Quasifission and fusion-fission in massive nuclei reactions. Comparison of reactions leading to the Z=120 element

The yields of evaporation residues, fusion-fission and quasifission fragments in the ${}^{48}$Ca+${}^{144,154}$Sm and ${}^{16}$O+${}^{186}$W reactions are analyzed in the framework of the combined theoretical method based on the dinuclear system concept and advanced statistical model. The measured yields of evaporation residues for the ${}^{48}$Ca+${}^{154}$Sm reaction can be well reproduced. The measured yields of fission fragments are decomposed into contributions coming from fusion-fission, quasifission, and fast-fission. The decrease in the measured yield of quasifission fragments in ${}^{48}$Ca+${}^{154}$Sm at the large collision energies and the lack of quasifission fragments in the ${}^{48}$Ca+${}^{144}$Sm reaction are explained by the overlap in mass-angle distributions of the quasifission and fusion-fission fragments. The investigation of the optimal conditions for the synthesis of the new element $Z$=120 ($A$=302) show that the ${}^{54}$Cr+${}^{248}$Cm reaction is preferable in comparison with the ${}^{58}$Fe+${}^{244}$Pu and ${}^{64}$Ni+${}^{238}$U reactions because the excitation function of the evaporation residues of the former reaction is some orders of magnitude larger than that for the last two reactions.