init iated emuls ion and suspens ion p r o c e s s e s wi l l supplant conventional p r o c e s s e s .

II. COPOLYMERIZATION

Much work has been done on radiation-init iated copolymerizat ion, both in homogeneous and heterogeneous s y s t e m s . Table III g ives a survey of papers published during the last few y e a r s only (beginning in 1963). Below are d i scussed in s o m e detail only s y s t e m s having industrial in teres t .

1. Ethylene copo lymers [13, 14]

Numerous m o n o m e r s wi l l copolymer ize with ethylene under the inf luence of gamma radiation. Some monomers that are pract ical ly in-capable of homopolymerizat ion under the influence of ionizing radiation, such as propene and 1-butene, eas i ly copo lymer ize with ethylene. TableIV shows resu l t s of Steinberg and Colombo [13] obtained at 20°C and with a total p r e s s u r e of 680 atm.

2. Tetraf luoroethylene (TFE) copolymers

2 . 1 . With vinyl chloride (VC) [17]

The copolymerizat ion was invest igated at -78°C. The react ion w a s inhibited by DPPH. The reactivity parameters were determined as 7.75 ( q , VC), and 0.03 (R 2 , TFE). The rate of copolymerizat ion de-c r e a s e s with increas ing concentration of TFE in the monomer mixture; the most active s p e c i e s in the react ion chain are the VC radica ls .

2 . 2 . With ethylene [18]

At -78°C.and a d o s e - r a t e of 2 X 105 rad/h, and with a molar concen-tration of 44.7% of ethylene in the monomer mixture, the convers ion amounted to 9% within 42 h. The rate of copolymerizat ion d e c r e a s e s sharply with in-c r e a s i n g ethylene concentrat ion in the monomer mixture . The melt ing point of the s ta t i s t i ca l copo lymers decreased with increas ing ethylene concentrat ion from 320°C (~ 10 mole % ethylene) to 240°C 78 mole% ethylene) .

2 . 3 . With propene [21]

The react ion was studied at -78°C and with a d o s e - r a t e o f 4 . 0 X 10 5rad/h. With a molar concentrat ion of 33.6% propene in the monomer mixture , and an irradiat ion t ime of 100 h, the convers ion was 7%. The rate of co -po lymerizat ion i n c r e a s e s with increas ing concentration of TFE in the m o n o m e r mixture . Radical s c a v e n g e r s inhibit the react ion.

P L - 2 3 6 / 7 1 3 5

2 . 4 . With isobutene [19, 20]

This s y s t e m shows a remarkable behaviour. At -78°C, and over a wide range of compos i t ions of the m o n o m e r mixture, the copo lymer being formed always has an a lmost alternating s tructure . The copolymer contains 45 mole% of T F E . The copo lymer izat ion rate i s proportional to the square root of the d o s e - r a t e , and the convers ion i s d irect ly propor-tional to the radiation dose . The react ion i s inhibited by radical s c a v e n g e r s (pyrogallol , p-benzoquinone) .

3. Styrene c o p o l y m e r s

3 . 1 . With isobutene [31]

The react ion was studied at 0°C in the p r e s e n c e of ZnO. The react iv i ty p a r a m e t e r s w e r e 3.3 (isobutene) and 0.2 ( s tyrene) . The react ion mechani sm i s supposed to be part ial ly ionic .

3 . 2 . With methyl methacrylate [32]

The react ion was studied in the p r e s e n c e of 7-AI2O3 . The react ion i s of the radical type at t empera tures of 30 and 0°C, whereas at -78°C it i s said to be ionic .

4 . Acry loni tr i l e copo lymers

4 . 1 . With s tyrene [23, 25]

The react ion was studied at t empera tures of 15, 0, - 20 and -78°C. At a temperature of 15°C and at convers ions up to 6-7%, the copo lymer izat ion rate i s d irect ly proportional to the dose . The react ion rate i n c r e a s e s with increas ing concentrat ion of AN in the monomer mixture . The dependency of the copo lymer iza t ion p a r a m e t e r s rj (AN) and r2 ( s tyrene) on the react ion temperature i s shown in Table V. The copolymer obtained by irradiat ing a sol id m o n o m e r mixture at -78°C has an alternating s tructure . Simulta-neously with the copolymerizat ion , homopolymerizat ion of s tyrene takes place in a second sol id phase.

4 . 2 . With methyl methacrylate [23, 26]

This s y s t e m was invest igated in a range of t emperatures between 52.5 and -78°C, and with d o s e - r a t e s of 2 X 104, 3 . 5 X 104, 6 . 1 X 104, and 11. 0 X 104 rad /h . At a temperature of 15°C and convers ions of up to 6-8%, the react ion rate was direct ly proportional to the dose . At higher con-v e r s i o n s , the react ion rate had a higher dependence on the d o s e - r a t e . This i s explained by a Trommsdorf f e f fect . The rate of copolymerizat ion has a posi t ive temperature coef f ic ient . At 15°C, the copolymerizat ion rate de-c r e a s e s with increas ing concentration of AN in the monomer mixture . An opposite e f fect i s observed at a temperature of -78°C. Here , the react ion rate i n c r e a s e s approximately with the molar concentration of AN in the (solid) m o n o m e r mixture . Apparently, the react ivity of the m o n o m e r s i s complete ly different in the sol id state than in the liquid state, probably


T A B L E III. S U R V E Y OF P A P E R S ON RADIATION-INITIATED C O P O L Y M E R I Z A T I O N ( 1 9 6 3 - 6 6 )

C o m o n o m e r Remarks Ref.

Ethylene

Styrene [ 1 ] M e t h y l m e t h a c r y l a t e [ 1 ] V i n y l a c e t a t e [ 1 ] Acry loni tr i l e [ 1 ] Isobutylene [1 , 2 ] Chlorotr i f luoroethy lene [ 1 ] T r a n s - 2 - b u t e n e [ 1 ] C i s - 2 - b u t e n e [ 1 ] 1 - B u t e n e [ 1 ] M e t h y l acry la te [ 1 ] Isoprene [ 1 ] Propylene [ 1 . 2 ] V i n y l ch lor ide [1 . 2] 1 - O c t e n e [1 , 2 ]

Propylene

Chlorotr i f luoroethy lene Alternating 1 : 1 c o p o l y m e r [ 3 ] V i n y l ch lor ide [ 4 ]

Te tra f luoroe thy lene

Viny l chlor ide Mel ts higher than PVC [ 5 ] Ethylene Crysta l l ine c o p o l y m e r [ 6 ] Isobutylene Alternat ing c o p o l y m e r [7 , 8] Propylene [ 9 ]

Butadiene

Isobutylene [ 1 0 ]

Acryloni tr i le

Styrene The c o p o l y m e r obtained by so l id - s ta te c o p o l y m e r i z a t i o n has an al ternat ing structure

M e t h y l m e t h a c r y l a t e [11 , 14] Ethylene ox ide [15 ] Propylene o x i d e [15 ] V i n y l ch lor ide [16 ] Formaldehyde [17 ]

V i n y l i d e n e c h l o r i d e

I sobuty lene [ 1 8 ]

P L - 2 3 6 /9 1 3 7

Styrene

Isobutylene M e t h y l m e t h a c r y l a t e Unsaturated polyesters

V i n y l a c e t a t e

Isopropenyl a c e t a t e

A c r y l i c ac id

A U y l a m i n e

M e t h a c r y l i c ac id

A l l y l a m i n e

Formaldehyde

a - M e t h y l s t y r e n e M e t h y l m e t h a c r y l a t e Acry loni tr i l e A c e t a l d e h y d e n-Butyraldehyde Styrene

Carbonyl ha l ide

M a l e i c anhydride

Ethylene Methy l s tyrene Styrene

Carbon m o n o x i d e

Ethylene Propylene 1 - B u t y l e n e Isobutylene Ethy lene imine Propy lene imine

Sulphur d iox ide

Propylene Butadiene

Isoprene 2 , 3 - D i m e t h y l b u t a d i e n e Styrene Viny l a c e t a t e A l l y l a c e t a t e A l l y l a l c o h o l Viny l chloride C y c l o h e x a n e Chloroprene

[19 ] Anion ic m e c h a n i s m at - 7 8 °C [20, 21]

[22]

[23]

The c o p o l y m e r s are p o l y a m p h o l y t e s [24 ]

[24, 25]

[ 1 7 ] [17 ] [17] [17] [17 ]

The c o p o l y m e r has a constant [26 ] c o m p o s i t i o n (90% C H 2 0 )

[ 2 7 ]

Alternat ing c o p o l y m e r [ 2 8 ] Alternat ing c o p o l y m e r [29 ] Alternat ing c o p o l y m e r [30 ]

[1, 31 , 32] Po lyketones with a l ternat ing [33] structure [33]

[33]: Al ternat ing , crys ta l l ine c o p o l y m e r [34 ]

[34 ]

Alternat ing 1 : 1 - p o l y s u l p h o n e s [ 3 5 ] Alternat ing 1 : 1 -po lysu lphones [ 3 6 , 3 7 ] (1 , 4 - c i s and -trans) 1 : 1 [ 3 7 ] 1 : 1 [ 3 7 ] 2 : 1 at 30°C, 1 : 1 at - 7 8 ° C [ 3 8 - 4 0 ] 1 : 1 . c e i l i n g t e m p , of - 2 0 ° C [ 4 1 , 4 2 ] 1 : 1 [ 4 3 ] 1 : 1 [ 4 4 ] 2 : 1 at 25°C , 1 . 5 : 1 at - 78°C [ 4 5 ] 1 : 1 [ 4 6 ] Compos i t ion of the c o p o l y m e r depends [ 3 7 ] on react ion temperature and c o m p o s i t i o n of m o n o m e r mixture


T A B L E IV. R E S U L T S F R O M R E F . [13] AT A T E M P E R A T U R E OF 20°C AND A T O T A L PRESSURE OF 680 atm

C o m o n o m e r

C o m p o s i t i o n of batch (g) Dose

(Mrad) Percentage convers ion

C o m o n o m e r Ethylene C o m o n o m e r

Dose (Mrad)

Percentage convers ion

MMA 4 2 . 6 2 3 . 5 8 . 8 9 6 . 9

V i n y l a c e t a t e 4 2 . 8 2 5 . 2 1 8 . 9 8 9 . 1

Isobutylene 4 1 . 8 1 5 . 0 1 5 . 6 2 2 . 4

Propylene 4 3 . 1 1 1 . 8 1 4 . 7 2 8 . 5

V i n y l ch lor ide 4 0 . 1 3 0 . 0 0 . 9 2 4 7 . 1

1 - B u t e n e 4 6 . 5 8 . 3 0 . 9 2 8 . 2

Styrene 4 0 . 5 2 3 . 6 1 9 . 5 2 4 . 3

Acryloni tr i le 3 3 . 2 5 2 . 9 1 4 . 0 1 9 . 9

T A B L E V. D E P E N D E N C Y OF P A R A M E T E R S r ^ A N ) and r 2

(STYRENE) ON THE REACTION T E M P E R A T U R E

Temperature

CC) State V A N ) r2(styrene)

15 l iquid 0 . 0 3 0 . 3 3

0 l iquid 0 . 0 3 0 . 3 3

- 2 0 l iquid 0 . 2 8 0

- 7 8 Sol id 0 0

T A B L E VI. C O P O L YMERIZ ATI ON P A R A M E T E R S OF AN(r x ) AND MMA (r2) A T D I F F E R E N T REACTION T E M P E R A T U R E S

Temperature

CC) V A N ) r 2 (MMA)

- 7 8 0 . 0 1 0 . 1 3

- 2 0 0 . 1 0 1 . 3 0

0 0 . 1 0 1 . 3 0

15 0 . 0 8 1 . 1 0

52 0 . 1 5 1 . 1 5

P L - 2 3 6 / 7 139

because of a change in the polymerizat ion mechan i sm. Table VI shows the copolymerizat ion parameters of AN (rj) and MMA (r2) at different react ion t emperatures .

4 . 3 . With vinyl chloride [28]

The react ion was invest igated at t emperatures of 30 and -78°C, and at a d o s e - r a t e of 1. 1 X 1 0 4 r a d / h . At both t emperatures the copo lymer izat ion rate d e c r e a s e s with increas ing percentage of vinyl chloride in the m o n o m e r mixture . Only at very high concentrat ions of VC does the rate again in-c r e a s e rapidly. Apparently AN acts in smal l concentrat ions as a re tarder for the po lymerizat ion of VC.

4 . 4 . With ethylene oxide and propylene oxide [28]

The react ion was studied at t emperatures of 30, -78 and -196°C, and at d o s e - r a t e s between 2 X 1 0 4 a n d 1 .8 X 106 rad/h . F o r the copo lymer i -zation of AN with ethylene oxide the rate d e c r e a s e s with an increas ing percentage of ethylene oxide in the monomer mixture. This e f fec t i s s trongest at 30°C and weakest at -196°C. At normal t emperatures (0-30°C), the percentage of the copolymer of ethylene oxide i s a lmost independent of the compos i t ion of the monomer mixture , and i s about 5-8%. At low temperatures , the percentage of ethylene oxide units in the copo lymer r e a c h e s a maximum of 60-70% (with a molar ratio E O / A N of 10 in the monomer mixture) .

The copo lymer izat ion of acry loni tr i le with propylene oxide w a s studied at -78°C (liquid phase) with a d o s e - r a t e of 2 X 104 rad/h . The rate of copo lymer izat ion i s increased by polar so lvents such as chlorinated hydro-carbons or d imethyl formamide . Furthermore , the copo lymer y ie ld i s d irect ly proportional to the radiation dose up to rather high c o n v e r s i o n s . This i s ev idence that the copolymerizat ion proceeds by an ionic m e c h a n i s m . In a manner somewhat different from the E O / A N copolymerizat ion, the copolymerizat ion rate in this c a s e i n c r e a s e s with decreas ing temperature .

5. Vinyl acetate - isopropen.yl acetate copo lymers [35]

The copo lymer izat ion of VAc with i sopropenyl acetate was studied at 30, 0 and -78°C, with a d o s e - r a t e of 1 . 1 X 104 rad/h . The c o p o l y m e r i -zation rate d e c r e a s e s with an increas ing percentage of VAc in the monomer mixture . T'he convers ion of a 1 :1 (by volume) monomer mixture after a radiation dose of 3. 3 X 104 rad was found to be 0. 35%. The react ion rate at - 78°C was higher than that at 0°C.

6. Formaldehyde copo lymers [38]

Under irradiat ion, formaldehyde c o p o l y m e r i z e s with the fol lowing m o n o m e r s ( i n order of decreas ing copolymerizat ion rates ) : a - m e t h y l s t y r e n e , s tyrene, methyl methacrylate , acrylonitr i le , and ethylene oxide.

The copo lymers with s tyrene have been equal ly thoroughly studied. The react ion was performed at -78°C with d o s e s up to 107 rad. The


react ion rate i n c r e a s e s with an increas ing percentage of formaldehyde in the m o n o m e r mixture . Until 70 mole% of CH 2 0 in the monomer mixture i s reached, the copolymer has a constant composi t ion of 90 mole% oxymethylene and 10 mole% styrene. Above 70 mole% CH 2 0 in the monomer mixture , the percentage of oxymethylene in the copolymer approaches 100.

At 170°C the copo lymers begin to decompose . A few s tyrene units in polyoxymethylene improve the heat stabil ity of this mater ia l cons iderably .

7. Maleic anhydride - ethylene copolymers [40]

This was studied at t emperatures of 30, 40 and 65°C, at a d o s e - r a t e of 3.0 X 105 rad/h . The composi t ion of the copolymer i s a lmost equi-molecular , and pract ical ly independent of the composi t ion of the monomer mixture . The ra te -de termin ing step i s the addition of ethylene to a po lymer chain with a t ermina l male i c anhydride radical . During the copo lymer i -zation, the react ion b e c o m e s heterogeneous; the o v e r - a l l activation energy of the radiat ion-init iated copolymerizat ion was found to be 1 .8 k c a l / m o l e ; for the copolymerizat ion initiated with a z o - b i s ( i s o -butyronitri le) , a value of 27. 5 k c a l / m o l e was found. This cons iderable d i f ference i s a consequence of the fact that the formation of radicals by radiation requires no activation energy.

8. Carbon monoxide c o p o l y m e r s

8 . 1 . With ethylene [13, 43, 44]

Carbon monoxide i s eas i ly copolymerizable with ethylene and f o r m s copo lymers (ethylene polyketones) with rather interest ing propert i e s . Copolymers with a low carbonyl content are formed only with a very high e x c e s s of ethylene in the monomer mixture . Only 5% of CO in the monomer mixture l eads to the formation of copo lymers containing 45% CO. The react ion rate shows a broad maximum at concentrat ions between 27. 5% and 39.2% CO in the monomer mixture (20°C) [13, 4 3 ) . The melt ing point of the copo lymers i n c r e a s e s , with increas ing carbonyl content, from 111°C (27% CO) to 242°C (50% CO). An alternating copo lymer begins to decompose at about 250°C.

Carbon monoxide i s not homopolymerizable . Pecul iar ly , copo lymers have been obtained with considerably m o r e than 50% CO. These copo lymers consequently contain e i ther 1, 2 -d icarbonyl groupings or oxygen-containing groups other than the carbonyl group. This question has not yet been re so lved .

8 . 2 . With ethylene imine or propylene imine [46]

The copolymerizat ion of cycl ic amines with carbon monoxide i s an interes t ing method for the synthes i s of polyamides . The copo lymers with ethylene imine or propylene imine have an alternating structure a lmost independent of the composi t ion of the monomer mixture. The copolymeri -zation of ethylene imine with carbon monoxide y i e l d s po lyamide-3 , which shows the s a m e i n f r a - r e d spectrum as the product obtained by the poly-addition of acry lamide . The polymer m e l t s (with decomposit ion) at 322-335°C.

P L - 2 3 6 / 7

9. Sulphur dioxide c o p o l y m e r s (polysulphones)

1 4 1

9 . 1 . With propene [47]

The react ion w a s studied at t e m p e r a t u r e s between 25 and -196°C. The m o n o m e r rat io in the p o l y m e r i s a l m o s t unity, independent of the c o m p o -s i t ion of the m o n o m e r m i x t u r e . The c o p o l y m e r has an alternating s t r u c -ture , s i n c e SO2 i s not h o m o p o l y m e r i z a b l e . The copo lymer iza t ion rate i n c r e a s e s with d e c r e a s i n g propene concentrat ion in the m o n o m e r mix ture .

9 . 2 . With conjugated d ienes [48]

Butadiene y i e l d s al ternating po lysu lphones with a m o n o m e r rat io of unity, independent of the c o m p o s i t i o n of the m o n o m e r mixture and of t e m p e r a t u r e (25 to -78°C). The s a m e resu l t w a s o b s e r v e d with i s o p r e n e as a c o m o n o m e r . The reac t ion rate shows a max imum at -45°C and a mono-m e r ratio of 1:2 ( i s o p r e n e : SO2). 2, 3 -d imethylbutadiene a l s o y i e l d s a l t e r -nating c o p o l y m e r s with a m o n o m e r rat io (in the p o l y m e r ) of unity. The r e a c t i o n rate i s much l o w e r than that for butadiene and i s o p r e n e . 2 -ch lorobutad iene (chloroprene) behaves d i f ferent ly in that it i s able to form polysulphones with m o r e than one ch loroprene unit per S 0 2 -uni t . High reac t ion t e m p e r a t u r e s favour the format ion of po ly(chloroprene sulphones) with a h igher percentage of ch loroprene uni ts .

9 . 3 . With s tyrene [52]

The reac t ion w a s inves t igated at 30 and -78°C, at a d o s e - r a t e of 5.2 X 10 s r a d / h . The polysulphones have an alternating s t ruc ture . At 30°C, the m o l a r rat io s t y r e n e / S 0 2 i s a l m o s t exac t ly two. M a s s s p e c t r o -m e t r i c inves t igat ion of the p y r o l y s i s products r e v e a l e d the al ternating s t ruc ture . At -78°C, po lysulphones are f o r m e d with a m o l a r ratio of a l m o s t unity ( 1 . 1 : 1 )

9 . 4 . With vinyl ch lor ide [57]

The compos i t ion of the poly(vinyl ch lor ide sulphones) i s prac t i ca l ly independent of the c o m p o s i t i o n of the m o n o m e r mix ture . It does depend, however , on the r e a c t i o n t e m p e r a t u r e . Be tween room temperature and about -50°C, the c o p o l y m e r s have a m o l a r rat io V C / S 0 2 of two. Sti l l l o w e r t e m p e r a t u r e s s e e m to favour e q u i m o l e c u l a r c o p o l y m e r s . The poly-sulphone obtained at -78°C showed a m o l a r rat io VC/SO2 of 1. 5. The reac t ion rate showed a m a x i m u m at -10°C, with 72% VC in the m o n o m e r mix ture .

