Mass dependence of onset of multifragmentation in low energy heavy-ion collisions

Based on the quantum molecular dynamics (QMD) picture, we calculate the energy and mass dependence of fragment production. For the present study, we simulated the reactions of $^{20}Ne+^{20}Ne$, $^{40}Ar+^{45}Sc$, $^{58}Ni+^{58}Ni$, $^{86}Kr+^{93}Nb$,$^{129}Xe+^{124}Sn$ and $^{197}Au+^{197}Au$ at central geometry. Our findings clearly show a linear mass dependence for the peak center-of-mass energy at which the maximal IMF production occurs. Such linear dependence for peak center-of-mass energy on the system size has also been observed in recent experimental studies. We also predict a similar behavior for the multiplicities of different kinds of fragments. Experiments are called for to verify this prediction.