Stochastic model of fission fragment angular distribution for excited compound nuclei

A dynamical approach to treatment of the fission fragment angular distribution is developed. The approach is based on the three-dimensional Langevin dynamics for shape collective coordinates joined with a Monte-Carlo algorithm for the degree of freedom associated with the projection K of the total angular momentum of fissioning system on the symmetry axis. The relaxation time of the tilting mode τK is estimated. From the fits to the experimental data on the fission fragment angular distribution of heavy fissioning compound systems the K equilibration time is deduced to be (2-4)·10-21 s for the temperatures ∼ 1-2 MeV. A modified one-body mechanism of nuclear dissipation with reduction coefficient of the contribution from the 'wall' formula ks=0.5 has been used in the calculations