Deuterium Totally Explained

Everything about Deuteron totally explained

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 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.

Differences between deuterium and common hydrogen (protium)

Chemical symbol

Deuterium is frequently represented by the chemical symbol D. Since it's an isotope of hydrogen with mass number 2, it's 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 ²H₂ or D₂, 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 is one of the arguments in favor of the Big Bang theory over the steady state theory of the universe. It is estimated that the abundances of deuterium have not evolved significantly since their production more than 14 billion years ago.
The world's leading "producer" of deuterium (technically, merely enricher 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 than H₂O.. 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 (D₂O), which is about 10.6% more dense than normal water (enough that ice made from it sinks in ordinary water). Heavy water is slightly toxic in eukaryotic animals, with 25% substitution of the body water causing cell division problems and sterility, and 50% substitution causing death by cytotoxic syndrome (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 wouldn't 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 metabolic tracers in humans and animals.

Quantum properties

The deuteron has spin +1 and is thus a boson. The NMR frequency of deuterium is significantly different from common light hydrogen. Infrared spectroscopy also easily differentiates many deuterated compounds, due to the large difference in IR absorption frequency seen in the vibration of a chemical bond containing deuterium, versus light hydrogen. The two stable isotopes of hydrogen can also be distinguished by using mass spectrometry.

Nuclear properties

Deuterium is one of only four stable nuclides with an odd number of protons and odd number of neutrons. (²H, ⁶Li, ¹⁰B, ¹⁴N; also, the long-lived radioactive nuclides ⁴⁰K, ⁵⁰V, ¹³⁸La, ^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 its proton and neutron coupled to a spin-1 state, which gives a stronger nuclear attraction; the corresponding spin-1 state doesn't 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're 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

au

. 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

downarrow

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 = 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-He₃ fusion reaction, though the breakeven point of D-He₃ is higher than that of most other fusion reactions; together with the scarcity of He₃, this makes it implausible as a practical power source until at least D-T and D-D fusion 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 behaves similarly to ordinary hydrogen, but it can be distinguished from ordinary hydrogen by its mass, using mass spectrometry or infrared spectrometry. Neutron scattering techniques particularly profit from availability of deuterated samples: The H and D cross sections are very distinct and different in sign, which allows contrast variation in such experiments. Further, a nuisance problem of ordinary hydrogen is its large incoherent neutron cross section, which is nil for D and delivers much clearer signals in deuterated samples. Hydrogen occurs in all materials of organic chemistry and life science, but can't be seen by X-ray diffraction methods. Hydrogen can be seen by neutron diffraction and scattering, which makes neutron scattering, together with a modern deuteration facility, indispensable for many studies of macromolecules in biology and many other areas.
   Deuterium is useful in hydrogen nuclear magnetic resonance spectroscopy (proton NMR). NMR ordinarily requires compounds of interest to be analyzed as dissolved in solution. Because of deuterium's nuclear spin properties which differ from the light hydrogen usually present in organic molecules, NMR spectra of hydrogen/protium are highly differentiable from that of deuterium, and in practice deuterium isn't "seen" by an NMR instrument tuned to light-hydrogen. Deuterated solvents (including heavy water, but also compounds like deuterated chloroform CDCl₃) are therefore routinely used in NMR spectroscopy, in order to allow only the light-hydrogen spectra of the compound of interest to be measured, without solvent-signal interference.
   Deuterium can also be used for femtosecond infrared spectroscopy, since the mass difference drastically affects the frequency of molecular vibrations; deuterium-carbon bond vibrations are found in locations free of other signals.
   Measurements of small variations in the natural abundances of deuterium, along with those of the stable heavy oxygen isotopes ¹⁷O and ¹⁸O, are of importance in hydrology, to trace the geographic origin of Earth's waters. The heavy isotopes of hydrogen and oxygen in rainwater (so-called meteoric water) are enriched as a function of the environmental temperature of the region in which the precipitation falls (and thus enrichment is related to mean latitude). The relative enrichment of the heavy isotopes in rainwater (as referenced to mean ocean water), when plotted against temperature falls predictably along a line called the global meteoric water line (GMWL). This plot allows samples of precipitation-originated water to be identified along with general information about the climate in which it originated. Evaporative and other processes in bodies of water, and also ground water processes, also differentially alter the ratios of heavy hydrogen and oxygen isotopes in fresh and salt waters, in characteristic and often regionally-distinctive ways.
   The proton and neutron making up deuterium can be dissociated through neutral current interactions with neutrinos. The cross section for this interaction is comparatively large, and deuterium was successfully used as a neutrino target in the Sudbury Neutrino Observatory experiment.

