Multifragment Production in Reactions ofS112n+S112nandS124n+S124natE/A=40MeV

Multiplicities of intermediate-mass fragments (IMFs), neutrons, and charged particles were measured for ${}^{112}\mathrm{Sn}{+}^{112}\mathrm{Sn}$ and ${}^{124}\mathrm{Sn}{+}^{124}\mathrm{Sn}$ at $E/A\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}40\mathrm{MeV}$. Significantly different scalings of the mean IMF multiplicities with neutron and charged-particle multiplicities are observed for the two reactions. These differences can be qualitatively understood in terms of fragment emission from an expanding evaporating source for which the initial rates of cooling by neutron and light-charged-particle emission depend on the neutron and proton numbers of the source according to statistical expectations.