This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440

Breuer, H.

Fatyga, M.

Kwiatkowski, K.

Mignerey, A.C.

Viola, V.E.

Wilson, W.

Woo, L.W.

English

IUScholarWorks

GLOBAL STUDIES OF THE MASS, ENERGY AND ANGULAR DISTRIBUTIONS I N  THE 200 MeV 4 ~ e  + 2 8 ~ i  REACTION 
L.W. Woo, K. Kwiatkowski, M. Fa tyga ,  W. Wilson and V.E. Vio la  
I nd i ana  Un ive r s i t y  Cyclo t ron  F a c i l i t y ,  Bloomington, I nd i ana  47405 
H. Breuer and A.C. Mignerey 
U n i v e r s i t y  of Maryland, Col lege  Park ,  Maryland 
Energy and angu l a r  d i s t r i b u t i o n s  have been 
E - 117.30 MeV 
measured f o r  t h e  117.3 MeV and 198.5 MeV a  + 2 8 ~ i  
systems.  Cross s e c t i o n s  f o r  a l l  fragments from A = 6 
t o  A = 29 were determined u s i n g  t h e  t ime-of - f l igh t  
technique  a t  t h e  Ind i ana  Un ive r s i t y  Cyclo t ron  F a c i l i t y .  
The mass r e s o l u t i o n  ranged from 0.4 mass u n i t s  f o r  t h e  
l i g h t e r  fragments t o  about  0.8 mass u n i t s  f o r  A > 25; 
t h e  t o t a l  energy spec t rum was measured down t o  -1 MeV. 
Energy s p e c t r a  a t  both 117.3 MeV and 198.5 MeV a r e  
c h a r a c t e r i z e d  by a  broad peak a t  low ene rg i e s  fo l lowed 
by an  exponen t i a l  t a i l  which becomes s y s t e m a t i c a l l y  
s t e e p e r  a s  a  f u n c t i o n  of both i n c r e a s i n g  ang l e  and 
fragment mass. S i m i l a r  behavior  i s  observed i n  
r e a c t i o n s  of 4 ~ e  w i th  12c  a t  160 MeV and pro tons  wi th  
2 7 ~ 1  a t  180 M ~ v . ~ , ~  The angu l a r  d i s t r i b u t i o n s  a r e  a l l  
forward-peaked and become i n c r e a s i n g l y  more 
30.0 20.0 30.0 40.0 
E (MeV) 
forward-peaked a s  t h e  mass i n c r e a s e s  (F ig .  2) .  Th i s  
f e a t u r e  i s  aga in  observed i n  a  + 1 2 c  r e a c t i o n s .  I n  
F igu re  1. Energy s p e c t r a  of A = 20 and 24 p roduc t s  
c o n t r a s t ,  t h e  h e a v i e r  f ragments  from t h e  p + 2 7 ~ 1  from t h e  r e a c t i o n  of 117.3 MeV 4 ~ e  i ons  w i th  2 8 ~ i ,  
observed  a t  an ang l e  of 30 degrees .  
r e a c t i o n  a t  180 MeV show a  two-component t y p e  of 
angu l a r  d i s t r i b u t i o n ,  one a s s o c i a t e d  w i th  fu s ion - l i ke  
E - 117.3 MeV E - 198.5 heV 
p roduc t s  and a  second w i th  p e r i p h e r a l  r e c o i l s .  
The t o t a l  i s o b a r i c  c r o s s  s e c t i o n s  a t  both ene rg i e s  
a r e  r a t h e r  s i m i l a r  i n  shape  (F ig .  3 )  and e x h i b i t  
maximum y i e l d s  f o r  A - 24. A l l  t h e  a -nucle i  y i e l d s  a r e  
s u b s t a n t i a l l y  enhanced,  presumably due t o  nuc l ea r  
b inding  energy  e f f e c t s .  Some p r e l im ina ry  c a l c u l a t i o n s  
have been performed based on t h e  i n t r a n u c l e a r  cascade  
