Doppler-shift attenuation method lifetime measurements of low-lying states in
111
In
D. Bucurescu, I. Ca
˘
ta-Danil, G. Ilas ¸, M. Ivas ¸cu, N. Ma
˘
rginean, L. Stroe, and C. A. Ur
Institute of Atomic Physics, P.O. Box MG-6, Bucharest 76900, Romania
Received 5 March 1996
The lifetimes of nine low-lying excited states in
111
In have been measured with the Doppler-shift attenuation
method in the
111
Cd( p , n ) reaction. A comparison of experimental quantities with predictions based on the
interacting boson-fermion model unravels the states due to the coupling of a g
9/2
proton hole to the quadrupole
vibrations of the core. S0556-28139602410-7
PACS numbers: 21.10.Tg, 21.10.Re, 21.60.Fw, 27.60.+j
I. INTRODUCTION
There is considerable experimental evidence indicating
that not all the low-lying states of the odd-mass In isotopes
( Z =49 can be explained by simple proton-hole excitations
in the Z =50 closed shell. Thus, especially in the heavier
isotopes above A =113 there were systematically observed
low-lying, low-spin positive-parity states which cannot be
explained by a coupling of a g
9/2
proton-hole to core states
1 and references therein. The ‘‘extra’’ states have been
characterized as rotational bands which coexist with spheri-
cal vibrational states below 2.0 MeV excitation 1–3. Al-
though not as extensive, experimental data indicate that a
similar situation may prevail in
111
In as well 4,5.
To understand such states, it is necessary to include ex-
plicitly configurations of the 50–82 shell as well. The most
successful approach has been that based on the unified model
1, in which both pictures, a hole coupled to a Sn core and
a particle coupled to a Cd core, were considered. The results
of these calculations are in good agreement with experimen-
tal data on both transfer reactions and electromagnetic tran-
sitions, for the In isotopes 113–121 2,3; lighter isotopes
have not been calculated with this model. By using the pic-
ture of a coexistence between the superfluid and normal
phases in nuclei, a reasonably good description of the prop-
erties of the light In isotopes 107–115 has been achieved,
however without attempting a detailed description of the
level schemes 6. Another theoretical calculation for
111
In,
based on the hole-phonon coupling, explained well several
positive-parity states 7; however, as the experimental data
were scarce, many members of the hole-phonon multiplets
could not be identified.
Low-lying states in
111
In, up to 3 MeV excitation, have
been observed by a variety of reactions: ( ,2n ) 7,
( p , n ) 4,8, and proton transfer reactions ( d ,
3
He9 and
(
3
He,d ) 5, as well as decay of
111
Sn — see also the
review in Ref. 10. One can thus assume that within this
energy range the excited levels are determined quasicom-
pletely, although a number of them do not have an unambi-
gous spin-parity assignment. In the absence of lifetime mea-
surements, the comparison with theoretical calculations
cannot be too detailed. Lifetime determinations for certain
states below 3.0 MeV excitation have been reported recently
11,12; nevertheless, as will be discussed later, the values
quoted for several low-lying states are, very likely, affected
by large errors.
In order to facilitate a more detailed comparison with
theoretical models, we performed Doppler-shift attenuation
model DSAM lifetime measurements with the ( p , n ) re-
action. Although it provides rather low recoil velocities, it is
nevertheless advantageous because i as a compound
nucleus reaction it populates most of the residual states irre-
spective of their detailed structure and ii it can be per-
formed almost at the threshold and thus populate only the
levels of interest, thus minimizing the effects of feeding from
other states.
After a presentation of the experimental results, we pro-
pose an interpretation of a part of the low-lying level scheme
FIG. 1. Examples of -ray spectra measured at two angles, for
the incident proton energy of 4.7 MeV. Only the rays measured in
this work are marked by their unshifted energies.
PHYSICAL REVIEW C NOVEMBER 1996 VOLUME 54, NUMBER 5
54 0556-2813/96/545/23136/$10.00 2313 © 1996 The American Physical Society