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Isotopes of hydrogen

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Isotopes ofhydrogen (1H)
Main isotopes[1]Decay
Isotopeabun­dancehalf-life(t1/2)modepro­duct
1H99.9855%stable
2H0.0115%stable
3Htrace12.32 yβ−3He
Abundance of deuterium is highly variable
Standard atomic weightAr°(H)

Hydrogen (1H) has three naturally occurringisotopes:1H,2H, and3H.1H and2H are stable, while3H has ahalf-life of12.32 years.[4][nb 1] Heavier isotopes also exist; all are synthetic and have a half-life of less than 1zeptosecond (10−21 s).[5][6]

Hydrogen is the onlyelement whose isotopes have different names that remain in common use today:2H isdeuterium[7] and3H istritium.[8] The symbols D and T are sometimes used for deuterium and tritium; IUPAC (International Union of Pure and Applied Chemistry) accepts said symbols, but recommends the standard isotopic symbols2H and3H, to avoid confusion in alphabetic sorting ofchemical formulas.[9]1H, with noneutrons, may be called protium to disambiguate.[10] During the early study of radioactivity, some other heavy radioisotopes were givennames, but such names are rarely used today.

The three most stable isotopes of hydrogen: protium (A = 1),deuterium (A = 2), andtritium (A = 3)

List of isotopes

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Note: "y" means year, but "ys" meansyoctosecond (10−24 second).

Nuclide
ZNIsotopic mass(Da)[11]
[n 1]		Half-life[1]
Decay
mode[1]
[n 2]		Daughter
isotope
[n 3]		Spin and
parity[1]
[n 4][n 5]		Natural abundance(mole fraction)Note
Normal proportion[1]Range of variation
1H101.007825031898(14)Stable[n 6][n 7]1/2+[0.99972,0.99999][12]protium
2H (D)[n 8][n 9]112.014101777844(15)Stable1+[0.00001,0.00028][12]deuterium
3H (T)[n 10]123.016049281320(81)12.32(2) yβ−3He1/2+trace[n 11]tritium
4H134.02643(11)139(10) ysn3H2−
5H145.03531(10)86(6) ys2n3H(1/2+)
6H156.04496(27)294(67) ys2−#
7H167.052750(108)#652(558) ys1/2+#
This table header & footer:
  1. ^( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  2. ^Modes of decay:
    n:Neutron emission
  3. ^Bold symbol as daughter – Daughter product is stable.
  4. ^( ) spin value – Indicates spin with weak assignment arguments.
  5. ^# – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  6. ^Unlessproton decay occurs.
  7. ^This and3He are the only stable nuclides with more protons than neutrons.
  8. ^Produced inBig Bang nucleosynthesis.
  9. ^One of the few stableodd–odd nuclei
  10. ^Produced in Big Bang nucleosynthesis,[13] but its short life ensures that none today is primordial, and all then formed should have decayed to3He.
  11. ^Cosmogenic, also sometimes released from nuclear power plant cooling water

Hydrogen-1 (protium)

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1H consists of 1 proton and 1 electron: the only stable nuclide with no neutrons (seediproton for a discussion of why no others exist).
"Protium" redirects here. For other uses, seeProtium (disambiguation).

1H (atomic mass1.007825031898(14) Da) is the most common hydrogen isotope, with an abundance of > 99.98%. Itsnucleus consists of only a singleproton, so it has the formal nameprotium.

The proton has never been observed to decay, so1H is considered stable. It is the only stable nuclide with no neutrons. SomeGrand Unified Theories proposed in the 1970s predict thatproton decay can occur with a half-life between1028 and1036 years.[14] If so, then1H (and all nuclei now believed to be stable) are onlyobservationally stable. As of 2018, experiments have shown that the mean lifetime of the proton is > 3.6×1029 years.[15]

Hydrogen-2 (deuterium)

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Main article:Deuterium
Deuterium consists of 1 proton, 1 neutron, and 1 electron.

Deuterium,2H (atomic mass2.014101777844(15) Da), the other stable hydrogen isotope, has one proton and one neutron in its nucleus, called a deuteron.2H comprises 26–184 ppm (by population, not mass) of hydrogen on Earth; the lower number tends to be found in hydrogen gas and higher enrichment (150 ppm) is typical ofseawater. Deuterium on Earth has been enriched with respect to its initial concentration in theBig Bang andouter Solar System (≈ 27 ppm, atom fraction) and older parts of theMilky Way (≈ 23 ppm). Presumably the differential concentration of deuterium in theinner Solar System is due to the lower volatility ofdeuterium gas and compounds, enriching deuterium fractions incomets and planets exposed to significant heat from theSun over billions of years ofSolar System evolution.

