astaat

Astaat is a rare, naturally occurring radioactive chemical element with the symbol At and atomic number 85. It is an extremely unstable element, and no naturally occurring isotopes have a half-life longer than a few hours. All isotopes of astatine are radioactive, with the longest-lived isotope, astatine-210, having a half-life of 8.1 hours. Due to its scarcity and short half-life, astatine has very few practical applications. It is primarily used in scientific research, particularly in the study of nuclear physics and chemistry.

Astatine is a member of the halogen group of elements, which also includes fluorine, chlorine, bromine, and iodine. It is expected to share some of the chemical properties of these elements, although its radioactivity and scarcity make it difficult to study. It is a solid at room temperature and is thought to be a dark-colored, possibly metallic, substance. It is predicted to be the least electronegative of the halogens.

The element was first synthesized in 1940 by Dale Corson, Kenneth Ross MacKenzie, and Emilio Segrè at the University of California, Berkeley. They produced it by bombarding bismuth with alpha particles. The name "astatine" comes from the Greek word "astatos," meaning "unstable." Because of its rarity and instability, astatine is not found in significant quantities in nature. Trace amounts can be found in uranium and thorium ores, where it is produced through radioactive decay.