Deuterium

Deuterium, or heavy hydrogen (D or H₂), isotope of hydrogen in which the atomic nucleus contains a neutron as well as a proton, giving it an atomic weight of approximately 2. Deuterium was discovered by H.C. Urey in 1932 and is used as a tracer in biological research, in experiments for particle accelerators, and in the hydrogen bomb.

See also: Hydrogen.