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Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and
radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nucleus is the small, dense region consisting of s and s ...

radioactive
isotope of hydrogen. The
nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...
of tritium (t, sometimes called a triton) contains one
proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approximately one atomic mass unit, are collecti ...

proton
and two
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behav ...

neutron
s, whereas the nucleus of the common isotope
hydrogen-1 Hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all ...
(''protium'') contains just one proton, and that of
hydrogen-2 Deuterium (or hydrogen-2, symbol or , also known as heavy hydrogen) is one of two stable isotopes of hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. With a standard atomic weight o ...

hydrogen-2
(''deuterium'') contains one proton and one neutron. Naturally occurring tritium is extremely rare on Earth. The
atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gases surrounding a planet or other material body, that is held in ...

atmosphere
has only trace amounts, formed by the interaction of its gases with
cosmic ray Cosmic rays are high-energy proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approx ...
s. It can be produced artificially by irradiating
lithium Lithium (from el, λίθος, lithos, lit=stone) is a with the Li and  3. It is a soft, silvery-white . Under , it is the least dense metal and the least dense solid element. Like all alkali metals, lithium is highly and flammable, a ...

lithium
metal or lithium-bearing ceramic pebbles in a
nuclear reactor A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nucle ...

nuclear reactor
, and is a low-abundance byproduct in normal operations of nuclear reactors. Tritium is used as the energy source in
radioluminescent Radioluminescence is the phenomenon by which luminescence, light is produced in a material by bombardment with ionizing radiation such as alpha particles, beta particles, or gamma rays. Radioluminescence is used as a low level light source for ni ...
lights for watches, gun sights, numerous instruments and tools, and even novelty items such as self-illuminating key chains. It is used in a medical and scientific setting as a
radioactive tracerA radioactive tracer, radiotracer, or radioactive label, is a chemical compound in which one or more atoms have been replaced by a radionuclide so by virtue of its radioactive decay it can be used to explore the mechanism of chemical reactions by tra ...
. Tritium is also used as a nuclear fusion fuel, along with more abundant
deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific elemen ...

deuterium
, in
tokamak A tokamak (; russian: токамáк) is a device which uses a powerful magnetic field to confine plasma (physics), plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement fusion, magnetic confinement devices ...
reactors and in
hydrogen bomb lenses2) Uranium-238 ("tamper") lined with beryllium reflector3) Vacuum ("levitated core")4) Tritium "boost" gas (blue) within plutonium or uranium hollow core 5) Radiation channel filled with polystyrene foam6) Uranium ("pusher/tamper")7) Lithium ...
s.


History

Tritium was first detected in 1934 by
Ernest Rutherford Ernest Rutherford, 1st Baron Rutherford of Nelson, (30 August 1871 – 19 October 1937) was a New Zealand-born British physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific resea ...
,
Mark Oliphant Sir Marcus Laurence Elwin "Mark" Oliphant, (8 October 1901 – 14 July 2000) was an Australian physicist and Humanitarianism, humanitarian who played an important role in the first experimental demonstration of nuclear fusion and in the History ...
and
Paul Harteck Paul Karl Maria Harteck (20 July 190222 January 1985) was an Austrian physical chemist. In 1945 under Operation Epsilon in "the big sweep" throughout Germany, Harteck was arrested by the allied British and American Armed Forces for suspicion o ...
after bombarding
deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific elemen ...

deuterium
with deuterons (a proton and neutron, comprising a deuterium nucleus). Deuterium is another isotope of hydrogen. However, their experiment could not isolate tritium, which was accomplished in 1939 by Luis Alvarez and
Robert CornogRobert Alden Cornog (July 7, 1912 – July 17, 1998), was a physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branches of science, area of interest. In ...
, who also realized tritium's radioactivity.
Willard Libby Willard Frank Libby (December 17, 1908 – September 8, 1980) was an American physical chemist Physical chemistry is the study of macroscopic The macroscopic scale is the length scale on which objects or phenomena are large enough to be vi ...
recognized that tritium could be used for
radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "di ...
of water and
wine Wine is an alcoholic drink typically made from Fermentation in winemaking, fermented grapes. Yeast in winemaking, Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different ...

wine
.


