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. (${\mathrm{\Gamma }}_n/{\mathrm{\Gamma }}_t$) for the first chance fission of ${}^{274}\mathrm{Hs}$ ($E^{*}=63\mathrm{MeV}$) 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 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.

Figure 1

Formation cross sections for new heavy elements using hot fusion reactions.

Figure 2

Schematic diagram of the experimental apparatus.

Figure 3

The moving source fits for various detector combinations for the ${}^{26}\mathrm{Mg}+{}^{248}\mathrm{Cm}$ reaction.

Figure 4

The calculated variation of ${\mathrm{\Gamma }}_n/{\mathrm{\Gamma }}_{\text{total}}$ with changes in $B_f$.