Tritium is a radioactive isotope of hydrogen, denoted as \( ^3H \) or T. It contains one proton and two neutrons in its nucleus, making it heavier than the most common hydrogen isotope, protium (\( ^1H \)), which has only one proton and no neutrons. Tritium is produced naturally in the atmosphere through interactions between cosmic rays and nitrogen.
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Tritium is the hydrogen isotope : its nucleus contains one proton and two neutrons. It undergoes beta decay to helium-3, emitting an electron and an electron antineutrino:This equation uses nuclear notation: the mass number stays3, while electric charge is conserved because the daughter nucleus has charge and the emitted electron has charge . The half-life is approximately12.3years.[ref]
DOE Fundamentals Handbook Chemistry Volume 2 of 2. CH-03, page24, Table2 and Disintegration
A motivating measurement is a long series of activity comparisons. A 2000 study calibrated tritiated-water standards with internal gas-proportional counting and liquid-scintillation intercomparisons. Activity data for one standard extending over38years gave a half-life of days, with the stated uncertainty one standard deviation. This is that study's measured result, rather than an assertion that every evaluation uses precisely the same value.[ref]
Calibration of the National Institute of Standards and Technology tritiated-water standards by M. P. Unterweger and others. Abstract, calibration methods and38-year SRM4927 record
For a closed sample with no added tritium, radioactive decay gives . After two half-lives, one quarter of the original tritium nuclei remain. The lost parent nuclei have become daughter nuclei; a smaller tritium activity does not mean the sample has lost the same fraction of its total atoms.
