Editing Heavy water (section)

==Applications==
===Nuclear magnetic resonance===
Deuterium oxide is used in [[nuclear magnetic resonance spectroscopy]] when using water as a solvent if the [[nuclide]] of interest is hydrogen. This is because the signal from light-water ({{sup|1}}H{{sub|2}}O) solvent molecules would overwhelm the signal from the molecule of interest dissolved in it. Deuterium has a different [[magnetic moment]] and therefore does not contribute to the [[H-1 NMR|{{sup|1}}H-NMR]] signal at the hydrogen-1 resonance frequency.

For some experiments, it may be desirable to identify the labile hydrogens on a compound, that is hydrogens that can easily exchange away as H{{sup|+}} ions on some positions in a molecule. With addition of D{{sub|2}}O, sometimes referred to as a ''D{{sub|2}}O shake'',<ref>{{cite web |url= https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_(Morsch_et_al.)/17%3A_Alcohols_and_Phenols/17.11%3A_Spectroscopy_of_Alcohols_and_Phenols |title= 17.11: Spectroscopy of Alcohols and Phenols |date= 26 August 2015 }}</ref> labile hydrogens exchange between the compound of interest and the solvent, leading to replacement of those specific {{sup|1}}H atoms in the compound with {{sup|2}}H. These positions in the molecule then do not appear in the {{sup|1}}H-NMR spectrum.

===Organic chemistry===
Deuterium oxide is often used as the source of deuterium for preparing specifically labelled [[isotopologue]]s of organic compounds. For example, C-H bonds adjacent to ketonic carbonyl groups can be replaced by C-D bonds, using acid or base catalysis. [[Trimethylsulfoxonium iodide]], made from [[dimethyl sulfoxide]] and [[methyl iodide]] can be recrystallized from deuterium oxide, and then dissociated to regenerate methyl iodide and dimethyl sulfoxide, both deuterium labelled. In cases where specific double labelling by deuterium and tritium is contemplated, the researcher must be aware that deuterium oxide, depending upon age and origin, can contain some tritium.

===Infrared spectroscopy===
Deuterium oxide is often used instead of water when collecting [[Fourier transform spectroscopy|FTIR]] spectra of proteins in solution. H{{sub|2}}O creates a strong band that overlaps with the [[amide]] I region of proteins. The band from D{{sub|2}}O is shifted away from the amide I region.

===Neutron moderator===
Heavy water is used in certain types of [[nuclear reactors]], where it acts as a [[neutron moderator]] to slow down neutrons so that they are more likely to react with the [[fissile]] [[uranium-235]] than with [[uranium-238]], which captures neutrons without fissioning.
The CANDU reactor uses this design. Light water also acts as a moderator, but because light water absorbs more [[neutron]]s than heavy water, reactors using light water for a reactor moderator must use [[enriched uranium]] rather than natural uranium, otherwise [[Critical mass|criticality]] is impossible. A significant fraction of outdated power reactors, such as the [[RBMK]] reactors in the USSR, were constructed using normal water for cooling but [[graphite-moderated reactor|graphite as a moderator]]. However, the danger of graphite in power reactors (graphite fires in part led to the [[Chernobyl disaster]]) has led to the discontinuation of graphite in standard reactor designs.

The breeding and extraction of plutonium can be a relatively rapid and cheap route to building a [[nuclear weapon]], as chemical separation of plutonium from fuel is easier than [[isotopic separation]] of U-235 from natural uranium.
Among current and past [[nuclear weapons states]], Israel, India, and North Korea<ref>{{Cite web|url=http://www-pub.iaea.org/MTCD/publications/PDF/TRS407_scr/D407_scr1.pdf|title=Heavy Water Reactors: Status and Projected Development}}</ref> first used plutonium from heavy water moderated reactors burning [[natural uranium]], while China, South Africa and Pakistan first built weapons using [[highly enriched uranium]].

