Astatine is a radioactive, chemical element. Its atomic number is 85, and its atomic weight is 210. It is part of the Group 17 (halogens) on the periodic table of elements. All of astatine's isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.3 hours.
The first creation of the element was in 1940 by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio G. Segrè at the University of California, Berkeley, who named it from the Greek estates (ἄστατος), meaning "unstable".[source?]
Astatine is highly radioactive and all its isotopes have half-lives of approximately 8 hours or less, the longest being astatine-210 with a half-life of a bit over eight hours. Some of its isotopes may be found in nature, but because it is so unstable, only about an ounce exists in the Earth's crust at any point in time. Chemists[who?] say it is the rarest element in the Earth's crust. Less reactive than iodine, astatine is the least reactive of the halogens. Only a few compounds with metals have been found, in the form of astatides of sodium, palladium, silver, thallium, and lead.
It can be used for cancer treatment and in radioactive tracers.[source?]
- Meyer, Geerd-J (2018-02-22). "Astatine". Journal of Labelled Compounds and Radiopharmaceuticals. 61 (3): 154–164. doi:10.1002/jlcr.3573. ISSN 0362-4803. PMID 29080397.