The role of shell evolution in shape coexistence

Abstract

We first review the shell evolution in exotic nuclei driven by nuclear forces. We then demonstrate that the underlying mechanism played by the balance of the tensor and central components in the effective nucleon-nucleon interaction is crucial when describing shape coexistence. This effect will be referred to as type II shell evolution, while the shell evolution passing through a series of isotopes or isotones is denoted as type I. We describe type II shell evolution in some detail for the case of the 68 Ni nucleus as an example. We present how the fission dynamics can be related to enhanced deformation triggered by type II shell evolution, at its initial stage. It is suggested that the island of stability may be related to the suppression of this mechanism.

Abrupt shape transition at neutron number N=60 : B(E2) values in SrRégis1, Jolie2, Saed-Samii3 et al. 2017Phys. Rev. C342270View full textAdd to dashboardCite

“…Level energy and B(E2) values were obtained within a single framework in good agreement with experiments, depicting the abrupt shape transition at N = 60 as a consequence of type II shell evolution involving many proton particle-hole excitations to the g 9/2 orbit [3,4]. Let us briefly explain the type II shell evolution.…”

“…7. Since the rapid shape transition in these isotopes is caused by type II shell evolution [3,4] leading to shape coexistence of different forms, the spherical, prolate, oblate, and triaxial characters of the states are indicated in this figure. In Table II the theoretical B(E2) values are given.…”

“…Detailed explanation on the type II shell evolution are given in Ref. [4], particularly with Fig. 1, while discussions with concrete cases can be found in Ref.…”

Are There Signatures of Harmonic Oscillator Shells Far from Stability? First Spectroscopy of Zr110

“…3 and Fig. 4 type II shell evolution [64], wherein the low-lying spectroscopy of Zr isotopes with N 60 is understood as coming from a modification of the neutron single particle energies driven by the deformation-triggered promotion of protons from the fp shell to the g 9/2 orbital. This is consistent with the results of the sensitivity study, where improved agreement is obtained for a larger deformation, when more protons are promoted into the g 9/2 orbital.…”

First Measurement of Collectivity of Coexisting Shapes Based on Type II Shell Evolution: The Case of Zr96

“…In order to guide the later discussion we briefly review the main points of type II shell evolution due to the tensor force, as presented in [4,8]. The effect of the monopole part of the tensor force depends on the spin-orbit coupling of the respective orbitals.…”