View source for Isotopes of hydrogen

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{{infobox hydrogen isotopes}}

[[Hydrogen]] ({{sub|1}}H) has three naturally occurring [[isotope]]s: {{sup|1}}H, {{sup|2}}H, and {{sup|3}}H. {{sup|1}}H and {{sup|2}}H are stable, while {{sup|3}}H has a [[half-life]] of {{val|12.33|(2)}} years.<ref name=NUBASE2020a>{{Cite journal |last1=Kondev |first1=F. G. |last2=Wang |first2=M. |last3=Huang |first3=W. J. |last4=Naimi |first4=S. |last5=Audi |first5=G. |date=March 2021 |title=The NUBASE2020 evaluation of nuclear physics properties \ast|journal=Chinese Physics C |language=en |volume=45 |issue=3 |pages=030001 |doi=10.1088/1674-1137/abddae |bibcode=2021ChPhC..45c0001K |s2cid=233794940 |issn=1674-1137|doi-access=free}}</ref>{{refn|group=nb|name=NUBASE2020 tropical year|Note that 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: {{nowrap|1=1 y = 365.2422 d = 31 556 926 s}} }} Heavier isotopes also exist; all are synthetic and have a half-life of less than 1 [[zeptosecond]] (10{{sup|−21}}&nbsp;s).<ref>{{cite journal
 |author=Y. B. Gurov|year=2004
 |title=Spectroscopy of superheavy hydrogen isotopes in stopped-pion absorption by nuclei
 |journal=[[Physics of Atomic Nuclei]]
 |volume=68 |issue=3 |pages=491–497
 |bibcode = 2005PAN....68..491G
 |doi=10.1134/1.1891200
 |s2cid=122902571
 |display-authors=etal}}</ref><ref name="Korsheninnikov">
{{cite journal
 |author=A. A. Korsheninnikov|year=2003
 |title=Experimental Evidence for the Existence of {{sup|7}}H and for a Specific Structure of {{sup|8}}He
 |journal=[[Physical Review Letters]]
 |volume=90 |issue=8 |pages=082501
 |bibcode=2003PhRvL..90h2501K
 |doi=10.1103/PhysRevLett.90.082501
 |display-authors=etal |pmid=12633420}}</ref>
Of these, {{sup|5}}H is the least stable, while {{sup|7}}H is the most.

Hydrogen is the only [[chemical element|element]] whose isotopes have different names that remain in common use today: {{sup|2}}H is [[deuterium]]<ref>{{GoldBookRef|file=D01648|title=deuterium}}</ref> and {{sup|3}}H is [[tritium]].<ref>{{GoldBookRef|file=T06513|title=tritium}}</ref> 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 {{sup|2}}H and {{sup|3}}H, to avoid confusion in alphabetic sorting of [[chemical formula]]s.<ref>{{RedBook2005|page=48}}</ref> {{sup|1}}H, with no [[neutron]]s, may be called protium to disambiguate.<ref>{{GoldBookRef|file=P04903|title=protium}}</ref> (During the early study of radioactivity, some other heavy radioisotopes were given [[Chemical symbol#Symbols for named isotopes|names]], but such names are rarely used today.)

[[File:Hydrogen Deuterium Tritium Nuclei Schmatic-en.svg|thumb |upright=1.8|left|The three most stable isotopes of hydrogen: protium (''[[mass number|A]]''&nbsp;=&nbsp;1), [[deuterium]] (''A''&nbsp;=&nbsp;2), and [[tritium]] (''A''&nbsp;=&nbsp;3).]]
{{clear}}

