Q-value effects on the production of superheavy nuclei

The formation of superheavy nucleus 270Hs via the 4n evaporation channel of fusion reactions 26Mg+248Cm, 30Si+244Pu, 36S+238U, and 48Ca+226Ra is studied using a two-parameter Smoluchowski equation. The evaporation residual cross sections of the reactions 48Ca+226Ra and 36S+238U are obviously enhanced because of their large negative Q values. The enhancement is due to the fact that the excitation energy corresponding to the maximum yield of the evaporation residue depends on the reaction Q value, and the maximum cross section sensitively depends on the increment of this excitation energy relative to the effective threshold energy of which the channel for fission after 4n emission opens