View source for Tritium

{{Short description|Isotope of hydrogen with two neutrons}}
{{other uses}}
{{redirect|3H}}
{{Use American English|date=September 2020}}
{{Use dmy dates|date=September 2019}}
{{Infobox isotope
|image = Tritium-Glowring - 320s.jpg
|name = Tritium, hydrogen-3, T
|alternate_names = hydrogen-3, T, {{sup|3}}T
|mass_number = 3
|symbol  = H
|num_neutrons = 2
|num_protons = 1
|abundance = [[trace radioisotope|10{{sup|−18}}]] in hydrogen<ref>
 {{cite encyclopedia
 | title=Tritium
 | publisher=Encyclopædia Britannica
 | date=21 July 2023
 | url=https://www.britannica.com/science/tritium
 }}
</ref>
|halflife = 12.32&nbsp;years
|decay_mode1 = [[Beta emission]]
|decay_energy1 = 0.018590
|decay_product = Helium-3
|decay_symbol = He
|decay_mass = 3
|mass  = 3.01604928
|spin  = {{sfrac|1|2}}
|excess_energy = {{val|14,949.794|0.001}}
|binding_energy = {{val|8481.7963|0.0009}}
}}

'''Tritium''' ({{ety|grc|''τρίτος'' (trítos)|third}}) or '''hydrogen-3''' (symbol '''T''' or '''{{sup|3}}H''') is a rare and [[radioactive]] [[isotope of hydrogen]] with a half-life of ~12.3 years. The tritium [[atomic nucleus|nucleus]] (t, sometimes called a ''triton'') contains one [[proton]] and two [[neutron]]s, whereas the nucleus of the common isotope [[Isotopes of hydrogen#Hydrogen-1 (Protium)|hydrogen-1]] (''protium'') contains one proton and no neutrons, and that of non-radioactive hydrogen-2 (''[[deuterium]]'') contains one proton and one neutron. Tritium is the heaviest [[nuclear drip line|particle-bound]] isotope of hydrogen. It is one of the few nuclides with a distinct name. The use of the name hydrogen-3, though more systematic, is much less common.

Naturally occurring tritium is extremely rare on Earth. The [[atmosphere]] has only trace amounts, formed by the interaction of its gases with [[cosmic ray]]s. It can be produced artificially by irradiation of [[lithium]] or lithium-bearing ceramic pebbles in a [[nuclear reactor]] and is a low-abundance byproduct in normal operations of nuclear reactors.

Tritium is used as the energy source in [[radioluminescence|radioluminescent]] lights for watches, [[iron sights#Contrast enhancements|night sights]] for firearms, numerous instruments and tools, and novelty items such as self-illuminating key chains. It is used in a medical and scientific setting as a [[radioactive tracer]]. Tritium is also used as a [[nuclear fusion]] fuel, along with more abundant [[deuterium]], in [[tokamak]] reactors and in [[hydrogen bomb]]s. Tritium has also been used commercially in [[Betavoltaic device|betavoltaic devices]] such as [[NanoTritium batteries]].

{{Toclimit}}

== History ==
Tritium was first detected in 1934 by [[Ernest Rutherford]], [[Mark Oliphant]] and [[Paul Harteck]] after bombarding [[deuterium]] with deuterons (deuterium nuclei). Deuterium is another isotope of hydrogen, which occurs naturally with an abundance of 0.015%.<ref>
{{cite journal
 |last1=Oliphant   |first1=M.L. |author1-link=Mark Oliphant
 |last2=Harteck    |first2=P.   |author2-link=Paul Harteck
 |last3=Rutherford |first3=L.   |author3-link=Ernest Rutherford
 |year=1934
 |title=Transmutation effects observed with heavy hydrogen
 |journal=Nature
 |volume=133  |issue=3359  |page=413
 |doi=10.1038/133413a0 |bibcode=1934Natur.133..413O
 |s2cid=4078529 |url=http://www.chemteam.info/Chem-History/Rutherford-1934a/Rutherford-1934a.html
 |doi-access=free
}}</ref><ref>
{{cite journal
 |last1=Oliphant   |first1=M.L.E. |author1-link=Mark Oliphant
 |last2=Harteck    |first2=P.     |author2-link=Paul Harteck
 |last3=Rutherford |first3=L.     |author3-link=Ernest Rutherford
 |year=1934
 |title=Transmutation Effects Observed with Heavy Hydrogen
 |journal=Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
 |volume=144  |issue=853  |page=692
 |bibcode=1934RSPSA.144..692O
 |doi=10.1098/rspa.1934.0077  |doi-access=free
}}
</ref> Their experiment could not isolate tritium, which was first accomplished in 1939 by [[Luis Walter Alvarez|Luis Alvarez]] and [[Robert Cornog]], who also realized tritium's radioactivity.<ref>
{{cite journal
 |last1=Alvarez |first1=Luis   |author1-link=Luis Walter Alvarez
 |last2=Cornog  |first2=Robert |author2-link=Robert Cornog
 |year=1939
 |title=Helium and Hydrogen of Mass 3
 |journal=Physical Review
 |volume=56  |issue=6  |page=613
 |bibcode=1939PhRv...56..613A  |doi=10.1103/PhysRev.56.613
}}
</ref><ref>
{{cite book
 |last1=Alvarez |first1=Luis W.
 |last2=Trower  |first2=W. Peter 
 |year=1987
 |title=Discovering Alvarez: Selected works of Luis W. Alvarez, with commentary by his students and colleagues
 |pages=[https://archive.org/details/discoveringalvar0000alva/page/26 26]–30
 |publisher=University of Chicago Press
 |isbn=978-0-226-81304-2
 |url=https://archive.org/details/discoveringalvar0000alva  
 |url-access=registration
}}
</ref> [[Willard Libby]] recognized in 1954 that tritium could be used for [[radiometric dating]] of water and [[wine]].<ref>
{{cite journal
 |last1=Kaufman |first1=Sheldon
 |last2=Libby   |first2=W.
 |year=1954
 |title=The natural distribution of tritium
 |journal=Physical Review
 |volume=93  |issue=6  |page=1337
 |doi=10.1103/PhysRev.93.1337 |bibcode=1954PhRv...93.1337K
}}
</ref>

== Decay ==
The half life of tritium is listed by the [[National Institute of Standards and Technology]] as {{nowrap|4,500 ± 8 days}} ({{nowrap|12.32 ± 0.02 years}})<ref>
{{Cite journal
 |last1 = Lucas      |first1 = L.L.
 |last2 = Unterweger |first2 = M. P.
 |name-list-style = amp
 |year  = 2000
 |title = Comprehensive review and critical evaluation of the half-life of tritium
 |journal = [[Journal of Research of the National Institute of Standards and Technology]]
 |volume = 105  |issue = 4  |pages = 541–549
 |doi    = 10.6028/jres.105.043  |pmid = 27551621  |pmc= 4877155
 }}</ref> – an annualized rate of approximately 5.5% per year. Tritium decays into [[helium-3]] by [[beta-minus decay]] as shown in this nuclear equation:
: {| border="0"
|- style="height:2em;"
|{{nuclide|Hydrogen|3|}}&nbsp;||→&nbsp;||{{nuclide|link=yes|helium|3|}}&nbsp;||+&nbsp;||{{SubatomicParticle|link=yes|Electron}}&nbsp;||+&nbsp;||{{SubatomicParticle|link=yes|Electron Antineutrino}}
|}
<!-- simpler
:<chem>^3_1H \to ^3_2{He^+} + {e^-} + \bar{\nu}_e</chem>
-->
releasing 18.6&nbsp;[[Electronvolt|keV]] of energy in the process. The [[electron]]'s kinetic energy varies, with an average of 5.7&nbsp;keV, while the remaining energy is carried off by the nearly undetectable [[Electron neutrino#Electron antineutrino|electron antineutrino]]. [[Beta particle]]s from tritium can penetrate only about {{convert|6.0|mm}} of air, and they are incapable of passing through the dead outermost layer of human skin.<ref>
{{cite report
 |title=Hydrogen-3
 |series=Nuclide safety data sheet
 |website=ehso.emory.edu
 |url=http://www.ehso.emory.edu/content-forms/3anuclidedatasafetysheets.pdf
 |archive-url=https://web.archive.org/web/20130520184942/http://www.ehso.emory.edu/content-forms/3anuclidedatasafetysheets.pdf
 |archive-date=2013-05-20
}}</ref> Because of their low energy compared to other beta particles, the amount of [[bremsstrahlung]] generated is also lower. The unusually low energy released in the tritium beta decay makes the decay (along with that of [[Isotopes of rhenium|rhenium-187]]) useful for absolute neutrino mass measurements in the laboratory.

The low energy of tritium's radiation makes it difficult to detect tritium-labeled compounds except by using [[liquid scintillation counting]].

