A radioactive rare-earth element prepared by fission of uranium or by neutron bombardment of neodymium, having nearly 50 isotopes and isomers, of which the most stable have half-lives of 2.62 years (Pm-147), 5.53 years (Pm-146), and 17.7 years (Pm-145). Promethium-147 is most easily obtained and is used as a source of beta rays. Atomic number 61; melting point 1,042°C; boiling point 3000°C; specific gravity 7.264 (25°C); valence 3.
A radioactive chemical element, one of the rare-earth elements, obtained from fission of uranium or neutron bombardment of neodymium and used in phosphorescent paint, as a power source, X-ray source, etc.: symbol, Pm; at. no. 61
A radioactive metallic element of the lanthanide series. Promethium does not occur in nature but is prepared through the fission of uranium. It has 17 isotopes, one of which is used to make long-lived miniature batteries that work at extreme temperatures for up to five years. The longest-lived isotope, Pm 147, has a half-life of 2.5 years and is used as a source of beta rays. Atomic number 61; melting point 1,168°C; boiling point 2,460°C; valence 3.
A metallic chemical element (symbol Pm) with an atomic number of 61.