Protactinium: historical information
Protactinium is found in pitchblende and ores form Zaire and is one of the rarest and most expensive naturally occurring elements. Protactinium was identified by Fajans and GΔhring in 1913 who named the new element brevium ("brief"). The metal itself was not isolated until 1934 when Aristid Grosse developed two methods. One involved reduction of the pentoxide Pa2O5 with a stream of electrons in a vacuum and the second involved heating the iodide PaI5 under vacuum.