Synthesis of heavy and superheavy elements by reactions of massive nuclei

By comparing theoretical and experimental excitation functions of evaporation residues resulting from the same compound nucleus or heavy and superheavy nuclei, it is possible to understand the effect of the entrance channel and the shell structure of reacting nuclei on the fusion mechanism. The competition of complete fusion with the quasifission process is strongly related to the intrinsic fusion barrier B-fus* and the quasifission barrier B-qf, 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 Gamma(n)/Gamma(f) 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 allow us to reach useful conclusions about the mechanism of the fusion-fission process and the production of the evaporation residues. We analyze the Ar-40 + Hf-176, Kr-86 + Xe-130, and Sn-124 + Zr-92 reactions leading to Th-216*; the S-32 + W-182 and Ni-60 + Sm-154 reactions leading to Th-214*; the Ca-48 + Cm-248 reaction leading to the (296)116 compound nucleus; and the Ca-48 + Cf-249 reaction leading to the (297)118 compound nucleus. (C) 2003 MAIK "Nauka/lnterperiodica".