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

Breuer, H.

Fatyga, M.

Kwiatkowski, K.

Mignerey, A.

Viola, V.E.

Walker, T.P.

Wilson, W.

Woo, L.W.

English

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TOTAL 2, A, ENERGY AND ANGULAR DISTRIBUTIONS OF FRAGMENTS PRODUCED REACTIONS OF 100- AND 200-MeV 4 ~ e  WITH 2 8 ~ i  
K. Kwiatkowski, W. Wilson, M. Fatyga, V.E. Viola, L.W. Woo, and T.P. Walker 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
8 .  Breuer and A.C. Mignerey 
University of Maryland, College Park, Maryland 20742 
In order to test intermediate-energy models for 
description of the total reaction cross section in 
I 
nucleus-nucleus collisions, complete energy and angular 
distributions have been measured with discrete nuclidic 
resolution for all fragments emitted in the reaction of 
100- and 200-MeV 4 ~ e  ions with 28~i. Self-supporting 
targets of separated 2 8 ~ i  were bombarded with "200 nA 
beams from IUCF in these experiments. 
Two detector telescope systems were employed. One 
of these was designed for complete definition of the 
mass and energy yields for all fragments with energies 
> 0.05 MeV/nucleon. This detector consisted of a 
channel-plate fast timing start detector followed 60 cm 
downstream by a stack of silicon detectors of 
thicknesses 48-, 400-, 2000- and 2000-pm, respectively. 
The 48-pm detector served as a stop signal for time-of- 
flight determination. In Fig. 1 a plot of ~t~ (mass 
parameter) versus fragment energy is shown, indicating 
. , I 1 1  1- v' 
0 2 0  40 
E (MeV) 
- 
the on-line mass resolution attainable with this 
>;? .., ... nr -c r  ...-- .r-r - ' - -- .. -. .. 
- -s.--.. - ..- . . . 
- . ..". !: .----..-..--. .. . L.. - .. . ._. 
, . ' 'C.. --. ..-. .. . . . . .-.-., _ .. . . 
.I-.--,- ..-. -- , .- . . . 
.-.... A ..-_. 
system. Also shown in Fig. 1 is a projection of the 
Fi ure 1. Mass spectra observed at 30 deg in the 
mass spectrum with an energy gate from 8-10 MeV. refction of 200-MeV 'He ions with 28~i. Upper curve 
plots mass parameter ~t~ versus fragment energy; lower 
The second detector system was designed to yield curve shows a projection of the above mass spectrum in 
an energy window from 8-10 MeV. 
discrete nuclidic Z and A information for the fragments 
down to as loV an energy as possible. This system Based upon preliminary analysis of the data, the 
employed two channel-plate fast-timing units for time- mass and charge distributions from this reaction are 
of-flight measurement, followed by a gas-ionization observed to populate a broad range of residual nuclei, 
detector operating at 7.5 torr of isobutane for AE which emerge with significant amounts of kinetic 
information, and a silicon detector stack of 50-, 500- energy, as observed in proton-induced reactionso1 
and 5000-pm thickness, respectively. Discrete However, in contrast with the proton-induced reactions 
resolution for all fragments with energies > 0.2 MeV/ the yields of fragments with 4 < Z < 8 at backward 
nucleon was achieved with this system. angles are suppressed. Analysis of these data is 
c u r r e n t l y  i n  p rog re s s .  The r e s u l t s  w i l l  be examined 
b o t h  w i th  i n t r a n u c l e a r  c a scade  and pre-equi l ibr ium 
