PHYSICAL REVIEW C
VOLUME 58, NUMBER 6
Structure of the neutron deficient
DECEMBER 1998
107
In
S. K. Tandel,1 S. B. Patel,1 P. Joshi,2 G. Mukherjee,2 R. P. Singh,2 S. Muralithar,2 P. Das,3 and R. K. Bhowmik2
1
Department of Physics, University of Mumbai, Mumbai-400 098, India
2
Nuclear Science Centre, P.O. Box 10502, New Delhi-110 067, India
3
Department of Physics, Indian Institute of Technology, Mumbai-400 076, India
~Received 15 May 1998!
High spin states in the nucleus 107In have been investigated using the reaction 66Zn( 45Sc,2p2n) at a beam
33
energy of 162 MeV. Levels up to a spin 2 \ and an excitation energy 7 MeV have been established from g-g
coincidence measurements. Two DI51 sequences have been observed, in addition to a large number of other
states arising from single particle excitations. The configuration p g 21
9/2 ^ n h 11/2 coupled to neutrons in the d 5/2
and g 7/2 orbitals appears to have a dominant contribution to the observed negative parity states.
@S0556-2813~98!07112-X#
PACS number~s!: 21.10.Re, 23.20.Lv, 25.70.Gh, 27.60.1j
The excited states of neutron deficient nuclei with Z
'50 are expected to be predominantly single particle in nature, due to the proximity of the spherical shell gap for protons. However, other excitation mechanisms also play a role
in generating angular momentum. Rotational bands characterized by enhanced E2 transitions indicating the presence of
well-deformed states arise as a result of particle-hole excitations across the Z550 shell gap @1–3#. These involve the
occupation of the intruder h 11/2 orbital, in addition to the g 9/2
subshell. Another mode of excitation which is seen to manifest itself in nuclei near closed shells, where both the particles and holes are in high-j orbitals, is the shears mechanism @4–6#. In this case, bands of magnetic dipole transitions
with large B(M 1) values of the order of several units of m 2N
are seen. The recently observed band of M 1 transitions in
105
Sn has been attributed to the shears mechanism @6#. Sequences of magnetic dipole transitions have, however, been
observed in a large number of nuclei near closed shells
@7–9#. In the present work, we report the observation of two
such series of M 1 transitions in the nucleus 107In, along with
a large number of single particle states.
The low and intermediate spin states of the odd A neutron
deficient In isotopes have previously been studied and qualitatively understood in terms of a p g 9/2 hole coupled to the
adjacent Sn core @9–11#. However, this simple picture can
account only for the positive parity states, and is besides not
expected to hold for the states at high angular momenta. The
object of the present work was to search for shears and intruder bands which have been predicted and also observed in
a few of the neighboring nuclei.
The energy levels in the nucleus 107In had previously been
studied using light ions and recently using heavy-ion projectiles @9,12–14#. The present experiment utilized the reaction
66
Zn( 45Sc,2p2n) 107In at a beam energy of 162 MeV to populate the high spin states in this nucleus. The predictions of
statistical model calculations which indicated that this would
be the dominant reaction channel were borne out experimentally ~Fig. 1!. The isotopically enriched (.99%) 66Zn target
had a thickness of 1 mg cm22 with a 25 mg cm22 Pb backing. With the use of the heavy 45Sc projectile delivered by
the 15 UD pelletron at the Nuclear Science Center, New
0556-2813/98/58~6!/3738~4!/$15.00
PRC 58
Delhi, it was possible to detect a large number of previously
unobserved states. The gamma detector array ~GDA! @15#
consisting of twelve Compton suppressed high purity Ge
~HPGe! detectors was used to record g-g coincidence data,
while a fourteen element BGO filter measured the multiplicity information. Two BGO elements were required to fire for
a coincidence event to be considered valid. Since the HPGe
array consisted of four detectors each at 50°, 98°, and 144°
with respect to the beam axis, it was also possible to obtain
DCO ~directional correlation of oriented states! information
~Table I! for assigning multipolarities to the observed transitions @16#. The electric or magnetic character of the transitions could not be determined in the absence of angular distribution measurements. A total of 150 million g-g
coincidence events were recorded during the course of the
experiment.
