Tritium - Wikipedia
Tritium (/ ˈ t r ɪ t i ə m / or / ˈ t r ɪ ʃ i ə m /; symbol T or 3 H, also known as hydrogen-3) is a radioactive isotope of hydrogen.The nucleus of tritium (sometimes called a triton) contains one proton and two neutrons, whereas the nucleus of protium (by far the most abundant hydrogen isotope) contains one proton and no neutrons.