Incorporation of a tilting coordinate into the multidimensional Langevin dynamics of heavy-ion-induced fission: Analysis of experimental data from fusion-fission reactions

Abstract

A four-dimensional dynamical model was developed and applied to study fission characteristics in a wide range of a fissility parameter. Three collective shape coordinates and the $K$ 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 ${k}_{s}$ of the contribution from a ``wall'' formula has been used in the study. The inclusion of the $K$ coordinate in the dynamical consideration and use of the ``chaos-weighted wall formula'' with a deformation-dependent scaling factor ${k}_{s}({q}_{1})$ lead to fairly good reproduction of the variances of the fission-fragment mass distribution and the prescission neutron multiplicity for a number of fissioning compound nuclei in a wide fissility range. The four-dimensional dynamical calculations describe better experimental prescission neutron multiplicity and variances of fission-fragment mass distribution for heaviest nuclei with respect to a three-dimensional dynamical model, where the $K$ coordinate is assumed to be equal to zero. The estimate of a dissipation coefficient for the orientation degree of freedom, ${\ensuremath{\gamma}}_{K}\ensuremath{\simeq}0.077$ ${(\text{MeV}\phantom{\rule{0.16em}{0ex}}\text{zs})}^{\ensuremath{-}1/2}$, is good for heavy nuclei and a larger value of ${\ensuremath{\gamma}}_{K}\ensuremath{\simeq}0.2$ ${(\text{MeV}\phantom{\rule{0.16em}{0ex}}\text{zs})}^{\ensuremath{-}1/2}$ is needed for nuclei with mass ${A}_{\mathrm{CN}}$ $\ensuremath{\simeq}$ 200.