(TID-4500, AEC Research and Development Report ARGONNE

ANE-6799 I n s t r u m e n t s ( T I D - 4 5 0 0 , 30th Ed. ) AEC R e s e a r c h and D e v e l o p m e n t R e p o r t

ARGONNE NATIONAL LABORATORY 9700 South C a s s Avenue A r g o n n e , I l l i no i s 60440

A SHIELDED E N C L O S U R E FOR N E U T R O N RADIOGRAPHIC INSPECTION O F E N C A P S U L A T E D , IRRADIATED S P E C I M E N S

by

W. N. B e c k and H. B e r g e r

Meta l lurgy P r o g r a m s 6.1 ,32 and 12,1.3

P a r t of the m a t e r i a l in th i s r e p o r t h a s a p p e a r e d iji the fol lowing M e t a l l u r g y D i v i s i o n P r o g r e s s R e p o r t :

R e p o r t No. P a g e s Date

A N L - 6 6 7 7 133-134 196Z

M a r c h 1964

O p e r a t e d by The U n i v e r s i t y of Ch icago u n d e r

C o n t r a c t W - 3 1 - 1 0 9 - e n g - 3 8 wi th the

U. S. A t o m i c E n e r g y C o m m i s s i o n

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

1

T A B L E O F C O N T E N T S

P a g e

ABSTRACT 3

INTRODUCTION 3

THE S H I E L D E D ENCLOSURE 4

T R A N S F E R CASK 6

N E U T R O N RADIOGRAPHY TECHNIQUE 7

A C K N O W L E D G E M E N T S 9

R E F E R E N C E S 10

LIST O F F IGURES

T i t l e P

D i a g r a m of Sh ie lded E n c l o s u r e and C a p s u l e T r a n s f e r C a s k . . .

N e u t r o n Shie ld E n c l o s u r e and T r a n s f e r C a s k Adjacen t to

the R e a c t o r , , , , ,

C o m p a r i s o n of G a m m a A u t o r a d i o g r a p h y and N e u t r o n R a d i o g r a p h y of Highly I r r a d i a t e d R e f r a c t o r y A l l o y - c l a d U - P u - F s Al loy F u e l S p e c i m e n s in Unopened I r r a d i a t i o n Capsule

A S H I E L D E D E N C L O S U R E FOR N E U T R O N RADIOGRAPHIC I N S P E C T I O N O F E N C A P S U L A T E D , IRRADIATED S P E C I M E N S

by

W N. B e c k and H. B e r g e r

A B S T R A C T

A n e u t r o n sh i e l d e n c l o s u r e for n e u t r o n r a d i o g r a p h i c i n s p e c t i o n of e n c a p s u l a t e d , i r r a d i a t e d fuel s p e c i m e n s h a s b e e n f a b r i c a t e d . An ex i s t i ng s h i e l d e d c a s k w a s modi f ied to h a n d l e a c o m p l e t e i r r a d i a t i o n e x p e r i m e n t f r o m the C P - 5 r e ­a c t o r . The i n s p e c t i o n t e c h n i q u e m a k e s u s e of a po t en t i a l l y r a d i o a c t i v e s c r e e n to d e t e c t the n e u t r o n i m a g i n g b e a m af ter it h a s p a s s e d t h r o u g h the i n s p e c t i o n object . The r a d i o a c t i v e i m a g e on the s c r e e n i s m a d e v i s i b l e by a l lowing i t to d e c a y in c l o s e c o n t a c t wi th p h o t o g r a p h i c f i lm. C o n t r a s t r e s o l u t i o n of the s y s t e m is 0.76 m m (0.030 in.) o r b e t t e r . C o n t r a s t s e n s i t i v i t y is in the o r d e r of 1 to 2 p e r c e n t .

INTRODUCTION

In the e v a l u a t i o n of a fuel m a t e r i a l for p o w e r r e a c t o r s , it i s e s s e n ­t i a l to sub j ec t p r o t o t y p e fuel s p e c i m e n s to v a r i o u s cond i t ions of high t e m ­p e r a t u r e and high b u r n u p . Such e x p e r i m e n t s can be p e r f o r m e d with su i t ab l e i n s t r u m e n t e d c a p s u l e s in wh ich fuel s p e c i m e n s a r e i n t r o d u c e d into an i r r a d i a t i o n fac i l i ty . (1) In l i eu of a d e s t r u c t i v e e x a m i n a t i o n of the c a p s u l e , p e r i o d i c n o n d e s t r u c t i v e r a d i o g r a p h i c i n s p e c t i o n s of the c o n t e n t s a r e e s ­s e n t i a l in d e t e r m i n i n g if the i r r a d i a t i o n p e r i o d should be t e r m i n a t e d or if the condi t ion of the s p e c i m e n s w a r r a n t s a con t inua t ion of the i r r a d i a t i o n .