The [[Uranverein|Nazi nuclear program]], operating with more modest means than the contemporaraneous Manhattan Project and hampered by many leading scientists having been driven into exile (many of them ending up working for the Manhattan Project), as well as continuous infighting, wrongly dismissed graphite as a moderator due to not recognizing the effect of impurities. Given that [[isotope separation]] of uranium was deemed too big a hurdle, this left heavy water as a potential moderator. Other problems were the ideological aversion regarding what propaganda dismissed as "[[Jewish physics]]" and the mistrust between those who had been enthusiastic Nazis even before 1933 and those who were ''[[Mitläufer]]'' or trying to keep a low profile. In part due to allied sabotage and commando raids on [[Norsk Hydro]] (then the world's largest producer of heavy water) as well as the aforementioned infighting, the German nuclear program never managed to assemble enough uranium and heavy water in one place to achieve [[Critical mass|criticality]] despite possessing enough of both by the end of the war.

In the U.S., however, the first experimental atomic reactor (1942), as well as the [[Manhattan Project]] Hanford production reactors that produced the plutonium for the [[Trinity test]] and [[Fat Man]] bombs, all used pure carbon (graphite) neutron moderators combined with normal water cooling pipes. They functioned with neither enriched uranium nor heavy water. Russian and British plutonium production also used graphite-moderated reactors.

There is no evidence that civilian heavy water power reactors—such as the CANDU or [[Atucha I nuclear power plant|Atucha]] designs—have been used to produce military fissile materials. In nations that do not already possess nuclear weapons, nuclear material at these facilities is under [[IAEA]] safeguards to discourage any diversion.

Due to its potential for use in [[nuclear weapon]]s programs, the possession or import/export of large industrial quantities of heavy water are subject to government control in several countries. Suppliers of heavy water and heavy water production technology typically apply [[IAEA]] (International Atomic Energy Agency) administered safeguards and material accounting to heavy water. (In Australia, the ''Nuclear Non-Proliferation (Safeguards) Act 1987''.) In the U.S. and Canada, non-industrial quantities of heavy water (i.e., in the gram to kg range) are routinely available without special license through chemical supply dealers and commercial companies such as the world's former major producer [[Ontario Hydro]].

===Neutrino detector===
The [[Sudbury Neutrino Observatory]] (SNO) in [[Greater Sudbury|Sudbury]], [[Ontario]] uses 1,000 tonnes of heavy water on loan from [[Atomic Energy of Canada Limited]]. The [[neutrino detector]] is {{convert|6800|ft|m}} underground in a mine, to shield it from [[muon]]s produced by [[cosmic ray]]s. SNO was built to answer the question of whether or not electron-type [[neutrino]]s produced by fusion in the [[Sun]] (the only type the Sun should be producing directly, according to theory) might be able to turn into other types of neutrinos on the way to Earth. SNO detects the [[Cherenkov radiation]] in the water from high-energy electrons produced from [[electron neutrino|electron-type neutrino]]s as they undergo charged current (CC) interactions with [[neutron]]s in [[deuterium]], turning them into protons and electrons (however, only the electrons are fast enough to produce Cherenkov radiation for detection).

SNO also detects neutrino electron scattering (ES) events, where the neutrino transfers energy to the electron, which then proceeds to generate Cherenkov radiation distinguishable from that produced by CC events. The first of these two reactions is produced only by electron-type neutrinos, while the second can be caused by all of the neutrino flavors. The use of deuterium is critical to the SNO function, because all three "flavours" (types) of neutrinos<ref>{{cite web |url=http://www.sno.phy.queensu.ca/sno/sno2.html |title=The SNO Detector |publisher=The Sudbury Neutrino Observatory Institute, Queen's University at Kingston |access-date=10 September 2007 |archive-date=7 May 2021 |archive-url=https://web.archive.org/web/20210507204823/https://sno.phy.queensu.ca/sno/sno2.html |url-status=dead }}</ref> may be detected in a third type of reaction as well, neutrino-disintegration, in which a neutrino of any type (electron, [[muon neutrino|muon]], or [[tau neutrino|tau]]) scatters from a deuterium nucleus ([[deuteron]]), transferring enough energy to break up the loosely bound deuteron into a free [[neutron]] and [[proton]] via a neutral current (NC) interaction.

