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=                               Helium                               =
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                            Introduction
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{{Redirect|2He|the isotope of helium with two nucleons
({{chem2|^{2}He}})|Helium-2}}



Helium (from ) is a chemical element; it has symbol He and atomic
number 2. It is a colorless, odorless, non-toxic, inert, monatomic gas
and the first in the noble gas group in the periodic table. Its
boiling point is the lowest among all the elements, and it does not
have a melting point at standard pressures. It is the second-lightest
and second-most abundant element in the observable universe, after
hydrogen. It is present at about 24% of the total elemental mass,
which is more than 12 times the mass of all the heavier elements
combined. Its abundance is similar to this in both the Sun and
Jupiter, because of the very high nuclear binding energy (per nucleon)
of helium-4 with respect to the next three elements after helium. This
helium-4 binding energy also accounts for why it is a product of both
nuclear fusion and radioactive decay. The most common isotope of
helium in the universe is helium-4, the vast majority of which was
formed during the Big Bang. Large amounts of new helium are created by
nuclear fusion of hydrogen in stars.

Helium was first detected as an unknown, yellow spectral line
signature in sunlight during a solar eclipse in 1868 by Georges Rayet,
Captain C. T. Haig, Norman R. Pogson, and Lieutenant John Herschel,
and was subsequently confirmed by French astronomer Jules Janssen.In
his initial report to the French Academy of Sciences about the 1868
eclipse, Janssen made no mention of a yellow line in the solar
spectrum. See:
* Janssen (1868)
[https://books.google.com/books?id=hpZDAQAAIAAJ&pg=PA838
"Indication de quelques-uns des résultats obtenus à Cocanada, pendant
l'éclipse du mois d'août dernier, et à la suite de cette éclipse"]
(Information on some of the results obtained at Cocanada, during the
eclipse of the month of last August, and following that eclipse),
'Comptes rendus' ... , 67 : 838-839.
* Wheeler M. Sears, 'Helium: The Disappearing Element' (Heidelberg,
Germany: Springer, 2015),
[https://books.google.com/books?id=5SvABgAAQBAJ&pg=PA44 p. 44.]
* Françoise Launay with Storm Dunlop, trans., 'The Astronomer Jules
Janssen: A Globetrotter of Celestial Physics' (Heidelberg, Germany:
Springer, 2012),
[https://books.google.com/books?id=3YaAup49nqoC&pg=PA45 p. 45.]
However, subsequently, in an unpublished letter of 19 December 1868 to
Charles Sainte-Claire Deville, Janssen asked Deville to inform the
French Academy of Sciences that : "Several observers have claimed the
bright D line as forming part of the spectrum of the prominences on 18
August. The bright yellow line did indeed lie very close to D, but the
light was more refrangible [i.e., of shorter wavelength] than those of
the D lines. My subsequent studies of the Sun have shown the accuracy
of what I state here." (See: (Launay, 2012), p. 45.) Janssen is often
jointly credited with detecting the element, along with Norman
Lockyer. Janssen recorded the helium spectral line during the solar
eclipse of 1868, while Lockyer observed it from Britain. However, only
Lockyer proposed that the line was due to a new element, which he
named after the Sun. The formal discovery of the element was made in
1895 by chemists Sir William Ramsay, Per Teodor Cleve, and Nils
Abraham Langlet, who found helium emanating from the uranium ore
cleveite, which is now not regarded as a separate mineral species, but
as a variety of uraninite. In 1903, large reserves of helium were
found in natural gas fields in parts of the United States, by far the
largest supplier of the gas today.

Liquid helium is used in cryogenics (its largest single use, consuming
about a quarter of production), and in the cooling of superconducting
magnets, with its main commercial application in MRI scanners.
Helium's other industrial uses--as a pressurizing and purge gas, as a
protective atmosphere for arc welding, and in processes such as
growing crystals to make silicon wafers--account for half of the gas
produced. A small but well-known use is as a lifting gas in balloons
and airships. As with any gas whose density differs from that of air,
inhaling a small volume of helium temporarily changes the timbre and
quality of the human voice. In scientific research, the behavior of
the two fluid phases of helium-4 (helium I and helium II) is important
to researchers studying quantum mechanics (in particular the property
of superfluidity) and to those looking at the phenomena, such as
superconductivity, produced in matter near absolute zero.

On Earth, it is relatively rare--5.2 ppm by volume in the atmosphere.
Most terrestrial helium present today is created by the natural
radioactive decay of heavy radioactive elements (thorium and uranium,
although there are other examples), as the alpha particles emitted by
such decays consist of helium-4 nuclei. This radiogenic helium is
trapped with natural gas in concentrations as great as 7% by volume,
from which it is extracted commercially by a low-temperature
separation process called fractional distillation. Terrestrial helium
is a non-renewable resource because once released into the atmosphere,
it promptly escapes into space. Its supply is thought to be rapidly
diminishing. However, some studies suggest that helium produced deep
in the Earth by radioactive decay can collect in natural gas reserves
in larger-than-expected quantities, in some cases having been released
by volcanic activity.


