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

Bacher, A.D.

Emery, G.T.

Geesaman, D.F.

Glover, C.W.

Jones, W.P.

Lindgren, R.A.

Nann, H.

Olmer, C.

Segel, R.E.

van der Werf, S.Y.

Zeidman, B.

English

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FRAGMENTATION OF HIGH-SPIN PARTICLE-HOLE STATES IN 2 6 ~ g  
D.F. Geesaman and B. Zeidman 
Argonne National Laboratory, Argonne, Illinois 60439 
C. Olmer, A.D. Bacher, G.T. Emery, C.W. Glover, H. Nann and W.P. Jones 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
S .Y. van der Werf 
Kernfysisch Versneller Institut, Groningen, The Netherlands 
R.E. Segel 
Northwestern University, Evanston, Illinois 60204 
R .A. Lindgren 
University of Massachusetts, Amherst, Mass. 01003 
I A considerable body of information is now being final class, mesonic renormalizations of the spin ! obtained on the excitation of spin-flip degrees of current have been considered, l1 and, for isovector 
I freedom in medium-energy inelastic scattering and transitions, the explicit introduction of delta-hole I 
I charge-exchange reactions. The isovector spin-flip states. 12, l3 Delta-hole states are thought to affect 
I 
I strength seems to be systematically quenched,1 but low-multipolarity modes much more than those of high 
i ! there is no general agreement on the quenching multipolarity .I4 
mechanism, and it may be that various mechanisms 
contribute differently for transitions of high and low 
multipolarity, or in different regions of the periodic 
table. There are less data on isoscalar spin-flip 
excitations, but results from both (p,p') and ( x , n t )  
work indicate an even larger quenching for at least 
some of these transitions. 2'4 
I Several theoretical explanations have been offered 
for this reduction in spin-flip strength. These 
explanations divide into three general classes; valence 
shell fragmentation, renormalization by admixture of 
higher energy particle-hole configurations (e.g. 3 d w  
admixtures into 1 %.I states), and the introduction of 
non-nucleonic degrees of freedom. Among the kinds of 
valence-shell effects considered have been 
particle-vibration coupling,5 larger-basis shell model 
calculations, and the effects of deformation. 98 
Admixtures of 3 60 and 5 .hw configurations have been 
considered for both heavy9 and lightlo nuclei. In the 
The aim of this experiment was to try to learn 
something about the contributions of these mechanisms 
by studying the quenching as a function of 
single-particle occupation probability, ground-state 
isospin, and multipolarity. The sd-shell seemed to 
provide good targets for the work. In addition to the 
"stretched" 6'  state^,^'^ several 1+ states are known 
from previous work. l5 
Measurements of differential cross section and 
analyzing power have been carried out for 2 6 ~ g  at 
135-MeV bombarding energy. Data were taken in 5' steps 
from 10" to 60° over an excitation-energy range of 0 to 
20 MeV. Based on the data shown in Figs. 1 and 2, five 
6' states have been identified, at excitation energies 
of 9.18 + 0.03, 11.98 + 0.03, 12.48 + 0.03, 12.85 + 
0.03, and 18.05 + 0.05 MeV. The 18.05-MeV level is 
believed to be a T=2 state. 
DWIA calculations are being performed to extract 
transition strengths for these states. With these data 
and that previously p~blished~,~ on 2 4 ~ g  and 28~i, we 
will be able to study the systematics of quenching of 
spin-f lip strength under controlled changes in nuclear 
structure. This should provide additional insight into 
the underlying quenching mechanism. 
I- I l l  
Figure 1. Angular distributions for 5 states identified Figure 2. Analyzing powers for the 6' states observed 
--
as 6-  states in the 26~g(p,p') reaction. in the 26~g(p, p' ) reaction. 
1 )  E.g., F. Pe t rov i ch  and W.G. Love, Nucl. Phys. M54 ,  9) I. Hamamoto, J. L i c h t e n s t a d t ,  and G.F. Ber tsch ,  
