Precompound Decay from a Time-Dependent Point of View

A model is proposed for following the progress of nucleon-induced nuclear reactions as a function of time. It predicts that the majority of protons and high-energy neutrons emitted from heavy targets in these reactions appear before internal statistical equilibrium has been established. However, for the 18-MeV ($p,xn$) reaction with ${\mathrm{Ta}}^{181}$ the model predicts fewer high-energy neutrons than are observed experimentally. Further, there is a difference in shape between the predicted and observed spectrum. The same differences arise when a comparison is made between the experimental spectrum and that predicted by Griffin's model for decay. It is suggested that these differences arise because both models fail to consider surface reactions explicitly.