0 50 100 150 0 50 100 150 
(INC) model, u s ing  t h e  code C L U S T ~  which is a  modified LAB. ANGLE 1DEG.l LAB. ANGLE (DEB.) 
v e r s i o n  of V E G A S . ~  The p r e d i c t e d  angu l a r  d i s t r i b u t i o n s  F igu re  2. Angular  d i s t r i b u t i o n s  f o r  A = 20 and 24 
f ragments  from t h e  r e a c t i o n  of 117.3 and 198.5 MeV 4 ~ e  
a r e  small a t  0" and peak around 30". One p o s s i b l e  w i t h  2 8 ~ i .  Dot ted  l i n e s  r e p r e s e n t  r e s u l t s  of an  
i n t r a n u c l e a r  cascade  code c a l c u l a t i o n .  
e x p l a n a t i o n  f o r  t h e  low c a l c u l a t e d  c r o s s  s e c t i o n s  a t  0" 
BEAM ENERGY - 198.5 MeV 
~ ' ' ' ' ' ' - 7 - ~ 1 - ~ ~ ~ r  - A ' ]  
Fragment nett  
Figu re  3. I s o b a r i c  y i e l d s  f o r  v a r i o u s  r e a c t i o n  
products  from 117 MeV (dashed l i n e )  4 ~ e  i ons  wi th  
2 8 ~ i .  S o l i d  curve i s  t he  r e s u l t  of an i n t r a n u c l e a r  
cascade  c a l c u l a t i o n .  
60- 
The I N C  model o v e r p r e d i c t s  t h e  dominance of ( a , a ' )  
and (a,2p2n) t ypes  of r e a c t i o n s ,  whereas 
expe r imen t a l l y  we observe  t h e  major y i e l d  t o  occur  f o r  
r e a c t i o n s  which r e s u l t  i n  t h e  removal of 4  mass u n i t s  
from t h e  t a r g e t .  The unde rp red i c t i on  of t h e  i s o b a r i c  
c ro s s - s ec t i ons  becomes more s eve re  f o r  t h e  l i g h t e r  
masses. I f  we assume t h a t  energy d e p o s i t i o n  i s  
p r o p o r t i o n a l  t o  t h e  number of nucleons removed, t h e  I N C  
model i s  u n d e r p r e d i c t i n g  t h e  energy depos i t ed  by t h e  
p r o j e c t i l e  by a  s i gn f  i c i a n t  amount. 
1 )  A.  Gokmen e t  a l . ,  Phys. Rev. C 2, 1595 (1984).  
40- 
20 - 
I - 
1 * *\ ,' 
, , 
10 15 20 25 30 
eo;-- -. EXFT 
- INC CALC. 
I 
' \  1 ,  
i s  t h a t  t h e  cascade model supp re s se s  l a r g e  l i n e a r  
- 
- 
momentum t r a n s f e r s  t o  t h e  t a r g e t - l i k e  r e s i d u a l  n u c l e i .  
The q u a l i t a t i v e  agreement a t  t h e  i n t e r m e d i a t e  ang l e s  
sugges t s  t h a t  t h e  model i s  more s u c c e s s f u l  i n  
2 )  K. Kwiatkowski e t  a l . ,  Phys. L e t t .  50, 1648 
(1983).  
3 )  G.J. Mathews e t  a l . ,  Phys. Rev. C 25, 2181 (1982).  
4 )  K. Chen e t  a l . ,  Phys. Rev. 166, 949 (1963).  
p r e d i c t i n g  p e r i p h e r a l  processes .  


Global Studies of the Mass, Energy and Angular Distributions in the 200 MeV 4-He + 28-Si Reaction

https://scholarworks.iu.edu/dspace/bitstream/2022/984/1/iucf_1985_72-73.pdf

Global Studies of the Mass, Energy and Angular Distributions in the 200 MeV 4-He + 28-Si Reaction

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