Decay

While tritium has several different experimentally determined values of its
half-life Half-life (symbol ''t''1⁄2) is the time required for a quantity to reduce to half of its initial value. The term is commonly used in nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents an ...
, the
National Institute of Standards and Technology The National Institute of Standards and Technology (NIST) is a physical sciences Physical science is a branch of natural science that studies abiotic component, non-living systems, in contrast to life science. It in turn has many branches, e ...
lists (). It decays into
helium-3 Helium-3 (3He see also helion) is a light, stable isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons A proton is a subatomic particle, symbol or , with a positive electric charge Ele ...

helium-3
by
beta decay In , beta decay (''β''-decay) is a type of in which a (fast energetic or ) is emitted from an , transforming the original to an of that nuclide. For example, beta decay of a transforms it into a by the emission of an electron accompanie ...

beta decay
as per this nuclear equation: : and it releases 18.6 
keV In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular suc ...
of energy in the process. The
electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

electron
's kinetic energy varies, with an average of 5.7 keV, while the remaining energy is carried off by the nearly undetectable
electron antineutrino The electron neutrino () is a subatomic lepton In particle physics Particle physics (also known as high energy physics) is a branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowle ...
.
Beta particle A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β ...
s from tritium can penetrate only about 6.0 mm of air, and they are incapable of passing through the dead outermost layer of human skin. The unusually low energy released in the tritium beta decay makes the decay (along with that of
rhenium-187 Naturally occurring rhenium (75Re) is 37.4% 185Re, which is Stable isotope, stable, and 62.6% 187Re, which is Radionuclide, unstable but has a very long half-life (4.12×1010 years). Among elements with a known stable isotope, only indium and tellu ...
) appropriate for absolute neutrino mass measurements in the laboratory (the most recent such experiment being
KATRIN Katrin is a feminine given name. It is a German and Swedish contracted form of Katherine Katherine, Catherine, and other variations are feminine names A name is a term used for identification by an external observer. They can identify a cl ...
). The low energy of tritium's radiation makes it difficult to detect tritium-labeled compounds except by using
liquid scintillation counting Liquid scintillation counting is the measurement of radioactive activity of a sample material which uses the technique of mixing the active material with a liquid scintillator (e.g. zinc sulfide), and counting the resultant photon emissions. The pur ...
.


Production


Lithium

Tritium is most often produced in
nuclear reactor A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nucle ...

nuclear reactor
s by
neutron activation Neutron activation is the process in which neutron radiation induced radioactivity, induces radioactivity in materials, and occurs when atomic nucleus, atomic nuclei capture free neutrons, becoming heavier and entering excited states. The excited n ...
of
lithium-6 Naturally occurring lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to ...

lithium-6
. The release and diffusion of tritium and helium produced by the fission of lithium can take place within ceramics referred to as breeder ceramics. The production of tritium from lithium-6 in such breeder ceramics is possible with neutrons of any energy, and is an
exothermic In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these qu ...
reaction yielding 4.8 MeV. In comparison, the fusion of deuterium with tritium releases about 17.6 MeV of energy. For applications in proposed fusion energy reactors, such as
ITER ITER (initially the International Thermonuclear Experimental Reactor, "iter" meaning "the way" or "the path" in Latin) is an international nuclear fusion research and engineering megaproject aimed at replicating the fusion processes of the Su ...
, pebbles consisting of lithium bearing ceramics including Li2TiO3 and Li4SiO4, are being developed for tritium breeding within a helium-cooled pebble bed, also known as a breeder blanket. : High-energy neutrons can also produce tritium from
lithium-7 Naturally occurring lithium (3Li) is composed of two stable isotopes, lithium-6 and lithium-7, with the latter being far more abundant on Earth. Both of the natural isotopes have an unexpectedly low nuclear binding energy per nucleon ( for lithi ...

lithium-7
in an
endothermic In thermochemistry Thermochemistry is the study of the heat energy which is associated with chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substanc ...
(net heat consuming) reaction, consuming 2.466 MeV. This was discovered when the 1954
Castle Bravo Castle Bravo was the first in a series of high-yield thermonuclear weapon design tests conducted by the United States at Bikini Atoll, Marshall Islands, as part of ''Operation Castle''. Detonated on March 1, 1954, the device was the most powerful n ...
nuclear test produced an unexpectedly high yield. :


Boron

High-energy neutrons irradiating
boron-10 Boron is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...
will also occasionally produce tritium: : A more common result of boron-10 neutron capture is and a single
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Proto ...

alpha particle
.