== Production ==

=== Lithium ===
Tritium is most often produced in [[nuclear reactor]]s by [[neutron activation]] of [[lithium-6]]. The release and diffusion of tritium and helium produced by the fission of lithium can take place within ceramics known as [[Breeding blanket|breeder ceramics]]. Production of tritium from lithium-6 in such breeder ceramics is possible with neutrons of any energy, though the cross section is higher when the incident neutrons have lower energy, reaching more than 900 [[barn (unit)|barn]]s for [[thermal neutron]]s. This is an [[exothermic]] reaction, yielding 4.8&nbsp;[[MeV]].<ref name="t-breeding">{{cite journal |last=Rubel |first=M. |title=Fusion neutrons: tritium breeding and impact on wall materials and components of diagnostic systems |date=2019 |journal= Journal of Fusion Energy |volume=38 |issue=3–4 |pages=315–329 |doi=10.1007/s10894-018-0182-1|s2cid=125723024 |doi-access=free |bibcode=2019JFuE...38..315R }}</ref> In comparison, [[Deuterium–tritium fusion|fusion of deuterium with tritium]] releases about 17.6&nbsp;MeV. For applications in proposed fusion energy reactors, such as [[ITER]], pebbles consisting of lithium bearing ceramics including Li{{sub|2}}TiO{{sub|3}} and Li{{sub|4}}SiO{{sub|4}}, are being developed for tritium breeding within a helium-cooled pebble bed, also known as a breeder blanket.<ref>
{{cite journal
 | last1 = Hanaor   | first1 = Dorian A.H.
 | last2 = Kolb     | first2 = Matthias H.H.
 | last3 = Gan      | first3 = Yixiang
 | last4 = Kamlah   | first4 = Marc
 | last5 = Knitter  | first5 = Regina
 | year = 2015
 | title = Solution based synthesis of mixed-phase materials in the Li{{sub|2}}TiO{{sub|3}}–Li{{sub|4}}SiO{{sub|4}} system
 | journal = Journal of Nuclear Materials
 | volume = 456  | pages = 151–161
 | doi = 10.1016/j.jnucmat.2014.09.028
 | arxiv = 1410.7128  | bibcode = 2015JNuM..456..151H
 | s2cid = 94426898
}}
</ref>

: {{nuclide|link=yes|lithium|6}} + [[Neutron|n]] → {{nuclide|link=yes|helium|4}} (2.05 MeV) + {{nuclide|hydrogen|3}} (2.75 MeV)

High-energy neutrons can also produce tritium from [[lithium-7]] in an [[endothermic]] reaction, consuming 2.466&nbsp;MeV. This was discovered when the 1954 [[Castle Bravo#High yield|Castle Bravo]] nuclear test produced an unexpectedly high yield.<ref name=ieer>
{{cite report
 |last=Zerriffi |first=Hisham
 |date=January 1996
 |title=Tritium: The environmental, health, budgetary, and strategic effects of the Department of Energy's decision to produce tritium
 |publisher=[[Institute for Energy and Environmental Research]]
 |url=http://www.ieer.org/reports/tritium.html#(11)
 |access-date=15 September 2010
}}
</ref> Prior to this test, it was incorrectly assumed that {{nuclide|lithium|7}} would absorb a neutron to become {{nuclide|lithium|8}}, which would beta-decay to {{nuclide|link=yes|beryllium|8}}, which in turn would decay to two {{nuclide|helium|4}} nuclei on a total timeframe much longer than the duration of the explosion.

: {{nuclide|link=yes|lithium|7}} + [[Neutron|n]] → {{nuclide|link=yes|helium|4}} + {{nuclide|hydrogen|3}} + [[Neutron|n]]

=== Boron ===
High-energy neutrons irradiating [[Boron#Enriched boron (boron-10)|boron-10]], also occasionally produce tritium:<ref>
{{cite journal
 | last = Jones  | first = Greg 
 | year = 2008
 | title = Tritium Issues in Commercial Pressurized Water Reactors
 | journal = Fusion Science and Technology
 | volume = 54  | issue = 2  | pages = 329–332
 | doi = 10.13182/FST08-A1824
 | bibcode = 2008FuST...54..329J 
 | s2cid = 117472371 
}}</ref>

: {{nuclide|link=yes|boron|10}} + n → 2 {{nuclide|helium|4}} + {{nuclide|hydrogen|3}}

A more common result of boron-10 neutron capture is {{sup|7}}Li and a single [[alpha particle]].<ref>
{{cite web
 | last = Sublette  | first = Carey 
 | date = 17 May 2006
 | title = Nuclear Weapons FAQ Section 12.0 Useful Tables
 | publisher = Nuclear Weapons Archive
 | url = http://nuclearweaponarchive.org/Nwfaq/Nfaq12.html
 | access-date = 19 September 2010
}}
</ref>

Especially in [[pressurized water reactor]]s which only partially [[thermal neutron|thermalize]] neutrons, the interaction between relatively fast neutrons and the [[boric acid]] added as a [[chemical shim]] produces small but non-negligible quantities of tritium.

=== Deuterium ===
{{See also|Heavy water#Tritium production}}
Tritium is also produced in [[Pressurized heavy-water reactor|heavy water-moderated reactor]]s whenever a [[deuterium]] nucleus captures a neutron. This reaction has a small absorption [[cross section (physics)|cross section]], making [[heavy water]] a good [[neutron moderator]], and relatively little tritium is produced. Even so, cleaning tritium from the moderator may be desirable after several years to reduce the risk of its escaping to the environment. [[Ontario Power Generation]]'s "Tritium Removal Facility" is capable of processing up to {{convert|2500|t}} of heavy water a year, and it separates out about {{convert|2.5|kg|abbr=on}} of tritium, making it available for other uses.<ref>
{{cite web
 | last = Whitlock  | first= Jeremy 
 | title = Section D: Safety and Liability – How does Ontario Power Generation manage tritium production in its CANDU moderators? 
 | publisher = Canadian Nuclear FAQ
 | url = http://www.nuclearfaq.ca/cnf_sectionD.htm#x5
 | access-date = 19 September 2010
}}
</ref>
[[CANDU reactor]]s typically produce {{convert|130|g}} of tritium per year, which is recovered at the Darlington Tritium Recovery Facility (DTRF) attached to the 3,512 MW{{sub|electric}} [[Darlington Nuclear Generating Station]] in Ontario. The total production at DTRF between 1989 and 2011 was {{convert|42.5|kg}} – with an activity of {{convert|409|MCi}}: an average of about {{convert|2|kg}} per year.<ref>{{cite journal |title=Tritium supply and use: a key issue for the development of nuclear fusion energy |first1= Richard J. |last1=Pearson |first2=Armando B. |last2=Antoniazzi |first3=William J. |last3=Nuttall |doi=10.1016/j.fusengdes.2018.04.090 |doi-access=free |journal=[[Fusion Engineering and Design]] |volume=136 |date=November 2018 |pages=1140–1148 |publisher=Elsevier|bibcode= 2018FusED.136.1140P }}</ref>

Deuterium's absorption cross section for [[thermal neutron]]s is about 0.52 [[barn (unit)|millibarn]], whereas that of [[oxygen-16]] ({{sup|16}}O) is about 0.19 millibarn and that of [[oxygen-17]] ({{sup|17}}O) is about 240 millibarns. While {{sup|16}}O is by far the most common [[isotope of oxygen]] in both natural oxygen and heavy water; depending on the method of [[isotope separation]], heavy water may be slightly richer in {{sup|17}}O and [[oxygen-18|{{sup|18}}O]]. Due to both [[neutron capture]] and (n,[[alpha particle|α]]) reactions (the latter of which produce [[carbon-14|{{sup|14}}C]], an undesirable long-lived beta emitter, from {{sup|17}}O) they are net "neutron consumers" and are thus undesirable in a moderator of a natural uranium reactor which needs to keep neutron absorption outside the fuel as low as feasible. Some facilities that remove tritium also remove (or at least reduce the content of) {{sup|17}}O and {{sup|18}}O, which can – at least in principle – be used for [[isotope labeling]].

India, which also has a large fleet of [[pressurized heavy water reactor]]s (initially CANDU technology but since indigenized and further developed [[IPHWR]] technology), also removes at least some of the tritium produced in the moderator/coolant of its reactors but due to the dual use nature of tritium and the Indian nuclear bomb program, less information about this is publicly available than for Canada.

