Due to its scarcity, high radioactivity and toxicity, there are currently no uses for protactinium outside of basic research.
Protactinium-231 (which is made by the alpha decay of Uranium-235 followed by beta decay of Thorium-231) could possibly sustain a nuclear chain reaction and might be used to build a nuclear weapon. The critical mass, according to Walter Seifritz, is 750±180 kg. Other authors conclude that no chain reactions are possible in Protactinium-231.
Protactinium was first discovered in 1913, when Kasimir Fajans and O. H. Göhring encountered short-lived isotope 234m-Pa, with a half-life of about 1.17 minutes, while they were studying the decay chain of 238-U. They gave the new element the name Brevium (Latin brevis, brief, short); the name was changed to Protoactinium in 1918 when two groups of scientists (Otto Hahn and Lise Meitner of Germany and Frederick Soddy and John Cranston of the UK) independently discovered 231-Pa. The name was shortened to Protactinium in 1949.
In 1961, the United Kingdom Atomic Energy Authority was able to produce 125 g of 99.9% pure protactinium, processing 60 tons of waste material in a 12-stage process and spending 500,000 USD. For many years to come, this was the world's only way to get the element. It is said that the metal was sold to laboratories for a cost of 2,800 USD / g in the following years.
Protactinium is both toxic and highly radioactive. It requires precautions similar to those used when handling plutonium.