• tritium
  • The hydrogen isotope having mass number 3; it is one form of heavy hydrogen, the other being deuterium.
Abstract from DBPedia
    Tritium (/ˈtrɪtiəm/ or /ˈtrɪʃiəm/, from Ancient Greek τρίτος (trítos) 'third') or hydrogen-3 (symbol T or 3H) is a rare and radioactive isotope of hydrogen. The nucleus of tritium (t, sometimes called a triton) contains one proton and two neutrons, whereas the nucleus of the common isotope hydrogen-1 (protium) contains one proton and zero neutrons, and that of hydrogen-2 (deuterium) 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 artificially by irradiating lithium metal or lithium-bearing ceramic pebbles in a nuclear reactor and is a low-abundance byproduct in normal operations of nuclear reactors. Tritium is used as the energy source in radioluminescent lights for watches, gun sights, numerous instruments and tools, and even novelty items such as self-illuminating key chains. It is used in a medical and scientific setting as a radioactive tracer. Tritium is also used as a nuclear fusion fuel, along with more abundant deuterium, in tokamak reactors and in hydrogen bombs.

    三重水素(さんじゅうすいそ)またはトリチウム(英: tritium、記号: T)は、質量数が3である水素の同位体、すなわち陽子1つと中性子2つから構成される核種であり、半減期12.32年で3Heへとβ崩壊する放射性同位体である。 重水素(2H)と三重水素(3H)とを併せて重水素(heavy hydrogen)と呼ばれることがある。三重水素核は三重陽子 (英: triton) とも呼ばれる。 三重水素は、その質量が軽水素の約3倍、二重水素の約1.5倍と差が大きいことから、物理的性質も大きく異なる。一方、化学的性質は最外殻電子の数(水素の場合は1)によって決まる要素が大きいため、三重水素の化学的性質は軽水素や重水素とほぼ同じであることが多い。同位体効果の項も参照。