III. RADIATION-INDUCED GRAFT COPOLYMERIZATION

Just as a l loys c o m p r i s e a s p e c i f i c area of c o m p o s i t i o n a l s tud ies in meta l lurgy , so , too, graft c o p o l y m e r s occupy the analogous area in m a c r o -m o l e c u l a r c h e m i s t r y . Although in the las t few y e a r s s e v e r a l new t e c h -niques for cata lyt ic graf t ing have been deve loped, the importance of radi -ation graft ing r e m a i n s undiminished, which i s a d irec t c o n s e q u e n c e of the


decidedly s i m p l e r techniques afforded by radiation. These radiation tech-niques may be conveniently divided into the fol lowing four groups:

(i) Direct irradiat ion of a mixture of m o n o m e r with po lymer , (ii) Grafting of monomer to a radiat ion-peroxidized polymer .

(ii i) Grafting of monomer to a po lymer containing trapped rad ica l s . (iv) Cross - l ink ing of a mixture of two or more p o l y m e r s .

(i) Upon irradiat ing the m o n o m e r - p o l y m e r mixture, react ion c e n t r e s (radicals) are formed in both the polymer s tructure and the monomer . Thus by this method a graft copo lymer can be formed s imultaneous ly with a homopolymer , the latter constituting an unintentional by-product. How-ever , the y ie ld of graft copo lymer wi l l exceed that of homopolymer by an amount dependent upon how low the monomer concentration i s , and how much grea ter G r (polymer) i s than G r (monomer) . On this b a s i s one can theoret ica l ly predict from a knowledge of Gr va lues for monomer and po lymer whether or not the method might be suitable for a spec i f i c s y s t e m . The va lues of Gr for the most commonly used m o n o m e r s and po lymers may be found in Tables VII and VIII [59, 60 ] . The direct method i s the most technical ly f eas ib le and usual ly g ives the highest y i e l d s . The homo-polymerizat ion diff iculty i s by-passed , in most c a s e s , by irradiat ing m o n o m e r - s w o l l e n po lymer . Somet imes , however , it i s n e c e s s a r y to irradiate the p o l y m e r s in the p r e s e n c e of gaseous m o n o m e r s . Often the polymerizat ion p r o c e s s b e c o m e s diffusion control led ( s i m i l a r to the situation that occurs for homopolymerizat ion in a very v i s c o u s medium), and the gel e f fect may appear. Other compl icat ions may ar i se with the onset of the c o a l e s c e n c e ef fect , and this may or may not be favourable depending on the s y s t e m .

(ii) This method, whereby grafting occurs v ia radiation-peroxicjized polymer, i s in real i ty a two- s tage p r o c e s s . F i r s t , the po lymer i s i rrad i -ated in an oxygen-containing atmosphere so that peroxy compounds are formed. Then in the p r e s e n c e of monomer these compounds may be thermal ly degraded into radical ini t iators . This method i s somewhat i m -pract ical compared with method (i), but it r e su l t s in graft copo lymers qf a higher purity. The long l i f e - t i m e of the perox ides i s e spec ia l l y use fu l from a technical standpoint. The two s tages , peroxidation and grafting, may be carr i ed out in different p laces . F o r those m o n o m e r s and so lvents with re lat ive ly high t rans fer constants , this method finds l e s s utility s ince an e x c e s s of homopolymer i s formed.

(ii i) Grafting with trapped radicals i s of technical in teres t in those c a s e s where very pure graft copo lymers are des ired . Although the y i e lds are usual ly low, they may be enhanced by employing a lower temperature during the irradiat ion of the po lymer .

(iv) F o r technical reasons , the c r o s s - l i n k i n g of a mixture of two p o l y m e r s can only rare ly be ut i l ized. The y i e l d s are low, radiation s o u r c e s of high intensity are required, and the preparation of the homo-geneous mixture i s diff icult .

Var ious types of radiation s o u r c e s have been used for these methods of graft copolymerizat ion , including e lec tron a c c e l e r a t o r s [61-63], mixed

P L - 2 3 6 /9 1 4 3

T A B L E VII. RADICAL Y I E L D S OF S E L E C T E D MONOMERS

Monomer G r Method o f de terminat ion

Butadiene Very s m a l l

Styrene 0 . 6 9 Kinet ics and DPPH

Ethylene 4 Kinet ics

Acry lon i tr i l e 5 . 6 Kinet ics

5 DPPH

M e t h y l m e t h a c r y l a t e 1 1 . 5 Kinet ics

5 . 5 - 6 DPPH

M e t h y l acry la te 6 . 3 DPPH

V i n y l a c e t a t e 12 Kinet ics

9 . 6 DPPH

V i n y l chlor ide Presumably c l o s e to 10

T A B L E VIII. P O L Y M E R S

E X P E C T E D RADICAL YIELDS OF S E L E C T E D

Polymer Expected Gr

Polybutadiene

Polyisoprene

Polystyrene

p o l y e t h y l e n e

Po ly i sobuty lene

Po ly (methy l m e t h a c r y l a t e ) P o l y v i n y l a c e t a t e ) Po ly (methy l acry la te )

S i l i c o n e

C e l l u l o s e P o l y v i n y l a l c o h o l )

P o l y v i n y l ch lor ide) Po ly (v iny l idene ch lor ide)

Po lyamides Fluoro po lymers

2 - 4

2 - 4

1 . 5 - 3 . 0

6 - 8

6 - 8

6 or 12

3 . 6 or 7 . 2

10

1 0 - 1 5

Probably high


radiation in nuclear reactors , gamma radiation from 60Co [59] and secon-dary radiation from the nuclear react ion 1 0B(n, a )7Li [64] , F o r technical irradiation, large beta s o u r c e s using 90Sr, 1 4 7Pm and 144Co have been suggested [65] .

In the l i terature there are hundreds of sc ient i f i c publications and patents concerned with the radiation grafting of different mater ia l s and synthetic substances with every conceivable monomer . Nearly all these are of technical in teres t because grafting i s not only a source of complete ly new products , but a l so provides a method for altering the c h a r a c t e r i s t i c s of po lymers in des i red direct ions . Because of the very large number of resu l t s , a drast ic se lec t ion must be made. The scope of this summary has therefore been narrowed to give a brief picture only of those s y s t e m s that are e spec ia l l y interest ing e i ther because of the methods employed or because of unusual c h a r a c t e r i s t i c s in the resultant copo lymers .

1. Polyethylene

Either high- or l o w - p r e s s u r e polyethylene i s often used in conjunction with methods (i) and (ii) . Styrene has proved to be a very good m o n o m e r because of i t s good swel l ing propert ies and low G-va lues . F o r low radi-ation d o s e - r a t e s , the yield i s proportional to the d o s e - r a t e , w h e r e a s in the region of 5-72 r a d / s , the grafting rate i s independent of the d o s e - r a t e [66] . The y i e lds can be increased by the addition of 2-propanol [66] and methanol [68], and, in fact, a maximum yie ld was observed for a 50-60% concen-tration of methanol . It has a lso been found that the grafting i s not homo-geneous . The amorphous reg ions of the polyethylene are grafted more e a s i l y than the crys ta l l ine regions , so that the graft polymer i s concen-trated in the amorphous areas [66] . Generally, the product resul t ing from the s y s t e m i s harder and more res i s tant to the e f f ec t s of so lvents . The s y s t e m may a l so be used to produce cat ion-exchange membrane by the s imple expedient of sulphonating a grafted f i lm [69] .

In acryloni tr i le , polyethylene does not swe l l quite as wel l . The y i e lds are lower in this c a s e , but the result ing graft copo lymer has interes t ing optical propert i e s [70] .

The graft ing of methyl methacrylate i s hindered by a strong gel e f fect , although a high degree of grafting can be achieved with pulsed radiation [71]. Thus, f i l m s of h i g h - p r e s s u r e polyethylene having a thickness of 0 .031. . . 0.05 m m w e r e irradiated with a total dose of 3 X 1 0 4 r a d . This dose was de l ivered in 30 s ingle pulses , each having a duration of 2 min. Between pu l ses , a period of 28 min was allowed for the diffusion of m o n o m e r . It was found that the optimum temperature for the react ion was 25°C, at which point the rate of graft ing i s 2000 t i m e s greater than the rate of homopolymerizat ion.

In addition, s e v e r a l other m o n o m e r s have been grafted to polyethylene by means of radiation. T h e s e include acryl ic acid [72] , vinyl carbanole [69], vinyl pyridine [73] , vinyl s tearate [73], vinyl acetate [63] , vinyl pyrrol idone [74] and vinylidene chloride [63] , F luor ine-conta in ing and polyfunctional m o n o m e r s have been used for the c r o s s - l i n k i n g of polyethylene [75, 76 ] .

P L - 2 3 6 /9 1 4 5

2. Polypropylene

This has been grafted by the usual methods [72] . The peroxide method proves to be fa s t er in this c a s e than for polyethylene [77, 78] .

3. Polyisobutylene

Treated with s tyrene according to method (i), polyisobutylene y i e l d s a mixture of graft copo lymer and homopolymer. The removal of graft copo lymer i s accompl i shed by extract ion with cyclohexane [79] .

4 . Po lys tyrene

B e c a u s e of i t s low Gr value, polystyrene g ives only low y ie lds when grafted by methods (i) or (ii). Never the l e s s , the radiation y ie ld of perox ides may be i n c r e a s e d by carrying out the irradiat ion in rad ia t ion-sens i t ive so lvents such as chloroform [80] .

5. Poly(methyl methacrylate)

This can e a s i l y be grafted with acrylonitr i le [81] and methyl aery late [82] . A transparent product i s obtained when acrylonitri le i s grafted from a 25% methanol solution. The product result ing from a graft with vinyl pyrrol idone can be swol len in water [83] . Graft copo lymers of poly (methyl methacrylate) with vinyl acetate have been prepared in emuls ion s y s t e m s , and a l so polyvinyl acetate with butyl methacrylate , po"ly(butylmethacrylate) and polyvinyl acetate with s tyrene, and polyvinyl acetate with acry loni tr i le and methyl methacrylate [84] ,

6. Polyvinyl alcohol

This i s often radiation grafted with s tyrene, methyl methacrylate and other m o n o m e r s [85, 86] to improve i t s hydrophobic propert ies and to provide better p r o c e s s i n g at higher t emperatures . Grafting with aery lamide and 2 -methy l -5 -v iny lpyr id ine or 4-vinylpyridine improves the dyeabil ity of polyvinyl alcohol f ibres [87] , Yie lds may be increased by the addition of water [86] . No graft copo lymers are formed us ing solut ions of acry lo -nitr i le in benzene or dimethyl formamide because of their hydrophobic propert i e s . F o r grafting, it has been shown that it i s better to use a 6% solution of acryloni tr i le in water [85] .

7. Nylon

Nylon f i b r e s have been grafted with methyl methacrylate , acryl ic acid, acrylonitr i le , vinyl acetate, methyl acrylate and ethyl acrylate [88] . Again, the p r e s e n c e of water i n c r e a s e s the y i e lds . By means of grafting, nylon's dynamic c h a r a c t e r i s t i c s at different t emperatures have been al tered. To improve the dyeabil ity of nylon-6 f ibres , the direct method of graft ing may be used with acry lamide . In addition, the e l ec t r i ca l propert ies of po lyamides have been shown to undergo modif icat ion by grafting [89] .

Severa l other f ibres have been grafted using the direct method ( e . g . natural s i lk and polycaprolactam [90]). The dyeability of polyterophthalate

10


f i b r e s has been improved by radiation grafting with 4-v inylpyridine . F i b r e s prepared in this way w e r e dyeable with acid dyes . By treating the f ibres af terwards with a 5% solution of dimethyl sulphate in methanol, the surface r e s i s t a n c e i s lowered so that the build-up of static charge i s hindered [80] .

8. Poly(vinyl pyrrolidone)

Grafted with acrylonitr i le , poly(vinyl pyrrolidone) finds use as an ion-exchange membrane [91] .

9. Polyvinyl chloride

This can eas i ly be grafted with many different monomers because it i s swel lable in virtual ly all monomers and has ahigh Gr value. F r o m a tech-nical point of v iew, the grafts with polyfunctional monomers are of particu-lar interest (e. g. with dial lyl maleinate , diallyl sebacinate , dial lyl phthalate, ethylene glycol dimethacrylate and tr ia l ly l cyanurate [92]). These mono-m e r s are used as p l a s t i c i z e r s for PVC; the shee t s are coated and then irradiated with a dose of from 106. . . 108 rad. Below the softening point, the resultant product has a rubber- l ike character . By grafting PVC f i lms with acrylonitr i le , a transparent f i lm has been obtained [93] . Trans-parent, hard f i l m s can also be prepared by grafting with styrene and methyl methacrylate [94, 95] ,

10. Tef lon

Tef lon graf t s di f fer from those of other po lymers because of the low swel l ing of Tef lon in so lvents and monomers [73, 81, 96] , Therefore , under normal conditions, the grafting occurs only near the sur face . How-ever , at low d o s e - r a t e s and higher temperatures it i s poss ib le to induce graft ing in the deeper l a y e r s of Tef lon f i lm [97] . There has been a lso s o m e s u c c e s s with grafting in Tef lon emuls ions [93] . The maximum yield for an emuls ion s y s t e m with s tyrene has been found to be 8% (80°C); s imi lar ly , there i s an 8% maximum yield for butyl methacrylate (55°C). Polyf luoroethylene f i l m s that have been 3. . . 5% surface grafted with s tyrene have good adhesive propert ies [97] . Tef lon i s often grafted to improve its dyeabil ity [98] . Grafts with acryl ic acid yie ld ion-exchange membranes [99].

11. Cel lu lose

Cel lu lose graft ing has been thoroughly studied over the last few y e a r s , part icularly by the Japanese [100] . The radiation grafting of ce l lu lose acetate with vinyl acetate l owers the softening point; here vinyl acetate acts as an internal p la s t i c i zer [101] . By the addition of smal l amounts of bifunctional m o n o m e r s , one obtains an eas i ly formable product. Indeed, this method has been used in industry s ince 1957 [102] . Cel lulose f ibres have often been grafted to i n c r e a s e their hydrophobic c h a r a c t e r i s t i c s . The m o n o m e r s normal ly used in this application are s tyrene and, in particular, acryloni tr i le [102-105] . In this c a s e , the radiation y i e l d s were found to be cr i t i ca l ly affected by monomer and solvent concentration, the ratio of monomer and ce l lu lose concentration, the initial form of the ce l lu lose and the p r e s e n c e of t r a c e s of oxygen [104] . Vinyl and al lyl

PL-23 6/9 147

compounds have a l so been grafted to other text i le f i b r e s not only to improve their hydrophobic propert ies but a l so to i n c r e a s e their r e s i s t a n c e to bi-o log ica l damage [106, 107] ,

12. Natural rubber

This has been grafted with p -ch loros tyrene and 2,5 d ich loros tyrene . By this means the rubber b e c o m e s more suscept ib le to radiation vulcani -zation [108] . Methyl methacrylate i s graftable only to extracted rubber. It i s a l so poss ib le to graft the latex i tse l f [109-111] .

13. Other u s e s

Radiation graft ing has a l so been used for dyeing natural and synthetic subs tances . Dyes with po lymer izab le groups have been used, including diazotated 2 - a m i n o - 4 - s u l p h o - 4 - a c r y l o y l aminodiphenylsulphone or 3 - s u l p h o - 7 - a m i n o - 1-naphthol [112] .

By means of graft ing with spec ia l monomers , products with part icular ly good adhesive propert i e s have been obtained. Thus, polypropylene grafted with v iny l -d i - (2 -chloroethyl )phosphate has good adhesion with s e v e r a l m e t a l s [113] . The adhesion of ink to polyethylene was improved by graft ing a mixture of polyethylene and sulphur dioxide [61] . Radiation graft ing i s additionally used for the improvement of the mechanica l propert ies of semi-conduct ing p o l y m e r s . A semi-conduct ing m a t e r i a l with good e l e c t r i -ca l and mechanica l propert i e s was prepared by a graft of acetylene mono-m e r s and cyanoethylene with g l a s s f ibres and subsequent thermal treatment [67] .

IV. POLYMERIZATION UNDER UNUSUAL CONDITIONS

1. Ionic po lymerizat ion of liquid m o n o m e r s

It has been remarked that " r e s e a r c h in radiation chemis try i s m o r e productive of publications than any other f ie ld , because every paper a s -ser t ing a mechani sm has to be fol lowed by another in which the a s s e r t i o n i s retracted" [114] . One need examine only the tortuous his tory of radiation-init iated po lymerizat ion to appreciate the aptness of this quip.

F o r many y e a r s the universa l ly accepted view prevai led that radiation-initiated po lymerizat ion in liquid m o n o m e r s was uniquely a free radical p r o c e s s . This conclus ion had been based on the kinetic behaviour exhi-bited by these s y s t e m s by us ing c r i t e r i a developed from y e a r s of exper i -mental data a m a s s e d in s tudies of chemica l ly and photochemical ly in i -tiated react ions . In 1957, however , the f i r s t f i s s u r e s appeared in the f r e e radical shibboleth with the d i s covery of the low- temperature ionic poly-mer iza t ion of liquid i sobutylene [115] . By 1960, a host of m o n o m e r s including s tyrene [116] , butadiene [117], formaldehyde [118] and acry loni -tr i l e [119] had been identif ied as being suscept ib le to ionic polymerizat ion . Without exception, however , these po lymerizat ions occurred under what must be t ermed "extreme" condit ions; that i s , they w e r e carr ied out at very low temperature (to favour ionic over f r e e radical propagation), and s o m e t i m e s with an added second phase (to act as an e l ec tron trap) or an

148 HUMMEL e t a l .

homogeneous ly distributed second component of reasonably high d ie l ec tr i c constant (to promote ion stabi l izat ion) .

Since 1960, the schoo l s of Metz, Wi l l iams and Okamura have steadi ly h a m m e r e d at the last bast ion of the radical hypothesis by demonstrat ing that ionic propagation s p e c i e s are respons ib le for the radiation poly-m e r i z a t i o n of s e v e r a l m o n o m e r s under "normal" condit ions ( i . e . bulk and solution po lymerizat ion at room temperature) .

The elucidation of this complete ly unsuspected and absolutely funda-mental fact was brought about by s imply employing highly purified mono-m e r s . In part icular, water content has been shown to be the cr i t i ca l factor [120-124] . Thus, under suff ic ient ly anhydrous condit ions the normal f ree radical propagation i s vast ly overshadowed by a super imposed ionic contri-bution for such m o n o m e r s as s tyrene [120- 122, 125 -130 ] , o - m e t h y l s t y r e n e [123 , 124, 129, 131, 132], j3-pinene [123, 124, 131 ], isobutyl vinyl ether [131], cyc lohexene oxide [134] , and o thers . The evidence for ionic mecha-n i s m s has been manifested by very high rates of po lymerizat ion [120-138] , l inear dependence of rate of po lymerizat ion on dose rate of radiation [120, 121, 127-129] , non-dependence of molecu lar weight on d o s e - r a t e [120-122, 125, 126, 128] , mo lecu lar weights that vary inverse ly with react ion temperature [120-122] , temperature coe f f i c i ent s of low magnitude [120-122, 128] , sens i t iv i ty to ionic s c a v e n g e r s [120 - 122] and direct observat ion of ionic s p e c i e s by pulse rad io lys i s [136] ,

The explanation currently in vogue for the sudden appearance of this ionic phenomenon i s that a substantial radiolytic y ie ld of reasonably long-l ived f ree ions i s always generated in the react ion s y s t e m , r e g a r d l e s s of purity. However, un le s s the s y s t e m has been stringently dried, the growing chains are terminated in the o l igomer stage by a very ef f ic ient react ion with m o l e c u l e s or, perhaps, ions of water . As to the nature of these po lymer ic ions in anhydrous s y s t e m s , it i s general ly be l ieved that they are cat ionic , although there i s no agreement as to whether they are carbonium ions or carbonium radical ions . Indeed, in certa in s y s t e m s such as o - m e t h y l s t y r e n e and s tyrene there i s evidence for the s imultaneous propagation of carbonium ions and carbanions (in addition to a f ree radical contribution) [120, 128, 129, 134] , And now the re levance of the opening remark can be fully understood: for the moment, the state of the art has c o m e full c i r c l e and we are l iv ing with Lind's theor i e s of forty y e a r s ago.