A p inho le a u t o r a d i o g r a p h i c t e chn ique h a s been u s e d s u c c e s s f u l l y in i m a g i n g the ou t l ine of h igh ly r a d i o a c t i v e ob j ec t s wi th in c a p s u l e s , l^) An i m p r o v e m e n t of t h i s t e c h n i q u e i s found in the app l i ca t i on of n e u t r o n r a d i ­o g r a p h y , which m a k e s i t p o s s i b l e to ident i fy c o m p o n e n t s wi th in the i r r a ­d ia t ed c a p s u l e s o t h e r than the ind iv idua l s e c t i o n s of fuel m a t e r i a l , wj

To be ab le to e x t r a c t a c o m p l e t e t e s t c a p s u l e f r o m the r e a c t o r , to n e u t r o n - r a d i o g r a p h the c o n t e n t s , and then to r e t u r n i t to the i r r a d i a t i o n fac i l i ty , i t w a s n e c e s s a r y to p r e p a r e s p e c i a l handl ing d e v i c e s and s h i e l d e d e n c l o s u r e s . A p o r t a b l e s h i e l d e d e n c l o s u r e wi th a c a s s e t t e d i s c h a r g e and r e c h a r g e m a g a z i n e •was t h e r e f o r e d e s i g n e d and f a b r i c a t e d . Th i s e n c l o s u r e

w a s d e s i g n e d for u s e wi th an ex i s t i ng n e u t r o n r a d i o g r a p h i c fac i l i ty , h o r i ­zonta l n e u t r o n b e a m ho le , 6H1, of the J u g g e r n a u t r eac to r , ! ' ^ ) An ex i s t i ng f u e l - t r a n s f e r c a s k •which h a d b e e n mod i f i ed for p inho le a u t o r a d i o g r a p h y w a s f u r t h e r mod i f i ed to h a n d l e a c o m p l e t e 3 . 3 5 - m ( l l - f t ) C P - 5 i r r a d i a t i o n e x p e r i m e n t .

THE SHIELDED E N C L O S U R E

The b e a m ho le opening a t the s ide of the J u g g e r n a u t r e a c t o r i s l o c a t e d 67 .3 c m (26,5 in.) above f loor l eve l . The c o l l i m a t e d b e a m a p e r t u r e i s 64 m m x 102 m m (2.5 x 4 in.) and h a s a n e u t r o n b e a m i n t e n s i t y of the o r d e r of 1 O'' n e u t r o n s / c m - s e c at a t h e r m a l to e p i t h e r m a l flux r a t i o of a p p r o x i m a t e l y 3,6 to 1.

In the d e s i g n of the e n c l o s u r e , t h r e e c o n c e p t u a l r e q u i r e m e n t s had to be naet: ( l ) a d e q u a t e g a m m a sh i e ld ing should be p r o v i d e d to al low o p ­e r a t i n g p e r s o n n e l to •work in c l o s e p r o x i m i t y to the e x p e r i m e n t , * (2) the n e u t r o n b e a m i n t e n s i t y and s c a t t e r should be r e d u c e d to a l eve l which would not p r e s e n t a h a z a r d to p e r sonnel , and (3) p r o v i s i o n s should be m a d e •whereby the c a s s e t t e con ta in ing the d e t e c t o r s could be p o s i t i o n e d d i r e c t l y beh ind and in l ine wi th the n e u t r o n b e a m , and be r e m o v a b l e and r e p l a c e ­ab le wi thou t d i s t u r b i n g the i r r a d i a t i o n c a p s u l e .

