Self-consistent microscopic description of fission the scission mechanism

Abstract

A microscopic description based on the Hartree-Fock-Bogolyubov approach with various types of constraining fields is used to extract the characteristic features of the collective dynamics of the fission phenomenon at low energy. The two-body force employed is the density-dependent finite range interaction Dl which is particularly suitable for describing the average field together with the pairing field in nuclei. Results are presented for the ²⁴⁰Pu nucleus. The potential energy surface obtained when varying the total elongation of the system, mass-asymmetry and axial asymmetry is presented. Its general behaviour is in fair agreement with the data known from experiments. The results of a careful study of the scission of the nucleus are also analyzed. They show in particular that scission occurs via a collective mode completely different from the elongation one, that corresponds to excitation of hexadecapole type. Important consequences concerning the mechanism of the scission process follow from this fact. It explains in particular how the fragments can emerge from fission with a variety of excitation energies ranging from very small values (cold fission events) to much larger ones (hot fission events).