Magnetic rotational bands in
108
Sb
D. G. Jenkins,
1
R. Wadsworth,
1
J. Cameron,
2
R. M. Clark,
3
D. B. Fossan,
4
I. M. Hibbert,
1,
* V. P. Janzen,
5
R. Kru
¨
cken,
3,†
G. J. Lane,
4,‡
I. Y. Lee,
3
A. O. Macchiavelli,
3
C. M. Parry,
1
J. M. Sears,
4
J. F. Smith,
4,§
and S. Frauendorf
6
1
Department of Physics, University of York, Heslington, York Y01 5DD, United Kingdom
2
Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada L85 4M1
3
Lawrence Berkeley National Laboratory, Berkeley, California 94720
4
Department of Physics, State University of New York at Stony Brook, Stony Brook, New York 11794-3800
5
Chalk River Laboratories, AECL Research, Chalk River, Ontario, Canada K0J 1J0
6
FZ Rossendorf, Postfach 510119, D-01314 Dresden, Germany
Received 29 June 1998
High-spin states in
108
Sb were populated using the
54
Fe(
58
Ni,3pn ) reaction at a beam energy of 243 MeV
and the subsequent decay was studied using the Gammasphere array. A new sequence of magnetic dipole
transitions has been observed in addition to a previously known M 1 band in
108
Sb. These bands may be
interpreted, within the tilted axis cranking model as magnetic rotational bands with g
7/2
2
( g
9/2
)
-1
h
11/2
and h
11/2
g
7/2
( g
9/2
)
-1
( g
7/2
d
5/2
) configurations. S0556-28139801711-7
PACS numbers: 21.10.Re, 23.20.Lv, 25.70.Gh, 27.60.+j
I. INTRODUCTION
Magnetic dipole bands, characterized by strong M 1 tran-
sitions with relatively weak or absent E 2 crossover transi-
tions, have been observed in both the lead region 1–4 and,
more recently, in the tin region 5,6. These structures are
readily distinguished from conventional rotational bands by
their large B ( M 1) values several
N
2
indicating strong
magnetic character. The small B ( E 2) values B ( E 2)
0.1 e
2
b
2
) 4 associated with these structures indicate
that they have low quadrupole deformation. Indeed, the dis-
tinctive properties of these bands strongly suggest that the
majority of their aligned angular momentum is generated by
a mechanism other than collective rotation. Such structures
are believed to be examples of a phenomenon known as
magnetic rotation for which a rotating magnetic dipole vec-
tor breaks the symmetry of the nucleus. The configurations
and properties of these bands have been successfully de-
scribed within the tilted axis cranking TAC model 7. In
this model, the proton and neutron angular momentum vec-
tors, at the bandhead, are nearly perpendicular and the
aligned angular momentum is generated by the shears
mechanism, namely, the gradual alignment of these vectors
with the total angular momentum vector, I , which is tilted at
some angle, , with respect to the three axis the symmetry
axis of the nuclear density distribution. A definitive signa-
ture of this shears mechanism is that the B ( M 1) values will
decrease with increasing angular momentum, since they are
proportional to the square of the perpendicular component of
the magnetic dipole vector.
The TAC model 7–9 suggests that regular shears bands
consisting of M 1 transitions should exist in regions of low
deformation and in proximity to shell closures such as Z
=50 and Z =82. Such bands have recently been observed in
105
Sn 5 and
106,108
Sn 6. The structures in
108
Sn were suc-
cessfully interpreted in terms of the model. In the lighter
isotopes,
105,106
Sn, however, the calculations had more lim-
ited success. The reasons for this were thought to result from
the failure of the TAC model to fully include higher-order
nuclear deformations such as hexadecapole components
and possible proton-neutron interactions 6.
Other sequences of magnetic dipole transitions are known
to exist in several neighboring nuclei in this mass region, for
example, in
110,112
Sb 10,11,
108
Cd 12,
110
In and
111
In
13,14. Although these structures have not yet been explic-
itly interpreted within the TAC model as examples of mag-
netic rotation shears bands, they are likely to have a struc-
ture similar to the dipole bands in the tin isotopes. The
present work provides an interpretation within the TAC
model of a pair of magnetic dipole bands in an antimony
nucleus.
II. EXPERIMENTAL DETAILS AND DATA ANALYSIS
Excited states in the nucleus
108
Sb were populated using
the
54
Fe(
58
Ni,3pn ) reaction at a beam energy of 243 MeV. A
58
Ni beam accelerated by the 88-inch cyclotron at the
Lawrence Berkeley National Laboratory was incident on a
target composed of 600 g/cm
2
enriched
54
Fe on a backing
of 15.2 mg/cm
2
of gold. The full implementation of the
Gammasphere array with 95 HPGe detectors was used to
detect the resulting decay.
The data were unfolded and used to produce a --
cube, containing 2.110
10
triples events, which was ana-
lyzed using the RADWARE analysis program, LEVIT8R 15.
This backed target data cube was explored for detailed infor-
*Present address: Oliver Lodge Laboratory, University of Liver-
pool, PO Box 147, Liverpool L69 3BX, U.K.
†
Present address: Wright Nuclear Structure Laboratory, Physics
Department, Yale University, New Haven, CT 06520.
‡
Present address: Lawrence Berkeley National Laboratory, Berke-
ley, CA 94720.
§
Present address: Nuclear Physics Group, Schuster Laboratory,
University of Manchester, Brunswick Street, Manchester M13 9PL,
U.K.
PHYSICAL REVIEW C NOVEMBER 1998 VOLUME 58, NUMBER 5
PRC 58 0556-2813/98/585/27037/$15.00 2703 ©1998 The American Physical Society