هادی اسلامی زاده

The dynamics of fission of the excited compound nuclei 256Fm,215Fr ,187Ir ,172Yb,162Yb and 142Ce produced in fusion reactions with 158.8 MeV 18O has been studied by solving three- and four-dimensional Langevin equations with dissipation generated through the chaos weighted wall and window friction formula. Constant dissipation coefficients of K, gk , and a non-constant dissipation coefficient of K have been used to reproduce the experimental data for both symmetric and asymmetric splitting of the fissioning systems. The average kinetic energies of fission fragments, the prescission neutron multiplicities, the fission time and the variances of the mass and kinetic energy of fission fragments have been calculated for the excited compound nuclei 256Fm,215Fr ,187Ir ,172Yb,162Yb and results of the calculations compared with each other and with the experimental data. Comparison of the theoretical results with the experimental data calculated by using different values of gk was shown that the difference between the results of calculations for symmetric and asymmetric simulations of the fission process of excited intermediate nuclei is low whereas for heavy compound nuclei is slightly high. In other words, the effect of asymmetry parameter on the fission process of intermediate nuclei is smaller than heavy nuclei. Furthermore, it was shown that the prescission neutron multiplicity decreases rapidly with the increase in fragment asymmetry.