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

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.

Comments: 11 pages, 3 figures