The e n c l o s u r e in wh ich the r a d i o g r a p h i s t a k e n i s a l e a d - f i l l e d s t e e l c a s i n g , A m i n i m u m t h i c k n e s s of 25 .4 c m (lO in.) of l e ad i s u s e d in the i m m e d i a t e v i c i n i t y of the r a d i o a c t i v e m a t e r i a l , but i s t a p e r e d to 6 in. a t the e x t r e m i t y •which f r o n t s the r e a c t o r face . A c r o s s s e c t i o n of the i n s t a l l a t i o n i s shown d i a g r a m m a t i c a l l y in F i g u r e 1, Shie ld ing i s p r o v i d e d on t h r e e s i d e s and top , but not on the b o t t o m , which r e s t s on the f loor , o r on the f ront wh ich bu t t s a g a i n s t t h e r e a c t o r . The top of the sh ie ld i s p r o ­v ided with a 1 0 , 2 - c m (4- in , ) ho le which a l igns wi th the hole of the t r a n s f e r ca sk . Spec i a l c o n e - s h a p e d s l e e v e s fit the ho le , wh ich s e r v e to guide and p o s i t i o n the c a p s u l e s w i th in the s h i e l d e d e n c l o s u r e . P r o p e r a l i g n m e n t of the t r a n s f e r c a s k o v e r t h i s ho l e i s a s s u r e d by the l a r g e , t a p e r e d r ing bo l t ed to the top of the sh i e ld ing .

P o s i t i o n e d d i r e c t l y beh ind the v e r t i c a l hole in the sh ie ld ing i s a s l id ing c a s s e t t e r a c k wh ich is s u p p o r t e d by r o l l e r s and i s gu ided in a t r a c k . The r a c k i s m a d e to hold a s t a n d a r d a l u m i n u m - f r o n t X - r a y c a s ­s e t t e for 12.7 X 1 7 . 7 - c m (5 x 7 - in . ) f i lm. The c a s s e t t e i s f r a m e caged in the m i d d l e of the r a c k . A 2 0 . 3 - c m (8- in . ) -wide s lab of l e ad on e i t he r s ide of the c a s s e t t e s e r v e s a s b i o l o g i c a l s h i e l d to p r e v e n t g a m m a ac t iv i ty f r o m s t r e a m i n g f r o m the s lo t opening in the e n c l o s u r e . The p o r t i o n of r a c k

*The g a m m a a c t i v i t y of the i r r a d i a t e d c a p s u l e s h a s been m e a s u r e d to be in e x c e s s of 5 x 10^ R / h r at 30 c m (l ft).

guides which p r o j e c t s out f r o m the e n c l o s u r e is f u r t h e r e n c a s e d in 5,1 c m (2 in,) of s t e e l . M a n i p u l a t i o n of the s l i de r a c k i s a c c o m p l i s h e d with a hand l e a t t a c h e d to the r a c k , o p e r a t e d t h r o u g h a s lo t in a 5 . 1 - c m (2- in . ) s t e e l p r o j e c t i o n c a s i n g . R e m o v a l of the c a s s e t t e f r o m the r a c k i s a ided by a p l u n g e r at the b o t t o m of the c a s i n g , wh ich p u s h e s aga in s t the bo t t om of the c a s s e t t e . In o r d e r to a s s u r e a d e q u a t e sh ie ld ing of the e n c l o s u r e a t the s ide o p p o s i t e the s l i de r a c k p r o j e c t i o n , a 1 5 . 2 - c m (6- in . ) b lock of l ead sh i e ld ing w a s added to c o m p e n s a t e for d i s p l a c e m e n t of sh ie ld ing m a d e n e c e s s a r y by the r a c k guide ex tens ion . The p l a c e m e n t of t h i s sh ie ld ing can be s e e n in F i g u r e 2.

5 0 C M SCALE

106-7502 Rev.

F i g u r e 1. D i a g r a m of Sh ie lded E n c l o s u r e and C a p s u l e T r a n s f e r C a s k

106-7338

F i g u r e 2 N e u t r o n Sh ie ld E n c l o s u r e and T r a n s f e r C a s k Ad jacen t to the R e a c t o r

N e u t r o n b a c k s c a t t e r af fect ing the de tec t ing foi ls i s m i n i m i z e d by a 0 6 - c m (0 2 5 - i n ) - t h i c k b o r o n p l a t e m o u n t e d m the r a c k , d i r e c t l y behind the c a s s e t t e

