Skyrme forces and the fusion-fission dynamics of the132Sn+64Ni→196Pt*reaction

Abstract

The dependence of the fusion-fission process on Skyrme forces is studied by using the dynamical cluster-decay model (DCM) and the $\ensuremath{\ell}$-summed extended-Wong model in the ${}^{132}\mathrm{Sn}+{}^{64}\mathrm{Ni}\ensuremath{\rightarrow}{{}^{196}\mathrm{Pt}}^{*}$ reaction, where the nuclear proximity potential is obtained by using the semiclassical extended Thomas-Fermi (ETF) approach in the Skyrme energy density formalism (SEDF) under the frozen density approximation. The DCM gives an excellent fit to the measured fusion evaporation residue (ER) and the fission cross sections below and above barrier energies, with ER data needing ``barrier lowering'' at below-barrier energies for each Skyrme force (an in-built property of the DCM). The fission cross sections show a contribution of quasifission (qf) at the above-barrier two or three highest energies, depending on the Skyrme force. Calculations are illustrated for three Skyrme forces, GSkI, SSk, and SIII. Another interesting result is that there is a change of fission mass distribution from a predominantly asymmetric one to a symmetric one with a decrease in the $N/Z$ ratio of the compound nucleus, independent of the choice of nuclear interaction potential, which gives an opportunity to address the isospin effects in the Pt${}^{*}$ nucleus. Within the $\ensuremath{\ell}$-summed extended-Wong model we find that the GSkI and SSk forces fit the total fusion cross-section data exactly, whereas the SIII force needs ``barrier modification'' in order to fit the data at below-barrier energies. This happens because the isospin and neutron-proton asymmetry nature of GSkI and SSk forces is different from that of the SIII force, and because the center-of-mass energy ${E}_{\mathrm{c}.\mathrm{m}.}$ dependence of the barrier height for the SIII force and that of Blocki et al. [Ann. Phys. (NY) 105, 427 (1977)] differs strongly (by a constant amount of $\ensuremath{\sim}$7 MeV) from those for GSKI and SSk forces. Note that, because of the associated preformation factor with each fragment, the DCM has the advantage of treating various decay processes separately, whereas the Wong model describes only the total fusion cross section, a sum of cross sections due to all contributing processes.