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

Abstract

Mechanisms of the radiolytic formation of⁹⁹Tc^IVO₂·nH₂O colloids were studied by bremsstrahlung irradiation of an aqueous pertechnetate (Tc^VIIO₄^-) 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).