Shape Coexistence in 78 Ni and the new Island of Inversion

TL;DR

This paper uses large-scale shell model calculations to predict shape coexistence and deformation phenomena in neutron-rich isotopes around 78 Ni, revealing a new island of inversion and the persistence of magicity.

Contribution

It introduces a comprehensive valence space including full pf-shell and sdg-shell, highlighting shape coexistence and deformation in 78 Ni.

Findings

78 Ni retains its doubly magic nature.

Presence of a deformed prolate band at low excitation energy.

Prediction of a new island of inversion at N=50.

Abstract

Large Scale Shell Model calculations (SM-CI) predict that the region of deformation which comprises the heaviest Chromium and Iron isotopes at and beyond N=40 will merge with a new one at N=50 in an astonishing parallel to the N=20 and N=28 case in the Neon and Magnesium isotopes. We propose a valence space including the full pf-shell for the protons and the full sdg shell for the neutrons; which represents a comeback of the the harmonic oscillator shells in the very neutron rich regime. The onset of deformation is understood in the framework of the algebraic SU3-like structures linked to quadrupole dominance. Our calculations preserve the doubly magic nature of the ground state of 78 Ni, which, however, exhibits a well deformed prolate band at low excitation energy, providing a striking example of shape coexistence far from stability.