![Promethium element card: symbol Pm, atomic number 61, atomic mass [145], electron configuration [Xe] 4f⁵ 6s², oxidation states +3, Lanthanide, f-block, period 6, solid at room temperature.](https://stage.chemistry-dictionary.com/wp-content/uploads/2026/09/promethium-chemical-element.webp)
Promethium sits in the f-block of the periodic table between neodymium and samarium. Its name comes from Prometheus, the ancient Greek titan who stole fire. Because all of its isotopes are highly unstable, scientists have studied it less than other lanthanides.
The metal breaks down rapidly by emitting energetic beta particles during radioactive decay. This continuous radiation is strong enough to make the surrounding air glow with a pale blue light. When promethium salts dissolve in water, they turn the liquid a pale pink color.
A common student misconception is that promethium only exists because humans make it. In reality, tiny traces form naturally when uranium atoms split apart in the Earth’s crust. However, the entire crust contains less than one kilogram of promethium at any time.
Another mistake is confusing the type of radiation that promethium releases. It emits beta particles, which are fast electrons, rather than heavy alpha particles. Scientists must produce usable amounts of promethium inside nuclear reactors.
They do this by hitting neodymium atoms with a stream of slow neutrons. They can also extract the element from the waste of spent nuclear fuel. Because it presents a severe radiation hazard, researchers must work behind thick lead shielding.