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

Bacher, A.D.

Devins, D.W.

Emery, G.T.

Friesel, D.L.

Jones, W.P.

Nann, H.

Olmer, C.

English

IUScholarWorks

Figure 4. Data and PWIA predictions with L-0 and La2 
as a function of transferred momentum. In the PWIA 
calculation, the free cross section was assumed to be 
constant . 
Figure 3. Pole graph re resenting the 10~(a,6~ia)a E quasifree scattering of Li + a. 
SEARCH FOR 3p-3h STATES IN THE A116 SYSTEM 
H. Nann, A.D. Bacher, D.W. Devins, G.T. Emery, D.L. Friesel, W.P. Jones, 
and C. Olmer 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
Recently there has been considerable interest, 
both experimentally and theoretically, in the location 
of three particle-three hole (3p-3h) states in the A-16 
system. The most direct evidence that a given state 
has a predominant 3p-3h configuration comes from 
three-nucleon transfer data where this state is 
strongly populated. In addition such states are only 
weakly excited in simpler reactions involving the 
transfer of one or two nucleons. 
We have embarked on a program to search for 3p-3h 
states in 16N-160 with the (6~i,3~e) and (6~i,t) 
reactions on 13c at a bombarding energy of 99 MeV. For 
the purpose of comparison the (6~i,3~e) and (6~i,t) 
reactions on 12c were also measured under identical 
conditions. 
Figure 1 shows spectra of the 1 3 ~ ( 6 ~ i , 3 ~ e ) 1 6 ~  and 
13~(6~i,t)160 reactions at an angle of 15". States in 
160at 6.13, 11.09, 14.40, 14.80, 20.80, and 24.80MeV 
and states in 16N at 7.65, 9.81, 11.21, and 11.81 MeV 
are strongly populated. Analogue pairs of states are 
clearly seen. The strong group of states at 14.40 and 
14.80 MeV in 160 has no counterpart in the 16N 
CHANNEL ' NUMBER 
Ptgure 1. Spectra for the 1 3 ~ ( 6 ~ i , 3 ~ e ) 1 6 ~  and 
C( Li,t)160 reactions at a 6 ~ i  bombarding energy of 
99'MeV and a laboratory angle of 15' taken with a 
solid-state detector telescope. 
spectrum, thus suggesting a T=O assignment. 
Since the ground state of 13c can be described in 
first order as (p1/2)'3 with respect to 160 as a core, 
the transfer of three nucleons in the [(p1/2)2d5/2], 
[P1/2(d5/2)2] and (dgI2l3 configurations can lead to 
lp-lh, 2p-2h, and 3p-3h final states of the 
[~1/2-'dg/21. [(~1/2)-~(d5/2)~ I. and [(~1/2)-~ (dg/213 I 
configurations, respectively. Due to momentum 
mismatch, the high-spin states of these configurations 
are expected to be strongly excited. The lp-lh and 
2p-2h configurations should also be strongly excited in 
the simpler one- and two-nucleon transfer 
reactions.1-3) 
In the weak coupling model, the level spacing of 
the 3p-3h states in 16N-160 are the same as those for 
the 3p-4h states in 1 5 ~ - 1 5 0  and for the 3p states in 
19p-19Ne. Figure 2 shows excitation energies of 3p-4h 
statee in 15~-150 and 3p states in 19R' together with 
the corresponding 3p-3h states in 16~-160 as suggested 
by the present experiment. The coupling of the 
3 transferred three nucleons in the (d5/2) 5 4 / 2  and 
3 (d5/2) 5.1312 configurations to the ground state of 13c 
as a core results in two doublets of spins 4',5and 
6',7'. The resolution in the present experiment (- 200 
keV) was not good enough to separate these two 
doublets. Additional evidence that the 7.65 and 11.81 
MeV states in 16N and the 20.80 and 24.80 MeV states in 
160 are predominantly of the 3p-3h configuration comes 
from the comparison to one-and two-nucleon transfer 
data to these states. All of them are, if at all, only 
weakly excited in one-nucleon transfer reactions. l) In 
the 14~(a,2~e)16~ rea~tion,~) levels at 6.62 and 7.69 
MeV (unresolved doublet) were most strongly populated 
and have been interpreted as [14~(g.s.,1+) @ 
2 (d5/2) 5-41 2p-2h configuration states. We concluded 
