Tritium

Tritium is an isotope of hydrogen, the lightest element. Tritium has one proton and two neutrons. It heavier than ordinary hydrogen or its isotope deuterium. Hydrogen does not have any neutrons, only a proton. The chemical symbol for Tritium is ³H or T.

In nature, tritium is made when cosmic rays hit nitrogen in the Earth's atmosphere. Tritium has a half-life of a little more than twelve years, so there is not much in the atmosphere. People make much more tritium in nuclear reactors, so that they can make things from it.