Optical properties of insulators can be dominated by trace-level impurities and/or other defects that may be difficult to identify using direct chemical analysis. The present work investigates the origins of coloration in BaSO4 powders following exposure to high energy photons (1.33 and 1.17 MeV γ from a 60Co source)using a through the combination ofexperimental and computational predictions of defect energies and a suite of complementary experimental techniques. We conclude that a slight greying observed in some BaSO4 powders is caused by activation of sulfate radicals that are stabilized by nearby barium vacancies or trace amounts of sodium substitution on the barium site. Electron–hole pairs activated by exposure to gamma irradiation and trapped by these defect couples lead to visible absorption centered around ∼650 nm. Such trapped electronic defects are stable at room temperature but can be ‘healed’ byeither thermal annealing above 300 °Cor ultraviolet bleaching. Such gamma-induced colorationwill therefore have has no impact on the mass density that dominates radiopacity nor on the chemical or physical properties of BaSO4and is not an indication of any sort of toxic contamination.

中文翻译：

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γ 诱导的 BaSO 变暗的起源[公式省略]


绝缘体的光学特性可能以痕量杂质和/或其他缺陷为主，这些缺陷可能难以使用直接化学分析来识别。这项工作通过结合缺陷能量的实验和计算预测以及一套互补的实验技术，研究了暴露于高能光子（来自 60Co 源的 1.33 和 1.17 MeV γ）后 BaSO4 粉末着色的来源。我们得出结论，在一些 BaSO4 粉末中观察到的轻微灰色是由于硫酸根自由基的激活引起的，这些自由基被附近的钡空位或钡位上的微量钠取代所稳定。通过暴露于 γ 射线照射而被激活并被这些缺陷对捕获的电子-空穴对导致以 ∼650 nm 为中心的可见光吸收。这种捕获的电子缺陷在室温下是稳定的，但可以通过 300 °C 以上的热退火或紫外线漂白来“愈合”。因此，这种 γ 诱导的着色对主导射线不透明度的质量密度没有影响，也对 BaSO4 的化学或物理性质没有影响，也不表明存在任何类型的有毒污染。