This work was supported by the National Science Foundation Grant NSF PHY 78-22774 A02 & A03 and by Indiana Universit

Ahmad, M.

Anderson, B.D.

Baldwin, A.R.

Fazely, A.

Foster, C.C.

Madey, R.

Tandy, P.C.

Watson, J.W.

English

IUScholarWorks

1) C.D. Goodman, C.A. Gouldlng, M.B. Greenfield, J. 
Rapaport, D.E. Bainum, C.C. Foster, W.G. Love, and 
F. Petrovich, Phys. Rev. Lett. 44, 1755 (1980). 
2) K. Ikeda, S. Fujii and J.I. Fujita, Phys. Lett. 2, 
169 (1962). 
3) J.I. Fujita and K. Ikeda, Nucl. Phys. 67, 145 
(1965). 
Ex-E,,, (MeV) 
Figure 2. 115~n(p,n), 165~o(p,n), and 208~b(p,n) 
spectra obtained at elab = 0°, Ep = 160 MeV. The IAS 
peaks are positioned at Ex - EIAS = 0. 
HIGH-SPIN "STRETCHED" STATES EXCITED IN (p,n) REACTIONS 
M. Ahmad, B.D. Anderson, A.R. Baldwin, A. Fazely, R. Madey, 
P.C. Tandy, and J.W. Watson 
Kent State University, Kent, Ohio 44242 
C.C. Foster 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
The excitation of unnatural parity states of high excitations are especially interesting because of their 
angular momentum is an area of strong current strong sensitivity to the isovector-tensor part of the 
interest 1'6) in medium-energy physics. Isovector nucleon-nucleon force. In the momentum-transfer region 
between 1 and 2 fm-l, the isovector-tensor term observed the strong excitation of a 0 hw stretched 
dominates1) for unnatural parity transitions (AJ C AL). state, namely, the Jn = 7+ state at 1.096 MeV with a 
Interest has been focused7s8) on high-spin states with 
a major configuration of the "stretched" particle-hole 
type because the number of terms contributing to the 
amplitude for (p,n) reactions7) or inelastic scat- 
tering8) is severely reduced. A stretched particle- 
hole configuration is one where the particle and hole 
are both in stretched subshells (j = R + 1/2), and are 
coupled to the maximum possible angular momentum 
Rp + Rh + 1. 
Previous theoretical and experimental work on the 
excitation of particle-hole stretched states in 
inelastic scattering and (p,n) reactions involved major 
configurations with the particle in the next major 
shell above the hole; accordingly, we refer to such 
states as "1 hw" stretched states. They have odd 
parity. Lindgren et a ~ . ~ )  give a partial summary of 
this work. There is another class of unnatural parity 
stretched states that can be excited by (p,n) reactions 
on targets with N > Z. In the major configuration for 
these states, the proton particle and the neutron hole 
have the same quantum number& n, R, and j; accordingly, 
we refer to these states as "0 h w "  stretched states. 
They have even parity. Such states are known from 
low-energy work on (3~e,t) reactions where large 
2-transfers are reached easily. A 1 %o stretched state 
has a unique particle-hole configuration in a basis 
which includes 0,1, and 2 k w  excitations; a 0 h w  
stretched state has a unique particle-hole configura- 
tion in a basis which includes 0 and 1 %w excitations. 
We note that the Pauli exclusion principle prohibits 
the excitation of 0 %u stretched states by (p,n) 
reactions on self-conjugate targets or by inelastic 
scattering on any target. 
In the 48~a(p,n)48~c reaction at 160 MeV, we 
,vfel ) proton-particle neutron-hole major 
(If7/2 712 
configuration. Neutron energy and angular distribu- 
tions were measured by the time-of-flight technique 
with the beam swinger facility with two detector 
stations. We achieved an overall time resolution of 
about 0.50 ns including the beam burst width, the 
intrinsic resolution of the detectors, the energy 