The level structure proposed for 107In involves modifications and extension over previously reported data @9,12–14#.
Several new transitions, viz., the 553, 647, 1035 keV g rays
deexciting the low spin single particle states were placed in
FIG. 1. The total projection of the g-g matrix, indicating the
relative population of a few of the nuclei originating from the dominant channels in the reaction used, by means of a comparison of the
intensities of the transitions to the ground states in each of these
nuclei.
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©1998 The American Physical Society
BRIEF REPORTS
PRC 58
3739
TABLE I. Energies, initial and final spin states, relative intensities, and DCO ratios for the g-ray transitions in 107In.
E g ~keV!a
109
150
159
204
251
288
316
351
360
383
393
413
427
439
444
469
488
504
510
520
532
553
612
647
661
664
677
742
791
851
948
1002
1035
1044
1144
1279
1311
1334
1415
1429
1438
1533
1748
I ip
I pf
23 2
2
19 1
2
21 2
2
23 2
2
29 ( 2 )
2
21 2
2
17 1
2
19 2
2
21 2
2
27 2
2
23 2
2
21 2
2
25 2
2
31 ( 2 )
2
25 2
2
13 1
2
23 2
2
29 ( 2 )
2
23 2
2
11 1
2
17 1
2
31 ( 2 )
2
13 1
2
29 ( 2 )
2
19 2
2
27 ( 2 )
2
31 ( 2 )
2
25 2
2
21 1
2
27 2
2
29 ( 2 )
2
33 ( 2 )
2
27 2
2
19 2
2
29 ( 2 )
2
21 2
2
27 2
2
21 2
2
31 ( 2 )
2
21 2
2
21 1
2
23 2
2
11 1
2
29 ( 2 )
2
19 2
2
( 33
2 )
13 1
2
19 2
2
21 2
2
21 2
2
25 2
2
21 1
2
21 2
2
29 ( 2 )
2
21 1
2
19 1
2
21 1
2
21 1
2
91
2
19 1
2
25 2
2
19 1
2
19 1
2
31 ( 2 )
2
91
2
17 1
2
19 1
2
19 1
2
19 1
2
Ig
R DCOb
1.2~7!
68.7~1!
12.7~1!
26.9~1!
3.2~14!
1.5~11!
10.1~2!
2.0~14!
9.4~4!
7.4~6!
32.8~2!
25.3~3!
1.3~15!
100
2.8~17!
4.2~8!
3.3~17!
2.8~17!
4.7~11!
2.6~19!
11.5~4!
4.7~11!
21.0~2!
1.9~11!
8.4~4!
2.5~10!
3.1~10!
1.3~15!
20.1~1!
8.3~3!
3.3~14!
23.5~2!
3.8~15!
2.9~14!
1.6~19!
1.3~30!
3.6~8!
2.7~17!
0.53~26!
0.58~3!
0.55~4!
0.61~3!
0.35~24!
0.67~21!
0.53~10!
0.58~29!
0.48~12!
0.36~12!
0.50~4!
0.61~1!
68.8~1!
13.4~3!
20.0~3!
10.2~3!
2.2~17!
0.96~2!
0.49~7!
0.64~6!
0.46~7!
1.07~2!
0.35~16!
0.58~16!
0.40~15!
0.51~14!
0.46~9!
0.45~4!
0.43~14!
0.63~25!
0.70~4!
0.45~9!
0.80~4!
0.68~18!
0.74~22!
The g-ray energies are rounded off to the nearest integer.
R DCO5I g 1 (50°) gated by g 2 (98°)/I g 1 (98°) gated by g 2 (50°).
