Astatine

Astatine, with the chemical symbol At and atomic number 85, transports us into the realm of extreme rarity and fascinating instability. This chemical element was first discovered in 1940 by the Austrian physicist Karl Wilhelm Tönnies. However, it wasn't until 1942 that Emilio Segrè and his colleagues at the Lawrence Berkeley National Laboratory in the USA successfully isolated Astatine.

Astatine is the rarest element among the halogens on Earth, mainly forming as an intermediate product in the decay chain of heavy radioactive elements. The discoverers faced significant challenges due to Astatine's extreme instability and rapid decay.

The key isotopes of Astatine and their half-lives are At-210 (8.1 hours), At-211 (7.2 hours), and At-213 (125 nanoseconds).