Thorium is a radioactive metal in the actinide series. As a fertile material, it has been considered an alternative to uranium in nuclear fuel, and thorium is three times as abundant as uranium. Thorium dioxide has the highest melting point of any oxide. The primary source of thorium is the mineral monazite.
An isomer of thorium-239 has an excitation energy near optical energy, and it might be possible to use a laser to turn the decay on and off.
Thorium News 2010-04-05 - (ct) - Thorium One aims to recycle nulcear fuel waste product
2010-03-29 - (sd) - Why do nuclear reactors and nuclear-fission bombs use uranium or plutonium rather than thorium?