Deuterium is not radioactive, and is not a significant toxicity hazard. Water enriched in2H is calledheavy water. Deuterium and its compounds are used as a non-radioactive label in chemical experiments and in solvents for1H-nuclear magnetic resonance spectroscopy. Heavy water is used as aneutron moderator and coolant for nuclear reactors. Deuterium is also a potential fuel for commercialnuclear fusion.

Hydrogen-3 (tritium)

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Main article:Tritium
Tritium consists of 1 proton, 2 neutrons, and 1 electron.

Tritium,3H (atomic mass3.016049281320(81) Da), has one proton and two neutrons in its nucleus (called atriton). It isradioactive,β− decaying intohelium-3 withhalf-life12.32 years.[nb 1][4] Traces of3H occur naturally due to cosmic rays interacting with atmospheric gases.3H has also been released innuclear tests. It is used infusion bombs, as a tracer inisotope geochemistry, and inself-powered lighting devices.

The most common way to produce3H is to bombard a naturalisotope of lithium,6Li, with neutrons in anuclear reactor.

Tritium can be used in chemical and biological labeling experiments as aradioactive tracer.[16][17]Deuterium–tritium fusion uses2H and3H as its main reactants, giving energy through the loss of mass when the two nuclei collide and fuse at high temperatures.

Hydrogen-4

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4H (atomic mass4.02643(11) Da), with one proton and three neutrons, is a highlyunstable isotope. It has been synthesized in the laboratory by bombarding tritium with fast-moving deuterons;[18] the triton captured a neutron from the deuteron. The presence of4H was deduced by detecting the emitted protons. It decays byneutron emission into3H with ahalf-life of139(10) ys (1.39(10)×10−22 s).

In the 1955 satirical novelThe Mouse That Roared, the namequadium was given to the4H that powered theQ-bomb that the Duchy ofGrand Fenwick captured from the United States.[citation needed]

Hydrogen-5

[edit]

5H (atomic mass5.03531(10) Da), with one proton and four neutrons, is highly unstable. It has been synthesized in the lab by bombarding tritium with fast-moving tritons;[18][19] one triton captures two neutrons from the other, becoming a nucleus with one proton and four neutrons. The remaining proton may be detected, and the existence of5H deduced. It decays by doubleneutron emission into3H and has ahalf-life of86(6) ys (8.6(6)×10−23 s) – the shortest half-life of any known nuclide.[4]

Hydrogen-6

[edit]

6H (atomic mass6.04496(27) Da) has oneproton and fiveneutrons. It has ahalf-life of294(67) ys (2.94(67)×10−22 s). In 2025,6H was produced using an 855 MeV electron beam impinging upon on a7Li target.[20]

Hydrogen-7

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7H (atomic mass7.05275(108) Da) has oneproton and sixneutrons. It was first synthesized in 2003 by a group of Russian, Japanese and French scientists atRiken'sRadioactive Isotope Beam Factory by bombardinghydrogen withhelium-8 atoms; all six of the helium-8's neutrons were donated to the hydrogen nucleus. The two remaining protons were detected by the "Riken telescope", a device made of several layers of sensors, positioned behind the target of the RI Beam cyclotron.[6]7H has a half-life of652(558) ys (6.52(558)×10−22 s).[4]

Decay chains

[edit]

4H and5H decay directly to3H, which then decays to stable3He. Decay of the heaviest isotopes,6H and7H, has not been experimentally observed.[1]H13→12.32 yHe23+e−H14→139 ysH13+n01H15→86 ysH13+201n{\displaystyle {\begin{array}{rcl}\\{\ce {^{3}_{1}H}}&{\ce {->[12.32\ {\ce {y}}]}}&{\ce {{^{3}_{2}He}+e^{-}}}\\{\ce {^{4}_{1}H}}&{\ce {->[139\ {\ce {ys}}]}}&{\ce {{^{3}_{1}H}+{^{1}_{0}n}}}\\{\ce {^{5}_{1}H}}&{\ce {->[86\ {\ce {ys}}]}}&{\ce {{^{3}_{1}H}+{2_{0}^{1}n}}}\\{}\end{array}}}

Decay times are inyoctoseconds (10−24 s) for all these isotopes except3H, which is in years.

