Supported by the National Science Foundation and Indiana Universit

Daehnick, W.W.

Easwar, N.

Jones, W.P.

Maher, J.V.

Segel, R.E.

Singh, P.P.

Soga, F.

English

IUScholarWorks

with  only L=O and 1 cont r ibut ions .  The behavior of 
the background subt rac ted  under t he  GR is  shown i n  
Fig. 3. Also shown is the  p l o t  of t h e  analyzing power 
A(8) of t he  continuum a t  Ex Q, 21-25 MeV a s  a funct ion  
of 8. It is found t h a t  A(8) i n  both cases is near ly  
a constant  and has an average value of Q, 0.06. The 
present  work ind i ca t e s  t h a t  simultaneous measurement 
of A(8) and a(€) ) ,  bes ides  confirming the  GQR and GMR 
s t r eng ths  obtained from other  measurements, can a l s o  
put  much more s t r i n g e n t  l i m i t s  on t he  amount of L=4 
s t r e n g t h  al lowable i n  t h i s  region. 
A more d e t a i l e d  ana lys i s  of t he  da t a  and compari- 
sons wi th  DWBA ca l cu l a t i ons  a r e  i n  progress.  
1 )  F.E. Bertrand,  Annu. Rev. Nucl. Sc i .  26, 457 (1976). 
2) Proc. Giant Multipole Resonance Topical  Conference, 
Oak Ridge, TN (1979). 
3) P.P. Singh, e t  a l . ,  IUCF Annual Report, 1979. 
92 
Continuum Zr(F.p', I 
Under the 104 MeV 
GR Region 
- 4 
f A A Continuum Above the 
2 4 r GR Region r 1 ,(21- 25 MeV) 
4 
Fi-qure 3. The behavior of the background subtracted 
from under the GR and the cuntinuwn above the GR a t  
Ex = 21-25 MeV. 
SEARCH FOR a-CLUSTER STATES I N  THE GIANT RESONANCE REGION 
W.W. Daehnick, N. Easwar, and J .V .  Maher 
University o f  Pittsburgh, Pittsburgh, Pennsylvania 15260 
R.E. Segel 
Northwestern University, Evanston, IZZinois 60204 
W.P. Jones,  F. Soga and P.P. Singh 
Indiana University CycZotron Fac& Zity, BZoom&ngton, Indiana 4 7405 
We have measured ( 6 ~ i , d )  spec t r a  a t  10' f o r  t h e  r eac t ion  and those  reported2 t o  be  i s o s c a l a r  g i an t  
i n t e r a c t i o n  of 90 MeV 6 ~ i  with t a r g e t s  of 12c, 160, quadrupole resonance fragments i n  a 2 8 ~ i ( a  , 1 ) 2 8 ~ i  
2 4 ~ g , 5 4 ~ e ,  9 0 ~ r ,  and l g 6 p t .  Spectra from t h e  12c and study. Several  s t a t e s  i n  t he  e x c i t a t i o n  energy 
160 (mylar) t a r g e t s  exh ib i t  t he  same s e l e c t i v i t y  region 8-10 MeV a r e  weakly populated i n  58~ i ,  but no 
reported1 f o r  t h i s  r eac t ion  with lower energy 6 ~ i ,  s t r u c t u r e  is observed above t h e  slowly-rising breakup 
but  s t a t e s  a t  high e x c i t a t i o n  energy a r e  l e s s  obscured background i n  t h e  region of t he  g i an t  quadrupole re-  
by the  breakup background a t  t h i s  h igher  energy. The sonance. No t r a n s i t i o n s  populat ing d i s c r e t e  s t a t e s  
breakup background on 24Mg i s  a l s o  s u f f i c i e n t l y  weak a r e  observed f o r  t h e  heavier  t a rge t s .  Future work 
t h a t  many t r a n s i t i o n s  t o  h ighly  exc i t ed  s t a t e s  i n  2 8 ~ i  w i l l  concent ra te  on s tudying  t h e  g i an t  quadrupole re-  
s tand  ou t  c l e a r l y ;  t h e r e  is some c o r r e l a t i o n  between sonance of 28~ i .  
the  e x c i t a t i o n  energies  of s t a t e s  populated i n  t h i s  
1) A. A. Ogloblin, Proceedings of the International 1969) , p. 231 
Conference on Nuclear Reactions Induced by Heavy 
