Investigation of ?ssion properties and evaporation residue measurement in the reactions using 238U target nucleus

摘要

Fragment mass distributions for ?ssion after full momentum transfer were measured in the reactionsof 30Si,34,36 S,31P,40Ar + 238U at bombarding energies around the Coulomb barrier. Mass distributions change signi?cantly as a function of incident beam energy. The asymmetric ?ssion probability increases at sub-barrier energy. The phenomenon is interpreted as an enhanced quasi?ssion probability owing to orientation effects on fusion and/or quasi?ssion. The evaporation residue (ER) cross sections were measured in the reactions of 30Si + 238U and 34S + 238U to obtain information on fusion. In the latter reaction, signi?cant suppression of fusion was implied. This suggests that ?ssion events different from compound nucleus are included in the masssymmetric fragments. The results are supported by a model calculation based on a dynamical calculation using Langevin equation, in which the mass distribution for fusion-?ssion and quasi?ssion fragments are separately determined.