Soft-to-hard mode transition in the dynamical dipole mode induced in dissipative heavy-ion collisions

The collective dipole dynamics evolving in intermediate dinuclear systems with exotic shape and charge distributions formed in charge asymmetric fusion entrance channels are systematically studied by solving a microscopic transport Boltzmann-Nordheim-Vlasov (BNV) equation and analyzing the obtained dipole signal. The BNV analysis shows a typical transition in the dipole oscillation frequency related to a transition from soft-to-hard mode in the dynamical dipole mode. The relative pre-equilibrium γ-ray emission probability is also evaluated by using the classical bremsstrahlung approach. In particular, by using this approach an analytical formula that gives the time-dependent γ rate during the equilibration of the collective mode versus the statistical GDR is extrapolated. The results are in agreement with other models and the few existing experimental data.