Dissipation strength of the tilting degree of freedom in fusion-fission reactions

Abstract

The four-dimensional Langevin model was applied to calculate a wide set of experimental observables for compound nuclei, formed in heavy-ion fusion-fission reactions. A modified one-body mechanism for nuclear dissipation with a reduction coefficient k s of the contribution from a "wall" formula was used for shapes parameters. Different possibilities of deformation-dependent dissipation coefficient for the K coordinate (γ K ) were investigated. Presented results demonstrate that the influence of the k s and γ K parameters on the calculated quantities can be selectively probed. It was found that it is possible to describe experimental data with the deformation-dependent γ K coefficient. One of the possibility is to use large values of γ K 0.2 (MeV zs) −1/2 for compact shapes featuring no neck and small values of γ K 0.0077 (MeV zs) −1/2 for elongated shapes.Fission still is one of the most interesting and challenging topics in nuclear physics providing a perfect opportunity to investigate the large scale evolution of initial compound nucleus into fission products. During the past two decades stochastic approach based on multidimensional Langevin equations has been extensively and rather successfully used to elucidate many problems of collective nuclear dynamics in fusion-fission reactions at high excitation energies [1,2]. A reasonable choice of collective degrees of freedom for modeling shape evolution and considering particle evaporation allow modeling the complex interplay between static and dynamical effects in fission and succeeding in explaining a wide range of experimental data [3,4].

Fission fragment distributions within dynamical approach

“…It would also be desirable to emphasize that the systematic calculations of the MED distribution of fragments and prescission neutron multiplicities performed within 3D [19,27,49] and 4D [61,63,159,213,230] stochastic approach have made it possible to unambiguously choose, after a long discussion, which nuclear viscosity mechanism (two-body or one-body) is realized during nuclear fission. A simultaneous description of the fission fragment MED parameters and the mean prescission neutron multiplicities is attained for the one-body mechanism of viscosity in its modified variant [56,57] with the reduction coefficient k s = 0.25-0.5 for the contribution from the wall formula.…”