General ly , the various purif icat ion s c h e m e s for preparing these dry m o n o m e r s have four s teps in common, all of which are per formed in a vacuum environment: d is t i l lat ion of monomer, bake-out of preparat ive apparatus, degass ing of monomer , and contacting of m o n o m e r with a drying agent such as activated s i l i c a gel [120, 121, 123, 125-129, 131, 135] , Na-K alloy [122, 130] or barium oxide [137] . As might be expected for an ionic polymerizat ion, these e laborate s c h e m e s do not n e c e s s a r i l y yie ld reproduceable re su l t s . However, for the s tyrene and o - m e t h y l s t y r e n e s y s t e m s , reproducibi l i ty has been attained [120, 121, 1 2 7 - 1 2 9 ] , F o r this c a s e , it i s in teres t ing to note that s tyrene at 0°C, when exposed to ^Co-g a m m a rays at a d o s e - r a t e of 1 Mrad/h, p o l y m e r i z e s at a rate of 94%/h, compared with the c l a s s i c a l f r e e radica l value of 0.2%/h for these condit ions.

Armed with the above fac ts and a reasonable imagination, one can s e e many p o s s i b i l i t i e s for exper imenta l and theoret ica l work in this area of pure, dry m o n o m e r s . F o r example , al l the previous f r e e radical work should be repeated under the m o r e stringent conditions - including the

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r a d i o l y s i s of h y d r o c a r b o n s . It would a l s o be l o g i c a l to i n v e s t i g a t e c o -p o l y m e r i z a t i o n . F o r c o m o n o m e r s y s t e m s of n o r m a l pur i ty , a n d d e p e n d i n g upon the type of in i t ia t ion , the c o p o l y m e r i z a t i o n p r o c e e d s e x c l u s i v e l y by e i t h e r an i o n i c m e c h a n i s m or a f r e e r a d i c a l m e c h a n i s m . D e p e n d i n g on the m e c h a n i s m , e a c h p a i r of m o n o m e r s h a s a c h a r a c t e r i s t i c s e t of r e a c t i v i t y r a t i o s . T h u s , d e s p i t e the fact that t h e r e a r e i n f i n i t e l y m a n y p o s s i b l e s e q u e n t i a l and o v e r - a l l c o m p o s i t i o n s , on ly a few of t h e s e c o p o l y m e r s a r e a c t u a l l y a c c e s s i b l e . In a r a d i a t i o n - i n i t i a t e d u l t r a - p u r e s y s t e m , h o w e v e r , the p o l y m e r i z a t i o n p r o c e e d s v i a the s i m u l t a n e o u s o p e r a t i o n of two o r m o r e m e c h a n i s m s . F u r t h e r , the d e g r e e of the ion ic c o n t r i b u t i o n s c a n be c o n t r o l l e d by the w a t e r content . T h e s e f a c t o r s l ead to the c o n c l u s i o n that s y s t e m s of pure m o n o m e r s open a pathway to c o p o l y m e r s of r a d i c a l l y d i f f e r e n t s t r u c t u r e and p r o p e r t i e s .

F o r t h o s e wi th an e v e n m o r e in trep id i m a g i n a t i o n , it i s p o s s i b l e to d i s c u s s the p r a c t i c a l app l i ca t ion of t h e s e t e c h n i q u e s . In the pas t , i n d u s t r y had shunned rad ia t ion b e c a u s e p o l y m e r i z a t i o n r a t e s w e r e low and the c o s t of rad ia t ion w a s high. The s i tuat ion h a s now b e e n r e v e r s e d , and the r e -ac t ion r a t e s a r e e x t r a o r d i n a r i l y high, w h i l e rad ia t ion c o s t s have l e s s e n e d . F o r s u c h w e l l - e n t r e n c h e d t e c h n o l o g i e s a s s t y r e n e p o l y m e r i z a t i o n , it i s probably f r u i t l e s s to c o n s i d e r s e r i o u s l y the d e v e l o p m e n t of a r a d i a t i o n p r o c e s s . H o w e v e r , t h e r e are s o m e in tr igu ing p o s s i b i l i t i e s f o r t h o s e m o n o m e r s that h a v e been , o r w i l l be , n e g l e c t e d b e c a u s e of t h e r m a l s e n s i t i -v i ty o r d i f f i c u l t i e s in c a t a l y s t n e u t r a l i z a t i o n .

M o d i f i c a t i o n s s l a n t e d t o w a r d s c o s t r e d u c t i o n a re the n e c e s s a r y and s u f f i c i e n t c o n d i t i o n s f o r f e a s i b i l i t y . It h a s a l r e a d y b e e n d e m o n s t r a t e d that the p r e s e n c e of a d r y i n g agent i s not a b s o l u t e l y n e c e s s a r y , and that ad-s o r b e d w a t e r on the g l a s s r e a c t i o n s u r f a c e s i s the p r i m a r y c o n t r i b u t o r to i on d e s t r u c t i o n in rad ia t ion p o l y m e r i z a t i o n s y s t e m s [120, 122, 128] . One c a n e n v i s a g e a cont inuous f low s y s t e m in which , b e f o r e s t a r t - u p , r e m o v a l of w a t e r f r o m the apparatus s u r f a c e s would be a c c o m p l i s h e d by a s u p e r -heated s t r e a m of dry n i t rogen . Dur ing o p e r a t i o n the dry r e a c t o r , coup led wi th a r e a s o n a b l y good d i s t i l l a t i o n , would e n s u r e the s t a b i l i z a t i o n of i o n i c s p e c i e s . Of c o u r s e , the s o u r c e of d r y n i t r o g e n would a l s o be u s e d to d i s -p l a c e d i s s o l v e d o x y g e n in the m o n o m e r , and a s a subs t i tu te f o r a v a c u u m e n v i r o n m e n t . P e r i o d i c a l l y , a s the w a t e r c o n c e n t r a t i o n approached a c r i t i c a l l e v e l , the r e a c t i o n s y s t e m would r e q u i r e "reac t iva t ion" wi th the heated n i t r o g e n p u r g e .

A s a s p e c i f i c p o s s i b i l i t y , m o r e than one i n d u s t r i a l f i r m h a s i n v e s t i g a t e d the i r r a d i a t i o n of l iquid t r i o x a n e to f o r m p o l y o x y m e t h y l e n e , thus hoping to b y - p a s s the c o n s i d e r a b l e p r o c e s s d i f f i c u l t i e s that a re e n c o u n t e r e d in a c o n v e n t i o n a l c a t a l y t i c s y s t e m . The unfortunate r e s u l t w a s that r a d i a t i o n s i m p l y would not p o l y m e r i z e l iquid t r i o x a n e . H o w e v e r , it h a s r e c e n t l y been announced that l iquid t r i o x a n e , when s u b j e c t e d to the new p u r i f i -ca t ion t echn ique , i s indeed s u s c e p t i b l e to rad ia t ion p o l y m e r i z a t i o n [ 1 3 8 ] . It should a l s o be b o r n e in mind that if r e s e a r c h p r o d u c e s the p r e v i o u s l y m e n t i o n e d unique c o p o l y m e r s ( o r t e r p o l y m e r s ) , then a rad ia t ion p r o c e s s would be the s o l e product ion p o s s i b i l i t y .

2 . S o l i d - s t a t e p o l y m e r i z a t i o n

The advent of s t e r e o s p e c i f i c p o l y m e r i z a t i o n by c h e m i c a l i n i t i a t o r s ( Z i e g l e r - N a t t a c a t a l y s t s ) l ed to an i n c r e a s e d i n t e r e s t in the p o s s i b i l i t i e s


of p r e p a r i n g p o l y m e r s by the i r r a d i a t i o n of the s o l i d m o n o m e r . It w a s e x p e c t e d that the s t r u c t u r e of the p o l y m e r might r e p r o d u c e the o r d e r e d , c r y s t a l l i n e f o r m of the s o l i d m o n o m e r . T h e eventua l d i s c o v e r y that only a few m o n o m e r s r e a d i l y p o l y m e r i z e d to c r y s t a l l i n e produc t s l ed to a m o r e fundamenta l i n v e s t i g a t i o n of the p o l y m e r i z a t i o n m e c h a n i s m s . The s ub-sequent muddled a s p e c t of radiat ion p o l y m e r i z a t i o n in the s o l i d s ta te , if nothing e l s e , i s a c l e a r d e m o n s t r a t i o n that the s c i e n t i f i c w o r l d i s not a l w a y s m o r e c o m f o r t a b l e in the so l id p h a s e than in the l iquid p h a s e .

The r e a c t i o n s in the s o l i d s ta te appear to be quite d i f f e r e n t f r o m t h o s e in the c o r r e s p o n d i n g l iquid m o n o m e r s , be ing l a r g e l y dominated by the c r y s t a l l i n e e n v i r o n m e n t and or i en ta t ion of the m o n o m e r u n i t s . No s i n g l e pat tern of behav iour e m e r g e s f r o m the v e r y n u m e r o u s m o n o m e r i c s y s t e m s s tudied , although a c l a s s i f i c a t i o n of m o n o m e r s has been s u g g e s t e d b a s e d on the v a r i a t i o n of the rate of p o l y m e r i z a t i o n when changing f r o m the l iquid to the s o l i d s ta te [139] .

Most of the v a r i o u s s y s t e m s that have been i n v e s t i g a t e d a re b e l i e v e d to p r o c e e d by an anionic m e c h a n i s m ( e . g . c e t y l m e t h a c r y l a t e [ 1 4 0 ] , t r i oxane [ 1 4 1 ] , a c r y l o n i t r i l e [142 ] , d iketene [143 ] , (3-propiolactone [ 1 4 4 ] ) . Such a m e c h a n i s m would depend on e l e c t r o n c a p t u r e by m o n o m e r m o l e c u l e s . Although th i s would i m p l y the e x i s t e n c e of s t a b i l i z e d carbon ium ions , the p o s s i b i l i t y of c a t i o n i c propagat ion has not been s e r i o u s l y c o n s i d e r e d , e v e n in the c a s e of t r i o x a n e . Other s y s t e m s have been a s s i g n e d a f r e e r a d i c a l m e c h a n i s m , inc luding the thoroughly s tudied m o n o m e r a c r y l a m i d e [ 1 4 5 ] , and a l s o the a c r y l i c a c i d [ 1 4 6 ] , and m e t h y l and e thyl a c r y l a t e s y s t e m s [ 1 4 7 ] , One v e r y i n t e r e s t i n g theory i s that al l s o l i d - s t a t e p o l y m e r i z a t i o n s p r o c e e d v i a c h a i n - c a r r y i n g e x c i t e d m o l e c u l e s [148] .

In s e v e r a l i n s t a n c e s , t h e s e a s s i g n m e n t s of m e c h a n i s m s have been m a d e on the b a s i s of r a t h e r dubious l o g i c . F o r e x a m p l e , m a n y ESR s t u d i e s have shown the e x i s t e n c e of f r e e r a d i c a l s in an i r r a d i a t e d s o l i d m o n o m e r . Al l too o f ten , it h a s not b e e n r e a l i z e d that t h e s e a re not n e c e s s a r i l y the s p e c i e s r e s p o n s i b l e f o r in i t ia t ion or propagat ion , p a r t i c u l a r l y if they a r e ion r a d i c a l s . Other m e t h o d s of r e a s o n i n g have a t tempted to u t i l i z e l iquid phase k i n e t i c s for the i n t e r p r e t a t i o n of s o l i d - s t a t e p h e n o m e n a . F o r e x a m p l e , the o b s e r v a t i o n that oxygen or o ther f r e e r a d i c a l s c a v e n g e r s do not r e t a r d c e r t a i n s o l i d - s t a t e r e a c t i o n s h a s of ten b e e n i n t e r p r e t e d a s e v i d e n c e f o r an ionic m e c h a n i s m , e v e n if t h e r e w a s no p o s s i b i l i t y of oxygen d i f fus ing through the c r y s t a l s t r u c t u r e . And in s p i t e of the dearth of knowledge about s o l i d - s t a t e r e a c t i o n s , a f i r s t - o r d e r d e p e n d e n c e of r e a c t i o n rate on d o s e - r a t e h a s b e e n c o n s i d e r e d a s s t r o n g e v i d e n c e f o r ion ic cha in c a r r i e r s . It i s hard ly s u r p r i s i n g , then, that in the s o l i d - s t a t e l i t e r a t u r e one o f ten f inds the a s s i g n m e n t of d i f f e r e n t m e c h a n i s m s to the s a m e m o n o m e r by d i f f e r e n t au thors .

Undoubtedly m o r e e f f o r t should be devoted to the quant i tat ive eva luat ion of r e s u l t s f r o m the m o r e s e c u r e vantage point of s o l i d - s t a t e c h e m i s t r y and p h y s i c s . In t h i s way , it might be hoped that s o m e of the p r e s e n t e m b a r a s s -m e n t s would be e l i m i n a t e d . (The s u p r e m e e x a m p l e of th i s i s m e t h y l m e t h a c r y l a t e , t h i s m o n o m e r having b e e n r e p o r t e d to be both c o m p l e t e l y u n p o l y m e r i z a b l e [149, 150] and d e c i d e d l y p o l y m e r i z a b l e [151, 152 ] . )

M o r e o v e r , it would be p o s s i b l e f o r s o l i d - s t a t e p o l y m e r i z a t i o n to b e c o m e a v a l u a b l e too l in i t s e l f f o r i n v e s t i g a t i n g the m o b i l i t y of o r g a n i c m o l e c u l e s wi th in c r y s t a l l i n e and a m o r p h o u s s o l i d s , the nature and d i s t r i b u -

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t ion of d e f e c t s and d i s l o c a t i o n s , and the i n f l u e n c e of t e m p e r a t u r e and p r e s s u r e on t h e i r b e h a v i o u r .

Of c o u r s e , t h e r e are s o m e ex tenuat ing c i r c u m s t a n c e s f o r the p r e s e n t c o n f u s i o n , one of wh ich i s the p r e v a l e n c e of p o s t - i r r a d i a t i o n e f f e c t s . Such a f t e r - e f f e c t s a s p o l y m e r i z a t i o n , c h a i n - s c i s s i o n , d e g r a d a t i o n and ox idat ion c a n o c c u r b e c a u s e of the t rapp ing of r e a c t i v e s p e c i e s in the c r y s t a l l a t t i c e . An e x a m p l e of the s i tuat ion c r e a t e d by a f t e r - e f f e c t s i s typ i f i ed by s t y r e n e . The anionic s o l i d - s t a t e p o l y m e r i z a t i o n that w a s i n i t i a l l y r e p o r t e d [153] w a s s u b s e q u e n t l y shown to be a p o s t - p o l y m e r i z a t i o n o c c u r r i n g during the e x t r a c t i o n of u n r e a c t e d m o n o m e r [ 1 5 4 ] .

N e v e r t h e l e s s , r e a c t i o n r a t e s h a v e b e e n s u c c e s s f u l l y m e a s u r e d by the t e c h n i q u e s of d i f f e r e n t i a l t h e r m a l a n a l y s i s [ 1 5 5 ] , d i l a t o m e t r y [156 ] , o p t i c a l and e l e c t r o n m i c r o s c o p y [ 1 5 7 - 1 5 9 ] , and o p t i c a l b i r e f r i n g e n c e [160, 1 6 1 ] . S o m e t i m e s t h e s e r e a c t i o n r a t e s a r e c o n s i d e r a b l y e n h a n c e d by m o n o m e r o r i e n t a t i o n within the l a t t i c e , and s t e r e o r e g u l a r p o l y m e r s m a y be f o r m e d d i r e c t l y in su i tab le c r y s t a l s (notably , the c y c l i c c o m p o u n d s [162 ] ) . In o t h e r m o n o m e r s , c r y s t a l l i n i t y i m p e d e s the r e a c t i o n , w h i c h then t e n d s to be in i t i a t ed at c r y s t a l l i n e d e f e c t s to g i v e an a m o r p h o u s p o l y m e r wi th in the o r i g i n a l c r y s t a l l i n e l a t t i c e ( e . g . a c r y l a m i d e ) . V e r y d i f f e r e n t r e a c t i o n r a t e s m a y be o b s e r v e d in the s a m e m o n o m e r , depending on i t s c r y s t a l l i n e o r a m o r p h o u s e n v i r o n m e n t ( e . g . N - v i n y l - c a p r o l a c t a m [ 1 6 3 ] , c a l c i u m a c r y l a t e , and b a r i u m m e t h a c r y l a t e [ 1 6 4 ] ) .

Other e x p e r i m e n t s have e m p h a s i z e d the e f f e c t of e x t e r n a l s t r e s s , s u c h a s m a g n e t i c f i e l d ( thus enhanc ing the rate of p o l y m e r i z a t i o n of f o r m a l d e h y d e [ 1 6 5 ] ) o r p r e s s u r e ( thus enhanc ing the ra te of p o l y m e r i z a t i o n of t r i o x a n e [166] and a c r y l a m i d e [ 1 6 7 ] ) . S t i l l o t h e r s have c o n c e n t r a t e d on the in-f l u e n c e of c r y s t a l l i t e s i z e and p e r f e c t i o n , e . g . t r i o x a n e [168] and o t h e r r ing c o m p o u n d s [162] p o l y m e r i z e d f r o m l a r g e c r y s t a l s a r e b e t t e r o r i e n t e d . A l s o , the e f f e c t of n o n - r e a c t i v e g r o u p s wi th in the s o l i d h a s been e x p l o r e d ( e . g . m e t h y l m e t h a c r y l a t e , v i n y l a c e t a t e , and s t y r e n e in s o l i d m i x t u r e s wi th p a r a f f i n o i l [ 1 6 9 ] ) .

In b inary s y s t e m s that f o r m s o l i d s o l u t i o n s , a c e r t a i n n u m b e r of c o p o l y m e r i z a t i o n s have b e e n c a r r i e d out ( e . g . a c r y l a m i d e - m e t h a c r y l a m i d e [ 1 7 0 ] , 3 - c h l o r o m e t h y l - 3 - e t h y l o x e t a n e wi th 3 - f l u o r o m e t h y l - 3 - e t h y l o x e t a n e and 3 , 3 - b i s ( c h l o r o m e t h y l ) - o x e t a n e [ 1 7 1 ] ) . In addit ion, m i x e d c r y s t a l s ( 3 - c h l o r o m e t h y l - 3 - e t h y l o x e t a n e wi th d i k e t e n e and t r i o x a n e [171]) and e u t e c t i c - f o r m i n g s y s t e m s ( a c r y l a m i d e - a c e n a p h t h y l e n e [170] and a c r y l i c m o n o m e r s wi th c r o t o n i c ac id [172]) h a v e b e e n i n v e s t i g a t e d . C o p o l y m e r s h a v e a l s o b e e n f o r m e d in g l a s s - l i k e m i x t u r e s of n o n - e u t e c t i c - f o r m i n g m o n o m e r p a i r s wi th p a r a f f i n o i l [ 1 7 3 ] .

T y p i c a l l y , the p r e v i o u s l y m e n t i o n e d e r u d i t e c o m p l e x i t i e s have c a u s e d i n d u s t r y no g r e a t i n c o n v e n i e n c e , a s can be d e d u c e d by the f l u r r y of s o l i d -s t a t e patent l i t e r a t u r e o v e r the l a s t ' f e w y e a r s . (An e x c e l l e n t e x a m p l e i s t r i o x a n e [ 1 7 4 - 1 7 8 ] . ) P e r h a p s the m o s t p r o m i s i n g i n d u s t r i a l o p p o r t u n i t i e s a r e to be found in the o r d e r e d p o l y m e r s of c y c l i c m o n o m e r s . E v a l u a t i o n of the p h y s i c a l and m e c h a n i c a l p r o p e r t i e s of the p o l y m e r f r o m 3, 3 - b i s ( c h l o r o m e t h y l ) - c y c l o oxabutane (Penton) s u g g e s t s that the p o l y m e r s f r o m c y c l i c m o n o m e r s might be u s e f u l f o r the p r o d u c t i o n of o r i e n t e d f i l m s and f o r i n j e c t i o n m o u l d i n g s [ 1 7 9 ] . P o l y m e r s p r e p a r e d f r o m d ike tene and j3 -propio lactone in the s o l i d s t a t e h a v e b e e n s h o w n to h a v e a h i g h e r m e l t i n g point and b e t t e r c r y s t a l l i n i t y than the p o l y m e r s obta ined by ion ic c a t a l y s t s


[ 1 6 2 ] , A l s o , the r e c e n t l y s y n t h e s i z e d h i g h - m e l t i n g N - s u b s t i t u t e d p o l y i -m i d e s of m a l e i c ac id ( a p p r o x i m a t e l y 300°C) [ 180] could have c o n s i d e r a b l e u t i l i t y .

S i m i l a r to the b i o l o g i c a l s c i e n c e s , the u s e of c a n a l c o m p l e x e s a s m o l e c u l a r t e m p l a t e s f o r c a r r y i n g out s e l e c t i v e and s t e r e o s p e c i f i c s o l i d -s t a t e p o l y m e r i z a t i o n by r a d i a t i o n has b e e n i n v e s t i g a t e d [181, 1 8 2 ] , Thus , h i g h - m e l t i n g t r a n s 1 : 4 p o l y m e r s of 2 , 3 - d i m e t h y l b u t a d i e n e , 2 , 3 - d i c h l o r o -butadiene , 1 , 3 - c y c l o h e x a d i e n e , and c y c l o h e x a d i e n e m o n o x i d e have b e e n p r e p a r e d [181] . T h i s h igh ly i m a g i n a t i v e method h o l d s p r o m i s e f o r p r o -duc ing m a n y i n t e r e s t i n g new p o l y m e r s v i a s o l i d - s t a t e i r r a d i a t i o n .

