THE STUDY OF FUSION-FISSION AND QUASIFISSION PROCESSES IN THE REACTIONS ⁴⁸Ca+²⁰⁸Pb, ²³²Th, ²³⁸U, ²⁴⁴Pu, ²⁴⁸Cm

Mass-energy distributions and capture cross sections have been measured in the reactions ⁴⁸Ca + ²⁰⁸Pb, ²³²Th, ²³⁸U, ²⁴⁴Pu, and ²⁴⁸Cm at energies around the Coulomb barrier. The properties of the fusion-fission and quasifission processes were studied in dependence on the interaction energies and ion-target combinations. In the reaction ⁴⁸Ca+²⁰⁸Pb the fusion-fission process is dominant. In the reactions of 48Ca with actinide targets the asymmetric quasifission becomes the dominant process. Nevertheless, the analysis of mass and energy distributions has shown that a significant part of symmetric fragments in the range ACN/2 ± 20 u may be attributed to fusion-fission process for the reactions ⁴⁸Ca+²³⁸U, ²⁴⁴Pu, and ²⁴⁸Cm. Using this analysis we estimated the fusion-fission crosssections σ_FF, the survival probabilities W_sur and the lower limits for fission barriers of ^254-256No, ^283-286Cn, ^289-292Fl, and ^293-296Lv compound nuclei.