Natural hydrogen is a mixture of two stable isotopes 1H and 2H and one radioactive isotope 3H. Protium, 1H, has no neutrons in its nucleus and is the most common form of hydrogen, with an atomic mass of ~1.0078 Da (dalton) and an isotopic abundance of ~99.972% of all hydrogen on Earth. Deuterium, 2H, contains one proton and one neutron in the nucleus giving it an atomic mass of ~2.014 Da, with an abundance on Earth of ~0.028% complementing that of 1H to yield ~100%. Tritium, 3H, bears one proton and two neutrons in its nucleus yielding an atomic mass of ~3.016 Da. Tritium is radioactive with a half-life of 12.32 years.