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

Anderson, B.D.

Baldwin, A.R.

Foster, C.C.

Lebo, C.

Madey, R.

Watson, J.W.

English

IUScholarWorks

HIGH-SPIN STATES EXCITED VIA (p,n) REACTIONS 
B.D. Anderson, C. Lebo, J.W. Watson, A.R. Baldwin, and R. Madey 
Kent S t a t e  Univers i ty ,  Kent, Ohio 44242 
C.C. Foster  
Indiana Univers i ty  Cyclotron F a c i l i t y ,  Bloomington, Indiana 47405 
The (p , n)  charge-exchange reac t  ion  o f f e r s  two nuc le i  with A > 28. The neutron exci ta t ion-energy 
important d i f f e rences  f o r  the  study of high-spin s p e c t r a  f o r  the  4 0 ~ a ( p , n ) 4 0 ~ c  reac t ion  a r e  presented i n  
s t a t e s  i n  comparison with i n e l a s t i c  proton o r  e l e c t r o n  Fig. 1. The large-angle spec t ra  a r e  seen t o  be 
s c a t t e r i n g .  F i r s t ,  t he  (p,n) r eac t ion  on 
sel f -conjugate  nuc le i  necessa r i ly  populates only T=1 
i s o s p i n  s t a t e s ,  whereas ( p , p l )  and ( e , e f )  may e x c i t e  
both T=O and T=1 s t a t e s .  This s e l e c t i v i t y  of the  (p,n) 
r eac t ion  can be used t o  i d e n t i f y  fragmented o r  broad 
T=l s t r e n g t h  with no i n t e r f e r i n g  T=O background. 
Second, the  (p,n) r e a c t i o n  on nuc le i  with a neutron 
40 4 0 ~ a ( p , n )  sc 1 2. 
133.5 MeV 
- 
excess can e x c i t e  pa r t i c l e -ho le  s t a t e s  where t h e  I 
p a r t i c l e  and hole  have the  same R and j quantum 
numbers. I n e l a s t i c  s c a t t e r i n g  reac t ions  cannot e x c i t e  
such s t a t e s  because the  Pau l i  p r i n c i p l e  fo rb ids  two 
protons o r  two neutrons i n  the  same o r b i t a l  from 
occupying the  same quantum s t a t e .  I f  the  p a r t i c l e  and 
hole  exc i t ed  i n  the  (p,n) r e a c t i o n  have j = R + 112 and 
t h e  j's a r e  coupled t o  the  maximum possible  angular 
momentum, the  s t a t e  is  of a "s t re tched" conf igurat ion 
wi th  (usual ly)  an unique s t r u c t u r e  wi thin  2 ria of 
exc i t a t ion .  Because these  0 liw s t r e t ched  s t a t e s  
involve p a r t i c l e  and hole  l e v e l s  a t  o r  near the  Fermi 
su r face ,  they a r e  usua l ly  not  fragmented. This  is i n  
c o n t r a s t  t o  the  general  s i t u a t i o n  f o r  a 1 & type of 
s t r e t c h e d  s t a t e ,  e s p e c i a l l y  i n  medium- o r  heavy-mass 
nucle i .  Recently we used the  (p,n) r eac t ion  t o  take 
advantage of both of these  oppor tun i t i e s  provided by 
t h e  (p,n) react ion.  0.~1 0 2 0 10 0 
The 4 0 ~ a ( p , n ) 4 0 ~ c  r e a c t i o n  was s tudied a t  135 MeV 
Ex (MeV) 
t o  search f o r  the  (f d-1 ), 6 's t re tched s t a t e .  
712' 512 
This 1 hw s t r e t c h e d  s t a t e  has been observed i n  A = 24 pi re I. Excitation-energy spectra for the 
and 28 nuc le i ,  but  was s u r p r i s i n g l y  "missing" i n  4 0 ~ a ( p , n ) 4 0 ~ c  reac t ion  a t  133.5 MeV. 
dominated by a broad complex of strength around Ex = 7 
MeV. The angular distribution for this complex is 
consistent with that expected (from DWIA calculations) 
for a transition to a 6- state. Furthermore, the 
excitation-energy and structure observed in this 
complex is consistent with that observed for the d5/2 