See also

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Notes

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  1. ^abNUBASE2020 uses thetropical year to convert between years and other units of time, not theGregorian year. The relationship between years and other time units in NUBASE2020 is as follows:1 y = 365.2422 d = 31 556 926 s

References

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  1. ^abcdefKondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021)."The NUBASE2020 evaluation of nuclear properties"(PDF).Chinese Physics C.45 (3) 030001.doi:10.1088/1674-1137/abddae.
  2. ^"Standard Atomic Weights: Hydrogen".CIAAW. 2009.
  3. ^Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04)."Standard atomic weights of the elements 2021 (IUPAC Technical Report)".Pure and Applied Chemistry.doi:10.1515/pac-2019-0603.ISSN 1365-3075.
  4. ^abcdKondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (March 2021)."The NUBASE2020 evaluation of nuclear physics properties".Chinese Physics C.45 (3): 030001.Bibcode:2021ChPhC..45c0001K.doi:10.1088/1674-1137/abddae.ISSN 1674-1137.S2CID 233794940.
  5. ^Y. B. Gurov; et al. (2004). "Spectroscopy of superheavy hydrogen isotopes in stopped-pion absorption by nuclei".Physics of Atomic Nuclei.68 (3):491–497.Bibcode:2005PAN....68..491G.doi:10.1134/1.1891200.S2CID 122902571.
  6. ^abA. A. Korsheninnikov; et al. (2003). "Experimental Evidence for the Existence of7H and for a Specific Structure of8He".Physical Review Letters.90 (8) 082501.Bibcode:2003PhRvL..90h2501K.doi:10.1103/PhysRevLett.90.082501.PMID 12633420.
  7. ^IUPAC,Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "deuterium".doi:10.1351/goldbook.D01648
  8. ^IUPAC,Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "tritium".doi:10.1351/goldbook.T06513
  9. ^International Union of Pure and Applied Chemistry (2005).Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK):RSC–IUPAC.ISBN 0-85404-438-8. p. 48.Electronic version.
  10. ^IUPAC,Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "protium".doi:10.1351/goldbook.P04903
  11. ^Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*".Chinese Physics C.45 (3) 030003.doi:10.1088/1674-1137/abddaf.
  12. ^ab"Atomic Weight of Hydrogen".CIAAW. Retrieved24 June 2021.
  13. ^Coc, Alain (2009). "Big-bang nucleosynthesis: A probe of the early Universe".Nuclear Instruments and Methods in Physics Research Section A.611 (2–3):224–230.Bibcode:2009NIMPA.611..224C.doi:10.1016/j.nima.2009.07.052.
  14. ^Ed Kearns (2009)."Grand Unified Theories and Proton Decay"(PDF). Boston University. p. 15.
  15. ^The SNO+ Collaboration; Anderson, M.; Andringa, S.; Arushanova, E.; Asahi, S.; Askins, M.; Auty, D. J.; Back, A. R.; Barnard, Z.; Barros, N.; Bartlett, D. (2019-02-20)."Search for invisible modes of nucleon decay in water with the SNO+ detector".Physical Review D.99 (3) 032008.arXiv:1812.05552.Bibcode:2019PhRvD..99c2008A.doi:10.1103/PhysRevD.99.032008.S2CID 96457175.
  16. ^Pfizer Japan."SARS-CoV-2 mRNA Vaccine (BNT162, PF-07302048)"(PDF).Pharmaceuticals and Medical Devices Agency (Japan). 2.6.5.5B, pp. 6–8. Archived fromthe original(PDF) on 24 March 2022. Retrieved5 June 2021.[3H]-Labelled LNP-mRNA
  17. ^Green, Joanne Balmer; Green, Michael H. (2020)."Vitamin A Absorption Determined in Rats Using a Plasma Isotope Ratio Method".The Journal of Nutrition.150 (7):1977–1981.doi:10.1093/jn/nxaa092.PMC 7330459.PMID 32271921.
  18. ^abG. M. Ter-Akopian; et al. (2002). "Hydrogen-4 and Hydrogen-5 from t+t and t+d transfer reactions studied with a 57.5-MeV triton beam".AIP Conference Proceedings.610:920–924.Bibcode:2002AIPC..610..920T.doi:10.1063/1.1470062.
  19. ^A. A. Korsheninnikov; et al. (2001). "Superheavy Hydrogen5H".Physical Review Letters.87 (9) 92501.Bibcode:2001PhRvL..87i2501K.doi:10.1103/PhysRevLett.87.092501.PMID 11531562.
  20. ^Shao, Tianhao; et al. (2025)."Measurement of6H Ground State Energy in an Electron Scattering Experiment at MAMI-A1".Physical Review Letters.134 (16) 162501.arXiv:2501.01232.doi:10.1103/PhysRevLett.134.162501.PMID 40344098.

Further reading

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Group12 3456789101112131415161718
PeriodHydrogen and
alkali metals		Alkaline
earth metals		Pnicto­gensChal­co­gensHalo­gensNoble gases
①12
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③1112131415161718
④192021222324252627282930313233343536
⑤373839404142434445464748495051525354
⑥55561 asterisk71727374757677787980818283848586
⑦87881 asterisk103104105106107108109110111112113114115116117118
⑧119120
1 asterisk5758596061626364656667686970 
1 asterisk8990919293949596979899100101102
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