Astatine - History

History

In 1869, when Dmitri Mendeleev published his periodic table, the space under iodine was empty; after Niels Bohr established the physical basis of the classification of chemical elements, it was suggested that the fifth halogen belonged there. Before its officially recognized discovery, it was called "eka-iodine" (from Sanskrit eka – "one") to imply it was one space under iodine (in the same manner as eka-silicon, eka-boron, and others). Scientists tried to find it in nature; given its rarity, these attempts resulted in a number of false discoveries.

The first claimed discovery of eka-iodine was made by Fred Allison and his associates at the Alabama Polytechnic Institute (now Auburn University) in 1931. The discoverers named element 85 "alabamine", and assigned it the symbol Ab, designations that were used for a few years afterward. In 1934, however, H. G. MacPherson of University of California, Berkeley disproved Allison's method and the validity of his discovery. This erroneous discovery was followed by another claim in 1937, by the chemist Rajendralal De. Working in Dhaka, British India (now Bangladesh), he chose the name "dakin" for element 85, which he claimed to have isolated as the thorium series equivalent of Radium F (polonium-210) in the radium series. The properties he reported for dakin do not correspond to those of astatine, and the true identity of dakin is not known.

In 1940, the Swiss chemist Walter Minder announced the discovery of element 85 as the beta decay product of Radium A (polonium-218), choosing the name "helvetium" (from Helvetia, "Switzerland"). However, Berta Karlik and Traude Bernert were unsuccessful in reproducing his experiments, and subsequently attributed Minder's results to contamination of his radon stream (radon-222 is the parent isotope of polonium-218). In 1942, Minder, in collaboration with the English scientist Alice Leigh-Smith, announced the discovery of another isotope of element 85, presumed to be the product of Thorium A (polonium-216) beta decay. They named this substance "anglo-helvetium", but Karlik and Bernert were again unable to reproduce these results.

In 1940, Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè finally isolated the element at the University of California, Berkeley. Instead of searching for the element in nature, the scientists created it by bombarding bismuth-209 with alpha particles. The name "astatine" comes from the Greek word αστατος (astatos, meaning "unstable"), due to its propensity for radioactive decay (later, all isotopes of the element were shown to be unstable), together with the ending "-ine", found in the names of the four previously discovered halogens. Three years later, astatine was found as a product of naturally occurring decay chains by Karlik and Bernert. Since then, astatine has been determined to be in three out of the four natural decay chains.