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Isotopes of hydrogen: Map


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Hydrogen (H) (Standard atomic mass: 1.00794(7) u) has three naturally occurring isotopes, denoted 1H, 2H, and 3H. Other, highly unstable nuclei (4H to 7H) have been synthesized in the laboratory but not observed in nature.

Hydrogen is the only element that has different names for its isotopes in common use today. (During the early study of radioactivity, various heavy radioactive isotopes were given names; but such names are rarely used today). The symbols D and T (instead of 2H and 3H) are sometimes used for deuterium and tritium. IUPAC states that while this use is common it is not preferred.

Hydrogen-1 (protium)

1H is the most common hydrogen isotope with an abundance of more than 99.98%. Because the nucleus of this isotope consists of only a single proton, it is given the descriptive but rarely used formal name protium.

Hydrogen-2 (deuterium)

2H, the other stable hydrogen isotope, is known as deuterium and contains one proton and one neutron in its nucleus. Deuterium comprises 0.0026 – 0.0184% (by population, not by mass) of hydrogen samples on Earth, with the lower number tending to be found in samples of hydrogen gas and the higher enrichments (0.015% or 150 ppm) typical of ocean water. Deuterium is not radioactive, and does not represent a significant toxicity hazard. Water enriched in molecules that include deuterium instead of normal hydrogen is called heavy water. Deuterium and its compounds are used as a non-radioactive label in chemical experiments and in solvents for 1H-NMR spectroscopy. Heavy water is used as a neutron moderator and coolant for nuclear reactors. Deuterium is also a potential fuel for commercial nuclear fusion.

Hydrogen-3 (tritium)

3H is known as tritium and contains one proton and two neutrons in its nucleus. It is radioactive, decaying into helium-3 through β− decay with a half-life of 12.32 years. Small amounts of tritium occur naturally because of the interaction of cosmic rays with atmospheric gases; tritium has also been released during nuclear weapons tests. It is used in thermonuclear fusion weapons, as a tracer in isotope geochemistry, and specialized in self-powered lighting devices. Tritium was once routinely used in chemical and biological labelling experiments as a radiolabel (this has become less common). D-T nuclear fusion uses tritium as its main reactant, along with deuterium, liberating energy through the loss of mass when the two nuclei collide and fuse under massive temperatures.


4H is a highly unstable isotope of hydrogen. The nucleus consists of a proton and three neutrons. It has been synthesised in the laboratory by bombarding tritium with fast-moving deuterium nuclei. In this experiment, the tritium nuclei captured neutrons from the fast-moving deuterium nucleus. The presence of the hydrogen-4 was deduced by detecting the emitted protons. Its atomic mass is 4.02781 ± 0.00011. It decays through neutron emission and has a half-life of (1.39 ± 0.10) × 10−22 seconds.


5H is a highly unstable isotope of hydrogen. The nucleus consists of a proton and four neutrons. It has been synthesised in the laboratory by bombarding tritium with fast-moving tritium nuclei. In this experiment, one tritium nucleus captures two neutrons from the other, becoming a nucleus with one proton and four neutrons. The remaining proton may be detected, and the existence of hydrogen-5 deduced. It decays through double neutron emission and has a half-life of at least 9.1 × 10−22 seconds.


6H decays through triple neutron emission and has a half-life of 3×10−22 seconds. It consists of 1 proton and 5 neutrons.


7H consists of a proton and six neutrons. It was first synthesised in 2003 by a group of Russian, Japanese and French scientists at RIKEN's RI Beam Science Laboratory by bombarding hydrogen with helium-8 atoms. In the resulting reaction, the helium-8's neutrons were donated to the hydrogen's nucleus. The two remaining protons were detected by the "RIKEN telescope", a device composed of several layers of sensors, positioned behind the target of the RI Beam cyclotron.

Hydrogen-like exotic atoms

Positronium (Ps or e+e)

Positronium is an exotic atom made up of a positron (the electron's antiparticle, also called antielectron) and an electron, and is given the symbol Ps or e+e. It decays to 2 or more photons (in the form of gamma radiation) due to annihilation.

Muonium (Mu or µ+e)

Muonium is an exotic atom made up of an antimuon (the muon's antiparticle) and an electron, and is given the symbol Mu or µ+e. During the muon's lifetime, muonium can enter into compounds such as muonium chloride (MuCl) or sodium muonide (NaMu).

Antihydrogen ( )

Antihydrogen is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron (also called antielectron) and an antiproton.


Nuclide properties
Nuclide Z(p) N(n) mass (u) half-life nuclear spin
( J P )

(mole fraction)

(mole fraction)
1 0 Stable +
1 1 Stable 1+
1 2 +
1 3 [ ] 2
1 4 > ? ( +)
1 5 [ ] 2
1 6 [ ] 1/2+



  1. Gurov YB, Aleshkin DV, Berh MN, Lapushkin SV, Morokhov PV, Pechkurov VA, Poroshin NO, Sandukovsky VG, Tel'kushev MV, Chernyshev BA, Tschurenkova TD. (2004). Spectroscopy of superheavy hydrogen isotopes in stopped-pion absorption by nuclei. Physics of Atomic Nuclei 68(3):491–497.
  2. Korsheninnikov AA. et al. (2003). Experimental Evidence for the Existence of 7H and for a Specific Structure of 8He. Phys Rev Lett 90, 082501.
  3. Miessler GL, Tarr DA. (2004). Inorganic Chemistry 3rd ed. Pearson Prentice Hall: Upper Saddle River, NJ, USA
  4. Hydrogen-4 and Hydrogen-5 from t+t and t+d transfer reactions studied with a 57.5-MeV triton beam, G. M. Ter-Akopian et al., Nuclear Physics in the 21st Century: International Nuclear Physics Conference INPC 2001, American Institute of Physics Conference Proceedings 610, pp. 920-924, .
  5. AME2003 atomic mass evaluation, Atomic Mass Data Center. Accessed on line November 15, 2008.
  6. p. 27, The NUBASE evaluation of nuclear and decay properties, G. Audi, O. Bersillon, J. Blachot, and A. H. Wapstra, Nuclear Physics A 729 (2003), pp. 3–128.
  7. Commercially available materials may have been subjected to an undisclosed or inadvertent isotopic fractionation. Substantial deviations from the given mass and composition can occur.
  8. Uncertainties are given in concise form in parentheses after the corresponding last digits, and denote one standard deviation.
  9. Spins with weak assignment arguments are enclosed in parentheses.
  10. Representative isotopic composition (RIC): refers to that in water.
  11. Range of natural variation (RNV): The precision of the isotope abundances and atomic mass is limited through variations. The given ranges should be applicable to any normal terrestrial material.
  12. Greater than . See proton decay.
  13. Tank hydrogen has a abundance as low as (mole fraction).
  14. Value is not purely derived from experimental data, but at least partly from systematic trends.

In fiction

In the 1955 satirical novel The Mouse That Roared, the name quadium was given to the hydrogen-4 isotope that powered the Q-bomb that the Duchy of Grand Fenwick captured from the United Statesmarker.

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