Standard State: Solid at 298 K
Color: Silvery metallic
The first isotope of element 91 to be discovered was a short lived member of the
naturally occurring uranium decay series. It was identified by K. Fajans and O.H.
Gohring in 1913 and they named the new element brevium. When the longer-live
isotope 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.
In 1959 and 1961, it was announced that the Great Britain Atomic Energy Authority
extracted by 12-stage process 125g of 99.9% protactinium, the world's only stock of
the metal for many years to come. Protactinium is one the rarest and most expensive
naturally occurring elements.