RADIOLYSIS OF WATER AT ELEVATED-TEMPERATURES .2. IRRADIATION WITH GAMMA-RAYS AND FAST-NEUTRONS UP TO 250-DEGREES-C

Determination of G-values of water decomposition products in neutral water formed by irradiation with gamma-rays and fast neutrons at elevated temperatures up to 250 degrees C was carried out by a combination of the NaNO2, acetone + methanol, and HClO4 + methanol solutions, which had been established at room temperature. From the measurement of the H-2 yields for these solutions, the G(H2), G(H2) + G(H), and G(eaq-) + G(H) + G(H2), respectively, have been determined. Consequently, the G(H2), G(H) and G(eaq-) were obtained. By using a mass balance relation, the value for water decomposition, G(-H2O), was calculated. The yields of H2O2, formaldehyde and ethyleneglycol produced as a function of dose in the NaNO2 and HClO4 + methanol solutions were chosen to derive the G(OH) and G(H2O2) by fitting the simulated calculation to the experimental results. In the gamma-radiolysis, the G-values obtained in the present experiment are in good agreement with recently reported ones except for the G(OH) and G(H2O2). The G(equ-) for gamma-radiolysis is in a good agreement with the reported values up to 200 degrees C, but slightly lower at 250 degrees C. The water decomposition gives a similar pattern with G(eaq-) yields. The G(OH) does not change significantly with temperature, which is contrary to the evaluation by other groups and the G(H2O2) tends to increase with temperature. In the fast neutron radiolysis, although a similar change of the G-values with temperature was observed, the higher molecular products of G(H2) and G(H2O2) and the lower radical yields of G(H) and especially G(eaq-) were determined. It was made clear that the LET effect still remains even at elevated temperatures. Concerning the experimental results, it is suggested that the spur size would expand at higher temperatures and the fraction of the intra spur reactions decreases. Consequently, the amount of radicals diffusing out from the spur increases. To confirm this assumption, an additional measurement of H-2 yields in the 10(-3) mol.kg(-1) HClO4 solutions with different concentrations of methanol irradiated with gamma-rays and fast neutrons was also made.