T R A N S F E R CASK

The c a s k which w a s s u i t a b l e for hand l ing a c o m p l e t e i r r a d i a t i o n a s s e m b l y w a s one -which i s a l s o u s e d for p inho le a u t o r a d i o g r a p h y The c a s k h a s a 10 1-cm (4 - in ) c e n t r a l ho le and 25 4 c m (10 m ) of l e ad sh ie ld ­ing The b o t t o m i s equ ipped wi th one g a t e , and the top i s c l o s e d with a

plug . The c a s k w a s mod i f i ed by the addi t ion of a 1 0 , 1 - c m ( 4 - i n . ) - t h i c k e x t e n s i o n tube which i s bo l ted to the top of the ca sk , A s t e e l co l l e t , 10.1 c m (4 in.) th ick , which i s at the top of t h i s ex t ens ion , c l a m p s a g a i n s t the body of the a s s e m b l y sh i e ld p lug . Th i s co l l e t i m m o b i l i z e s the a s s e m ­bly and p r e v e n t s g a m m a r a d i a t i o n f r o m s t r e a m i n g out of the top of the c a s k . The c a s k i s n o r m a l l y t r a n s p o r t e d h o r i z o n t a l l y on a dol ly bu t i s t u r n e d u p r i g h t when be ing l o a d e d and un loaded .

In o p e r a t i o n , the c a s k i s p l a c e d o v e r a v e r t i c a l t h i m b l e ho le of the C P - 5 r e a c t o r , which c o n t a i n s an e x p e r i m e n t . The c a p s u l e i s pu l l ed into the c a s k , the ga te i s c l o s e d , and the sh ie ld plug i s c l a m p e d in the co l l e t . It i s t r a n s p o r t e d to the J u g g e r n a u t r e a c t o r and p l a c e d on the sh i e lded en ­c l o s u r e . The ga te i s opened , the co l l e t l o o s e n e d , and the e x p e r i m e n t i s l o w e r e d un t i l the c a p s u l e i s d i r e c t l y in f ront of the c a s s e t t e - h o l d e r c a r ­r i a g e . The c a s s e t t e con ta in ing the foi ls i s then t r a n s f e r r e d into the e n c l o ­s u r e , d i r e c t l y beh ind the c a p s u l e ,

A p h o t o g r a p h of the t r a n s f e r c a s k i s shown in F i g u r e 2,

N E U T R O N RADIOGRAPHY TECHNIQUE

The i n s p e c t i o n m e t h o d m a k e s u s e of a p o t e n t i a l l y r a d i o a c t i v e s c r e e n to d e t e c t the n e u t r o n i m a g i n g b e a m af te r i t h a s p a s s e d t h rough the ob jec t to be i n s p e c t e d . The r a d i o a c t i v e i m a g e on the s c r e e n can be m a d e v i s i b l e by a l lowing the s c r e e n to d e c a y in c l o s e con t ac t •with p h o t o g r a p h i c f i lm. S ince the g a m m a ac t i v i t y of the s p e c i m e n wi l l not inf luence the r a d i o a c ­t iv i ty of the d e t e c t i n g s c r e e n , i t wi l l t h e r e f o r e not inf luence the final r a d i o g r a p h .

N e u t r o n r a d i o g r a p h s b a s e d on th i s a u t o r a d i o g r a p h i c t echn ique have b e e n s u c c e s s f u l l y t a k e n by the u s e of any of s e v e r a l p o t e n t i a l l y r a d i o a c t i v e s c r e e n m a t e r i a l s to d e t e c t the n e u t r o n i m a g e . M a t e r i a l s such as r h o d i u m , s i l v e r , i n d i u m , d y s p r o s i u m , and gold have been p a r t i c u l a r l y useful . The spec i f i c d e t e c t i o n t e c h n i q u e s u s e d in the in i t i a l e x p e r i m e n t s for the i n s p e c ­t ion of r a d i o a c t i v e s p e c i m e n s e m p l o y e d s i l v e r , d y s p r o s i u m , and i n d i u m s c r e e n s , a s r e p o r t e d p r e v i o u s l y , (3)

T h e s e m e t h o d s p r o v i d e both a c o a r s e , fas t r e s u l t for a l i g n m e n t p u r p o s e s when s c r e e n s of s h o r t - h a l f - l i f e s i l v e r a r e u s e d (the ha l f - l i f e of Ag^°^ i s 2.3 m i n ) and a slo^wer, f i n e - g r a i n f i lm i m a g e for the a c t u a l in ­s p e c t i o n w h e n the l o n g e r - h a l f - l i f e m a t e r i a l s a r e u s e d (the h a l f - l i v e s of In^^^ and Dy a r e 54 m i n and 2,3 h r , r e s p e c t i v e l y ) . The m a j o r change m a d e s ince t h i s p r o c e d u r e w a s r e p o r t e d h a s b e e n in the a l i g n m e n t p r o c e d u r e .

