The metal and oxide nanoparticles (NPs) containing various elements with high atomic number () are considered as prospective sensitizers for the production of radicals upon X-ray irradiation of aqueous solutions, which can be used for different applications in medical treatment and material modification. The common basis for the sensitizing effect in oxygen-free systems is concerned with increase of the absorbed dose due to the presence of high- atoms (known as physical enhancement, relatively insensitive to the NP size). In this work we report the first experimental evidence for extra enhancement of the radical yield in a model oxygen-free aqueous organic system irradiated with X-rays (45 kVp) in the presence of W(VI) compounds, both in homogeneous solutions of NaWO and in the form of ultra-small NPs of WO. Meanwhile, in the case of larger WO NPs the radical yield is consistent with physical enhancement mechanism. In the case of systems containing HfO NPs only physical enhancement was observed, independent of the NP size. Unusually large enhancement of radical production and size effect for W(VI) in homogeneous and NP forms was tentatively attributed to the radiation-chemical processes involving intermediate formation of metastable W(V) due to reactions of hydrated electron.

中文翻译：

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X 射线照射的含有均匀和纳米颗粒形式的 W(VI) 的水-有机体系中自由基产生的异常增强

含有各种高原子序数元素的金属和氧化物纳米粒子（NPs）被认为是在水溶液的X射线照射下产生自由基的潜在敏化剂，可用于医疗和材料改性的不同应用。无氧系统中敏化效应的共同基础是由于高原子的存在而导致吸收剂量的增加（称为物理增强，对纳米颗粒尺寸相对不敏感）。在这项工作中，我们报告了第一个实验证据，证明在 W(VI) 化合物存在的情况下，在 NaWO 均相溶液中，用 X 射线 (45 kVp) 照射的模型无氧水性有机体系中自由基产率的额外提高以及超小 WO 纳米颗粒的形式。同时，在较大的WO NPs的情况下，自由基产率与物理增强机制一致。在含有 HfO NP 的系统中，仅观察到物理增强，与 NP 尺寸无关。均相和 NP 形式的 W(VI) 的自由基产生和尺寸效应的异常大幅增强暂时归因于涉及由于水合电子反应而导致亚稳态 W(V) 中间形成的辐射化学过程。