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Astatine (Gr.: άστατος, unstable) is a chemical element, having the chemical symbol At. Its atomic number (the number of protons) is 85. It has a standard atomic weight of 210 g•mol −1 and is a solid in its elemental form. The total amount of astatine present in the earth's crust is less than 1 ounce (28 grams).
Astatine was first synthesized in 1940 by D.R. Corson, K.R. MacKenzie, and E. Segre at the University of California by bombarding bismuth with alpha particles. The longest-lived isotopes, with naturally occurring uranium and thorium isotopes, and traces of 217At are equilibrium with 233U and 239Np resulting from integration of thorium and uranium with naturally produced neutrons.
Astatine can be produced by bombarding bismuth with energetic alpha particles to obtain the relatively long-lived 209-211At, which can be distilled from the target by heating in air.
The "time of flight" mass spectrometer has been used to confirm that this highly radioactive halogen behaves chemically very much like other halogens, particularly iodine. Astatine is said to be more metallic than iodine, and, like iodine, it probably accumulates in the thyroid gland. Workers at the Brookhaven National Laboratory have recently used reactive scattering in crossed molecular beams to identify and measure elementary reactions involving astatine.
This article was sourced from Los Alamos National Labs on 27 June, 2008.