Protactinium

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Protactinium (play /ˌprtækˈtɪniəm/ PROH-tak-TIN-ee-əm) is a chemical element with the symbol Pa and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds where protactinium is usually present in the oxidation state +5, but can also assume +4 and even +2 or +3 states. The average concentrations of protactinium in the Earth's crust is typically on the order of a few parts per trillion, but may reach up to a few parts per million in some uraninite ore deposits. Because of the scarcity, high radioactivity and high toxicity, there are currently no uses for protactinium outside of scientific research, and for this purpose, protactinium is mostly extracted from the spent nuclear fuel.

Protactinium was first identified in 1913 by Kasimir Fajans and Oswald Helmuth Göhring and named brevium because of the short half-life of the specific isotope studied, namely protactinium-234. A more stable isotope of protactinium was discovered in 1918, and therefore the name was changed to protoactinium and then to protactinium in 1949. The new name meant "before actinium" and reflected the fact that actinium is a product of radioactive decay of protactinium.

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