Astatine

Category: halogen Atomic number: 85 Colour: n/a Melting point: 302°C (576°F) Boiling point: 337°C (639°F) First identified: 1940

Emilio Segrè, the co-discoverer of the first ‘artificial’ element technetium in 1937, spent the following summer at Berkeley; and when Italy passed anti-Semitic laws that would have barred him from being a professor, he chose to stay there, and ended up using the particle accelerator at Berkeley to discover another new element, ‘astatine’, whose name is derived from astatos, the Greek word for ‘unstable’.

It only occurs naturally as part of a complex radioactive pathway. It has ten highly radioactive isotopes, none of which has a half-life of more than eight hours. To create a tiny quantity, Segrè and Dale Corson bombarded bismuth-209 with particles to form astatine-211, albeit not in a quantity large enough to be seen. It is one of the halogens, and probably has similar properties to them.

Segrè went on to work at the Manhattan Project, and there has not been much work done on astatine since. It is thought, however, that it could be used to treat some kinds of cancer. The radioactive isotope iodine-131 has been used for this, but has the disadvantage of emitting beta particles (high-energy electrons), which can damage other tissue outside of the tumour. Astatine-211 is an alpha emitter with a very short half-life, which might make it a better option in future.