The potential energy surfaces of even-even ${}^{146–156}\mathrm{Sm}$ are investigated in the constrained reflection-asymmetric relativistic mean-field approach with parameter set PK1. It is shown that the critical-point candidate nucleus ${}^{152}\mathrm{Sm}$ marks the shape/phase transition not only from $U(5)$ to $\mathit{SU}(3)$ symmetry, but also from the octupole-deformed ground state in ${}^{150}\mathrm{Sm}$ to the quadrupole-deformed ground state in ${}^{154}\mathrm{Sm}$. By including the octupole degree of freedom, an energy gap near the Fermi surface for single-particle levels in ${}^{152}\mathrm{Sm}$ with ${\beta }_2=0.14~0.26$ is found and the important role of the octupole deformation driving pair $\nu 2f_{7/2}$ and $\nu 1i_{13/2}$ is demonstrated.

• Received 24 December 2009

DOI:https://doi.org/10.1103/PhysRevC.81.034302