=== Fission ===
Tritium is an uncommon product of the [[nuclear fission]] of [[uranium-235]], [[plutonium-239]], and [[uranium-233]], with a production of about one atom per 10{{sup|4}} fissions.<ref name=anl>
{{cite web
 |url         = http://www.ead.anl.gov/pub/doc/tritium.pdf
 |title       = Tritium (Hydrogen-3) – Human Health Fact sheet
 |date        = August 2005
 |access-date = 19 September 2010
 |publisher   = [[Argonne National Laboratory]]
 |archive-url = https://web.archive.org/web/20100208152633/http://www.ead.anl.gov/pub/doc/tritium.pdf
 |archive-date = 8 February 2010
 }}
</ref><ref>
{{cite conference
 | last1 = Serot    | first1 = O.
 | last2 = Wagemans | first2 = C.
 | last3 = Heyse    | first3 = J.
 | title = AIP Conference Proceedings
 | year = 2005
 | chapter = New results on helium and tritium gas production from ternary fission
 | conference = International Conference on Nuclear Data for Science and Technology
 | series = AIP Conference Proceedings
 | publisher = [[American Institute of Physics]]
 | volume = 769  | pages = 857–860
 | doi = 10.1063/1.1945141  | bibcode = 2005AIPC..769..857S
}}</ref> The main pathways of tritium production include [[ternary fission]]. The release or recovery of tritium needs to be considered in the operation of [[nuclear reactor]]s, especially in the [[nuclear reprocessing|reprocessing of nuclear fuel]] and storage of [[spent nuclear fuel]]. The production of tritium is not a goal, but a side-effect. It is discharged to the atmosphere in small quantities by some nuclear power plants.<ref name="National Academies Press">
{{cite book
 |title=Effluent Releases from Nuclear Power Plants and Fuel-Cycle Facilities
 |date=29 March 2012
 |publisher=National Academies Press (US)
 |language=en
 |url=https://www.ncbi.nlm.nih.gov/books/NBK201991/
}}
</ref> [[Nuclear reprocessing#Voloxidation|Voloxidation]] is an optional additional step in nuclear reprocessing that removes volatile fission products (such as all isotopes of hydrogen) before an aqueous process begins. This would in principle enable economic recovery of the produced tritium but even if the tritium is only disposed and not used, it has the potential to reduce tritium contamination in the water used, reducing radioactivity released when the water is discharged since [[tritiated water]] cannot be removed from "ordinary" water except by isotope separation.
{{Annual discharge of tritium from nuclear facilities}}
Given the [[specific activity]] of tritium at {{convert|9650|Ci/g|TBq/g}}, one [[Becquerel|TBq]] is equivalent to roughly {{convert|2.8|mg}}.

==== Fukushima Daiichi ====
{{main|Fukushima disaster cleanup}}
In June 2016 the Tritiated Water Task Force released a report<ref name=TWTFR>
{{cite report 
 |title=Tritiated Water Task Force Report
 |website=www.meti.go.jp/english  |lang=en
 |publisher=Ministry of Economy, Trade and Industry
 |place=Tokyo, Japan
 |url=http://www.meti.go.jp/english/earthquake/nuclear/decommissioning/pdf/20160915_01a.pdf
}}
</ref> on the status of tritium in tritiated water at [[Fukushima Daiichi nuclear disaster|Fukushima Daiichi nuclear plant]], as part of considering options for final disposal of the stored contaminated cooling water. This identified that the March 2016 holding of tritium on-site was 760&nbsp;[[Becquerel|TBq]] (equivalent to 2.1&nbsp;g of tritium or 14&nbsp;mL of pure tritiated water) in a total of 860,000&nbsp;m{{sup|3}} of stored water. This report also identified the reducing concentration of tritium in the water extracted from the buildings etc. for storage, seeing a factor of ten decrease over the five years considered (2011–2016), 3.3&nbsp;MBq/L to 0.3&nbsp;MBq/L (after correction for the 5% annual decay of tritium).

According to a report by an expert panel considering the best approach to dealing with this issue, "[[Heavy water#Production|Tritium could be separated theoretically]], but there is no practical separation technology on an industrial scale. Accordingly, a controlled environmental release is said to be the best way to treat low-tritium-concentration water."<ref>
{{cite web
 |title=JP Gov "No drastic technology to remove Tritium was found in internationally collected knowledge"
 |date=December 2013
 |website=Fukushima Diary
 |url=http://fukushima-diary.com/2013/12/jp-gov-no-drastic-technology-to-remove-tritium-was-found-in-internationally-collected-knowledge/
}}
</ref> After a public information campaign sponsored by the Japanese government, the gradual release into the sea of the tritiated water began on 24 August 2023 and is the first of four releases through March 2024.<ref>{{Cite news |date=2023-08-26 |title=The science behind the Fukushima waste water release |language=en-GB |url=https://www.bbc.com/news/world-asia-66610977 |access-date=2023-12-19}}</ref> The entire process will take "decades" to complete.<ref>{{cite news |last1=McCurry |first1=Justin |title=Rosy-cheeked face of tritium dropped from Fukushima's publicity drive |work=[[the Guardian]] |date=16 April 2021 |page=29}}</ref> China reacted with protest.<ref>{{cite news| url = https://www.washingtonpost.com/world/2021/04/14/china-japan-fukushima-water-drink/| title = China to Japanese official: If treated radioactive water from Fukushima is safe, 'please drink it' - The Washington Post| newspaper = [[The Washington Post]]}}</ref><ref>{{Cite web|url=https://thediplomat.com/2021/04/japan-faces-growing-pressure-to-rethink-releasing-fukushimas-wastewater-into-ocean/|title = Japan Faces Growing Pressure to Rethink Releasing Fukushima's Wastewater into Ocean}}</ref>
The IAEA has endorsed the plan. The water released is diluted to reduce the tritium concentration to less than 1500 Bq/L, far below the limit recommended in drinking water by the WHO.<ref>{{Cite web|url=https://www.scmp.com/news/china/diplomacy/article/3129412/why-japan-going-dump-radioactive-water-fukushima-nuclear-plant|title=Why is Japan dumping radioactive water at sea?|date=13 April 2021}}</ref>

=== Helium-3 ===
Tritium's [[decay product]] [[helium-3]] has a very large cross section (5330 barns) for reacting with [[Neutron temperature#Thermal|thermal neutrons]], expelling a proton; hence, it is rapidly converted back to tritium in [[nuclear reactor]]s.<ref>
{{cite web
 |title=Helium-3 neutron proportional counters
 |website=mit.edu
 |publisher=Massachusetts Institute of Technology
 |place=Cambridge, MA
 |url=http://web.mit.edu/8.13/www/tgm-neutron-detectors.pdf
 |archive-url=https://web.archive.org/web/20041121073851/http://web.mit.edu/8.13/www/tgm-neutron-detectors.pdf
 |archive-date=21 November 2004
}}
</ref>
: {{nuclide|link=yes|helium|3}} + n → {{nuclide|hydrogen|1}} + {{nuclide|hydrogen|3}}

=== Cosmic rays ===
Tritium occurs naturally due to [[cosmic ray]]s interacting with atmospheric gases. In the most important reaction for natural production, a [[Neutron temperature#Fast|fast neutron]] (which must have energy greater than 4.0&nbsp;[[Electronvolt|MeV]]<ref>
{{cite web
 | last1 = Young  | first1 = P.G.
 | last2 = Foster | first2 = D.G. Jr.
 | date = September 1972
 | name-list-style = amp
 | title = An evaluation of the neutron and gamma-ray production cross-sections for nitrogen
 | publisher = [[Los Alamos Scientific Laboratory]]
 | place =  [[Los Alamos, NM]]
 | url = https://fas.org/sgp/othergov/doe/lanl/lib-www/la-pubs/00320217.pdf
 | access-date= 19 September 2010
}}
</ref>) interacts with atmospheric [[nitrogen]]:
: {{nuclide|link=yes|nitrogen|14}} + n → {{nuclide|link=yes|carbon|12}} + {{nuclide|hydrogen|3}}

Worldwide, the production of tritium from natural sources is 148&nbsp;peta[[becquerel]]s per year. The global equilibrium inventory of tritium created by natural sources remains approximately constant at 2,590&nbsp;petabecquerels. This is due to a fixed production rate, and losses proportional to the inventory.<ref name=physics.isu.edu-RIN-Tritium>
{{cite web
 |title=Tritium information section
 |series=Radiation Information Network 
 |department=Physics Department
 |publisher=Idaho State University
 |url=http://www.physics.isu.edu/radinf/tritium.htm
 |archive-url=https://web.archive.org/web/20160303184224/http://www.physics.isu.edu/radinf/tritium.htm
 |archive-date=3 March 2016
}}</ref>

===Production history===
==== USA ====
Tritium for American [[nuclear weapon]]s was produced in special [[heavy water reactor]]s at the [[Savannah River Site]] until their closures in 1988. With the [[START I|Strategic Arms Reduction Treaty]] (START) after the end of the [[Cold War]], the existing supplies were sufficient for the new, smaller number of nuclear weapons for some time.

