Astatine is a very rare radioactive chemical element with the chemical symbol At and atomic number 85. It occurs on Earth as the decay product of various heavier elements. All its isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.1 hours.
Three reasons Astatine stands out
- 1
Radioactive, it's the rarest element.
- 2
At any given moment, only about 25 grams of it exist in the entire Earth's crust combined.
- 3
Its most stable isotope has a half-life of just 8.1 hours, so any that forms quickly vanishes.
The element that barely exists
Astatine appears fleetingly in natural radioactive decay chains; at any moment Earth’s crust probably contains far less than a kilogram. No one has assembled enough to see a bulk sample. Its chemistry is inferred from tracer experiments, and selected isotopes are studied for targeted alpha-particle cancer therapy.