Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 48 (2015)

Decay spectroscopy of neutron-rich Z ≈ 60 isotopes
E. Ideguchi,∗1 Mn. Tanaka,∗1 R. Yokoyama,∗3 G. S. Simpson,∗2 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∗10The neutron-rich A∼150 region contains a wide variety of shape phenomena, including shape coexistence
and possible static octupole and hexadecapole deformations. After the systematic studies of the excitedlevels of these isotopes, it was found that the nuclei
beyond N = 90 or 92 in this region show characteristics
of strong quadrupole deformation, such as low-energy
2+ levels and the energy ratio of 4+ to 2+ levels ofnearly 3.3. In addition, K isomers were systematicallyobserved,1) which indicates stable axial-symmetric deformation because K is a good quantum number insuch nuclei and large ∆K transitions are strongly hindered.
In our studies of neutron-rich Nd isotopes throughisomer spectroscopy using the EURICA spectrometer,2) K isomers were systematically observed up toN = 100.3) Gamma rays decaying from the isomer andthose of ground-state rotational bands in low-lying levels were observed. The trend of decreasing 4+ → 2+
transition energy with increasing neutron number may
indicate the development of quadrupole deformation in
neutron-rich Nd isotopes.
Such development of deformation will reﬂect in theconﬁguration of the ground state, and therefore, thespin and parity of neighboring odd and odd-odd nuclei
will be useful for understanding the deformed structure. This can be investigated through β-γ spectroscopy.
In order to study the β decay of neutron-rich Pr isotopes, which are parent nuclei of the Nd isotope, β-γ

spectroscopic measurement was performed at RIBF.
The in-ﬂight ﬁssion of 238 U at 345 MeV/u was employed to produce neutron-rich Pr isotopes and theirneighbors. Nuclei of interest were selected and transported to the ﬁnal focal plane, F11, using the BigRIPS
fragment separator. These isotopes were stopped at
the active stopper, WAS3ABi,4) and β-γ spectroscopyof these isotopes was performed using the EURICA
setup at F11.
Figure 1 shows a γ-ray energy spectrum after the βdecay of 156 Pr. Gamma peaks at 67 and 155 keV areclearly identiﬁed in the spectrum, and they correspondto the previously reported 2+ → 0+ and 4+ → 2+transitions of 156 Nd,1) respectively. Based on the obtained results, we will assign the spin and parity of theparent nucleus, 156 Pr. In addition, γ transitions associated with the non-yrast levels of 156 Nd will be alsoinvestigated.
These data are currently being analyzed.

∗1

Research Center for Nuclear Physics, Osaka University
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, Debrecen, Hungary∗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 University∗2Fig. 1. Gamma-ray energy spectrum after β decay of 156 Pr.

References
1) G. S. Simpson et al.: Phys Rev. C 80, 024304 (2009).
2) S. Nishimura: Nucl. Phys. News 22, No. 3 (2012).
3) Mn. Tanaka et al.: RIKEN Accel. Prog. Rep. 47, xvii
(2014).
4) S. Nishimura, et al.: RIKEN Accel. Prog. Rep. 46, 182(2013).

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