Tritium (symbol or ) 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 (the most abundant hydrogen isotope) contains no neutrons and one proton. Decay While Tritium has several different experimentally-determined values of its half-life, the NIST recommends 4500±8 days (approximately 12.32 years). It decays into helium-3 by the reaction All atomic nuclei, being composed of proton… (More on Tritium)