Excitation energy dependence of shell effects on nuclear level densities

It is now well known that the deviation of the single particle states from a uniform distribution results in a shell correction energy to the liquid drop model value of the nuclear mass. The ground state shell correction energies have been calculated by well known macroscopicmicroscopic formulations. In an earlier work, Ramamurthy et al. [1] have calculated the excitation energy dependence of the nuclear entropy S ( which determines the nuclear level densities for the excited nucleus) starting from the single particle states for a modified spherical harmonic potential with parameters of Seeger and Perisho [2]. Fig.1 shows the results of this calculations for two typical cases of doubly closed shell 208 Pb with shell correction energy Δshell ( defined as difference between experimental mass of the nucleus and its liquid drop mass) of -9.2 MeV and for spherical shape 242 Pu with Δshell of 14.5 MeV .