Islands of shape coexistence: theoretical predictions and experimental evidence

TL;DR

This paper predicts specific regions in the nuclear chart where shape coexistence occurs, supported by theoretical models and experimental data, revealing 'islands' of shape coexistence in atomic nuclei.

Contribution

It introduces a dual shell mechanism within proxy-SU(3) symmetry and covariant density functional theory to identify nuclear regions with shape coexistence, a novel approach in nuclear structure physics.

Findings

Shape coexistence is restricted to specific nuclear regions.

Data supports existence of these shape coexistence islands.

Nuclei with certain energy level arrangements are central to these islands.

Abstract

Parameter-free theoretical predictions based on a dual shell mechanism within the proxy-SU(3) symmetry of atomic nuclei, as well as covariant density functional theory calculations using the DDME2 functional indicate that shape coexistence (SC) based on the particle-hole excitation mechanism cannot occur everywhere on the nuclear chart, but is restricted on islands lying within regions of 7-8, 17-20, 34-40, 59-70, 96-112, 146-168 protons or neutrons. Systematics of data for even-even nuclei possessing K=0 (beta) and K=2 (gamma) bands support the existence of these islands, on which shape coexistence appears whenever the K=0 bandhead 0_2^+ and the first excited state of the ground state band 2_1^+ lie close in energy, with nuclei characterized by 0_2^+ lying below the 2_1^+ found in the center of these islands. In addition a simple theoretical mechanism leading to multiple shape coexistence is briefly discussed.