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

Anderson, B.D.

Baldwin, A.R.

Brown, B.A.

Elaasar, M.

Foster, C.C.

Jacobs, W.W.

Madey, R.

Manley, D.M.

Mostajaboddavati, M.

Tamimi, N.

Watson, J.W.

Zhang, W.M.

English

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HIGH-SPIN STRETCHED STATES IN NUCLEI EXCITED VIA (p,n) REACTIONS 
B.D. Anderson, A.R. Baldwin, M. Elaasar, R. Madey, D.M. Manley, 
M. Mostajaboddavati, N. Tamimi, J.W. Watson, and W.M. Zhang 
Kent State University, Kent, Ohio 44242 
C.C. Foster and W.W. Jacobs 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
B.A. Brown 
Michigan State University, East Lansing, Michigan 48824 
The (p,n) reaction provides unique information in 
the study of isovector particle-hole states in nuclei. 
We performed new measurements in October 1986 to 
continue our (p,n) studies of high-spin stretched state 
excitations. The targets studied were 20~e, 24~g, 
45~c, 1 4 4 ~ ~ ,  and 208~b. The measurements were 
performed with the IUCF neutron time-of-flight 
beam-swinger facility at an incident beam energy of 135 
MeV. Large-volume neutron detectors were placed in 
detector stations (or huts) at 0°, 24 O ,  and 45" with 
respect to the undeflected beam direction; the flight 3 
paths were 133.6, 131.2, and 81.4 m respectively. The 
overall energy resolution was about 300 keV in the 
first two huts and about 400 keV in the third hut. 
The (p,n) reaction on the self-conjugate nuclei 
*ONe and 24~g provides an umambiguous mapping of the 
isovector strength, including the excitation of both 
the "0 dw", 5+ and the "1 ma", 6- strength. A time-of- 
flight spectrum for the 24~g(p,n)24~1 reaction at 45' CHANNEL NUMBER 
is shown in the top panel of Fig. 1. The analog of the 
Figure 1. Time-of-flight spectra from the (p,n) 
known T=l, 6- state (at Ex = 15.1 MeV in 24~g) is seen reaction at 135 MeV. 
clearly, as well as a likely candidate for the [(d512), 
(d512)-l]5+ state at lower excitation energy. The The time-of-flight spectrum for the 
fragmentation of the T=l, 6' strength observed here 144~m(p,n)144~u reaction at 37.5" is shown in the 
will be extracted and compared with that observed in middle panel of Fig. 1. A likely candidate for the 
(p,pT) and (e,et) studies.l~~ The excitation of the [(hllI2), (hllI2)-']11+, "0 A" stretched state is 
"0 Aw" 5+ state, which is not possible in (p,pl) or seen. It is interesting that the 144~m(p,~-) reaction 
(e,el) inelastic-scattering studies, will contribute does not seem to show a strong excitation of the 
additional information on the neutron and proton 
occupancies in the d512 orbital. 
expected 3112- stretched state formed from a 2p-lh 
con£ iguration in the hi112 orbital. While additional 
spectral analysis may clarify the situation, this 
result is somewhat surprising since similar stretched 
states are observed to be strongly excited with the 
(p,nw) reaction for targets near (high-spin) neutron 
subshell closure throughout the periodic table. The 
analysis of the strength observed in the (p,n) 
excitation of the 11+ state will provide additional 
information on the fragmentation of the h11/2 orbital. 
In an earlier experimental run, we studied the 
208~b(p,n)208~i reaction. unfortunately, the energy 
resolution in that run was only about 800 keV at the 
larger angles. We observed a strong concentration of 
strength near 3 MeV of excitation with an angular 
distribution consistent with a transition to the 
[(I~~/~), (i13/2)-1]13+ '*o Awl* stretched state.4 The 
DWIA normalization factor required for this state is 
-0.9; which is 50% larger than that required for any 
other "0 d w "  stretched-state excitation observed thus 
far. Either this case is anomalously high, or the peak 
observed is actually an unresolved complex of states. 
In the bottom panel of Fig. 1, we show a time-of-flight 
spectrum from our recent experimental run for a 208~b 
target at 37.5'; the energy resolution was about 400 
keV. The spectrum shows two peaks separated by about 
800 keV. The larger peak has -213 of the total 
observed strength and, if we assume that it is the 13+ 
state, then the amount of "0&" stretched-state 
strength for this case will be reduced to an amount 
consistent with that observed in other nuclei. 
The measurements of this recent experimental run 
are now being analyzed more completely. 
1) G.S. Adams et al., Phys. Rev. Lett. 38, 1387 
(1977). 
2) H. Zarek et al., Phys. Rev. Lett. 38, 750 (1977). 
3) W.W. Jacobs et al., IUCF Scientific and Technical 
Report, p. 58 (1984); to be published. 
4) B.D. Anderson et al., Phys. Rev. Lett. 52, 1872 
(1984 ) . 


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

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

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