Shape transition around 222Ra based on finite-temperature covariant density functional theory

Abstract

The shape evolution and potential energy surfaces of even–even [Formula: see text]Ra are investigated in the [Formula: see text] plane by the covariant density functional theory. For octupole-deformed [Formula: see text]Ra, the free energy surfaces, the deformations, the pairing gaps, the excitation energy as well as the specific heat with increasing temperature are analyzed. Based on the specific heat, [Formula: see text]Ra exhibits three distinct discontinuities as the temperature rises. The first pairing transition occurs at [Formula: see text][Formula: see text]MeV, while the second one happens at [Formula: see text][Formula: see text]MeV when octupole deformation disappears, and the third one takes place at [Formula: see text][Formula: see text]MeV as quadrupole deformation approaches zero. The gaps at [Formula: see text] and [Formula: see text] in the single-particle levels are responsible for the octupole global minima. The shape transitions not only occur between even–even [Formula: see text]Ra, but also occur with increasing temperature for [Formula: see text]Ra.