Atomic number: 90

Symbol: Th

Category: actinide 

Density at 25°C: solid: density: 10 g·cm−3

Named after the norse god thor, this element is radioactive and historically known for it's use in lantern mantles, which incidentally, does not have anything to do with radioactivity, but just heat resistance. Now it considered more as a viable substitute for safer nuclear fuel.

Thorium crystal. image: adapted from wikipedia

Use, natural applications or common combinations: 

  • Thorium dioxide in heat resistant ceramics
  • Mag-Thor magnesium alloy
  • arc welding tips
  • anti reflection coatings,  thorium fluoride (ThF4

Basic characteristics:

  • Standard atomic weight: 232.038 06(2)
  • Melting point: 1842 °C
  • Boiling point:  4788 °C
  • Radioactivity: all radioactive
    • 232Th with a half-life of 14.05 billion years  via alpha decay