[thawr-ee-uh
m, thohr-] 
| 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. |
| tho·ri·um (thôr'ē-əm, thōr'-) 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 1.41 × 1010 years. It is used in magnesium alloys, and isotope 232 is a source of nuclear energy. 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 Table at element. [After Thor.] |
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.
| 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. |