Tritium in the Atmospheric Environment

The production rate of natural tritium, produced constantly in the upper atmosphere by nuclear reactions between secondary cosmic rays and nitrogen or oxygen atoms, is estimated to be 0.2 to 0.25 tritium atom cm s which yields 1–1.3 EBq tritium inventory in the world. The naturally occurring tritium has been found in various environmental materials which contain hydrogen atom as a constituent element. The concentration of tritium in the environment had increased by nuclear tests in 1950s–1960s that had released a large amount of artificial tritium to the environment. The amount of tritium emitted from the nuclear tests would be 240 EBq and we can still detect the bomb tritium in environmental samples such as underground water more than 40 years after the test ban treaty in 1963. Peaceful use of nuclear energy has also increased environmental tritium concentrations such as around nuclear power stations and nuclear fuel reprocessing plants due to controlled release of tritium as airborne and liquid effluents. Tritium is found in the atmosphere as 3 different chemical forms that are water vapor, hydrogen, and hydrocarbon. We report atmospheric tritium concentrations of 3 chemical species measured in the general environment of Japan.