 Tritium is used as a radioactive tracer, in radioluminescent light sources for watches and instruments, and as a fuel for nuclear fusion reactions. | Tritium is a radioactive isotope of hydrogen. Naturally occurring tritium is extremely rare on Earth, where trace amounts are formed by the interaction of the atmosphere with cosmic rays. It can be produced by irradiating lithium in a nuclear reactor. |  |
 | Tritium presents no radiation threat when encapsulated properly. Tritium is used today in glow-in-the-dark lighting for signs and is trending as key ring accessories. |  |
 | Tritium tubes are gas-filled, thin glass vials with inner surfaces coated with a phosphor. The gaseous tritium in these light sources undergoes beta decay, releasing electrons that cause the phosphor layer to fluoresce. Tritium radiation cannot penetrate intact human skin. Light sources can glow for ten years or more without needing any kind of charging. |  |
