Isomer-delayed gamma-ray spectroscopy of neutron-rich ¹⁶⁶Tb

¹ Department of Physics, University of Surrey, Guildford GU2 7XH, UK
² National Physical Laboratory, Teddington, 11 0LW, UK
³ RIKEN Nishina Center, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan
⁴ International Research Center for Nuclei and Particles in the Cosmos, Beihang University, Beijing 100191, China
⁵ School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191, China
⁶ Department of Physics, the University of Hong Kong, Pokfulam Road, Hong Kong
⁷ KU Leuven, Instituut voor Kern- en Stralings fysica, 3001 Leuven, Belgium
⁸ Department of Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
⁹ Department of Physics, Tohoku University, Aoba, Sendai, Miyagi 980-8578, Japan
¹⁰ School of Computing, Engineering and Mathematics, University of Brighton, BN2 4JG, UK
¹¹ Department of Nuclear Physics, R.S.P.E., Australian National University, Canberra, A.C.T.02000, Australia
¹² Nuclear Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
¹³ Department of Physics, Osaka University, Machikaneyama-machi 1-1, Osaka 560-0043, Toyonaka, Japan
¹⁴ School of Physics, Peking University, Beijing 100871, China
¹⁵ Department of Applied Physics, School of Science, Xi’an Jiaotong University, China
¹⁶ Institute for Nuclear Research, Hungarian Academy of Sciences, PO Box 51, Debrecen, Hungary
¹⁷ Department of Physics, Chung-Ang University, Seoul 156-756, Republic of Korea
¹⁸ NU Hanoi University of Science, 334 Nguyen Trai, Thanh Xuan, Hanoi, Vietnam
¹⁹ Department of Physics, College of Science in Zulfi, Almajmaah University, PO Box 1712, 11932, Saudi Arabia
²⁰ Department of Physics, Sungkyunkwan University, Suwon 440-746, Republic of Korea
²¹ School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3JZ, UK
²² Department of Physics, Central Michigan University, Mount Pleasant, Michigan 48859, USA
²³ Research Center for Nuclear Physics (RCNP), Osaka University, Ibaraki, Osaka 567-0047, Japan
²⁴ GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany
²⁵ Hoseo University, Asan, Chungnam 336-795, Korea
²⁶ Horia Hulubei National Institute of Physics and Nuclear Engineering,(IFIN-HH), 077125 Bucharest, Romania
²⁷ School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
²⁸ Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, 35020 Legnaro, Italy

^a e-mail: l.a.gurgi@surrey.ac.uk

Published online: 13 September 2017

Abstract

This short paper presents the identification of a metastable, isomeric-state decay in the neutron-rich odd-odd, prolate-deformed nucleus ¹⁶⁶Tb. The nucleus of interest was formed using the in-flight fission of a 345 MeV per nucleon ²³⁸U primary beam at the RIBF facility, RIKEN, Japan. Gamma-ray transitions decaying from the observed isomeric states in ¹⁶⁶Tb were identified using the EURICA gamma-ray spectrometer, positioned at the final focus of the BigRIPS fragments separator. The current work identifies a single discrete gamma-ray transition of energy 119 keV which de-excites an isomeric state in ¹⁶⁶Tb with a measured half-life of 3.5(4) μs. The multipolarity assignment for this transition is an electric dipole and is made on the basis internal conversion and decay lifetime arguments. Possible two quasi-particle Nilsson configurations for the initial and final states which are linked by this transition in ¹⁶⁶Tb are made on the basis of comparison with Blocked BCS Nilsson calculations, with the predicted ground state configuration for this nucleus arising from the coupling of the v(1^-/2)[521] and π(3⁺/2) Nilsson orbitals.