Production of265Sg in the248Cm(22Ne,5n)265Sg reaction and decay properties of two isomeric states in265Sg

Abstract

Two isomeric states of ${}^{265}$Sg, i.e., ${}^{265}$Sg${}^{a}$ and ${}^{265}$Sg${}^{b}$, proposed in Ch. E. D\"ullmann and A. T\"urler [Phys. Rev. C 77, 064320 (2008)] were produced in the ${}^{248}$Cm(${}^{22}$Ne,5$n$)${}^{265}$Sg reaction. Decay properties of ${}^{265}$Sg${}^{a,b}$ were investigated with a rotating-wheel apparatus for $\ensuremath{\alpha}$ and spontaneous fission (SF) spectrometry under low background conditions attained by a gas-jet transport system coupled to the RIKEN gas-filled recoil ion separator. Based on genetically correlated $\ensuremath{\alpha}$-$\ensuremath{\alpha}$(-$\ensuremath{\alpha}$) and $\ensuremath{\alpha}$-SF decay chains, 18 and 24 events were assigned to ${}^{265}$Sg${}^{a}$ and ${}^{265}$Sg${}^{b}$, respectively. The half-life ${T}_{1/2}$ and $\ensuremath{\alpha}$-particle energy ${E}_{\ensuremath{\alpha}}$ of ${}^{265}$Sg${}^{a}$ were measured to be 8.5${}_{\ensuremath{-}1.6}^{+2.6}$ s and 8.84 $\ifmmode\pm\else\textpm\fi{}$ 0.05 MeV, respectively, and those of ${}^{265}$Sg${}^{b}$ were 14.4${}_{\ensuremath{-}2.5}^{+3.7}$ s and 8.69 $\ifmmode\pm\else\textpm\fi{}$ 0.05 MeV. As a daughter product of ${}^{265}$Sg${}^{a,b}$, the decay properties of the 3-s isomeric state in ${}^{261}$Rf, i.e., ${}^{261}$Rf${}^{b}$, were also derived: ${T}_{1/2}$ $=$ 2.6${}_{\ensuremath{-}0.5}^{+0.7}$ s, ${E}_{\ensuremath{\alpha}}$ $=$ 8.51 $\ifmmode\pm\else\textpm\fi{}$ 0.06 MeV, and SF branch ${b}_{\mathit{SF}}$ $=$ 0.82 $\ifmmode\pm\else\textpm\fi{}$ 0.09. These results confirm and refine the decay pattern suggested for the decay chain ${}^{269}$Hs $\ensuremath{\rightarrow}$ ${}^{265}$Sg${}^{a,b}$ $\ensuremath{\rightarrow}$ ${}^{261}$Rf${}^{a,b}$ $\ensuremath{\rightarrow}$ ${}^{257}$No $\ensuremath{\rightarrow}$ in D\"ullmann and T\"urler. The production cross sections for ${}^{265}$Sg${}^{a}$ and ${}^{265}$Sg${}^{b}$ were determined to be 180${}_{\ensuremath{-}60}^{+80}$ and 200${}_{\ensuremath{-}50}^{+60}$ pb at 117.8 MeV, respectively, and they are discussed by comparing with the literature data as well as the theoretical prediction.