Proceedings of the 1983 RCNP International Symposium on LIGHT ION REACTION MECHANISM 16-20 MAY, 1983 Edited by H. Ogata, T. Kammuri and I. Katayama RESEARCH CENTER FOR NUCLEAR PHYSICS OSAKA UNIVERSITY IBARAKI, OSAKA, JAPAN
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 -