Isospin effects in the isospin fractionation process in intermediate energy heavy ion collisions

Based on the isospin dependent quantum molecular dynamics model we investigated the isospin effects of isospin fractionation (N/Z)(gas)/(N/Z)(liq) from the neutron-proton ratio of colliding system and impact parameter. Here (N/Z)(gas) and (N/Z)(liq) is the neutron-proton ratio of nucleon emission for gas phase and that of fragment emission for liquid phase, respectively. Our results show that the (N/Z)(gas)/(N/Z)(liq) increases with the neutron-proton ratio of colliding systems when the system mass, incident energy and impact parameters are fixed. For the neutron-rich systems, the (N/Z)(gas)/(N/Z)(liq) depends sensitively to the form of symmetry potential and weakly on the isospin effect of the in-medium nucleon-nucleon cross section; For the neutron-poor colliding system, however, the (N/Z)(gas)/(N/Z)(liq) is not sensitive to both the form of symmetry potential and the isospin effect of the in-medium nucleon-nucleon cross section. We also found that the dependence of (N/Z)(gas)/(N/Z)(liq) on the impact parameter is not obvious. Detailed discussion and explanation for leading to these results are presented in the paper. According to these results, we propose that (N/Z)(gas)/(N/Z)(liq) can be directly compared with the experimental data to get the information about symmetry potential.