Protactinium

Category: actinide Atomic number: 91 Colour: silver Melting point: 1,568°C (2,854°F) Boiling point: 4,027°C (7,280°F) First identified: 1913

Protactinium has had a few different names over the years. In 1900, the English scientist William Crookes noted that there was an unknown radioactive substance in some uranium ores: he called it uranium-X. In 1913, the Polish–American chemist Kasimir Fajans isolated the isotope protactinium-234, which he named ‘brevium’ due to its half-life of about a minute. However, when the German physicist Lise Meitner isolated a different isotope, protactinium-231, with a half-life of 33,000 years, Fajans suggested renaming the element. Meitner called it ‘protoactinium’, because the element forms actinium when it decays, losing an alpha particle in the process. This was a bit awkward to pronounce, so eventually it was shortened to protactinium.

There are few practical applications for this scarce element (which is hard to refine). However, it can be used to reconstruct the movements of bodies of water in the ocean by comparing the proportions of protactinium-231 and thorium-230. Both are present in small amounts due to the decay of uranium particles in the sea. But the thorium decays faster than the protactinium, so researchers can use the ratio between the two to model the circulation of water.