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This is astatine.

Symbol As
Atomic number 85
Atomic mass (210) amu

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


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.


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