Protactinium Facts

What is protactinium? What is it used for? Where is it found? Let's find out the answers to these questions, along with many more facts about this metallic element from the following article.
A dense, silver-gray metallic element, protactinium ranks high among some of the costliest elements that occur naturally. This chemical element is highly reactive when exposed to oxygen, inorganic acids, or water vapor, and its concentrated presence in the Earth's crust is extremely limited. It often occurs as a trillionth fraction of the Earth's crust at most places but its concentration may be higher in areas which are rich in deposits of uraninite ores. At such places, the fraction of concentration may go as high as a few parts of a million.


Before proceeding to lift the veil off the facts about protactinium, let's take a look at its properties.

Properties of Protactinium
Atomic Number91
Element CategoryActinide
Standard Atomic Weight231.03588g.mol-1
Electrons per shell2, 8, 18, 32, 20, 9, 2
Density (near room temperature)15.37
Melting Point1568°C
Electronegativity1.5 (Pauling Scale)
Atomic Radius163 pm
Covalent Radius200 pm
Atomic Mass231.03588 unified amu
Lattice StructureTetragonal
Lattice Constant3.920
Magnetic OrderingParamagnetic
Number of Neutrons140


Check out the following facts to get a closer insight into this very rare and extremely costly metallic element.
  • Protactinium was discovered in the year 1913, by Kasimir Fajans and Oswald Helmuth Göhring. Before its identification, the possibility of existence of a chemical element between thorium and uranium was predicted by Dmitri Mendeleev, in the year 1871.
  • A different isotope of this element was discovered by a team led by German scientists Otto Hahn and Lise Meitner, along with another team led by British scientists Frederick Soddy and John Cranston, independently.
  • It occurs in two isotopes - 231Pa and 234Pa. There are two different energy states of isotope 234Pa.
  • The alpha emitting protactinium is formed from uranium-235 decay, whereas the beta radiating isotope 234Pa is formed from uranium-238 decay. As much as 99.8% of uranium decays to result into 234Pa first.
  • Most of it is sourced from thorium that is present in nuclear reactors.
  • Due to its rare occurrence, high radioactivity, toxicity, and extremely expensive extraction, there are no significant uses of this element. Its uses are mostly confined to basic scientific research.
  • Since it is formed from the decay of uranium which is formed in nuclear reactors, it is believed that this element may be a possible supporter of nuclear chain reaction which may, theoretically, be of use in making nuclear weapons. Walter Seifritz had made a similar estimate and had come up with an associated critical mass of 750±180 kg. However, this estimate has been unanimously ruled out by later scientists and physicists.
  • Possibilities of using it as a tracer in the fields of geology and paleoceanography have surfaced recently.
  • Extremely small traces of this element are present in most natural objects including food and water. As a result, it is often ingested and even inhaled from the air we breathe. Since the traces of its presence are insignificant to the extent of nearly being non-existent, its toxicity and radioactivity does not adversely affect our systems. Out of this trace amount of protactinium that we ingest, only about 0.05% is absorbed by the body, while the remaining is expelled via excretion.
That was a crisp listing of some interesting facts about this element. The chemical compounds formed by it mostly contain it in the oxidation state +5, though its occurrence in +4, +3, and +2 states, are also possible.