Nuclear shape transition at finite temperature in a relativistic mean field approach

The relativistic Hartree-BCS theory is applied to study the temperature dependence of nuclear shape and pairing gap for Er-166 and Er-170. For both the nuclei, we find that as temperature increases the pairing gap vanishes leading to phase transition from superfluid to normal phase as is observed in nonrelativistic calculation. The deformation evolves from prolate shapes to spherical shapes at T similar to 2.7 MeV. Comparison of our results for heat capacity with the ones obtained in the nonrelativistic mean field framework indicates that in the relativistic mean field theory the shape transition occurs at a temperature about 0.9 MeV higher and is relatively weaker. The effect of thermal shape fluctuations on the temperature dependence of deformation is also studied. Relevant results for the level density parameter are further presented.