The a l i g n m e n t of the i n s p e c t i o n ob jec t , tha t i s , p l a c i n g the ob jec t in the n e u t r o n b e a m in such a p o s i t i o n a s to r e v e a l the d e s i r e d i n f o r m a t i o n , had been c h e c k e d by obta in ing a n e u t r o n i m a g e on a s i l v e r s c r e e n , t r a n s ­f e r r i n g i t to a fas t X - r a y f i lm such a s Kodak Type KK f i lm for the a u t o ­r a d i o g r a p h i c e x p o s u r e , and then deve lop ing the f i lm. Th is p r o c e d u r e took s o m e t i m e in tha t the n e u t r o n e x p o s u r e t i m e w a s about 7 min , the a u t o r a ­d i o g r a p h i c e x p o s u r e r e q u i r e d a t h r e e ha l f - l i f e d e c a y (about 7 m i n ) , and the f i lm d e v e l o p m e n t r e q u i r e d at l e a s t 5 m in . T h i s t echn ique w a s i m p r o v e d by modify ing the n e u t r o n b e a m to p r o v i d e a h i g h e r n e u t r o n i n t e n s i t y , * which p e r m i t t e d a r e d u c t i o n in the e x p o s u r e t i m e . A second , and m o r e s ign i f i can t , i m p r o v e m e n t in the t e c h n i q u e , in which a fas t P o l a r o i d f i lm w a s u s e d , r e s u l t e d in f u r t h e r d e c r e a s e s in e x p o s u r e and d e v e l o p m e n t t i m e . The c o m b i n a t i o n of t h e s e i m p r o v e m e n t s r e s u l t s in the p r o d u c t i o n of a n e u t r o n P o l a r o i d p r i n t s u i t a b l e for a l i g n m e n t p u r p o s e s in a to ta l t i m e of l e s s t han 3 min . The t e c h n i q u e e m p l o y e d a r h o d i u m s c r e e n and P o l a r o i d R a d i o g r a p h i c P a c k e t s Type 3000X. A c o m p l e t e d e s c r i p t i o n of the m e t h o d h a s been g iven e l s e w h e r e , w)

The c o m p l e t e e x p o s u r e t e c h n i q u e for a t yp i ca l c a p s u l e i s then as fo l lows :

(1) Af ter the c a p s u l e i s l o w e r e d in to the f i r s t e x p o s u r e p o s i t i o n , the a l i g n m e n t i s c h e c k e d by m a k i n g a n e u t r o n e x p o s u r e wi th a 0.025 x 12,7 X 1 7 , 7 - c m (0,010 x 5 x 7 - in , ) r h o d i u m m e t a l s c r e e n d e t e c t o r in an a l u m i n u m -f ront X - r a y c a s s e t t e . N e u t r o n e x p o s u r e t i m e i s 15 sec open t i m e on the r e m o t e l y c o n t r o l l e d s h u t t e r . S h u t t e r open and c l o s e t i m e adds a n o t h e r I j m in . The r h o d i u m s c r e e n i s t hen p l a c e d m con tac t wi th the P o l a r o i d f i lm and allo^wed a 1-min decay . The P o l a r o i d p r i n t i s then deve loped and i n s p e c t e d ,

(2) When the a l i g n m e n t i s a s d e s i r e d , a 0.025 x 12.7 x 1 7 , 7 - c m (O.OlO x 5 X 7- in . ) i n d i u m m e t a l s c r e e n i s p l a c e d in a c a s s e t t e and i n s e r t e d in to the e x p o s u r e pos i t i on . The n e u t r o n e x p o s u r e t i m e r e q u i r e d i s 4. 5 m i n , p l u s s h u t t e r open and c l o s e t i m e . The i n d i u m s c r e e n is then t a k e n to a d a r k r o o m and p l a c e d into a c a s s e t t e con ta in ing 2 s h e e t s of Kodak Type AA X - r a y f i lm, one on each s ide of the s c r e e n . The c a s s e t t e i s then c l o s e d and the i n d i u m is a l lowed at l e a s t a 1-hr d e c a y be fo re the f i lms a r e deve loped .

