deuterium
[doo-teer-ee-uhm, dyoo-] Show IPA
deuterium , isotope of hydrogen with mass no. 2.
The deuterium nucleus, called a deuteron, contains one proton and one neutron.
Deuterium is also called heavy hydrogen, and water in which the hydrogen atoms are deuterium is called heavy water (deuteriumoxide, D 2 O). Deuterons are sometimes used in particle accelerators, and heavy water is used in "swimming pool" nuclear reactors as a
moderator.
The deuterium nucleus, called a deuteron, contains one proton and one neutron.
Deuterium is also called heavy hydrogen, and water in which the hydrogen atoms are deuterium is called heavy water (deuteriumoxide, D 2 O). Deuterons are sometimes used in particle accelerators, and heavy water is used in "swimming pool" nuclear reactors as a
moderator.
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or deuterium oxide
Water composed of two atoms of deuterium (D; a heavy isotope of hydrogen) and one atom of oxygen (O), chemical formula D 2 O. Water from most natural sources contains about 0.015 percent deuterium oxide; this can be enriched or purified by distillation, electrolysis, or chemical processing. Heavy water isused as a moderator in nuclear power plants, slowing down thefast neutrons so that they can react with the fuel in the reactor.Heavy water is also used in research as an isotopic tracer forchemical reactions and biochemical pathways. Water with tritium (T 2 O) rather than deuterium may also be called heavy water.
Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
or heavy hydrogen
Isotope of hydrogen, chemical symbol 2 H or D, atomic number 1(but atomic weight approximately 2). Harold C. Urey won a Nobel Prize for its discovery and isolation. Its nucleus contains one proton and one neutron. A stable substance found in naturally occurring hydrogen compounds to the extent of about 0.015 percent , deuterium can be purified by distillation of hydrogen or by electrolysis of water. It enters into all the same chemical reactions as ordinary hydrogen; it forms D 2 and HD, analogous to molecular hydrogen (H 2 ), and D 2 O ( heavy water), analogous to ordinary water (H 2 O). Nuclear fusion of deuterium atoms or of deuterium and tritium at high temperatures releases enormous amounts of energy. Such reactions have been used in nuclear weapons and experimental power reactors. Deuterium is useful as a tracer in research into reaction mechanisms and biochemical path ways.
Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.@ copyright
Deuterium , also called heavy hydrogen , is a stable isotope of hydrogen with a natural abundance in the oceans of Earth of approximately one atom in 6500 of hydrogen (~154 PPM).Deuterium thus accounts for approximately 0.015% (on a weight basis, 0.030%) of all naturally occurring hydrogen in the oceans on Earth (see VSMOW; the abundance changes slightly from one kind of natural water to another). Deuterium abundance on Jupiter is about 6 atoms in 10,000 (0.06% atom basis); these ratios presumably reflect the early solar nebula ratios, and those after
the Big Bang. There is little deuterium in the interior of the Sun,since thermonuclear reactions destroy it. However, it continues to persist in the outer solar atmosphere at roughly the same concentration as in Jupiter.
the Big Bang. There is little deuterium in the interior of the Sun,since thermonuclear reactions destroy it. However, it continues to persist in the outer solar atmosphere at roughly the same concentration as in Jupiter.
The nucleus of deuterium, called a deuteron , contains one
proton and one neutron, whereas the far more common hydrogen nucleus contains no neutrons. The isotope name is formed from the Greek deuteros meaning "second", to denote the two particles composing the nucleus.
proton and one neutron, whereas the far more common hydrogen nucleus contains no neutrons. The isotope name is formed from the Greek deuteros meaning "second", to denote the two particles composing the nucleus.
