Competition between fusion-fission and quasifission processes in the S-32+W-184 reaction

The angular distributions of fission fragments for the S-32 + W-184 reaction at center-of-mass energies of 118.8, 123.1, 127.3, 131.5, 135.8, 141.1, and 144.4 MeV are measured. The experimental fission excitation function is obtained. The anisotropy (A(exp)) is found by extrapolating each fission fragment angular distribution. The measured fission cross sections of the S-32 + W-182,W-184 reaction are decomposed into fusion-fission, quasifission, and fast-fission contributions by the dinuclear system model (DNS). The angular momentum distributions of the dinuclear system and compound nucleus calculated by the DNS model are used to reproduce the experimental capture and fusion excitation functions for both reactions and quantities K-0(2), < l(2)>, and A(exp), which characterize angular distributions of the fission products at the considered range of beam energy. The total evaporation residue excitation function for the S-32 + W-184 reaction calculated in the framework of the advanced statistical model is close to the available experimental data only up to about E-c.m. approximate to 160 MeV. The underestimation of the experimental data at high excitation energies E-c.m. > 160 MeV is explained by the fact that the statistical model cannot reproduce the cross section of evaporation residues formed by the nonequilibrium mechanism, that is, without formation of the compound nucleus in the statistical equilibrium state.