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The g values for the primary species formed in the y-radiolysis of light and heavy water have been measured as a function of temperature up to 300°C. With the exception ofg(H,) andg(D,), all the g values are consistent with the generally accepted diffusion-kinetic model of spurs, i.e. with an increase in temperature, the g values of the free radicals increased while those of peroxide decreased. The g values for H, and D, increased with temperature which suggests that they are formed by other mechanisms in addition to radical-radical reactions in the spur.Water-cooled nuclear power reactors operate with either light or heavy water as the primary heat-transport medium. Since radiolysis of this water has been associated with corrosion and hydriding of in-core components, computer packages are being developed to model the radiation chemistry of the water as it passes through the reactor core. The computer models require a knowledge of the g values for the primary species formed from both fast neutron and y-radiations [see reaction (l)] as well as the rate constants for all of the reactions involving these species. radiation H'O ___e,, OH, H, H', H'O', HO, (1)The term ' g value' will be used for the yield of the primary species in reaction (1) CQ.s after the ionizing event and ' G value' will be used for the experimentally determined yields from which g values are deduced. This information is required for the operating temperature range (250-3 15 "C) found in nuclear reactors.In this paper, estimates of the g values for the primary species formed in reaction (l), for both light and heavy water, have been made as a function of temperature for low linear energy transfer (LET) radiation. The results presented here supersede those given in our earlier paper for light water.'Experimentally, the estimation of g values at higher temperatures is straightforward. The difficulty is in finding chemical systems which are both thermally stable above 100 "C and whose radiation chemistry is well defined. Pulse radiolysis experiments have a further complication ; the molar absorption coefficient of the species formed has to be known at the temperature being studied. Steady-state radiolysis experiments at high temperatures do not have this problem because all analyses are generally made at room temperature. The approach taken in this report was to estimate the g values of all the primary products over as wide a range of temperature as possible and then ensure that there was a material balance.J.

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The g-values of primary species formed in the γ-radiolysis of water have been estimated for the temperature range 25–300 °C. The g-values for the hydrated electron, the hydroxyl radical, and molecular hydrogen all increase approximately 50% over this temperature range. The g-values for the minor products, hydrogen peroxide and atomic hydrogen, probably also increase with temperature; however, there is evidence from some of the experimental data which suggests that these g-values may slightly decrease with increasing temperature. Keywords: radiolysis, g-values, temperature dependence.

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