Shell effects in hot isobaric nuclei

Level densities for hot isobaric nuclei are investigated by incorporating the isospin fluctuations in the statistical theory of nuclei. The single-particle level density parameter a is extracted as a function of temperature for various isospins of the system. At large temperatures, the empirical value of a≃A/8 is reproduced. A new method of extracting the neutron-proton asymmetry parameter is proposed. The neutron-proton asymmetry parameter is found to depend very strongly on deformation and isospin at low temperatures. The effect of the shell structure on the asymmetry energy is predominant for certain isospins corresponding to stable neutron-proton combinations. Results are presented for A=42, 44, 46, and 208. The excitation energy versus isospin plot for constant entropy of the system exhibits pockets similar to yrast traps in high-spin states of highly excited nuclei.