The Binary Decay of Hot Heavy Nuclei — Fission, Evaporation, and Also Flow ?

Abstract

Nuclear fission, appropriately characterized as “one of the most interesting processes of collective flow of nuclear matter” [’], is for a pretty large interval of excitation energy (E*) the dominating decay mode of sufficiently intense heated heavy nuclei. This binary disintegration into two fission fragments (FF) of nearly equal mass (M E ) mainly competes with the emission of gamma-quanta, neutrons and —at temperatures higher than T 3 MeV [21) — light charged particles (LCP). Recently, a dynamical description of this complex interplay has been developped [31. It should be well established now that fission represents an overdamped collective motion over a saddle in the hyperplane of potential energy to a considerably large-deformed scission configuration, and proceeds in a time scale of several units times 10-20 s [’]. The total kinetic energy (TKE) of the fragments is then defined by the Coulomb repulsion between the preformed FF at the scission point. A parametrization of the TKE has been given earlier by Viola et al. [41considering that being governed explicitely by the Coulomb term Z, where Z and A ATdenote the atomic number and the mass number of the fissioning nucleus, respectively. The consequence is a rather constant value of the mean relative velocity2.4 s) between the FF fairly well reproduced by the experimental observations.