Molecular Product and Free Radical Yields in the Decomposition of Water by Protons, Deuterons, and Helium Ions

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Abstract
With the formic acid-oxygen dosimeter (0.01 [image] formic acid, 0.001 N sulfuric acid, saturated with oxygen), molecular product, free radical, and water decomposition yields have been measured for cyclotron-produced protons, deuterons, and helium ions, and 3.4 Mev [alpha]-particles. Molecular product yields, g(H2) and g(H2O2), increase while the free radical yields, g(OH) and g(H), and the observable yield of water decomposition, g(-H2O), decrease with increasing linear energy transfer (LET) of the incident radiation. However, if it is assumed that the recombination of radicals in the reaction H + OH[long dash]) H2O equals g(H2) + g(H2O2), then the total amount of water decomposing into free radicals, g(-H2O)T = g(-H2O) + g(H2) + g(H2O2), is constant at 4.50 [plus or minus] 0.13 for all cyclotron-produced particles used in this work. These particles range in energy from 20.9 Mev (deuterons) having the lowest LET, to 8.35 Mev (helium ions) having the highest LET. The results are discussed in terms of the free radical model for cylindrical diffusion and are shown to agree well with the one-radical model calculations of Fricke and Flanders. The primary radiation yields, designated by the lower case g(x), are obtained from the experimental yields, G(H2), G(H2O2), g(-O2), and G(CO2) by the following series of equations applicable to the formic acid-oxygen dosimeter g(H2)=G(H2); g(H2O2) = G(H2O2) - G(-O2); g(H) = 2G(-O2) - G(CO2); g(OH) =G(CO2).

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