Experimental study of the U 238 ( S 36 , 3 − 5 n ) Hs 269 − 271 reaction leading to the observation of Hs 270

The deformed doubly magic nucleus 270Hs has so far only been observed as the four-neutron (4n) evaporation residue of the reaction 26Mg+248Cm, where a maximum cross section of 3 pb was measured. Theoretical studies on the formation of 270Hs 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 48Ca+226Ra and 36S+238U 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 36S+238U that are similar to those of the 26Mg+248Cm reaction. Here, we report on the first measurement of evaporation residues formed in the complete nuclear fusion reaction 36S+238U and the observation of 270Hs, which is produced in the 4n evaporation channel, with a measured cross section of 0.8$ +2.6\atop{-0.7} $ 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 26Mg+248Cm reaction at similar excitation energy.