Study of viscosity on the fission dynamics of the excited nuclei ²²⁸U produced in ¹⁹F + ²⁰⁹Bi reactions

A two-dimensional (2D) dynamical model based on Langevin equations was applied to study the fission dynamics of the compound nuclei ²²⁸U produced in ¹⁹F + ²⁰⁹Bi reactions at intermediate excitation energies. The distance between the centers of masses of the future fission fragments was used as the first dimension and the projection of the total spin of the compound nucleus onto the symmetry axis, K, was considered as the second dimension in Langevin dynamical calculations. The magnitude of post-saddle friction strength was inferred by fitting measured data on the average pre-scission neutron multiplicity for ²²⁸U. It was shown that the results of calculations are in good agreement with the experimental data by using values of the post-saddle friction equal to 6–8 × 10²¹s^-1. (author)