thorium
  • A lustrous silver-white radioactive metallic element whose atomic number is 90. It is soft, ductile, and can be extruded, drawn, and welded. It has about 30 known isotopes, all unstable. It is used, for instance, as a nuclear fuel, in lamps, lasers, semiconductors, and in photoelectric devices. Its chemical symbol is Th.
  • chemical symbol Th

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