{{convert|225|kg|abbr=on}} of tritium was produced in the United States from 1955 to 1996.{{efn|Total U.S. tritium production since 1955 has been about 225&nbsp;kilograms, an estimated 150&nbsp;kilograms of which have decayed into helium-3, leaving a current inventory of about 75&nbsp;kg of tritium. — Zerriffi & Scoville (1996)<ref name="IEER Production">
{{cite web
 |last1=Zerriffi |first1=Hisham
 |last2=Scoville |first2=Herbert Jr.
 |date=January 1996
 |title=Tritium: The environmental, health, budgetary, and strategic effects of the Department of Energy's decision to produce tritium
 |page=5  |language=en
 |publisher=[[Institute for Energy and Environmental Research]]
 |url=http://www.ieer.org/wp/wp-content/uploads/downloads/2012/05/Tritium_1996_Zerriffi.pdf
 |access-date=6 September 2018
 |archive-url=https://web.archive.org/web/20141016031739/http://www.ieer.org/wp/wp-content/uploads/downloads/2012/05/Tritium_1996_Zerriffi.pdf
 |archive-date=16 October 2014
}}
</ref>}} Since it continually decays into helium-3, the total amount remaining was about {{convert|75|kg|abbr=on}} at the time of the report,<ref name="IEER Production" /><ref name=ieer/>
and about {{convert|16|kg|abbr=on}} as of 2023.<ref>27 years have passed since 1996, i.e. 2.25 half-lives, which reduce the 75kg of 1996 to 75/2^(2.25) ≈15.8 kg.</ref>

Tritium production was resumed with [[irradiation]] of rods containing [[lithium]] (replacing the usual [[control rod]]s containing [[boron]], [[cadmium]], or [[hafnium]]), at the reactors of the commercial [[Watts Bar Nuclear Plant]] from 2003 to 2005 followed by extraction of tritium from the rods at the Tritium Extraction Facility at the [[Savannah River Site]] beginning in November 2006.<ref>
{{cite web
 | title=Defense Programs
 | department = [[Savannah River Site]]
 | publisher = U.S. Department of Energy
 | url=http://www.srs.gov/general/programs/dp/index.htm
 | access-date=20 March 2013
}}
</ref><ref>
{{cite web
 | title = Tritium Extraction Facility
 | series = Factsheets
 | date = December 2007
 | department = [[Savannah River Site]]
 | publisher = U.S. Department of Energy
 | url = http://www.srs.gov/general/news/factsheets/tef.pdf
 | access-date = 19 September 2010
}}
</ref> Tritium leakage from the rods during reactor operations limits the number that can be used in any reactor without exceeding the maximum allowed tritium levels in the coolant.<ref>
{{cite press release
 |last=Horner |first=Daniel
 |date=November 2010
 |title=GAO finds problems in tritium production
 |website=Arms Control Today
 |url=http://www.armscontrol.org/act/2010_11/GAOTritium 
}}
</ref>

== Properties ==
Tritium has an [[atomic mass]] of {{val|3.01604928|ul=Da}}. Diatomic tritium ({{chem2|T2}} or {{chem2|^{3}H2}}) is a gas at [[standard temperature and pressure]]. Combined with [[oxygen]], it forms [[tritiated water]] ({{chem2|^{3}H2O}}).

Compared to hydrogen in its natural composition on Earth, tritium has a higher [[melting point]] (20.62&nbsp;K vs. 13.99&nbsp;K), a higher [[boiling point]] (25.04&nbsp;K vs. 20.27&nbsp;K), a higher [[Critical point (thermodynamics)|critical temperature]] (40.59&nbsp;K vs. 32.94&nbsp;K) and a higher critical pressure (1.8317&nbsp;MPa vs. 1.2858&nbsp;MPa).<ref>{{Cite web |last=PubChem |title=Hazardous Substances Data Bank (HSDB): 6467 |url=https://pubchem.ncbi.nlm.nih.gov/source/hsdb/6467#section=Chemical-Physical-Properties&fullscreen=true |access-date=2023-02-27 |website=pubchem.ncbi.nlm.nih.gov |language=en}}</ref>

Tritium's [[specific activity]] is {{convert|9650|Ci/g|Bq/g|lk=on}}.<ref>
{{cite report
 |title=H-3
 |series=Radionuclide Safety Data Sheets 
 |department=OSEH
 |publisher=University of Michigan
 |url=http://www.oseh.umich.edu/radiation/h3.shtml
 |access-date=20 March 2013
}}
</ref>

Tritium figures prominently in studies of [[nuclear fusion]] due to its favorable reaction [[cross section (physics)|cross section]] and the large amount of energy (17.6&nbsp;MeV) produced through its reaction with deuterium:
: {{nuclide|hydrogen|3}} + {{nuclide|hydrogen|2}} → {{nuclide|helium|4}} + [[Neutron|n]]

All atomic nuclei contain protons as their only charged particles. They therefore repel one another because like charges repel ([[Coulomb's law]]). However, if the atoms have a high enough temperature and pressure (for example, in the core of the Sun), then their random motions can overcome such repulsion, and they can come close enough for the [[strong nuclear force]] to take effect, fusing them into heavier atoms.

A tritium nucleus (triton), containing one proton and two neutrons, has the same charge as any hydrogen nucleus, and it experiences the same electrostatic repulsion when close to another nucleus. However, the neutrons in the triton increase the attractive strong nuclear force when close enough to another nucleus. As a result, tritium can fuse more easily with other light atoms, than ordinary hydrogen can.

The same is true, albeit to a lesser extent, of deuterium. This is why [[brown dwarf]]s ("failed" [[Fusor (astronomy)|stars]]) cannot fuse normal hydrogen, but they do fuse a small minority of deuterium nuclei.

[[File:Gaseous tritium light source.jpg|thumb|right|[[Radioluminescent]] {{convert|1.8|Ci|GBq|lk=on}} {{convert|6|x|0.2|in|mm}} tritium vials are thin, tritium-gas-filled glass vials whose inner surfaces are coated with a [[phosphor]]. The vial shown here is brand-new.]]

Like the other isotopes of [[hydrogen]], tritium is difficult to confine. Rubber, plastic, and some kinds of steel are all somewhat permeable. This has raised concerns that if tritium were used in large quantities, in particular for [[fusion reactor]]s, it might contribute to [[radioactive contamination]], though its short half-life should prevent significant long-term accumulation in the atmosphere.

The high levels of atmospheric [[nuclear weapons testing]] that took place prior to the enactment of the [[Partial Nuclear Test Ban Treaty]] proved to be unexpectedly useful to oceanographers. The high levels of tritium oxide introduced into upper layers of the oceans have been used in the years since then to measure the rate of mixing of the upper layers of the oceans with their lower levels.

== Health risks ==
Since tritium is a low energy [[beta particle|beta (β) emitter]], it is not dangerous externally (its β particles cannot penetrate the skin),<ref name=physics.isu.edu-RIN-Tritium/> but it can be a radiation hazard if inhaled, ingested via food or water, or absorbed through the skin.<ref>
{{cite report
 |first=I.
 |last=Fairlie
 |date=June 2007
 |title=Tritium Hazard Report: Pollution and Radiation Risk from Canadian Nuclear Facilities
 |url=http://www.greenpeace.org/raw/content/canada/en/documents-and-links/publications/tritium-hazard-report-pollu.pdf
 |access-date=21 September 2008
 |archive-date=20 May 2010
 |archive-url=https://web.archive.org/web/20100520210058/http://www.greenpeace.org/raw/content/canada/en/documents-and-links/publications/tritium-hazard-report-pollu.pdf
}}</ref><ref>
{{cite report
 |last=Osborne |first=R.V.
 |date=August 2007
 |title=Review of the Greenpeace report: "Tritium Hazard Report: Pollution and Radiation Risk from Canadian Nuclear Facilities"
 |website=nuclearfaq.ca
 |url=http://www.nuclearfaq.ca/ReviewofGreenpeacereport_Final.pdf
}}
</ref><ref name=US-NRC-Trit-Bkg/><ref>
{{cite report
 |title=Tritium Facts and Information
 |publisher=Pennsylvania Department of Environmental Protection
 |url=http://www.dep.state.pa.us/brp/Radiation_Control_Division/Tritium.htm
 |archive-url=https://web.archive.org/web/20130515162757/http://www.dep.state.pa.us/brp/Radiation_Control_Division/Tritium.htm
 |archive-date=15 May 2013
}}
</ref><ref>{{Cite journal |last=Travis |first=C.C. |date=1984 |title=Metabolism of organically-bound tritium |url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/16/045/16045522.pdf?r=1 |journal=Oak Ridge National Laboratory |via=IAEA}}</ref>

