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Pronunciation: tho're-um

Definition: A radioactive metallic element; atomic no. 90, atomic wt. 232.0381. 232Th, the only naturally occurring nuclide, with a half-life of 14 × 109 years, is used in colloidal form in electron microscopy as a stain for acid mucopolysaccharides.

[Thor, Norse god of thunder]

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© Copyright 2018 Wolters Kluwer. All Rights Reserved. Review Date: Sep 19, 2016.