Dynamical treatment of fission fragment angular distribution

Abstract

A dynamical approach to the treatment of fission fragment angular distribution is developed. The approach is based on three-dimensional Langevin dynamics for shape collective coordinates joined with the Monte Carlo algorithm for the degree of freedom associated with the projection K of the total angular momentum of the fissioning system on the symmetry axis. The relaxation time of the tilting mode τ K is estimated. From fits to experimental data on the fission fragment angular distribution of heavy fissioning compound systems, the K equilibration time is deduced to be ∼4 × 10 −21 s for temperatures ∼1-2 MeV. A modified one-body mechanism of nuclear viscosity with the reduction coefficient of the contribution from the 'wall' formula k s = 0.25 has been used in calculations.

Role of asymmetry parameter and dissipation coefficient ofKcoordinate in angular distribution of fission fragments

“…The compound nuclei formed in such reactions have a temperature of about 1 MeV and low angular momenta. It has been found that the standard saddle-point transition-state model frequently predicted low values of the angular distribution anisotropy for reactions with more massive ions of carbon, oxygen, and heavier ions [14,15], and the experimental data are closer to the values obtained according to the scission-point transition-state model.…”

Four-dimensional Langevin dynamics of heavy-ion-induced fission

“…An explicit expression for the friction tensor is given in Refs. [21,23,42]. The value k s = 1.0 corresponds to the standard "wall" and "wall-pluswindow" formulas [36,37,43], whereas values 0.2 < k s < 0.5 allow the reproduction of different features of the massenergy distribution, particle multiplicities in multidimensional Langevin calculations [5,6,11,24,25,42,44], and the widths of isoscalar giant resonances over a broad range of nuclear masses [38].…”

“…[19]. Such description is more consistent than the application of the Metropolis algorithm [20,21,49]. The Langevin equation for the K coordinate allows the modeling of the relaxation process of K states depending on the instantaneous physical properties of fissioning system such as temperature and moment of inertia instead of treating the corresponding relaxation time τ K as a free parameter [20][21][22].…”

“…An alternative dynamical description of the evolution of the orientation degree of freedom on the basis of a Metropolis algorithm and an algorithm of Kubo-Anderson process was previously developed in Refs. [20][21][22]. This approach was successfully applied to describe fragment angular distributions from excited compound nuclei fission.…”

Study of fusion and fission cross sections and pre-fission particles multiplicities for excited nuclei 227 Pa

“…Furthermore, we also use the three-dimensional Langevin model was developed in references (Karpov et al, 2001(Karpov et al, , 2007Nadtochy et al, 2002;Ryabov et al, 2008) to reproduce experimental data on the average pre-fission proton and alpha multiplicities for 227 Pa. The dynamical model has been described in detail in our previous papers (Eslamizadeh, 2011b(Eslamizadeh, , 2012b(Eslamizadeh, , 2013.…”