Diffusion-Kinetic Theories for LET Effects on the Radiolysis of Water

Abstract

Diffusion-kinetic methods are used to investigate the effects of incident particle linear energy transfer (LET) on the radiolysis of water and aqueous solutions. Chemically realistic deterministic diffusion-kinetic calculations examining the scavenging capacity dependences of the scavenged yield of e[sub aq][sup [minus]] and of OH demonstrate that the scavenged yields are related to the underlying time-dependent kinetics in the absence of the scavenger by a simple Laplace transform relationship. This relationship is also shown to link the effect of an e[sub eq][sup [minus]] scavenger on the formation of H[sub 2] with the time dependence of H[sub 2] production in the absence of the scavenger. The simple Laplace relationship does not work well when applied to H[sub 2]O[sub 2] formation in high-LET particle tracks even though such a relationship is valid with low-LET particles. It is found that while the secondary reaction of H[sub 2]O[sub 2] with e[sub aq][sup [minus]] can be neglected in low-LET particle radiolysis, it is of considerable significance in the tracks produced by high-LET particles. The increased importance of this reaction with increasing LET is the major reason for the failure of the Laplace relationship for H[sub 2]O[sub 2]. 55 refs., 9 figs., 2 tabs.