مشخصات پژوهش

Fission processes of the excited compound nuclei 197Tl, 217Fr, 224Th, and 254Fm in a wide range of mass numbers produced in fusion reactions have been simulated in the framework of the modified statistical model and different observables were reproduced for these nuclei. In the statistical calculations have been considered the effects of the projection of the total spin of the compound nucleus onto the symmetry axis 𝐾, the temperature dependence of the location and height of fission transition points, and the classical collective motion of the excited compound nuclei about the ground state. Furthermore, in the present research, particle binding energies as a function of deformation of nuclei and subbarrier fission have been considered for more accurate reproduction of the experimental data. The fission cross section, the evaporation residue cross section, the fission probability, the average prescission neutron multiplicity, and the anisotropy of fission fragments’ angular distribution have been calculated for the excited compound nuclei 197Tl, 217Fr, 224Th, and 254Fm. In the statistical simulations, the scaling factor of the fission barrier height, 𝑟𝑠, and the temperature coefficient of the effective potential, 𝑘, were considered as a free parameter. For each reaction the parameters 𝑟𝑠 and 𝑘 were adjusted to reproduce a single fission cross section and a single evaporation residue cross section. It was shown that the results of calculations are in good agreement with the experimental data by using appropriate values for these parameters equal to 𝑘=0.0182±0.0050Me⁢V−2 and 𝑟𝑠=1.0005±0.0020 for 197Tl ; 𝑘=0.0063±0.0040Me⁢V−2 and 𝑟𝑠=1.0042±0.0015 for 217 Fr; 𝑘=0.0060±0.0040Me⁢V−2 and 𝑟𝑠=1.0050±0.0020 for 224Th; 𝑘=0.0025±0.0015Me⁢V−2 and 𝑟𝑠=1.0100±0.0014 for 254Fm . Furthermore, by using appropriate values of parameters 𝑘 and 𝑟𝑠 I have calculated the average prescission neutron multiplicity, the fission probability, and the anisotropy of fission fra