Radiolysis is the dissociation of molecules by radiation. It is the cleavage of one or several chemical bonds resulting from exposure to high-energy flux. For example water dissociates under alpha radiation into hydrogen and oxygen. The chemistry of concentrated solutions under ionizing radiation is extremely complex. Radiolysis can locally modify redox conditions, and therefore the speciation and the solubility of the compounds. Pulse radiolysis is a recent method of initiating fast reactions to study reactions occurring on timescales faster than approximately oen ten-thousanth of a second, when simple mixing of reagents is too slow and other methods of initiating reactions have to be used.

Of all the radiation-chemical reactions that have been studied the most important is the decomposition of water. Water when exposed to radiation undergoes a breakdown sequence into hydrogen peroxide, hydrogen radicals and assorted oxygen compounds such as ozone which when converted back into oxygen releases great amounts of energy. Some of these are explosive. This decomposition is produced mainly by the alpha particles, that can be entirely absorbed by very thin layers of water. The current interest in nontraditional methods for the generation of hydrogen has prompted a revisitation of radiolytic splitting of water, where the interaction of various types of ionizing radiation (α, β, and γ) with water produces molecular hydrogen. This reevaluation was further prompted by the current availability of large amounts of radiation sources contained in the fuel discharged from nuclear reactors. This spent fuel is usually stored in water pools, awaiting permanent disposal or reprocessing. The yield of hydrogen resulting from the irradiation of water with β and γ radiation is low (G-values = <1 molecule per 100 electron-volt of absorbed energy) but this is largely due to the rapid reassociation of the species arising during the initial radiolysis. If impurities are present or if physical conditions are created that prevent the establishment of a chemical equilibrium, the net production of hydrogen can be greatly enhanced.

A suggestion has been made by R Bogdanov and A.T. Philac of the Saint Petersburg State University that in the early stages of the Earth’s development when its radioactivity was almost two orders of magnitude higher than at present, radiolysis could be the principal source of atmospheric oxygen, which ensured the conditions for the origin and development of life.

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