Astatine

History

(Gr. astatos: unstable) 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.

Properties

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.

Sources

This radioactive element occurs naturally from uranium and thorium decay. It 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 total amount of astatine in Earth's crust is estimated to be less than 1 oz (28 g) at any one time. This amounts to less than one teaspoon of the element.

Uses

Isotopes