Measurement of the Survival Probabilities for Hot Fusion Reactions

This is the publisher’s final pdf. The published article is copyrighted by the American Physical Society and can be found at: http://journals.aps.org/prl/.We have studied the fission-neutron emission competition in highly excited ²⁷⁴Hs (Z = 108) (where the\ud fission barrier is due to shell effects) formed by a hot fusion reaction. Matching cross bombardments\ud (²⁶Mg + ²⁴⁸Cm and ²⁵Mg + ²⁴⁸Cm) were used to identify the properties of first chance fission of ²⁷⁴Hs. A\ud Harding-Farley analysis of the fission neutrons emitted in the [superscript 25,26]Mg + ²⁴⁸Cm was performed to identify\ud the prescission and postscission components of the neutron multiplicities in each system. (Γ[subscript n]/Γ[subscript t]) for the\ud first chance fission of ²⁷⁴Hs (E* = 63 MeV) is 0.89 ± 0.13; i.e., ∼90% of the highly excited nuclei survive.\ud The high value of that survival probability is due to dissipative effects during deexcitation. A proper\ud description of the survival probabilities of excited superheavy nuclei formed in hot fusion reactions requires\ud consideration of both dynamic and static (shell-related) effects