Synthesis of the isotopes of elements 118 and 116 in theCf249andCm245+Ca48fusion reactions

Abstract

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 ${}^{245}\mathrm{Cm}$ (${}^{48}\mathrm{Ca}$, $\mathit{xn}$)${}^{293-x}116$ 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 $E^{*}=29.2\pm 2.5$ and $34.4\pm 2.3$ MeV. During an irradiation with a total beam dose of $4.1\times {10}^{19}$ ${}^{48}\mathrm{Ca}$ projectiles, three similar decay chains consisting of two or three consecutive $\alpha$ 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 ${}^{294}118$ ($E_{\alpha }=11.65\pm 0.06$ MeV, $T_{\alpha }=0.{89}_{-0.31}^{+1.07}$ ms) produced in the $3n$-evaporation channel of the ${}^{249}\mathrm{Cf}+{}^{48}\mathrm{Ca}$ reaction with a maximum cross section of $0.5_{-0.3}^{+1.6}$ pb.