Technetium(IV) Oxide Colloids and the Precursor Produced by Bremsstrahlung Irradiation of Aqueous Pertechnetate Solution

Technetium nanocolloidMechanisms of the radiolytic formation of 99TcIVO2??nH2O colloids were studied by bremsstrahlung irradiation of an aqueous pertechnetate (TcVIIO4???) solution under different conditions; pH of the target solution, concentration of TcO4??? and presence or absence of radical scavengers and of seed particles of TcO2??nH2O. Colloid particles (30 ??? 130 nm) of TcO2??nH2O ??? a coagulate of nanoparticles with the size of 2 nm ??? were radiolytically produced at pH higher than 3, whereas a soluble Tc(IV) species but colloid was formed at lower pH. The soluble Tc(IV) species transformed to the TcO2??nH2O colloid when the pH of the solution was raised to 3 or higher after the irradiation. This fact suggests that the soluble Tc(IV) species is a precursor of the TcO2??nH2O colloid. The presence of TcO2??nH2O seed particles in the target solution of TcO4??? did not enlarge of the partcile size, revealing that the solidification would take place rather in the solution than on the surface of nanoparticles. The reduction of TcO4??? in acidic solutions proceeded mainly through processes involving a bimolecular reaction of TcO4??? with hydrogen radicals, followed by the successive disproportionation reactions of Tc(VI) and Tc(V)