Ions, eds. R. Boch and W.R. Hering, (Heidelberg, 2) F.E. Bertrand et al., Phys. Rev. Lett. 40, 635 (1978). 
DECAY MODES OF ISOSCALAR GIANT RESONANCES THROUGH (a,a' y) COINCIDENCE STUDIES 
J. Wiggins, P.P. Singh, S. Kailas, M. Saber, and T. Sjoreen 
Indiana University CycZotron FadZity ,  BZoodngton, IN 4 7405 
A. Drentje, M. Harakeh, and A. van der Woude 
Kernfysisch VersneZZer Inst i tuut ,  Groningen, The N e t h e r h d s  
Using the 150 MeV alpha beam from IUCF the par- column of Ta6le I. Also presented is continuum be- 
ticle decay channels of isoscalar giant resonances in havior for initial sharp cut-off distributions with 
6 2 ~ i  are being investigated by observing the discreet maximum spins 3 and 7 K (the maximum spin transfer 
gama transitions of residual nuclei in coincidence from semi-classical momentum transfer at radius R = 
with scattered alpha particles. The particles were 1.2 A-I~ 3, . We conclude that it would be difficult to 
identified with a solid state silicon telescope at a extract the resonance admixture in the observed 
laboratory angle of 15.8', and gamma-rays were detected pattern. Also, angular correlations with the alpha 
using three Ge(Li) detectors located at 40°, 94', and particle are not strong. This may be due to the cou- 
150' with respect to the beam. Isoscalar resonance- pling of the average d-wave neutron and at least one 
like structure at 65 MeV is observed in alpha- p-wave gamma-ray to this initial orientation. 
gamma coincidence spectra and the gamma-producing Figure 1 presents the side feeding strength with 
decays proceed predominantly through one neutron excitation in 6 1 ~ i  for spins 112, 312, 512, and 712 
emission. populations. Ignoring nuclear structure, the dipole 
In the statistical model of decay calculated by transitions from 4 MeV excitation would go as (4-E) 
the computer code MB 11l from an initial spin of 21i 
Table I. Percentage sLdefeeding strength i n  'l~i from 
in 6 2 ~ i  at 16.4 MeV excitation, the particle decay decay of 11.2 to 23.8 MeV excitation of 6 2 ~ i  
distribution is predicted to be 92% neutron, 7% proton, 
MB I1 CALCULATION 
and 1% alpha evaporation. Reasonable sharp cut-off Spin in Sharp cut-of f approx. Initial 
6 1 ~ i  Jmax=7 Jmax=3 512 Measurement 
initial distributions vary these predictions by less 
than one percent. The evaporation neutrons are dis- 112 1.5 5 7 12 (1) 
tributed as approximately 16% s-wave, 40% p-wave, 34% 312 5 17 2 2 21 (3) 
d-wave, 8% f-wave, and 1% g-wave, and leave the resid- 512 9 2 5 31 26 (1) 
ual 61~i-nucleus in a broad band with an upper limit 712 14 23 25 24 (2) 
around 6.5 MeV excitation and with a wide spin dis- 9 / 2 &  71 2 1 16 17 (2) 
higher 
tribution centered around 2-3 Ii. Purely statistical 
dipole transitions directly to the low-lying states 
Errors include only statistics and do not reflect the 
without regard to nuclear structure yields the inten- errors introduced from estimations of ground state, 
first excited state, or 912 and higher strengths from 
sity patterns in spin as indicated in the fourth systematics of the data. 


Search for a-Cluster States in the Giant Resonance Region

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Search for a-Cluster States in the Giant Resonance Region

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