Liquid-gas phase transition and isospin fractionation in intermediate energy heavy ion collisions

The liquid-gas phase transition in the heavy ion collisions and nuclear matter has been an important topic and got achievements, such as, based on the studies by H. Q. Song et al the critical temperature of liquid-gas phase transition enhances with increasing the mass of system and reduces as the increase of the neutron proton ratio of system. As we know that both the liquid-gas phase transition and the isospin fractionation occur in the spinodal instability region at the nuclear density below the normal nuclear density. In particular, these two dynamical processes lead to the separation of nuclear matter into the liquid phase and gas phase. In this case to compare their dynamical behaviors is interested. We investigate the dependence of isospin fractionation degree on the mass and neutron proton ratio of system by using the isospin dependent quantum molecular dynamics model. We found that the degree of isospin fractionation (N/Z)(n)/(N/Z)(imf) decreases with increasing the mass of the system. This is just similar to the enhance of the critical temperature of liquid-gas phase transition T-c as the increase of system mass. Because the enhance of T-c is not favorable for the liquid-gas transition taking place, which reduces the isospin fractionation process and leads to decrease of (N/Z)(n)/(N/Z)(imf). However the degree of isospin fractionation enhances with increasing the neutron proton ratio of the system. It is just corresponding to the reduce of T-c of the liquid-gas phase transition as the increase of the isospin fractionation of the system. Because the reduce of T-c enhances the liquid-gas phase transition process and also prompts the isospin fractionation process leading the increase of the isospin fractionation degree. To sum up, there are very similar dynamical behaviors for the degree of isospin fractionation and the critical temperature of the liquid-gas phase transition. So dynamical properties of the liquid-gas phase transition can be measured and studied through the studies of isospin fractionation experimentally.