Isospin effect in intermediate energy heavy ion collisions

The isospin effect in central and peripheral heavy-ion collisions at intermediate energies is studied by means of improved quantum molecular dynamics and isospin dependent quantum molecular model. It is shown that the influence of the density dependence of the symmetry potential on the average N/Z ratio of the products in central and peripheral reactions exhibits different character due to the different mechanism of particle emission. We find that the average N/Z ratio of emitted nucleons in neutron-rich heavy ion collisions is sensitive to the symmetry potential for both central and peripheral cases. Furthermore, for peripheral neutron-rich heavy ion collisions, the N/Z ratio of intermediate mass fragments is also sensitive to the density dependence of the symmetry potential, which provides us with a useful probe to the symmetry potential.