Microscopic analysis of octupole shape transitions in neutron-rich actinides with relativistic energy density functional

TL;DR

This paper systematically analyzes octupole shape transitions in neutron-rich actinides using a relativistic energy density functional, revealing a progression from spherical to octupole-deformed shapes and discussing the microscopic mechanisms involved.

Contribution

It introduces a comprehensive relativistic mean-field approach to study octupole deformations and shape transitions in actinides, providing new insights into their microscopic origins.

Findings

Evidence of shape transition from spherical to octupole-deformed shapes.

Identification of stable octupole-deformed and octupole-soft equilibrium shapes.

Discussion of single-nucleon orbital evolution driving octupole deformation.

Abstract

Quadrupole and octupole deformation energy surfaces, low-energy excitation spectra, and electric transition rates in eight neutron-rich isotopic chains -- Ra, Th, U, Pu, Cm, Cf, Fm, and No -- are systematically analyzed using a quadrupole-octupole collective Hamiltonian model, with parameters determined by constrained reflection-asymmetric and axially-symmetric relativistic mean-field calculations based on the PC-PK1 energy density functional. The theoretical results of low-lying negative-parity bands, odd-even staggering, average octupole deformations $\langle\beta_3\rangle$, and $B(E3; 3^-_1\to 0^+_1)$ show evidence of a shape transition from nearly spherical to stable octupole-deformed, and finally octupole-soft equilibrium shapes in the neutron-rich actinides. A microscopic mechanism for the onset of stable octupole deformation is also discussed in terms of the evolution of single-nucleon orbitals with deformation.