THE ISOSPIN DISTRIBUTION OF FRAGMENTS IN REACTIONS 96Ru + 96Ru, 96Ru + 96Zr, 96Zr + 96Ru, and 96Zr + 96Zr AT BEAM ENERGY 400 AMeV

The isospin distribution of particles and fragments in collisions 96Ru + 96Ru, 96Ru + 96Zr, 96Zr + 96Ru and 96Zr + 96Zr at beam energy 400 AMeV is studied with isospin-dependent QMD model. We find that the rapidity distribution of differential neutron–proton counting in neutron rich nucleus–nucleus collisions at intermediate energies is sensitive to the isospin-dependent part of nuclear potential. The study of the N/Z ratio of nucleons, light charged particles (LCP) and intermediate mass fragments (IMF) shows that the isospin-dependent part of nuclear potential drives IMF to be more isospin symmetric and emitted nucleons to be more neutron rich. From the study of the time evolution of the isospin distribution in emitted nucleons, LCP and IMF we find that neutrons diffuse much faster than protons at the beginning and the final isospin distribution is a result of dynamical balance of symmetry potential and Coulomb force under the charge conservation.