Heavy hydrogen, the oxide of which is heavy water used to slow down neutrons emitted in nuclear fission.
An isotope of hydrogen which has one neutron (as opposed to zero neutrons in hydrogen); SYN. heavy hydrogen.
Naturally occurring heavy isotope of hydrogen, mass number 2 (one proton and one neutron), discovered by Harold Urey 1932. It is sometimes given the symbol D. In nature, about one in every 6,500 hydrogen atoms is deuterium. Combined with oxygen, it produces “heavy water” (D2O), used in the nuclear industry.