pro·me·thi·um /-θiəm/
 烯土類元素


 pro·me·thi·um /prəˈmɪθɪəm/ 名詞
 鏂


 promethium
      n : 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: Pm, {atomic
          number 61]


 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.