RIKEN Accel. Prog. Rep. 47 (2014)

HIGHLIGHTS OF THE YEAR

Isomer spectroscopy of neutron-rich Nd isotopes∗1Research 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 University of Oslo
∗6 The University of Brighton∗7 Department of Physics, Osaka University∗8 ILL, 38042 Grenoble Cedex∗9 Department of Physics, Rikkyo University∗10 University of Tsukuba∗11 MTA Atomki∗12 Peking University∗13 Hoseo University∗14 Department of Physics, Tohoku University∗15 The University of Surrey∗16 University of York∗17 Instituto de Estructura de la Materia, CSIC
∗18 Universidad Autónoma de Madrid∗19 Beihang University∗20 Department of Physics, The University of Tokyo∗2140158

Nd

120
1008060
40
2000Counts/keV

Prolate-deformed nuclei are found to appear
in the neutron-rich part of the nuclear landscapearound Z = 60 and beyond N = 90, after the systematic studies of excited states. In strongly deformed
nuclei, quantum number K is known to be a goodquantum number. Since transitions with large changes
in K are suppressed, many nuclei in this region haveisomeric states. In addition to the quadrupole deformation, appearances of higher-order deformations suchas octupole and hexadecupole deformations have beenpredicted1) ; however, they are not yet understood well.
Isomer spectroscopy is a useful method to gain information on such structures of these nuclei.
Neutron-rich 60 Nd isotopes have been investigatedby means of isomeric γ-ray spectroscopy. Such isotopes were produced by the in-ﬂight ﬁssion of 238 U
at RI Beam Factory in RIKEN Nishina Center, andwere selected and identiﬁed by using the BigRIPS separator. The identiﬁcation of the nuclei was performedon the basis of the ∆E-TOF-Bρ method, which allows
an event-by-event determination of their atomic number and the mass-to-charge ratio, where ∆E, TOF,and Bρ denote energy loss, time of ﬂight, and magnetic
rigidity, respectively. The identiﬁed particles were implanted into passive and active stoppers. A passive
stopper made of Cu was used for the measurement ata high count rate, while the WAS3ABi2) active stopper consisting of ﬁve double-sided silicon strip detectors was used for the β-γ spectroscopy. Delayed γ rays
were detected by the germanium cluster detector array
EURICA3) . Gamma rays previously known from theCounts/keV

Mn. Tanaka,∗1 E. Ideguchi,∗1 G. Simpson,∗2 R. Yokoyama,∗3 S. Nishimura,∗4 P. Doornenbal,∗4 G. Lorusso,∗4P.-A.Söderström,∗4 Z.Xu,∗20 J.Wu,∗4,∗12 N. Aoi,∗1 H. Baba,∗4 F.Bello,∗5 F. Browne,∗4,∗6 R. Daido,∗7 Y. Fang,∗7N. Fukuda,∗4 G. Gey,∗2,∗4,∗8 S. Go,∗3,∗4 N. Inabe,∗4 T. Isobe,∗4 D. Kameda,∗4 K. Kobayashi,∗9 M. Kobayashi,∗3T. Komatsubara,∗10 T. Kubo,∗4 I. Kuti,∗11 Z. Li,∗12 M. Matsushita,∗3 S. Michimasa,∗3 C.-B. Moon,∗13H. Nishibata,∗7 I. Nishizuka,∗14 A. Odahara,∗7 Z. Patel,∗4,∗15 S. Rice,∗15 E. Sahin,∗5 L. Sinclair,∗4,∗16T. Sumikama,∗14 H. Suzuki,∗4 H. Takeda,∗4 J. Taprogge,∗17,∗18 Zs. Vajta,∗11 H. Watanabe,∗19 and A. Yagi∗7200

400

600

800

1000701200

1400
Energy (keV)

160

Nd60
50403020
1000200

400600

800

1000

1200

1400
Energy (keV)

Fig. 1. Gamma-ray energy spectra for 158
60 Nd98 and160
60 Nd100 . Marked peaks are the γ rays identified newly.
The spread peak at ∼ 700 keV comes from (n,n′ ) reaction with Ge.

5− K-isomeric state of 156 Nd4) were observed, and new
K-isomeric states of heavier isotopes were discovered.
Figure 1 shows the γ-ray energy spectra of 158 Nd
and 160 Nd using both the passive and active stopper
data. We have observed three strong peaks at 151.6,233.4, and 1198.2 keV for 158 Nd, and two strong peaks
at 150.2 and 893.0 keV for 160 Nd. In both 158 Nd
and 160 Nd, the half-lives of γ rays were preliminarily obtained as 0.339(20) µs and 1.63(21) µs, respectively. From the systematics of Nd isotopes, the energy of the ﬁrst 2+ states will be around 70 keV. However, such low-energy γ transition is highly converted,and accordingly, the 70-keV peaks could not be observed. Further analysis to make spin-parity assignments based on the decay pattern and coincidence relations is now in progress.
References
1) P. Möller et al.: Atomic Data and Nuclear Data Tables
59, 185 (1995).
2) S. Nishimura et al.: RIKEN Accel. Prog. Rep. 46, 182(2013).
3) S. Nishimura: Prog. Theor. Exp. Phys. 03C006 (2012).
4) G. S. Simpson et al.: Phys. Rev. C 80, 024304 (2009).

- xvii -