Isotopes of hydrogen

Main isotopes of Chemistry:hydrogen (1H) | Iso­tope | Decay

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| abun­dance | half-life (t1/2) | mode | pro­duct
1H | 99.99%  | stable
2H | 0.01%  | stable
3H | trace | 12.32 y  | β− | 3He
Standard atomic weight Ar, standard(H)|

* [1.00784, 1.00811][1]
* Conventional: 1.008

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Hydrogen (1H) has three naturally occurring isotopes: 1H, 2H, and 3H. 1H and 2H are stable, while 3H has a half-life of 12.32 years.[2][nb 1] Heavier isotopes also exist; all are synthetic and have a half-life of less than 1 zeptosecond (10−21 s).[3][4]

Hydrogen is the only element whose isotopes have different names that remain in common use today: 2H is deuterium[5] and 3H is tritium.[6] 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 symbols 2H and 3H, to avoid confusion in alphabetic sorting of chemical formulas.[7] 1H, with no neutrons, may be called protium to disambiguate.[8] During the early study of radioactivity, some other heavy radioisotopes were given names, but such names are rarely used today.

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

## Contents

* 1 List of isotopes
* 2 Hydrogen-1 (protium)
* 3 Hydrogen-2 (deuterium)
* 4 Hydrogen-3 (tritium)
* 5 Hydrogen-4
* 6 Hydrogen-5
* 7 Hydrogen-6
* 8 Hydrogen-7
* 9 Decay chains
* 10 See also
* 11 Notes
* 12 References
* 13 Further reading

## List of isotopes

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

Nuclide
| Z | N | Isotopic mass (u)
[n 1] | Half-life
| Decay
mode
[n 2] | Daughter
isotope
[n 3] | Spin and
parity
[n 4][n 5] | Physics:Natural abundance (mole fraction) | Note

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Normal proportion  | Range of variation
1H  | 1  | 0  | 1.007825031898(14) | 1918 | Stable[n 6][n 7] | 1/2+  | [0.99972, 0.99999][9] | protium
2H (D)[n 8][n 9] | 1  | 1  | 2.014101777844(15) | 1932 | Stable | 1+  | [0.00001, 0.00028][9] | deuterium
3H (T)[n 10] | 1  | 2  | 3.016049281320(81) | 1934 | 12.32(2) y | β− | 3He | 1/2+  | trace[n 11] |  | tritium
4H  | 1  | 3  | 4.02643(11) | 1981 | 139(10) ys | n | 3H  | 2−  |  |
5H  | 1  | 4  | 5.03531(10) | 2001 | 86(6) ys | 2n  | 3H  | (1/2+)  |  |
6H  | 1  | 5  | 6.04496(27) | 1984 | 294(67) ys |  |  | 2−#  |  |
7H  | 1  | 6  | 7.052750(108)#  | 2003 | 652(558) ys |  |  | 1/2+#  |  |

1. ↑ ( ) - Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
2. ↑ Modes of decay:  n: | Neutron emission

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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. ↑ Unless proton decay occurs.
7. ↑ This and 3He are the only stable nuclides with more protons than neutrons.
8. ↑ Produced in Big Bang nucleosynthesis.
9. ↑ One of the few stable odd–odd nuclei
10. ↑ Produced in Big Bang nucleosynthesis,[10] but its short life ensures that none today is primordial, and all then formed should have decayed to 3He.
11. ↑ Cosmogenic, also sometimes released from nuclear power plant cooling water

## Hydrogen-1 (protium)

1H consists of 1 proton and 1 electron: the only stable nuclide with no neutrons (see diproton for a discussion of why no others exist).

"Protium" redirects here. For other uses, see Protium (disambiguation).

1H (atomic mass 1.007825031898(14) Da) is the most common hydrogen isotope, with an abundance of > 99.98%. Its nucleus consists of only a single proton, so it has the formal name protium.

