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Tritium (Hydrogen-3) What is it? Tritium is the only radioactive isotope of hydrogen. (An isotope is a different form of an element that has the same number of protons in the nucleus but a different number of neutrons.) The nucleus of a tritium atom consists of a proton and two neutrons. This contrasts with the nucleus of an ordinary hydrogen atom (which consists solely of a proton) and deuterium atom (which consists of one proton and one neutron). Ordinary hydrogen comprises over 99.9% of all naturally occurring hydrogen. Deuterium comprises about 0.02% and tritium comprises about a billionth of a billionth (10-18) percent. The most common forms of tritium are tritium gas and tritium oxide, also called "tritiated water." In tritiated water, a tritium atom replaces one of the hydrogen atoms so the chemical form is HTO rather than H2O. The chemical properties of tritium are essentially the same as those of ordinary hydrogen. It decays with a half-life of 12 years by emitting a beta particle to produce helium-3. Where does it come from? Tritium is naturally present as a very small percentage of ordinary hydrogen in water, both liquid and vapor. Tritium is also produced as a fission produce in nuclear weapons tests and in nuclear power reactors, with a yield of about 0.01%. That is, about one atom of tritium is produced per 10,000 fissions. What's in the Environment? Tritium is present in water (liquid and vapor) as a result of natural processes in the atmosphere, as well as from fallout from past atmospheric nuclear weapons tests and the operation of nuclear reactors and fuel reprocessing plants. The form of most concern, tritium oxide (HTO), is generally indistinguishable from normal water and can move rapidly through the environment in the same manner as water. Tritium is naturally present in surface waters at about 10 to 30 picocuries per liter (pCi/L). The maximum contaminant level developed by the Environmental Protection Agency for tritium in drinking water supplies is 20,000 pCi/L or 0.02 microcuries per liter. |