thorium

[thawr-ee-uhm, thohr-]
noun Chemistry.
a grayish-white, lustrous, somewhat ductile and malleable, radioactive metallic element present in monazite: used as a source of nuclear energy, as a coating on sun-lamp and vacuum-tube filament coatings, and in alloys. Symbol: Th; atomic weight: 232.038; atomic number: 90; specific gravity: 11.7.
Compare thoria.


Origin:
< Neo-Latin (1829); see Thor, -ium

thoric [thawr-ik, thor-] , adjective
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World English Dictionary
thorium (ˈθɔːrɪəm)
 
n
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]
 
'thoric
 
adj

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Etymonline
Word Origin & History

thorium
rare metallic element, 1832, from Mod.L., named 1828-9 by its discoverer, Swed. chemist Jöns Jakob Berzelius (1779-1848) in honor of the Scand. god Thor (q.v.).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

thorium tho·ri·um (thôr'ē-əm)
n.
Symbol Th
A radioactive metallic element that is used in magnesium alloys; its longest-lived isotope, Th 232, has a half-life of 1.41 × 1010 years. Atomic number 90; atomic weight 232.038; approximate melting point 1,750°C; approximate boiling point 4,800°C; approximate specific gravity 11.7; valence 4.

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American Heritage
Science Dictionary
thorium   (thôr'ē-əm)  Pronunciation Key 
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, Th 232, is also its most stable, having a half-life of 14.1 billion years. Atomic number 90; atomic weight 232.038; approximate melting point 1,750°C; approximate boiling point 4,500°C; approximate specific gravity 11.7; valence 4. See Periodic Table.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
She soon repeated the experiment with thorium, which behaved in similar ways.
Phosphate rock sequesters uranium, thorium, and decay daughters.
The reason is that the ash left over when coal is burned contains radioactive
  elements, notably uranium and thorium.
Thorium hardly gets a mention as a safer option, there is more thorium around
  than uranium.
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