مشخصات پژوهش

A stochastic approach based on one- and two-dimensional Langevin equations is applied to calculate the pre-scission neutron multiplicity, fission probability, anisotropy of ¯ssion fragment angular distribution, fission cross section and the evaporation cross section for the compound nuclei 188Pt, 227Pa and 251Es in an intermediate range of excitation energies. The chaos weighted wall and window friction formula are used in the Langevin equations. The elongation parameter, c, is used as the ¯rst dimension and projection of the total spin of the compound nucleus onto the symmetry axis, K, considered as the second dimension in Langevin dynamical calculations. A constant dissipation coe±cient of K, °K =0:077(MeV zs)?1=2, is used in two-dimensional calculations to reproduce the above mentioned experimental data. Comparison of the theoretical results of the pre-scission neutron multiplicity, ¯ssion probability, ¯ssion cross section and the evaporation cross section with the experimental data shows that the results of two-dimensional calculations are in better agreement with the experimental data. Furthermore, it is shown that the two-dimensional Langevin equations together with a dissipation coe±cient of K, °K = 0:077(MeV zs)?1=2, can satisfactorily reproduce the anisotropy of ¯ssion fragment angular distribution for the heavy compound nucleus 251Es. However, a larger value of °K =0:250(MeV zs)?1=2 is needed to reproduce the anisotropy of ¯ssion fragment angular distribution for the lighter compound nucleus 227Pa.