Octupole degree of freedom for the critical-point candidate nucleus $^{152}$Sm in a reflection-asymmetric relativistic mean-field approach

TL;DR

This study investigates shape and phase transitions in samarium isotopes using a reflection-asymmetric relativistic mean-field approach, highlighting the role of octupole deformation in the critical-point nucleus $^{152}$Sm.

Contribution

It introduces the inclusion of octupole degrees of freedom in the relativistic mean-field model to analyze shape transitions in samarium isotopes, revealing new insights into the critical-point behavior.

Findings

$^{152}$Sm marks a shape/phase transition point.

Octupole deformation influences the energy gap near the Fermi surface.

Pairing of specific neutron orbitals drives octupole deformation.

Abstract

The potential energy surfaces of even-even $^{146-156}$Sm are investigated in the constrained reflection-asymmetric relativistic mean-field approach with parameter set PK1. It is shown that the critical-point candidate nucleus $^{152}$Sm marks the shape/phase transition not only from U(5) to SU(3) symmetry, but also from the octupole-deformed ground state in $^{150}$Sm to the quadrupole-deformed ground state in $^{154}$Sm. By including the octupole degree of freedom, an energy gap near the Fermi surface for single-particle levels in $^{152}$Sm with $\beta_2 = 0.14 \sim 0.26$ is found, and the important role of the octupole deformation driving pair $\nu 2f_{7/2}$ and $\nu 1i_{13/2}$ is demonstrated.