Competition Between Fusion-Fission and Quasifission in Heavy-Ion Reactions Leading to Superheavy Elements

The process of fusion-fission of heavy and superheavy nuclei (SHE) formed in the reactions with ⁴⁸Ca and ⁵⁸Fe ions at energies near and below the Coulomb barrier has been studied. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR) using the time-of-flight spectrometer of fission fragments CORSET and the neutron multi-detector DEMON. The neutron multiplicities <M_n> and the γ-ray multiplicities <M_γ> in coincidence with fission fragments were investigated. A weak dependence of <M_γ> as a function of the excitation energy E* for quasi-fission in comparison with fusion-fission was found. The different dependence of <M_γ> as a function of fission fragment mass or total kinetic energy (TKE) for fusion-fission and quasi-fission processes was observed. As well as for <M_γ> noticeable differences have been observed in the values of neutron multiplicities <M_n> for different mechanisms of superheavy compound nucleus decay (fusion-fission or quasi-fission), Thus, the fusion-fission and quasi-fission processes manifest itself in the γ-ray and neutron multiplicities as a function of mass, TKE, excitation energy of the compound system and entrance channel in significantly different ways.