Deuterium

Tritium is also produced in heavy water-moderated reactors whenever a
deuterium Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific elemen ...

deuterium
nucleus captures a neutron. This reaction has a quite small absorption
cross section Cross section may refer to: * Cross section (geometry), the intersection of a 3-dimensional body with a plane * Cross section (electronics), a common sample preparation technique in electronics * Cross section (geology), the intersection of a 3-dim ...
, making
heavy water Heavy water (deuterium oxide, , ) is a form of water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). I ...

heavy water
a good
neutron moderator In nuclear engineering Nuclear engineering is the branch of engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehi ...
, 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 Ontario Power Generation Inc. (OPG) is a business corporation registered under the Corporations Act with Government of Ontario The Government of Ontario (french: Gouvernement de l'Ontario), formally ''Her Majesty's Government of Ontario'', is ...
's "Tritium Removal Facility" processes up to of heavy water a year, and it separates out about of tritium, making it available for other uses.
CANDU reactor The CANDU (Canada Deuterium Uranium) is a Canadian pressurized heavy-water reactor design used to generate electric power. The acronym refers to its deuterium Deuterium (or hydrogen-2, symbol or , also known as heavy hydrogen) is one of two ...
s typically produce 130 g of tritium per year, which is recovered at the Darlington Tritium Recovery Facility (DTRF). The total production at DTRF between 1989 and 2011 was 42.5 kg (409 M Ci), which averages to about 2 kg per year. Deuterium's absorption cross section for
thermal neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a ...
s is about 0.52
millibarn A barn (symbol: b) is a metric unit of area Area is the quantity that expresses the extent of a two-dimensional region, shape, or planar lamina, in the plane. Surface area is its analog on the two-dimensional surface of a three-dimensi ...
s, whereas that of
oxygen-16 Oxygen-16 (16O) is a stable A stable is a building in which livestock Livestock are the domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influenc ...

oxygen-16
() is about 0.19 millibarns and that of
oxygen-17 Oxygen-17 (17O) is a low-abundance, natural, stable A stable is a building in which livestock Livestock are the domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a signif ...

oxygen-17
() is about 240 millibarns.


Fission

Tritium is an uncommon product of the
nuclear fission Nuclear fission is a reaction Reaction may refer to a process or to a response to an action, event, or exposure: Physics and chemistry *Chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic tr ...

nuclear fission
of
uranium-235 Uranium-235 (235U) is an Isotopes of uranium, isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope t ...

uranium-235
,
plutonium-239 Plutonium-239 (239Pu, Pu-239) is an isotopes of plutonium, isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also o ...

plutonium-239
, and
uranium-233 Uranium-233 (233U) is a fissile In nuclear engineering Nuclear engineering is the branch of engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, i ...

uranium-233
, with a production of about one atom per 10,000 fissions. The release or recovery of tritium needs to be considered in the operation of
nuclear reactor A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nucle ...

nuclear reactor
s, especially in the reprocessing of nuclear fuels and in the storage of
spent nuclear fuel Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor (usually at a nuclear power plant). It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor and ...
. The production of tritium is not a goal, but rather a side-effect. It is discharged to the atmosphere in small quantities by some nuclear power plants.


Fukushima Daiichi

In June 2016 the Tritiated Water Task Force released a report on the status of tritium in tritiated water at 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  TBq (equivalent to 2.1 g of tritium or 14 mL of pure tritiated water) in a total of 860,000 m3 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 MBq/L to 0.3 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, "''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.''" After a public information campaign sponsored by the Japanese government, the gradual release into the sea of the tritiated water will start in 2023. The process will take "decades" to complete. China reacted with protest.


