Formation Mechanisms of Technetium Colloids Under High Radiation Dose

用线性加速器产生的韧致辐射照射高锝酸盐水溶液，发现了二氧化锝水合物纳米粒子的辐解形成。透射电子显微镜显示的粒径分布在50和130 nm之间的胶体，和粒子被发现作为纳米粒子的聚集体。通过色散X-射线光谱法证实了胶体的组成。通过电子衍射分析发现胶体为非晶态结构。在自由基清除剂如氧气和一氧化二氮气体的存在下，胶体的产率被强烈抑制。然而，90%的Tc被发现作为胶体的Ar-饱和溶液。在Tc（IV）物种作为二氧化锝胶体前体的形成过程中，水合电子在高锝酸根离子的还原过程中起着重要作用，随后Tc（VI）和Tc（V）发生连续的反离子化反应。可溶性Tc（IV）物种在320 nm（强）和500 nm（弱）处显示吸收峰。超滤前后各物种的吸收光谱无变化。我们发现水合二氧化锝纳米粒子是通过将NaGH溶液添加到Tc（IV）可溶性物种的溶液中形成的。这一事实强烈表明，Tc（IV）可溶性物种作为纳米粒子的前体。

Radiolytic formation of the nanoparticles of technetium dioxide hydrate was found 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, and the particle was found as an aggregate of nanoparticles. 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 inhibited in the presence of radical scavengers such as oxygen and nitrous oxide gases. However, 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).The nanoparticles were radiolytically produced only at solution's pH higher than 3, while a soluble Tc(IV) species were newly formed at pH lower than 3. The soluble Tc(IV) species showed absorption peaks at 320 nm (strong) and 500 nm (weak). The absorption spectra of the species were not changed before and after ultrafiltration. We found that the nanoparticles of technetium dioxide hydrate were formed by addition of NaGH solution to the solution of Tc(IV) soluble species. This fact strongly suggests that the Tc(IV) soluble species act as a precursor of the nanoparticles.