What is the most unstable radioactive element

Chemistry: Astatine is the rarest element on earth

What is the rarest element on earth? Gold or platinum? Or maybe the element dysprosium from the rare earth group? Judging by the exotic name and the (in) awareness level, it should be Dysprosium. Who has ever heard of it?

But no, the rarest chemical element is astatine (abbreviation: At). It is a halogen and therefore a relative of chlorine and iodine. However, it is estimated that only 0.0000000000000000000000003 weight percent occurs in the earth's shell - i.e. in the top 16 kilometers of the earth's crust and the atmosphere.

For comparison: the proportion of gold and platinum in the earth's shell is 0.0000005 percent each, that of dysprosium is even 0.004 percent. The solution to the extraordinary rarity of the element astatine - there are only a few trillionths of a gram in the earth's shell - is the fact that it is unstable, disintegrated within a short time and thus disappeared. Astatine only exists because some uranium isotopes are also unstable and, in turn, gradually disintegrate into astatine.

Given its rarity, it is not surprising that researchers had to search for astatine for a long time. Dimitri Mendeleev had already predicted its existence in 1869 in view of a gap in the periodic table of which he was the spiritual father.

From 1931 onwards, researchers repeatedly claimed to have found the piece of the puzzle and called it Eka-Jod ("after iodine"), Alabamin (derived from Alabama), Dakin (Dhaka in what was then British India), Helvetium (Switzerland) or Anglohelvetium ( England-Switzerland). Researchers were able to prove it with certainty in 1940, when they named it astat after A-stat (Greek for inconsistent). The researchers made it artificially by shooting alpha particles (helium atomic nuclei) at bismuth atoms. In 1943, other researchers found it to be a decay product of uranium.

Of course, astatine has hardly any economic significance. Extracting it from uranium would be extremely costly, especially since it disintegrated again after hours. Astat is only used for the irradiation of certain tumors and as a radioactive substance in thyroid diagnostics. Because the element cannot be stored, it is freshly recovered for this purpose by irradiating it with bismuth.