: a radioactive metallic element of the rare-earth group obtained as a fission product of uranium or from neutron-irradiated neodymium — see Chemical Elements Table
Examples of promethium in a Sentence
Recent Examples on the WebOne promethium isotope, with eighty-eight neutrons, has a half-life of a few days; the other, with eighty-six neutrons, has a half-life of a few years.
Neima Jahromi, The New Yorker, 27 Dec. 2019
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