V. P I L O T - P L A N T INVESTIGATIONS

1. B a s i c a s p e c t s of r a d i a t i o n - i n d u c e d chain r e a c t i o n s

S i n g l e - s t e p r a d i a t i o n - c h e m i c a l r e a c t i o n s have G - v a l u e s up to about 10 ( i . e . 10 m o l e c u l e s changed p e r 100 eV a b s o r b e d rad ia t ion e n e r g y ) . If the fu l l rad ia t ion e n e r g y of a 6 0 C o - s o u r c e wi th an act iv i ty of 1 0 4 C i (1 .60 X 1 0 2 4 e V / h ) w e r e to be absorbed in a c h e m i c a l s y s t e m p r o d u c i n g a c e r t a i n m o l e c u l a r type wi th a G - v a l u e of 3, then the y i e l d of t h i s compound would be a p p r o x i m a t e l y 0.1 m o l e / h . When the r e a c t i v e s p e c i e s a r e r e -produced during e a c h s tep , a chain r e a c t i o n w i l l take p l a c e . The y i e l d s of r a d i a t i o n - i n d u c e d cha in r e a c t i o n s are 102 to 10® t i m e s l a r g e r than the y i e l d s of s i n g l e - s t e p r e a c t i o n s , depending on the s y s t e m . T h e o r e t i c a l l y , at l e a s t , any r e a c t i o n c h a i n i s in f in i t e ly long . The r e a c t i o n p r o d u c t s m a y be s m a l l m o l e c u l e s o r p o l y m e r s ; in the l a t t e r c a s e , the p r o d u c t s of e a c h s t e p f o r m a cha in .

In many c a s e s the s p e c i e s n e c e s s a r y f o r the in i t ia t ion of a cha in r e -ac t ion ( r a d i c a l s , r a d i c a l i o n s , ion m o l e c u l e s , and e x c i t e d m o l e c u l e s ) can a l s o be p r o d u c e d in the s y s t e m by c o n v e n t i o n a l c h e m i c a l m e a n s . Radiat ion in i t ia t ion o f f e r s , h o w e v e r , the f o l l o w i n g p r i n c i p a l a d v a n t a g e s :

(1) Without d i s t u r b i n g the s y s t e m , the in i t ia t ion ra te c a n be v a r i e d within w i d e l i m i t s , e v e n during the r e a c t i o n .

(2) In the c a s e of r a d i c a l p r o c e s s e s , the cha in l ength can be c o n t r o l l e d by the d o s e - r a t e . The u s e of m o d i f i e r s i s t h e r e f o r e u n n e c c e s s a r y .

(3) S ince no c h e m i c a l i n i t i a t o r s a r e p r e s e n t , the f ina l product c o n t a i n s no f o r e i g n end g r o u p s o r o ther i m p u r i t i e s in troduced by the i n i t i a t o r .

(4) Many chain r e a c t i o n s c a n be in i t ia ted u n d e r c o n d i t i o n s w h e r e c h e m i c a l i n i t i a t o r s f a i l (low t e m p e r a t u r e s , s o l i d m o n o m e r s ) .

O n e - s t e p or s h o r t - c h a i n r e a c t i o n s are a t t r a c t i v e f o r indus try only when the c o s t of rad ia t ion i s low ( " c h e m i c a l r e a c t o r " ) , o r when the pro f i t on the r e a c t i o n product i s h igh . To the l a t t er type b e l o n g s the rad ia t ion m o d i f i -c a t i o n of p l a s t i c s ( c r o s s - l i n k i n g and ox idat ion) .

It c a n be shown that an act iv i ty of 5 X 1 0 4 C i 6 0Co w i l l be s u f f i c i e n t to s tudy r a d i a t i o n - i n i t i a t e d cha in r e a c t i o n s on a p i l o t -p lant s c a l e . Le t u s a s s u m e that the fu l l rad ia t ion e n e r g y of t h i s s o u r c e i s a b s o r b e d by the c h e m i c a l s y s t e m . T h i s would then m e a n an e n e r g y a b s o r b a n c e of 8 X 10 2 4 e V / h . If a c e r t a i n r e a c t i o n product i s f o r m e d wi th a G - v a l u e of 1, then 0 .133 m o l e s of th i s compound a r e f o r m e d e a c h hour . To obtain the y i e l d of a cha in r e a c t i o n in g r a m s p e r hour , w e h a v e to m u l t i p l y th i s

P L - 2 3 6 / 9 1 5 3

v a l u e wi th the ac tua l G - v a l u e of the r e a c t i o n , wi th the m o l e c u l a r we ight of the r e a c t i o n product (or of the m o n o m e r unit in the c a s e of p o l y m e r s ) and wi th the f r a c t i o n of the rad ia t ion a c t u a l l y a b s o r b e d by the s y s t e m .

The h igh ly t e m p e r a t u r e - r e s i s t a n t , a l t e r n a t i n g e t h y l e n e - c a r b o n m o n o x i d e c o p o l y m e r i s f o r m e d with a G - v a l u e of at l e a s t 10 3 . Let u s a s s u m e that o n e - f i f t h of the to ta l e n e r g y e m i t t e d by the s o u r c e i s a b s o r b e d by the s y s t e m . T h e n the y i e l d of t h i s p r o c e s s would be at l e a s t 0 .2 X 0 .133 X 103 X 56 = 15 0 0 g of c o p o l y m e r p e r hour . F r o m th i s e x a m p l e , it c a n be s e e n that the a c t u a l cha in l ength of the r e a c t i o n h a s a v e r y s t r o n g i n f l u e n c e on the e c o n o m y of the p r o c e s s . S ince the f r e q u e n c y of t e r m i n a t i o n r e a c t i o n s i s not only i n f l u e n c e d by the d o s e - r a t e , but a l s o by the pur i ty of the s y s t e m and the s i z e of the r e a c t i o n v e s s e l , it i s u s e l e s s to i n v e s t i g a t e i n d u s t r i a l l y i n t e r e s t i n g s y s t e m s on a t e s t - t u b e s c a l e .

An e x a m p l e f o r a c h a i n - r e a c t i o n wi th l o w - m o l e c u l a r we ight r e a c t i o n p r o d u c t s i s the su lphox idat ion of p a r a f f i n s . A G - v a l u e of 10 3 f o r an a lky l su lphon ic ac id of m o l e c u l a r we ight 300 i s e a s i l y obta inab le . T h i s p r o c e s s d o e s not r e q u i r e high p r e s s u r e s and, c o n s e q u e n t l y , no th ick-w a l l e d v e s s e l s , s o that a rad ia t ion y i e l d of 50% should be within r e a c h . The y i e l d of a lky l su lphonic ac id would be about 20 k g / h .

2 . S u g g e s t i o n s f o r a rad ia t ion c h e m i c a l p i lot plant

The i r r a d i a t i o n unit i s the h e a r t of the pi lot plant . We have p r o p o s e d the f o l l o w i n g s p e c i f i c a t i o n s to obta in o p t i m u m p e r f o r m a n c e and w i d e v a r i a b i l i t y :

(1) The d o s e - r a t e s wi th in the c h e m i c a l s y s t e m should be r a t h e r u n i f o r m . It w a s t h e r e f o r e d e c i d e d to c o n s t r u c t a c o r o n a s o u r c e wi th 12 o r 16 s i n g l e r o d s , p r e f e r a b l y c o n s i s t i n g of p e n c i l - t y p e 60Co with a to ta l a c t i v i t y of 5 X 1 0 4 C i .

(2) With f ixed c o r o n o i d s , the v o l u m e of the i n n e r c y l i n d r i c a l part should not e x c e e d 100 l i t r e s . To a c h i e v e m a x i m u m d o s e - r a t e s it w a s d e s i r a b l e to m a k e the d i a m e t e r of the c r o w n of s o u r c e s v a r i a b l e .

(3) F o r l o w e s t d o s e - r a t e s , and to r e a c h as m a n y i n t e r m e d i a t e d o s e -r a t e s as p o s s i b l e , it w a s d e s i r a b l e to m a k e the s o u r c e p e n c i l s independent ly m o v a b l e . A l s o , it w a s n e c e s s a r y to graduate the a c t i v i t i e s of the s i n g l e s o u r c e s a c c o r d i n g to a s y m m e t r i c a l s c h e m e .

F o u r c o m p a n i e s have m a d e p r o p o s a l s f o r the c o n s t r u c t i o n of an i r r a d i -at ion unit of th i s t y p e . The r e s u l t s a r e d i s c u s s e d b e l o w .

The a r c h i t e c t u r a l p r o b l e m s w e r e s o l v e d by the Arch i tekturbf l ro H e i e r & M o n s e , Co logne , F e d e r a l Republ ic of G e r m a n y . A tota l v i e w of the w h o l e pi lot plant i s g i v e n in F i g . 1. Next to the s o u r c e bui ld ing (3) t h e r e a r e two l a r g e r o o m s (4) f o r the p r e p a r a t i o n and p u r i f i c a t i o n of the raw m a t e r i a l s , a s w e l l a s f o r the handl ing of the r e a c t i o n p r o d u c t s . Op-p o s i t e t h e s e r o o m s , beyond a s m a l l c o u r t y a r d , i s a bui ld ing (5) con ta in ing s t o r a g e r o o m s and the c e n t r a l e n e r g y supply . A l a r g e gangway, the "spine", c o n n e c t s al l p a r t s of the c o m p l e x . To the l e f t of the t e c h n i c a l bu i ld ings are c o n v e n t i o n a l l a b o r a t o r i e s (2) f o r the e v a l u a t i o n of the p o l y m e r s and f o r rout ine i n v e s t i g a t i o n s . The a d m i n i s t r a t i v e o f f i c e s of the plant (1) b o r d e r s on the s t r e e t . On the o t h e r s i d e of the c o m p l e x , and at s o m e d i s t a n c e f r o m the l a b o r a t o r i e s , t h e r e i s a h o u s e f o r the c a r e t a k e r of the plant . The

1 5 4 H U M M E L e t a l .

FIG. 1. Lay-out of a radiation pilot plant. 1, Administration; 2, Laboratories; 3, Source building; 4 , Technical buildings; 5, Warehouse; 6, Caretaker's house.

w h o l e c o m p l e x w a s planned in deta i l , but the d e t a i l s , h o w e v e r , w i l l not be g i v e n h e r e .

In the f o l l o w i n g p a r a g r a p h s , we s h a l l p r e s e n t a s h o r t d i s c u s s i o n of the p r o p o s a l s of f our c o m p a n i e s ( in a lphabet ica l o r d e r ) f o r a p i l o t - p l a n t i r r a d i a t i o n uni t .

(1) A t o m i c E n e r g y of Canada, L t d . , Ottawa, Canada

T h i s c o m p a n y o f f e r s an i n t e r e s t i n g i r r a d i a t i o n unit ( F i g . 2, w i th two independent w a y s of o p e r a t i n g the s o u r c e s ) . Two s tandard c o n t a i n e r s w i t h 8 coba l t r o d s e a c h are c o m b i n e d to f o r m a unit with 16 r o d s . The d i a m e t e r of t h i s c o r o n a s o u r c e i s v a r i a b l e b e t w e e n 355 m m and 760 m m . The unit can , a l t e r n a t i v e l y , be bui l t wi th a pneumat ic d r i v e w h e r e the s o u r c e s r ide on a c u s h i o n of a ir , o r wi th two independent dr iv ing m e c h a n i s m s , one p n e u m a t i c and one m e c h a n i c a l . The l a t t e r i s r a t h e r c o m p l i c a t e d but h a s a c e r t a i n s a f e t y advantage .

The s tandard c o n t a i n e r s c a n a l s o be u s e d for sh ipping the s o u r c e s .

(2) H . S . M a r s h Ltd . , Reading , England

The c o r o n a s o u r c e c o n s i s t s of 16 s i n g l e s o u r c e s with a f ixed d i a m e t e r f o r the c r o w n of 70 cm ( F i g . 3, o i l - f l o w s y s t e m ) . The s i n g l e s o u r c e s a r e

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FIG. 2. Proposal for a radiation unit from Atomic Energy of Canada, Ltd. Combined air-flow and mechanical driving system.

1. -Free access to inner irradiation space. Diameter 68.5 c m . 2. Adjustment of diameter of the source-pipe ring. 3. Intermediate conducting pipes-4. Source holder with lead filling. 5. N. B. A false base or a raised platform round the assembly can be set up in the chamber at any required

height. 6. Duct through chamber wall. 7. Air extraction pipe and mechanical emergency withdrawal system for the sources. 8. Iris-pattern variation of the source pipes. Min. diameter 35.5 cm. Max. diameter 76 cm. 9. Free space for emergency evacuation system. Diameter 20 c m . (Evacuation system to be constructed

of the p e n c i l type and can be o p e r a t e d independent ly . In t h e i r l o w e s t p o s i t i o n they are s h i e l d e d by a l ead c o n t a i n e r that a l s o can be u s e d a s a t r a n s p o r t c o n t a i n e r . It b e a r s a c e n t r a l b o r i n g with a d i a m e t e r of 10 c m which c a n be u s e d f o r cont inuous r e a c t i o n s and a s a d i s c h a r g e opening f o r d i s c o n t i n u o u s p r o c e s s e s , e s p e c i a l l y in c a s e s of e m e r g e n c y .

The s o u r c e s a r e m o v e d in s t a i n l e s s - s t e e l t u b e s . Two dr iv ing m e c h a n i s m s are o f f e r e d :

(a) A s y s t e m w h e r e the coba l t s o u r c e s in t h e i r s t a i n l e s s - s t e e l canning " s w i m " in an o i l s t r e a m . T h e y are kept in t h e i r w o r k i n g p o s i t i o n as long a s the o i l i s s t r e a m i n g . When the o i l s t r e a m i s s topped, the s o u r c e s s ink to t h e i r s h i e l d e d p o s i t i o n .

(b) A s y s t e m w h e r e the s o u r c e s a r e f i x e d on top of h y d r a u l i c a l l y m o v e d s t e e l r o d s .

(3) Gebrt ider S u l z e r AG, Winter thur , S w i t z e r l a n d

T h i s c o m p a n y o f f e r s a v e r y v e r s a t i l e unit . The s o u r c e c o n t a i n e r i s f i x e d on top of o r wi thin the c e i l i n g of the i r r a d i a t i o n c e l l ( F i g . 4) . A c o r o n a a s s e m b l y of s t e e l t u b e s hangs f r o m the c e i l i n g ; the s i n g l e s o u r c e s a r e m o v e d by a " T e l e f l e x " d r i v e . The d i a m e t e r of the c o r o n a s o u r c e i s v a r i a b l e b e t w e e n 340 m m and a s m u c h as 2340 m m , s o that the d o s e - r a t e can be v a r i e d wi th in w i d e l i m i t s .

by client)

156 H U M M E L e t a l .

FIG. 3. Proposal for a radiation unit from H.S. Marsh & Co. Air-flow system.

The unit can hold a m a x i m u m of 20 s i n g l e - s o u r c e p e n c i l s with a total ac t iv i ty of 105 Ci of 6 0Co. A m o r e m o d e s t m o d e l p o s s e s s e s 12 s o u r c e r o d s wi th a tota l ac t iv i ty of 5 X 1 0 4 Ci of ^feo. I r r a d i a t i o n s c a n a l s o be p e r -f o r m e d in an i n n e r tube of the s o u r c e c o n t a i n e r . T h i s i s impor tant f o r f low s y s t e m s that r e q u i r e v e r y high d o s e - r a t e s b e c a u s e of the s h o r t i r r a d i -at ion t i m e s .

F i g u r e 4 s h o w s , a l s o , a h o r i z o n t a l c r o s s - s e c t i o n of the unit and the labyr inth . Two m a n i p u l a t o r s a r e prov ided . The i r r a d i a t i o n c h a m b e r can be o b s e r v e d through a l ead g l a s s window.

T h e S u l z e r unit i s adaptable a l s o f o r i n d u s t r i a l product ion . P o l y m e r s b e i n g f o r m e d with G - v a l u e s in the r a n g e of 1 0 4 - 10 5 (which a r e e a s i l y a t ta inable ) could be p r o d u c e d on a 1000 ton p e r y e a r s c a l e .

(4) Hans W S l i s c h m i l l e r , M e e r s b u r g , Lake C o n s t a n c e , F e d e r a l Republ i c of G e r m a n y

A c r o s s - s e c t i o n of the unit i s s h o w n in F i g . 5. The s o u r c e i s of the c o r o n a type wi th 16 s i n g l e r o d s . The d i a m e t e r i s v a r i a b l e b e t w e e n 2 0 0 m m and 1000 m m . In the r e s t pos i t i on , the cobal t r o d s a re s i n g l y s h i e l d e d in p i e - w e d g e s e g m e n t s . T h e s e s e g m e n t s can be u s e d a s t r a n s p o r t c o n t a i n e r s . The c o n s t r u c t i o n of the s o u r c e a l s o a l l o w s the l oad ing of the

P L - 2 3 6 / 9 1 5 7

SECTION ttn

1 RADIATION ROOM 5 STORAGE- AND COOLING 9 MANIPULATORS UNIT FOR SOURCES

2 CONTROL ROOM 6 S T E E L SHIELDING 1 0 CONVEYOR SYSTEM

3 LABYRINTH ? QQNJROL CONSOLE AND 1 1 C R A N E 6 1 " ^ M O V A B L E

4 SOURCE GUIDE TUBES SOURCE DRIVE UNIT 12 CRANE 5 1 8 LEAD GLASS WINDOW ALL DIMENSIONS IN METRES

FIG.4. Proposal for a radiation unit from Gebruder Sulzer AG. Teleflex system.


FIG. 5. Proposal for a radiation unit from Hans Walischmiller. Mechanical drive system and hydraulic lift . 1, Lead shield; 2, Source in shielded position; 3, Source travelling tube; 4, Concrete; 5, Push rods; 6, Hydraulic lift .

s o u r c e in s i tu . The s i n g l e s o u r c e s a r e f i xed on top of s t e e l rods d r i v e n h y d r a u l i c a l l y o r e l e c t r o m e c h a n i c a l l y .

An a t t r a c t i v e f e a t u r e of t h i s unit i s a hydraul ic l i f t w i t h i n the c y l i n d r i c a l i r r a d i a t i o n v o l u m e . To i n s e r t r e a c t i o n v e s s e l s , the p l a t f o r m i s r a i s e d to the upper p lane of the c r o w n of the s o u r c e . A f t e r s e c u r i n g the v e s s e l (which m a y w e i g h a s m u c h a s s e v e r a l hundred k i l o g r a m s ) , the p la t form i s l o w e r e d to the w o r k i n g p o s i t i o n .

F i n a l l y , the s o u r c e a l s o h a s an ax ia l bor ing f o r cont inuous p r o c e s s e s and f o r e m e r g e n c y un loading .

E a c h of the un i t s d e s c r i b e d has a n u m b e r of a d v a n t a g e s and, a l s o , a f ew d i s a d v a n t a g e s . N e v e r t h e l e s s , the n u m b e r of p o s s i b l e i m p r o v e m e n t s i s l i m i t e d . C o n s e q u e n t l y , w e b e l i e v e that w e have d e s c r i b e d r e a s o n a b l e p o s s i b i l i t i e s f o r the c o n s t r u c t i o n of an i r r a d i a t i o n unit f o r a pi lot p lant . To r e a c h a f ina l d e c i s i o n , the f o l l o w i n g a s p e c t s m a y be of i m p o r t a n c e :

(1) V a r i a b i l i t y of d o s e - r a t e s i s a c r u c i a l point . T h u s , the d i a m e t e r of the c o r o n a s o u r c e should be v a r i a b l e , o r the s o u r c e s m u s t be ind iv idua l ly m o b i l e . The b e s t , but m o s t e x p e n s i v e , s o l u t i o n i s a c o m b i n a t i o n of both.

P L - 2 3 6 / 9 1 5 9

(2) T r a n s p o r t and handl ing of h e a v y equ ipment i s e a s i e r and s a f e r by " r o l l i n g t r a n s p o r t " than by "hanging t r a n s p o r t " . T h e r e f o r e , hanging s o u r c e s have a c e r t a i n advantage . P r o p o s a l (4), hav ing the m o v a b l e p l a t f o r m wi th in the s o u r c e , o f f e r s a r e a s o n a b l e c o m p r o m i s e .

