Measurement of the Survival Probabilities for Hot Fusion Reactions

We have studied the fission-neutron emission competition in highly excited (274)Hs (Z = 108) (where the fission barrier is due to shell effects) formed by a hot fusion reaction. Matching cross bombardments (Mg-26 + Cm-248 and Mg-25 + Cm-248) were used to identify the properties of first chance fission of (274)Hs. A Harding-Farley analysis of the fission neutrons emitted in the Mg-25,Mg-26 + Cm-248 was performed to identify the prescission and postscission components of the neutron multiplicities in each system. (Gamma(n)/Gamma(t)) for the first chance fission of (274)Hs (E* = 63 MeV) is 0.89 +/- 0.13; i.e., similar to 90% of the highly excited nuclei survive. The high value of that survival probability is due to dissipative effects during deexcitation. 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.