Application of a temperature-dependent liquid-drop model to dynamical Langevin calculations of fission-fragment distributions of excited nuclei

Abstract

A stochastic approach to fission dynamics based on three-dimensional Langevin equations was applied to calculation of the mass-energy and angular distributions of fission fragments. The dependence of the mass-energy distribution parameters on the angular momentum and the anisotropy of the fission-fragment angular distribution on excitation energy have been studied in a wide range of the fissility parameter. A temperature-dependent finite-range liquid-drop model was used in a consistent way to calculate the functional of the Helmholtz free energy and level-density parameter. The modified one-body mechanism of nuclear dissipation (the so-called surface-plus-window dissipation) was used to determine the dissipative forces in Langevin equations. The evaporation of light prescission particles was taken into account on the basis of a statistical model combined with Langevin dynamics. The calculated parameters of the mass-energy distribution and their angular dependencies are in good quantitative agreement with the available experimental data at the value of the reduction coefficient of the contribution from the wall formula equal to 0.25. Analysis of the anisotropy of the fission-fragment angular distribution performed with the saddle-point transition state model and scission-point transition state model indicates that it is necessary to take into account the dynamical aspects of the fission-fragment angular distribution formation.

Two-mode fission – experimental verification and characterization of two fission-modes

“…The calculations are in good agreement with experimental data of lowenergy actinide fission. A number of dynamical models of fission have also been developed using, such as the Langevin approach [71] and the time-dependent HartreeFock-Bogoliubov method [66]. Further quantitative interpretation of mass-division mechanism will add considerably to experimental and theoretical studies related to systematic characters of fission.…”

Effect of N/Z in pre-scission neutron multiplicity for16,18O+194,198Pt systems

“…The fission width is calculated following the work of Kramers [4] where the dynamics of the fission degree of freedom is considered similar to that of a Brownian particle in a heat bath. The temperature of the heat bath which represents all the other nuclear degrees of freedom is given by the compound nuclear temperature T. The driving force in a thermo dynamical system such as a hot nucleus is provided by the free energy of the system [5,6]. The rotational energy of the compound nucleus is obtained using the shape-dependent rigid body moment of inertia and is included in the FRLDM potential [7].…”

Mass-energy distribution of fragments in Langevin dynamics of fission induced by heavy ions

“…It should be noted that the driving force in an excited system is not simply the negative gradient of the bare potential V(q), but should contain a thermodynamical correction [7,8,22]. In the present study the Helmholtz free energy F(q) is the thermodynamical driving potential.…”