In 1900, William Crookes isolated protactinium as an intensely radioactive material from uranium; however, he could not characterize it as a new chemical element and thus named it uranium-X.Crookes dissolved uranium nitrate in ether, the residual aqueous phase contains most of the 234 90Th and 234/ 91Pa. His method was still used in the 1950s to isolate 234 90Th and 234/ 91Pa from uranium compounds. Protactinium was first identified in 1913, when Kasimir Fajans and Oswald Helmuth Göhring encountered the isotope 234Pa during their studies of the decay chains of uranium-238: 238 92U → 234/ 90Th → 234/ 91Pa → 234/ 92U. They named the new element brevium (from the Latin word, brevis, meaning brief or short) because of its short half-life, 6.7 hours for 234 91Pa.