Helium-3

Tritium's
decay product In nuclear physics Nuclear physics is the field of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and ...
helium-3 Helium-3 (3He see also helion) is a light, stable isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons A proton is a subatomic particle, symbol or , with a positive electric charge Ele ...

helium-3
has a very large cross section (5330 barns) for reacting with
thermal neutrons The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion (physics), motion. It is defined as th ...
, expelling a proton; hence, it is rapidly converted back to tritium in
nuclear reactor A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nucle ...

nuclear reactor
s. :


Cosmic rays

Tritium occurs naturally due to
cosmic ray Cosmic rays are high-energy proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approx ...
s interacting with atmospheric gases. In the most important reaction for natural production, a
fast neutron The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion (physics), motion. It is defined as th ...

fast neutron
(which must have energy greater than 4.0 
MeV In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "P ...
) interacts with atmospheric
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
: : Worldwide, the production of tritium from natural sources is 148  petabecquerels per year. The global equilibrium inventory of tritium created by natural sources remains approximately constant at 2,590 petabecquerels. This is due to a fixed production rate, and losses proportional to the inventory.


Production history

According to a 1996 report from
Institute for Energy and Environmental ResearchThe Institute for Energy and Environmental Research (IEER) is an anti-nuclear organization which focuses on the environmental safety of nuclear weapons A nuclear weapon (also called an atom bomb, nuke, atomic bomb, nuclear warhead, A-bomb, ...
on the
US Department of Energy The United States Department of Energy (DOE) is a Cabinet of the United States, cabinet-level department of the Federal government of the United States, United States government concerned with the United States' policies regarding energy and s ...
, only of tritium had been produced in the United States from 1955 to 1996. Since it continually decays into helium-3, the total amount remaining was about at the time of the report. Tritium for American
nuclear weapon A nuclear weapon (also known as an atom bomb, atomic bomb, nuclear bomb or nuclear warhead, and colloquially as an A-bomb or nuke) is an explosive device that derives its destructive force from nuclear reaction In nuclear physics Nucl ...
s was produced in special
heavy water reactor A pressurized heavy-water reactor (PHWR) is a nuclear reactor A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction 300px, A possible nuclear fission chain reaction: ...
s at the
Savannah River Site The Savannah River Site (SRS) is a U.S. Department of Energy (DOE) reservation in the United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United ...
until their closures in 1988. With the Strategic Arms Reduction Treaty (START) after the end of the
Cold War The Cold War was a period of geopolitical Geopolitics (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country loc ...
, the existing supplies were sufficient for the new, smaller number of nuclear weapons for some time. The production of tritium was resumed with
irradiation Irradiation is the process by which an object is exposed to radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior th ...

irradiation
of rods containing
lithium Lithium (from el, λίθος, lithos, lit=stone) is a with the Li and  3. It is a soft, silvery-white . Under , it is the least dense metal and the least dense solid element. Like all alkali metals, lithium is highly and flammable, a ...

lithium
(replacing the usual
control rod Control rods are used in nuclear reactor A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction 300px, A possible nuclear fission chain reaction: 1) A uranium-235 ato ...
s containing
boron Boron is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

boron
,
cadmium Cadmium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical eleme ...

cadmium
, or
hafnium Hafnium is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

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 new Tritium Extraction Facility at the
Savannah River Site The Savannah River Site (SRS) is a U.S. Department of Energy (DOE) reservation in the United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United ...
beginning in November 2006. 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.


Properties

Tritium has an atomic mass of 3.01604928  u. Diatomic tritium ( or ) is a gas at
standard temperature and pressure Standard temperature and pressure (STP) are standard Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for personal identification Norm, convention or requirement * Standard (metrology), ...
. Combined with
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
, it forms a liquid called
tritiated water Tritiated water is a radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nucleus is the small, ...
(). Tritium's
specific activity Specific activity is the activity per quantity of a radionuclide A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide A nuclide (or nucleide, from atomic nucleus, nucleus, also known as nuclear species) is ...
is . Tritium figures prominently in studies of
nuclear fusion Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products ...

