Microscopic description of nuclear shape evolution from spherical to octupole-deformed shapes in relativistic mean-field theory

Reflection asymmetric relativistic mean-field theory is used to investigate the shape evolution for even-even Th isotopes. The calculated deformations, matter density distributions, and potential energy surfaces demonstrate clearly the shape evolution from spherical to octupole deformed. Especially, it is shown that Th isotopes suffer two types of shape transition when the neutron number increases from $N=126$ to $N=156$. One is from spherical to octupole deformed around $N=134$, and another is from octupole to quadrupole deformed around $N=150$.