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

Abstract

A four-dimensional dynamical model based on Langevin equations was developed and applied to calculate a wide set of experimental observables for the reactions 16 O + 208 Pb → 224 Th and 16 O + 232 Th → 248 Cf over a wide range of excitation energy. The fusion-fission and evaporation residue cross sections, fission fragment mass-energy distribution parameters, prescission neutron multiplicities, and anisotropy of angular distribution of fission fragments could be reasonably reproduced using a modified one-body mechanism for nuclear friction with a reduction coefficient of the contribution from a wall formula k s 0.25 and a dissipation coefficient for the orientation degree of freedom (K coordinate) γ K 0.077 (MeV zs) −1/2 . Inclusion of the K coordinate into calculation of potential energy changes the stiffness of the nucleus with respect to mass asymmetry coordinate for the values of K = 0 and results in a shift of the Businaro-Gallone point towards larger Z 2 /A values. The experimental data on the fission fragment mass-energy distribution parameters together with mean prescission neutron multiplicity for heavy fissioning nuclei are reproduced through the four-dimensional Langevin calculations more accurately than through three-dimensional calculations.

Dynamical evolution of spectator systems produced in ultrarelativistic heavy-ion collisions

“…At Coulomb barrier energies, the method was successfully used to get insight into nuclear dynamics, and more specifically friction of nuclear matter [29,30,42]. The approach also demonstrated to be a pre-requisite tool for un-ambiguously understanding the dynamics and subtle time evolution of nuclei across the Businaro-Gallone transition [37].…”

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

“…[12][13][14] it was argued that chaos-theory related ideas [14] can be used to calculate the value of the reduction coefficient k s as a function of deformation of the fissioning nucleus. The applications of this approach to calculate the coefficient k s (q) for studying different fission characteristics were rather successful, and have shown that such calculations yield almost the same results as those using the constant k s coefficient from the interval 0.25 < k s < 0.5 [6,12,15].…”

“…The detailed description of the model could be found in Refs. [2,4] and here we give only a short summary. Three collective shape coordinates and the orientation degree of freedom (K coordinate) were considered dynamically from the ground state deformation to the scission into fission fragments.…”

“…In the present study we used recently developed 4D dynamical model for the description of fissioning nucleus shape evolution based on a stochastic approach [1,2,4,7,8]. The detailed description of the model could be found in Refs.…”

“…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]. The significance of orientation degree of freedom (K coordinate), which is the projection of the total angular momentum onto the symmetry axis of fissioning nucleus, was demonstrated and an overdamped Langevin equation for K coordinate were introduced [5,6].…”