Investigation of dissipation in the tilting degree of freedom from four-dimensional Langevin dynamics of heavy-ion-induced fission

Abstract

A four-dimensional dynamical model based on Langevin equations was applied to calculate a wide set of experimental observables for heavy fissioning compound nuclei. Three collective shape coordinates plus the tilting coordinate were considered dynamically from the ground state deformation to the scission into fission fragments. A modified one-body mechanism for nuclear dissipation with a reduction coefficient ks of the contribution from a ‘wall’ formula was used for shapes parameters. Different possibilities of deformation-dependent dissipation coefficient for the tilting coordinate ( ) were investigated. Presented results demonstrate that the influence of the ks and γK parameters on the calculated quantities can be selectively probed. The nuclear viscosity with respect to the nuclear shape parameters influences the , the fission fragment mass–energy distribution parameters, and the angular distribution of fission fragments. At the same time the viscosity coefficient γK affects the angular distribution of fission fragments only. The independence of anisotropy on the fission fragment mass is found at both Langevin calculations performed with deformation-dependent and constant γK coefficients.

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

“…1 in order not to complicate figure. Our investigations [16] show that only the anisotropy of fission fragment angular distribution is dependent on both k s and γ K values, as it was found in previous investigation with heavy compound nuclei [6]. The comparison of theoretical 4D calculations with experimental data for the 200 Pb is presented in fig.…”

“…After appearance of the neck in nuclear shape the γ const K value is joined smoothly with γ neck K (q), which was obtained in Refs. [5,16]. The third one is given by equation…”

Fission fragment distributions within dynamical approach

“…Recent theoretical dynamical 4D Langevin calculations [61,63,159,[212][213][214] realized the pure dynamical treatment of the K-mode relaxation process. The investigations were made for light, medium and heavy compound nucleus formed in the heavy ion collisions (from 162 Yb to 264 Rf).…”

“…Above-mentioned recent works [63,159,213,214] demonstrated that the impact of the dissipation coefficient for shape parameters (k s ) and the one for the Kmode (γ K ) on the calculated observables can be selec-tively probed. The nuclear viscosity with respect to nuclear shape parameters influences the emitted particle multiplicities (n pre ), the fission fragment MED parameters, and the angular distribution of fission fragments.…”

“…The question of value and deformation dependence of γ K were investigated through several works [63,159,213,214]. Initially deduced by Lestone constant value γ K = 0.077 (MeV zs) −1/2 was proved [61,63] to be a good approximation for fission of heavy compound nucleus with A CN 250.…”