What is PROTACTINIUM?

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What is PROTACTINIUM?

Protactinium formerly known as protoactinium is a chemical element with symbol Pa and atomic number 91. It is a dense, silvery-gray actinide metal which 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, protactinium is mostly extracted from spent nuclear fuel.

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, 231 P a, was discovered in 1917 by Otto Hahn and Lise Meitner, and they chose the name proto-actinium, but the I U P A C finally named it "protactinium" in 1949 and confirmed Hahn and Meitner as discoverers. The new name meant " precursor of actinium" and reflected that actinium is a product of radioactive decay of protactinium. John Arnold Cranston (working with Frederick Soddy and Ada Hitchins) 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.

The longest-lived and most abundant naturally occurring isotope of protactinium, protactinium 231, has a half life of 32,760 years and is a decay product of uranium 235. Much smaller trace amounts of the short lived nuclear isomer protactinium 234 m occur in the decay chain of uranium 238. Protactinium 233 results from the decay of thorium 233 as part of the chain of events used to produce uranium 233 by neutron irradiation of thorium 232. It is an undesired intermediate product in thorium based nuclear reactors and is therefore removed from the active zone of the reactor during the breeding process. Analysis of the relative concentrations of various uranium, thorium and protactinium isotopes in water and minerals is used in radiometric dating of sediments which are up to 175,000 years old and in modeling of various geological processes.