The r a d i o g r a p h s p r o d u c e d by t h i s l a t t e r p r o c e d u r e a r e of r e a s o n ­ably h igh qua l i ty . Since the o b j e c t - d e t e c t o r d i s t a n c e i s he ld to l e s s than 5.08 c m (2 in.) by the d e s i g n of the e x p o s u r e c h a m b e r , the h i g h - c o n t r a s t

*The r e m o v a l of e x t r a g r a p h i t e in the b e a m c o l l i m a t e r i m p r o v e d the n e u t r o n i n t e n s i t y by a f ac to r of about 3, F u r t h e r d i s c u s s i o n of the b e a m c h a r a c t e r i s t i c s a r e c o n t a i n e d in r e f e r e n c e 5,

r e s o l u t i o n c a p a b i l i t y of t h e r a d i o g r a p h i c s y s t e m i s 0 ,076 c m ( 0 . 0 3 0 i n . ) o r b e t t e r , (5) R a d i o g r a p h i c c o n t r a s t s e n s i t i v i t y n o r m a l l y a c h i e v e d w i t h u s e of t h e i n d i u m s c r e e n m e t h o d i s of t h e o r d e r of 1 t o 2 p e r c e n t .

A n e x a m p l e of t h e r a d i o g r a p h i c r e s u l t i s s h o w n i n F i g u r e 3.

Gamma Autoradiograpli of Unopened Capsule

106-7003

P

Neutron Radiograph of Unopened Capsule

Optical Photograph of Clad Fuel Specimens after Capsule Was Opened

Figure 3. Comparison of Gamma Autoradiography and Neutron Radiography of Highly Irradiated Refractory Alloy-clad U-Pu-Fs Alloy Fuel Specimens in Unopened Irradiation Capsule. The heater coils are not visible in the autoradiograph. The heater was also removed before the optical photograph was taken.

A C K N O W L E D G E M E N T S

T h e a u t h o r s a r e p l e a s e d t o a c k n o w l e d g e t h e a s s i s t a n c e of R. J , F o u s e k , I. R , K r a s k a , a n d R. E . D i c k e n s i n t h e d e s i g n a n d u s e of t h i s e q u i p m e n t a n d p r o c e d u r e . T h e c o o p e r a t i o n of t h e J u g g e r n a u t r e a c t o r p e r ­s o n n e l i s a l s o g r a t e f u l l y a c k n o w l e d g e d .

REFERENCES

1, B e c k , W. N. , and F o u s e k , R. J , , I n s t r u m e n t e d T e m p e r a t u r e - c o n t r o l l e d C a p s u l e s for I r r a d i a t i o n s in the C P - 5 R e a c t o r , A N L - 6 5 5 4 (1962),

2, B e c k , W, N. , A P i n h o l e C a m e r a A u t o r a d i o g r a p h i c T e c h n i q u e for E n ­c a p s u l a t e d I r r a d i a t e d F u e l S p e c i m e n s , A N L - 6 5 3 3 (1962).

3, B e r g e r , H. , and B e c k , W. N. , N e u t r o n R a d i o g r a p h i c I n s p e c t i o n of R a d i o a c t i v e I r r a d i a t e d R e a c t o r F u e l S p e c i m e n s , N u c l e a r Sc i ence and E n g i n e e r i n g , 15, 4 1 1 - 4 1 4 (1962).

4, F o l k r o d , J . R. , E m b e r , G. , Kolb , W., Sa lu ja , J . , and Moon, D. P . , D e s i g n S u m m a r y R e p o r t on the J u g g e r n a u t R e a c t o r , A N L - 6 6 1 6 (1962).

5, B e r g e r , H. , C h a r a c t e r i s t i c s of a T h e r m a l N e u t r o n B e a m for N e u t r o n R a d i o g r a p h y , J o u r n a l of Appl ied R a d i a t i o n and I s o t o p e s (to be p u b l i s h e d ) .

6, B e r g e r , H . , K r a s k a , I. R. , and D i c k e n s , R. E. , A P o l a r o i d F i l m Method for T r a n s f e r N e u t r o n R a d i o g r a p h y , N u c l e a r S c i e n c e and Engi -n e e r i n g , 18, 137-138 (1964).