A Theoretical Survey of the Radiation Chemistry of Water and Aqueous Solutions

Abstract

In this paper the various kinds of available evidence are examined in an attempt to determine the detailed mechanism of the action of high-energy radiation on water and aqueous solutions. The analysis employed is not exhaustive, but rather is concerned with effects which are presently believed to be most important. For example, it is now generally accepted that local heating, as such, is relatively unimportant and that most effects of high-energy radiations are due to electronic excitation, ionization, and dissociation of molecules. Specifically, in the case of water, it has for some years been customary to explain most radiation phenomena on the basis of action of H and OH radicals formed in irradiated water. In most respects such a radical mechanism seems to be able to explain experimental results, although it is by no means certain that other entities are unimportant. A detailed description of the radiolysis of water must be in agreement with experimental and theoretical requirements which can be put into two categories: a. Requirements from chemical experiments. b. Requirements from physical and theoretical considerations. At present it appears that the requirements of chemical experiment are better defined than those of theory, and for this reason they are discussed first. It is well known that a complete theoretical description of the tracks of ionizing radiations in water has not been given. The great unknown is the fate of the slow electron from ionization processes and, as we shall see, this uncertainty makes the geometrical arrangement of H and OH radicals impossible to predict from theory. An attempt has been made to draw conclusions, from the assembled requirements, regarding the nature of the radiolysis mechanism. This attempt is aided by a detailed calculation made by Samuel and Magee (1) on a radical diffusion model. Such a model was suggested by Lea (2, 3) and Allen (4), but no detailed study had previously been made. A critical examination of this model is made on the basis of experimental results.