nuclear fusion
because of its favorable reaction
cross section Cross section may refer to: * Cross section (geometry), the intersection of a 3-dimensional body with a plane * Cross section (electronics), a common sample preparation technique in electronics * Cross section (geology), the intersection of a 3-dim ...
and the large amount of energy (17.6 MeV) produced through its reaction with deuterium: : All atomic nuclei contain protons as their only electrically charged particles. They therefore repel one another because like charges repel. 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 electrical repulsion (called the
Coulomb force Coulomb's law, or Coulomb's inverse-square law, is an experimental physical law, law of physics that quantifies the amount of force between two stationary, electric charge, electrically charged particles. The electric force between charged bodi ...
), and they can come close enough for the
strong nuclear force In nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions. Other forms of nuclear matter are also studied. Nuclear physics should not be confused with atomic physics, which ...
to take effect, fusing them into heavier atoms. The tritium nucleus, containing one proton and two neutrons, has the same charge as the nucleus of ordinary hydrogen, and it experiences the same electrostatic repulsive force when brought close to another atomic nucleus. However, the neutrons in the tritium nucleus increase the attractive strong nuclear force when brought close enough to another atomic nucleus. As a result, tritium can more easily fuse with other light atoms, compared with the ability of ordinary hydrogen to do so. The same is true, albeit to a lesser extent, of deuterium. This is why
brown dwarf A brown dwarf is a type of substellar object that has a mass between the most massive gas giant planets and the least massive stars, approximately 13 to 80 Jupiter mass, times that of Jupiter (). Unlike main sequence stars, brown dwarfs do not a ...

brown dwarf
s (so-called 'failed'
stars A star is an astronomical object consisting of a luminous spheroid of plasma held together by its own gravity. The nearest star to Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. ...
) cannot utilize ordinary hydrogen, but they do fuse the small minority of deuterium nuclei. Like the other isotopes of
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

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 Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion, nuclear fusion reactions. In a fusion process, two lighter atomic nucleus, atomic nuclei combine to form a heavier nucleus, whil ...
s, it may contribute to
radioactive contamination Radioactive contamination, also called radiological contamination, is the deposition of, or presence of radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is t ...
, although its short half-life should prevent significant long-term accumulation in the atmosphere. The high levels of atmospheric
nuclear weapons testing Nuclear weapons tests are experiments carried out to determine nuclear weapons' effectiveness, yield Yield may refer to: Measures of output/function Computer science * Yield (multithreading) is an action that occurs in a computer program duri ...
that took place prior to the enactment of the
Partial Nuclear Test Ban Treaty The Partial Test Ban Treaty (PTBT) is the abbreviated name of the 1963 Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and Under Water, which prohibited all test detonations of nuclear weapon A nuclear weapon (als ...
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

Tritium is an isotope of hydrogen, which allows it to readily bind to
hydroxyl radical The hydroxyl radical is the diatomic molecule . The hydroxyl radical is very stable as a dilute gas, but it decays very rapidly in the condensed phase. It is pervasive in some situations. Most notably the hydroxyl radicals is produced from the d ...

hydroxyl radical
s, forming
tritiated water Tritiated water is a radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nucleus is the small, ...
(T), and to carbon atoms. Since tritium is a low energy
beta emitter (the accompanying antineutrino is omitted). The inset shows beta decay of a free neutron. Neither of these depictions shows the intermediate virtual boson. In nuclear physics Nuclear physics is the field of physics that studies atomic nuclei ...
, it is not dangerous externally (its beta particles are unable to penetrate the skin), but it can be a radiation hazard if inhaled, ingested via food or water, or absorbed through the skin. HTO has a short
biological half-life Biological half-life (also known as elimination half-life, pharmacologic half-life) of a biological substance such as medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug us ...

biological half-life
in the human body of 7 to 14 days, which both reduces the total effects of single-incident ingestion and precludes long-term
bioaccumulation Bioaccumulation is the gradual accumulation of substances, such as pesticides Pesticides are substances that are meant to control pest (organism), pests. The term pesticide includes all of the following: herbicide, insecticides (which may incl ...
of HTO from the environment. 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 the winter season is twice that of the summer season.


