tho·ri·um /ˈθoriəm, ˈθɔr-/
  放射性金屬元素,符號Th,原子序90,釷
  tho·ri·um /ˈθorɪəm, ˈθɔr-/ 名詞
  釷
  Tho·ri·um n.  Chem. A metallic element found in certain rare minerals, as thorite, pyrochlore, monazite, etc., and isolated as an infusible gray metallic powder which burns in the air and forms thoria; -- formerly called also thorinum. Symbol Th. Atomic weight 232.0.
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  thorium
       n : a soft silvery-white tetravalent radioactive metallic
           element; isotope 232 is used as a power source in nuclear
           reactors; occurs in thorite and in monazite sands [syn: Th,
            atomic number 90]
  thorium
  Symbol: Th
  Atomic number: 90
  Atomic weight: 232.038
  Grey radioactive metallic element. Belongs to actinoids. Found in monazite sand
  in Brazil, India and the US.  Thorium-232 has a half-life of 1.39x10^10 years.
  Can be used as a nuclear fuel for breeder reactors. Thorium-232 captures slow
  neutrons and breeds uranium-233. Discovered by Jons J. Berzelius in
  1829.