Revealing microscopic origins of shape coexistence in the Ni isotopic chain

¹ Department of Physics, University of Milano and INFN, Via Celoria 16, 20133, Milano, Italy
² Institute of Nuclear Physics,PAN, 31–342 Kraków, Poland
³ Horia Hulubei National Institute of Physics and Nuclear Engineering – IFIN HH, Bucharest 077125, Romania
⁴ Département de Physique, Université libre de Bruxelles, B–1050 Bruxelles, Belgium
⁵ Center for Nuclear Study, University of Tokyo, Hongo, Bunkyo–ku, Tokyo 113–0033, Japan
⁶ Department of Physics, University of TokyoN, Hongo, Bunkyo–ku, Tokyo 113–0033, Japan
⁷ RIKEN Nishina Center, 2–1 Hirosawao, Wako, Saitama 351–0198, Japan
⁸ Instituut voor Kern– en Stralingsfysica, KU Leuven, B–3001 Leuven, Belgium
⁹ National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA

^* Corresponding author: silvia.leoni@mi.infn.it

Published online: 4 December 2019

Abstract

In a two–neutron transfer experiment, performed in Bucharest in July 2016 at sub–Coulomb barrier energy,a photon decay hindered – solely – by a nuclear shape change was identified in the ⁶⁶Ni nucleus. Such a rare process, at spin zero, was clearly observed before only in actinide nuclei in the 1970’s,where fission isomers were found. The experimental findings on ⁶⁶Ni have been well reproduced by the Monte Carlo Shell Model Calculations of the Tokyo group, which predict a multifaceted scenario of coexistence of spherical, oblate and prolate shapes in neutron–rich Ni isotopes. The results on ⁶⁶Ni encouraged a comprehensive gamma–spectroscopy investigation of neutron–rich Ni isotopes, in particular ⁶²Ni and ⁶⁴–Ni, at IFIN–HH (Bucharest), IPN Orsay and ILL (Grenoble), employing different reaction mechanisms to pin down the wave function composition of selected excited states. The aim is to shed light on the microscopic origin of deformation in neutron–rich Ni nuclei, possibly locating other examples of “shape–isomer–like” structures inthis region.