Environmental contamination

Tritium has leaked from 48 of 65 nuclear sites in the US. In one case, leaking water contained of tritium per liter, which is 375 times the EPA limit for drinking water. The US
Nuclear Regulatory Commission The Nuclear Regulatory Commission (NRC) is an independent agency of the United States government Independent agencies of the United States federal government The federal government of the United States (U.S. federal government or U.S. ...
states that in normal operation in 2003, 56
pressurized water reactor A pressurized water reactor (PWR) is a type of light-water nuclear reactor A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction 300px, A possible nuclear fission cha ...

pressurized water reactor
s released of tritium (maximum: 2,080 Ci; minimum: 0.1 Ci; average: 725 Ci) and 24
boiling water reactor A boiling water reactor (BWR) is a type of light water nuclear reactor A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reacto ...
s released (maximum: 174 Ci; minimum: 0 Ci; average: 27.7 Ci), in liquid effluents. According to the U.S.
Environmental Protection Agency A biophysical environment is a biotic Biotics describe living or once living components of a community; for example organisms, such as animals and plants. Biotic may refer to: *Life, the condition of living organisms *Biology, the study of life ...
, self-illuminating exit signs improperly disposed in municipal landfills have been recently found to contaminate waterways.


Regulatory limits

The legal limits for tritium in
drinking water Drinking water, also known as potable water, is water that is safe to drinking, drink or use for food preparation. The amount of drinking water required to maintain good health varies, and depends on physical activity level, age, health-related ...

drinking water
vary widely from country to country. Some figures are given below: : The American limit is calculated to yield a dose of 4.0  millirems (or 40 
microsievert The sievert (symbol: SvNot be confused with the sverdrup In oceanography Oceanography (from the Ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divide ...
s in
SI units The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system The metric system is a system of measurement A sys ...
) per year. This is about 1.3% of the natural background radiation (roughly 3,000 μSv).


Use


Biological radiometric assays

Tritium has been used for biological radiometric assays, in a process akin to
radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material Organic matter, organic material, or natural organic matter refers to the large source of ...
. For example in one paper, sup>3H was traced through the body of Sprague-Dawley rats.


Self-powered lighting

The beta particles emitted by the radioactive decay of small amounts of tritium cause chemicals called ''
phosphor A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or ...

phosphor
s'' to glow. This
radioluminescence Radioluminescence is the phenomenon by which light is produced in a material by bombardment with ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves ...
is used in self-powered lighting devices called ''betalights'', which are used for night illumination of firearm sights, watches,
exit sign An exit sign is a pictogram in a public facility (such as a building, aircraft, or boat) denoting the location of the closest emergency exit in case of fire or other emergency that requires evacuation. Most relevant code (law), codes (fire code ...

exit sign
s, map lights, navigational compasses (such as current-use M-1950 U.S. military compasses), knives and a variety of other devices. , commercial demand for tritium is 400 grams per year and the cost is approximately US$30,000 per gram.


Nuclear weapons

Tritium is an important component in nuclear weapons. It is used to enhance the efficiency and yield of
fission bomb A nuclear weapon (also known as an atom bomb, atomic bomb, nuclear bomb or nuclear warhead, and colloquially as an A-bomb or nuke) is an explosive device that derives its destructive force from nuclear reaction In nuclear physics and nu ...
s and the fission stages of hydrogen bombs in a process known as "boosted fission weapon, boosting" as well as in Neutron generator, external neutron initiators for such weapons.


Neutron initiator

These are devices incorporated in
nuclear weapon A nuclear weapon (also known as an atom bomb, atomic bomb, nuclear bomb or nuclear warhead, and colloquially as an A-bomb or nuke) is an explosive device that derives its destructive force from nuclear reaction In nuclear physics Nucl ...
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 ions of tritium and deuterium to energies above the 15 
keV In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular suc ...
or so needed for deuterium-tritium fusion and directs them into a metal target where the tritium and deuterium are Adsorption, adsorbed as hydrides. High-energy fusion neutrons 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