The gating transition is a stretched quadrupole. A value of R DCO
close to 0.5 indicates that the transition under consideration is dipole in nature, while a value near 1.0 means that it is a quadrupole.
a
b
the level scheme, firmly establishing the structure below an
excitation energy of 3 MeV. The relative placement of the
316 and 1533 keV transitions proposed in Ref. @12# is confirmed by our data both on the basis of intensity consider-
FIG. 2. The two sequences of magnetic dipole transitions observed in 107In. The g rays denoted by asterisks are not part of these
sequences.
ations and the observed coincidence relationships between
the 316, 742, 791, and 1533 keV transitions. The 948, 1044,
288, and 427 keV transitions as well as the 1748, 351, 661,
and 469 keV lines have been placed in the level scheme for
the first time, although it was not possible to firmly assign
the spins and parities for the states which are deexcited by
these g rays. The transitions feeding the 3315 keV state
which is deexcited by the 520 and 1311 keV g rays could not
be determined.
The following modifications to the recently reported work
@12# are suggested from our data. In sequence 1 @Figs. 2~a!
and 3#, we have found no evidence for the 916 keV g ray
connecting the 5566 and 4651 keV levels. However, we have
observed a 1144 keV transition between the 5183 and 4039
keV states. In sequence 2 @Fig. 2~b!#, the series of transitions
determined by us is in the order 316, 360, 510, 488, and 444
keV. These transitions are found to be coincident with the
1415, 439, 150, and 1533 keV g rays as well as the 1334
keV line. The 444 keV g ray has been newly determined by
us to be part of this sequence. The relative placements of the
510, 488, 444, and 1334 keV transitions follow intensity
considerations, and differ from those suggested in Ref. @12#.
Besides, the placement of the 677 keV transition connecting
the 4213 and 3537 keV states appears to be erroneous since
it is coincident with both the 316 and 360 keV transitions,
and is not coincident with the g rays above the 4213 keV
level, which suggests that it feeds this state. While the 109
keV transition connects sequence 1 to 2, some branching of
intensity is also observed from sequence 2 to 1 @Fig. 2~a!#,
but it has not been possible to isolate the transitions which
form part of this link.
3740
BRIEF REPORTS
FIG. 3. Level structure of
PRC 58
107
The most interesting aspect of the structure was the observation of two sequences of magnetic dipole transitions
viz. the 159, 204, 393, 612, 532, 383, and 504 keV g rays
deexciting to the 3283 keV state at 192 \ and the 316, 360,
510, 488, and 444 keV lines feeding the 3537 keV level with
a spin 212 \ ~Figs. 2 and 3!. These two sequences are quite
similar in structure with the transition energies exhibiting a
gradual increase with spin upto 272 \, beyond which they are
not very regular. The excitation energies of the negative par-
In deduced from the present work.
ity states in the odd A In isotopes exhibit a steady decrease
with an increase in the number of neutrons which indicates a
contribution to the inherent structure of these states from the
strongly downsloping h 11/2 orbital. Therefore, a configuration
involving one neutron in the negative parity h 11/2 orbital and
another neutron in a positive parity orbital, viz., the g 7/2 or
d 5/2 orbitals along with a p g 9/2 proton hole is probably responsible for the negative parity states. In addition, a systematic comparison of the level structure of the neighboring odd
PRC 58
BRIEF REPORTS
A In isotopes reveals an identical behavior, i.e., the energies
of the M 1 transitions exhibit a steady increase from the 192 2
to the 272 2 states, while the subsequent 292 2 → 272 2 transition
is lower in energy. These two factors lead us to conclude that
the fully aligned p (g 9/2) 21 ^ n (h 11/2 ,g 7/2) configuration with
the other neutrons in the d 5/2 and g 7/2 orbitals coupled to a
spin zero, is probably the dominant component of the configuration for the 272 2 state in the odd A In isotopes. The
subsequent spin is generated by the gradual alignment of the
neutrons in the d 5/2 and g 7/2 orbitals.
