The first isotope of protactinium to be discovered was Pa 234m (also called UX2), an ephemerous member of the natural decay series of U 238. This isotope was identified by Fajans and Gohring in 1913, who called it brevium at the time. Almost simultaneously, in 1918, two research scientist teams isolated a more stable isotope (Pa 231), of the decay series of U 235. These teams were led by Hahn and Meitner, and by Soddy and Cranston. Initially christened protoactinium, the element saw its name being contracted for protactinium.