Before detonation, a few grams of tritium-deuterium gas are injected into the hollow "pit (nuclear weapon), pit" of fissile plutonium or uranium. 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 
MeV In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "P ...
) 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 increase in fission. The energy released by the fusion itself is much smaller because the amount of fusion fuel is so much smaller. The effects of boosting include: * increased yield (for the same amount of fission fuel, compared to detonation without boosting) * 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 – and also 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, hence becoming unavailable for fusion. Furthermore, its
decay product In nuclear physics Nuclear physics is the field of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and ...
, helium-3, absorbs neutrons if exposed to the ones emitted by nuclear fission. This potentially offsets or reverses the intended effect of the tritium, which was to generate many free neutrons, if too much helium-3 has accumulated from the decay of tritium. Therefore, it is necessary to replenish tritium in boosted bombs periodically. The estimated quantity needed is 4 grams per warhead. To maintain constant levels of tritium, about 0.20 grams per warhead per year must be supplied to the bomb. One mole (unit), mole of deuterium-tritium gas would contain about 3.0 grams of tritium and 2.0 grams of deuterium. In comparison, the 20 moles of plutonium in a nuclear bomb consists of about 4.5 kilograms of
plutonium-239 Plutonium-239 (239Pu, Pu-239) is an isotopes of plutonium, isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also o ...

plutonium-239
.


Tritium in hydrogen bomb secondaries

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 A nuclear weapon (also known as an atom bomb, atomic bomb, nuclear bomb or nuclear warhead, and colloquially as an A-bomb or nuke) is an explosive device that derives its destructive force from nuclear reaction In nuclear physics and nu ...
stage in a thermonuclear weapon (History of the Teller–Ulam design, Teller-Ullam staging), the Thermonuclear weapon, sparkplug, a cylinder of 235U/239Pu 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 238U or 238U/235U 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 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 experimental fusion reactor
ITER ITER (initially the International Thermonuclear Experimental Reactor, "iter" meaning "the way" or "the path" in Latin) is an international nuclear fusion research and engineering megaproject aimed at replicating the fusion processes of the Su ...
and the National Ignition Facility (NIF) will use deuterium-tritium fuel. The Fusion power#Deuterium/tritium, deuterium-tritium reaction is favorable since it has the largest fusion cross section (about 5.0 barn (unit), barns) and it reaches this maximum cross section at the lowest energy (about 65 
keV In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular suc ...
center-of-mass) of any potential fusion fuel. 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.


Analytical chemistry

Tritium is sometimes used as a radiolabel. It has the advantage that almost all organic chemicals contain hydrogen, making it easy to find a place to put tritium on the molecule under investigation. It has the disadvantage of producing a comparatively weak signal.


Electrical power source

Tritium can be used in a betavoltaic device to create an atomic battery to generate electricity.


Use as an oceanic transient tracer

Aside from chlorofluorocarbons, tritium can act as a transient tracer and has the ability to "outline" the biological, chemical, and physical paths throughout the world oceans because of its evolving distribution. 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 TU is defined as the ratio of 1 tritium atom to 1018 hydrogen atoms, approximately equal to 0.118 Bq/liter. As noted earlier, nuclear weapons testing, primarily in the high-latitude regions of the Northern Hemisphere, throughout the late 1950s and early 1960s introduced large amounts of tritium into the atmosphere, especially the stratosphere. Before these nuclear tests, there were only about 3 to 4 kilograms of tritium on the Earth's surface; but these amounts rose by 2 or 3 orders of magnitude during the post-test period. Some sources reported natural background levels were exceeded by approximately 1,000 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. Recent scientific sources have estimated atmospheric levels at the height of weapons testing to approach 1,000 TU and pre-fallout levels of rainwater to be between 5 and 10 TU. In 1963 Valentia Island Ireland recorded 2,000 TU in precipitation.Wunsch, Carl. (2015). Modern observational physical oceanography : understanding the global ocean. Princeton : Princeton University Press. p. 44 Figure 2.29. .


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, hydrologic cycle as well as the ventilation and formation of water masses in the North Atlantic Ocean. 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. Bomb-tritium also enters the deep ocean around the Antarctic. Most of the bomb tritiated water (HTO) throughout the atmosphere can enter the ocean through the following processes: :(a) precipitation :(b) vapor exchange :(c) river runoff These processes make HTO a great tracer for time-scales of up to a few decades. Using the data from these processes for 1981, the 1 TU isosurface lies between 500 and 1,000 meters deep in the subtropical regions and then extends to 1,500–2,000 meters south of the Gulf Stream due to recirculation and ventilation in the upper portion of the Atlantic Ocean. 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 year time-scales. 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 meters (1980s), which corresponds to a deepening rate of approximately 18 meters per year. There are also tritium increases at 1,500 meters depth in the late 1970s and 2,500 meters in the middle of the 1980s, both of which correspond to cooling events in the deep water and associated deep water ventilation. 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 TU. 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. The sub-polar gyre tends to be freshened (ventilated) by the NADW and is directly related to the high tritium values (> 1.5 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.