The proton has never been observed to decay, so 1H is considered stable. It is the only stable nuclide with no neutrons. Some Grand Unified Theories proposed in the 1970s predict that proton decay can occur with a half-life between 1028 and 1036 years.[11] If so, then 1H (and all nuclei now believed to be stable) are only observationally stable. As of 2018, experiments have shown that the mean lifetime of the proton is > 3.6×1029 years.[12]

## Hydrogen-2 (deuterium)

Main article: Physics:Deuterium

Deuterium consists of 1 proton, 1 neutron, and 1 electron.

Deuterium, 2H (atomic mass 2.014101777844(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 of seawater. Deuterium on Earth has been enriched with respect to its initial concentration in the Big Bang and outer Solar System (≈ 27 ppm, atom fraction) and older parts of the Milky Way (≈ 23 ppm). Presumably the differential concentration of deuterium in the inner Solar System is due to the lower volatility of deuterium gas and compounds, enriching deuterium fractions in comets and planets exposed to significant heat from the Sun over billions of years of Solar System evolution.

Deuterium is not radioactive, and is not a significant toxicity hazard. Water enriched in 2H is called heavy water. Deuterium and its compounds are used as a non-radioactive label in chemical experiments and in solvents for 1H-nuclear magnetic resonance 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)

Main article: Physics:Tritium

Tritium consists of 1 proton, 2 neutrons, and 1 electron.

Tritium, 3H (atomic mass 3.016049281320(81) Da), has one proton and two neutrons in its nucleus (called a triton). It is radioactive, β− decaying into helium-3 with half-life 12.32 years.[nb 1][2] Traces of 3H occur naturally due to cosmic rays interacting with atmospheric gases. 3H has also been released in nuclear tests. It is used in fusion bombs, as a tracer in isotope geochemistry, and in self-powered lighting devices.

The most common way to produce 3H is to bombard a natural isotope of lithium, 6Li, with neutrons in a nuclear reactor.

Tritium can be used in chemical and biological labeling experiments as a radioactive tracer.[13][14] Deuterium–tritium fusion uses 2H and 3H as its main reactants, giving energy through the loss of mass when the two nuclei collide and fuse at high temperatures.

## Hydrogen-4

4H (atomic mass 4.02643(11) Da), with one proton and three neutrons, is a highly unstable isotope. It has been synthesized in the laboratory by bombarding tritium with fast-moving deuterons;[15] the triton captured a neutron from the deuteron. The presence of 4H was deduced by detecting the emitted protons. It decays by neutron emission into 3H with a half-life of 139(10) ys (1.39(10)×10−22 s).

In the 1955 satirical novel The Mouse That Roared, the name quadium was given to the 4H that powered the Q-bomb that the Duchy of Grand Fenwick captured from the United States.[citation needed]

## Hydrogen-5

5H (atomic mass 5.03531(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;[15][16] 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 of 5H deduced. It decays by double neutron emission into 3H and has a half-life of 86(6) ys (8.6(6)×10−23 s) – the shortest half-life of any known nuclide.[2]

## Hydrogen-6

6H (atomic mass 6.04496(27) Da) has one proton and five neutrons. It has a half-life of 294(67) ys (2.94(67)×10−22 s). In 2025, 6H was produced using an 855 MeV electron beam impinging upon on a 7Li target.[17]

## Hydrogen-7

7H (atomic mass 7.05275(108) Da) has one proton and six neutrons. It was first synthesized in 2003 by a group of Russian, Japanese and French scientists at Riken's Radioactive Isotope Beam Factory by bombarding hydrogen with helium-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.[4] 7H has a half-life of 652(558) ys (6.52(558)×10−22 s).[2]

## Decay chains

4H and 5H decay directly to 3H, which then decays to stable 3He. Decay of the heaviest isotopes, 6H and 7H, has not been experimentally observed.[18] A13A2123H→12.32 y32He+eA−A14A2124H→139 ys31H+10nA15A2125H→86 ys31H+201n

Decay times are in yoctoseconds (10−24 s) for all these isotopes except 3H, which is in years.

