Dynamical cluster-decay model for hot and rotating light-mass nuclear systems applied to the low-energy S-32+Mg-24 -> Ni-56(*) reaction

The dynamical cluster-decay model (DCM) is developed further for the decay of hot and rotating compound nuclei (CN) formed in light heavy-ion reactions. The model is worked out in terms of only one parameter, namely the neck-length parameter, which is related to the total kinetic energy TKE(T) or effective Q value Q(eff)(T) at temperature T of the hot CN and is defined in terms of the CN binding energy and ground-state binding energies of the emitted fragments. The emission of both the light particles (LP), with Aless than or equal to4,Zless than or equal to2, as well as the complex intermediate mass fragments (IMF), with 42, is considered as the dynamical collective mass motion of preformed clusters through the barrier. Within the same dynamical model treatment, the LPs are shown to have different characteristics compared to those of the IMFs. The systematic variations of the LP emission cross section sigma(LP) and IMF emission cross section sigma(IMF) calculated from the present DCM match exactly the statistical fission model predictions. A nonstatistical dynamical description is developed for the first time for emission of light particles from hot and rotating CN. The model is applied to the decay of Ni-56* formed in the S-32+Mg-24 reaction at two incident energies E-c.m.=51.6 and 60.5 MeV. Both the IMFs and average TKE_ spectra are found to compare resonably well with the experimental data, favoring asymmetric mass distributions. The LPs' emission cross section is shown to depend strongly on the type of emitted particles and their multiplicities.