Shape transition with temperature of the pear-shaped nuclei in covariant density functional theory

TL;DR

This paper investigates how pear-shaped nuclei change shape with temperature using covariant density functional theory, revealing specific temperature-induced shape and pairing transitions in certain radium and barium isotopes.

Contribution

It provides the first detailed finite-temperature analysis of shape transitions in pear-shaped nuclei within covariant density functional theory, including pairing effects.

Findings

Identification of pairing transition at ~0.4-0.5 MeV.

Observation of shape transitions at 0.9-1.0 MeV.

Transition temperatures correlate with ground state deformations.

Abstract

The shape evolutions of the pear-shaped nuclei $^{224}$Ra and even-even $^{144-154}$Ba with temperature are investigated by the finite-temperature relativistic mean field theory with the treatment of pairing correlations by the BCS approach. The free energy surfaces as well as the bulk properties including deformations, pairing gaps, excitation energy, and specific heat for the global minimum are studied. For $^{224}$Ra, three discontinuities found in the specific heat curve indicate the pairing transition at temperature 0.4 MeV, and two shape transitions at temperatures 0.9 and 1.0 MeV, namely one from quadrupole-octupole deformed to quadrupole deformed, and the other from quadrupole deformed to spherical. Furthermore, the gaps at $N=$136 and $Z=$88 are responsible for stabilizing the octupole-deformed global minimum at low temperatures. Similar pairing transition at $T\sim$0.5 MeV and shape transitions at $T$=0.5-2.2 MeV are found for even-even $^{144-154}$Ba. The transition temperatures are roughly proportional to the corresponding deformations at the ground states.