Multidimensional Stochastic approach to the fission dynamics of excited nuclei

摘要

The purpose of this review is to discuss the results obtained over the last five years from calculations of the mass-energy, charge, and angular distributions of fragments formed during the fission of excited nuclei. The calculations are performed within the stochastic approach to fission dynamics, which is based on a multidimensional Langevin equation, and carried out for a wide range of fissility parameters and excitation energies of compound nuclei. A temperature-dependent finite-range liquid-drop model, taking into account a diffuse nuclear surface, is used in a consistent way to calculate the potential energy and level-density parameter. In order to describe the dissipation of collective motion, a modified one-body mechanism of nuclear viscosity including a reduction coefficient of the contribution made by the "wall" formula is used. The evaporation of light prescission particles is taken into account on the basis of a statistical model combined with Langevin dynamics. Calculations performed in multidimensional Langevin dynamics satisfactorily reproduce all the parameters of experimentally observed distributions of fission fragments and the prefission neutron multiplicity as a function of compound-nucleus parameters. In order to attain a simultaneous reproduction of the mass-energy distribution of fission fragments and the prefission neutron multiplicity, the reduction coefficient needs to be half or less of the total one-body viscosity. In this review, problems that need to be solved to facilitate further development of the multidimensional stochastic approach to fission dynamics are discussed.