Transport model studies on the fast fission of the target-like fragments in heavy ion collisions

Abstract

The fission of the target-like fragments (TLF) in heavy ion collisions (40Ar+197Au, b=8 fm) at beam energies from 20 to 40 MeV/u has been studied by an improved quantum molecular dynamics model (ImQMD). The time scale at a few 100 fm/c (10−21 s) of the TLF fission is consistent with the picture that fast fission occurs. The dynamic feature of the fast fission is illustrated by the mass asymmetry and the angular distribution of the fission axis. The effect of the surface energy coefficient and the beam energy on the dynamic feature of the fission is demonstrated. At higher beam energy, or with larger surface energy coefficient, the mass asymmetry of the fission fragments is larger and the angular distribution of the fission axis shows a more pronounced peak near beam direction, coincidentally the fission time scale is shorter. The variation suggests that the fission observables can be used as sensitive probes to the surface energy coefficient of nucleus. Irrelevant to the beam energy or the surface energy coefficient, the mean value of the relative velocity of the fission fragments situates in the vicinity of 2.4 cm/ns, in accordance with the Viola systematics applied in statistic fission. This value can be used as a calibration constant in all heavy ion fission experiments. The studies demonstrate the applicability of the transport model in the description of fast fission as a large amplitude collective motion mode in heavy ion collisions.