Probing of the Isospin-Dependent Mean Field and Nucleon-Nucleon Cross Section in a Medium by Nucleon Emissions

We study the isospin effects of the mean field and two-body collision on the nucleon emissions at the intermediate energy heavy ion collisions by using an isospin-dependent transport theory. The calculated results show that the nucleon emission number N_n depends sensitively on the isospin effect of nucleon nucleon cross section and weakly on the isospin-dependent mean field for neutron-poor system in higher beam energy region. In particular, the correlation between the medium correction of two-body collision and the momentum-dependent interaction enhances the dependence of nucleon emission number N_n on the isospin effect of nucleon nucleon cross section. On the contrary, the ratio of the neutron proton ratio of the gas phase to the neutron proton ratio of the liquid phase, i.e., the degree of isospin fractionation <(N/Z)_gasb/<(N/Z)_liq>_b depends sensitively on the isospin-dependent mean field and weakly on the isospin effect of two-body collision for neutron-rich system in the lower beam energy region. In this case, N_n and <(N/Z)_gasb/<(N/Z)_liq>_b are the probes for extracting the information about the isospin-dependent nucleon nucleon cross section in the medium and the isospin-dependent mean field, respectively.