Differences between deuterium and common hydrogen(protium)
Chemical symbol
Deuterium is frequently represented by the chemical symbol D.Since it is an isotope of hydrogen with mass number 2, it is also represented by ²H. IUPAC allows both D and ²H, although ²H is preferred. The reason deuterium has a distinct chemical symbol may be its large mass difference with protium (¹H); deuterium has a mass of 2.014 u, compared to the mean hydrogen atomic weight of 1.007947 u, and protium's mass of 1.007825 u. The isotope weight ratios within other chemical elements are largely insignificant in this regard, explaining the lack of unique isotope symbols elsewhere.Natural abundance
Deuterium occurs in trace amounts naturally as deuterium gas,written ²H 2 or D 2 , but most natural occurrence in the universe is bonded with a typical ¹H atom, a gas called hydrogen deuteride (HD or ¹H²H).
The existence of deuterium on Earth, elsewhere in the solar system (as confirmed by planetary probes), and in the spectra of stars, is an important datum in cosmology. Stellar fusion destroys deuterium, and there are no known natural processes (for example, see the rare cluster decay), other than the Big Bang nucleosynthesis, which might have produced deuterium at anything close to the observed natural abundance of deuterium.This abundance seems to be a very similar fraction of hydrogen,wherever hydrogen is found. Thus, the existence of deuterium isone of the arguments in favor of the Big Bang theory over the steady state theory of the universe. It is estimated that theabundances of deuterium have not evolved significantly since their production about 13.7 billion years ago.
The world's leading "producer" of deuterium (technically, merelyen richer or concentrator of deuterium) was Canada, until 1997 when the last plant was shut down (see more in the heavy water article). Canada uses heavy water as a neutron moderator for the operation of the CANDU reactor design. India is now probably the world's largest concentrator of heavy water,also used in nuclear power reactors.
Physical properties
The physical properties of deuterium compounds can be different from the hydrogen analogs; for example, D2O is more viscous thanH2O.. Deuterium behaves chemically similarly to ordinary hydrogen,but there are differences in bond energy and length for compounds of heavy hydrogen isotopes which are larger than the isotopic differences in any other element. Bonds involving deuterium and tritium are somewhat stronger than the corresponding bonds in light hydrogen, and these differences are enough to make significant changes in biological reactions (see heavy water).
Deuterium can replace the normal hydrogen in water molecules to form heavy water (D 2 O), which is about 10.6% more dense thannormal water (enough that ice made from it sinks in ordinar y water). Heavy water is slightly toxic in eukaryotic animals, with 25% substitution of the body water causing cell division problemsand sterility, and 50% substitution causing death by cytotoxicsyndrome (bone marrow failure and gastrointestinal lining failure). Prokaryotic organisms, however, can survive and grow in pure heavy water (though they grow more slowly). Consumption of heavy water would not pose a health threat to humans unless very large quantities (in excess of 10 liters) were consumed over many days. Small doses of heavy water (a few grams in humans,containing an amount of deuterium comparable to that normally present in the body) are routinely used as harmless metabolictracers in humans and animals.
Quantum properties
The deuteron has spin +1 and is thus a boson. The NMR frequencyof deuterium is significantly different from common light hydrogen.Infrared spectroscopy also easily differentiates many deuteratedcompounds, due to the large difference in IR absorption frequencyseen in the vibration of a chemical bond containing deuterium,versus light hydrogen. The two stable isotopes of hydrogen canalso be distinguished by using mass spectrometry.
Nuclear properties
Deuterium is one of only four stable nuclides with an odd numberof protons and odd number of neutrons. ( 2 H, 6 Li, 10 B, 14 N;also, the long-lived radioactive nuclides 40 K, 50 V, 138 La, 180mTa occur naturally.) Most odd-odd nuclei are unstable with respect to beta decay, because the decay products are even-even, and are therefore more strongly bound, due to nuclear pairing effects. Deuterium, however, benefits from having itsproton and neutron coupled to a spin-1 state, which gives a stronger nuclear attraction; the corresponding spin-1 state does not exist in the two-neutron or two-proton system, due to the Pauli exclusion principle which would require one or the other identical particle with the same spin to have some other different quantum number, such as orbital angular momentum. But orbital angular momentum of either particle gives a lower binding energy for the system, primarily due to increasing distance of the particles in the steep gradient of the nuclear force. In both cases,this causes the di-proton and di-neutron nucleus to be unstable.