Scientific discoveries
========================
The first evidence of helium was observed on August 18, 1868, as a
bright yellow line with a wavelength of 587.49 nanometers in the
spectrum of the chromosphere of the Sun. The line was detected by
French astronomer Jules Janssen during a total solar eclipse in
Guntur, India. This line was initially assumed to be sodium. On
October 20 of the same year, English astronomer Norman Lockyer
observed a yellow line in the solar spectrum, which he named the D3
because it was near the known D1 and D2 Fraunhofer lines of sodium. He
concluded that it was caused by an element in the Sun unknown on
Earth. Lockyer named the element with the Greek word for the Sun,
ἥλιος ('helios'). It is sometimes said that English chemist Edward
Frankland was also involved in the naming, but this is unlikely as he
doubted the existence of this new element. The ending "-ium" is
unusual, as it normally applies only to metallic elements; probably
Lockyer, being an astronomer, was unaware of the chemical conventions.
In 1881, Italian physicist Luigi Palmieri detected helium on Earth for
the first time through its D3 spectral line, when he analyzed a
material that had been sublimated during a recent eruption of Mount
Vesuvius.

On March 26, 1895, Scottish chemist Sir William Ramsay isolated helium
on Earth by treating the mineral cleveite (a variety of uraninite with
at least 10% rare-earth elements) with mineral acids. Ramsay was
looking for argon but, after separating nitrogen and oxygen from the
gas, liberated by sulfuric acid, he noticed a bright yellow line that
matched the D3 line observed in the spectrum of the Sun. These samples
were identified as helium by Lockyer and British physicist William
Crookes.See:
*
*   It was independently isolated from cleveite in the same year by
chemists Per Teodor Cleve and Abraham Langlet in Uppsala, Sweden, who
collected enough of the gas to accurately determine its atomic
weight.See:
*
*  English translation:
*
*   Helium was also isolated by American geochemist William Francis
Hillebrand prior to Ramsay's discovery, when he noticed unusual
spectral lines while testing a sample of the mineral uraninite.
Hillebrand, however, attributed the lines to nitrogen. His letter of
congratulations to Ramsay offers an interesting case of discovery, and
near-discovery, in science.

In 1907, Ernest Rutherford and Thomas Royds demonstrated that alpha
particles are helium nuclei by allowing the particles to penetrate the
thin glass wall of an evacuated tube, then creating a discharge in the
tube, to study the spectrum of the new gas inside. In 1908, helium was
first liquefied by Dutch physicist Heike Kamerlingh Onnes by cooling
the gas to less than 5 K. He tried to solidify it by further reducing
the temperature but failed, because helium does not solidify at
atmospheric pressure. Onnes' student Willem Hendrik Keesom was
eventually able to solidify 1 cm3 of helium in 1926 by applying
additional external pressure.See:
* Preliminary notice: Keesom, W. H. (17 July 1926) Letters to the
Editor: "Solidification of helium," 'Nature', 118 : 81.
* Preliminary notice: Keesom, W. H. (1926)
[https://archive.org/stream/ComptesRendusAcademieDesSciences0183/ComptesRendusAcadmieDesSciences-Tome183-Juillet-dcembre1926#page/n25/mode/2up
"L'hélium solidifié,"]  'Comptes rendus' ... , 183 : 26.
* Keesom, W. H. (1926) "Solid Helium," 'Communications from the
Physical Laboratory at the University of Leiden', 17 (184) .

In 1913, Niels Bohr published his "trilogy" on atomic structure that
included a reconsideration of the Pickering-Fowler series as central
evidence in support of his model of the atom.  This series is named
for Edward Charles Pickering, who in 1896 published observations of
previously unknown lines in the spectrum of the star ζ Puppis (these
are now known to occur with Wolf-Rayet and other hot stars). Pickering
attributed the observation (lines at 4551, 5411, and 10123 Å) to a new
form of hydrogen with half-integer transition levels. In 1912, Alfred
Fowler managed to produce similar lines from a hydrogen-helium
mixture, and supported Pickering's conclusion as to their origin.
Bohr's model does not allow for half-integer transitions (nor does
quantum mechanics) and Bohr concluded that Pickering and Fowler were
wrong, and instead assigned these spectral lines to ionised helium,
He+. Fowler was initially skeptical but was ultimately convinced that
Bohr was correct, and by 1915 "spectroscopists had transferred [the
Pickering-Fowler series] definitively [from hydrogen] to helium."
Bohr's theoretical work on the Pickering series had demonstrated the
need for "a re-examination of problems that seemed already to have
been solved within classical theories" and provided important
confirmation for his atomic theory.

