Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium (sometimes called triton) contains one proton and two neutrons, whereas the nucleus of protium (the most abundant hydrogen isotope) contains no neutrons. Tritium combines with oxygen to form a liquid called tritiated water (T2O or partially tritiated THO), somewhat like heavy water (deuterium oxide).
Properties
Tritium is radioactive with a half-life of 12.32 years, decaying into helium-3 releasing 18.6 keV of energy. The electron has an average kinetic energy of 6.5 keV, while the remaining energy is carried off undetectably by the electron antineutrino. The low-energy beta radiation from tritium cannot penetrate the skin of most life forms, so tritium is only dangerous if inhaled or ingested. Its low energy also makes it difficult to detect tritium labelled compounds except by using liquid scintillation counting.
Production
Tritium occurs naturally due to cosmic rays interacting with atmospheric gases. In the most important reaction for natural tritium production, a fast neutron interacts with atmospheric nitrogen. Because of tritium's relatively short half-life, however, tritium produced in this manner does not accumulate over geological timescales, and its natural abundance is negligible. Industrially, tritium is produced in nuclear reactors by neutron activation of lithium-6.
Tritium is also produced in heavy water-moderated reactors when deuterium captures a neutron; however, this reaction has a much smaller cross section and is only a useful tritium source for a reactor with a very high neutron flux. It can also be produced from boron-10 through neutron capture.
Applications
Tritium figures prominently in studies of nuclear fusion due to its favorable reaction cross section and the high energy yield of 17.6 MeV for its reaction with deuterium. All atomic nuclei, being composed of protons and neutrons, repel one another because of their positive charge. However, if the atoms have a high enough temperature and pressure (as is the case in the core of suns, for example), then their random motions can overcome such electrical repulsion, and they can come close enough for the strong nuclear force to take effect, fusing them into heavier atoms. Since tritium has the same charge as ordinary hydrogen, it experiences the same electrical repulsive force. However, due to its higher mass, it is less responsive to such forces, and thus can more easily fuse with other atoms. The same is also true, albeit to a lesser extent, of deuterium, and that is why brown dwarfs (so called failed stars) can not burn hydrogen, but do indeed burn deuterium.
Tritium is used in nuclear weapons to obtain higher yields through nuclear fusion. However, as it decays and is difficult to contain, many nuclear weapons contain lithium instead, since the high neutron fluxes will produce tritium from the lithium when the bomb detonates.
Like hydrogen, it is difficult to confine tritium; rubber, plastic, and some kinds of steel are all somewhat permeable. This has raised concerns that if tritium is used in quantity, in particular for fusion reactors, it may contribute to radioactive contamination.
The emitted electrons from small amounts of Tritium cause phosphors to glow so as to make self-illuminating devices. The same process has been used to make self-illuminating gun sights for firearms. These take the place of Radium, which causes bone cancer, and so has been banned for decades.
