Chemical Fact Sheet


Chemical Abstract Number (CAS #) 7440-13-3
Analytical Methods 200.8 - 6020
Atomic Symbol Pa

Synopsis from the CRC Handbook of Chemistry and Physics 92nd Edition 2011-2013

Protactinium — (Gr. protos, first), Pa; at. wt. 231.03588(2); at. no. 91; m.p. 1572 °C; sp. gr. 15.37 (calc.); valence 4 or 5. The first isotope of Element 91 to be discovered was 234Pa, also known 4-28 The Elements as UX2, a short-lived member of the naturally occurring 238U decay series. It was identified by K. Fajans and O. H. Gohring in 1913 and they named the new element brevium. When the longer-lived isotope 231Pa was identified by Hahn and Meitner in 1918, the name protoactinium was adopted as being more consistent with the characteristics of the most abundant isotope. Soddy, Cranson, and Fleck were also active in this work. The name protoactinium was shortened to protactinium in 1949. In 1927, Grosse prepared 2 mg of a white powder, which was shown to be Pa2O5. Later, in 1934, from 0.1 g of pure Pa2O5 he isolated the element by two methods, one of which was by converting the oxide to an iodide and “cracking” it in a high vacuum by an electrically heated filament by the reaction 2PaI5 2Pa 5I2 → + Protactinium has a bright metallic luster that it retains for some time in air. The element occurs in pitchblende to the extent of about 1 part 231Pa to 10 million of ore. Ores from Congo-Kinshasa have about 3 ppm. Protactinium has twenty- eight isotopes and isomers, the most common of which is 231Pr with a half-life of 32,500 years. A number of protactinium compounds are known, some of which are colored. The element is superconductive below 1.4 K. The element is a dangerous toxic material and requires precautions similar to those used when handling plutonium. In 1959 and 1961, it was announced that the Great Britain Atomic Energy Authority extracted by a 12-stage process 125 g of 99.9% protactinium, the world’s only stock of the metal for many years to come. The extraction was made from 60 tons of waste material at a cost of about $500,000. Protactinium is one of the rarest and most expensive naturally occurring elements.

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