Deuterium as an isospin singlet
Due to the similarity in mass and nuclear properties between the
proton and neutron, they are sometimes considered as two symmetric types of the same object, a nucleon. While only the proton has an electric charge, this is often negligible due of the weakness of the electromagnetic interaction relative to the strong nuclear interaction. The symmetry relating the proton and neutron is known as isospin and denoted tau .
proton and neutron, they are sometimes considered as two symmetric types of the same object, a nucleon. While only the proton has an electric charge, this is often negligible due of the weakness of the electromagnetic interaction relative to the strong nuclear interaction. The symmetry relating the proton and neutron is known as isospin and denoted tau .
Isospin is an SU(2) symmetry, like ordinary spin, so is completely analogous to it. The proton and neutron form an isospin doublet,with a "down" state down arrow being a neutron, and an "up" state uparrow being a proton.
A pair of nucleons can either be in an antisymmetric state of isospin called singlet, or in a symmetric state called triplet. In terms of the "down" state and "up" state, the singlet is
- frac{1}{sqrt{2}}Big(|uparrow downarrow rangle - |downarrowuparrow rangleBig).
The triplet is left( begin{array}{ll} uparrowuparrow frac{1}{sqrt{2}}(uparrowdownarrow + downarrowuparrow) downarrowdownarrow end{array} right) And thus consists of threetypes of nuclei, which are supposed to be symmetric - adeuterium nucleus (actually a highly excited state of it), a nucleuswith two protons, and a nucleus with two neutrons. The lattertwo nuclei are not stable or nearly stable, and therefore so is thistype of deuterium (meaning that it is indeed a highly excited state of deuterium).
Approximated wavefunction of the deuteron
The total wavefunction of both the proton and neutron must beantisymmetric, because they are both fermions. Apart from theirisospin, the two nucleons also have spin and spatial distributionsof their wavefunction. The latter is symmetric if the deuteron issymmetric under parity (i.e. have an "even" or "positive" parity) ,and antisymmetric if the deuteron is antisymmetric underparity (i.e. have an "odd" or "negative" parity). The parity is fullydetermined by the total orbital angular momentum of the twonucleons: if it is even then the parity is even (positive), and if it isodd then the parity is odd (negative).
The deuteron, being an isospin singlet, is antisymmetric under
nucleons exchange due to isospin, and therefore must be symmetric under the double exchange of their spin and location.Therefore it can be in either of the following two different states:
nucleons exchange due to isospin, and therefore must be symmetric under the double exchange of their spin and location.Therefore it can be in either of the following two different states:
- Symmetric spin and symmetric under parity. In this case, theexchange of the two nucleons will multiply the deuterium wave function by (-1) from isospin exchange, (+1) fromspin exchange and (+1) from parity (location exchange), for atotal of (-1) as needed for antisymmetry.
- Antisymmetric spin and antisymmetric under parity. In this case, the exchange of the two nucleons will multiply the deuterium wavefunction by (-1) from isospin exchange, (-1)from spin exchange and (-1) from parity (location exchange),again for a total of (-1) as needed for antisymmetry.
In the first case the deuteron has is a Spin triplet, so that its total spin s is 1. It also has an even parity and therefore even orbital angular momentum l ; The lower its orbital angular momentum, the lower its energy. Therefore the lowest possibleen ergy state has s =1, l =0.
In the second case the deuteron has is a spin singlet, so that its
total spins is 0. It also has an odd parity and therefore odd orbital angular momentum l . Therefore the lowest possible energy state has s =0, l =1.
total spins is 0. It also has an odd parity and therefore odd orbital angular momentum l . Therefore the lowest possible energy state has s =0, l =1.
Since s =1 gives a stronger nuclear attraction, the deuterium ground state is in the s =1, l =0 state.
The same considerations lead to the possible states of an isospin triplet having s =0, l =even or s =1, l =odd. Thus the state of lowest energy has s =1, l =1, higher than that of the isospin
singlet.
singlet.
