Fission and quasifission of composite systems with Z=108−120 : Transition from heavy-ion reactions involving S and Ca to Ti and Ni ions

Abstract

Background: Suppression of compound nucleus formation in the reactions with heavy ions by a quasifission process in dependence on the reaction entrance channel.Purpose: Investigation of fission and quasifission processes in the reactions $^{36}\mathrm{S},^{48}\mathrm{Ca},^{48}\mathrm{Ti}$, and $^{64}\mathrm{Ni}+\phantom{\rule{0.16em}{0ex}}^{238}\mathrm{U}$ at energies around the Coulomb barrier.Methods: Mass-energy distributions of fissionlike fragments formed in the reaction $^{48}\mathrm{Ti}+\phantom{\rule{0.16em}{0ex}}^{238}\mathrm{U}$ at energies of 247, 258, and 271 MeV have been measured using the double-arm time-of-flight spectrometer CORSET at the U400 cyclotron of the Flerov Laboratory of Nuclear Reactions and compared with mass-energy distributions for the reactions $^{36}\mathrm{S},^{48}\mathrm{Ca},^{64}\mathrm{Ni}+\phantom{\rule{0.16em}{0ex}}^{238}\mathrm{U}$.Results: The most probable fragment masses as well as total kinetic energies and their dispersions in dependence on the interaction energies have been investigated for asymmetric and symmetric fragments for the studied reactions. The fusion probabilities have been deduced from the analysis of mass-energy distributions.Conclusion: The estimated fusion probability for the reactions S, Ca, Ti, and Ni ions with actinide nuclei shows that it depends exponentially on the mean fissility parameter of the system. For the reactions with actinide nuclei leading to the formation of superheavy elements the fusion probabilities are of several orders of magnitude higher than in the case of cold fusion reactions.