Revealing microscopic origins of shape coexistence in the Ni isotopic chain

Silvia Leoni,Yusuke Tsunod,Bogdan Fornal,Nicolae Marginean,Michele Sferrazza,Takaharu Otsuka,G De Angelis,L Corradi

doi:10.1051/epjconf/201922301032

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.

Highlights

The shape is one of the most fundamental properties of the atomic nucleus
It is only very recently that an example of “shape-isomer-like” structure was found by our collaboration in the 66Ni nucleus [13], while coexistence of spherical, oblate and prolate shapes along the Ni isotopic chain was observed in experiments performed at ISOLDE/CERN, MSU and RIKEN [1416]
One of the most prominent examples is the Monte Carlo Shell Model (MCSM) of the Tokyo group [17], which correctly predicts the occurrence of shape isomerism in 66Ni, together with other possible cases in the lighter 62,64Ni stable isotopes, with reduced magnitude

Summary

Introduction

The shape is one of the most fundamental properties of the atomic nucleus. Spherical shapes naturally appear in the vicinities of magic nuclei. One of the most prominent examples is the Monte Carlo Shell Model (MCSM) of the Tokyo group [17], which correctly predicts the occurrence of shape isomerism in 66Ni, together with other possible cases in the lighter 62,64Ni stable isotopes, with reduced magnitude. In this proceeding we report on the research program of our collaboration, aiming at a detailed investigation, with different probes, of the microscopic structure of neutron-rich Ni isotopes, from mass A=62 to A=66. The aim of this research program is to shed light on the microscopic origin of nuclear deformation, not least shape isomerism, using different reaction mechanisms, to probe MCSM predictions

Experimental Investigation

Selectivity of transfer reactions

Conclusion