Tritium ordinary hydrogen, but they do fuse the small minority of deuterium nuclei. Like the other isotopes of hydrogen, tritium is difficult to confine. Rubber, plastic, and some kinds of steel are all somewhat permeable. This has raised concerns that if tritium were used in large quantities, in particular for fusion reactors, it may contribute to radioactive contamination, although its short half-life should prevent significant long-term accumulation in the atmosphere. The high levels of atmospheric nuclear weapons testing that took place prior to the enactment of the Partial Test Ban Treaty proved to be unexpectedly useful to oceanographers. The high levels
Tritium radioluminescence vials so that the flashlight can be easily located in the dark. Tritium is used to illuminate the iron sights of some small arms. The reticle on the SA80's optical SUSAT sight as well as the LPS 4x6° TIP2 telescopic sight of a PSL rifle, contains a small amount of tritium for the same effect as an example of tritium use on a rifle sight. The electrons emitted by the radioactive decay of the tritium cause phosphor to glow, thus providing a long-lasting (several years) and non-battery-powered firearms sight that is visible in dim lighting conditions. The tritium glow is