Source size scaling of fragment production in projectile breakup

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 $A_{\mathrm{source}}\sim 35 \mathrm{and} 190$, 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.