The analysis just given is in fact only approximate, both because isospin is not an exact symmetry, and more importantly because
the strong nuclear interaction between the two nucleons is related to angular momentum in a way that mixes different s and l states. That is, s and l are not constant in time (they do not commute with the Hamiltonian), and over time a state such as s =1, l =0 may become a state of s =1, l =2. Parity is still constant in time so these do not mix with odd l states (such as s =0, l =1). Therefore the quantum state of the deuterium is a superposition (a linear combination) of the s =1, l =0 state and the s =1, l =2 state, even though the first component is much bigger. Since the total angular momentum j is also a good quantum number (it is a constant in time), both components must have the same j , and therefore j =1. This is the total spin of the deuterium nucleus.
the strong nuclear interaction between the two nucleons is related to angular momentum in a way that mixes different s and l states. That is, s and l are not constant in time (they do not commute with the Hamiltonian), and over time a state such as s =1, l =0 may become a state of s =1, l =2. Parity is still constant in time so these do not mix with odd l states (such as s =0, l =1). Therefore the quantum state of the deuterium is a superposition (a linear combination) of the s =1, l =0 state and the s =1, l =2 state, even though the first component is much bigger. Since the total angular momentum j is also a good quantum number (it is a constant in time), both components must have the same j , and therefore j =1. This is the total spin of the deuterium nucleus.
To summarize, the deuterium nucleus is antisymmetric in terms of
isospin, and has spin 1 and even (+1) parity. The relative angularmomentum of its nucleons l is not well defined, and the deuteriumis a superposition of mostly l =0 with some l =2.
isospin, and has spin 1 and even (+1) parity. The relative angularmomentum of its nucleons l is not well defined, and the deuteriumis a superposition of mostly l =0 with some l =2.
Magnetic and electric multipoles
In order to find theoretically the deuterium magnetic dipole moment mu , one uses the formula for a nuclear magnetic moment
- mu =
- overrightarrow{mu} = g^{(l)}overrightarrow{l} +g^{(s)}overrightarrow{s}
Since the proton and neutron have different values for g (l) and g(s) , one must separate their contributions. Each gets half of thedeuterium orbital angular momentum overrightarrow{l} and spinoverrightarrow{s} . One arrives at
- mu =
By using the same identities as here and using the value g (l) p =1 in nuclear magneton units, we arrive at the following result, innuclear magneton units
- mu =
- mu = {1over 2}({g^{(s)}}_p + {g^{(s)}}_n) = 0.879
- mu = -{1over 4}({g^{(s)}}_p + {g^{(s)}}_n) + {3over 4} =0.310
The measured value of the deuterium magnetic dipole moment, innuclear magneton units, is 0.857. This suggests that the state of the deuterium is indeed only approximately s =1, l =0 state, andis actually a linear combination of (mostly) this state with s =1, l =2 state.
The measured electric quadropole of the deuterium is 0.2859 efm², where e is the proton electric charge and fm is fermi. Whilethe order of magnitude is reasonable, since the deuterium radius isof order of 1 fermi (see below) and its electric charge is e, theabove model does not suffice for its computation. Morespecifically, the electric quadropole does not get a contribution from the l =0 state (which is the dominant one) and does get a contribution from a term mixing the l =0 and the l =2 states,because the electric quadrupole operator does not commute with angular momentum. The latter contribution is dominant in the absence of a pure l =0 contribution, but cannot be calculated without knowing the exact spatial form of the nucleons wavefunction inside the deuterium.
Higher magnetic and electric multipole moments cannot becalculated by the above model, for similar reasons.
Deuterium radius
The square root of the average squared radius of the deuterium,measured experimentally, is sqrt{langle r^2 rangle} = 0.96 fermi(= 0.96 fm).
Applications
Deuterium is useful in nuclear fusion reactions, especially in combination with tritium, because of the large reaction rate (or nuclear cross section) and high energy yield of the D-T reaction.There is an even higher-yield D-He 3 fusion reaction, though the break even point of D-He 3 is higher than that of most other fusion reactions; together with the scarcity of He 3 , this makes it implausible as a practical power source until at least D-T and D-Dfusion reactions have been performed on a commercial scale. Unlike protium, deuterium undergoes fusion purely via the strong interaction, making its use for commercial power plausible.
