Experimental study of the U(S, 3-5)Hs reaction leading to the observation of Hs

Graeger, R.*; Ackermann, D.*; Chelnokov, M.*; Chepigin, V.*; Dllmann, C. E.*; Dvorak, J.*; Even, J.*; Gorshkov, A.*; Heberger, F. P.*; Hild, D.*; Hbner, A.*; Jger, E.*; Khuyagbaatar, J.*; Kindler, B.*; Kratz, J. V.*; Krier, J.*; Kuznetsov, A.*; Lommel, B.*; Nishio, Katsuhisa   ; Nitsche, H.*; Omtvedt, J. P.*; Petrushkin, O.*; Rudolph, D.*; Runke, J.*; Samadani, F.*; Schdel, M.*; Schausten, B.*; Trler, A.*; Yakushev, A.*; Zhi, Q.*

The deformed doubly-magic nucleus Hs so far has only been observed as the four-neutron (4n) evaporation residue of the reaction Mg + Cm, where a maximum cross section of 3 pb was measured. Theoretical studies on the formation of Hs in the 4n evaporation channel of fusion reactions with different entrance channel asymmetry in the framework of a two-parameter Smoluchowski equation predict the reactions Ca + Ra and S + U to result in higher cross sections due to lower reaction Q-values. Here, we report on the first measurement of evaporation residues formed in the fusion reaction S + U and the observation of Hs, produced in the 4n evaporation channel, with a measured cross section of 0.8 pb at 51 MeV excitation energy. The one event cross section limits 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 Mg + Cm reaction at a similar excitation energy.