1 499c (1981). Phys. L e t t .  z, 213 (1980). 
2)  G.S. Adams, A.D. Bacher, G.T. Emery, W.P. Jones ,  
R.T. Kouzes, D.W. M i l l e r ,  A. P i ck l e s imer ,  and G.E. 
Walker, Phys. Rev. L e t t .  38, 1387 (1977). 
3 )  C. Olmer, A.D. Bacher, G.T. Emery, W.P. Jones ,  D.W. 
M i l l e r ,  H. Nann, P. Schwandt, S. Yen, T.E. Drake, 
and R.J. Sobie,  Phys. Rev. C 2 361 (1984). 
4 )  C. Olmer, B. Zeidman, D.F. Geesaman, T.-S.H. Lee, 
R.E. Segel ,  L.W. Swenson, R.L. Boudrie,  G.S. 
Blanpied ,  H.A. Thiessen ,  C.L. Morris ,  and R.E. 
Anderson, Phys. Rev. L e t t .  43, 612 (1979). 
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(1980). 
6 )  A. Amusa and R.D. Lawson, Phys. Rev. L e t t .  51, 103 
(1983). 
7 )  L. Zamick, Phys. Rev. C 2, 667 (1984). 
10) P. Blunden, B. C a s t e l ,  and H. Toki, Z. Phys. A 312, 
247 (1983). 
11 )  W. KnGpfer, M. D i l l i g  and A. R ich t e r ,  Phys. L e t t .  
95, 349 (1980). 
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# 12)  M. Er icson,  A. F igureau ,  and C. Thevenet, Phys. 
L e t t .  s, 19 (1973); M. Rho, Nucl. Phys. A231, 
493 (1974); E. Oset and M. Rho, Phys. Rev. L e t t .  
42. 47 (1979). 
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13) A. Bohr and B.R. Mottelson,  Phys. L e t t .  100B, 10 
(1981). 
14 )  F. O s t e r f e l d ,  S. Krewald, J. Speth,  and T. Suzuki,  
Phys. Rev. L e t t .  49, 11 (1982). 
15)  W.L. Bendel, L.W. Fagg, R.A. Tobin and H.F. 
Ka i se r ,  Phys. Rev. 173, 1103 (1968). 
8 )  G.T. Emery, i n  Proc. I n t e r n .  Conf. Highly Exci ted  
S t a t e s  and Nuclear S t r u c t u r e ,  Orsay, France,  1983 
( t o  be publ i shed) .  
F.W. Hersman, J. Heisenberg,  J.R. Calarco ,  and T. Mill iman 
U n i v e r s i t y  of New Hampshire, Durham, New Hampshire 03824 
A. S c o t t ,  F.T. Baker, and V. Penumetcha 
U n i v e r s i t y  of Georgia,  Athens, Georgia 30601 
W.P. Jones ,  G.T. Emery, A.D. Bacher, and C. Olmer 
I n d i a n a  Un ive r s i t y  Cyclo t ron  F a c i l i t y ,  Bloomington, I nd i ana  47405 
M.A. Grimm 
U n i v e r s i t y  of L o u i s v i l l e ,  L o u i s v i l l e ,  Kentucky 40292 
M.L. Whiten 
Armstrong S t a t e  Col lege ,  Savannah, Georgia 31406 
J.J. Kel ly  
Los Alamos Na t iona l  Labora tory ,  Los Alamos, New Mexico 87545 
S p e c t r a  of 200 MeV p o l a r i z e d  pro tons  s c a t t e r e d  3.585 MeV. Data f o r  t h e  1+ s t a t e  a t  3.486 MeV a t  8' 
from , 8 8 ~ r  were recorded a t  ang l e s  from 8' t o  44', and 9.5O were a l s o  obta ined .  These two c r o s s  s e c t i o n s  
! chosen such t h a t  s c a t t e r i n g  from t a r g e t  i m p u r i t i e s  were reduced f i r s t ,  and r epo r t ed  a t  t h e  1983 Spr ing  APS 
l e a s t  obscured phys ics  of i n t e r e s t .  These s p e c t r a  have meeting.l  
1 s i n c e  been reduced t o  c r o s s  s e c t i o n s  and ana lyz ing  Recent ly ,  e f f o r t  has  been d i r e c t e d  towards a 
powers f o r  e x c i t a t i o n  ene rg i e s  l e s s  than  4.2 MeV. The combined e l e c t r o n  s c a t t e r i n g  and p o l a r i z e d  pro ton  
I d a t a  s e t  covers  t h e  complete angu la r  range f o r  t h e  s c a t t e r i n g  a n a l y s i s  of t h e  t h r e e  lowest  l y i n g  2+ 
1 ground s t a t e ,  t he  2+ s t a t e s  a t  1.836, 3.218, and 4.035 s t a t e s .  E x i s t i n g  e l e c t r o n  s c a t t e r i n g  measurements2 
MeV, t h e  3- s t a t e  a t  2.734 MeV, and t h e  5' s t a t e  a t  performed a t  t h e  MIT-Bates l i n e a r  a c c e l e r a t o r  provide  


Fragmentation of High-spin Particle-hole States in 26-Mg

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Fragmentation of High-spin Particle-hole States in 26-Mg

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