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

Bent, R.D.

Green, M.C.

Hugi, M.

Kehayias, J.J.

Nann, H.

Ward, T.E.

English

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PROTON INDUCED A' PRODUCTION FROM 7 L i  
J.J. Kehayias, R.D. Bent, M.C. Green, M. Hugi, H. Nann, and T.E. Ward 
Indiana Univers i ty  Cyclotron F a c i l i t y ,  Bloomington, Indiana 47405 
Light  n u c l e i  o f f e r ,  i n  p r i n c i p l e ,  some advantages of known sp in  and p a r i t y  i n  8 ~ .  Because of t he  high 
i n  microscopic c a l c u l a t i o n s  of the  pion production y i e l d ,  i t  was poss ib l e  t o  ob ta in  complete angular  
process.  The smal l  number of nucleons involved makes d i s t r i b u t i o n s  of t he  d i f f e r e n t i a l  c ross  s e c t i o n  f o r  
f u l l  s h e l l  model c a l c u l a t i o n s  t r a c t a b l e  and reduces the  these  t h r e e  s t a t e s  dur ing the  course of sd-shel l  ( p , ~ - )  
importance of pion r e s c a t t e r i n g  e f f e c t s .  s t u d i e s  wi th  a r e l a t i v e l y  small  amount (- 1 s h i f t )  of 
Thus, l i g h t  nuc le i  should minimize the  nuclear  beam time. This occurred dur ing the  per iod fol lowing 
s t r u c t u r e  and pion d i s t o r t i o n  u n c e r t a i n t i e s  t h a t  t h e  i o n  source f i r e  when a polar ized beam was not 
normally plague ( p , ~ )  c a l c u l a t i o n s  and a l low a more ava i l ab le .  The angular  d i s t r i b u t i o n s  f o r  a l l  t h r e e  
c l e a r  cu t  t e s t  of o t h e r  p a r t s  of t he  r e a c t i o n  process. s t a t e s  [which have the  same (p3/2)4 conf igu ra t ion ]  a r e  
Lithium 7 is the  l i g h t e s t  t a r g e t  f o r  which the  (p,x') shown i n  Fig. 2. 
r e a c t i o n  l eads  t o  a f i n a l  nucleus t h a t  is bound. 
1)  J.J. Kehayias, R.D. Bent, M.C. Green, M. Hugi, H. 
During the  course  of (p,n') experiments on Nann and T.E. Ward, S tud ies  of 80(p,n') 1 9 ~ e *  and 
2 6 ~ g ( p , ~ ' ) 2 7 ~ i *  Reactions wi th  200 H e V  Polar ized 
sd-shel l  nuc le i ,  t h e  7 ~ i ( p , ~ ' ) 8 ~ g . s .  r e a c t i o n  was used Protons,  Contr ibut ion t o  t h i s  Annual Report. 
f o r  energy c a l i b r a t i o n  of s e v e r a l  spec t r a .  Fig. 1 
shows a t y p i c a l  7 ~ i  (p, A') spectrum, which conta ins  
t h r e e  sharp  peaks corresponding t o  we l l  resolved s t a t e s  
Excitation Energy (Mev) 
o G.S. 
= 205 MeV 0.78 MeV 
C.M. 
8, (Deg.) 
Figure  2. Angular d i s t r i b u t i o n s  of d i f f e r e n t i a l  c ross  
s e c t i o n s  f o r  t he  7 ~ i ( p , ~ ' ) 8 ~  r eac t ion  t o  t h r e e  s t a t e s  
of the f i n a l  nucleus. The e r r o r  ba r s  include both 
s t a t i s t i c a l  and background s u b t r a c t i o n  u n c e r t a i n t i e s .  
Figure  1. ' ~ i ( ~ ,  A - ) ~ B  spectrum a t  T~~~~ = 205 MeV and 
oALab = 30°. 
PION PRODUCTION TO THE CONTINUUM 
J.J. Kehayias, R.D. Bent, M.C. Green, R.E. Pollock, T.G. Throwe, and T.E. Ward 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
Nuclear pion production has turned out to be a 
difficult process to understand because of the complex 
interplay between the reaction dynamics and nuclear 
structure effects. It has been suggested1 that studies 
of pion production to the continuum, where the high 
momentum (- 550 MeV/c) incident nucleon does not have 
to be "caught" by the nucleus, may help elucidate the 
reaction mechanism by reducing the nuclear structure 
uncertainties. 
We have measured differential cross sections for 
(p, x') transitions to the continuum for several targets 
covering a wide mass range. The large momentum bite 
(pmax/pdn = 1.6) of the QQSP spectrometer is ideal for 
