Scavenger concentration dependences of yields in radiation chemistry

Analytic models are used to show that at low concentrations the effect of scavengers on radiation chemical yields should be expressed as a power series in the square root of the scavenger concentration. The coefficients of the different terms in the series are determined by the initial distribution of separations of the reactants and by the interparticle forces. Conventional empirical functions used to describe the scavenger concentration dependence of radiation chemical yields are shown to be equivalent to a power series in which all the coefficients are defined by a single fitting parameter. The importance of the terms of higher order than the square root of the scavenger concentration is emphasized, and the need for a second fitting parameter to account for the difference between the coefficients of these terms and the square root term is demonstrated. A new function to describe the scavenger dependence of radiation chemical yields is discussed, and it is shown to reproduce other existing empirical fitting functions, even those which do not have the correct square root of scavenger concentration asymptote, over the limited concentration range that is experimentally accessible.