Organisms can take up H{{sup|3}}HO, as they would H{{sub|2}}O.<ref>{{Cite journal |last=Bhatia |first=A.L. |date=2005 |title=Impact of low-level radiation with special reference to tritium in environment |url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/36/113/36113778.pdf?r=1 |journal=ISRE04. Proceedings of the Third International Symposium on Radiation Education |via=IAEA}}</ref> Plants convert H{{sup|3}}HO into organically bound tritium (OBT), and are consumed by animals. H{{sup|3}}HO is retained in humans for around 12 days, with a small portion of it remaining in the body.<ref name=":0">{{Cite journal |last1=Van Den Hoek |first1=J. |last2=Gerber |first2=G.B. |last3=Kirchmann |first3=R. |date=1986 |title=Similarities and differences in the transfer of Tritium and Carbon-14 along the food chain |url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/17/054/17054687.pdf?r=1 |journal=Emergency Planning and Preparedness for Nuclear Facilities |via=IAEA}}</ref> Tritium can be passed along the food chain as one organism feeds on another, though the metabolism of OBT is less understood than that of H{{sup|3}}HO.<ref name=":0" /> Tritium can incorporate to [[RNA]] and [[DNA]] molecules within organisms which can lead to somatic and genetic impacts. These can emerge in later generations.<ref>{{Cite journal |last1=Šimek |first1=Dalibor |last2=Dubšek |first2=Frantisek |date=1997 |title=Tritium in liquid releases on nuclear power plants with VVER and PWR reactors and some ways to solutions of its reduction |url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/29/006/29006324.pdf |journal=Proceedings of the 2nd International Symposium on Safety and Reliability Systems of PWRS and VVERs |via=IAEA}}</ref>

H{{sup|3}}HO has a short [[Biological half-life#Water|biological half-life]] in the human body of 7 to 14&nbsp;days, which both reduces the total effects of single-incident ingestion and precludes long-term [[bioaccumulation]] of H{{sup|3}}HO from the environment.<ref name="US-NRC-Trit-Bkg" /><ref name="j1">
{{cite journal 
 | last1 = Singh   | first1 = V. P. 
 | last2 = Pai     | first2 = R. K. 
 | last3 = Veerender | first3 = D. D. 
 | last4 = Vishnu  | first4 = M. S. 
 | last5 = Vijayan | first5 = P. 
 | last6 = Managanvi | first6 = S. S. 
 | last7 = Badiger | first7 = N. M. 
 | last8 = Bhat    | first8 = H. R. 
 | year = 2010 
 | title = Estimation of biological half-life of tritium in coastal region of India 
 | journal = Radiation Protection Dosimetry 
 | volume = 142  | issue = 2–4  | pages = 153–159 
 | pmid = 20870665   | doi = 10.1093/rpd/ncq219 
}}
</ref> The biological half-life of tritiated water in the human body, which is a measure of body water turn-over, varies with the season. Studies on the biological half-life of occupational radiation workers for free water tritium in a coastal region of [[Karnataka]], India, show that the biological half-life in winter is twice that of the summer.<ref name="j1" /> If tritium exposure is suspected or known, drinking uncontaminated water will help replace the tritium from the body. Increasing sweating, urination or breathing can help the body expel water and thereby the tritium contained in it. However, care should be taken that neither [[dehydration]] nor a depletion of the body's [[electrolytes]] results, as the [[Water intoxication|health consequences of those things]] (particularly in the short term) can be more severe than those of tritium exposure.

== Environmental contamination ==
{{Globalize||United States|date=January 2022}}
Tritium has leaked from 48 of 65 nuclear sites in the US. In one case, leaking water contained {{convert|7.5|μCi}} of tritium per liter, which is 375 times the current EPA limit for drinking water, and 28 times the [[World Health Organization]]'s recommended limit.<ref>[https://www.nbcnews.com/id/wbna43475479 Radioactive tritium leaks found at 48 US nuke sites]. NBC News (21 June 2011). Retrieved on 16 October 2014.</ref> This is equivalent to {{convert|0.777|ng/L}} or roughly 0.8 [[parts per trillion]].

The US [[Nuclear Regulatory Commission]] states that in normal operation in 2003, 56 [[pressurized water reactor]]s released {{convert|40600|Ci}} of tritium (maximum: {{convert|2,080|Ci|abbr=on}}; minimum: {{convert|0.1|Ci|abbr=on}}; average: {{Convert|725|Ci|abbr=on}}) and 24 [[boiling water reactor]]s released {{convert|665|Ci|TBq|abbr=on}} (maximum: {{convert|174|Ci|abbr=on}}; minimum: 0&nbsp;Ci; average: {{convert|27.7|Ci|abbr=on}}), in liquid effluents.<ref>[https://www.nrc.gov/reactors/operating/ops-experience/tritium/faqs.html#normal NRC: Frequently Asked Questions About Liquid Radioactive Releases] "What are normal amounts of tritium released from nuclear power plants?"</ref> {{convert|40600|Ci|abbr=on}} of tritium weigh about {{convert|4.207|g}}.


=== Regulatory limits ===
The legal limits for tritium in [[drinking water]] vary widely from country to country. Some figures are given below:
: {| class="wikitable"
|+ Tritium drinking water limits by country<ref>
 {{cite web
 |url=http://nuclearsafety.gc.ca/eng/resources/health/tritium/tritium-in-drinking-water.cfm
 |title=Tritium in drinking water
 |publisher=[[Canadian Nuclear Safety Commission]]
 |date=3 February 2014
 |access-date=23 February 2017
 }}
</ref>
!valign="bottom"| Country
!valign="bottom"| Tritium limit<br/>(Bq/L)
!valign="bottom"| Equivalent dose<br />([[microsievert|μSv]]/year){{efn|Based on ICRP Report 30 calculation: {{val|1.8e-11|u=Sv/Bq}}, {{val|730|u=L/year}}, {{val|1e6|u=μSv/Sv}}; quoted in <ref>{{cite web |title=Standards and Guidelines for Tritium in Drinking Water (INFO-0766) |url=https://nuclearsafety.gc.ca/eng/resources/health/tritium/standards-and-guidelines-for-tritium-in-drinking-water.cfm |website=Canadian Nuclear Safety Commission |language=en |date=3 February 2014}}</ref> }}
|-
| Australia
|align="right"| 76,103{{efn|This figure is derived from the guideline dose of 1&nbsp;mSv per year from all sources of radiation in drinking water in The Australian Drinking Water Guidelines 6, assuming that tritium is the only radionuclide present in the water.<ref name="The Australian Drinking Water Guidelines 6">
 {{cite web
 |date=March 2015
 |title=Australian Drinking Water Guidelines 6
 |page=98  |language=en
 |publisher= National Health and Medical Research Council, National Resource Management Ministerial Council, Commonwealth of Australia, Canberra
 |url=https://www.nhmrc.gov.au/file/16934/download?token=gAKh3uQk
 }}</ref>}}
|1,000
|-
| Japan
|align="right"| 60,000
|{{#expr:60000 * 1.8 / 1e11 * 730 * 1e6 round 2}}
|-
| Finland
|align="right"| 30,000
|{{#expr:30000 * 1.8 / 1e11 * 730 * 1e6 round 2}}
|-
| World Health Organization
|align="right"| 10,000
|{{#expr:10000 * 1.8 / 1e11 * 730 * 1e6 round 2}}
|-
| Switzerland
|align="right"| 10,000
|{{#expr:10000 * 1.8 / 1e11 * 730 * 1e6 round 2}}
|-
| Russia
|align="right"| 7,700
|{{#expr:7700 * 1.8 / 1e11 * 730 * 1e6 round 2}}
|-
| Canada (Ontario)
|align="right"| 7,000
|{{#expr:7000 * 1.8 / 1e11 * 730 * 1e6 round 2}}
|-
| United States
|align="right"| 740
|{{#expr:740 * 1.8 / 1e11 * 730 * 1e6 round 2}}
|-
| Norway
|align="right"| 100<ref>
 {{cite web  |url=https://lovdata.no/dokument/SF/forskrift/2015-07-03-870
 |title=Forskrift om visse forurensende stoffer i næringsmidler
 |language=no
 |publisher=[[Lovdata]]
 |date=10 July 2015
 |access-date=7 January 2023
 }}</ref>
|{{#expr:100 * 1.8 / 1e11 * 730 * 1e6 round 2}}
|-
|}
The American limit results in a dose of 4.0&nbsp;[[Roentgen equivalent man|millirem]]s (or 40&nbsp;micro[[sievert]]s in [[SI units]]) per year per EPA regulation 40CFR141, and is based on outdated dose calculation standards of National Bureau of Standards Handbook 69 circa 1963. Four millirem per year is about 1.3% of the natural background radiation (~3&nbsp;mSv). For comparison, the [[banana equivalent dose]] (BED) is set at 0.1&nbsp;μSv, so the statutory limit in the US is set at 400 BED. Updated dose calculation standards based on International Commission on Radiological Protection Report 30 and used in the NRC Regulation 10CFR20 results in a dose of 0.9&nbsp;millirem (9&nbsp;μSv) per year at 740&nbsp;Bq/L (20&nbsp;nCi/L).<ref name=US-NRC-Trit-Bkg>
{{cite report
 | title = Backgrounder on Tritium, Radiation Protection Limits, and Drinking Water Standards
 | date = 15 March 2011
 | publisher = U.S. [[Nuclear Regulatory Commission]]
 | url = https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/tritium-radiation-fs.html
 | access-date = 10 February 2012
}}
</ref>