continuum studies, allowing about a 25 MeV range of 
excitation energy of the residual nucleus to be Excitation Energy (MeV) 
recorded at a single magnetic field setting of the Figure 1. Selected (p,n+) and (p,x') spectra. 
spectrometer. Figure 1 shows some of the spectra ~ ~ ~ a b  = 190 MeV and @,Lab = 45' for all except 
2og~i(p,n-), for which T~~~~ = 192 MeV and enLab = 30'. 
obtained. The data are preliminary and have not yet 
been corrected for non-linearities in energy 2p-lh states. This suggests a similarity in the 
calibration and variation in pion detection efficiency reaction mechanism for pion production to discrete and 
across the focal plane. For most of the spectra, continuum states. 
measurements were made for more than one spectrometer Figure 2 shows the x' spectrum from the 
field setting. The resulting overlapping spectra will 209~i(p,n-)210~t reaction calculated by ~ i b b s ~  in a 
allow extraction of information about the higher part model in which target emission is the total mechanism 
of the continuum and also will make possible 
corrections for local variations in detector 
for negative pion production. He assumed that the 
negative pion is produced from one of the neutrons in 
efficiency. Additional data have been taken with the target and that the cross section to a state at a 
polarized beam, which will provide information about given energy can be represented (on the average) by the 
the analyzing power in the continuum. cross section to a "typical" state which, for 
Preliminary analysis indicates that the angular simplicity, he chose to have a pure two proton particle 
distribution of the differential cross section for - one neutron hole configuration 
(p, n-) transitions to the continuum is similar to that {[(1hg12)-1 2g912]0- x 2~912~9/2-. The density of 
for the strong transitions to the low-lying stretched "typical" states at high energies where Pauli exclusion 
Figure 2. Calculated spectrum for  negative pion 
production from protons on 209~i. The curves labeled 
E I  and Fi3 a re  shown t o  estimate s e n s i t i v i t y  t o  the 
l e v e l  densi ty  assumption. [Taken from Ref. 21. 
e f f e c t s  should be unimportant was taken t o  vary a s  the 
energy raised t o  the number of "par t i c les"  minus one; 
i.e., as  Fi2. To make the energy densi ty  more r e a l i s t i c  
a t  low energies  the form p(E) = 0.004 (E + 1 5 ) ~  was 
used. The spectrum calculated using t h i s  funct ion is 
the shape of the spectrum f o r  two neighboring powers 
(normalized t o  the same peak value). There is a very 
not iceable  difference i n  these curves, ind ica t ing  t h a t  
the number of nucleons involved i n  the pion production 
process a f f e c t s  the shape of the continuum i n  a ra ther  
d i r e c t  way. Although the Fi2 spectrum shape is s imi la r  
t o  what we have observed f o r  the 2 0 9 ~ i ( p ,  x') 2 1 0 ~ t  and 
2 0 8 ~ b ( p ,  x ' ) 2 0 9 ~ i  react ions (see Fig. I) ,  correct ions 
f o r  va r ia t ions  i n  detector  e f f i c iency  and energy 
non-linearity must be applied t o  the data  before 
meaningful comparisons can be made. Nevertheless, we 
a r e  hopeful t h a t ' a  de ta i l ed  analysis  of the da ta  
together with more ref ined ca lcu la t ions  w i l l  shed l i g h t  
on the ( p , ~ )  react ion mechanism. 
1) G.E. Walker, Pion Production and Absorption i n  
Nuclei, ed. R.D. Bent (American I n s t i t u t e  of 
Physics Conf. Proc. No. 79, New York, 1982) pp. 
270, 430. 
2) W.R. Gibbs, i b i d ,  p. 313. 
labeled E* i n  Fig. 2. Also shown, f o r  comparison, is  


Proton Induced Pi- Production from 7-Li

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Proton Induced Pi- Production from 7-Li

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