New information on survival probabilities in hot fusion reactions

Recently we studied the fission-neutron emission competition in highly excited (E$^{\ast}$ = 63 MeV) $^{274}$Hs (Z=108) (where the fission barrier is due to shell effects) formed by a hot fusion reaction. At this excitation energy, these shell effects are expected to be ``washed out'' leaving a barrier height of $\leq$ 1 MeV. Matching cross bombardments ($^{26}$Mg + $^{248}$Cm and $^{25}$Mg + $^{248}$Cm) were used to identify the properties of first chance fission of $^{274}$Hs. A Harding-Farley analysis of the fission neutrons emitted in the $^{25,26}$Mg + $^{248}$Cm reaction was performed to identify the pre- and post-scission components of the neutron multiplicities in each system. ($\Gamma$$_{n}$/$\Gamma$$_{t}$) for the first chance fission of $^{274}$Hs is 0.89 $\pm$ 0.13, i.e., $\sim$ 90\% of the highly excited nuclei survive. The high value of that survival probability is due to dissipative effects (Kramers) during de-excitation. A proper description of the survival probabilities of excited superheavy nuclei formed in hot fusion reactions requires consideration of both dynamic and static (shell-related) effects. A re-analysis of several hot fusion survival probabilities under these constraints is presented.