Negative parity has been suggested for the states linked
by the magnetic dipole transitions in previous works, with a
similar structure being reported in neighboring nuclei. The
negative parity assignment is more probable since it is much
more likely that the 1429, 1438, and 1533 keV transitions
have an E1 rather than an M 1 character. If these states in2
deed bear negative parity, the p g 21
9/2 ^ n (h 11/2) configuration
for the M 1 bands suggested in a recent work @17#, is effectively ruled out. Besides, the theoretically predicted @17#
shears bands in 107In have significantly higher values of spin
than the observed M 1 bands. These factors seem to indicate
2
that the shears mechanism with a p g 21
9/2 ^ n (h 11/2) configuration as suggested in Ref. @17# is probably not responsible
for the observed M 1 bands in 107In. However, a mechanism
involving the gradual alignment of the spins of the neutrons
in the h 11/2 , g 7/2 , and d 5/2 orbitals may play a role in generating angular momentum. The recently reported structure of
109
In @12# exhibits M 1 bands quite similar to those observed
in 107In. A noteworthy aspect is that the structure of 107,109In
deduced from the present work and Ref. @12# is at variance
with the data quoted in Ref. @17#. As a result, we feel that the
data referred to in Ref. @17#, especially for 107In, cannot be
@1#
@2#
@3#
@4#
@5#
R. Wadsworth et al., Phys. Rev. C 53, 2763 ~1996!.
S. M. Mullins et al., Phys. Lett. B 318, 592 ~1993!.
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G. Baldsiefen et al., Nucl. Phys. A574, 521 ~1994!.
S. Frauendorf, J. Meng, and J. Reif, in Proceedings of the
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@6# A. Gadea et al., Phys. Rev. C 55, R1 ~1997!.
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@8# D. Seweryniak et al., Nucl. Phys. A589, 175 ~1995!.
3741
utilized to make an inference regarding the underlying structure of the magnetic dipole bands.
The positive parity states in the odd A In isotopes have a
similar structure with the 29 1 ground state arising from a p 9/2
hole, and various admixtures from the d 5/2 and the g 7/2 orbitals giving rise to the other observed positive parity levels,
viz., the 112 1 , 132 1 , 172 1 , 192 1 , and 212 1 states. The large and
almost constant energy difference between the 192 1 and 212 1
states in 103In, 105In, and 107In reflects the fact that a similar
p (g 9/2) 21 ^ n (g 7/2 ,d 5/2) fully aligned configuration is responsible for the 212 1 states in these isotopes, and the
21
strongly repulsive ( p g 21
9/2 n d 5/2) 7 1 and ( p g 9/2 n g 7/2) 8 1 twobody matrix elements contribute to an increase in the energy
of the stretched configuration in the 212 1 state in comparison
with the nonstretched configuration in the 192 1 state, as suggested in Ref. @12#. The other newly observed states in 107In
also arise from single particle excitations, however, since the
spins and parities of these levels have not been established, it
is not possible to determine the nature of the configuration
responsible for these states. In conclusion, the level structure
of 107In has been significantly extended and thirteen transitions have been placed in the level scheme for the first time.
The negative parity states are generated as a result of h 11/2 ,
g 7/2 , and d 5/2 neutron excitations coupled to the g 9/2 proton
hole, with the 272 2 state having a dominant contribution from
the fully aligned p (g 9/2) 21 ^ n (h 11/2 ,g 7/2) configuration. The
positive parity states can be attributed to a p (g 9/2) 21
^ n (g 7/2 ,d 5/2) configuration.
The authors wish to gratefully acknowledge the efforts of
the pelletron staff at the Nuclear Science Center in providing
the 45Sc beam.
@9#
@10#
@11#
@12#
@13#
@14#
@15#
@16#
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