==List of isotopes==
Note: "y" means year, but "ys" means [[yoctosecond]] (10{{sup|−24}} second).
{{Isotopes table
|symbol=H
|refs=NUBASE2020, AME2020 II
|notes=mass#, unc(), var[], spin#, spin(), daughter-st, n, note
}}
|-
| {{sup|1}}H
| 1
| 0
| {{val|1.007825031898|(14)}}
| colspan=3 align=center|'''Stable'''<ref group="n">Unless [[proton decay]] occurs.</ref><ref group="n">This and '''{{sup|3}}He''' are the only stable nuclides with more protons than neutrons.</ref>
| 1/2+
| colspan="2" style="text-align:center" | [{{val|0.99972}}, {{val|0.99999}}]<ref name="Atomic Weight of Hydrogen">{{Cite web|title=Atomic Weight of Hydrogen|url=https://ciaaw.org/hydrogen.htm|access-date=24 June 2021|website=CIAAW}}</ref>
| Protium
|-
| [[Deuterium|{{sup|2}}H]] (D)<ref group="n">Produced in [[Big Bang nucleosynthesis]].</ref><ref group="n">One of the few stable [[even and odd atomic nuclei#Odd proton, odd neutron|odd-odd nuclei]]</ref>
| 1
| 1
| {{val|2.014101777844|(15)}}
| colspan=3 align=center |'''Stable'''
| 1+
| colspan="2" style="text-align:center" | [{{val|0.00001}}, {{val|0.00028}}]<ref name="Atomic Weight of Hydrogen" />
| Deuterium
|-
| [[Tritium|{{sup|3}}H]] (T){{refn|group=n|Produced in Big Bang nucleosynthesis,<ref>{{cite journal |title=Big-bang nucleosynthesis: A probe of the early Universe |first=Alain |last=Coc |journal=Nuclear Instruments and Methods in Physics Research Section A |volume=611 |issue=2–3 |date=2009 |pages=224–230 |doi=10.1016/j.nima.2009.07.052|bibcode=2009NIMPA.611..224C }}</ref> but its short life ensures that none today is primordial, and all then formed should have decayed to '''{{sup|3}}He'''.}}
| 1
| 2
| {{val|3.016049281320|(81)}}
| {{val|12.33|(2)|u=y}}
| [[beta decay|β{{sup|−}}]]
| '''{{sup|3}}He'''
| 1/2+
| Trace<ref group="n">[[Cosmogenic]]</ref>
|
| Tritium

|-
| {{sup|4}}H
| 1
| 3
| {{val|4.02643|(11)}}
| {{val|139|(10)|ul=ys}}
| [[neutron emission|n]]
| {{sup|3}}H
| 2−
|
|
|-
| {{sup|5}}H
| 1
| 4
| {{val|5.03531|(10)}}
| {{val|86|(6)|u=ys}}
| 2n
| {{sup|3}}H
| (1/2+)
|
|
|-
| {{sup|6}}H
| 1
| 5
| {{val|6.04496|(27)}}
| {{val|294|(67)|u=ys}}
| 
| 
| 2−#
| 
| 
|-
| {{sup|7}}H
| 1
| 6
| {{val|7.052750|(108)}}#
| {{val|652|(558)|u=ys}}
|
|
| 1/2+#
| 
| 
{{Isotopes table/footer}}

== Hydrogen-1 (protium)<span class="anchor" id="Hydrogen-1_(Protium)"></span><span class="anchor" id="Hydrogen-1"></span> ==
[[File:H-1 atom.png|thumb|right|210px|{{sup|1}}H consists of 1 proton and 1 electron: the only stable nuclide with no neutrons (see [[diproton]] for a discussion of why no others exist)]]{{Redirect|Protium}}
'''{{sup|1}}H''' (atomic mass {{val|1.007825031898|(14)|ul=Da}}) is the most common hydrogen isotope, with an abundance of >99.98%. Its [[atomic nucleus|nucleus]] consists of only a single [[proton]], so it has the formal name '''protium'''.

The proton has never been observed to decay, so {{sup|1}}H 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 {{val|e=28}} and {{val|e=36}} years.<ref>{{cite web |title=Grand Unified Theories and Proton Decay |author=Ed Kearns |publisher=Boston University |date=2009 |page=15 |url=https://physics.bu.edu/NEPPSR/TALKS-2009/Kearns_GUTs_ProtonDecay.pdf}}</ref> If so, then {{sup|1}}H (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 >{{val|3.6|e=29}} years.<ref>{{Cite journal |last1=The SNO+ Collaboration |last2=Anderson |first2=M. |last3=Andringa |first3=S. |last4=Arushanova |first4=E. |last5=Asahi |first5=S. |last6=Askins |first6=M. |last7=Auty |first7=D. J. |last8=Back |first8=A. R. |last9=Barnard |first9=Z. |last10=Barros |first10=N. |last11=Bartlett |first11=D. |date=2019-02-20 |title=Search for invisible modes of nucleon decay in water with the SNO+ detector |journal=Physical Review D |volume=99 |issue=3 |pages=032008 |doi=10.1103/PhysRevD.99.032008 |arxiv=1812.05552 |bibcode=2019PhRvD..99c2008A |s2cid=96457175 |doi-access=free}}</ref>

