promethium(redirected from Prometheum)
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n. Symbol Pm
A radioactive element of the lanthanide series that is prepared by fission of uranium or by neutron bombardment of neodymium and has over 30 isotopes, the most stable of which have half-lives of 2.62 years (Pm-147), 5.53 years (Pm-146), and 17.7 years (Pm-145). Promethium-147, the most easily obtained isotope, 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. See Periodic Table.
(Elements & Compounds) a radioactive element of the lanthanide series artificially produced by the fission of uranium. Symbol: Pm; atomic no: 61; half-life of most stable isotope, 145Pm: 17.7 years; valency: 3; melting pt: 1042°C; boiling pt: 2460°C (approx.)
[C20: New Latin from Prometheus]
pro•me•thi•um(prəˈmi θi əm)
a rare-earth, metallic, trivalent element. Symbol: Pm; at. no.: 61.
Symbol Pm A radioactive metallic element of the lanthanide series. Promethium does not occur in nature, but it can be found as a product of the fission of uranium. It has 17 isotopes, one of which can be used to make miniature batteries that work at extreme temperatures for up to five years. Atomic number 61. See Periodic Table.
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|Noun||1.||promethium - a soft silvery metallic element of the rare earth group having no stable isotope; was discovered in radioactive form as a fission product of uranium|