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2 definitions found
 for promethium
From WordNet (r) 3.0 (2006) :

  promethium
      n 1: 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 [syn: promethium,
           Pm, atomic number 61]

From The Elements (07Nov00) :

  promethium
  Symbol: Pm
  Atomic number: 61
  Atomic weight: (147)
  Soft silvery metallic element, belongs to the lanthanoids. Pm-147, the
  only natural isotope, is radioactive and has a half-life of 252 years.
  Eighteen radioisotopes have been produced, but all have very short
  half-lives. Found only in nuclear decay waste. Pm-147 is of interest as
  a
  beta-decay source, however Pm-146 and Pm-148 have to be removed from it
  first, as they generate gamma radiation. Discovered by J.A. Marinsky,
  L.E. Glendenin and C.D. Coryell in 1947.
  

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