c a l c u l a t i o n s .  
1 )  K. Kwiatkowski e t  a l . ,  Phys. Rev. L e t t ,  50, 1648 
1983).  
0 2 4 6 8 10 12 44 I6 I8 20 
E (MeV) 
F i g u r e  2. AE-E spectrum f o r  f ragments  e m i t t e d  i n  
200-MeV 4 ~ e  + 2 8 ~ i  r e a c t i o n .  
INTERMEDIATE MASS FRAGMENT EMISSION I N  200 MeV 3 ~ e - ~ ~ ~ ~ ~ ~ ~  REACTIONS ON Ag AND Au TARGETS 
J.S. Bashkin, K. Kwiatkowski, M. Fa tyga ,  H.J. ~arwowski '  and V.E. V io l a  
I nd i ana  U n i v e r s i t y  C yc lo t ron  F a c i l i t y ,  Bloomington, I nd i ana  47405 
The cha rge  d i s t r i b u t i o n s  and energy s p e c t r a  of  
in te rmedia te -mass  f ragments  (IMF's: 3<Z<14) from t h e  
r e a c t i o n  of 198.6- and 270-MeV 3 ~ e  w i th  Ag and Au 
t a r g e t s  have been measured a t  IUCF. Se l f - suppo r t i ng  
t a r g e t s  of  t h i c k n e s s  =2 mg/cm2 were bombarded wi th  3 ~ e  
beams of 100 nA i n  t h e  64-inch d i ame te r  s c a t t e r i n g  
chamber. Fragment a t o ~ n i c  numbers were i d e n t i f i e d  w i th  
a AE-E t e l e s c o p e  c o n s i s t i n g  of a g r i dded  g a s  ion- 
chamber element (AE), ope ra t ed  a t  8.4 t o r r  of  
i sobu t ane ,  and a 165- Irn p a r t i a l l y  d e p l e t e d  s i l i c o n  
s u r f a c e  b a r r i e r  s t opp ing  d e t e c t o r .  D i f f e r e n t i a l  c r o s s  
s e c t i o n s  were measured over  t h e  angu l a r  range  
15°<01ab<1610. 
The angu l a r  d i s t r i b u t i o n s  and energy s p e c t r a  
s u g g e s t  t h a t  a t  l e a s t  two s e p a r a t e  mechanisms a r e  
r e s p o n s i b l e  f o r  t h e  p roduc t i on  of  IMF's. The f i r s t  i s  
c o n s i s t e n t  w i t h  a s t a t i s t i c a l  emiss ion  mechanism, a s  
ev idenced  by approxiroately i s o t r o p i c  angu l a r  
d i s t r i b u t i o n s  from 80-160 deg and a s s o c i a t e d  energy  
s p e c t r a  peaked near  t h e  Coulomb energy p r e d i c t e d  by 
f i s s i o n  s y s t e m a t i c s ,  assuming a b ina ry  process .  These 
can  be de sc r i bed  r a t h e r  we l l  by t h e  s t a t i s t i c a l  model 
of  ~ 0 r e t t o . l  The peaks of  t h e  s p e c t r a  cor respond t o  a 
s e p a r a t i o n  d i s t a n c e  o f  t h e  cha rge  c e n t e r s  o f  about  1.8 
( ~ ~ 1 / 3 + ~ ~ 1 / 3 ) f 1 1 1 ,  imply ing  a h igh ly  s t r e t c h e d  
c o n f i g u r a t i o n  f o r  t h e  e m i t t i n g  system a t  t h e  s c i s s i o n  
p o i n t .  A r a p i d i t y  a n a l y s i s  of  t h e s e  energy s p e c t r a  is 
c o n s i s t e n t  w i th  s t a t i s t i c a l  emiss ion  from a sou rce  
moving w i th  t h e  compound nucleus  v e l o c i t y  . 
The second IMF mechanism i s  evidenced  by s t r o o g l y  
forward peaked angu l a r  d i s t r i b u t i o n s  which e x h i b i t  a n  
i n c r e a s i n g l y  pronounced high-energy colnponent a s  one  


Total, Z, A, Energy and Angular Distrubutions of Fragments Produced Reactions of 100- and 200- MeV 4-He with 28-Si.

https://scholarworks.iu.edu/dspace/bitstream/2022/1115/1/iucf_1984_106-107.pdf

Total, Z, A, Energy and Angular Distrubutions of Fragments Produced Reactions of 100- and 200- MeV 4-He with 28-Si.

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