Formation Mechanisms of Technetium Colloids Under High Radiation Dose

用直线加速器产生的轫致辐射辐照高技术酸水溶液，发现了二氧化钛水合物纳米颗粒的辐射分解形成。透射电镜显示胶体的粒径分布在50 ~ 130 nm之间，为纳米颗粒集合体。用色散x射线光谱法确定了胶体的组成。通过电子衍射分析发现胶体具有非晶态结构。在自由基清除剂如氧气和氧化亚氮气体的存在下，胶体的产率受到强烈抑制。然而，90%的Tc被发现为饱和ar溶液的胶体。在作为二氧化锝胶体前体的Tc（IV）的形成过程中，发现水合电子在高锝酸盐离子的还原过程中起着重要作用，随后是Tc（VI）和Tc(V)的连续歧化反应。纳米粒子仅在pH高于3时才会被放射性分解生成，而在pH低于3时则会形成可溶的Tc（IV）。可溶性Tc（IV）在320 nm（强）和500 nm（弱）处有吸收峰。超滤前后物质的吸收光谱没有变化。我们发现，在Tc（IV）可溶性物质的溶液中加入NaGH溶液可以形成纳米二氧化钛水合物。这一事实有力地表明，Tc（IV）可溶性物质是纳米颗粒的前体。

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.