Pacific and Indian oceans

In a 1998 study, tritium concentrations in surface seawater and atmospheric water vapor (10 meters above the surface) were sampled at the following locations: the Sulu Sea, the Fremantle Bay, the Bay of Bengal, the Penang Bay, and the Strait of Malacca. Results indicated that the tritium concentration in surface seawater was highest at the Fremantle Bay (approximately 0.40 Bq/liter), which could be accredited to the mixing of runoff of freshwater from nearby lands due to large amounts found in coastal waters. Typically, lower concentrations were found between 35th parallel south, 35 and 45th parallel south, 45 degrees south latitude 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 approximately one order of magnitude greater than surface seawater concentrations (ranging from 0.46 to 1.15 Bq/liter). 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). 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 (isopycnals) in the upper ocean. Some of these maxima even correlate well with salinity extrema. 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). Results indicated that the tritium was well-mixed (at 6 to 7 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. The depth penetration of bomb tritium can be separated into 3 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 approximately 28% of the total amount of tritium. ;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 2 sources are diffusion downward from the mixed layer and lateral expansions outcropping strata (poleward); it contains about 58% of the total tritium. ;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.


Mississippi River System

Nuclear fallout from
Cold War The Cold War was a period of geopolitical Geopolitics (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country loc ...
weapons testing settled in the United States throughout the Mississippi River System. Tritium concentrations can be used to understand the residence times of continental hydrologic systems (as opposed to the usual oceanic hydrologic systems) which include surface waters such as lakes, streams, and rivers. Studying these systems can also provide societies and municipals with information for agricultural purposes and overall river water quality. 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. The largest tritium concentrations were found in 1963 at all the sampled locations throughout these rivers and correlate well with the peak concentrations in precipitation due to the nuclear bomb tests in 1962. The overall highest concentrations occurred in the Missouri River (1963) and were greater than 1,200 TU while the lowest concentrations were found in the Arkansas River (never greater than 850 TU and less than 10 TU in the mid-1980s). Several processes can be identified using the tritium data from the rivers: direct runoff and outflow of water from groundwater reservoirs. Using these processes, it becomes possible to model the response of the river basins to the transient tritium tracer. Two of the most common models are the following: ; Piston-flow approach: tritium signal appears immediately; and ; Well-mixed reservoir approach: outflow concentration depends upon the residence time of the basin water Unfortunately, both models fail to reproduce the tritium in river waters; thus, a two-member mixing model was developed that consists of 2 components: a prompt-flow component (recent precipitation – "piston") and a component where waters reside in the basin for longer than 1 year ("well-mixed reservoir"). Therefore, the basin tritium concentration becomes a function of the residence times within the basin, sinks (radioactive decay) or sources of tritium, and the input function. For the Ohio River, the tritium data indicated that about 40% of the flow was composed of precipitation with residence times of less than 1 year (in the Ohio basin) and older waters consisted of residence times of about 10 years. Thus, the short residence times (less than 1 year) corresponded to the "prompt-flow" component of the two-member mixing model. As for the Missouri River, results indicated that residence times were approximately 4 years with the prompt-flow component being around 10% (these results are due to the series of dams in the area of the Missouri River). 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 grams of tritium has flowed out of the River and into the Gulf between 1961 and 1997, an average of 7.7 PBq/yr. And current fluxes through the Mississippi River are about 1 to 2 grams per year as opposed to the pre-bomb period fluxes of roughly 0.4 grams per year.


See also

*Hypertriton *List of elements facing shortage


Footnotes


References


External links

* * * * * * * {{Authority control Isotopes of hydrogen Environmental isotopes Radiochemistry Radioisotope fuels Nuclear fusion fuels Radionuclides used in radiometric dating