Description
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Astatine is a radioactive halogen that occurs from the decay of uranium-235 and uranium-238. It is the heaviest of all the halogens and has been named the rarest element on Earth. Astatine has an atomic weight of 210, a melting point of 576 °F, and the boiling point of this element is not currently known. Compounds of astatine have been created and studied for possible applications in nuclear medicine, but currently there are no commercial uses for astatine as it is so rare and toxic.
Isolation
The quick half life of astatine makes isolation procedures from nature impossible. As this element is not obtainable from natural sources it must be created instead.
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Astatine only has a half life of approximately 8.3 hours. Any studies or projected work that is to be done on astatine that is synthesized must be performed quickly before it disintegrates. The only way that astatine can be created is in a nuclear reactor using the element bismuth. In this process, the bismuth isotope, number 209, is bombarded with alpha particles from the nuclei of the isotope, number 4, of helium. This results in the formation of the astatine isotope number 211. The bismuth target must be cooled during this process because astatine is extremely volatile. Once this process is completed, the bismuth target is then heated to between 300 - 1112 °F. The heating process takes place under nitrogen and this reaction produces a stream of astatine in its elemental form. The minute quantities of astatine that are produced are then collected on a finger of cold glass.