Occurrence of a chiral-like pair band and a six-nucleon noncollective oblate isomer in I-120

Abstract

We report for the first time two distinctive features in the odd-odd nucleus I-120: a pair of doublet bands and a high-spin isomer built on the pi h(11/2)nu h(11/2) configuration. For producing the excited states of 120I, a fusion-evaporation reaction Sn-118(Li-6, 4n) at E-lab=48MeV was employed. The beam was provided by the 14UD tandem accelerator of the Heavy Ion Accelerator Facility at the Australian National University. The observed doublet structure built on the positive-parity states is the first case and unique in isotopes with Z=53. The emerging properties are indicative of the known chiral characteristics, leading to a doubling of states for the pi h(11/2)nu h(11/2) configuration. In contrast, the high-spin isomer with a half-life of 49(2) ns at spin-parity J(pi)=25(+) can be explained in terms of a noncollective oblate structure with the full alignment of six valence nucleons outside the Sn-114 core: three protons (g(7/2))(1)(d(5/2))(1)(h(11/2))(1) and three neutrons (h(11/2))(3). This is an outstanding case that reveals a pure single-particle structure consisting of equal numbers of valence protons and neutrons outside the semi-double shell closure of Sn-114 with Z=50 and N=64. (C) 2018 The Author(s). Published by Elsevier B.V.