Isospin effect in multifragmentation process of heavy ion collisions at intermediate energy

From the simulation of intermediate energy heavy ion collisions by using th e isospin dependent quantum molecular dynamics (IQMD), we have investigated the isospin effects on the multifragmentation process in intermediate ener gy heavy ion collisions: reverse reactions Xe-120 + Ca-40, Cd-120+ Ar-40, K r-76+ Ca-40 and Zn-76+ Ar-40. To describe isospin effects appropriately, QM D was modified properly. The density dependent mean field contains correct isospin term including symmetry energy and Coulomb potential. The in-medium n-n cross section is different for neuron-neutron (proton-proton) and neut ron-proton collisions. And finally Pauli blocking was counted by distinguis hing neutrons and protons. In addition, the initial condition of the ground state of two colliding nuclei also contains isospin information. The calcu lated results show a prominent isospin effects for the multifragmentation p rocess among the colliding systems with different neutron or proton excess. The correlation between N-imf and N-c for neutron-deficient systems are al ways larger than those for neutron-rich systems in intermediate energy regi on for all of colliding systems studied here, and the mechanism causing the above isospin effects is mainly due to the fact that the mean n-n cross se ction for the neutron-rich system is smaller than that of neutron-deficient system. Thus one can combine experimental studies and theoretical simulati ons to investigate the isospin effect of multifragmentation process and to extract the information on isospin dependence of in-medium n-n cross sectio n from the correlation between N-imf and N-c.