In 1943, three years after astatine was first synthesized artificially in a nuclear reactor, it was discovered that the element occurs naturally in miniscule amounts in the earth’s crust. In fact it is the single rarest naturally occurring element, with a total of just 1 oz. or 28 grams at any given time. About thirty isotopes of the element have been synthesized or found to occur naturally, the longest-lived of which is 210At with a half-life of 8.1 hours.
Taken all together these facts about the element contribute to its almost complete lack of applications. One exception has been an ongoing exploration of the potential uses of 211At in radiotherapy. The isotope is an α particle emitter with a convenient half-life of 7.2 hours. Like the element above it in the periodic table, iodine, astatine has a tendency to be metabolized in the thyroid gland and could therefore be used to monitor medical conditions involving the thyroid and the throat area in general. In addition, the short-range nature of the α emission of this isotope suggests that it could be used to treat cancers in all parts of the body while reducing the risk to neighboring tissue that is often a problem in the use of other more established radio-therapeutic isotopes. And if that were not promise enough, 211At does not produce any harmful β radiation as do many other isotopes currently used in radio-medicine.
But although these therapeutic potentially attractive properties have been explored for more than thirty-five years, problems concerning the safe delivery of 211At to human subjects, as well as issues relating to the ready production of the isotope, continue to delay the in vivo implementation of this rarest of all elements.