Protactinium is a chemical element with the symbol Pa and atomic number 91. It is a dense, silvery-gray actinide metal that readily reacts with oxygen, water vapor, and inorganic acids. It forms various chemical compounds in which protactinium is usually present in the oxidation state +5, but it can also assume +4 and even +3 or +2 states. Concentrations of protactinium in the Earth’s crust are typically a few parts per trillion but may reach up to a few parts per million in some uraninite ore deposits. Because of its scarcity, high radioactivity, and high toxicity, there are currently no uses for protactinium outside scientific research, and for this purpose, It is mostly extracted from spent nuclear fuel.
|Atomic Mass||231.0359 g.mol -1|
|Discovered by||K. Kajans and O.H. Gohring in 1913|
It 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. Pa-234. A more stable isotope of protactinium 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. John Arnold Cranston is also credited with discovering the most stable isotope in 1915 but delayed his announcement due to being called up for service in the First World War.
Physical Properties of Protactinium
- It 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.
- its melting point is lower than that of thorium and higher than that of uranium.
- At room temperature, Pa crystallizes in the body-centered tetragonal structure which can be regarded as distorted body-centered cubic lattice; this structure does not change upon compression up to 53 GPa.
- It is paramagnetic and no magnetic transitions are known for it at any temperature. It becomes superconductive at temperatures below 1.4 K.