Naturally occurring tritium is extremely rare on Earth, where trace amounts are formed by the interaction of the atmosphere with cosmic rays.
Beta particles from tritium can penetrate only about 6.0 mm of air, and they are incapable of passing through the dead outermost layer of human skin.The unusually low energy released in the tritium beta decay makes the decay (along with that of rhenium-187) appropriate for absolute neutrino mass measurements in the laboratory (the most recent experiment being KATRIN).While tritium has several different experimentally determined values of its half-life, the National Institute of Standards and Technology lists and it releases 18.6 ke V of energy in the process.The electron's kinetic energy varies, with an average of 5.7 ke V, while the remaining energy is carried off by the nearly undetectable electron antineutrino.Since it continually decays into helium-3, the total amount remaining was about 75 kg (165 lb) at the time of the report.
Tritium for American nuclear weapons was produced in special heavy water reactors at the Savannah River Site until their closures in 1988.
For applications in proposed fusion energy reactors, such as ITER, pebbles consisting of lithium bearing ceramics including Li High-energy neutrons can also produce tritium from lithium-7 in an endothermic (a net heat consuming reaction) reaction, consuming 2.466 Me V.
This was discovered when the 1954 Castle Bravo nuclear test produced an unexpectedly high yield.
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.
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.