Synthesis of the isotopes of elements 118 and 116 in the Cf249 and Cm245+Ca48 fusion reactions

The decay properties of ${}^{290}116$ and ${}^{291}116$, and the dependence of their production cross sections on the excitation energies of the compound nucleus, ${}^{293}116$, have been measured in the $^{245}\mathrm{Cm}$ ($^{48}\mathrm{Ca}$, $\mathit{xn}$)${}^{293\ensuremath{-}x}116$ reaction. These isotopes of element 116 are the decay daughters of element 118 isotopes, which are produced via the $^{249}\mathrm{Cf}+^{48}\mathrm{Ca}$ reaction. We performed the element 118 experiment at two projectile energies, corresponding to ${}^{297}118$ compound nucleus excitation energies of ${E}^{*}=29.2\ifmmode\pm\else\textpm\fi{}2.5$ and $34.4\ifmmode\pm\else\textpm\fi{}2.3$ MeV. During an irradiation with a total beam dose of $4.1\ifmmode\times\else\texttimes\fi{}{10}^{19}$ $^{48}\mathrm{Ca}$ projectiles, three similar decay chains consisting of two or three consecutive $\ensuremath{\alpha}$ decays and terminated by a spontaneous fission (SF) with high total kinetic energy of about 230 MeV were observed. The three decay chains originated from the even-even isotope ${}^{294}118$ (${E}_{\ensuremath{\alpha}}=11.65\ifmmode\pm\else\textpm\fi{}0.06$ MeV, ${T}_{\ensuremath{\alpha}}=0.{89}_{\ensuremath{-}0.31}^{+1.07}$ ms) produced in the $3n$-evaporation channel of the $^{249}\mathrm{Cf}+^{48}\mathrm{Ca}$ reaction with a maximum cross section of $0.{5}_{\ensuremath{-}0.3}^{+1.6}$ pb.