spread from the 29.3 ' 0.5 mg/cm2 target thickness and 
the beam energy spread. Typical energy resolutions, 
therefore, were 450 keV in the first detector station 
at 68.0 m and 400 keV in the second detector station at 
76.3 m. 
Fig. 1 shows energy spectra for the 48~a(p,n)48~c 
reaction at laboratory scattering angles of 24.O0, 
30.5", 35.8", and 42.2". The energy scale is expressed 
in terms of the excitation energy in 48~c. In the 24" 
to 42" region, the typical momentum transfers range 
from 1.2 to 2.2 fm'l, which is the momentum transfer 
region where the tensor force is expected to excite 
high-spin stretched states. In the region of 
excitation energy between 10 and 25 MeV, where 1 %w 
stretched states with either a ( ~ g  ,vf'l )8' or 
912 712 
,vd'l )6' con£ iguration would be expected to 
('£712 512 
occur, we observed no sharp peaks in the spectra.lO) 
We set an upper limit of 60 vblsr for the excitation of 
1 %w stretched states in 48~c. Adams et a ~ . ~ )  reported 
the absence of 1 %w stretched states in the 3 2 ~  and
40~a(p,p') reactions at 135 MeV. 
The only states excited strongly in the spectra of 
Fig. 1 are the 6+ ground state and the 7+ state at 
1.096 MeV. These states are members of the low-lying 
1 particle-hole multiplet with a (nf ,vf' ) 
712 712 
configuration .9) 
We note that the 7+ (Ex = 1.096 MeV) member of the 
48 
~ a ( p , n ) ~ ~ ~ c  160 MeV 
2 1 1  , , , , , , , , , , , , , , , , , ~ I , , , ~ I , I  
24.0" 
EXCITATION ENERGY, Ex  (MeV) 
Figure 1. Neutron energy spectra at laboratory angles 
of 24.0°, 30.5", 35.8", and 42.2" for the 48~a(p,n)48~c 
reaction at 160 MeV. 
(~f712,~f;~2 ) multiplet is a 0 k w  stretched state. 
figure 2 shows the angular distribution of the cross 
48~a(p,n)48sc (7:1.096 MeV) 
ANGLE, ecm(DEGREES) 
;;gure 2.b Angular distribution of the 
Ca(p,n) 8sc(7+, 1.096 MeV) reaction at 160 MeV. 
Shown also are DWIA calculations made with the computer 
code DWBA70 with 40Ca optical model parameters and 
lf712 harmonic oscillator wave-functions. The dotted, 
dashed, and dash-dotted curves represent contributions 
from the isovector central (C), tensor (T), and 
spin-orbit (L'S) terms, respectively, of the effective 
interaction. The solid curve represents the coherent 
sum of these three isovector terms. 
section for the 7+(~,=1.096 MeV) state. Also shown is a 
DWIA calculation made with the computer code DWBA~O~O) to the 7+ stretched state. 
with the effective interaction of ~ove, l) 40 ~a optical- The normalization factor of 0.50 is significantly 
model parameters from Schwandt et a1. ,I1) and larger than those reported by Lindgren et a ~ . ~ )  for 
If harmonic-oscillator wave functions. The DWIA (p,p') transitions to states which are strictly of the 
712 
calculation was multiplied by 0.50. Also shown are the stretched 1 %a type except for the 14-state of 208~b. 
results of calculations with each one of the three Although comparison of our data for the 7+ 0 %LI.I 
isovector terms (viz., central, spin-orbit, and tensor) stretched state with inelastic electron scattering data 
. 
of the effective interaction which can contribute to is not possible because 0 %w stretched states cannot be 
unnatural parity transitions. From Fig. 2, it is clear excited in inelastic scattering, the relatively large 
that the isovector-tensor term in the effective normalization factor for the 7+ state is encouraging 
interaction is primarily responsible for the transition since 4 8 ~ a  is known to be a reasonably good shell-model 
5 4 
nucleus. 