== Use ==
{{More citations needed section|date=January 2022}}

=== Radiometric assays in biology and medicine ===
[[File:TritiationPyridine.svg|class=skin-invert-image|thumb|Partial tritiation of [[pyridine]] ({{chem2|C5H5N}}).  The catalyst is not shown.|left|268px]]
'''Tritiation''' of drug candidates allows detailed analysis of their absorption and [[metabolism]].<ref>{{cite journal |doi=10.1021/acs.chemrev.1c00795 |title=Recent Developments for the Deuterium and Tritium Labeling of Organic Molecules |date=2022 |last1=Kopf |first1=Sara |last2=Bourriquen |first2=Florian |last3=Li |first3=Wu |last4=Neumann |first4=Helfried |last5=Junge |first5=Kathrin |last6=Beller |first6=Matthias |journal=Chemical Reviews |volume=122 |issue=6 |pages=6634–6718 |pmid=35179363 |s2cid=246942228 |doi-access=free }}</ref> Tritium has also been used for biological radiometric assays, in a process akin to [[radiocarbon dating]]. For example, [<sup>3</sup>H] [[retinyl acetate]] was traced through the bodies of rats.<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>

=== Self-powered lighting ===
[[File:Tritium-watch.jpg|thumb|upright|right|[[Hanowa|Swiss Military watch]] with tritium-illuminated face]]
{{Main|Tritium radioluminescence}}
The beta particles from small amounts of tritium cause chemicals called ''[[phosphor]]s'' to glow. This [[radioluminescence]] is used in self-powered lighting devices called ''betalights'', which are used for night illumination of firearm sights, watches, [[exit sign]]s, map lights, navigational compasses (such as current-use [[Cammenga#U.S. M-1950 3H Lensatic Compass|M-1950 U.S. military compasses]]), knives and a variety of other devices.{{efn|Tritium has replaced [[radioluminescent paint]] containing [[radium]] in this application. Exposure to [[radium]] causes [[bone cancer]], and its casual use has been banned in most countries for decades.}} {{As of|2000}}, commercial demand for tritium is {{convert|400|g|lb}} per year<ref name="ieer" /> and the cost is {{convert|30,000|$/g}}<ref>
{{cite report
 |last=Willms |first=Scott
 |date=14 January 2003
 |title=Tritium Supply Considerations
 |publisher=[[Los Alamos National Laboratory]]
 |place=[[Los Alamos, NM]]
 |url=http://fire.pppl.gov/fesac_dp_ts_willms.pdf
 |access-date=1 August 2010
}}
</ref> or more.<ref>{{Cite journal |last=Jassby |first=Daniel |date=2022-05-25 |title=The Quest for Fusion Energy |url=https://inference-review.com/article/the-quest-for-fusion-energy |journal=Inference |language=en |volume=7 |issue=1}}</ref>

=== Nuclear weapons ===
Tritium is an important component in nuclear weapons; it is used to enhance the efficiency and yield of [[fission bomb]]s and the fission stages of [[hydrogen bomb]]s in a process known as "[[boosted fission weapon|boosting]]" as well as in [[Neutron generator|external neutron initiator]]s for such weapons.

==== Neutron initiator ====
These are devices incorporated in [[nuclear weapon]]s which produce a pulse of neutrons when the bomb is detonated to initiate the [[fission reaction]] in the fissionable core (pit) of the bomb, after it is compressed to a [[critical mass]] by explosives.  Actuated by an ultrafast switch like a [[krytron]], a small [[particle accelerator]] drives [[ion]]s of tritium and deuterium to energies above the 15&nbsp;[[Electronvolt|keV]] or so needed for deuterium-tritium fusion and directs them into a metal target where the tritium and deuterium are [[Adsorption|adsorbed]] as [[hydride]]s. High-energy [[fusion neutron]]s from the resulting fusion radiate in all directions. Some of these strike plutonium or uranium nuclei in the primary's pit, initiating a [[nuclear chain reaction]]. The quantity of neutrons produced is large in absolute numbers, allowing the pit to quickly achieve neutron levels that would otherwise need many more generations of chain reaction, though still small compared to the total number of nuclei in the pit.

==== Boosting ====
{{Main|Boosted fission weapon}}
Before detonation, a few grams of tritium–deuterium gas are injected into the hollow "[[pit (nuclear weapon)|pit]]" of fissile material. The early stages of the fission chain reaction supply enough heat and compression to start deuterium–tritium fusion; then both fission and fusion proceed in parallel, the fission assisting the fusion by continuing heating and compression, and the fusion assisting the fission with highly energetic (14.1-[[Electronvolt|MeV]]) neutrons. As the fission fuel depletes and also explodes outward, it falls below the density needed to stay critical by itself, but the fusion neutrons make the fission process progress faster and continue longer than it would without boosting. Increased yield comes overwhelmingly from the increased fission. The energy from the fusion itself is much smaller because the amount of fusion fuel is much smaller. Effects of boosting include:
* increased yield (for the same amount of fission fuel, compared to unboosted)
* the possibility of [[variable yield]] by varying the amount of fusion fuel
* allowing the bomb to require a smaller amount of the very expensive fissile material
* eliminating the risk of predetonation by nearby nuclear explosions
* not so stringent requirements on the implosion setup, allowing for a smaller and lighter amount of high explosives to be used

The tritium in a [[warhead]] is continually undergoing radioactive decay, becoming unavailable for fusion. Also, its [[decay product]], helium-3, absorbs neutrons. This can offset or reverse the intended effect of the tritium, which was to generate many free neutrons, if too much helium-3 has accumulated. Therefore, boosted bombs need fresh tritium periodically. The estimated quantity needed is {{convert|4|g}} per warhead.<ref name=ieer/> To maintain constant levels of tritium, about {{convert|0.20|g}} per warhead per year must be supplied to the bomb.

One [[mole (unit)|mole]] of deuterium-tritium gas contains about {{convert|3.0|g}} of tritium and {{convert|2.0|g}} of deuterium. In comparison, the 20&nbsp;moles of plutonium in a nuclear bomb consists of about {{convert|4.5|kg}} of [[plutonium-239]].

==== Tritium in hydrogen bomb secondaries ====
{{see also|Nuclear weapon design}}
Since tritium undergoes radioactive decay, and is also difficult to confine physically, the much larger secondary charge of heavy hydrogen isotopes needed in a true [[hydrogen bomb]] uses solid [[Lithium hydride#Lithium deuteride|lithium deuteride]] as its source of deuterium and tritium, producing the tritium ''in situ'' during secondary ignition.

During the detonation of the primary [[fission bomb]] stage in a thermonuclear weapon ([[History of the Teller–Ulam design|Teller–Ulam staging]]), the [[Thermonuclear weapon|sparkplug]], a cylinder of {{sup|235}}U/{{sup|239}}Pu at the center of the fusion stage(s), begins to fission in a chain reaction, from excess neutrons channeled from the primary.  The neutrons released from the fission of the sparkplug split [[lithium-6]] into tritium and helium-4, while lithium-7 is split into helium-4, tritium, and one neutron. As these reactions occur, the fusion stage is compressed by photons from the primary and fission of the {{sup|238}}U or {{sup|238}}U/{{sup|235}}U jacket surrounding the fusion stage. Therefore, the fusion stage breeds its own tritium as the device detonates. In the extreme heat and pressure of the explosion, some of the tritium is then forced into fusion with deuterium, and that reaction releases even more neutrons.

Since this fusion process requires an extremely high temperature for ignition, and it produces fewer and less energetic neutrons (only fission, deuterium-tritium fusion, and {{nuclide|lithium|7}} splitting are net neutron producers), [[lithium deuteride]] is not used in boosted bombs, but rather for multi-stage hydrogen bombs.

=== Controlled nuclear fusion ===
Tritium is an important fuel for controlled nuclear fusion in both [[Magnetic confinement fusion|magnetic confinement]] and [[inertial confinement fusion]] reactor designs. The [[National Ignition Facility]] (NIF) uses deuterium–tritium fuel, and the experimental fusion reactor [[ITER]] will also do so. The [[Fusion power#Deuterium, tritium|deuterium–tritium reaction]] is favorable since it has the largest fusion cross section (about 5.0&nbsp;[[barn (unit)|barns]]) and it reaches this maximum cross section at the lowest energy (about 65&nbsp;[[Electronvolt|keV]] center-of-mass) of any potential fusion fuel. As tritium is very rare on earth, concepts for fusion reactors often include the breeding of tritium. During the operation of envisioned breeder fusion reactors, [[Breeding blanket]]s, often containing lithium as part of ceramic pebbles, are subjected to neutron fluxes to generate tritium to complete the fuel cycle.<ref>{{cite journal |last1=Gan |first1=Y |last2=Hernandez |first2=F |last3=et |first3=al |title=Thermal Discrete Element Analysis of EU Solid Breeder Blanket Subjected to Neutron Irradiation |journal=Fusion Science and Technology |date=2017 |volume=66 |issue=1 |pages=83–90 |doi=10.13182/FST13-727 |arxiv=1406.4199 |url=https://hal.science/hal-02356062v1/file/1406.4199.pdf}}</ref>

The [[Tritium Systems Test Assembly]] (TSTA) was a facility at the [[Los Alamos National Laboratory]] dedicated to the development and demonstration of technologies required for fusion-relevant deuterium–tritium processing.

