Encyclopedia
Deuterium, also called
heavy hydrogen, is a stable isotope of
hydrogen with a natural abundance in the
oceans of
planet Earth of approximately one
atom in 6500 of hydrogen. Deuterium thus accounts for approximately 0.015% of all naturally occurring hydrogen . The
nucleus of deuterium, called a
deuteron, contains one
proton and one
neutron, whereas the far more common hydrogen nucleus consists only of a proton and no neutrons. The isotope name is formed from the Greek
deuteros of which one translation is "two", an obvious reference to the two subatomic particles comprising the nucleus.
Chemical symbol, occurrence, and properties
As an isotope of
hydrogen, the accepted chemical symbol for deuterium is
2H. Despite this, the unofficial
chemical element-like symbol - D - has been adopted by many. The significant difference in relative atomic weight compared with pure protium may well be the reason for this; Deuterium's atomic weight is 2.014 amu, compared to the mean hydrogen weight of 1.007947 amu, and protium's of 1.007825 amu. The isotope weight ratios within other chemical elements are largely insignificant in this regard, explaining the lack of unique isotope symbols elsewhere.
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 .
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, verses light hydrogen. The two stable isotopes of hydrogen can also be distinguished by using
mass spectrometry.
The physical properties of deuterium compounds can be different from the hydrogen analogs; for example, D
2O is more
viscous than H
2O.
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 .
Deuterium can replace the normal hydrogen in water molecules to form heavy water , which is about 10.6% more dense than normal water . Heavy water is modestly 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 . Prokaryotic organisms, however, can survive and grow in pure heavy water . Consumption of heavy water would not pose a health threat to humans unless very large quantities were consumed over many days. Small doses of heavy water are routinely used as harmless metabolic tracers in humans and animals.
The existence of deuterium on Earth, elsewhere in the
solar system , and in the spectra of
stars, is an important datum in cosmology. Stellar fusion destroys deuterium, and there are no known natural processes , 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 favour of the
Big Bang theory over the steady state theory of the universe.
The world's leading "producer" of deuterium is
Canada, in the form of heavy water. Canada uses heavy water as a neutron moderator for the operation of the
CANDU reactor design.
Applications
Deuterium is useful in
nuclear fusion reactions, especially in combination with
tritium, because of the large reaction rate and high
energy yield of the D-T reaction, and in the even higher-yield D-He
3 fusion reaction, though the breakeven is higher than with most other fusion reactions, making it implausible as a practical power source until at least D-T and D-D fusion reactions have been performed. 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 cannot 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. 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 is not "seen" by an NMR instrument tuned to light-hydrogen. Deuterated solvents 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 are enriched as a function of the environmental temperature of the region in which the precipitation falls . The relative enrichment of the heavy isotopes in rainwater , when plotted against temperature falls predictably along a line called the global meteoric water line . 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 .
Deuterium, as large quantities of salted, but otherwise very pure, heavy water, is essential to the operation of the
Sudbury Neutrino Observatory.
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 , could not 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, and first detected in late 1931 by
Harold Urey, a chemist at
Columbia University. Urey
distilled five
liters of cryogenically-produced liquid hydrogen to 1 milliliter of liquid and showed spectroscopically that it contained a very small amount of an isotope of hydrogen with an atomic mass of 2; 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 that it had not noticeably affected previous measurements of 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
During
World War II,
Nazi Germany was known to be conducting experiments using heavy water as moderator for a
nuclear reactor design. Such experiments were a source of concern because they 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 the
Vemork deuterium production/enrichment facility in
Norway.
After World War II ended, the Allies discovered that Germany was not putting as much serious effort into the program as has had been previously thought. The Germans had completed only a small, partly-built experimental reactor . By the end of the war, the Germans did not 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 , they would 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 in both the U.S. and
U.S.S.R, for example .
Data
- density: 0.180 kg/m3 at STP .
- atomic weight: 2.01355321270.
- mean abundance in ocean water about 0.0156 % of H atoms = 1/6400 H atoms.
Data at approximately 18 K for D
2 :
- solid: 195 kg/m3
- gas: 0.452 kg/m3
- viscosity: 1.3 µPa·s
- specific heat capacity at constant pressure cp:
- solid: 2950 J/
- gas: 5200 J/
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 at Brookhaven National Laboratory. A complete atom, with a positron orbiting the nucleus, would be called antideuterium, but as of 2005 antideuterium has not yet been created. The symbol for antideuterium is the same as for deuterium, except with a bar over it.
Appearances in pop culture
- The reactions of matter and antimatter are the basis for warp travel in the Star Trek universe, with deuterium and anti-deuterium being used as a fuel of sorts.
- In the Star Trek episode The City on the Edge of Forever Earth's time-line had been altered by a member of the Enterprise crew, and the German Nazis were "able to complete their heavy water experiments" and win World War II. Captain Kirk and Mr. Spock go back in time to attempt to repair and restore Earth's original time-line.
See also
- Isotopes of hydrogen
- Tritium
- Heavy water
References