(3) The d r i v i n g m e c h a n i s m f o r the s o u r c e s should be a s s a f e a s p o s s i b l e . Any s h u t - d o w n of the plant due to s o u r c e t r o u b l e ( s t i c k i n g of a s o u r c e , c o r r o s i o n of the d r i v e m e c h a n i s m ) i s e x -t r e m e l y c o s t l y . No m a t e r i a l s u s c e p t i b l e to rad ia t ion d a m a g e should , t h e r e f o r e , be u s e d in the c o n s t r u c t i o n of the unit . M o s t p r o b l e m a t i c i s the u s e of h y d r a u l i c s y s t e m s wi th o r g a n i c m e d i a . E v e n s t a i n l e s s s t e e l m a y p r e s e n t p r o b l e m s in the p r e s e n c e of o x y g e n and w a t e r , s i n c e . p a s s i v i t y i s s u s p e n d e d in a r a d i a t i o n f i e l d .

3. S u g g e s t i o n s f o r l a r g e - s c a l e r a d i a t i o n - i n d u c e d cha in r e a c t i o n s

It i s not the p u r p o s e of t h i s r e p o r t to g i v e d e t a i l e d data f o r p r o m i s i n g rad ia t ion c h e m i c a l p r o c e s s e s . D e s p i t e that w e a re i n c l i n e d to g ive at l e a s t s u c c i n c t h in t s on i n t e r e s t i n g c h a i n r e a c t i o n s .

3. 1. Chain r e a c t i o n s with l o w - m o l e c u l a r p r o d u c t s

T h e r e a r e h u n d r e d s of p u b l i c a t i o n s on th i s s u b j e c t . The f o l l o w i n g p r o c e s s e s s e e m to h a v e an i n d u s t r i a l i n t e r e s t :

3 . 1 . 1 . Oxidat ion of a r o m a t i c h y d r o c a r b o n s . H e r e , the c a t a l y z e d o x i -dat ion of b e n z e n e in aqueous p h a s e y i e l d s pheno l (G(phenol) = 70) j If it w e r e p o s s i b l e to l e n g t h e n the cha in , the p r o c e s s would be c o m p e t i t i v e wi th o t h e r w e l l - e s t a b l i s h e d s y n t h e s e s .

3 . 1 . 2 . C h l o r i n a t i o n of a r o m a t i c h y d r o c a r b o n s . H e x a c h l o r o c y c l o h e x a n e i s f o r m e d w i t h r a t h e r h igh G - v a l u e s (up to 4 X 105) . It i s not c e r t a i n , a s s u g g e s t e d in e a r l i e r p a p e r s , that the y i e l d of the g a m m a c o m p o n e n t i s h i g h e r c o m p a r e d wi th the p h o t o c h e m i c a l p r o c e s s .

3 . 1 . 3 . S u l p h o c h l o r i n a t i o n of a l iphat ic h y d r o c a r b o n s . G - v a l u e s up to 10 7

have b e e n r e p o r t e d .

3 . 1 . 4 . Su lphoxidat ion of a l iphat ic h y d r o c a r b o n s . The h i g h e s t G - v a l u e s s e e m to be in the r a n g e of 6 X 103 .

3 . 1 . 5 . C a r b o c h l o r i n a t i o n of a l iphat i c h y d r o c a r b o n s . A l iphat i c ac id c h l o r i d e s are f o r m e d by the i r r a d i a t i o n of CO and Cl 2 wi th p a r a f f i n s in a cha in r e a c t i o n of m e d i u m length.

3 . 1 . 6 . H y d r o b r o m i n a t i o n of e t h y l e n e . T h i s p r o c e s s has a l r e a d y b e e n d e v e l o p e d by the Dow C h e m i c a l Co. , Midland. The G - v a l u e of the r e a c t i o n i s 3.9 X 1 0 4 , and the capac i ty of the Dow plant a few y e a r s ago w a s 500 t o n s per y e a r .


3 . 1 . 7 . H y d r o c h l o r i n a t i o n of o l e f i n s . D e p e n d i n g upon the o l e f i n and the c o n d i t i o n s , the G - v a l u e s a r e b e t w e e n 1 0 2 and 1 0 3 ( s h o r t - c h a i n r e a c t i o n ) .

3 . 2 . R a d i a t i o n - i n i t i a t e d p o l y m e r i z a t i o n

S e v e r a l s u g g e s t i o n s on t h i s s u b j e c t h a v e a l r e a d y b e e n m a d e in t h i s p a p e r , s o that o n l y a f ew s u m m a r i z i n g r e m a r k s w i l l be g i v e n h e r e .

3 . 2 . 1 . P o l y m e r i z a t i o n in the g a s e o u s p h a s e . T h e p o l y m e r p r e c i p i t a t e s i n l i q u i d o r s o l i d f o r m . T h e p o l y m e r i z a t i o n of e t h y l e n e h a s b e e n m o s t i n t e n s e l y s t u d i e d , e s p e c i a l l y by an A m e r i c a n g r o u p ( S t e i n b e r g et a l . , B N L ) and an I t a l i a n g r o u p ( M u n a r i e t a l . ). M o r e than 6 0 p u b l i c a t i o n s h a v e a p p e a r e d in the l a s t f e w y e a r s .

3 . 2 . 2 . S o l i d - s t a t e p o l y m e r i z a t i o n and c o p o l y m e r i z a t i o n . T h i s t e c h n i q u e i s p r o m i s i n g . U n f o r t u n a t e l y , the r e a c t i o n s a r e w e l l u n d e r s t o o d . On the o t h e r hand, the p o l y m e r s f o r m e d by a s o l i d - s t a t e p r o c e s s a r e o f t e n h i g h l y o r d e r e d and o f t e n h a v e o u t s t a n d i n g p r o p e r t i e s .

3 . 2 . 3 . P o l y m e r i z a t i o n i n the p r e s e n c e of s p e c i a l a d d i t i v e s . B o t h the r e a c t i o n r a t e and the m e c h a n i s m of c e r t a i n p o l y m e r i z a t i o n s a r e s t r o n g l y i n f l u e n c e d by c e r t a i n i n o r g a n i c c o m p o u n d s (ZnO, t - A 1 ^ D 3 , s i l v e r s a l t s ) that a c t a s r a t e p r o m o t e r s .

3 . 2 . 4 . C o p o l y m e r i z a t i o n . O b s e r v i n g c e r t a i n c o n d i t i o n s of t e m p e r a t u r e , and of the p u r i t y of the m o n o m e r s a s w e l l , r a d i a t i o n - i n i t i a t e d c o p o l y m e r i -z a t i o n m a y y i e l d u s e f u l c o p o l y m e r s that cannot be p r e p a r e d by c o n v e n -t i o n a l p r o c e s s e s .

3 . 2 . 5 . G r a f t i n g of p o l y m e r s . T h i s t e c h n i q u e h o l d s p r o m i s e i n t h e t e x t i l e i n d u s t r y . M a n y i n d u s t r i a l l y i m p o r t a n t q u a l i t i e s of f i b r e s ( s u c h a s c o t t o n , w o o l and p o l y p r o p y l e n e ) a r e g r e a t l y e n h a n c e d by g r a f t i n g w i t h a p r o p e r m o n o m e r . T h i s t e c h n i q u e h a s b e e n s t u d i e d by ( a m o n g o t h e r s ) the S c h o o l of T e x t i l e s of the R e s e a r c h T r i a n g l e I n s t i t u t e ( R a l e i g h , N . C . ) , and by n u m e r o u s J a p a n e s e a u t h o r s .

3 . 2 . 6 . E m u l s i o n p o l y m e r i z a t i o n and c o p o l y m e r i z a t i o n . T h i s t e c h n i q u e d o e s not y i e l d n e w p r o d u c t s . It may, h o w e v e r , h a v e s o m e a d v a n t a g e s o v e r the c o n v e n t i o n a l p r o c e s s e s .

A C K N O W L E D G E M E N T S

W e a r e v e r y g r a t e f u l to A t o m i c E n e r g y of Canada , Ltd . , H . S . M a r s h , L t d . , G e b r i i d e r S u l z e r AG, and M r . H a n s W S l i s c h m i l l e r f o r p r o v i d i n g c o n s t r u c t i o n p l a n s and p r o p o s a l s w i thout c h a r g e . ( T h e s e p l a n s a r e s t r i c t l y p r o p r i e t a r y . ) W e a r e a l s o g r a t e f u l to the B u n d e s m i n i s t e r i u m f u r w i s s e n -s c h a f t l i c h e F o r s c h u n g and t o the D e u t s c h e F o r s c h u n g s g e m e i n s c h a f t f o r g r a n t i n g f e l l o w s h i p s to M. R y s k a a n d R . C . P o t t e r r e s p e c t i v e l y . F i n a l l y , w e thank the B M W F f o r f i n a n c i n g the p i l o t - p l a n t s t u d y .

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R E F E R E N C E S

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[2] CHAPIRO, A. , MAEDA, N. . J. Chim. phys. 56 (1959) 230. [3] NAKASHIO, S., UEDA, M., TAKAHASHI, K., Makromolek. Chem. 89 (1965) 245. [4] Makromolek. Chem. 83 (1965) 23. [5] CHAPIRO, A. , JENDRYCHOWSKA-BONAMOUR. A.M. , ROUSSEL, D. , C . r . hebd. Séanc. Acad.Sci . ,

Paris 258 914. [6] BALLANTINE, D . S . , GLINES, A. , COLOMBO, T . , MANOWITZ, E.. USAEC BNL Rep. 294 (1954). [7] MEZHIROVA, L.P. , JAKOVLEVA, M.K. , MATVEJEVA, A.V. , ABKIN, A .D . , CHOMIKOVSKIJ, P .N. ,

MEDVEDEV, S.S. , Vysokomol. Soedin. 1_ (1959) 68. [8] ALLEN, P .E .M. , BURNETT, G.M., DOWNER, J . M . , MELVILLE, H. , Makromolek. Chem. 38

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Ser. (in press); Angew. Chemie 75 (1963) 330 ; ACS Polymer Preprints 7 2 (1966) 725; J. Polym. Sci. , Part С (in press).

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THE USE OF LOW-ENERGY ELECTRON ACCELERATORS FOR THE CURING OF PAINTS AND THIN FILMS

F.L. DALTON WANTAGE RESEARCH LABORATORY, ATOMIC ENERGY RESEARCH ESTABLISHMENT, WANTAGE, BERKS, UNITED KINGDOM

Abstract

THE USE OF LOW-ENERGY ELECTRON ACCELERATORS FOR THE CURING OF PAINTS AND THIN FILMS. Considerable industrial interest has been aroused in the use of accelerators based on transformer-rectifier sets operating in the 150-300 kV range, and in insulating core transformers above 300 kV, for the curing of paint films and the initiation of reactions taking place in thin surface coatings. An indication is given here of the position that has been reached in the commercialization of such processes, and some problems are set out that need to be solved before large-scale exploitation can be achieved. Some general remarks on the advantages of radiation curing and the cost of equipment are also offered.

INTRODUCTION

A c o n s i d e r a b l e amount of industr ia l i n t e r e s t has been a r o u s e d in the l a s t few y e a r s by the p o s s i b i l i t y of us ing e l e c t r o n a c c e l e r a t o r s operat ing in the range 150-500 kV for the t rea tment of thin f i l m s and s u r f a c e coa t ings . Such m a c h i n e s can be made much m o r e cheaply than a c c e l e r a -t o r s with e n e r g i e s of 2 MeV or m o r e , s i n c e a s i m p l e t r a n s f o r m e r r e c t i f i e r s y s t e m can supply the n e c e s s a r y vo l tage up to 300 kV, and the u s e of an insulated c o r e t r a n s f o r m e r ex tends th is w e l l above the range of our p r e s e n t i n t e r e s t . Most s u r f a c e coat ing appl icat ions do not invo lve t h i c k n e s s e s of m o r e than 20 thousands of an inch, and the t r a n s f o r m e r r e c t i f i e r s y s t e m i s t h e r e f o r e adequate as a vo l tage supply. High c u r r e n t s , l eading to d o s e - r a t e s in the s a m p l e f r o m 100 to 1000 M r a d / m i n , m a y be obtained by producing e l e c t r o n s f r o m a heated f i l ament , a c c e l e r a t i n g them in vacuo , and al lowing them to e m e r g e f r o m the equipment through a thin window. Af ter a c c e l e r a t i o n the e l e c t r o n b e a m i s scanned in a m a n n e r analogous to that u s e d in a TV tube s o that a b e a m of convenient width for prac t i ca l u s e with f lat s h e e t or cont inuous m a t e r i a l i s obtained. B e a m s 4 ft wide a r e obtained on c o m m e r c i a l l y ava i lab le equipment at the p r e s e n t t i m e . F i g u r e 1 shows the m e a n range of e l e c t r o n s in m a t e r i a l of unit dens i ty as a funct ion of e n e r g y . B e c a u s e of i n c r e a s e d absorpt ion of e l e c t r o n s by the window and by the a i r gap be tween the window and the products to be i rrad ia ted , it s e e m s unl ike ly that e n e r g i e s below 1 5 0 - 2 0 0 kV w i l l be u s e d in prac t i ce even for the i rradiat ion of e x t r e m e l y thin f i l m s .

SCOPE OF LOW-ENERGY ACCELERATORS

The g r e a t e s t potential in the method l i e s in the p o s s i b i l i t y of cur ing paint f i l m s and other s u r f a c e coat ings at a h igher s p e e d and m o r e

1 6 5

1 6 6 DALTON

. r u

kV

FIG. 1. Electron mean range in unit density mater ia l .

c h e a p l y than c a n be done in c o n v e n t i o n a l o v e n s . T h e r a n g e of p a i n t s s u i t a b l e f o r e l e c t r o n c u r i n g i s l i m i t e d by the c h e m i c a l n a t u r e of the r e a c t i o n s i n d u c e d by the m e t h o d . T h e s e r e a c t i o n s a r e f r e e r a d i c a l c h a i n r e a c t i o n s , and the h a r d e n i n g of the paint i s c a u s e d by p o l y m e r i z a -t i o n of a v i n y l c o m p o u n d w h i c h in the c o u r s e of i t s p o l y m e r i z a t i o n r e a c t s w i t h the r e s i n c o n t e n t of the paint to f o r m a t h r e e - d i m e n s i o n a l n e t w o r k . T h i s m e a n s that t o t a l - f o r m i n g ( s o l v e n t - f r e e ) p a i n t s s h o u l d be u s e d , and the l a r g e s t e x i s t i n g c l a s s of s u c h p a i n t s i s the u n s a t u r a t e d p o l y e s t e r m o n o m e r t y p e u s e d f o r w o o d f i n i s h i n g . The l i m i t a t i o n in the u s e of t h e s e p a i n t s h a s b e e n due l a r g e l y to d i f f i c u l t y in c u r i n g , and the e l e c t r o n c u r i n g t e c h n i q u e c o u l d w e l l l e a d to an e x t e n s i o n of the f o r m u l a t i o n s of the p a i n t s and the p u r p o s e s f o r w h i c h t h e y a r e u s e d . T h e c u r i n g of o t h e r m a j o r c l a s s e s of i n d u s t r i a l p a i n t s i s b a s e d on c o n d e n s a t i o n r e a c t i o n s , w h i c h a r e not i n d u c e d by e l e c t r o n b o m b a r d m e n t , and s o l v e n t e v a p o r a t i o n . T h i s m e a n s that s o m e m o d i f i c a t i o n of a c r y l i c , v i n y l , e p o x y and u r e t h a n e p a i n t s i s e s s e n t i a l b e f o r e r a d i a t i o n c u r i n g c a n b e u s e d w i t h t h e m , and i n s u f f i c i e n t a t t e n t i o n h a s b e e n g i v e n to t h i s a s p e c t of r a d i a t i o n c u r i n g a l though s o m e s i g n i f i c a n t w o r k now b e i n g c a r r i e d out w i l l be m e n t i o n e d l a t e r .

O t h e r f i e l d s in w h i c h the t e c h n i q u e m a y be u s e d a r e in the c r o s s -l i n k i n g of thin p l a s t i c f i l m s and the m o d i f i c a t i o n of the p r o p e r t i e s of t e x t i l e s . Such d e v e l o p m e n t s a r e a l s o m e n t i o n e d b e l o w . In g e n e r a l , any f r e e r a d i c a l r e a c t i o n that n e e d s to be c a r r i e d out r a p i d l y and at r o o m

P L - 2 3 6 / 3 1 6 7

t e m p e r a t u r e in a thin l a y e r i s a potent ia l t a r g e t for l o w - e n e r g y e l e c t r o n t r e a t m e n t , and th i s h a s l e d to s p e c i f i c i n t e r e s t s c o v e r i n g a wide range of p r o j e c t s be ing a r o u s e d in m a n y c o m p a n i e s . A demand for t rea t ing g r e a t e r t h i c k n e s s e s of m a t e r i a l , e . g . f or p o l y e s t e r p r e - i m p r e g n a t e d g l a s s f ibre m a t s , at v e r y high i n t e n s i t i e s h a s a l s o a r i s e n , but th i s r e q u i r e s m o r e e x p e n s i v e and s p e c i a l i z e d equipment than that u s e d in the thin f i l m work , and i s out s ide the s c o p e of th i s r e v i e w .

A D V A N T A G E S OF RADIATION CURING

Speed of c u r e

Curing t i m e s of o n e - t e n t h of a s e c o n d or l e s s can be r e a d i l y a c h i e v e d ; on cont inuous s t r i p s p e e d s of 2 0 - 2 0 0 f t / m i n can be obtained with pa ints r e q u i r i n g a v e r a g e d o s e s to c u r e . St i l l h igher s p e e d s should be obta inable with r e l a t i v e l y l i t t l e d e v e l o p m e n t w o r k . A s w e l l a s the obv ious a d v a n t a g e s of rapid c u r e , l a r g e s a v i n g s a r e o f t en m a d e by shor ten ing the t i m e during which a coa ted s u r f a c e i s l iab le to dust d a m a g e , s i n c e c o n s i d e r a b l e r e -coat ing i s o f t en n e c e s s a r y when long drying t i m e s are u s e d under f a c t o r y cond i t ions .

Space

S o m e 5 or 6 ft of the product ion l ine a r e n e e d e d to handle the through-put of o v e n s which m a y be 1 0 0 - 2 0 0 ft in l ength .

U s e on h e a t - s e n s i t i v e s u b s t r a t e s

B e c a u s e the cur ing p r o c e s s t a k e s p lace at r o o m t e m p e r a t u r e , the cur ing of c o a t i n g s on hardboard , p lywood and p l a s t e r b o a r d can be c a r r i e d out Continuously without damage to the b a s e m a t e r i a l . The cur ing of high g l o s s p o l y e s t e r l a c q u e r s on paper i s a l s o f e a s i b l e . D i f f i c u l t i e s of change of co lour of paint at oven t e m p e r a t u r e a r e a l s o e l i m i n a t e d .

E l i m i n a t i o n of c a t a l y s t f r o m paint

S ince the cur ing r e a c t i o n s a r e induced by e l e c t r o n b o m b a r d m e n t , no c a t a l y s t or a c c e l e r a t o r i s needed in the paint , and th i s l e a d s to an u n l i m i t e d pot l i f e and e l i m i n a t e s the need for t w o - p a c k s y s t e m s and r e g u l a r m a c h i n e c l e a n i n g .

E l i m i n a t i o n of s o l v e n t

Although the need to u s e s o l v e n t - f r e e paints for rad ia t ion c u r i n g has m a d e c o n s i d e r a b l e d e v e l o p m e n t work n e c e s s a r y , the u s e of such f o r m u l a t i o n s e l i m i n a t e s the need f o r s o l v e n t r e c o v e r y equipment and r e d u c e s a t m o s p h e r i c pol lut ion p r o b l e m s .

Speed of o p e r a t i o n

S w i t c h - o n and s w i t c h - o f f a r e in s tantaneous w h e r e a s o v e n s m a y take hours or e v e n days to heat up and c o o l down. T h i s g i v e s e l e c t r o n cur ing

1 6 8 D A L T O N

a l a r g e advantage , p a r t i c u l a r l y on l i n e s w h e r e u n f o r e s e e n breakdown i s p o s s i b l e .

