Fusion dynamics of symmetric systems near barrier energies

The enhancement of the sub-barrier fusion cross sections was explained as the lowering of the dynamical fusion barriers within the framework of the improved isospin-dependent quantum molecular dynamics (ImIQMD) model. The numbers of nucleon transfer in the neck region are appreciably dependent on the incident energies, but strongly on the reaction systems. A comparison of the neck dynamics is performed for the symmetric reactions $^{58}$Ni+$^{58}$Ni and $^{64}$Ni+$^{64}$Ni at energies in the vicinity of the Coulomb barrier. An increase of the ratios of neutron to proton in the neck region at initial collision stage is observed and obvious for neutron-rich systems, which can reduce the interaction potential of two colliding nuclei. The distribution of the dynamical fusion barriers and the fusion excitation functions are calculated and compared them with the available experimental data.