Plutonium(IV) oxidation has been studied in 1 to 20 mol/1 HNO3 under 1 to 14 W/1 internal alpha-irradiation and at plutonium concentrations from 2 to 100 mmol/1. Curium isotopes have been
used as the basic alpha-irradiation sources. It has been established that in the systems investigated both oxidation of plutonium(IV)
and reduction of plutonium(VI) take place, resulting with time in reaching the equilibrium between plutonium(IV) and plutonium(VI).
The presence of plutonium(IV) enhances the reduction of plutonium(VI). The rate constants for plutonium(IV) oxidation and
plutonium(VI) reduction have been estimated and their dependences upon the concentrations of nitric acid, plutonium(IV) and
plutonium(VI) as well as upon the dose rate investigated. An equation has been derived which permits to calculate the concentrations
of plutonium(IV) and plutonium(VI) at any desired time.