Activity Concept in Radiation Chemistry

Abstract

The decomposition of aqueous solutions by ionizing radiations has been interpreted by assuming an initial solvent decomposition into H atoms and OH radicals. Radical recombination gives rise to the observed molecular products H2 and H2O2. Substantiating this hypothesis, it has been demonstrated that reaction of solutes with the radicals depress the yields of the molecular products. The linear dependence of the molecular yields on the cube root of the solute molarity applies very well for dilute solutions of strong electrolytes, i.e., where the molarity and the activity are essentially equal; however, in more concentrated solutions considerable deviation is observed. It is in this region that the activity of an electrolyte manifests itself, and therefore the cube root of the activity is the criterion rather than the molarity. For this study particular attention was addressed to the depression of hydrogen yields by aqueous sodium nitrate solutions. Alteration of the molecular hydrogen yield was demonstrated by varying the scavenging solute concentration and the activity of the scavenging solute. The addition of three different salts representing uni-univalent, di-univalent, and tri-univalent electrolytes was used to alter the ionic strength of the solutions.