Evidence for radial-energy scaling of nonequilibrium neutron yield in damped ${}_{}{}^{139}{}_{}{}^{}\mathrm{Ar}$ reactions

Emission patterns of neutrons from damped ${}_{}{}^{139}{}_{}{}^{}$La${+}^{40}$Ar reactions at $E_{\mathrm{lab}=400\mathrm{}}$ and 600 MeV, mostly consistent with sequential evaporation from accelerated fragments, reveal the existence of a high-energy component at all kinetic energy losses. The average multiplicity associated with this nonequilibrium component is found to scale with the radial kinetic energy at contact, with a threshold of $E_{\mathrm{rad}\mathrm{\approxeq }2}$ MeV/nucleon. Boltzmann-master-equation and Fermi-jet models disagree with the data, the latter model requiring enhanced high-momentum components.