A Study on Formation and Growing Processes of the Colloids Containing Long-Lived Radionuclides by Means of Laser Induced Photoacoustic Spectroscopy

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Radiolytic formation of the colloids of technetium dioxide hydrate was investigated by irradiation of aqueous pertechnetate solutions with bremsstrahlung generated from a linear accelerator. Transmission electron microscopy revealed the size distribution of the colloids between 50 and 130 nm. The composition of the colloids was confirmed by dispersive x-ray spectrometry. An amorphous structure of the colloids was found by electron diffraction analysis. The yield of the colloids was strongly affected by dissolved gases in solutions. In the solutions saturated with oxygen gas or nitrous oxide gas, no colloids were formed, while 90 % of Tc was found as the colloids for the Ar-saturated solutions. In the formation of Tc(IV) species as a precursor of technetium dioxide colloids, it was found that hydrated electrons played an important role on the reduction processes of pertechnetate ions followed by successive disproportionation reactions of Tc(VI) and Tc(V).Laser induced photoacoustic spectroscopy was applied to a study on the formation and growing processes of technetium sulfide colloids. Analysis of the photoacoustic signals from technetium sulfide colloid particles revealed that the colloid particle the size of colloid particles increased by deposition of technetium sulfide on the particle surfaces, not by coagulation of colloid particles.