Astatine

Astatine, chemical element, symbol At; for physical constants see Periodic Table. Astatine was synthesized in 1940 by Corson, MacKenzie, and Segre at the University of California by bombarding bismuth with alpha particles. Minute quantities of astatine exist in nature as isotopes produced from uranium and thorium reacting with naturally produced neutrons. Astatine is radioactive and belongs to the halogen group of elements. It behaves chemically very much like them and is reported to be more metallic than iodine. The longest-lived isotope, astatine-210, has a half-life of 8.1 hours. Twenty-eight isotopes of astatine are known.