Entrance channel effects on the isospin fractionation at intermediate energy heavy ion collisions

We investigate the dependence of isospin fractionation degree on the entrance channel condition, which includes the impact parameter, the beam energy, the mass and the neutron-proton ratio of the colliding system as well as quantifying the gas phase and the liquid phase by using the isospin dependent quantum molecular dynamics model. We found that the isospin fractionation degree increases markedly with the enhancements of the neutron-proton ratio of system and the beam energy; however, it decreases with increasing system mass as well as slowly increases with the enhancement of the impact parameter. In particular, the property for the sensitive dependence of isospin fractionation degree on the symmetry potential and its weak dependence on the in-medium nucleon-nucleon cross-section is preserved for all the neutron-rich systems and all the impact parameters in the relative lower beam energy region. In this case, the isospin fractionation degree for all the neutron-rich systems can be directly compared with the experimental data to extract the information on the symmetry potential in the relative lower beam energy region.