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

A four-dimensional dynamical model based on Langevin equations was developed and applied to calculate a wide set of experimental observables for the reactions ¹⁶O+²⁰⁸Pb→²²⁴Th and ¹⁶O+²³²Th→²⁴⁸Cf 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 kₛ0.25 and a dissipation coefficient for the orientation degree of freedom (K coordinate) γK 0.077 (MeV0.16em0exzs)^-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 Z²/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.