Isospin effect of charged particle multiplicity in intermediate energy heavy ion collisions

The dependence of He and intermediate mass fragments (IMF) production rates in the reactions 55 MeV/u 40Ar +58,64Ni on the isospin, impact parameter and primary excitation energy of the reaction system was studied by using the 4π charged particle multidetector array system (MUDAL). For the mentioned two reaction systems, the measured He particle contribution in the total charged particle multiplicity increases with increasing the total charged particle multiplicity but the contribution of IMFs in the total charged particle multiplicity increases with increasing the total charged particle multiplicity at lower total charged particle multiplicities, and latterly it drops down with further increases of the total charged particle multiplicities. The experimental results of these two reaction systems with the same nuclear charge indicate that the contributions of He and IMFs in the total charged particle multiplicities are obviously isospin dependent