COST OF RADIATION CURING

It i s d i f f i cu l t to g ive a c c u r a t e c o s t f i g u r e s f o r the rad ia t ion cur ing p r o c e s s for s e v e r a l r e a s o n s . A m e r i c a n equipment has to date had on ly a l i m i t e d s a l e , whi le in the United Kingdom we a re s t i l l in the d e v e l o p m e n t s t a g e . A l a r g e proport ion of the capi ta l i n v e s t m e n t i s in the 3 0 0 - k V t r a n s f o r m e r r e c t i f i e r s e t , and the p r i c e of t h e s e i s dependent to a s m a l l ex tent only on t h e i r output c u r r e n t , s o that o v e r - a l l c o s t i s not s i m p l y r e l a t e d to throughput. To g i v e s o m e g e n e r a l i d e a s of c o s t , h o w e v e r , it m a y be sa id that a 30 kVA a c c e l e r a t o r , capable of t rea t ing 1 0 0 - 1 2 0 m i l l i o n f t 2 of m a t e r i a l in an 8000-hour y e a r if an a v e r a g e cur ing d o s e i s a s s u m e d , would c o s t a p p r o x i m a t e l y £30 000 i n s t a l l e d in the United Kingdom if built a s a " o n e - o f f " i t e m . P r o f e s s i o n a l s ta f f would not be n e e d e d f o r rout ine running of the equipment although e x p e r t s e r v i c i n g two o r three t i m e s a y e a r i s d e s i r a b l e . Much m o r e a c c u r a t e e s t i m a t e of c o s t s for equipment to t r e a t a s p e c i f i c throughput of a s p e c i f i c product can na tura l ly be m a d e if de ta i l ed i n f o r m a t i o n is a v a i l a b l e .

EXISTING EQUIPMENT'

The f i r s t c o m m e r c i a l l y ava i lab le a c c e l e r a t o r s w e r e the High Vol tage C o r p o r a t i o n ' s I . C . T . 300 and 500; t h e s e m a c h i n e s o p e r a t e at 300 and 500 kV r e s p e c t i v e l y , and have scann ing h e a d s up to 4 ft w ide . T h e y u s e in su la ted c o r e t r a n s f o r m e r s to g e n e r a t e the a c c e l e r a t i n g v o l t a g e and this m e a n s that the capi ta l c o s t of the 300 kV equipment i s r a t h e r high. The m a x i m u m output of the 500 kV m a c h i n e i s 20 m A though not m o r e than 15 m A can be u s e d with one scanning head . Irrad ia t ion of s a m p l e s i s c a r r i e d out by the High Vo l tage Corporat ion for i n t e r e s t e d c o m p a n i e s on a c o m m e r c i a l b a s i s .

The f i r s t 3 0 0 - k V equipment b a s e d on a t r a n s f o r m e r r e c t i f i e r s y s t e m d e s i g n e d s p e c i f i c a l l y for cur ing paint f i l m s and s i m i l a r c o a t i n g s w a s the "Dynaco te" , in troduced by Radiat ion D y n a m i c s Inc. T h i s p r o v i d e s a 1 - 2 5 m A b e a m which m a y be s canned o v e r 2 or 4 ft . A double p o w e r supply i s a v a i l a b l e if two h e a d s are r e q u i r e d . T h i s c o m p a n y a l s o m a k e s rad ia t ion f a c i l i t i e s ava i lab le at c o m m e r c i a l r a t e s .

The T e x a s N u c l e a r Corpora t ion o f f e r s 3 0 0 - k V equ ipment but d e t a i l s a r e not y e t to hand. The F o r d Motor Company has i n s t a l l e d i t s own equ ipment and h a s done a c o n s i d e r a b l e amount of r e s e a r c h and d e v e l o p -m e n t w o r k al though l i t t l e de ta i l ed i n f o r m a t i o n i s a v a i l a b l e . P a t e n t s f i l e d by the c o m p a n y c o v e r d e v e l o p m e n t s in m a c h i n e d e s i g n and a l s o in paint f o r m u l a t i o n ; c o n s i d e r a b l e e m p h a s i s h a s b e e n la id on the d e v e l o p m e n t of rad ia t ion c u r i n g of a c r y l i c r e s i n s . F o r d t e c h n i c a l knowledge r e l e v a n t to wood f i n i s h i n g has been l i c e n s e d to B o i s e C a s c a d e , who a re s a i d to be s t a r t i n g p i l o t - s c a l e product ion in Apr i l 1967. L o w - e n e r g y e l e c t r o n a c c e l e r a t o r s have been u s e d for s o m e y e a r s by the C r y o v a c D i v i s i o n of W . R . G r a c e & Company in the product ion of the ir s h r i n k a b l e polythene packaging f i l m C r y o v a c L . D e e r i n g Mi l l ikan have r e c e n t l y announced that s i m i l a r equ ipment i s be ing u s e d in a new method of producing c r e a s e -and s o i l - r e s i s t a n t f i n i s h e s for p o l y e s t e r cotton f a b r i c s .

P L - 2 3 6 / 3 1 6 9

No l a r g e - s c a l e d e m o n s t r a t i o n equipment i s at p r e s e n t a v a i l a b l e in E u r o p e , although a n u m b e r of e x p e r i m e n t a l a s s e m b l i e s e x i s t . In p a r t i c u l a r , the Wantage R e s e a r c h L a b o r a t o r y has two e x p e r i m e n t a l 150 -kV m a c h i n e s , one t r e a t i n g s a m p l e s up to in. w ide and the o ther s a m p l e s up to 6 in . In v i e w of the i n t e r e s t a r o u s e d by the r e s u l t s obta ined on t h e s e a c c e l e r a t o r s , a 3 0 0 - k V 1 0 0 - m A i n s t a l l a t i o n having a 4 - f t head h a s b e e n d e v e l o p e d , wh ich it i s hoped to c o m m i s s i o n in July 1967. The m a c h i n e w i l l be u s e d in the Wantage r e s e a r c h p r o g r a m m e , but t i m e w i l l be m a d e a v a i l a b l e to i n t e r e s t e d c o m p a n i e s . T e c h n i c a l l y , th i s equ ipment should prov ide a su i tab le pi lot f a c i l i t y f o r a l l the a p p l i c a t i o n s of e l e c t r o n cur ing e n v i s a g e d s o far .

T Y P E S OF PAINT S U I T A B L E FOR RADIATION CURING

A s h a s a l r e a d y b e e n ind ica ted , the m o s t w i d e l y s tud ied paints to date a r e t h o s e b a s e d on u n s a t u r a t e d p o l y e s t e r m o n o m e r m i x t u r e s , the m o n o m e r in m o s t c a s e s be ing s t y r e n e . The r a d i a t i o n - i n d u c e d cur ing of such m i x t u r e s w a s r e p o r t e d by Cal l inan [1] and s tudied in m o r e deta i l by C h a r l e s b y and h i s c o - w o r k e r s [2] who , in addit ion to s tudying a range of p h y s i c a l p r o p e r t i e s , s h o w e d that the cur ing r e q u i r e d r e l a t i v e l y l ow total d o s e s , and pointed out that ra te of c u r e w a s propor t iona l to the s q u a r e root of the rad ia t ion i n t e n s i t y . M o r e r e c e n t l y , B u r l a n t and H i n s c h [3] , work ing at h igher i n t e n s i t i e s , have r e p o r t e d r a t e s d i r e c t l y p r o p o r t i o n a l to , or independent o f , i n t e n s i t y , and work at Wantage h a s shown that the i n t e n s i t y exponent i s , in f a c t , a funct ion of i n t e n s i t y , the p r e c i s e f o r m of th i s funct ion depending on the d e t a i l e d f o r m u l a t i o n of the s y s t e m . At a p r a c t i c a l l e v e l it i s c l e a r that , a l though s o m e c l a i m s for i m p r o v e d a d h e s i o n have been m a d e , r a d i a t i o n - c u r e d p o l y e s t e r m o n o m e r s y s t e m s g i v e f i n i s h e s s i m i l a r to t h o s e obta ined by convent iona l cur ing , and that t h e s e cari be obta ined at d o s e s in the 2 - 1 0 Mrad r a n g e . W h e r e a s m o s t r e p o r t e d w o r k has b e e n c a r r i e d out on s i m p l i f i e d s y s t e m s , a n u m b e r of U . K . c o m p a n i e s w o r k i n g in c o l l a b o r a t i o n with the Wantage R e s e a r c h L a b o r a t o r y have obta ined data on fu l ly compounded r e s i n s y s t e m s c o v e r i n g a wide r a n g e of s p e c i f i c a t i o n s .

P o l y e s t e r paints a r e not at p r e s e n t u s e d on a v e r y wide s c a l e i n d u s t r i a l l y , but the new cur ing method m a y w e l l open up new f i e l d s for t h e m . The m a i n o b j e c t i o n s to t h e i r u s e have been d i f f i cu l ty in c u r i n g , the need for a t w o - p a c k s y s t e m that l i m i t s s h e l f l i f e and n e c e s s i t a t e s f requent c l e a n i n g of equ ipment , t o g e t h e r with the d i f f i cu l ty of obtaining " t a c k - f r e e " s u r f a c e s . None of t h e s e p r o b l e m s a r i s e s if radiat ion c u r i n g i s u s e d , and th i s m a k e s unsa tura ted p o l y e s t e r s m u c h m o r e a t t r a c t i v e m a t e r i a l s to the paint m a n u f a c t u r e r . T h i s i s l ead ing to new t y p e s of f o r m u l a t i o n for u s e w h e r e p o l y e s t e r s have p r e v i o u s l y been c o n s i d e r e d u n p r a c t i c a l . A s e c o n d group of paints s tudied in de ta i l by the F o r d Motor Company in the United S ta tes of A m e r i c a a r e the a c r y l i c s . The F o r d Motor Company h a s announced the d e v e l o p m e n t of p r a c t i c a l rad ia t ion -c u r e d a c r y l i c s , but no d e t a i l s have been r e l e a s e d . In the United Kingdom, work at the Wantage R e s e a r c h L a b o r a t o r y h a s c o n c e n t r a t e d on the d e v e l o p -m e n t of s o l v e n t - f r e e a c r y l i c f o r m u l a t i o n s and c o n s i d e r a b l e s u c c e s s has b e e n a c h i e v e d , although aga in no d e t a i l s have ye t b e e n r e l e a s e d . L e s s de ta i l ed work has been c a r r i e d out in v a r i o u s l a b o r a t o r i e s on a range of o ther paint s y s t e m s . U n m o d i f i e d e p o x i e s a r e not a m e n a b l e to rad ia t ion

1 7 0 D A L T O N

cur ing but e p o x y - a c r y l i c s have been s tudied by Radiat ion D y n a m i c s in the United S ta tes of A m e r i c a and at the Wantage R e s e a r c h L a b o r a t o r y in the United Kingdom, Radiat ion D y n a m i c s have a l s o r e p o r t e d work ing on PVC p l a s t i s o l s and p l a s t i s o l s with s t y r e n a t e d p o l y e s t e r s .

A R E A S OF I N T E R E S T IN WHICH FURTHER D E V E L O P M E N T WORK IS REQUIRED

A c c e l e r a t o r s

An i m p r o v e m e n t in the d e s i g n of a c c e l e r a t o r s for t r e a t i n g f la t s u r f a c e s i s p o s s i b l e and n e c e s s a r y , a s i s the d e v e l o p m e n t of a range of i n s t r u m e n t s of v a r y i n g output to c o v e r v a r y i n g c o m m e r c i a l r e q u i r e m e n t s . L i t t l e work h a s ye t b e e n c a r r i e d out on the t r e a t m e n t of shaped s u r f a c e s , and the product ion of m a c h i n e s capable of i r r a d i a t i n g c a r b o d i e s and o ther l a r g e v o l u m e i t e m s could l ead to v e r y l a r g e - s c a l e u s e of the rad ia t ion cur ing method .

Pa int s y s t e m s

The d e v e l o p m e n t of rad ia t ion cur ing paints of v a r i o u s t y p e s to the s t a g e at which a range of c o m m e r c i a l l y a c c e p t a b l e f i n i s h e s can be o f f e r e d i s u r g e n t l y n e e d e d if m a c h i n e t echno logy i s not to d e v e l o p m o r e rap id ly than paint t e c h n o l o g y . With the except ion of the p o l y e s t e r pa int s , v e r y l i t t l e e f f o r t has b e e n put into t h i s . The r e q u i r e m e n t ex tends beyond paints to m a t e r i a l s such a s print ing inks and t e x t i l e f i n i s h e s .

CONCLUSIONS

The l o w - e n e r g y e l e c t r o n i rrad ia t ion technique a p p e a r s to o f f e r g r e a t a d v a n t a g e s in a n u m b e r of s u r f a c e coat ing a p p l i c a t i o n s , and a rapid d e v e l o p m e n t p r o g r a m m e i s n e c e s s a r y to i m p r o v e the range of m a c h i n e s a v a i l a b l e and to produce m a n y m o r e t y p e s of coat ing su i table for e l e c t r o n c u r i n g . In E u r o p e , the c o n s t r u c t i o n of p i l o t - s c a l e f a c i l i t i e s i s e s s e n t i a l b e f o r e c o m m e r c i a l exp lo i ta t ion can be a c h i e v e d , and the equipment under c o n s t r u c t i o n at the Wantage R e s e a r c h L a b o r a t o r y of the U . K . A . E . A . r e p r e s e n t s a m a j o r s t e p in th i s d i rec t ion .

R E F E R E N C E S

[1] CALLINAN, T.D. , ONR Symposium, Rep. ACR-2 (1954) 24; Electl Engng, N.Y. 74 (1955) 510; Electl Equip. (July 1956); Insulation, Lond. (August 1956).

[2] CHARLESBY, A. , WHYCHERLEY, V . , Int. J. appl. Radiat. Isotopes 2 (1957) 26; CHARLESBY, A . , WHYCHERLEY, V. , GREENWOOD, T . T . , Proc. R. Soc. , Ser. A, 244 (1958) 54.

[3] BURLANT, W. , H1NSCH, J. , J. Polym. Sci. A 3 (1965) 3587; I. Polym. Sci. A 2 (1964) 2135.

V . C O M M U N I C A T I O N S A N D C O M M E N T S

SUMMARY OF REMARKS ON THE

ADDITIVITY OF SIMULTANEOUS RADIATION E F F E C T S

J . S i l v e r m a n When a radiat ion e x p e r i m e n t i s p e r f o r m e d in mixed n e u t r o n - g a m m a

f i e l d s , it i s f requent ly a s s u m e d that the e f f e c t s a r e addit ive in a l inear m a n n e r . To obtain the net neutron e f f e c t , s o m e i n v e s t i g a t o r s p e r f o r m the e x p e r i m e n t in a pure g a m m a f i e ld and subtract the g a m m a e f f e c t f r o m the r e s u l t obtained in the mixed f i e ld . T h i s procedure can lead to s e r i o u s e r r o r s and has apparent ly done so in the c a s e of the r a d i o l y s i s of the po lypheny l s .

The pr inc ip le of n o n - l i n e a r i t y i s an old one, we l l r e c o g n i z e d by a l m o s t a l l p h o t o c h e m i s t s , s o m e p o l y m e r c h e m i s t s and a few radiat ion s c i e n t i s t s .

F o r e x a m p l e , in the p o l y m e r i z a t i o n of v inyl m o n o m e r s by heat and g a m m a s the proper e x p r e s s i o n for the rad ia t ion- induced f r e e rad ica l r e a c t i o n rate i s g iven by

R n = R2t - R b

w h e r e R n = rate of rad ia t ion- induced po lymer iza t ion , Rt = o v e r - a l l rate including radiat ion and t h e r m a l

e f f e c t s , and Rb = rate of t h e r m a l p o l y m e r i z a t i o n a lone .

S i m i l a r l y , if the s a m e r e a c t i o n i s o b s e r v e d in a mixed radiat ion f ie ld , it i s wrong to conclude that

R n = Rn, y " R y

w h e r e the t h r e e s y m b o l s are the neutron- induced rate , the mixed f i e ld rate and the g a m m a - i n d u c e d rate r e s p e c t i v e l y .

The proper e x p r e s s i o n i s

R n - r 2 R :

A s ign i f i cant t h e r m a l e f f e c t c o m p l i c a t e s the k ine t i c s s t i l l fur ther . In a c o m p l e x r e a c t i o n (such a s the d e c o m p o s i t i o n of polyphenyls ) , it

i s of ten u n r e a s o n a b l e to use a m o d e l of the fo l lowing type:

Rn,y = knIn + M f + R b

w h e r e kn and k^ r e f e r to the y i e l d s o f the neutron and g a m m a r e s p e c t i v e l y , the I ' s r e f e r to the d o s e ra te s , A i s the power of the d o s e - r a t e dependence , and Rb i s the t h e r m a l blank.

If A i s not equal to unity, the e x p r e s s i o n i s c er ta in ly inval id. If it i s unity at low dose ra te s , it may s t i l l be inval id at h igher dose r a t e s w h e r e saturat ion e f f e c t s occur .

1 7 1

1 7 2 C O M M U N I C A T I O N S A N D C O M M E N T S

V A C U U M U L T R A - V I O L E T RADIATION

N. Getof f

Introduct ion

The v a c u u m u l t r a - v i o l e t ( v . u . v . ) l ight i s an e l e c t r o m a g n e t i c rad ia t ion wi th a w a v e l e n g t h < 2000 A T h i s l ight i s s t r o n g l y a b s o r b e d by oxygen , l e a d i n g to the f o r m a t i o n of o z o n e , and i s t h e r e f o r e invo lved in s e v e r a l p h o t o c h e m i c a l p r o c e s s e s in the a t m o s p h e r e .

S ince the e n e r g y p e r quantum in the w a v e l e n g t h range i s r e l a t i v e l y high, i . e . 6 . 6 e V / q u a n t u m at X =o1849 A, 8 . 4 e V / q u a n t u m at X = 1470 A and 10. 1 e V / q u a n t u m at A. = 1236 A, the v . u . v . l ight r e p r e s e n t s a l ink b e t w e e n u. v . l ight in i t s u s u a l s e n s e (X > 2000 A) and i o n i z i n g r a d i a t i o n s . In fact , it w a s found v e r y r e c e n t l y that h y d r o c a r b o n s , i . e . n -butane , can be i o n i z e d , . u s i n g the a r g o n r e s o n a n c e l i n e s at 1067 and 1048 A [1, 2 ] . A p a r t f r o m th i s , by i r r a d i a t i n g w a t e r in the l iquid s ta te wi th v . u . v . l ight , s o l v a t e d e l e c t r o n s ^-~e -aq) a r e f o r m e d wi th a quantum y i e l d , 4> —e-aq) = 0 . 0 3 a t l 8 4 9 A [3] a n d 0 . 0 6 a t 1470 A [4] .

T h e v . u . v . l ight a s a new tool of i r r a d i a t i o n h a s b e c o m e i n c r e a s i n g l y i m p o r t a n t in the l a s t 10 y e a r s . One can now a c h i e v e an e f f i c i e n t l ight i n t e n s i t y (10 1 4 - 10 1 5 q u a n t a / s ) to produce m e a s u r a b l e a m o u n t s of produc t s .

v . u . v . rad ia t ion s o u r c e s

G a s f i l l i n g The v . u . v . l ight s o u r c e s a r e e l e c t r o d e l e s s d i s c h a r g e l a m p s c o n -

ta in ing a r a r e g a s o r g a s m i x t u r e of about 1 m m p r e s s u r e , p o w e r e d by m i c r o w a v e e n e r g y . S o m e r e s o n a n c e e m i s s i o n s for a t o m s a r e p r e s e n t e d in T a b l e I.

T h e v . u . v . l ight obta inable has w a v e l e n g t h s ranging f r o m 5 8 4 . 4 to about 2000 A. U s u a l l y a l a m p i s f i l l ed wi th a r a r e g a s and c o n s i s t s of a P y r e x tube to wh ich a quartz f i n g e r conta in ing a B a - A l - N i a l l o y (get ter) i s a t t a c h e d . The g e t t e r a b s o r b s the i m p u r i t i e s in the r a r e g a s and one c a n a c h i e v e a c h r o m a t i c pur i ty in the l a m p e m i s s i o n . Ins tead of g e t t e r the s a m e r e s u l t c a n be obta ined by u s i n g a r e f r i g e r a n t f o r the g a s i m -p u r i t i e s , i . e . l iquid o x y g e n in the c a s e of a xenon r e s o n a n c e l a m p o r l iquid n i t r o g e n f o r krypton f i l l i n g , e t c .

Window m a t e r i a l A s p e c i a l "window" i s n e e d e d through which the v . u . v . l ight produced

by the g a s d i s c h a r g e c a n be propagated to the s a m p l e . In the c a s e of w a v e l e n g t h s above 1050 A the r e q u i r e m e n t of t r a n s p a r e n c y i s a c h i e v e d by the w i n d o w s l i s t e d in T a b l e II.

F o r v . u . v . i r r a d i a t i o n of g a s an L i F window i s s tuck on to the one end of the l a m p . In t h i s c a s e , both l a m p s and r e a c t i o n v e s s e l s u s u a l l y r e q u i r e s u c h a window. The sapphire h a s the advantage of making p o s s i b l e a graded s e a l to the P y r e x and w i t h s t a n d s t e m p e r a t u r e s f r o m 77 to 700° K.

A f t e r pro longed u s e of the l a m p the window of L i F , CaF 2 , e t c . , b e -c o m e s c o l o u r e d f r o m the c r e a t i o n of "F" c e n t r e s . The c o l o u r a t i o n .

