Studies of superheavy nuclei produced in the ${}^{249}$Bk + ${}^{48}$Ca reaction were performed using the Dubna Gas Filled Recoil Separator. The cross section for the production of ${}^{293}$117 and ${}^{294}$117 isotopes was measured at five excitation energies of the ${}^{297}$117 compound nucleus ranging from 30 to 48 MeV and yielding maximum values of 1.1${}_{-0.6}^{+1.2}$ pb for the $3n$ and 2.4${}_{-1.4}^{+3.3}$ pb for the $4n$ reaction channels. Alpha emission from ${}^{281}$Rg competing with spontaneous fission ($\alpha$/SF decay probability 1:9) was observed for the first time leading to the identification of the new isotope ${}^{277}$Mt ($T_{\mathrm{SF}}\approx 5$ ms). The measured decay properties are in good agreement with those expected based on the properties of neighboring even-$Z$ and odd-$Z$ nuclei. The $\alpha$ energies and half-lives of odd-$Z$ isotopes observed in the ${}^{293}$117 and ${}^{294}$117 decay chains together with results obtained for lower-$Z$ superheavy nuclei demonstrate enhanced stability with increasing neutron number toward the predicted new magic number $N=184$.

• Received 6 April 2013

DOI:https://doi.org/10.1103/PhysRevC.87.054621

This article appears in the following collection:

Transuranium Elements and the Physical Review

This collection marks the 150th anniversary of Dmitri Mendeleev’s discovery of the Periodic Table of Elements.