This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit

Breuer, H.

Gokmen, A.

Kwiatkowski, K.

Mathews, G.J.

Mignerey, A.C.

Viola, V.E. Jr.

Ward, T.E.

Zhou, S.

English

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A GLOBAL STUDY OF THE p + 27Al REACTION AT 180-MEV* 
K. Kwiatkowski, S. Zhou, V.E. Viola, Jr., and T.E. Ward 
Indiana Univers i ty  Cyclotron F a c i l i t y ,  Bloomington, Indiana 47405 
G.J. Mathews 
Lawrence Livermore Laboratory,  Livermore, C a l i f o r n i a  94550 
H. Breuer, A. Gokmen, and A.C. Mignerey 
Univers i ty  of Maryland, College Park, Maryland 20742 
I n  order  t o  de r ive  a broader understanding of the  MeV/amu. Due t o  the  low ene rg ie s  of r e c o i l  nuc le i  from 
mechanisms which c h a r a c t e r i z e  nuc leonnuc leus  simple r eac t ions  such a s  (p,p ') and (p,pn),  t he  d a t a  
c o l l i s i o n s  a t  i n t e rmed ia t e  ene rg ie s ,  a g loba l  s tudy of f o r  A > 25 may miss a s u b s t a n t i a l  f r a c t i o n  of these  
t h e  p + 27Al r e a c t i o n  has been performed a t  IUCF. I n  i s o b a r i c  c ross  sec t ions .  Consequently, f o r  A=26 and 27 
these  measurements a channel-plate-fast-t iming d e t e c t o r  we have r e l i e d  on in-beam gamma ray d a t a ; l  t h e  e r r o r s  
and a t h r e e  element semiconductor d e t e c t o r  f o r  A=25 a r e  es t imated t o  be about 30 percent.  
t ime-of-fl ight t e l e scope  have been used t o  d e t e c t  Figure  2 shows r e p r e s e n t a t i v e  energy s p e c t r a  f o r  
d i r e c t l y  r e a c t i o n  products A < 27 formed i n  the  A=7, 16 and 22 fragments over a range of angles.  The 
bombardment of a 100 pg/cm2 27Al t a r g e t  with 180-MeV s p e c t r a  a r e  cha rac te r i zed  by a broad peak a t  low 
protons.  With t h i s  system a t iming r e s o l u t i o n  of ene rg ie s  followed by an exponent ia l  decrease  f o r  t he  
< 140 ps was achieved y i e l d i n g  a mass r e s o l u t i o n  of h igher  energies .  The s lopes  of t he  s p e c t r a  i n c r e a s e  
-0.4-0.8, depending on fragment mass and energy. A wi th  inc reas ing  fragment mass and angle.  For the  
sample mass spectrum is  shown i n  Fig. 1. For fragments l i g h t e s t  fragments,  t he  angular  d i s t r i b u t i o n s  a r e  
wi th  A > 6 the  lower d e t e c t i o n  l i m i t  was > 0.05 s t r o n g l y  forward-peaked, whereas f o r  t he  heav ies t  
MASS NUMBER E (MeV) 
Figure  1. Mass spectrum f o r  fragments wi th  ener  ies Y Figure  2. Energy s p e c t r a  f o r  fragments wi th  A = 7, 16 above 10 MeV observed a t  20 deg i n  180-MeV p + * Al  and 22 a t  angles  of 20°, 40° and 70' i n  the  180-MeV 
reac t ion .  p + 2 7 ~ 1  react ion.  
,,I 180 MeV H +  'hl 
Figure 3. Isobaric cross sections for fragments from 
180-MeV p + 27 reaction; solid line-experimental data, 
dashed line intranuclear cascade code prediction; and 
dotted line is semiempirical estimate of Silberberg and 
Tsao. 
fragments two components appear in the data, presumably 
arising from fusion-like processes in the forward 
direction and peripheral collisions involving 
f orward-peaked light-ions which lead to heavy fragment 
emission at more backward angles. 
In Fig. 3 the mass distribution of the reaction 
products with A > 6 is shown. Also shown are yield 
predictions based on intranuclear cascade-evaporation 
calculations2 and the semiempirical estimates of 
Silberberg and ~ s a o . ~  The calculations tend to 
overpredict the yields of target-like fragments and 
substantially underestimate yields of lighter 
fragments. This comparison suggests that 
proton-induced reactions lead to enhanced deposition 
relative to the model calculations, a result consistent 
with recent measurements on heavier n~clei.~ 
*Work supported in part by the U. S. Office of Naval 
Research and the Department of Energy. 
1) 0. Artun et al., Phys. Rev. Lett. 35, 773 (1975). 
2) K. Chen et al., Phys. Rev. 166, 949 (1968). 
3) R. Silberberg and C.H. Tsao, Ap. J. SUPP~. 25, 315 
(1973). 
4) F. Saint Laurent et al., Phys. Lett. llOB, 372 
(1982). 


A Global Study of the p+27-Al Reaction at 180 MeV

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A Global Study of the p+27-Al Reaction at 180 MeV

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