=== Electrical power source ===
Tritium can be used in a [[betavoltaic device]] to create an [[atomic battery]] to generate [[electricity]].

=== Use in Electron Tubes ===
Tritium is used in various electron tubes, such as the [[Zellweger off-peak|Zellweger ZE22/3 glow tube]]. These devices contain a small amount of tritium to ionize the fill gas, typically a noble gas like [[neon]] or [[argon]]. This ionization ensures reliable and consistent operation by providing a steady current when a high voltage is applied, enhancing the device's performance and stability. The tritium is sealed within a glass envelope with two electrodes, one of which is coated with the radioactive material to create an ion path between the electrodes.<ref>{{Cite web |title=Electron Tubes |url=https://www.orau.org/health-physics-museum/collection/consumer/miscellaneous/electron-tubes.html |access-date=2025-02-12 |website=Museum of Radiation and Radioactivity |language=en}}</ref>

== Use as an oceanic transient tracer ==
Aside from [[chlorofluorocarbon]]s, tritium can act as a transient tracer and can "outline" the biological, chemical, and physical paths throughout the world's oceans because of its evolving distribution.<ref name="Oceanus">
{{cite report
 |last1=Jenkins |first1=William J. |display-authors=etal
 |year=1996
 |article=Transient Tracers Track Ocean Climate Signals
 |title=Oceanus
 |publisher=Woods Hole Oceanographic Institution
 |url=http://www.whoi.edu/oceanus/viewArticle.do?id=2330
}}
</ref> Tritium has thus been used as a tool to examine ocean circulation and ventilation and, for such purposes, is usually measured in tritium units, where 1&nbsp;TU is defined as 1 tritium atom per 10{{sup|18}} hydrogen atoms,<ref name="Oceanus" /> equal to about 0.118 Bq/liter.<ref>
{{cite journal
 |first1=David A. |last1=Stonestrom  |display-authors=etal
 |date=2013
 |title=On the conversion of tritium units to mass fractions for hydrologic applications
 |journal=Isotopes Environ Health Stud
 |volume=9 |number=2 |pages=250–256
 |doi=10.1080/10256016.2013.766610  |pmid=23464868 |pmc=3664909
|bibcode=2013IEHS...49..250S }}
</ref><ref name="Eawag_3H">{{cite web | last1=Swiss Federal Institute of Aquatic Science and Technology | first1=Department Water Resources and Drinking Water | title=Tritium (<sup>3</sup>H) | website=Eawag | url=https://www.eawag.ch/en/department/wut/main-focus/environmental-isotopes/tritium-h3/ | access-date=2024-11-09}}</ref><ref name="Phillips2014">{{cite book |last1=Phillips |first1=F. M. |last2=Castro |first2=M. C. |title=Treatise on Geochemistry |date=1 January 2014 |publisher=Elsevier |isbn=978-0-08-098300-4 |pages=361–400 |url=https://doi.org/10.1016/B978-0-08-095975-7.00513-1 |language=en |chapter=7.11 – Groundwater Dating and Residence-Time Measurements|edition=Second |doi=10.1016/B978-0-08-095975-7.00513-1 }}</ref> As noted earlier, nuclear tests, mainly in the Northern Hemisphere at high latitudes, throughout the late 1950s and early 1960s introduced lots of tritium into the atmosphere, especially the [[stratosphere]]. Before these nuclear tests, there were only about 3-4 kg of tritium on the Earth's surface; but these amounts rose by 2-3 orders of magnitude during the post-test period.<ref name="Oceanus"/> Some sources reported natural background levels were exceeded by about 1,000&nbsp;TU in 1963 and 1964 and the isotope is used in the northern hemisphere to estimate the age of groundwater and construct hydrogeologic simulation models.<ref>
{{cite book
 |editor-last=Maidment |editor-first=David R.
 |year=1993
 |title=Handbook of Hydrology   |pages=6–39
 |place=New York, NY
 |publisher=McGraw-Hill
 |isbn=0-07-039732-5
}}
</ref> Estimated atmospheric levels at the height of weapons testing to approach 1,000&nbsp;TU and pre-fallout levels of rainwater to be between 5 and 10&nbsp;TU.<ref>
{{cite report
 |last=Cossairt |first=J. Donald
 |date=September 2012
 |title=Background Levels of Tritium  |pages=2–3
 |series=Environmental Protection Note |id=No. 28
 |department=Fermilab Environmental Safety & Health Section
 |publisher=[[Fermi National Accelerator Laboratory]]
 |place=Batavia, Illinois
 |url=http://esh-docdb.fnal.gov/cgi-bin/RetrieveFile?docid=2167&filename=EP%20Note%2028%20September%202012.pdf&version=1
}}
</ref> In 1963 [[Valentia Island]] Ireland recorded 2,000&nbsp;TU in precipitation.<ref>Wunsch, Carl. (2015). Modern observational physical oceanography : understanding the global ocean. Princeton : Princeton University Press. p. 44 Figure 2.29. {{ISBN|978-0-691-15882-2}}.</ref>

=== North Atlantic Ocean ===
While in the stratosphere (post-test period), the tritium interacted with and oxidized to water molecules and was present in much of the rapidly produced rainfall, making tritium a prognostic tool for studying the evolution and structure of the [[water cycle]] as well as the ventilation and formation of water masses in the North Atlantic.<ref name="Oceanus"/>

Bomb-tritium data were used from the Transient Tracers in the Ocean (TTO) program in order to quantify the replenishment and overturning rates for deep water located in the North Atlantic.<ref name="Bomb Tritium">
{{cite journal
 |last=Doney |first=Scott C.
 |year=1992
 |title=Bomb tritium in the deep north Atlantic
 |journal=Oceanography
 |volume=5 |issue=3 |pages=169–170
 |doi=10.5670/oceanog.1992.11 |doi-access=free
}}
</ref>

Bomb-tritium also enters the deep ocean around the Antarctic.<ref name="Bomb Tritium Antarctic">
{{cite journal
 |last1=Michel    |first1=Robert
 |first2=Peter M. |last2=Williams
 |date=1973
 |title=Bomb-produced tritium in the Antarctic Ocean
 |journal=Earth and Planetary Science Letters
 |volume=20  |issue=3  |pages=381–384
 |doi=10.1016/0012-821X(73)90013-7  |bibcode=1973E&PSL..20..381M
}}
</ref> Most of the bomb tritiated water (H{{sup|3}}HO) throughout the atmosphere can enter the ocean through the following processes:
* precipitation
* vapor exchange
* river runoff
These processes make H{{sup|3}}HO a great tracer for time scales of up to a few decades.<ref name="Bomb Tritium"/>

Using the data from these processes for 1981, the 1-TU isosurface lies between 500 and 1,000&nbsp;meters deep in the [[subtropical]] regions and then extends to 1,500–2,000&nbsp;meters south of the [[Gulf Stream]] due to recirculation and ventilation in the upper portion of the Atlantic Ocean.<ref name="Oceanus"/> To the north, the isosurface deepens and reaches the floor of the [[abyssal plain]] which is directly related to the ventilation of the ocean floor over 10–20&nbsp;year time-scales.<ref name="Oceanus"/>

Also evident in the Atlantic Ocean is the tritium profile near [[Bermuda]] between the late 1960s and late 1980s. There is a downward propagation of the tritium maximum from the surface (1960s) to 400&nbsp;meters (1980s), which corresponds to a deepening rate of about 18&nbsp;meters per year.<ref name="Oceanus" /> There are also tritium increases at 1,500&nbsp;m depth in the late 1970s and 2,500&nbsp;m in the middle of the 1980s, both of which correspond to cooling events in the deep water and associated deep water ventilation.<ref name="Oceanus"/>

From a study in 1991, the tritium profile was used as a tool for studying the mixing and spreading of newly formed [[North Atlantic Deep Water]] (NADW), corresponding to tritium increases to 4&nbsp;TU.<ref name="Bomb Tritium" /> This NADW tends to spill over sills that divide the [[Norwegian Sea]] from the North Atlantic Ocean and then flows to the west and equatorward in deep boundary currents. This process was explained via the large-scale tritium distribution in the deep North Atlantic between 1981 and 1983.<ref name="Bomb Tritium" /> The sub-polar gyre tends to be freshened (ventilated) by the NADW and is directly related to the high tritium values (>1.5&nbsp;TU). Also evident was the decrease in tritium in the deep western boundary current by a factor of 10 from the [[Labrador Sea]] to the [[Tropics]], which is indicative of loss to ocean interior due to turbulent mixing and recirculation.<ref name="Bomb Tritium" />

