Protactinium is a chemical element with the symbol Pa and atomic number 91. Protactinium has a bright metallic lustre which it retains for some time in air. 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. Protactinium is one of the rarest and most expensive naturally occurring elements. The element is an α-emitter and is a radiological hazard similar to polonium. Protactinium is a highly toxic and radioactive rare earth metal that requires special handling. It is found in pitchblende and ores form Zaire and is one of the rarest and most expensive naturally occurring elements.The first isotope of element 91 to be discovered was 234Pa, also known as UX2, a short-lived member of the naturally occuring 238U decay series. It was identified by K. Fajans and O.H. Gohring in 1913 and the named the new element brevium. When the longer-lived isotope 231-Pa 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. Sody, 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. Protactinium has 20 isotopes, the most common of which is 231Pa with a half-life of 32,700 years. It has no uses known.