Deuterium

Deuterium, hydrogen-2, D, ²H

Deuterium glowing in a gas discharge tube
General
Symbol	2H
Names	Deuterium, hydrogen-2, D, 2H, H-2, hydrogen-2, D, 2H
Protons (Z)	1
Neutrons (N)	1
Nuclide data
Natural abundance	0.0156% (Earth)[1]
Half-life (t1/2)	stable
Isotope mass	2.01410177811[2] Da
Spin	1+
Excess energy	13135.720±0.001 keV
Binding energy	2224.57±0.20 keV
Isotopes of hydrogen Complete table of nuclides

Deuterium (hydrogen-2, symbol ²H or D, also known as heavy hydrogen) is one of two stable isotopes of hydrogen; the other is protium, or hydrogen-1, ¹H. The deuterium nucleus (deuteron) contains one proton and one neutron, whereas the far more common ¹H has no neutrons.

The name deuterium comes from Greek deuteros, meaning "second".^[3][4] American chemist Harold Urey discovered deuterium in 1931. Urey and others produced samples of heavy water in which the ²H had been highly concentrated. The discovery of deuterium won Urey a Nobel Prize in 1934.

Nearly all deuterium found in nature was synthesized in the Big Bang 13.8 billion years ago, forming the primordial ratio of ²H to ¹H (≈26 deuterium nuclei per 10⁶ hydrogen nuclei). Deuterium is subsequently produced by the slow stellar proton–proton chain, but rapidly destroyed by exothermic fusion reactions. The deuterium-deuterium reaction has the second-lowest energy threshold, and is the most astrophysically accessible, occurring in both stars and brown dwarfs.

The gas giant planets display the primordial ratio of deuterium. Comets show an elevated ratio similar to Earth's oceans (156 deuterium nuclei per 10⁶ hydrogen nuclei). This reinforces theories that much of Earth's ocean water is of cometary origin.^[5][6] The deuterium ratio of comet 67P/Churyumov–Gerasimenko, as measured by the Rosetta space probe, is about three times that of Earth water. This figure is the highest yet measured in a comet, thus deuterium ratios continue to be an active topic of research in both astronomy and climatology.^[7]

Deuterium is used in most nuclear weapons, many fusion power experiments, and as the most effective neutron moderator, primarily in heavy water nuclear reactors. It is also used as an isotopic label, in biogeochemistry, NMR spectroscopy, and deuterated drugs.