LIGHT ION REACTION MECHANISMdp)-1983.pdfIn this paper we present measurements of the 17.85 MeV...

Proceedings of the

1983 RCNP International Symposium on

LIGHT ION REACTION MECHANISM

16-20 MAY, 1983

Edited by

H. Ogata, T. Kammur i and I . Katayama

RESEARCH CENTER FOR NUCLEAR PHYSICS OSAKA UNIVERSITY

IBARAKI, OSAKA, JAPAN

ause e x c i t a t i o n

at energy

lg cross s e c t i o n

m a t t e r i n g at

r the change of

th a t the

ther than the

Nakano and

ble d i s c u s s i o n s .

ab • 156 MeV

i =

40 SO

r. Phys.

to Prog.

L e t t e r s

DEUTERON PROJECTILE BREAKUP ON 2 8 S i AT E =17.85 MeV a

C. A. F i e l d s , R. J . Pet e r s o n , R. S. Raymond* and J . L. Ullmann

Nuclear Physics L a b o r a t o r y , Department o f P h y s i c s ,

U n i v e r s i t y o f Colorado, Boulder CO 80309 USA

and

R. J . deMeijer and E. H. L. Aa r t s

K e r n f y s i s c h V e r s n e l l e r I n s t i t u u t , R i j k s u n i v e r s i t e i t Groningen,

9747 AA Groningen, The Netherlands

and

M. B. G r e e n f i e l d

Department o f P h y s i c s , F l o r i d a A and M U n i v e r s i t y

T a l l a h a s s e e , FL 32307 USA

ABSTRACT

28, Deuteron breakup on ~ Si has been s t u d i e d a t 17.85 MeV using both

s i n g l e s and p-n coincidence t e c h n i q u e s . Angular c o r r e l a t i o n data were

obt a i n e d between 144 and -144 f o r protons and between 120 and -120 f o r

neu t r o n s . These r e s u l t s a l l o w the s e p a r a t i o n of the breakup r e a c t i o n i n t o

e l a s t i c , i n e l a s t i c , and a b s o r p t i v e p a r t s , and the d e t e r m i n a t i o n o f the

c o n t r i b u t i o n of each p a r t t o the r e a c t i o n c r o s s - s e c t i o n .

- 621 -

The f i r s t d iscovered and most f r e q u e n t l y s t u d i e d p r o j e c t i l e breakup

1) 2) process i s t h a t o f the de u t e r o n . At energies o f 190 and 56 MeV the

f e a t u r e s of the breakup process are s i m i l a r t o those observed i n the breakup 3 3-5)

o f He . The most common technique used t o study deuteron breakup has

been the measurement of the i n c l u s i v e (d,p) r e a c t i o n s p e c t r a . K l e i n f e l l e r

e t a l have r e c e n t l y measured t h i s r e a c t i o n a t low e n e r g i e s . So f a r o n l y a

few angular c o r r e l a t i o n s t u d i e s o f the (d,pn) r e a c t i o n have been made. 28

In t h i s paper we present measurements o f the 17.85 MeV Si ( d , p n )

r e a c t i o n c a r r i e d out a t the AVF c y c l o t r o n a t the U n i v e r s i t y of Colorado. At

o n l y 9 MeV per n u c l e o n , t h i s r e a c t i o n i s near the low-energy l i m i t f o r the

a p p l i c a t i o n o f d i r e c t r e a c t i o n , and t h e r e f o r e of d i r e c t breakup, models.

The measurements should t h e r e f o r e p r o v i d e a s t r o n g t e s t of such models. The

Si t a r g e t was chosen because i t s ground and f i r s t - e x c i t e d s t a t e s are e a s i l y

separated even w i t h s h o r t p a t h l e n g t h time o f f l i g h t measurements, and

because the long-range Coulomb breakup mechanism i s not expected t o be

dominant i n such a l i g h t n u cleus.

F i g . 1 shows the i n c l u s i v e p r o t o n spectrum a t 1 0 ° . This spectrum

e x h i b i t s a continuum s t r u c t u r e as w e l l as d i s c r e t e s t a t e s up to an

e x c i t a t i o n o f 15 MeV. The continuum s t r u c t u r e may be d i v i d e d i n t o a bump

v i s i b l e a t f o r w a r d angles and a t a i l t h a t i s v i s i b l e even at 1 4 4 ° . I t i s

c l e a r from t h i s s i n g l e s spectrum t h a t high r e s o l u t i o n i n the proton d e t e c t o r

i s needed i n order to d i s t i n g u i s h between the d i s c r e t e s t a t e s and the

continuum p a r t of the spectrum.

F i g . 2 shows the t o t a l k i n e t i c energy (TKE) spectra at 8 =-12.5°and n

8 = + / - 1 2 . 5° t o g e t h e r w i t h p r o j e c t e d p roton spectra i n coincidence w i t h both P

neutrons and c e r t a i n gates i n the r e l e v a n t TKE spectrum. I t f o l l o w s from

the TKE s p e c t r a t h a t the dominant r e a c t i o n s a t forw a r d angles are e l a s t i c

and i n e l a s t i c breakup. The p r o j e c t e d p r o t o n s p e c t r a c l e a r l y i n d i c a t e the

l a r g e c o n t r i b u t i o n s to the TKE spectra o f e i t h e r (d,n) t r a n s i t i o n s t o pr o t o n

unbound s t a t e s or (d,p) t r a n s i t i o n s t o neutron unbound s t a t e s . I n s u f f i c i e n t

p r o t o n energy r e s o l u t i o n may e a s i l y r e s u l t i n an ov e r e s t i m a t e of the cross-

s e c t i o n o f the p r o j e c t i l e breakup process by a f a c t o r o f two.

