Source size scaling of fragment production in projectile breakup

Abstract

Fragment production has been studied as a function of the source mass and excitation energy in peripheral collisions of $^{35}\mathrm{Cl}$+$^{197}\mathrm{Au}$ at 43 MeV/nucleon and $^{70}\mathrm{Ge}$+$^{\mathrm{nat}}\mathrm{Ti}$ at 35 MeV/nucleon. The results are compared to the Au+Au data at 600 MeV/nucleon obtained by the ALADIN Collaboration. A mass scaling, by ${A}_{\mathrm{source}}\ensuremath{\sim}35 \mathrm{and} 190$, strongly correlated to excitation energy per nucleon, is presented, suggesting a thermal fragment production mechanism. Comparisons to a standard sequential decay model and the lattice-gas model are made. Fragment emission from a hot, rotating source is unable to reproduce the experimental source size scaling.