The multifragment emission for central collisions of ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ (25–150 MeV/nucleon) on ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ was studied via the quantum molecular dynamics model. The distribution of intermediate mass fragments (IMFs) can be described by a power-law function with the parameter τ or an exponential function with the parameter λ. By increasing the beam energy, the mean multiplicity of IMFs and relative cross sections emitting multifragment first increase to their maximum values and then decrease; while the extracted τ, λ parameters and relative cross section for single IMF emission show the converse tendency. The calculation and relevant experiment suggest that the reactions have a critical energy point where the onset of multifragmentation takes place.

• Received 6 May 1994

DOI:https://doi.org/10.1103/PhysRevC.51.710