hole strength in 3 9 ~ a  observed directly in 40~a(p,pn) 
neutron knockout4 and in 40~a(p, d) neutron pickup. 
This observation of the T=l, 6' particle-hole strength 
is a good example of the advantage provided by the 
(p,n) reaction on a self-conjugate target. The T=l 
state observed here is obscured by the T-0 background 
in (p,p ' ) measurements. 
In our most recent experimental run to study 
stretched states, we studied the (p,n) reaction on the 
medium-mass and heavy-mass nuclei 58~i, 88~r, and 
208~b. We did not observe any clear indication of 
concentrated 1 Ew type excitations in these 
reactions, but did observe some highly-fragmented 1 
strength in the 58~i(p,n)58~u reaction [consistent 
with (e,el) observations6 of M8 strength in 58~i]; 
however, we observed strong 0 l'iw stretched-state 
excitations in the 88~r(p,n)88~ and 208~b(p ,n)208~i 
reactions. Large-angle excitation-energy spectra are 
shown for these targets in Fig. 2. We could describe 
these results briefly by saying that, in general, we 
see strong 0 h w  type transitions for medium- and 
heavy-weight targets, but find it difficult to identify 
1 r iw  strength in these nuclei. The reasons for these 
results appear straightforward. The 0 6 transitions 
generally are observed at low excitation energies and 
involve particle and hole states at or near the Fermi 
level in these nuclei; consequently, these 0 !Tw 
transitions generally are observed at low excitation 
energies and involve particle and hole states at or 
near the Fermi level in these nuclei; consequently, 
134.3 MeV 
0 1 ~ " " " ' " " ' " " "  12 8 4  0  
EXCITATION ENERGY(MeV1 
Figure 2. Large-angle excitation-energy spectra for 
the (p,n) reaction on 58~i, 88~r, and 208~b. 
these 0 75,) states are concentrated into single, sharp 
states seen in the (p,n) reaction. The 1 ?iw 
transitions, on the other hand, are observed at higher 
excitation energies and involve hole and/or particle 
states far from the Fermi level. These particle and 
hole levels are generally broad and fragmented 
resulting in broad and fragmented 1 5 w  strength. 
The 0 Rw stretched-state excitations seen in these 
various reactions are important for understanding the 
structure of these nuclei. Because 0 Tiw stretched 
transitions are more often concentrated into a single 
state, the strengths observed are primarily a measure 
of the target wavefunction, whereas the 1 liw strength 
is often highly fragmented and provides a formidable 
experimental task in simply identifying all of the 
stretched-configuration strength. Thus, a logical way 
to proceed in studying stretched particle-hole strength 
for a specific nucleus is to first measure and 
understand the 0 Iiw transition, and then to proceed to 
sea rch  f o r  t he  (usua l ly )  fragmented 1 lh s t r e t c h e d  3) G.S. Adams, A.D. Bacher, G.T. Emery, W.P. Jones,  
R. J. Kouzes, D.W. Mi l l e r ,  A. Pickles imer ,  and G.E. 
s t r eng th .  Walker, IUCF Progress Report ,  January 1977; and 
G.S. Adams, Indiana Univers i ty  Ph.D. d i s s e r t a t i o n  
(1977). 
1 )  G.S. Adams, A.D. Bacher, G.T. Emery, W. P. Jones,  
R.T. Kouzes, D.W. Mi l l e r ,  A. Picklesimer,  and G.E. 4) J.W. Watson, M. Ahmad, D.W. Devins, B.S. Flanders ,  
