Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 47 (2014)

Decay spectroscopy in the neutron-rich A∼140 region beyond the
doubly-magic 132Sn
R. Lozeva,∗1 A. Odahara,∗2 C.-B. Moon,∗3 S. Nishimura,∗4 P. Doornenbal,∗4 G. Lorusso,∗4 P.A. Söderström,∗4
T. Sumikama,∗5 H. Watanabe,∗6 T. Isobe,∗4 H. Baba,∗4 H. Sakurai,∗7,∗4 F. Browne,∗8,∗4 R. Daido,∗2 Y. Fang,∗2Z. Patel,∗9,∗4 S. Rice,∗9,∗4 L. Sinclair,10∗,4 J. Wu,∗11,∗4 Z.Y. Xu,∗7∗ A. Yagi,∗2 R. Yokoyama,∗12 T. Kubo,∗4N. Inabe,∗4 H. Suzuki,∗4 N. Fukuda,∗4 D. Kameda,∗4 H. Takeda,∗4 D.S. Ahn,∗4 D. Murai,∗13F.L. Bello Garrote,∗14 J.-M. Daugas,∗15 F. Didierjean,∗1 E. Ideguchi,∗16 T. Ishigaki,∗2 H.S. Jung,∗17
T. Komatsubara,∗18 Y.K. Kwon,∗18 S. Morimoto,∗2 M. Niikura,∗7 H. Nishibata,∗2 I. Nishizuka,∗5 T. Shimoda∗2and K. Tshoo∗18
An isomer and β-decay experiment was performedin the framework of the EURICA project at RIBF1,2)
aiming at detailed decay spectroscopy and systematical study of the nuclear shape in one of the mostinteresting, and yet unexplored regions of the nuclear chart, the one beyond the doubly-magic 132 Sn.
For these nuclei, we may expect gradual change fromspherical shape with predominantly single-particle-likestructures, to a more deformed, prolate shape withcollective-type of excitations, while with the increaseof the neutron-number also octupole collectivity may
develop. Furthermore, the perturbed shell structure ofthese nuclei by e.g. sub-shell gaps or intruder highj orbitals may also cause isomeric states, picturing inturn these exotic systems far off stability.
The experiment was performed using in-flight 238 U
fission at 345 MeV/u on Be target with a thickness of
2.9 mm. The beam intensity was between 1-5 pnA. The
nuclei of interest were transported and selected by BigRIPS and implanted in the active stopper, WAS3ABi,
consisting of five Si DSSD detectors1) . Twelve Ge
Cluster detectors and eighteen LaBr3 (Ce) detectors3) ,constituting the EURICA 4π array surrounding thestopper, detected the isomeric- or β-delayed γ-rays.
The experimentally obtained particle identification isshown in Fig. 1, where a line indicates the nuclei beyond which no half-lives are known according to4) . Our
preliminary data analysis of known half-lives for e.g.
138,139
Sb nuclei show a very good agreement with theISOLDE measurement 5) , providing an important in-Fig. 1. Particle identification of the exotic nuclear cocktail.

put to the nucleosynthesis data around the A = 130
solar-system r-process abundance peak.
Although the analysis is still in progress, our preliminary results show also several isomeric states before
and after a β-decay in e.g. in Sb and I nuclei. Isomers
are found also in the very neutron-rich Cs isotopes6) .
In addition, first excited states e.g. in the produced
even-even nuclei with the neutron increase will provide new and vital information for the shell structure
and the shape evolution in this region along with thedetailed studies of the other exotic isotopes populated
in the experiment.
References
1) S. Nishimura et al: RIKEN Accel. Prog. Rep. 45, L182
(2013).
2) P.-A. Söderström et al: Nucl. Instr. Meth. Phys. Res. B
317, 649 (2013).
3) Z. Patel et al: in this report.
4) G. Audi et al: Chi. Phys. C 36, 1157 (2012).
5) O. Arndt et al: Phys. Rev. C 84, 061307(R) (2011).
6) A. Yagi et al: in this report.

∗1

IPHC/CNRS and University of Strasbourg
Department of Physics, Osaka University∗3 Department of Physics, Hoseo University∗4 RIKEN Nishina Center∗5 Department of Physics, Tohoku University∗6 Department of Physics, Beihang University∗7 Department of Physics, University of Tokyo∗8 CEM, University of Brighton∗9 Department of Physics, University of Surrey∗10 Department of Physics, University of York∗11 Department of Physics, Peking University∗12 CNS, University of Tokyo∗13 Department of Physics, Rikkyo University∗14 Department of Physics, University of Oslo
∗15 CEA/DAM∗16 RCNP, Osaka University∗17 Department of Physics, University of Notre Dame
∗18 IBS∗2-4-