page_title: Tritium
section_title: Properties
hierarchical_section_title: Tritium / Properties
caption_attribution_description: English: A Gaseous tritium light source
context_page_description: Tritium or hydrogen-3 is a rare and radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of the common isotope hydrogen-1 contains just one proton, and that of hydrogen-2 contains one proton and one neutron.
  Naturally occurring tritium is extremely rare on Earth. The atmosphere has only trace amounts, formed by the interaction of its gases with cosmic rays. It can be produced by irradiating lithium metal or lithium-bearing ceramic pebbles in a nuclear reactor.
  Tritium is used as a radioactive tracer, in radioluminescent light sources for watches and instruments, and, along with deuterium, as a fuel for nuclear fusion reactions with applications in energy generation and weapons.
  The name of this isotope is derived from Greek τρίτος, meaning "third".
context_section_description: Tritium has an atomic mass of 3.0160492 u. Diatomic tritium (
  T
  ₂ or ³
  H
  ₂) is a gas at standard temperature and pressure. Combined with oxygen, it forms a liquid called tritiated water (
  T
  ₂
  O
  ).
  Tritium's specific activity is 9,650 curies per gram (3.57×10¹⁴ Bq/g).
  Tritium figures prominently in studies of nuclear fusion because of its favorable reaction cross section and the large amount of energy (17.6 MeV) produced through its reaction with deuterium:
  All atomic nuclei contain protons as their only electrically charged particles.  They therefore repel one another because like charges repel. However, if the atoms have a high enough temperature and pressure (for example, in the core of the Sun), then their random motions can overcome such electrical repulsion (called the Coulomb force), and they can come close enough for the strong nuclear force to take effect, fusing them into heavier atoms.
  The tritium nucleus, containing one proton and two neutrons, has the same charge as the nucleus of ordinary hydrogen, and it experiences the same electrostatic repulsive force when brought close to another atomic nucleus. However, the neutrons in the tritium nucleus increase the attractive strong nuclear force when brought close enough to another atomic nucleus. As a result, tritium can more easily fuse with other light atoms, compared with the ability of ordinary hydrogen to do so.
  The same is true, albeit to a lesser extent, of deuterium. This is why brown dwarfs (so-called failed stars) cannot utilize 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 of tritium oxide introduced into upper layers of the oceans have been used in the years since then to measure the rate of mixing of the upper layers of the oceans with their lower levels.
caption: Radioluminescent 1.8 curies (67 GBq) 6 by 0.2 inches (152.4 mm × 5.1 mm) tritium vials are thin, tritium-gas-filled glass vials whose inner surfaces are coated with a phosphor. The vial shown here is brand-new.
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