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The effects of the entrance channel and shell structure on the experimental evaporation residues have been studied by analyzing the 32S + 182W, 48Ti + 166Er and 60Ni + 154Sm reactions leading to 214Th*; the 40Ar + 181Ta reaction leading to 221Pa*; the 48Ca + 243Am, 248Cm, 249Cf reactions leading to the 291115, 296116 and 297118 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, $\Gamma_{\rm n} / \Gamma_{\rm f}$ 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.

of complete fusion with the quasifission process is strongly related to the intrinsic fusion barrier B ∗ and the quasifission barrier Bqf, as well as the size of the well in the nucleus–nucleus potential. In our calculations of the excitation functions for capture, fusion, and evaporation residues, we use the relevant variables such as mass asymmetry of nuclei in the entrance channel, potential energy surface, driving potential, spin distribution, and surviving probability of compound nucleus that are responsible for the mechanism of the fusion–fission process. As a result, we obtain a beam energy window for the capture of the nuclei before the system fuses and the Γn/Γf ratio at each step along the deexcitation cascade of the compound nucleus. Calculations performed in the framework of the model taking into account the nuclear shell effect and shape of colliding nuclei allowus to reach useful conclusions about the mechanism of the fusion –fission process and the production of the evaporation residues. We analyze the 40 Ar + 176 Hf, 86 Kr + 130 Xe, and 124 Sn + 92 Zr reactions leading to 216 Th ∗ ;t he 32 S + 182 Wa nd 60 Ni + 154 Sm reactions leading to 214 Th ∗ ;t he 48 Ca + 248 Cm reaction leading to the 296 116 compound nucleus; and the 48 Ca + 249 Cf reaction leading to the 297 118 compound nucleus. c � 2003 MAIK “Nauka/Interperiodica”.