Examination of coexistence of symmetric mass and asymmetric charge distributions of fission fragments

Using the improved scission-point model, the mass and charge distributions of fission fragments of the Hg-180,Hg-182,Hg-190,Hg-198* and Pb-202* formed in complete fusion reactions Ar-36 + Sm-144, Ca-40 + Nd-142, Ar-36 + Sm-154, alpha + Pt-194, and Ca-48 + Sm-154 are studied and compared with available experimental data. The transition is explained from the mass-asymmetric distribution in fissioning Hg-180(,)182(,)190* to the mass-symmetric distribution found in fissioning Hg-198* and Pb-202*. The retention of the asymmetric mass distributions is treated in the case of fissioning Hg-180(,)182(,)190* with increasing excitation energy. In the fissioning Hg-198* and Hg-l82*, completely different shapes are predicted for charge and mass yields.