173 C O M M U N I C A T I O N S A N D C O M M E N T S

T A B L E I. S O M E C U R R E N T R E S O N A N C E E M I S S I O N S F O R A T O M S [ 5 - 7 ]

Gas \ (in A)

Gas ( * (in A)

Hydrogen 1215. 7 Radon

1149 1786.1

Deuter ium 1215 .3 Bromine

1582 1633

Helium 5 8 4 . 4

Neon 735. 9 743. 7 Iodine

1799 1844 2064

Argon 1048.2 1066.7

Mercury (low -pressure)

1849 2537

Krypton 1164. 9 1235. 8

20 vol. % Nitrogen "1 80 vol. % Argon J

1495 1743

Xenon 1295. 6 1469.6

T A B L E II. V A C U U M U L T R A - V I O L E T T R A N S M I T T I N G M A T E R I A L S W I T H A T H I C K N E S S O F 1 m m [5, 6, 8]

Transmitt ing mater ia l v. u. v. light transmission

above 10% for X in A

Lithium fluoride 1050

Lithium fluoride (X-rayed) 1200

Calcium fluoride 1230

Strontium fluoride 1280

Barium fluoride 1350

Sapphire 1425

Cultured crystal quartz ~ 1450

Suprasil 1600


s ST w

GAS IN

FIG. 1. Vacuum ultra-violet irradiation apparatus;

A, antenna; LO, liquid oxygen; S, solution; St, stirrer; W, window.

h o w e v e r , can be b l e a c h e d by i r r a d i a t i o n with an o r d i n a r y m e d i u m p r e s s u r e m e r c u r y a r c .

F o r w a v e l e n g t h s be low 1050 A the v . u . v . l a m p s a r e w i n d o w l e s s and the r a r e g a s p r e s s u r e i s kept by d i f f e r e n t i a l pumping s y s t e m s [9],

R e c e n t l y we have c o n s t r u c t e d m o d i f i e d v . u . v . l a m p s , which a l low not only g a s , but l iqu ids , s o l u t i o n s or so l id s u b s t a n c e s to be i r r a d i a t e d a l s o [ 10]. F o r the i r r a d i a t i o n of s o l i d s argon i s p a s s e d through the s a m p l e c o n t a i n e r during the i r r a d i a t i o n . When s o l u t i o n s have to be i r r a d i a t e d a s a p p h i r e window, w h i c h i s s u b m e r g e d in the so lu t ion (F ig . 1), i s u s e d .

M i c r o w a v e g e n e r a t o r A s ment ioned above , the g a s d i s c h a r g e in the l a m p i s g e n e r a t e d by

m i c r o w a v e s f r o m a g e n e r a t o r suppl ied with an appropr ia te antenna. We u s e a "Radarmed 12 T 2 0 1 / 9 " g e n e r a t o r (2450 M c / s ) . I ts h ighes t p o w e r output i s u s u a l l y adjusted s o that the d i s c h a r g e in the l a m p i s about 1 - 2 c m f r o m the window to l i m i t the r e a b s o r p t i o n of the radiat ion .

A c t i n o m e t r y The i n t e n s i t y of a v . u . v . l a m p i s d e t e r m i n e d by us ing w e l l - e s t a b l i s h e d

a c t i n o m e t e r s y s t e m s s u c h a s C 0 2 , O2, e t c . [5],

[1] DOEPKER, R. D. , AUSLOOS, P. , J. chem. Phys, 42 (1965) 3746. [2] AUSLOOS, P . , LIAS, S. G. , J. chem. Phys. 45 (1966) 524. [3] GETOFF, N . , Mitt. Inst. Radiumforch., Wien (in press). [4] GETOFF, N. , SCHENCK, G. O. , J. phys. Chem. (in press) [5] McNESBY, J. R., OKABE, H. , in Advances in Photochemistry 3, (NOYES, W. A. , J r . , HAMMOND, G. S . ,

PITTS, J. N. , Jr . , Eds) Interscience, New York (1964). [6] FRIEDMAN, H. , in Physics of the Upper Atmosphere, (RATCLIFFE, J. A., Ed.) Academic Press, New York

(1960). [7] OKABE, H. , J. opt. Soc. Am. 54 (1964) 478. [8] KOLLER, L. R., Ultraviolet Radiation, .Wiley, New York (1965). [9] BACK, R. A., WALKER. D. C. , J. chem. Phys. 37 (1962) 2348.

[10] GETOFF, N. , SCHENCK, G. O. (in preparation).

R E F E R E N C E S


AQUEOUS SYSTEMS

D . F . S a n g s t e r

Radiat ion c h e m i s t r y r e s e a r c h c o v e r s m o r e than a t t e m p t s to d i s c o v e r new rad ia t ion c h e m i c a l p r o c e s s e s . More rad ia t ion c h e m i c a l i n v e s t i g a t i o n s have b e e n c a r r i e d out on w a t e r and aqueous s o l u t i o n s than on any o ther c l a s s of s y s t e m . The rate of publ icat ion i s s t i l l i n c r e a s i n g . T h i s i s a r e f l e c t i o n not only of the i n t e r e s t i n g fundamenta l p r o b l e m s which e x i s t in a q u e o u s s o l u t i o n s but a l s o of t h e i r i m p o r t a n c e in any a t o m i c e n e r g y p r o -g r a m m e .

I m p o r t a n c e of a q u e o u s s y s t e m s

In any a t o m i c e n e r g y p r o g r a m m e t h e r e a r e m a n y e x a m p l e s of w a t e r o r aqueous s o l u t i o n s subjec ted to i o n i z i n g radiat ion . In such c a s e s radiat ion c h e m i c a l e f f e c t s can be e x p e c t e d and it m a y be n e c e s s a r y to m i n i m i z e o r enhance t h e s e e f f e c t s a s a p p r o p r i a t e .

E x a m p l e s a r e :

(1) R e s e a r c h or power r e a c t o r s that a r e w a t e r or h e a v y - w a t e r m o d e r a t e d o r c o o l e d

( T h i s r e v i e w i s conf ined to the c o n d e n s e d s ta te s o phenomena with the s t e a m - c o o l i n g of r e a c t o r s are e x c l u d e d . ) For tunate ly , the net w a t e r r a d i o l y t i c d e c o m p o s i t i o n in r e a c t o r s u s i n g c o m p l e t e l y e n c l o s e d fue l i s m i n i m i z e d by back r e a c t i o n s r e f o r m i n g w a t e r prov ided the w a t e r i s m a i n -ta ined pure and the f r e e g a s s p a c e i s not l a r g e . The u s e of new a l l o y s and o t h e r m a t e r i a l s in w a t e r r e a c t o r s r a i s e s the p o s s i b i l i t y of c o r r o s i o n and s i m i l a r e f f e c t s under i r r a d i a t i o n . H o m o g e n e o u s r e a c t o r s in which the f i s s i l e m a t e r i a l i s d i s s o l v e d in the m o d e r a t o r and in so lu t ion r a i s e f u r t h e r and s e r i o u s p r o b l e m s .

(2) R e p r o c e s s i n g of i r r a d i a t e d fue l The m o s t favoured fue l r e c o v e r y and f i s s i l e m a t e r i a l s e p a r a t i o n p r o -

c e s s e s a r e s t i l l t h o s e b a s e d on a q u e o u s s y s t e m s us ing e i t h e r s o l v e n t e x -t r a c t i o n o r ion e x c h a n g e t e c h n i q u e s . In o p e r a t i o n any rad ia t ion c h e m i c a l e f f e c t s have been m i n i m i z e d to a s a t i s f a c t o r y l e v e l by l i m i t i n g a s f a r a s p o s s i b l e the t i m e of contact , by inc luding addi t ional s e p a r a t i o n s t a g e s or p r o c e d u r e s and by the addit ion of r e a g e n t s to c o u n t e r a c t the e f f e c t s . A g r e a t d e a l of ad hoc w o r k has b e e n done to a r r i v e at t h e s e c o n d i t i o n s , but they a r e not n e c e s s a r i l y the b e s t m e a n s of a c h i e v i n g the r e q u i r e d r e s u l t s .

(3) C h e m i c a l a n a l y t i c a l m e t h o d s So lut ions that m u s t be a n a l y s e d to ma in ta in c h e m i c a l c o n t r o l o v e r r e -

p r o c e s s i n g and o ther o p e r a t i o n s can s o m e t i m e s be e x t r e m e l y r a d i o a c t i v e . T h e r e have b e e n v e r y f ew s t u d i e s r e p o r t e d on the e f f e c t of rad ia t ion on a n a l y t i c a l m e t h o d s . S o m e i n t e r e s t i n g and u s e f u l work might be done on t h i s subjec t .

1 7 6 C O M M U N I C A T I O N S A N D COMMEN TS

(4) R a d i o i s o t o p e product ion G e n e r a l l y , it i s p o s s i b l e to c h o o s e s o l i d iner t t a r g e t s f o r i s o t o p e

produc t ion but in s o m e s p e c i a l i n s t a n c e s t h i s i s not p o s s i b l e . Radiat ion c h e m i c a l e f f e c t s could be quite s e v e r e in the high rad ia t ion f i e l d s that m u s t be u s e d .

(5) Self d e c o m p o s i t i o n of l a b e l l e d c o m p o u n d s R a d i o i s o t o p e s a r e o f t en p r e p a r e d and u s e d in aqueous so lu t ion and a r e

c o n s e q u e n t l y s t o r e d in a q u e o u s so lut ion . Some w o r k has been done on rad ia t ion c h e m i c a l e f f e c t s in t h e s e s o l u t i o n s o c c a s i o n e d by the rad ia t ion e m i t t e d by the r a d i o a c t i v e e l e m e n t s in the l a b e l l e d compound . S o m e a n o m a l i e s a r e found when the r e s u l t s a r e c o m p a r e d with t h o s e f r o m 6 0 C o i r r a d i a t i o n .

(6) S t e r i l i z a t i o n of p h a r m a c e u t i c a l s At p r e s e n t , m o s t s u r g i c a l g o o d s s u c h a s s y r i n g e s , c a t h e t e r s and

d r e s s i n g s a r e dry m a t e r i a l s and c o n s e q u e n t l y v e r y few rad ia t ion c h e m i c a l e f f e c t s a r e e n c o u n t e r e d . W h e r e t o p i c a l app l i ca t ion i s in tended s i d e e f f e c t s a r e probab ly not i m p o r t a n t but f o r p a r e n t e r a l in jec t ion it i s n e c e s s a r y to e n s u r e that no u n d e s i r a b l e b y - p r o d u c t s a r e f o r m e d w h i c h cou ld e n d a n g e r the pat ient . The r e p o r t e d e f f e c t of i r r a d i a t e d d e x t r o s e s o l u t i o n s on c a r r o t and m a m m a l i a n c e l l s s h o w s that c a r e f u l b i o l o g i c a l t e s t i n g i s n e e d e d , and i t m a y be that rad ia t ion c h e m i c a l s t u d i e s w i l l be ab le to show w a y s of m i n i m i z i n g the f o r m a t i o n of t o x i c p r o d u c t s without i n t e r f e r i n g unduly with the s t e r i l i z a t i o n .

(7) F o o d p r e s e r v a t i o n Rad ia t ion s p o i l a g e c a n be a big p r o b l e m when rad ia t ion i s u s e d in an

a t t e m p t to d i s i n f e s t o r p r e s e r v e f o o d s t u f f s . T h i s i s a c o m p l i c a t e d b i o l o g i -c a l and b i o c h e m i c a l p r o b l e m , and it m a y be that a s o l u t i o n c a n be found only by an i n t e n s i v e s tudy of m o d e l s y s t e m s of i n c r e a s i n g c o m p l e x i t y . P e r h a p s the f o r m a t i o n of p e r o x i d e s o r h y d r o p e r o x i d e s a r e i m p o r t a n t .

(8) Rad ia t ion b i o l o g y A s s u c h , rad ia t ion b i o l o g y i s ou t s ide the s c o p e of t h i s r e v i e w .

H o w e v e r , the p r o b l e m s that e x i s t might have a b e t t e r c h a n c e of be ing s o l v e d if m o r e w e r e known about the b e h a v i o u r of l e s s c o m p l e x c o m p o u n d s -m o d e l s y s t e m s . Many b i o l o g i c a l s y s t e m s can be c o n s i d e r e d a s c o n c e n -t r a t e d a q u e o u s s o l u t i o n s but it i s i m p o r t a n t to d i s t i n g u i s h d i r e c t i n t e r a c t i o n of rad ia t ion wi th c e l l c o n s t i t u e n t s f r o m the i n d i r e c t a c t i o n of s p e c i e s f r o m the r a d i o l y s i s of w a t e r .

(9) N e w c o m p o u n d s J u s t a s the s tudy of na tura l p r o d u c t s by the o r g a n i c c h e m i s t s h a s

l ed to the d i s c o v e r y and e v e n t u a l app l i ca t ion of m a n y n e w and n o v e l c o m -pounds , s o rad ia t ion could be a m e a n s of d i s c o v e r i n g new and potent ia l ly v a l u a b l e o r g a n i c c h e m i c a l s and b i o c h e m i c a l s .

(10) F i n e c h e m i c a l s T h e r e a p p e a r to be no e x i s t i n g a p p l i c a t i o n s of r a d i a t i o n c h e m i c a l

p r o c e s s e s in the m a n u f a c t u r e of f ine c h e m i c a l s f r o m a q u e o u s s o l u t i o n s .


It i s a t t r a c t i v e to c o n s i d e r the p o s s i b i l i t y of be ing able to a c h i e v e a c o m -p l i c a t e d o r g a n i c c h e m i c a l s y n t h e s i s in a s i n g l e s t ep . Al though s o m e r a d i a t i o n r e a c t i o n s a r e s u r p r i s i n g l y s e l e c t i v e , u s u a l l y a r a n g e of p r o d u c t s i s produced and the m a i n p r o b l e m b e c o m e s one of s e p a r a t i o n . Highly s e l e c t i v e s e p a r a t i o n p r o c e s s e s a r e now a v a i l a b l e .

(11) H e a v y c h e m i c a l s S i m i l a r r e m a r k s apply to the m a n u f a c t u r e of heavy c h e m i c a l s . T h i s

h a s b e e n c o n s i d e r e d f r o m t i m e to t i m e and h a s not proved e c o n o m i c a l l y o r t e c h n i c a l l y a t t r a c t i v e in m o s t c a s e s . T h e s e a p p r a i s a l s have o f t e n had to be b a s e d on s c a n t i n f o r m a t i o n , and t h e r e h a s been no i n d i c a t i o n that t h e r e i s good r e a s o n to undertake the e x t e n s i v e s tudy r e q u i r e d to e n a b l e a thorough a s s e s s m e n t to be m a d e . A r a d i a t i o n c h e m i c a l p r o c e s s m u s t be b e t t e r e c o n o m i c a l l y and t e c h n i c a l l y than any a l t e r n a t i v e b e f o r e it w i l l be u s e d .

(12) P o l y m e r s T h e r e h a s b e e n a c o n s i d e r a b l e amount of w o r k on the p o l y m e r i z a t i o n

of m o n o m e r s in a q u e o u s so lut ion . In app l i ca t ion , o ther s o l v e n t s a r e g e n e r a l l y p r e f e r r e d but in s o m e s p e c i f i c c a s e s a q u e o u s s o l u t i o n s Could be p r e f e r a b l e .

P r o b l e m s

The m o s t e x t e n s i v e l y and i n t e n s i v e l y i n v e s t i g a t e d s y s t e m in rad ia t ion c h e m i s t r y i s probably the f e r r o u s s u l p h a t e - s u l p h u r i c ac id so lu t ion u s e d in the F r i c k e d o s i m e t e r . Yet t h e r e s t i l l r e m a i n s work to be done on t h i s s y s t e m . In v e r y few s y s t e m s have a l l the important p r o d u c t s b e e n iden-t i f i e d .

Other a r e a s

A s e t of e x a m p l e s s i m i l a r to the above can be drawn up for e a c h a r e a of rad ia t ion c h e m i s t r y - g a s e s , o r g a n i c c o m p o u n d s and m i x t u r e s , s o l i d s , po lar s o l v e n t s , e t c .

Impact on c h e m i c a l s c i e n c e

T h e m o r e r e c e n t f i n d i n g s r e s u l t i n g f r o m radia t ion c h e m i s t r y r e s e a r c h have e l u c i d a t e d c h e m i c a l r e a c t i o n m e c h a n i s m s in g e n e r a l , but p a r t i c u l a r l y t h o s e i n v o l v i n g f r e e r a d i c a l s or f r e e r a d i c a l i n t e r m e d i a t e s , i o n - m o l e c u l e r e a c t i o n s o r e x c i t e d e l e c t r o n i c s t a t e s of m o l e c u l e s . Radiat ion can s o m e -t i m e s be a c o n t r o l l a b l e s o u r c e of s u c h s p e c i e s and can h e l p u s i n t e r p r e t c h e m i c a l e v e n t s in o t h e r f i e l d s .

C o n c l u s i o n

It i s hoped that t h e s e r e m a r k s w i l l i l l u s t r a t e that rad ia t ion c h e m i s t r y h a s a p u r p o s e and a funct ion o ther than that of d i s c o v e r i n g and d e v e l o p i n g new rad ia t ion c h e m i c a l p r o c e s s e s f o r i n d u s t r i a l u s e .

1 7 8 C O M M U N I C A T I O N S A N D COMMEN TS

SUMMARY OF REMARKS ON THE STATUS OF RADIATION PROCESSES

J . S i l v e r m a n

Since t h e i r e a r l i e s t d a y s , radiat ion p r o c e s s a p p l i c a t i o n s have been plagued by e x t r a v a g a n t c l a i m s that do not s u r v i v e c l o s e s c r u t i n y . The c r e d i b i l i t y g a p that f a c e s the app l i ed rad ia t ion c h e m i s t and e n g i n e e r i s far too g r e a t . T h i s p e r s i s t e n t p r o b l e m i s p a r t i c u l a r l y unfortunate at t h i s t i m e when the s u b j e c t can boas t of genuine a c c o m p l i s h m e n t and r e a l p r o m i s e .

T h e r e h a s not b e e n enough t i m e during t h i s P a n e l m e e t i n g to m a k e an e v a l u a t i o n of the m a n y p r o c e s s a p p l i c a t i o n s that have b e e n the subjec t of w i d e s p r e a d publ ic i ty in the pas t f ew y e a r s . In the v i e w of a l m o s t a l l P a n e l m e m b e r s , t h i s i s unfortunate . S e v e r a l a p p l i c a t i o n s w e r e d i s c u s s e d dur ing the P a n e l ' s d e l i b e r a t i o n . The a b s e n c e of s o m e d e f i n i t e s t a t e m e n t s a s to c u r r e n t s ta tus m a y l ead the r e a d e r to draw the i n f e r e n c e that n e a r l y a l l of t h e m have g r e a t m e r i t .

I have t h e r e f o r e p r e s e n t e d to the P a n e l m y p e r s o n a l j u d g e m e n t s r e -g a r d i n g s o m e a p p l i c a t i o n s . Although t h e r e w e r e many e x p r e s s i o n s of a g r e e m e n t , I r e p e a t that the v i e w s m a y not r e p r e s e n t t h o s e of the e n t i r e P a n e l s i m p l y b e c a u s e t h e r e w a s i n s u f f i c i e n t t i m e to d i s c u s s t h e m .

1. C r o s s - l i n k i n g of p o l y o l e f i n s

T h i s p r o c e s s i s a d e m o n s t r a b l e s u c c e s s . Heat shr inkab le packag ing f i l m , heat shr inkab le e l e c t r i c a l f i t t ings , f o a m e d insu la t ing tape, and f o a m e d padding f o r bathing s u i t s and l i n g e r i e a r e s o m e of the i n c r e a s i n g n u m b e r of produc t s m a d e by th i s radiat ion p r o c e s s .

2. Curing of paints and f i n i s h e s

T h i s i s one of the m o s t p r o m i s i n g of a l l p r o c e s s i n g a p p l i c a t i o n s . S e v e r a l m a j o r paint c o m p a n i e s have produced paint f o r m u l a t i o n s that c u r e to an e x c e l l e n t f i n i s h with s m a l l d o s e s of rad ia t ion . The d e v e l o p m e n t of r e l i a b l e l o w - v o l t a g e m a c h i n e s ' i s at hand and wide i n d u s t r i a l exp lo i ta t ion i s a l m o s t a c e r t a i n t y .

3. E t h y l e n e p o l y m e r i z a t i o n

T h e s u c c e s s of p i l o t - s c a l e e x p e r i m e n t s ( p a r t i c u l a r l y t h o s e at the J A E R I l a b o r a t o r y in T a k a s a k i , and at Brookhaven) has led to s i g n i f i c a n t i n d u s t r i a l i n v e s t m e n t in pr iva te f a c i l i t i e s f o r f u r t h e r s tudy. On the o ther hand, the publ i shed data on c o s t and product qual i ty s u g g e s t that the product w i l l be so ld to s p e c i a l i t y m a r k e t s and in m u c h s m a l l e r quant i t i e s than the p o l y e t h y l e n e now a v a i l a b l e .

