#radioactivity

• Astatine — A highly unstable radioactive chemical element of the halogen group, with atomic number 85 and symbol At; it is the rarest naturally occurring element in the Earth's crust, produced only transiently through the decay of uranium and thorium, and due to its extremely short half-life (a maximum of 8.1 hours for its most stable isotope), its physical properties are studied almost exclusively through artificial synthesis techniques in particle accelerators.
• Autunite — A mineral from the phosphate class, hydrated uranium and calcium phosphate, with the chemical formula Ca(UO2)2(PO4)2·10-12H2O, featuring a brilliant greenish-yellow color; it is a highly radioactive mineral that fluoresces under ultraviolet light, historically discovered in the Autun region (France) and used as a secondary uranium ore.