The deformed doubly magic nucleus ${}^{270}\mathrm{Hs}$ has so far only been observed as the four-neutron ($4n$) evaporation residue of the reaction ${}^{26}\mathrm{Mg}+{}^{248}\mathrm{Cm}$, where a maximum cross section of $3$ pb was measured. Theoretical studies on the formation of ${}^{270}\mathrm{Hs}$ in the $4n$ evaporation channel of fusion reactions with different entrance channel asymmetry in the framework of a two-parameter Smoluchowski equation predict that the reactions ${}^{48}\mathrm{Ca}+{}^{226}\mathrm{Ra}$ and ${}^{36}\mathrm{S}+{}^{238}\mathrm{U}$ result in higher cross sections due to lower reaction $Q$ values, in contrast to simple arguments based on the reaction asymmetry, which predict opposite trends. Calculations using hivap predict cross sections for the reaction ${}^{36}\mathrm{S}+{}^{238}\mathrm{U}$ that are similar to those of the ${}^{26}\mathrm{Mg}+{}^{248}\mathrm{Cm}$ reaction. Here, we report on the first measurement of evaporation residues formed in the complete nuclear fusion reaction ${}^{36}\mathrm{S}+{}^{238}\mathrm{U}$ and the observation of ${}^{270}\mathrm{Hs}$, which is produced in the $4n$ evaporation channel, with a measured cross section of $0.8_{-0.7}^{+2.6}$ pb at $51$-MeV excitation energy. The one-event cross-section limits ($68\%$ confidence level) for the $3n$, $4n$, and $5n$ evaporation channels at $39$-MeV excitation energy are $2.9$ pb, while the cross-section limits of the $3n$ and $5n$ channel at $51$ MeV are $1.5$ pb. This is significantly lower than the $5n$ cross section of the ${}^{26}\mathrm{Mg}+{}^{248}\mathrm{Cm}$ reaction at similar excitation energy.

• Received 17 March 2010

DOI:https://doi.org/10.1103/PhysRevC.81.061601