Formation of Tc(IV) Oxide Colloids by Bremsstrahlung Irradiation of Aqueous Solutions of Pertechnetate(II. Radiochemistry)

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Technetium(IV) oxide colloids (TcO_2・nH_2O) were formed by bremsstrahlung irradiation of aqueous solutions of pertechnetate (TcO_4^-). A transmission electron microscopy (TEM) analysis showed that the size of colloids distributed around 30 to 130 nm in diameter. The characteristic X-rays from technetium and oxygen were detected from colloid particles at the TEM measurements. Round-shaped colloids were produced by the irradiation at 40℃, whereas irregular-shaped colloid particles composed of tiny particles (2 nm in diameter) were produced at 17℃. The concentration of TcO_4^- in the target solution decreased with an increase of the absorbed dose, corresponding to an increase of the colloids yield. The yield of colloids sharply increased in the solution deaerated by Ar bubbling before irradiation, but strongly suppressed in the solution saturated with oxygen (O_2) or nitrous oxide (N_2O) gas. The fact suggests that hydrated electrons play an important role in the course of the reduction of TcO_4^- and that Tc(IV) oxide colloid is formed via successive disproportionation reactions of Tc(VI) and Tc(V).
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