Mechanisms Suppressing Superheavy Element Yields in Cold Fusion Reactions

Abstract

Superheavy elements are formed in fusion reactions which are hindered by fast nonequilibrium processes. To quantify these, mass-angle distributions and cross sections have been measured, at beam energies from below-barrier to 25% above, for the reactions of 48Ca,50Ti, and 54Cr with 208 Pb. Moving from 48Ca to 54Cr leads to a drastic fall in the symmetric fission yield, which is reflected in the measured mass-angle distribution by the presence of competing fast nonequilibrium deep inelastic and quasifission processes. These are responsible for reduction of the compound nucleus formation probablity PCN (as measured by the symmetric-peaked fission cross section), by a factor of 2.5 for 50Ti and 15 for 54Cr in comparison to 48 Ca. The energy dependence of PCN indicates that cold fusion reactions (involving 208Pb) are not driven by a diffusion process.