Dynamic study of fusion reactions for 40,48Ca+90,96Zr around the Coulomb barrier

By using the updated improved quantum molecular dynamics model in which a surface-symmetry potential term has been introduced, the excitation functions for fusion reactions of ^40,48Ca+^90,96Zr at energies around the Coulomb barrier have been studied. The experimental data of the fusion cross sections for ⁴⁰Ca+^90,96Zr have been reproduced remarkably well without introducing any new parameters. The fusion cross sections for the neutron-rich fusion reactions of ⁴⁸Ca+^90,96Zr around the Coulomb barrier are predicted to be enhanced compared with a non-neutron-rich fusion reaction. In order to clarify the mechanism of the enhancement of the fusion cross sections for neutron-rich nuclear fusions, we pay great attention to studying the dynamic lowering of the Coulomb barrier during a neck formation. The isospin effect on the barrier lowering is investigated. It is interesting that the effect of the projectile and target nuclear structure on fusion dynamics can be revealed to a certain extent in our approach. The time evolution of the N/Z ratio at the neck region has been firstly illustrated. A large enhancement of the N/Z ratio at neck region for neutron-rich nuclear fusion reactions is found.