Deuterium has an atomic mass of 2.01410. Deuterium atoms and ordinary hydrogen atoms have one electron. Chemically, deuterium reacts in the same way as ordinary hydrogen. But it generally reacts more slowly and less completely. Deuterium oxide is used as a moderator in heavy water nuclear reactors to reduce the speed of the neutrons released in a nuclear chain reaction.
Scientists frequently use deuterium to study organic and biochemical reactions.
In a process known as deuterium labeling, the heavy hydrogen atom serves as an isotopic tracer by acting as a substitute for one or more of the regular hydrogen atoms in a molecule. After the reaction is completed, the deuterium can be located by spectroscopic studies. This technique gives scientists important clues as to how the reaction takes place. Scientists use deuterons as bombarding particles in particle accelerators. One such device, a cyclotron, can accelerate deuterons to energy levels of millions or even billions of electron volts.