protactinium-231

isotope

Also known as: protoactinium

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July 13, 2026

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Protactinium-231 (²³¹Pa) is a radioactive isotope of protactinium, a chemical element in the actinoid series with atomic number 91. It is rarer than radium and occurs in uranium ores. Discovered in 1917, ²³¹Pa has a half-life of 32,760 years and decays into actinium-227.1

This isotope is significant in dating marine sediments, alongside thorium-230, due to their similar chemical properties and precipitation rates. The ratio of ²³¹Pa to ²³⁰Th allows for age determination of sediments up to 175,000 years old. Protactinium, in general, exhibits oxidation states of +4 and +5 and its compounds readily hydrolyze in water.21

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protactinium
The long-lived isotope protactinium-231 (originally called protoactinium for “before actinium” and later shortened to protactinium) was discovered (1917) independently by German chemist Otto Hahn and Austrian physicist Lise Meitner in pitchblende, by Fajans, and by British chemists Frederick Soddy, John Cranston, and Sir Alexander Fleck. This isotope
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The long-lived isotope protactinium-231 (originally called protoactinium for “before actinium” and later shortened to protactinium) was discovered (1917) independently by German chemist Otto Hahn and Austrian physicist Lise Meitner in pitchblende, by Fajans, and by British chemists Frederick Soddy, John Cranston, and Sir Alexander Fleck. This isotope
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Otto Hahn
Early life
…among the first to isolate protactinium-231, an isotope of the recently discovered radioactive element protactinium. Because nearly all the natural radioactive elements had then been discovered, he devoted the next 12 years to studies on the application of radioactive methods to chemical problems.
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…among the first to isolate protactinium-231, an isotope of the recently discovered radioactive element protactinium. Because nearly all the natural radioactive elements had then been discovered, he devoted the next 12 years to studies on the application of radioactive methods to chemical problems.
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Lise Meitner
…to isolate the isotope protactinium-231 (which they named), studied nuclear isomerism and beta decay, and in the 1930s (along with Strassmann) investigated the products of neutron bombardment of uranium. Because she was Jewish, she left Nazi Germany in the summer of 1938 to settle in Sweden.
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…to isolate the isotope protactinium-231 (which they named), studied nuclear isomerism and beta decay, and in the 1930s (along with Strassmann) investigated the products of neutron bombardment of uranium. Because she was Jewish, she left Nazi Germany in the summer of 1938 to settle in Sweden.
Read More