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[pruh-mee-thee-uh m] /prəˈmi θi əm/
noun, Chemistry
a rare-earth, metallic, trivalent element. Symbol: Pm; atomic number: 61.
1945-50; < New Latin; see Prometheus, -ium Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for promethium
  • Purification of promethium by liquid-liquid extraction.
British Dictionary definitions for promethium


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.)
Word Origin
C20: New Latin from Prometheus
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin and History for promethium

radioactive element, long one of the "missing elements," 1948, so called by discoverers Jacob Marinsky and Lawrence Glendenin, who detected it in 1945 in the fusion products of uranium while working on the Manhattan Project. From Prometheus, who stole fire from the gods and was punished for it, + element name ending -ium. "The name not only symbolizes the dramatic way in which the element may be produced in quantity as a result of man's harnessing of the energy of nuclear fission, but also warns man of the impending danger of punishment by the vulture of war." [Marinsky and Glendenin]

Online Etymology Dictionary, © 2010 Douglas Harper
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promethium in Medicine

promethium pro·me·thi·um (prə-mē'thē-əm)
Symbol Pm
A radioactive rare-earth element prepared by fission of uranium. Pm 145 is the longest-lived isotope with a half-life of 17.7 years. Atomic number 61; melting point 1,042°C; boiling point 3,000°C; valence 3.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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promethium in Science
Symbol Pm
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. See Periodic Table.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Article for promethium


(Pm), chemical element, only rare-earth metal of transition Group IIIb of the periodic table not detected in nature. Conclusive chemical proof of the existence of promethium, the last of the rare-earth elements to be discovered, was obtained (1947) by J.A. Marinsky, L.E. Glendenin, and C.D. Coryell, who isolated the radioactive isotope promethium-147 (2.7-year half-life) from uranium fission products at the research site at Oak Ridge, Tenn. Identification was firmly established by spectroscopy. Earlier investigators thought that they had found the element with atomic number 61 in naturally occurring rare earths and had prematurely called it illinium and florentium. Promethium-147 is effectively separated from the other rare-earth fission products by an ion-exchange method. Its soft beta radiation is converted to electricity in miniature batteries formed by sandwiching promethium between wafers of a semiconductor such as silicon; these batteries operate in extreme temperatures for five years. Promethium has also been prepared by slow neutron bombardment of the isotope neodymium-146; the resultant isotope, neodymium-147, decays by electron emission to promethium-147. The metal itself was first prepared (1963) by reduction of the fluoride, PmF3, with lithium

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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