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 (UX). Crookes dissolved uranium nitrate in ether, and the residual aqueous phase contains most of the and . His method was still used in the 1950s to isolate and 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: → → → . 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 . In 1917/18, two groups of scientists, Otto Hahn and Lise Meitner of Germany and Frederick Soddy and John Cranston of Great Britain, independently discovered another isotope of protactinium, 231Pa, having a much longer half-life of about 33,000 years. Thus the name "brevium" was changed to "protoactinium" as the new element was part of the decay chain of uranium-235 as the parent of actinium (from "prôtos" "first, before"). For ease of pronunciation, the name was shortened to "protactinium" by IUPAC in 1949. The discovery of protactinium completed one of the last gaps in the early versions of the periodic table, proposed by Mendeleev in 1869, and it brought to fame the involved scientists.