tritium

A radioactive isotope of hydrogen having one proton and two neutrons in the nucleus. It decays spontaneously to Helium-3 by the emission of an electron (beta ray), with a half-life of 12.3 years. Symbol ₁H³. Atomic weight 3.01605 (C-12 = 12.0000). It is one of the radioisotopes commonly used to label chemical compounds for use as tracers in biochemistry and chemistry. It is also used as one of the fusionable components of a hydrogen bomb.(Chem.)