Mass dependence in the production of light fragments in heavy-ion collisions

Abstract

Using the quantum molecular dynamics model coupled with the minimum spanning tree clusterization algorithm, we investigate the system-size effects in the production of light mass fragments (with mass $<~10).$ This was achieved by simulating the collision of symmetric nuclei like $\mathrm{Ca}+\mathrm{Ca},$ $\mathrm{Ni}+\mathrm{Ni},$ $\mathrm{Nb}+\mathrm{Nb},$ $\mathrm{Xe}+\mathrm{Xe},$ $\mathrm{Er}+\mathrm{Er},$ $\mathrm{Au}+\mathrm{Au},$ and $\mathrm{U}+\mathrm{U}$ at incident energies between 50 MeV/nucleon and 1 GeV/nucleon and over full range of impact parameter. Our detailed analysis shows that the triggering of the multifragmentation and its saturation is delayed in heavier systems. The striking result, which is independent of the incident energy as well as of the impact parameter, is that the mass dependence of the multiplicity of any kind of fragment exhibits a power law behavior $\ensuremath{\propto}{A}_{\mathrm{tot}}^{\ensuremath{\tau}},$ where $``{A}_{\mathrm{tot}}''$ is the mass of the composite system. Similar mass dependencies have already been reported in the literature for the fusion process at low incident energy as well as for the production of kaon and collective flow (and its disappearance) at intermediate energies. As reported for the production of kaons, the parameter $\ensuremath{\tau}$ depends on the colliding geometry as well as on the incident energy. No unique dependence of $\ensuremath{\tau}$ (such as, in the case of disappearance of flow) exists. The value of the parameter $\ensuremath{\tau}$ in central low energy collisions is close to 2/3, which suggests the dominance of the mean field. On the other hand, a linear dependence occurs at higher incident energies. Similar trends can also be seen in the preliminary reports of the FOPI experiments.