History

Lighter element isotopes suspected

The existence of nonradioactive isotopes of lighter elements had been suspected in studies of neon as early as 1913, and proven by mass spectroscopy of light elements in 1920. The prevailing theory at the time, however, was that the isotopes were due to the existence of differing numbers of "nuclear electrons" in different atoms of an element. It was expected that hydrogen, with a measured average atomic mass very close to 1 u, and a nucleus thought to be composed of a single proton (a known particle), couldn't contain nuclear electrons, and thus could have no 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 in late 1931 by Harold Urey, a chemist at Columbia University. Urey's collaborator, Ferdinand Brickwedde, distilled five liters of cryogenically-produced liquid hydrogen to 1 mL of liquid, using the low-temperature physics laboratory that had recently been established at the National Bureau of Standards in Washington, DC (now the National Institute of Standards and Technology). This concentrated the fraction of the mass-2 isotope of hydrogen to a degree that made its spectroscopic identification unambiguous; Urey called the isotope "deuterium" from the Greek and Latin words for "two." The amount inferred for normal abundance of this heavy isotope was so small (only about 1 atom in 6400 hydrogen atoms in ocean water) that it hadn't noticeably affected previous measurements of (average) hydrogen atomic mass. Urey was also able to concentrate water to show partial enrichment of deuterium. Gilbert Newton Lewis prepared the first samples of pure heavy water in 1933. The discovery of deuterium, coming before the discovery of the neutron in 1932, was an experimental 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

Main Article: Heavy water Shortly before the war, Hans von Halban and Lew Kowarski moved their research on neutron moderation from France to England, smuggling the entire global supply of heavy water (made in Norway) across in twenty-six steel drums.
During World War II, Nazi Germany was known to be conducting experiments using heavy water as moderator for a nuclear reactor design. (Heavy water is water in which the hydrogen is deuterium.) Such experiments were a source of concern because they might allow them to produce plutonium for an atomic bomb. Ultimately, it led to (what seemed to be important at that time) the Allied operation called the "Norwegian heavy water sabotage," the purpose of which was to destroy the Vemork deuterium production/enrichment facility in Norway.
After World War II ended, the Allies discovered that Germany wasn't putting as much serious effort into the program as had been previously 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 didn't even have a fifth the amount of heavy water needed to run the reactor, partially due to the Norwegian heavy water sabotage operation. However, even had the Germans succeeded in getting a reactor operational (as the U.S. did with a graphite reactor in late 1942), they'd still have been at least several years away from development of an atomic bomb with maximal effort. The engineering process, even with maximal effort and funding, required about two and a half years (from first critical reactor to bomb) in both the U.S. and U.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. Data at approximately 18 K for D₂ (triple point):

Density: � *Liquid: 162.4 kg/m³

*Gas: 0.452 kg/m³

Viscosity: 12.6 µPa·s at 300 Kelvin (gas phase)

Specific heat capacity at constant pressure c_p: � *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 antideuteron was first produced in 1965 at the Proton Synchrotron at CERN and the 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 hasn't yet been created. The symbol for antideuterium is the same as for deuterium, except with a bar over it.

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