Change in the pH of NaI and methyl alkyl ketone solutions under gamma irradiation

The effects of dissolved chemicals such as NaOH, NaI, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK) on solution pH after gamma irradiation were investigated. Upon irradiation with 1.6–24 kGy of gamma radiation (0.4–6 kGy h−1), the pH of the NaOH solutions decreased, while the OH− consumption increased with increasing initial solution pH. This was attributed to acid–base neutralization between the OH− in the solutions and the acidic species (HO2· and ·NO2) formed by irradiation. The pH of the acidic NaI solution increased after irradiation with 8 kGy dose (at 2 kGy h−1), which was attributed to I− oxidation by the products of water and air radiolysis. The pH values of the MIBK and MEK solutions decreased from 7 to 4.5 or lower upon irradiation with 40 kGy dose (at 10 kGy h−1), which indicates that the alkyl groups of the ketones do not significantly affect the rates of decomposition by irradiation. The pH of the mixed solution of ketone and NaI was in the range of 6.7–6.9 before irradiation but decreased to 4.5 after irradiation with 40 kGy dose. In the mixed solutions, CH3COR and I− competed with each other to contribute to pH change.