## See also

* Hydrogen atom
* Hydrogen isotope biogeochemistry
* Hydrogen-4.1 (Muonic helium)
* Muonium – acts like an exotic light isotope of hydrogen

## Notes

1. ↑ 1.0 1.1 NUBASE2020 uses the tropical year to convert between years and other units of time, not the Gregorian year. The relationship between years and other time units in NUBASE2020 is as follows: 1 y = 365.2422 d = 31 556 926 s

## References

1. ↑ Meija, Juris; Coplen, Tyler B.; Berglund, Michael; Brand, Willi A.; De Bièvre, Paul; Gröning, Manfred; Holden, Norman E.; Irrgeher, Johanna et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry 88 (3): 265–91. doi:10.1515/pac-2015-0305.
2. ↑ 2.0 2.1 2.2 2.3 Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (March 2021). "The NUBASE2020 evaluation of nuclear physics properties" (in en). Chinese Physics C 45 (3): 030001. doi:10.1088/1674-1137/abddae. ISSN 1674-1137. Bibcode: 2021ChPhC..45c0001K.
3. ↑ Y. B. Gurov (2004). "Spectroscopy of superheavy hydrogen isotopes in stopped-pion absorption by nuclei". Physics of Atomic Nuclei 68 (3): 491–497. doi:10.1134/1.1891200. Bibcode: 2005PAN....68..491G.
4. ↑ 4.0 4.1 A. A. Korsheninnikov (2003). "Experimental Evidence for the Existence of 7H and for a Specific Structure of 8He". Physical Review Letters 90 (8). doi:10.1103/PhysRevLett.90.082501. PMID 12633420. Bibcode: 2003PhRvL..90h2501K.
5. ↑ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006-) "deuterium". doi:10.1351/goldbook.D01648
6. ↑ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006-) "tritium". doi:10.1351/goldbook.T06513
7. ↑ 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.
8. ↑ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006-) "protium". doi:10.1351/goldbook.P04903
9. ↑ 9.0 9.1 "Atomic Weight of Hydrogen". https://ciaaw.org/hydrogen.htm.
10. ↑ 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. doi:10.1016/j.nima.2009.07.052. Bibcode: 2009NIMPA.611..224C.
11. ↑ Ed Kearns (2009). "Grand Unified Theories and Proton Decay". Boston University. p. 15. https://physics.bu.edu/NEPPSR/TALKS-2009/Kearns_GUTs_ProtonDecay.pdf.
12. ↑ The SNO+ Collaboration; Anderson, M.; Andringa, S.; Arushanova, E.; Asahi, S.; Askins, M.; Auty, D. J.; Back, A. R. et al. (2019-02-20). "Search for invisible modes of nucleon decay in water with the SNO+ detector". Physical Review D 99 (3). doi:10.1103/PhysRevD.99.032008. Bibcode: 2019PhRvD..99c2008A.
13. ↑ "SARS-CoV-2 mRNA Vaccine (BNT162, PF-07302048)". 2.6.5.5B, pp. 6–8. http://www.pmda.go.jp/drugs/2021/P20210212001/672212000_30300AMX00231_I100_1.pdf#page=16. "[3H]-Labelled LNP-mRNA"
14. ↑ 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. PMID 32271921.
15. ↑ 15.0 15.1 G. M. Ter-Akopian (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. doi:10.1063/1.1470062. Bibcode: 2002AIPC..610..920T.
16. ↑ A. A. Korsheninnikov (2001). "Superheavy Hydrogen 5H". Physical Review Letters 87 (9). doi:10.1103/PhysRevLett.87.092501. PMID 11531562. Bibcode: 2001PhRvL..87i2501K.
17. ↑ Shao, Tianhao et al. (2025). "Measurement of 6H Ground State Energy in an Electron Scattering Experiment at MAMI-A1". Physical Review Letters 134 (16). doi:10.1103/PhysRevLett.134.162501. PMID 40344098. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.134.162501.
18. ↑ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties". Chinese Physics C 45 (3). doi:10.1088/1674-1137/abddae. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf.

## Further reading

* Dumé, B. (7 March 2003). "Hydrogen-7 makes its debut". Physics World. https://physicsworld.com/cws/article/news/2003/mar/07/hydrogen-7-makes-its-debut.

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* Table of nuclides
* Categories: Isotopes
* Tables of nuclides
* Metastable isotopes
* Isotopes by element

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