In chemistry and biochemistry, deuterium is used as a non-radioactive isotopic tracer in molecules to study chemical reactions and metabolic pathways, because chemically it behavessimilarly to ordinary hydrogen, but it can be distinguished fromordinary hydrogen by its mass, using mass spectrometry orinfrared spectrometry.
Neutron scattering techniques particularly profit from availability ofdeuterated samples: The H and D cross sections are very distinctand different in sign, which allows contrast variation in suchexperiments. Further, a nuisance problem of ordinary hydrogen isits large incoherent neutron cross section, which is nil for D anddelivers much clearer signals in deuterated samples. Hydrogenoccurs in all materials of organic chemistry and life science, butcannot be seen by X-ray diffraction methods. Hydrogen can beseen by neutron diffraction and scattering, which makes neutronscattering, together with a modern deuteration facility,indispensable for many studies of macromolecules in biology andmany other areas.
Deuterium is useful in hydrogen nuclear magnetic resonancespectroscopy ( proton NMR). NMR ordinarily requires compounds ofinterest to be analyzed as dissolved in solution. Because ofdeuterium's nuclear spin properties which differ from the lighthydrogen usually present in organic molecules, NMR spectra ofhydrogen/protium are highly differentiable from that of deuterium,and in practice deuterium is not "seen" by an NMR instrumenttuned to light-hydrogen. Deuterated solvents (including heavywater, but also compounds like deuterated chloroform, CDCl 3 )are therefore routinely used in NMR spectroscopy, in order to allowonly the light-hydrogen spectra of the compound of interest to bemeasured, without solvent-signal interference.
Deuterium can also be used for femtosecondinfrared spectroscopy, since the mass difference drasticallyaffects the frequency of molecular vibrations; deuterium-carbonbond vibrations are found in locations free of other signals.
Measurements of small variations in the natural abundances ofdeuterium, along with those of the stable heavy oxygen isotopes17 O and 18 O, are of importance in hydrology, to trace thegeographic origin of Earth's waters. The heavy isotopes ofhydrogen and oxygen in rainwater (so-called meteoric water) areenriched as a function of the environmental temperature of theregion in which the precipitation falls (and thus enrichment isrelated to mean latitude). The relative enrichment of the heavyisotopes in rainwater (as referenced to mean ocean water), whenplotted against temperature falls predictably along a line called theglobal meteoric water line (GMWL). This plot allows samples ofprecipitation-originated water to be identified along with generalinformation about the climate in which it originated. Evaporativeand other processes in bodies of water, and also ground waterprocesses, also differentially alter the ratios of heavy hydrogenand oxygen isotopes in fresh and salt waters, in characteristic andoften regionally-distinctive ways.
The proton and neutron making up deuterium can bedissociated through neutral current interactions with neutrinos.The cross section for this interaction is comparatively large, anddeuterium was successfully used as a neutrino target in theSudbury Neutrino Observatory experiment.
