Astatine is a extremely rare radioactive chemical element, the rarest naturally occurring element in the Earth's crust.
Core Principles & Analysis
Dale Corson, Kenneth MacKenzie, and Emilio Segre synthesized astatine in 1940 at Berkeley by bombarding bismuth with alpha particles, naming it from the Greek for unstable.
It is the rarest naturally occurring element, with less than a gram present in Earth's crust at any time, and no isotope lives longer than 8.1 hours.
Astatine-211 is under clinical investigation as an alpha-particle emitter for targeted cancer radiotherapy.