atomic number 90

Definitions of atomic number 90
  1. noun
    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
    synonyms: Th, thorium
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    types:
    radiothorium, thorium-228
    radioactive isotope of thorium with mass number 228
    type of:
    metal, metallic element
    any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.
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