Islands of Shape Coexistence: Theoretical Predictions and Experimental Evidence

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.

Automated summary

Parameter-free theoretical predictions and covariant density functional theory calculations indicate that shape coexistence in atomic nuclei can only occur on islands within specific regions of the nuclear chart. The existence of these islands is supported by data for even-even nuclei possessing certain bands, where the energy levels of specific states are close to each other. This study also briefly discusses a theoretical mechanism for multiple-shape coexistence.