Measurement of the Survival Probabilities for Hot Fusion Reactions

We have studied the fission-neutron emission competition in highly excited $^{274}\mathrm{Hs}$ ($Z=108$) (where the fission barrier is due to shell effects) formed by a hot fusion reaction. Matching cross bombardments ($^{26}\mathrm{Mg}+^{248}\mathrm{Cm}$ and $^{25}\mathrm{Mg}+^{248}\mathrm{Cm}$) were used to identify the properties of first chance fission of $^{274}\mathrm{Hs}$. A Harding-Farley analysis of the fission neutrons emitted in the $^{25,26}\mathrm{Mg}+^{248}\mathrm{Cm}$ was performed to identify the prescission and postscission components of the neutron multiplicities in each system. (${\mathrm{\ensuremath{\Gamma}}}_{n}/{\mathrm{\ensuremath{\Gamma}}}_{t}$) for the first chance fission of $^{274}\mathrm{Hs}$ (${E}^{*}=63\text{ }\text{ }\mathrm{MeV}$) is $0.89\ifmmode\pm\else\textpm\fi{}0.13$; i.e., $\ensuremath{\sim}90%$ 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.

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