== Hydrogen-2 (deuterium)<span class="anchor" id="Hydrogen-2"></span> ==
{{Main|Deuterium}}
[[File:H-2 atom.png|210px|thumbnail|left|Deuterium consists of 1 proton, 1 neutron, and 1 electron.]]
''Deuterium'', '''{{sup|2}}H''' (atomic mass {{val|2.014101777844|(15)|ul=Da}}), the other stable hydrogen isotope, has one proton and one neutron in its nucleus, called a deuteron. {{sup|2}}H 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 [[comet]]s 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 {{sup|2}}H is called [[heavy water]]. Deuterium and its compounds are used as a non-radioactive label in chemical experiments and in solvents for {{sup|1}}H-[[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)<span class="anchor" id="Hydrogen-3"></span> ==
{{Main|Tritium}}
[[File:H-3 atom.png|210px|thumbnail|right|Tritium consists of 1 proton, 2 neutrons, and 1 electron.]]
''Tritium'', '''{{sup|3}}H''' (atomic mass {{val|3.016049281320|(81)|ul=Da}}), has one proton and two neutrons in its nucleus (triton). It is [[radioactive]], [[beta decay|β{{sup|−}} decaying]] into [[helium-3]] with [[half-life]] {{val|12.33|(2)|u=years}}.{{refn|group=nb|name=NUBASE2020 tropical year}}<ref name=NUBASE2020a/> Traces of {{sup|3}}H occur naturally due to cosmic rays interacting with atmospheric gases. {{sup|3}}H has also been released in [[nuclear tests]]. It is used in [[fusion bombs]], as a tracer in [[isotope geochemistry]], and in [[tritium radioluminescence|self-powered lighting]] devices.

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

Tritium can be used in chemical and biological labeling experiments as a [[radioactive tracer]].<ref name="BNT">{{cite web |author1=Pfizer Japan |website=Pharmaceuticals and Medical Devices Agency (Japan) |at=2.6.5.5B, pp. 6–8 |quote=[{{sup|3}}H]-Labelled LNP-mRNA |title=SARS-CoV-2 mRNA Vaccine (BNT162, PF-07302048) |access-date=5 June 2021 |url=http://www.pmda.go.jp/drugs/2021/P20210212001/672212000_30300AMX00231_I100_1.pdf#page=16 |archive-date=24 March 2022|archive-url=https://web.archive.org/web/20220324171847/http://www.pmda.go.jp/drugs/2021/P20210212001/672212000_30300AMX00231_I100_1.pdf#page=16 }}</ref><ref name="green20">{{cite journal |doi=10.1093/jn/nxaa092|pmc=7330459 |journal=The Journal of Nutrition |title=Vitamin A Absorption Determined in Rats Using a Plasma Isotope Ratio Method |year=2020 |last1=Green |first1=Joanne Balmer |last2=Green |first2=Michael H. |volume=150 |issue=7 |pages=1977–1981 |pmid=32271921}}</ref> [[Deuterium–tritium fusion]] uses {{sup|2}}H and {{sup|3}}H as its main reactants, giving energy through the loss of mass when the two nuclei collide and fuse at high temperatures.

== Hydrogen-4 ==
'''{{sup|4}}H''' ([[atomic mass]] {{val|4.02643|(11)}}), with one proton and three neutrons, is a highly [[radionuclide|unstable]] isotope. It has been synthesized in the laboratory by bombarding tritium with fast-moving deuterons;<ref name="Ter-Akopian">
{{cite journal
 |author=G. M. Ter-Akopian|year=2002
 |title=Hydrogen-4 and Hydrogen-5 from t+t and t+d transfer reactions studied with a 57.5-MeV triton beam
 |journal=[[AIP Conference Proceedings]]
 |volume=610 |pages=920–924
 |doi=10.1063/1.1470062
 |bibcode=2002AIPC..610..920T
 |display-authors=etal}}</ref> the triton captured a neutron from the deuteron. The presence of {{sup|4}}H was deduced by detecting the emitted protons. It decays by [[neutron emission]] into {{sup|3}}H with a [[half-life]] of {{val|139|(10)|ul=ys}} (or {{val|1.39e-22|(10)|u=s}}).

In the 1955 satirical novel ''[[The Mouse That Roared]]'', the name '''quadium''' was given to the {{sup|4}}H that powered the ''Q-bomb'' that the Duchy of [[Grand Fenwick]] captured from the United States.{{cn|date=July 2025}}

== Hydrogen-5 ==
'''{{sup|5}}H''' ([[atomic mass]] {{val|5.03531|(10)}}), with one proton and four neutrons, is highly unstable. It has been synthesized in the lab by bombarding tritium with fast-moving tritons;<ref name="Ter-Akopian" /><ref>
{{cite journal
 | author = A. A. Korsheninnikov| year = 2001
 | title = Superheavy Hydrogen {{sup|5}}H
 | journal = [[Physical Review Letters]]
 | volume = 87 | issue =  9| pages = 92501
 | bibcode=2001PhRvL..87i2501K
 | doi = 10.1103/PhysRevLett.87.092501
 | pmid=11531562
 |display-authors=etal}}</ref> 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 {{sup|5}}H deduced. It decays by double [[neutron emission]] into {{sup|3}}H and has a [[half-life]] of {{val|86|(6)|ul=ys}} ({{val|8.6e-23|(6)|u=s}}) – the shortest half-life of any known nuclide.<ref name=NUBASE2020a/>

