Formation of heavy and superheavy elements by reactions with massive nuclei

The effects of the entrance channel and shell structure on the experimental evaporation residues have been studied by analyzing the S-32 + W-182, Ti-48 + Er-166 and Ni-60 + Sm-154 reactions leading to Th-214(*); the Ar-40 + Ta-181 reaction leading to Pa-221(*); the Ca-48 + Am-243, Cm-248, Cf-249 reactions leading to the (291)115, (296)116 and (297)118 superheavy compound nuclei, respectively. The fusion mechanism and the formation of evaporation residues of heavy and superheavy nuclei have been studied. In calculations of the excitation functions for capture, fusion and evaporation residues we used such characteristics as mass asymmetry of nuclei in the entrance channel, binding energies and shape of colliding nuclei, potential energy surface, driving potential, partial-fusion cross-sections and survival probability of the compound nucleus, Gamma(n)/Gamma(f) ratio at each step along the de-excitation cascade of the compound nucleus. The calculations have allowed us to make useful conclusions about the mechanism of the fusion-fission process, which is in competition with the quasifission process, and the production of the evaporation residues.