F i g . 3 shows the angular c o r r e l a t i o n f o r the e l a s t i c breakup process

w i t h 0 f i x e d a t - 1 2 . 5° and 8 v a r i a b l e . S i m i l a r angular c o r r e l a t i o n s have " P + 2 8

been obtained f o r i n e l a s t i c breakup t o the 1.78 MeV 2 s t a t e o f S i . C o r r e l a t i o n s were a l s o measured w i t h the proton d e t e c t o r f i x e d at - 1 2 . 5° and

- 622 -

t i l e breakup 2)

6 MeV the

the breakup

breakup has

K l e i n f e l l e r

o f a r o n l y a

made.

V S i ( d , p n )

:olorado. At

i m i t f o r the

up, models,

models. The

3 are e a s i l y

ements, and

?cted t o be

i s spectrum

up t o an

i n t o a bump

'44c. I t i s

on d e t e c t o r

es and the

=-12.5 cand n

j w i t h both

o l l o w s from

3 re e l a s t i c

i d i c a t e the

s to p r o t o n

n s u f f i c i e n t

the cross-

up process

i t ions have , 2 8 c .

of S i .

-12.5 e and

7 5 0 i i i 1 1 1 ' 1 1 1 i i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 n 1 1 1 1 1 1 1 1 1 1 1 1 1

28 638

Si ( d , p )

10 d e q .

TTTT

i I I I I J l I I I I I I I I I I I I I I I I I I H I I I I I I I I I I I I I I I I I I I I I I I I

0 Channel F i g . 1: Proton s i n g l e s spectrum a t 10 .

1 1 [ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 M M

4.93

G.S.

1.27

H i l i f i i i J . J 9 0 0

the neutron d e t e c t o r v a r i a b l e . A l l of the d i r e c t breakup c o r r e l a t i o n s are

s i m i l a r i n shape; they show a peak f o r d e t e c t o r s on o p p o s i t e sides of the

beam. I he c o r r e l a t i o n s w i t h 8 f i x e d show a second maximum at 6 =50 c

n p maximum i s absent i n the f i x e d - p r o t o n c o r r e l a t i o n s . This s i t u a t i o n

This

i s

s i m i l a r to t h a t of the p-d c o r r e l a t i o n s measured i n the 52 MeV breakup o f 3 28 He on S i . In t h i s case i t was found t h a t the c o r r e l a t i o n w i t h 0 f i x e d

d showed a secondary maximum at 6 = 4 5 ° , w h i l e the c o r r e l a t i o n w i t h 0 f i x e d

4,5) P 3 P showed no secod maximum . For He breakup the angular c o r r e l a t i o n s could

be reproduced by c a l c u l a t i o n s using the q u a s i - f r e e breakup model (QFBM) w i t h 4)

the proton a s p e c t a t o r . Such c a l c u l a t i o n s are p r e s e n t l y being used t o

determine which p a r t i c l e i s the dominant s p e c t a t o r i n the breakup o f the

deuteron.

A c o r r e l a t i o n was a l s o o b t a i n e d w i t h the neutron counter f i x e d and

28

gates set on the r e g i o n o f the TKE spectrum above the 1.78 MeV s t a t e i n Si

e x c i t a t i o n . This c o r r e l a t i o n has a s i n g l e maximum a t about 1 2 ° , and a FWHM

of about 50 c.

I n t e g r a t i n g the angular c o r r e l a t i o n s over the angular range a l l o w s a

comparison w i t h the i n c l u s i v e breakup c r o s s - s e c t i o n a t 1 2 . 5 ° . The

- 623

F i g . 2: TKE and p r o j e c t e d proton s p e c t r a .

p r e l i m i n a r y r e s u l t s are l i s t e d i n t a b l e 1. From t a b l e 1 i t may be concluded

t h a t the e l a s t i c and i n e l a s t i c breakup t o g e t h e r c o n t r i b u t e about 20% o f the

c r o s s - s e c t i o n , w i t h the r e s t being a b s o r p t i v e breakup.

This work was fi n a n c e d i n p a r t by USDOE, NATO, FOM and ZWO.

•present address: Brookhaven N a t i o n a l Lab, Upton, NY 11973 USA

REFERENCES

1. R. Serber, Phys. Rev. 72. ( 1947) 1008

2. N. Matsuoka et aj _ , N u c l . Phys. A391 (1983) 357

3. E. H. L. Aa r t s e t a]_, Phys. L e t t . 105B (1981) 130

4. E. H. L. Aarts e t a l _ , N u c l . Phys. A380 ( 1982) 465

5. E. H. L. Aarts e t a ] , t o be p u b l i s h e d

6. J . K l e i n f e l l e r e t a±, N u c l . Phys. A370 (1981) 205

~ 624 -

28Si(d.pn)28Si(g.».) E "17 85MeV

0

e_--12.5*

tV

•120 - 80 -40 4 0 8 0

9 p L A B < d e 9 '

F i g . 3: Proton angular c o r r e l a t i o n .

Table 1

Comparison o f proton and neutron breakup bump c r o s s - s e c t i o n s a t 1 2 . 5°

to g e t h e r w i t h cross s e c t i o n s o b t a i n e d from the angular c o r r e l a t i o n

measurements.

6 = - 1 2 . 5 ° : n

E l a s t i c : 14+/-3

I n e l a s t i c : 11+/-3

A b s o r p t i v e : 85+/-10

T o t a l : 110+/-16

Sin g l e s neutron continuum bump: 100+/-50

• 1 2 . 5 ° :

E l a s t i c : 17+/-4

I n e l a s t i c : 9+/-4

A b s o r p t i v e : (unmeasured)

T o t a l : 26+/-6

S i n g l e s proton continuum bump: 148+/-20

- 625 -