A New Type of Shape Instability of Hot Nuclei and Prompt Nuclear Fragmentation

A novel mechanism of prompt nuclear fragmentation is proposed. Assuming micro-canonical or canonical equilibrium, it is shown that a strong enhancement of the accessible phase space volume, due to the diffuceness of the nuclear surface, leads to dynamical instabilities of hot nuclei and to prompt fragmentation. Equations are derived for the transition temperature T_T, for which the thermodynamical surface tension vanishes, as well as for the thermodynamical fissility parameter chi_td.