Microscopic description of quadrupole-hexadecapole coupling in radium, thorium, uranium and plutonium isotopes with the Gogny energy density functional

TL;DR

This paper investigates the role of quadrupole-hexadecapole coupling in the shape and stability of heavy nuclei like radium, thorium, uranium, and plutonium using advanced nuclear models, revealing significant deformation effects and shape coexistence phenomena.

Contribution

It provides a detailed microscopic analysis of quadrupole-hexadecapole interactions in heavy isotopes with the Gogny energy density functional, highlighting their impact on nuclear deformation and stability.

Findings

Hexadecapole deformations significantly influence ground and excited states.

A stable region with small negative hexadecapole deformation exists below N=184.

Transition from coupled to decoupled quadrupole and hexadecapole degrees of freedom is predicted.

Abstract

The emergence and stability of static hexadecapole deformations as well as the impact in the development of dynamic deformation due to collective motion considering quadrupole-hexadecapole coupling are studied for a selected set of radium, thorium, uranium and plutonium isotopes, using the Gogny Hartree-Fock-Bogoliubov and Generator Coordinate Method frameworks. Sizable hexadecapole deformations are found to play a significant role in the ground and excited states of nuclei in the neighborhood of $^{238}$U. For each of the studied isotopic chains, it is shown that a region with small negative hexadecapole deformation, just below the neutron magic number $N =184$, remains stable once zero-point quadrupole-hexadecapole fluctuations are taken into account. A transition is predicted, with increasing mass number, from a regime in which the quadrupole and hexadecapole degrees of freedom are interwoven to a regime in which they are decoupled, accompanied by an enhanced shape coexistence in the more neutron-rich sectors of the isotopic chains. It is also shown, that quadrupole-hexadecapole configuration mixing brings a nontrivial additional correlation energy gain comparable to the quadrupole correlation energy itself.