Astatine

Astatine
Symbol	As
Atomic number	85
Atomic mass	(210) amu

Astatine, named from the Greek for "unstable", was discovered in 1940.

Occurrence

It was first synthesized by bombarding bismuth (²⁰⁹Bi) atoms with helium nuclei (⁴4He, high-energy alpha particles). Sufficient quantities were obtained so that some of its properties can be studied. However, a cyclotron must be used to synthesize astatine. So, this makes it very expensive and limits its application and study.

Isotopes

All isotopes of astatine are radioactive. About 20 isotopes are known, the longest-lived being ²¹⁰At with a half-life of 8.3 hours and decays mainly by electron capture. Shown in the image is a recording of the detection of astatine in the notebook of its discoverer, D. R. Corson, an American physicist.

See also

Periodic table of the elements