Valency stabilization of polyvalent ions during gamma-irradiation of their aqueous solutions by sacrificial protection .2. Valency stabilization of Ce(IV) by bromate ions

The various aspects of valency stabilization of polyvalent ions during gamma-radiolysis have been further investigated. Ce(IV) ions, which are normally reduced in their aqueous solution. were found to be stabilized for increasing periods of time when they were irradiated in the presence of increasing amounts of bromate ions. It was found that the addition of about fifteen times excess of bromate ions to a 10(-3) N Ce(IV) solution stabilized the cerium ions in the tetravalent state for about 120 hours during irradiation at a dose rate of 336 Gy/h. Increasing the amount of bromate used resulted in a subsequent increase in the protection time. It has been also noted that while bromate ions protected Ce(IV) in solution, the latter ions showed a clear protective effect on the bromate used, i.e., there is a mutual protective effect. The probable mechanisms, conditions and limitations of the protection process have been discussed. Based on the data obtained in the present work, it has been suggested that the protection of Ce(IV) ions by bromate ions in aqueous solutions during gamma-radiolysis is very probably due to the preferential interaction of bromate with the reducing radiolysis products of water which are capable of reducing Ce(IV) to Ce(III).