Half-life: 14 billion years
Main emission lines: 238keV, 338keV, 583keV, 727keV, 911keV, 1588keV, 2614keV
Thorium is a very common isotope, both in nature and in the home. It is used to make special alloys for electrodes, gas lamp nets, and is found in minerals, building materials (often granite), etc. Unlike radium, it gives off very little radon.