4. W o o d - p l a s t i c c o m b i n a t i o n s

Al though the p r o s p e c t s of producing w i d e l y app l i cab le s u p e r - w o o d p r o d u c t s at c o m p e t i t i v e p r i c e s are not e n c o u r a g i n g , there i s s o m e hope that an i r r a d i a t e d w o o d - p l a s t i c product m a y be obta inable w h o s e s o l e advantage i s r e d u c e d w a t e r uptake and t h e r e f o r e b e t t e r d i m e n s i o n a l s t a -b i l i t y . A l s o t h e r e a r e s t r o n g i n d i c a t i o n s that a f ew pr ivate c o m p a n i e s w i l l s o o n o f f e r f o r s a l e s p e c i a l i t y i t e m s in s m a l l quant i t i e s .


5. Graf t p o l y m e r i z a t i o n s

B y t h i s t echn ique , an i n e x p e n s i v e b a s e p o l y m e r can be m o d i f i e d to have p r e m i u m q u a l i t i e s by a r a d i a t i o n - c u m - m o n o m e r t r e a t m e n t that i s i n h e r e n t l y c h e a p and s i m p l e . Industry h a s long been a w a r e of the m e t h o d and i t s m a n y a t t r a c t i v e a c c o m p l i s h m e n t s in the l a b o r a t o r y s u c h a s d y e a b l e p o l y p r o p y l e n e , e t c . H o w e v e r only two p r o d u c t s , a s t y r e n e g r a f t to T e f l o n , and a b a t t e r y - s e p a r a t o r m a t e r i a l b a s e d on p o l y o l e f i n s , have b e e n o f f e r e d f o r s a l e , b o t h b y R A I R e s e a r c h . The f i r s t i t e m h a s been wi thdrawn but the s e c o n d has b e e n s u c c e s s f u l and i s so ld in s m a l l but i n c r e a s i n g v o l u m e . R e c e n t l y D e e r i n g - M i l l i k e n announced that a t e x t i l e product m o d i f i e d by r a d i a t i o n g r a f t i n g would be o f f e r e d f o r sa l e ; i n d u s t r i a l i n t e r e s t in the s u c c e s s o r f a i l u r e of t h i s v e n t u r e i s v e r y high.

6. Sulphoxidat ion of a l k a n e s

A plant us ing th i s method of producing b iodegradab le d e t e r g e n t s w a s to have been e r e c t e d by E s s o . The pro jec t i s dormant and w i l l cont inue to be a s long a s n o n - r a d i a t i o n p r o d u c t s d o m i n a t e the m a r k e t .

7. N i t r o g e n f ixa t ion

S t e i n b e r g i s h i s m o s t e f f e c t i v e c o m p e t i t o r . His d u a l - p u r p o s e c h e m o -n u c l e a r p r o c e s s f o r n i t r o g e n f i x a t i o n i s m u c h m o r e e x p e n s i v e than the one in which he p r o p o s e s to u s e e l e c t r o l y s i s at the s i t e of a power r e a c t o r . F u r t h e r m o r e , e v e n if the c h e m o n u c l e a r p r o c e s s a c h i e v e s the m a x i m u m t h e o r e t i c a l G - v a l u e and the f o r m i d a b l e e n g i n e e r i n g o b s t a c l e s a r e o v e r -c o m e , it m a y f a c e c o m p a r a b l e a d v a n c e s in the t e c h n o l o g y of e l e c t r o l y s i s . Thus , whi l e c h e m o n u c l e a r p r o c e s s e s m a y produce public b e n e f i t s that j u s t i f y the c u r r e n t l e v e l of r e s e a r c h and d e v e l o p m e n t , the out look i s not v e r y c l e a r .

W O O D - P O L Y M E R COMBINATIONS

K. S inger

At p r e s e n t , two c o m m e r c i a l c o m p a n i e s in the United S ta tes of A m e r i c a and one c o m p a n y in F r a n c e o f f e r i r r a d i a t e d w o o d - p l a s t i c p r o d u c t s , but a s f a r a s I know they u s e only one type of p o l y m e r , n a m e l y p o l y m e t h y l m e t h a c r y l a t e , and a few t y p e s of wood. It i s s t i l l u n c e r t a i n how l a r g e the m a r k e t f o r t h e s e produc t s m a y b e c o m e , and whether the m o s t e c o n o m i c a l and p r a c t i c a l method of product ion w i l l be one applying i r r a d i a t i o n or one wi th c o n v e n t i o n a l c a t a l y s t s .

It s e e m s to m e that a n u m b e r of p r o b l e m s in the f a b r i c a t i o n p r o c e s s s t i l l r e q u i r e a good d e a l of r e s e a r c h e f for t , not only in i m p r e g n a t i o n t e c h n o l o g y (to obtain h o m o g e n e o u s products ) , but a l s o in u s e f u l p o l y m e r s and rad ia t ion t echno logy , for i n s t a n c e c o n c e r n i n g the type of rad ia t ion s o u r c e s .

I should l ike to c o n s i d e r t h e s e t h r e e f i e l d s in the l ight of the f o l l o w i n g ques t ion: wh ich p r o p e r t i e s of wood a r e m o s t important to i m p r o v e ?


I think the f o l l o w i n g o r d e r of p r i o r i t y could be g iven: (1) D i m e n s i o n a l s tab i l i ty ; (2) S u r f a c e p r o p e r t i e s such a s h a r d n e s s and a b r a s i o n r e s i s t a n c e ; (3) F i r e r e s i s t a n c e , rod r e s i s t a n c e and m e c h a n i c a l s t rength .

C o n c e r n i n g d i m e n s i o n a l s tab i l i za t ion , it r e m a i n s to be c l e a r l y d e m o n -s t r a t e d w h e t h e r g r a f t i n g of the p o l y m e r on to the wood s u b s t a n c e s i s of any i m p o r t a n c e o r not . A l s o the n u m b e r and c h a i n - l e n g t h of the g r a f t e d p o l y m e r m o l e c u l e s m a y have an i n f l u e n c e on th i s p r o p e r t y . F u r t h e r m o r e , the l o c a t i o n of the p o l y m e r in the wood, i . e . in the c e l l w a l l or in the c e l l c a v i t y , i s probab ly of i m p o r t a n c e , and t h i s l o c a t i o n d e p e n d s m o s t l y on the c h e m i c a l p r o p e r t i e s of the i m p r e g n a t e d m o n o m e r , but a l s o to s o m e extent on the i m p r e g n a t i o n t echnique appl i ed .

In any c a s e , it i s of the u t m o s t i m p o r t a n c e to obtain a h o m o g e n e o u s i m p r e g n a t i o n throughout the wood, and b a s e d on our e x p e r i e n c e , which i s supported by r e c e n t p r a c t i c a l i n v e s t i g a t i o n s in the United S t a t e s of A m e r i c a , t h e r e s t i l l r e m a i n p r o b l e m s on how to obta in l a r g e r e p r o d u c e a b l e and h o m o g e n e o u s w o o d - p o l y m e r s a m p l e s .

To i m p r o v e s u r f a c e p r o p e r t i e s , it i s n e c e s s a r y to d e v e l o p a good s u r f a c e i m p r e g n a t i o n t echn ique . We s h a l l h e r e have to d e a l with the s u r f a c e e f f e c t , which n o r m a l l y i s c o n s i d e r e d to be c a u s e d by m o n o m e r e v a p o r a t i o n during the f a b r i c a t i o n . Whether th i s exp lanat ion i s s u f f i c i e n t s t i l l n e e d s to be proved .

F i n a l l y , t h e r e i s m u c h work to do in us ing d i f f e r e n t a d d i t i v e s to the m o n o m e r s y s t e m s to obtain f i r e r e s i s t a n c e , rod r e s i s t a n c e or dyed produc t s . T h e p o s s i b l e inhibi t ing e f f e c t on the rad ia t ion p o l y m e r i z a t i o n which t h e s e a d d i t i v e s m a y c a u s e can be ra ther s u r p r i s i n g .

I should l ike to add a few w o r d s c o n c e r n i n g rad ia t ion t e c h n o l o g y . T o d a y 6 0 C o g a m m a s o u r c e s a r e n o r m a l l y c o n s i d e r e d to be m o s t su i table f o r t h i s p r o c e s s , but a s s o m e p o t e n t i a l app l i ca t ions would invo lve product s of l i m i t e d t h i c k n e s s , for i n s t a n c e v e n e e r s , knife hand le s and e v e n f l o o r i n g , h i g h - e n e r g y e l e c t r o n a c c e l e r a t o r s might be c o n s i d e r e d a s a potent ia l rad ia t ion s o u r c e f o r w o o d - p l a s t i c product ion . T h e r e i s not m u c h publ i shed w o r k c o n c e r n i n g the appl i ca t ion of h i g h - e n e r g y e l e c t r o n s , and h e r e i s c e r t a i n l y a subjec t that should be s e r i o u s l y i n v e s t i g a t e d . We publ i shed s o m e r e s u l t s at the Radiat ion C h e m i s t r y C o n f e r e n c e held in Tihany in 1966, ind ica t ing that by su i tab le c o m b i n a t i o n s of wood, m o n o m e r , t e m -p e r a t u r e and w a t e r content of the wood it would be p o s s i b l e to obta in c o m -p le te c o n v e r s i o n of m o n o m e r to p o l y m e r with radiat ion d o s e s be low 10 Mrad. One of the m o s t i m p o r t a n t p r o b l e m s in the e v e n t u a l app l i ca t ions of h i g h - e n e r g y e l e c t r o n s i s , of c o u r s e , the heat g e n e r a t i o n c a u s e d by the r e a c t i o n , and how th i s w i l l i n f l u e n c e the s i z e of wood i t e m s and the r a -d iat ion t e c h n i q u e . But a l s o in c o n n e c t i o n with 6 0 Co s o u r c e s t h e r e r e m a i n s o m e p r o b l e m s r e g a r d i n g the b e s t p r i n c i p l e s of plant c o n s t r u c t i o n , and what the d o s e r e q u i r e m e n t s would be when the p r o c e s s i s s c a l e d up. B a s e d on our e x p e r i e n c e with the R i s ^ 10 kCi 6 0 Co f a c i l i t y we should c o n s i d e r , f o r i n s t a n c e , the n e c e s s a r y d o s e for m e t h y l - m e t h a c r y l a t e c o n -v e r s i o n to be 3 Mrad, w h e r e a s m o s t r e c e n t l y publ i shed e c o n o m i c e v a l u a -t i o n s a r e b a s e d on a d o s e r e q u i r e m e n t of 1. 5 - 2 Mrad. I b e l i e v e that the n e c e s s a r y d o s e w i l l be the r e s u l t of an e c o n o m i c o p t i m i z a t i o n .

T h e s e f e w r e m a r k s a r e intended to draw the P a n e l ' s a t tent ion to s o m e of the p r o b l e m s w h i c h m u s t be f u r t h e r i n v e s t i g a t e d b e f o r e w o o d - p l a s t i c p r o d u c t s , in s p i t e of c o m m e r c i a l i z a t i o n having a l r e a d y begun, can r e a l l y b e e v a l u a t e d a s a new group of m a t e r i a l s .

L I S T O F P A R T I C I P A N T S

D. SANGSTER (Cha irman)

H. B I L D S T E I N

E . L . D A L T O N

A. DANNO

N. G E T O F F

W. HOLM

D. H U M M E L

S. IONESCU

S. MINC

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A t o m e n e r g i e , R e a k t o r z e n t r u m S e i b e r s d o r f , 2444 S e i b e r s d o r f , A u s t r i a

Radia t ion B r a n c h , I s o t o p e R e s e a r c h D i v i s i o n , Wantage R e s e a r c h L a b o r a t o r y , Wantage , B e r k s , United Kingdom

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R i s ^ R e s e a r c h E s t a b l i s h m e n t , R o s k i l d e , D e n m a r k

Inst i tut f u r P h y s i k a l i s c h e C h e m i e und K o l l o i d c h e m i e ,

U n i v e r s i t y of Cologne , S e v e r i n s w a l l 34, Co logne , F e d e r a l Republ ic of G e r m a n y

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Instytut Badan Jadrowych , U l i c a D o r o d n a 16, W a r s a w , P o l a n d

1 8 1

1 8 2 LIST OF PARTICIPANTS

E. PROKSCH

J. R. PUIG

T h e C h e m i c a l Inst i tute , O s t e r r e i c h i s c h e S t u d i e n g e s e l l s c h a f t fur

A t o m e n e r g i e , R e a k t o r z e n t r u m S e i b e r s d o r f , 2444 S e i b e r s d o r f , A u s t r i a

Centre d1 E tudes N u c l e a i r e s de Saclay, B . P . No. 2, 91 G i f - s u r - Y v e t t e (Seine et Oise ) , F r a n c e

J. S ILVERMAN U n i v e r s i t y of Mary land , S i l v e r Spring, M d . , United S ta te s of A m e r i c a

K. SINGER C h e m i s t r y D e p a r t m e n t , R i s ^ R e s e a r c h E s t a b l i s h m e n t , R o s k i l d e , D e n m a r k

M. S T E I N B E R G

Z . P . Z A G 6 R S K I

B r o o k h a v e n Nat iona l L a b o r a t o r y , Upton, Long Is land, N. Y. 11973, United States of A m e r i c a

Instytut Badan J a d r o w y c h , U l i c a Dorodna 16, W a r s a w , P o l a n d

S c i e n t i f i c S e c r e t a r i e s

K. BESWICK R. HARA

D i v i s i o n of R e s e a r c h and L a b o r a t o r i e s , IAEA, Karntner Ring 11, 1010 Vienna, A u s t r i a

E d i t o r

S. M. F R E E M A N ' D i v i s i o n of Sc i en t i f i c and T e c h n i c a l In format ion , IAEA, K a r n t n e r Ring 11,

1010 V i e n n a , A u s t r i a

Orde r s for Agency p u b l i c a t i o n s can be p l a c e d with your b o o k s e l l e r or any of our s a l e s

a g e n t s l i s t e d b e l o w :

A R G E N T I N A Comis ion N a c i o n a l de E n e r g i a Atomica Aven ida de l L i b e r t a d o r G e n e r a l San Martin 8250 B u e n o s Ai re s •» Sue . 29

A U S T R A L I A Hunte r P u b l i c a t i o n s , 23 McKil lop S t r ee t Melbourne , C . l

A U S T R I A Georg Fromme & Co. S p e n g e r g a s s e 39 A-1050 , V ienna V

B E L G I U M O f f i c e i n t e r n a t i o n a l de l ib ra i r ie 30, avenue Marnix B r u s s e l s 5

B R A Z I L L i v r a r i a Kosmos Ed i to r a Rua do R o s a r i o , 135-137 Rio de J a n e i r o

A g e n c i a E x p o e n t e O s c a r M. Si lva Rua Xav ie r de T o l e d o , 1 4 0 - 1 ° Andar (Ca ixa P o s t a l No. 5 .614) Sao P a u l o

BYELORUSSIAN S O V I E T S O C I A L I S T R E P U B L I C

See under USSR

CANADA The Q u e e n ' s P r i n t e r O t t a w a , Ontar io

C H I N A (Ta iwan) Books and S c i e n t i f i c S u p p l i e s S e r v i c e , L t d . , P . O . Box 83 T a i p e i

CZECHOSLOVAK SOCIALIST R E P U B L I C S . N . T . L . S p o l e n a 51 Nove Mes to P r a g u e 1

D E N M A R K E j n a r Munksgaard L td . 6 Nor regade Copenhagen K

F I N L A N D A k a t e e m i n e n K i r j a k a u p p a K e s k u s k a t u 2 H e l s i n k i

F R A N C E

Of f i ce i n t e r n a t i o n a l de d o c u m e n t a t i o n e t l ib ra i r ie 48, rue G a y - L u s s a c F - 7 5 , P a r i s 5 e

G E R M A N Y , F e d e r a l R e p u b l i c of R. Oldenbourg R o s e n h e i m e r S t r a s s e 145 8 Munich' 8

H U N G A R Y Kul tu ra Hungar i an T r a d i n g Co. for Books and N e w s p a p e r s P . O . B . 149 B u d a p e s t 62

I S R A E L H e i l i g e r and Co, 3 Na than S t r a u s s S t r ee t J e r u s a l e m

I T A L Y A g e n z i a E d i t o r i a l e I n t e r n a z i o n a l e O r g a n i z z a z i o n i U n i v e r s a l i ( A . E . I . O . U . ) Via Meravig l i 16 Milan

J A P A N

Maruzen Company L t d . 6 , Tor i Nichome N i h o n b a s h i ( P . O . Box 605) T o k y o C e n t r a l

M E X I C O L ib re r i a In te rnac iona l Av. Sonora 206 Mexico 11, D . F .

N E T H E R L A N D S N.V. Martin us Ni jhof f L a n g e Voorhout 9 The Hague

N E W Z E A L A N D Whitcombe & T o m b s , L td . G . P . O . Box 1894 Wel l ing ton , C . l

N O R W A Y J o h a n Grundt Tanum Karl J o h a n s ga te 43 O s l o

P A K I S T A N K a r a c h i E d u c a t i o n Soc ie ty Haroon C h a m b e r s South N a p i e r Road ( P . O . Box No. 4866) K a r a c h i 2

P O L A N D O s r o d e k R o z p o w s z e c h n i a n a Wydawnic tw Naukowych P o l s k a Akademia Nauk P a l a c Kultury i Nauk i Warsaw

R O M A N I A Car t imex Rue A. Br iand 14-18 B u c a r e s t

SOUTH A F R I C A Van S c h a i k ' s Books to re (P ty ) L t d . L ib r i Bu i ld ing Church S t r ee t ( P . O . Box 724) P r e t o r i a

S P A I N L i b r e n a B o s c h Ronda de la Un ive r s idad 11 B a r c e l o n a

S W E D E N C . E . F r i t z e s Kungl . H o v b o k h a n d e l F r e d s g a t a n 2 S tockholm 16

S W I T Z E R L A N D Libra i r i e P a y o t Rue Grenus 6 1211 Geneva 11

T U R K E Y Libra i r i e H a c h e t t e 469, I s t i k l a l C a d d e s i B e y o g l u , I s t a n b u l

UKRAINIAN S O V I E T SOCIALIST R E P U B L I C

See unde r USSR

UNION O F S O V I E T SOCIALIST R E P U B L I C S

Mezhdunarodnaya Kniga S m o l e n s k a y a - S e n n a y a 32*34 Moscow G-200

UNITED KINGDOM O F G R E A T BRITAIN AND N O R T H E R N I R E L A N D

Her M a j e s t y ' s S ta t ionery O f f i c e P . O . Box 569 L o n d o n , S . E . I

UNITED S T A T E S O F AMERICA N a t i o n a l Agency for I n t e r n a t i o n a l P u b l i c a t i o n s , I n c . 317 E a s t 34th S t ree t New York , N . Y . 10016

V E N E Z U E L A Sr. Brau l io Gabr ie l C h a c a r e s Gobernador a Cand i l i t o 37 Santa R o s a l i a (Apar tado P o s t a l 8092) C a r a c a s D , F ,

Y U G O S L A V I A J u g o s l o v e n s k a Knj iga T e r a z i j e 27 Be lg rade

IAEA p u b l i c a t i o n s can a l s o be p u r c h a s e d r e t a i l a t the Uni ted N a t i o n s B o o k s h o p a t Un i t ed N a t i o n s H e a d q u a r t e r s , New York, a t the n e w s - s t a n d a t the A g e n c y ' s Head -q u a r t e r s , V i e n n a , and at most c o n f e r e n c e s , s y m p o s i a and s e m i n a r s o r g a n i z e d by the A g e n c y .

In order to f a c i l i t a t e the d i s t r i b u t i o n of i t s p u b l i c a t i o n s , the Agency i s p r e p a r e d to a c c e p t p a y m e n t in UNESCO coupons or in l o c a l c u r r e n c i e s .

Orde r s and i n q u i r i e s from c o u n t r i e s where s a l e s a g e n t s h a v e not y e t been appo in ted may be s e n t to :

D i s t r ibu t ion and S a l e s Group, I n t e r n a t i o n a l Atomic Energy A g e n c y , Ka rn tne r Ring 11, A-1010, Vienna I , Aus t r i a

I N T E R N A T I O N A L A T O M I C E N E R G Y A G E N C Y V I E N N A , 1 9 6 8

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Radiation Chemistry and its Applications · RADIATION CHEMISTRY AND ITS APPLICATIONS (Technical Reports Series, No. 84) ABSTRACT. The report of a panel convened by the IAEA and held