This event is detected when the free neutron is absorbed by [[Chlorine-35|<sup>35</sup>Cl]]<sup>−</sup> present from [[NaCl]] deliberately dissolved in the heavy water, causing emission of characteristic capture gamma rays. Thus, in this experiment, heavy water not only provides the transparent medium necessary to produce and visualize Cherenkov radiation, but it also provides deuterium to detect exotic mu type (μ) and tau (τ) neutrinos, as well as a non-absorbent moderator medium to preserve free neutrons from this reaction, until they can be absorbed by an easily detected neutron-activated isotope.

===Metabolic rate and water turnover testing in physiology and biology===
{{main|Doubly labeled water test}}
Heavy water is employed as part of a mixture with H{{sub|2}}{{sup|18}}O for a common and safe test of mean metabolic rate in humans and animals undergoing their normal activities.The elimination rate of deuterium alone is a measure of body water turnover. This is highly variable between individuals and depends on environmental conditions as well as subject size, sex, age and physical activity.<ref>{{Cite journal|last1=Yamada|first1=Yosuke|last2=Zhang|first2=Xueying|last3=Henderson|first3=Mary E. T.|last4=Sagayama|first4=Hiroyuki|last5=Pontzer|first5=Herman|last6=Speakman|first6=John R. |date=2022|title= Variation in human water turnover associated with environmental and lifestyle factors|journal=Science|language=en|volume=378|issue=6622|pages=909–915|doi=10.1126/science.abm8668|pmid=36423296|pmc=9764345 |bibcode=2022Sci...378..909I }}</ref>

===Tritium production===
{{See also|Tritium#Deuterium}}
[[Tritium]] is the active substance in [[tritium illumination|self-powered lighting]] and controlled nuclear fusion, its other uses including [[autoradiography]] and [[radioactive label]]ing. It is also used in [[nuclear weapon design]] for [[boosted fission weapon]]s and [[tritium#Neutron initiator|initiators]]. Tritium undergoes [[beta decay]] into [[helium-3]], which is a stable, but rare, isotope of helium that is itself highly sought after. Some tritium is created in [[heavy water moderated reactor]]s when deuterium captures a neutron. This reaction has a small [[Neutron cross-section|cross-section]] (probability of a single neutron-capture event) and produces only small amounts of tritium, although enough to justify cleaning tritium from the moderator every few years to reduce the environmental risk of tritium escape. Given that helium-3 is a [[neutron poison]] with orders of magnitude higher capture cross section than any component of heavy or tritiated water, its accumulation in a heavy water neutron moderator or [[target (Physics)|target]] for tritium production must be kept to a minimum.

Producing a lot of tritium in this way would require reactors with very high neutron fluxes, or with a very high proportion of heavy water to [[nuclear fuel]] and very low [[neutron absorption]] by other reactor material. The tritium would then have to be recovered by [[isotope separation]] from a much larger quantity of deuterium, unlike production from [[lithium-6]] (the present method), where only chemical separation is needed.

Deuterium's absorption cross section for [[thermal neutron]]s is 0.52 milli[[barn (unit)|barn]] (5.2 × 10{{sup|−32}} m{{sup|2}}; 1 barn = 10{{sup|−28}} m{{sup|2}}), while those of [[oxygen-16]] and [[oxygen-17]] are 0.19 and 0.24 millibarn, respectively. {{sup|17}}O makes up 0.038% of natural [[oxygen]], making the overall cross section 0.28 millibarns. Therefore, in D{{sub|2}}O with natural oxygen, 21% of [[neutron capture]]s are on oxygen, rising higher as {{sup|17}}O builds up from neutron capture on {{sup|16}}O. Also, {{sup|17}}O may emit an [[alpha particle]] on neutron capture, producing radioactive [[carbon-14]].