In conclusion, we observed strong excitation of a 
0 h w  stretched state in the 48~a(p,n)48~c reaction 
at 160 MeV, namely, the 7+ state at 1.096 MeV, with a 
,vf-l ) major con£ iguration; however, we found ("712 712 
no evidence for 1 h w  stretched states based on 
,vf'l )8' or (nf ,vd'l )6' configurations. The 
(1g9/2 712 712 512 
excitation of stretched states of the 0 %w type should 
prove to be a useful tool for studying the isovector- 
tensor term of the effective nucleon-nucleon inter- 
action. 
1) W.G. Love in The (p,n) Reaction and the Nucleon- 
Nucleon Force, ed. by C.D. Goodman et al. (Plenum, 
New York, 1980), p. 23. 
2) R.A. Lindgren, W.J. Gerace, A.D. Bacher, W.G. Love, 
and F. Petrovich, Phys. Rev. Lett. 42, 1524 (1979). 
3) R.S. Henderson, B.M. Spicer, I.D. Svalbe, V.C. 
Officer, G.G. Shute, D.W. Devins, D.L. Friesel, 
W.P. Jones, and A.C. Attard, Aust. J. Phys. 32, 411 
(1979). 
4) G.S. Adams, A.D. Bacher, G.T. Emery, W.P. Jones, 
R.T. Kouzes, D.W. Miller, A. Picklesimer, and G.E. 
Walker, Phys. Rev. Lett. 2, 1387 (1977). 
5 )  A.D. Bacher, G.T. Emery, W.P. Jones, D.W. Miller, 
G.S. Adams, F. Petrovich, and W.G. Love, Bull. Am. 
Phys. Soc. 32, 945 (1978); and to be published. 
6) B.D. Anderson, M. Ahmad, A.R. Baldwin, A. Fazely, 
R. Madey, J.W.-Watson, and C. C. Foster, Bull. Am. 
Phys. Soc. 2, 729 (1980). 
7) P.J. Moffa and G.E. Walker, Nucl. Phys. A=, 140 
(1974). 
8) T.W. Donnelly and G.Ei Walker, Ann. Phys. (N.Y.) 
60, 217 (1970). 
- 
9) C. Gaarde, J.S. Larsen, M.N. Harakeh, S.Y. van der 
Werf, M. Igarashi, and A. Muller-Arnke, Nucl. Phys. 
A334, 248 (1980). 
10) J. Raynal and R. Schaeffer, Computer code DWBA70. 
11) P. Schwandt, A. Nadasen, P.P. Singh, M.D. 
Kaitchuck, W.W. Jacobs, J. Meek, A.D. Bacher, and 
P.T. Debevec, IUCF Technical and Scientific Report 
for Feb. 1, 1977 to Jan. 31, 1978, p. 79. 
MEASUREMENT OF THE 1 / ~  DEPENDENCE OF THE 7~i(p,n)7~e 
TOTAL REACTION CROSS SECTION 
T.E. Ward, C.C. Foster, and G.E. Walker 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
J. Rapaport 
Ohio University, Athens, Ohio 43701 
The excitation function, a(E) , of the 7~i(p,n)7~e 
reaction was measured in the intermediate energy range 
of 60-199 MeV using activation techniques and y-ray 
spectroscopy. This method has been used to measure the 
total cross section at energies of 25-44 MeV by Shery 
et a1.l) and at 120 MeV by Goulding et a ~ . ~ )  to
calibrate large volume neutron detectors. Details of 
the experimental procedure can be found in the IUCF 
1979 annual report.3) A summary of the results is given 
in Table 1. The total errors estimated for these 
measurements range from 8 to 14%. 
The measured1s4) excitation function, a(E), of 
the 7~i(p,n)7~e total reaction cross ssection is 
observed to vary inversely with the incident proton 
energy, E, from 25 to 200 MeV. A theoretical analysis, 
assuming the PWIA with an energy-independent, 
very-short-range interaction, using harmonic oscillator 
wave functions and neglecting exchange effects, yields 
a 1 1 ~  dependence for the summed inelastic scattering 
differential cross section to a particular state. This 
result implies that a(E) = 725.3 (11E) - 0.295 with a 
in millibarns, E in MeV and a determinant coefficient 
of 0.998. 
Further, it implies that the interaction strength 


High-Spin "Stretched" States Excited in (p,n) Reactions

https://scholarworks.iu.edu/dspace/bitstream/2022/2803/1/iucf_1980_52-55.pdf

High-Spin "Stretched" States Excited in (p,n) Reactions

Abstract

Similar works

Full text

Available Versions

IUScholarWorks