Results on the influence of neutron-richness on quasifission in intermediate mass reactions

Superheavy elements are primarily formed through heavy ion fusion reactions. Formation of a fully equilibrated compound nucleus is a critical step in this reaction mechanism but can be hindered by orders of magnitude by quasifission, a process in which the dinuclear system breaks apart prior to full equilibration. To provide a complete description of heavy-ion fusion it is important to characterize the quasifission process. The interplay between the fusion-fission and quasifission reaction channels was explored by measuring fission mass distributions in eight different combinations of Cr+W reactions, with varying neutron-richness, at the Australian National University. The reactions were measured in two energy regimes: one at 13% above the Bass fusion barrier and one at 52.0 MeV of excitation energy in the compound nucleus, . For the systems measured at Ec.m./ VBass = 1.13 the dependence on the neutron-richness is clear. However, for the reactions at = 52.0 MeV, the dependence is less clear and additional factors are shown to play a vital role, especially the influence of deformation on the effective fusion barrier. The present work demonstrates that quasifission is an important process in competition with heavy-ion fusion in reactions with intermediate mass projectiles, particularly with more neutron-rich systems.