Protactinium was first identified in 1913 by Kasimir Fajans and Oswald Helmuth Göhring and named brevium because of the short half-life of the specific isotope studied, i.e. protactinium-234. A more stable isotope of protactinium, Pa, was discovered in 1917/18 by Otto Hahn and Lise Meitner, and they chose the name proto-actinium, but the IUPAC finally named it "protactinium" in 1949 and confirmed Hahn and Meitner as discoverers. The new name meant "(nuclear) precursor of actinium" and reflected that actinium is a product of radioactive decay of protactinium. Protactinium is an actinide which is positioned in the periodic table to the left of uranium and to the right of thorium, and many of its physical properties are intermediate between those two actinides. Protactinium is both toxic and highly radioactive and thus all manipulations with it are performed in a sealed glove box. As protactinium is present in small amounts in most natural products and materials, it is ingested with food or water and inhaled with air. Only about 0.05% of ingested protactinium is absorbed into the blood and the remainder is excreted. From the blood, about 40% of the protactinium deposits in the bones, about 15% goes to the liver, 2% to the kidneys, and the rest leaves the body. The biological half-life of protactinium is about 50 years in the bones, whereas in other organs the kinetics has a fast and slow component. So in the liver 70% of protactinium have a half-life of 10 days and 30% remain for 60 days.
