thorium(redirected from Element 90)
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n. Symbol Th
A radioactive silvery-white metallic element that is recovered commercially from monazite. Its longest-lived isotope, the only one that occurs naturally, is Th-232 with a half-life of 14.1 billion years and is used as a nuclear fuel. Thorium is used in magnesium alloys, and its oxide is widely used in gas mantles of Welsbach burners. Atomic number 90; atomic weight 232.038; melting point 1,750°C; boiling point 4,788°C; specific gravity 11.72; valence 4. See Periodic Table.
(Elements & Compounds) a soft ductile silvery-white metallic element. It is radioactive and occurs in thorite and monazite: used in gas mantles, magnesium alloys, electronic equipment, and as a nuclear power source. Symbol: Th; atomic no: 90; atomic wt: 232.0381; half-life of most stable isotope, 232Th: 1.41 × 1010 years; valency: 4; relative density: 11.72; melting pt: 1755°C; boiling pt: 4788°C
[C19: New Latin, from Thor + -ium]
tho•ri•um(ˈθɔr i əm, ˈθoʊr-)
a grayish white, lustrous, radioactive metallic element: used as a source of nuclear energy, in sun-lamp and vacuum-tube filaments, and in alloys. Symbol: Th; at. wt.: 232.038; at. no.: 90; sp. gr.: 11.7.
thor•ic (ˈθɔr ɪk, ˈθɒr-) adj.
Symbol Th A silvery-white, radioactive metallic element of the actinide series. It is used for fuel in some nuclear reactors and for improving the high-temperature strength of magnesium alloys. The only naturally occurring isotope of thorium is also its most stable, having a half-life of 14 billion years. Atomic number 90. See Periodic Table.
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|Noun||1.||thorium - 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|
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.
monazite - a reddish-brown mineral containing rare earth metals; an important source of thorium and cerium
thorite - a radioactive mineral consisting of thorium silicate; it is a source of thorium that is found in coarse granite