History
Lighter element isotopes suspected
The existence of nonradioactive isotopes of lighter elements hadbeen suspected in studies of neon as early as 1913, and provenby mass spectroscopy of light elements in 1920. The prevailingtheory at the time, however, was that the isotopes were due tothe existence of differing numbers of "nuclear electrons" indifferent atoms of an element. It was expected that hydrogen,with a measured average atomic mass very close to 1 u , and anucleus thought to be composed of a single proton (a knownparticle), could not contain nuclear electrons, and thus could haveno heavy isotopes.Deuterium predicted and finally detected
Deuterium was predicted in 1926 by Walter Russell, using his"spiral" periodic table. It was first detected spectroscopically inlate 1931 by Harold Urey, a chemist at Columbia University. Urey'scollaborator, Ferdinand Brickwedde, distilled five liters ofcryogenically-produced liquid hydrogen to 1 mL of liquid, using thelow-temperature physics laboratory that had recently beenestablished at the National Bureau of Standards in Washington,D.C. (now the National Institute of Standards and Technology).This concentrated the fraction of the mass-2 isotope of hydrogento a degree that made its spectroscopic identificationunambiguous; Urey called the isotope "deuterium" from theGreek and Latin words for "two". The amount inferred for normalabundance of this heavy isotope was so small (only about 1 atomin 6400 hydrogen atoms in ocean water) that it had not noticeablyaffected previous measurements of (average) hydrogen atomicmass. Urey was also able to concentrate water to show partialenrichment of deuterium. Gilbert Newton Lewis prepared the firstsamples of pure heavy water in 1933. The discovery of deuterium,coming before the discovery of the neutron in 1932, was anexperimental shock to theory, and after the neutron was reported,deuterium won Urey the Nobel Prize in chemistry in 1934."Heavy water" experiments in World War II
Shortly before the war, Hans von Halban and Lew Kowarski movedtheir research on neutron moderation from France to England,smuggling the entire global supply of heavy water (made inNorway) across in twenty-six steel drums.
During World War II, Nazi Germany was known to be conductingexperiments using heavy water as moderator for a nuclear reactor design. ( Heavy water is water in which the hydrogen isdeuterium.) Such experiments were a source of concern becausethey might allow them to produce plutonium for an atomic bomb.Ultimately it led to the Allied operation called the " Norwegian heavy water sabotage," the purpose of which was to destroy theVemork deuterium production/enrichment facility in Norway. At thetime this was considered important to the potential progress ofthe war.
After World War II ended, the Allies discovered that Germany wasnot putting as much serious effort into the program as had beenpreviously thought. The Germans had completed only a small,partly-built experimental reactor (which had been hidden away).By the end of the war, the Germans did not even have a fifth theamount of heavy water needed to run the reactor, partially due tothe Norwegian heavy water sabotage operation. However, evenhad the Germans succeeded in getting a reactor operational (asthe U.S. did with a graphite reactor in late 1942), they would stillhave been at least several years away from development of anatomic bomb with maximal effort. The engineering process, evenwith maximal effort and funding, required about two and a halfyears (from first critical reactor to bomb) in both the U.S. andU.S.S.R, for example.
Data
- Density: 0.180 kg/m³ at STP (0 °C, 101.325 kPa).
- Atomic weight: 2.01355321270.
- Mean abundance in ocean water (see VSMOW) about 0.0156 %of H atoms = 1/6400 H atoms.
- Density:
- *Liquid: 162.4 kg/m 3
- *Gas: 0.452 kg/m 3
- *Solid: 2950 J/(kg·K)
- *Gas: 5200 J/(kg·K)
Anti-deuterium
An antideuteron is the antiparticle of the nucleus of deuterium,consisting of an antiproton and an antineutron. The antideuteronwas first produced in 1965 at the Proton Synchrotron at CERN andthe Alternating Gradient Synchrotron at Brookhaven National Laboratory. A complete atom, with a positron orbiting the nucleus,would be called antideuterium , but as of 2005 antideuterium hasnot yet been created. The proposed symbol for antideuterium is D, that is, D with an overbar.
Pycnodeuterium
Deuterium atoms can be absorbed into a palladium (Pd) lattice.They are effectively solidified as an ultrahigh density deuteriumlump ( Pycnodeuterium ) inside each octahedral space within theunit cell of the palladium host lattice. Some believe this can beused as a nuclear fuel in cold fusion. Although this mechanismdoes result in high concentrations of deuterium in volumes, thereality of actual cold fusion by this mechanism has not beengenerally accepted within the scientific community.
See also
References
Notes
General references
- Nuclear Data Evaluation Lab
- Mullins, Justin " Desktop nuclear fusion demonstrated with deuterium gas". New Scientist Retrieved on 2007-09-10.
- Annotated bibliography for Deuterium from the Alsos Digital Library for Nuclear Issues
- Missing Gas Found in Milky Way Space.com
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Last updated on Friday October 10, 2008 at 12:09:09 PDT (GMT -0700)
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