A silvery, radioactive metal.

Fact Box

Uses

Protactinium is little used outside of research.

History

Mendeleev said there should be an element between thorium and uranium, but it evaded detection. Then, in 1900, William Crookes separated an intensely radioactive material from uranium, but did not identify it. In 1913, Kasimir Fajans and Otto Göhring showed that this new element decayed by beta-emission and it existed only fleetingly. We now know it is a member of the sequence of elements through which uranium decays. It was the isotope protactinium-234, which has a half-life of 6 hours 42 minutes.