=== Pacific and Indian oceans ===
In a 1998 study, tritium concentrations in surface seawater and atmospheric water vapor (10&nbsp;meters above the surface) were sampled at the following locations: the [[Sulu Sea]], [[Fremantle Bay]], the [[Bay of Bengal]], [[Penang Bay]], and the [[Strait of Malacca]].<ref name="Tritium">
{{cite journal
 |last1=Kakiuchi  |first1=H.
 |last2=Momoshima |first2=N.
 |last3=Okai      |first3=T.
 |last4=Maeda |first4=Y.
 |title=Tritium concentration in ocean
 |date=1999
 |journal=Journal of Radioanalytical and Nuclear Chemistry
 |volume=239  |issue=3  |page=523
 |doi=10.1007/BF02349062
 |bibcode=1999JRNC..239..523K
 |s2cid=94876087
}}
</ref> Results indicated that the tritium concentration in surface seawater was highest at the Fremantle Bay (about 0.40&nbsp;Bq/liter), which could be accredited to the mixing of runoff of freshwater from nearby lands due to large amounts found in coastal waters.<ref name="Tritium" /> Typically, lower concentrations were found between [[35th parallel south|35]] and [[45th parallel south|45]]° south, and near the [[equator]]. Results also indicated that (in general) tritium has decreased over the years (up to 1997) due to the physical decay of bomb tritium in the [[Indian Ocean]]. As for water vapor, the tritium concentration was about one order of magnitude greater than surface seawater concentrations (ranging from 0.46 to 1.15&nbsp;Bq/L).<ref name="Tritium"/> Therefore, the water vapor tritium is not affected by the surface seawater concentration; thus, the high tritium concentrations in the vapor were concluded to be a direct consequence of the downward movement of natural tritium from the stratosphere to the troposphere (therefore, the ocean air showed a dependence on latitudinal change).<ref name="Tritium" />

In the [[North Pacific Ocean]], the tritium (introduced as bomb tritium in the Northern Hemisphere) spread in three dimensions. There were subsurface maxima in the middle and low latitude regions, which is indicative of lateral mixing (advection) and [[diffusion]] processes along lines of constant [[potential density]] ([[isopycnal]]s) in the upper ocean.<ref name="Circulation">
{{cite journal
 |last1=Fine    |first1=Rana A.
 |last2=Reid    |first2=Joseph L.
 |last3=Östlund |first3=H. Göte
 |year=1981
 |title=Circulation of Tritium in the Pacific Ocean
 |journal=Journal of Physical Oceanography
 |volume=11|issue=1|pages=3–14
 |doi=10.1175/1520-0485(1981)011<0003:COTITP>2.0.CO;2
 |bibcode = 1981JPO....11....3F
 |doi-access=free
}}
</ref> Some of these maxima even correlate well with [[salinity]] extrema.<ref name="Circulation" /> In order to obtain the structure for ocean circulation, the tritium concentrations were mapped on 3 surfaces of constant potential density (23.90, 26.02, and 26.81).<ref name="Circulation" /> Results indicated that the tritium was well-mixed (at 6 to 7&nbsp;TU) on the 26.81 isopycnal in the subarctic cyclonic gyre and there appeared to be a slow exchange of tritium (relative to shallower isopycnals) between this gyre and the anticyclonic gyre to the south; also, the tritium on the 23.90 and 26.02 surfaces appeared to be exchanged at a slower rate between the central gyre of the North Pacific and the equatorial regions.<ref name="Circulation" />

The depth penetration of bomb tritium can be separated into three distinct layers:
; Layer 1 : ''Layer 1'' is the shallowest layer and includes the deepest, ventilated layer in winter; it has received tritium via radioactive fallout and lost some due to advection and/or vertical diffusion and contains about 28% of the total amount of tritium.<ref name="Circulation" />
; Layer 2 : ''Layer 2'' is below the first layer but above the 26.81 [[isopycnal]] and is no longer part of the mixed layer. Its two sources are diffusion downward from the mixed layer and lateral expansions outcropping strata (poleward); it contains about 58% of the total tritium.<ref name="Circulation" />
; Layer 3 : ''Layer 3'' is representative of waters that are deeper than the outcrop isopycnal and can only receive tritium via vertical diffusion; it contains the remaining 14% of the total tritium.<ref name="Circulation" />

=== Mississippi River system ===
Trace amounts of radioactive materials from atomic weapons testing settled throughout the [[Mississippi River System]]. Tritium concentrations have been used to understand the [[residence time]]s of continental hydrologic systems such as lakes, streams, and rivers.<ref name="Mississippi">
{{cite journal
 |last1=Michel  |first1=Robert L.
 |year=2004
 |title=Tritium hydrology of the Mississippi River basin
 |journal=Hydrological Processes
 |volume=18  |issue=7  |page=1255
 |doi=10.1002/hyp.1403  |bibcode = 2004HyPr...18.1255M
 |s2cid=130033605
 |url=https://zenodo.org/record/1229196
}}
</ref> 
In a 2004 study, several rivers were taken into account during the examination of tritium concentrations (starting in the 1960s) throughout the Mississippi River Basin: [[Ohio River]] (largest input to the Mississippi River flow), [[Missouri River]], and [[Arkansas River]].<ref name="Mississippi" /> The highest tritium concentrations were found in 1963 across locations throughout these rivers.  The peak correlates with implementation of the US & Soviet atmospheric test ban treaty in 1962. The overall highest concentrations occurred in the Missouri River (1963) and were greater than 1,200&nbsp;TU while the lowest concentrations were found in the Arkansas River (never greater than 850&nbsp;TU and less than 10&nbsp;TU in the mid-1980s).<ref name="Mississippi" />

As for the mass flux of tritium through the main stem of the Mississippi River into the [[Gulf of Mexico]], data indicated that approximately 780&nbsp;grams of tritium has flowed out of the River and into the Gulf between 1961 and 1997,<ref name="Mississippi"/> an average of 21.7&nbsp;grams/yr and 7.7&nbsp;PBq/yr. Current fluxes through the Mississippi River are 1 to 2 grams, per year as opposed to the pre-bomb period fluxes of roughly 0.4&nbsp;grams per year.<ref name="Mississippi" />

== See also ==
* [[Hypertriton]]
* [[List of elements facing shortage]]

== Footnotes ==
{{notelist}}

== References ==
{{reflist}}

== External links ==
{{Commons}}
* {{cite web
 |title=Annotated bibliography for tritium
 |website=Alsos Digital Library
 |publisher=Washington and Lee University
 |url=http://alsos.wlu.edu/qsearch.aspx?browse=science/Tritium
 |access-date=3 March 2022
 |archive-date=14 May 2006
 |archive-url=https://web.archive.org/web/20060514063237/http://alsos.wlu.edu/qsearch.aspx?browse=science%2FTritium
}}
* {{cite web
 |title=Nuclear Data Evaluation Lab
 |url=http://atom.kaeri.re.kr/ 
}}
* {{cite report
 |title = Review of Risks from Tritium
 |collaboration = Independent Advisory Group on Ionising Radiation
 |date = November 2007
 |publisher = Health Protection Agency
 |id = RCE-4
 |place = London, UK
 |url = http://www.hpa.org.uk/web/HPAweb&HPAwebStandard/HPAweb_C/1197382220012
 |access-date = 3 March 2022
 |archive-date = 17 May 2013
 |archive-url = https://web.archive.org/web/20130517093153/http://www.hpa.org.uk/web/HPAweb%26HPAwebStandard/HPAweb_C/1197382220012
}}
* {{cite book
 |first=Kenneth D. |last=Bergeron
 |title=Tritium on Ice: The dangerous new alliance of nuclear weapons and nuclear power
 |date=17 September 2004
 |publisher=MIT Press
 |isbn=978-0-262-26172-2
 |url=https://books.google.com/books?id=sYKYZaxg0RUC 
}}{{full citation needed|date=November 2020|reason=date, publisher, ISBN}}
* {{cite web
 |title=Tritium production and recovery in the United States in FY2011
 |date=February 2010
 |website=Fissile Materials
 |url=http://www.fissilematerials.org/blog/2010/02/tritium_production_and_re.html 
}}
* {{cite web |title=Tritium removal mass transfer coefficient |website=ans.org |url=https://www.ans.org/pubs/journals/fst/article-1828/}}

{{Isotope sequence
 |element=hydrogen
 |lighter=[[deuterium]]
 |heavier=[[hydrogen-4]]
 |before=[[hydrogen-4]]
 |after=[[helium-3]]
}}

{{Authority control}}

[[Category:Tritium| ]]
[[Category:Isotopes of hydrogen]]
[[Category:Environmental isotopes]]
[[Category:Radiochemistry]]
[[Category:Radioisotope fuels]]
[[Category:Nuclear fusion fuels]]
[[Category:Radionuclides used in radiometric dating]]