that the 7.65 MeV state observed in the present 
c ( ~ L ~ ,  3 ~ e )  16N reaction is not identical to the 7.69- 
MeV 2p-2h doublet, since the 6.62-MeV 2p-2h state of 
the same configuration would also have to be excited 
quite strongly and we see no evidence for its 
formation. 
Fi ure 2. Excitation energies for 3p states in 19p, 
3pf3h states in 16N-160, and 3p-4h states in 1S~-150. 
F. Ajzenberg-Selove, Nucl. Phys. A281, 1 (1977). 3) R. Jahn, D.P. Stahel, G.J. Wozniak, R.J. de Meijer, 
and J. Cerny, Phys. Rev. C g ,  9 (1978). 
M.S. Zisman, E.A. McClatchie, and B.G. Harvey, Phys. 
Rev. C2, 1271 (1970). 
R.S. Tickle and W.S. Gray 
University of Michigan, Ann Arbor, Michigan 48109 
R.D. Bent 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
Using the 90-MeV 6 ~ i  beam at IUCF, we have studied 
the reactions 92 ,94 sg6 s g 8  ,100~o(6~i,8~)go sg2 sg4 ,96 sg8zr 
and also the reactions sg2 ,94~r(6~i,8~)88 sg2sr. 
These investigations had a twofold objective, first to 
study two-proton configurations in the Zr region and, 
second to examine the usefulness of the ( 6 ~ i , 8 ~ )  
reaction as a spectroscopic tool. 
The 8~ ions were momentum analyzed by the IUCF 
QDDM magnetic spectrograph and detected by a gridded 
ionization chamber1). Spectra were recorded at 
elab = 8" for all targets. Because 7~ and 9~ are 
proton unstable, 8~ is particularly easy to identify in 
a detector of-this type and was well separated from 
other ion species in the E-AE spectra. 
The experimental results obtained from 
bombardments of the Mo targets are shown in Fig. 1. 
Focusing attention on the 0+ + O+ transitions to the 
ground states (g.s.) and the first excited O+ states 
(0+2) in Zr, one immediately notices a pronounced 
dissimilarity between the 96 sg8zr spectra and the 
spectra of the three lighter-mass isotopes. For 
instance, in 9 8 ~ r  the 0+2 transition is twice as 
intense as that to the g.s., while in 90Zr the reverse 
is true with the 0+2 transition having only a quarter 
of the g.s. strength. 
The explanation for this variation in 0+2 strength 
relative to that of the g.s. can be traced to changes 
in the Zr proton configurations with neutron number. 
To provide a theoretical prediction of the 0+ + 0+ 
transition strengths observed for the five Mo targets, 
we have carried out exact finite-range distorted-wave 
Born approximation (EFR DWBA) calculations using the 
code DWUCK~~). The calculation assumes the reaction 
consists of a direct, one-step cluster transfer of a 
T=1, S=O proton pair. The code was used to calculate 
the ratio of the cross sections for the 0+2 states to 
those of the ground states for each of the five Zr 
iostopes. The proton configuration of the Zr ground 
states was assumed to be of the form a(P112)2 + 
8(g912)2. The 0+2 states were taken to be the 
orthogonal states B ( ~ ~ / ~ ) ~  -a(gg12)2. The neutrons 
were assumed to be inert. Except for 9 8 ~ r ,  where they 
were adjusted to yield exact agreement with experiment, 
the amplitudes a and B used in the EFR DWBA 
calculations were the same as those determined from 
single-proton pickup3) and stripping4) data and are 
based on averages of the experimentally obtained values 
given in Table 13 of Ref. 4. 
A comparison of the calculated and experimental 
ratios is given in Table 1, where it can be seen that 
the agreement is quite good. This suggests that the Zr 
wave function amplitudes and the simple reaction model 
we have used are basically correct. 
The results obtained from the three Zr targets are 


Search for 3p-3h States in the A=16 System

https://scholarworks.iu.edu/dspace/bitstream/2022/2825/1/iucf_1980_92-94.pdf

Search for 3p-3h States in the A=16 System

Abstract

Similar works

Full text

Available Versions

IUScholarWorks