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

Bent, R.D.

Cao, Z.-J.

Green, M.C.

Kehayias, J.J.

Nann, H.

Throwe, T.G.

Ward, T.E.

English

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MEASUREMENTS OF (p,z-) REACTIONS NEAR ZERO DEGREES 
T.E. Ward, R.D. Bent, Z.-J. Cao, M.C.  ree en*, J.J. ~eha~iast, H. Nann, M. ~ u ~ i s ,  and T.G. Throwe 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
The recent discovery1 of an extraordinary 
1800 
concentration of (p,n-) strength in a small 3-7 MeV 
excitation region has prompted a series of systematic 1500 G 
"bump" studies2 involving a large number of targets X 
- 1200 
at energies of 191, 200, and 206 MeV and at angles of 3 
900 
0" and 30"-150" for the best candidates 180, 48~a, and L 
U) -- 
Y 
90~r. Some few data was acquired for 13c, 180, 26~g, \ 600 e 
L 
and 4 8 ~ a  angular distributions. The most striking 300 
feature of these studies are the one or two "bumps" 
0 
observed in the (p,n-) spectra with cross sections 1-2 
orders of magnitude greater than the ground state 
transitions and comparable in magnitude to the strong 
(P, n+) transitions commonly observed. In Figs. la-c 
are shown some representative zero degree spectra taken 
with the QQSP at a proton energy sf 191 MeV (E201). 
Additional zero degree data at 166 MeV on the same 
target nuclei have yielded new information on the 
energy dependence of these reactions and has aided in 
developing rather complete angular distributions at 
these two energies for the best "bump" candidates. 
The occurance of these enhanced coherent pionic 
transitions may have important implications regarding 
the production mechanism and high momentum components 
of the nucleus. In the initial publications1 of the 
"bumps" the role of two-particle one-hole states in the 
context of a two nucleon model were discussed. ~ i l l i ~ ~  
and ~ibbs6 have developed target emission models which 
are suitable for calculating the angular distributions 
4 4 ~ a  ( p , ~ - ) ~ ~ ~ i  Tp = 191.25 MeV 
750 
600 .47 mg/crn2 at 0.00 deg 
450 
300 
150 
0 
- 42 Ca ( p , ~ - ) 4 3 ~ i  TD = 191.24 MeV 
Th=-3.6 deg 30.50 mg/cm2 
at 0.00 deg 
600 
I 
and asymmetries of the "bump" once their configurations EXC (MeV) 
have been identified. The energy dependence of the 
reaction is of interest within the context of these Figure la,b,c. Pion spectra obtained with the QQSP at 
0,,=3.6", Ep=191 MeV for the 42~a, 4 4 ~ a  and 4 8 ~ a  (p,n-) 
models as noted by ~ i b b s ~  and soga7 since the 2p-lh reactions. 
behavior i s  q u i t e  d i f f e r e n t  than the  t r a n s i t i o n s  t o  
s i n g l e  p a r t i c l e  s t a t e s .  
A summary of t he  r e s u l t s  of E201 a r e :  1 )  t h e  QQSP 
was t e s t e d  and run a t  zero  degrees  making i t  f u l l y  
o p e r a t i o n a l ,  2) h igh r e s o l u t i o n  n- s p e c t r a  were 
obta ined wi th  FWHM = 120-140 keV (see  Figs. l a , b , c ) ,  3) 
t h e  ground s t a t e  t r a n s i t i o n s  were observed f o r  t he  bes t  
"bump" candidates  a l lowing f o r  a more accu ra t e  energy 
c a l i b r a t i o n  (k60-80 keV), 4) t h e  continuum was measured 
up t o  an e x c i t a t i o n  of " 18 MeV, 5) t he  f o c a l  p lane  
e f f i c i e n c y  was measured us ing t h e  7 ~ i ( p  , T C - ) ~ B  r e a c t i o n ,  
and 6) t h e  e f f i c i e n c y  of t he  system was check us ing t h e  
9 ~ e ( p , n - ) 1 0  C g.s. t r a n s i t i o n .  The spec t roscop ic  
q u a l i t y  of t he  d a t a  is exempl i f ied  by our measurement 
of t he  7 ~ i ( p , n - ) 8 ~  r e a c t i o n  a s  shown i n  Fig. 2. Three 
l e v e l s  a r e  known i n  8 ~ ;  t he se  a r e  2+(g.s. ), l'(0.78 
MeV) and 3+(2.36 MeV). The widths of t he  1+ and 3' 
s t a t e s  were measured previous ly  t o  be 40+10 kev9 and 
390240 kevlO,  r e spec t ive ly .  The 1+ l e v e l  width was 
measured i n  t he  6 ~ i ( 3 ~ e , n ) 8 ~  r e a c t i o n  and t h e  3' l e v e l  
width i n  t he  ~ O B ( ~ , ~ ) ~ B  reac t ion .  I n  t he  p re sen t  s tudy 
we have measured t h e  1+ and 3+ l e v e l  widths t o  be 
26+5 keV and 370226 keV, r e s p e c t i v e l y ,  by comparison of 
t hese  l e v e l  widths  w i th  t he  ground s t a t e  l e v e l  width 
whose r e s o l u t i o n  was 123?19 keV. 
"present  address  : Physics Divis ion ,  Argonne Nat ional  
Lab, 9700 S. Cass Avenue, Argonne, IL 60439 
t ~ r e s e n t  address  : Medical Research Center,  
Brookhaven Nat ional  Lab, Upton, L.I. NY 11973 
§present  address  : TRIUMF, Vancouver, B. C. V6T 2A3 
Canada 
1) T. Throwe, J. Kehayias, K. Bent, W. Jacobs,  M. 
Green, K. P i t t s ,  S. Vigdor, and T. Ward, Phys. Kev. 
L e t t .  49, 1314 (1982); Nucl. Phys. Q,, 61c 
(1983). 
Exc (MeV) 
Figure  2. Pion Spectrum of t he  7 ~ i ( p , n ' ) 8 ~  r e a c t i o n  
a t  Ep=191 and OCm=3.6". The l e v e l  widths of t he  
1+(0.776 MeV) and 3+(2.363 MeV) s t a t e s  were measured 
t o  be 26+5 keV and 370+_26 keV, r e spec t ive ly .  
2) J. Kehayias e t  a l . ,  (E197) June 1982. 
3)  T. Ward e t  a l . ,  (E201) June 1982. 
4) T. Throwe e t  a l . ,  (E208) June 1982. 
5 )  M. D i l l i g ,  F. Soga, and J. Conte, Pion Production 
and Absorbtion i n  Nuclei - 1981, AIP Conf. Proc. 
1/79, p. 275. 
6) W. Gibbs, Pion Production and Absorbtion i n  
Nuclei- 1981. AIP Conf. Proc. #79. D. 297. 
7) F. Soga and M. D i l l i g ,  Pion Production and 
Absorbtion i n  Nuclei - 1981, A I P  Conf. Proc. #79, 
p. 289. 
8) F. Soga, e t  a l . ,  Phys. Rev. C 2, 570 (1981)- 
9) R. McGrath, e t  a l . ,  Phys. Let t .  2, 319 (1965)- 
10) R. McGrath, S. Cerny and E. Norbeck, Phys. Rev. 
Le t t .  25, 1442 (1967). 


Measurements of (p,pi ̄) Reactions Near Zero Degrees

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Measurements of (p,pi ̄) Reactions Near Zero Degrees

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