Tritium (or symbol
T or 3H
, also known as hydrogen-3) is a radioactive isotope of hydrogen.Isotope is variants of a particular element which differ in number of nuetrons. The nucleus of tritium (sometimes called a triton) contains one proton and two nuetrons, whereas the nucleus of protium (by far the most abundant hydrogen isotope) contains one proton and no neutrons. Naturally occurring tritium is extremely rare on Earth, where trace amounts are formed by the interaction of the atmosphere with cosmic rays.