Disappearance of Shell Effects at High Excitation. Self-consistent Calculations at Finite Temperatures

Self-consistent calculations of highly excited nuclei are presented. The changes in the average nuclear field as a function of temperature are discussed; they are found to be negligible in the calculation of the entropy versus excitation energy at a fixed deformation. The disappearance of shell effects at temperatures T ≃ 2-3 MeV in heavy nuclei is demonstrated both by calculations of deformation energy curves at different temperatures and by considering the asymptotic behaviour of the entropy. Finally, the validity of some simplifying approximations is discussed.