Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 47 (2014)

Search for K-isomers in neutron-rich Z≈60 isotopes
E. Ideguchi,∗1 G. Simpson,∗2 R. Yokoyama,∗3 Mn. Tanaka,∗1 S. Nishimura,∗4 P. Doornenbal,∗4P.-A. Söderström,∗4 G. Lorusso,∗4 Z. Xu,∗5 J. Wu,∗4,∗6 T. Sumikama,∗7 N. Aoi,∗1 H. Baba,∗4 F. Bello,∗8F. Browne,∗4,∗9 R. Daido,∗10 Y. Fang,∗10 N. Fukuda,∗4 G. Gey,∗2,∗4,∗11 S. Go,∗3,4 N. Inabe,∗4 T. Isobe,∗4D. Kameda,∗4 K. Kobayashi,∗12 M. Kobayashi,∗3 T. Komatsubara,∗13 T. Kubo,∗4 I. Kuti,∗14 Z. Li,∗6M. Matsushita,∗3 S. Michimasa,∗3 C.-B. Moon,∗15 H. Nishibata,∗10 I. Nishizuka,∗7 A. Odahara,∗10 Z. Patel,∗4,∗16
S. Rice,∗4,∗16 E. Sahin,∗8 L. Sinclair,∗4,∗17 H. Suzuki,∗4 H. Takeda,∗4 J. Taprogge,∗18,∗19 Zs. Vajta,∗14H. Watanabe,∗20 and A. Yagi∗10isomers in neutron-rich Nd isotopes, and the development of quadruple and hexadecupole deformations
as a function of neutron numbers will be investigated.
In addition, we have also found several more new microsecond isomeric states in this region4) . These data
are currently being analyzed.
In the Ba setting run, RI beams of 149−151 Ba,
151−153
La, and 154,155 Ce were mainly collected, as
shown in Fig. 2. The isotopes were stopped at theactive stopper, WAS3ABi,5) and beta-gamma spectroscopy of these isotopes was performed using theEURICA setup. All the isotopes indicated above are
newly studied with the aim of systematic investigationof octupole correlations, a study that has not been possible so far. Detailed analyses are underway.

The neutron-rich A∼150 region contains a wide variety of shape phenomena, including shape coexistence
and possible static octupole and hexadecapole deformations. Although quadrupole deformation has been
extensively examined across most of the nuclear chart,
both octupole and hexadecupole deformations remainmuch less well studied in comparison. These higherorder deformations can have a strong inﬂuence on
gamma-decay rates and the quasi-particle energies ofnuclei, and hence, their detailed studies are necessary
to test the various diﬀering predictions of several nuclear models. We have performed an experiment tosearch for µs isomers in the neutron-rich A= 150 ∼160
Nd, Ce, Ba nuclei and to study their β-decay, in order
to examine octupole and hexadecupole deformationsin this region. These studies have become possible
for the ﬁrst time using the world’s highest intensity
in-ﬂight RI beams available at RIBF with the higheﬃciecy gamma spectrometer, EURICA1) .
To study the excited levels of these A = 150 ∼ 160
isotopes, we have performed isomer and beta-gamma
spectroscopy using EURICA in two diﬀerent RI beamsettings. One setting involves focusing on the Nd region and the other, on the Ba region.
During the experiment for the Nd setting (seeFig. 1), a previously reported isomer in 156 Nd2) wasconﬁrmed and a new isomer in 158 Nd was identiﬁed. We also succeeded to ﬁnd some more isomers
in neutron-rich Nd isotopes up to 160 Nd3) . These ﬁndings will allow us to study the systematic analysis of61

Nd Setting PID

60.5

Z60

157

Nd

158

Nd

159

Nd

160

10

Nd

1

59.5
59

155

Pr156

Pr

157

Pr-1

1058.5
58
2.6

2.61

2.62

2.63

2.642.65

2.66

2.67

2.68

A/Q

Fig. 1. Particle identification (A/Q vs Z) plot for the Ndsetting run.
59

Ba Setting PID

58.5
58

∗1Research Center for Nuclear Physics, Osaka University∗2 LPSC, Université Grenoble-Alpes, CNRS/IN2P3∗3 Center for Nuclear Study, The University of Tokyo∗4 RIKEN Nishina Center∗5 Department of Physics, The University of Tokyo∗6 Peking University∗7 Department of Physics, Tohoku University∗8 University of Oslo
∗9 The University of Brighton∗10 Department of Physics, Osaka University∗11 ILL∗12 Department of Physics, Rikkyo University∗13 University of Tsukuba∗14 MTA Atomki∗15 Hoseo University∗16 The University of Surrey∗17 University of York∗18 Instituto de Estructura de la Materia, CSIC
∗19 Universidad Autónoma de Madrid∗20 Beihang University154

Z

57.5
57

Ce

155

102

Ce
10151

56.5
56

152

La
149

La

153

Ba

150

La

Ba

151

1

Ba

55.5
55
2.63

2.64

2.65

2.66

2.67

2.68

2.69

2.7

A/Q

Fig. 2. Particle identification plot for the Ba setting run.

References
1) S. Nishimura: Nucl. Phys. News 22, No. 3 (2012).
2) S. G. Simpson et al.: Phys Rev. C 80, 024304(2009).
3) Mn. Tanaka et al., in this report.
4) R. Yokoyama et al., in this report.
5) S.Nishimura, G.Lorusso, Z.Xu et al.: RIKEN Accel.
Prog. Rep. 46, 182 (2013).

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