THE KINETICS OF RADICAL REACTIONS IN THE TRACKS OF FAST ELECTRONS. A DETAILED STUDY OF THE SAMUEL–MAGEE MODEL FOR THE RADIATION CHEMISTRY OF WATER

Abstract

The kinetic behavior of a γ-ray spur produced in water, having H and OH radicals distributed spatially in the manner suggested by Samuel and Magee, has been studied using an electronic computer. The variation in yield of the molecular products H2, H2O2, and H2O with rate constants, diffusion constants, and spur size has been obtained. The model gives agreement with experiment choosing spurs with a small "radius" of the order of 10 Å. On simple assumptions, however, the model predicts no difference in the molecular yields between heavy and light water and no isotopic separation in the formation of molecular hydrogen from isotopically enriched light water. Various special assumptions needed to give agreement with experiment for these isotope effects are discussed. The observed isotopic separation in the formation of molecular hydrogen is attributed to the preferential dissociation of an H atom from an excited HDO molecule. It is found that the yield of molecular hydrogen is less sensitive to the presence of scavengers than the yield of hydrogen peroxide.