== Hydrogen-6 ==
'''{{sup|6}}H'''  ([[atomic mass]] {{val|6.04496|(27)}}) has one [[proton]] and five [[neutron]]s. It has a [[half-life]] of {{val|294|(67)|ul=ys}} ({{val|2.94e-22|(67)|u=s}}). In 2025, ⁶H was produced using an 855MeV electron beam impinging upon on a ⁷Li target.<ref>{{cite journal | url=https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.134.162501 | doi=10.1103/PhysRevLett.134.162501 | title=<nowiki>Measurement of <math><mrow><mmultiscripts><mrow><mi mathvariant="normal">H</mrow><mprescripts/><none/><mrow>6</mrow></mmultiscripts></mrow></math> Ground State Energy in an Electron Scattering Experiment at MAMI-A1</nowiki> | date=2025 | last1=Shao | first1=Tianhao | last2=Chen | first2=Jinhui | last3=Pochodzalla | first3=Josef | last4=Achenbach | first4=Patrick | last5=Christmann | first5=Mirco | last6=Distler | first6=Michael O. | last7=Doria | first7=Luca | last8=Esser | first8=Anselm | last9=Geratz | first9=Julian | last10=Helmel | first10=Christian | last11=Hoek | first11=Matthias | last12=Kino | first12=Ryoko | last13=Klag | first13=Pascal | last14=Ma | first14=Yu-Gang | last15=Markus | first15=David | last16=Merkel | first16=Harald | last17=Mihovilovič | first17=Miha | last18=Müller | first18=Ulrich | last19=Nagao | first19=Sho | last20=Nakamura | first20=Satoshi N. | last21=Nishi | first21=Kotaro | last22=Nishida | first22=Ken | last23=Oura | first23=Fumiya | last24=Pätschke | first24=Jonas | last25=Schlimme | first25=Björn Sören | last26=Sfienti | first26=Concettina | last27=Steger | first27=Daniel | last28=Steinen | first28=Marcell | last29=Thiel | first29=Michaela | last30=Wilczek | first30=Andrzej | journal=Physical Review Letters | volume=134 | issue=16 | page=162501 | pmid=40344098 | arxiv=2501.01232 | display-authors=1 }}</ref>

== Hydrogen-7 ==
'''{{sup|7}}H''' ([[atomic mass]] {{val|7.05275|(108)}}) has one [[proton]] and six [[neutron]]s. 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.<ref name="Korsheninnikov" /> {{sup|7}}H has a half-life of {{val|652|(558)|ul=ys}} ({{val|6.52e-22|(558)|u=s}}).<ref name=NUBASE2020a/>

==Decay chains==
{{sup|4}}H and {{sup|5}}H decay directly to {{sup|3}}H, which then decays to stable [[Helium-3|{{sup|3}}He]]. Decay of the heaviest isotopes, {{sup|6}}H and {{sup|7}}H, has not been experimentally observed.{{NUBASE2020|ref}}

:<math chem>\begin{array}{rcl}\\
\ce{^3_1H} &\ce{->[12.32\ \ce{y}]} &\ce{{^3_2He} + e^-} \\
\ce{^4_1H} &\ce{->[139\ \ce{ys}]} &\ce{{^3_1H} + {^1_0n}} \\
\ce{^5_1H} &\ce{->[86\ \ce{ys}]} &\ce{{^3_1H} + {2^1_0n}} \\{}
\end{array}</math>

Decay times are in [[yoctosecond]]s ({{val|e=-24|u=s}}) for all these isotopes except {{sup|3}}H, which is in years.

==See also==
* [[Hydrogen atom]]
* [[Hydrogen isotope biogeochemistry]]
* [[Exotic atom#Muonic helium (Hydrogen-4.1)|Hydrogen-4.1 (Muonic helium)]]
* [[Muonium]] – acts like an exotic light isotope of hydrogen
* {{Commons-inline}}

==Notes==
{{reflist|group=nb}}

==References==
{{Reflist}}

==Further reading==
*{{cite web
 |first=B. |last=Dumé
 |date=7 March 2003
 |title=Hydrogen-7 makes its debut
 |url=https://physicsworld.com/cws/article/news/2003/mar/07/hydrogen-7-makes-its-debut
 |work=[[Physics World]]
 |url-access=registration 
}}

{{Navbox element isotopes}}

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[[Category:Isotopes of hydrogen| ]]
[[Category:Hydrogen]]
[[Category:Lists of isotopes by element|Hydrogen]]