Walker, Phys. Rev. Let t .  38, 1387 (1977). D.L. F r i e s e l ,  N.S. Chant, P.G. Roos, and 
J. Waste l l ,  Phys. Rev. C 26, 961 (1982). 
2) S. Yen, R.J. Sobie, T.E. Drake, A.D. Bacher, G.T. 
Emery, W.P. Jones,  D.W. Mi l l e r ,  C. Olmer, P. 5) J. Kallne and B. Fagerstrom, p. 369 i n  High-Energy 
Schwandt, W.G. Love, and F. Pet rovich,  Phys. Let t .  Physics and Nuclear S t ruc tu re ,  ed. by G. T i b e l l  
105B, 421 (1981). (North-Holland, Amsterdam, 1974). 
6) R.A. Lindgren, C.F. Williamson, and S. Kowalski, 
Phys. Rev. Let t .  40, 504 (1978). 
ANALYZING-POWER MEASUREMENTS FOR (p ,n)  REACTIONS 
R. Madey, A. Fazely,  B.D. Anderson, A.R. Baldwin, A.M. Kalenda, C. Lebo, R.J. McCarthy, 
P.C. Tandy, and J.W. Watson 
Kent S t a t e  Univers i ty ,  Kent, Ohio 44242 
W. Ber tozzi ,  T. But i ,  M. Finn, J. Kelly,  M.A. Kovash, and B. Pugh 
Massachusetts I n s t i t u t e  of Technology, Cambridge, Massachusetts 02139 
C.C. Fos te r  
Indiana Univers i ty  Cyclotron F a c i l i t y ,  Bloomington, Indiana 47405 
We measured the  analyzing power1 f o r  t he  t h e  d i f f e r e n t i a l  c ross  s e c t i o n  f o r  t h e  same r e a c t i o n  a t  
160(p,n) 16~(4' ,  6.37 MeV) r e a c t i o n  a t  134.0 MeV and 135.2 MeV. Work is  s t i l l  i n  progress  on t h e  comparison 
t h e  d i f f e r e n t i a l  c r o s s  s e c t i o n  f o r  t he  same r e a c t i o n  a t  of our r e s u l t s  wi th  s i m i l a r  measurements of Yen e t  a l e 2  
3 
135.2 MeV. The shape of the  c ross  s e c t i o n  f o r  t he  of t he  analog r e a c t i o n  2 8 ~ i ( p , p  ' ) 2 8 ~ i ( 6 - ,  T=l, 
t r a n s i t i o n  t o  t h i s  unna tu ra l  p a r i t y  s t r e t c h e d  s t a t e  is 14.35 MeV). 
descr ibed we l l  by a distorted-wave The above s t u d i e s  r ep resen t  a po r t ion  of the  
impulse-approximation c a l c u l a t i o n  us ing a doc to ra l  d i s s e r t a t i o n  of A. ~ a z e l ~ . ~  D r .  Fazely 
(mi  , vp-l ) conf igu ra t ion  and the  e f f e c t i v e  received h i s  Ph.D. degree i n  August 1982. 
512 3 / 2 4 -  
i n t e r a c t i o n  der ived by Love and Franey from 
1)  R. Madey, A. Fazely,  B.D. Anderson, A.R. Baldwin, 
nucleon-nucleon phase s h i f t s .  The analyzing power from A.M. Kalenda, R.J. McCarthy, P.C. Tandy, J.W. 
Watson, W. Be r tozz i ,  T. But i ,  M. Finn, M. Kovash, B. 
t h i s  c a l c u l a t i o n  reproduces a l l  of t he  q u a l i t a t i v e  Pugh, and C.C. Fos te r ,  Phys. Rev. C 25, 1715 (1982). 
f e a t u r e s  of t he  d a t a  and suppor ts  t he  use of t he  2) S. Yen, R.J. Sobie, T.E. Drake, A.D. Bacher, G.T. 
Emery, W.P. Jones,  D.W. Mi l l e r ,  C. Olmer, P. 
impulse approximation a s  an e x c e l l e n t  s t a r t i n g  po in t  Schwandt, W.G. Love, and F. Pet rovich,  Phys. Let t .  
105B, 421 (1981). 
-
f o r  desc r ib ing  t h e  r e a c t i o n  mechanism. 
3) A. Fazely,  Ph.D. d i s s e r t a t i o n ,  Kent S t a t e  
We measured the  analyzing power f o r  t he  Univers i ty ,  1982. 
28~i(p ,n)28~(6 ' ,4 .95 MeV) r e a c t i o n  a t  133.5 MeV and 


High-Spin States Excited Via (p,n) Reactions

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High-Spin States Excited Via (p,n) Reactions

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