Radiation chemical diffusion kinetic calculations with prescribed and non-prescribed diffusion—I

Abstract Comparisons are made of species concentration profiles, and G values, both as functions of time, as calculated by the Schwarz modified prescribed diffusion method (1) and by the FACSIMILE numerical method. (2) This is done for spherically symmetrical (spur) cases and cylindrical (track) cases. It is shown that when the initial spatial distribution of the aquated electron is wider than that of the hydroxyl radical and the hydrogen ion, a depression is formed at early times at the centre of the electron concentration profile. The prescribed diffusion method cannot simulate this central minimum concentration and, therefore, tends to overestimate the amount of early inter-species reaction between e - aq and OH, and between e - aq and H + . This results in a faster predicted decay of G (e - aq ) when prescribed diffusion is used. The FACSIMILE method is also used to calculate the effect of an initial distribution with a central minimum in the e - aq concentration profile. Comparisons are made with experiment and with other recent modelling calculations.