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 compound nuclei Hg∗180,182,190,198 and Pb∗202 formed in complete fusion reactions Ar36+Sm144, Ca40+Nd142, Ar36+Sm154, α+Pt194, and Ca48+Sm154 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∗182, completely different shapes are predicted for charge and mass yields.