In 1938, Russian physicist Pyotr Leonidovich Kapitsa discovered that
helium-4 has almost no viscosity at temperatures near absolute zero, a
phenomenon now called superfluidity. This phenomenon is related to
Bose-Einstein condensation. In 1972, the same phenomenon was observed
in helium-3, but at temperatures much closer to absolute zero, by
American physicists Douglas D. Osheroff, David M. Lee, and Robert C.
Richardson. The phenomenon in helium-3 is thought to be related to
pairing of helium-3 fermions to make bosons, in analogy to Cooper
pairs of electrons producing superconductivity.

In 1961, Vignos and Fairbank reported the existence of a different
phase of solid helium-4, designated the gamma-phase. It exists for a
narrow range of pressure between 1.45 and 1.78 K.


Extraction and use
====================
After an oil drilling operation in 1903 in Dexter, Kansas produced a
gas geyser that would not burn, Kansas state geologist Erasmus Haworth
collected samples of the escaping gas and took them back to the
University of Kansas at Lawrence where, with the help of chemists
Hamilton Cady and David McFarland, he discovered that the gas
consisted of, by volume, 72% nitrogen, 15% methane (a combustible
percentage only with sufficient oxygen), 1% hydrogen, and 12% an
unidentifiable gas. With further analysis, Cady and McFarland
discovered that 1.84% of the gas sample was helium. This showed that
despite its overall rarity on Earth, helium was concentrated in large
quantities under the American Great Plains, available for extraction
as a byproduct of natural gas.

Following a suggestion by Sir Richard Threlfall, the United States
Navy sponsored three small experimental helium plants during World War
I. The goal was to supply barrage balloons with the non-flammable,
lighter-than-air gas. A total of 5700 m3 of 92% helium was produced in
the program even though less than a cubic meter of the gas had
previously been obtained. Some of this gas was used in the world's
first helium-filled airship, the U.S. Navy's C-class blimp C-7, which
flew its maiden voyage from Hampton Roads, Virginia, to Bolling Field
in Washington, D.C., on December 1, 1921, nearly two years before the
Navy's first 'rigid' helium-filled airship, the Naval Aircraft
Factory-built USS 'Shenandoah', flew in September 1923.

Although the extraction process using low-temperature gas liquefaction
was not developed in time to be significant during World War I,
production continued. Helium was primarily used as a lifting gas in
lighter-than-air craft. During World War II, the demand increased for
helium for lifting gas and for shielded arc welding. The helium mass
spectrometer was also vital in the atomic bomb Manhattan Project.

The government of the United States set up the National Helium Reserve
in 1925 at Amarillo, Texas, with the goal of supplying military
airships in time of war and commercial airships in peacetime. Because
of the Helium Act of 1925, which banned the export of scarce helium on
which the US then had a production monopoly, together with the
prohibitive cost of the gas, German Zeppelins were forced to use
hydrogen as lifting gas, which would gain infamy in the Hindenburg
disaster. The helium market after World War II was depressed but the
reserve was expanded in the 1950s to ensure a supply of liquid helium
as a coolant to create oxygen/hydrogen rocket fuel (among other uses)
during the Space Race and Cold War. Helium use in the United States in
1965 was more than eight times the peak wartime consumption.

After the Helium Acts Amendments of 1960 (Public Law 86-777), the U.S.
Bureau of Mines arranged for five private plants to recover helium
from natural gas. For this helium conservation program, the Bureau
built a 425 mi pipeline from Bushton, Kansas, to connect those plants
with the government's partially depleted Cliffside gas field near
Amarillo, Texas. This helium-nitrogen mixture was injected and stored
in the Cliffside gas field until needed, at which time it was further
purified.

By 1995, a billion cubic meters of the gas had been collected and the
reserve was US$1.4 billion in debt, prompting the Congress of the
United States in 1996 to discontinue the reserve. The resulting Helium
Privatization Act of 1996 (Public Law 104-273) directed the United
States Department of the Interior to empty the reserve, with sales
starting by 2005.

Helium produced between 1930 and 1945 was about 98.3% pure (2%
nitrogen), which was adequate for airships. In 1945, a small amount of
99.9% helium was produced for welding use. By 1949, commercial
quantities of Grade A 99.95% helium were available.

For many years, the United States produced more than 90% of
commercially usable helium in the world, while extraction plants in
Canada, Poland, Russia, and other nations produced the remainder. In
the mid-1990s, a new plant in Arzew, Algeria, producing 17 e6m3 began
operation, with enough production to cover all of Europe's demand.
Meanwhile, by 2000, the consumption of helium within the U.S. had
risen to more than 15 million kg per year. In 2004-2006, additional
plants in Ras Laffan, Qatar, and Skikda, Algeria were built. Algeria
quickly became the second leading producer of helium. Through this
time, both helium consumption and the costs of producing helium
increased. From 2002 to 2007 helium prices doubled.

, the United States National Helium Reserve accounted for 30 percent
of the world's helium. The reserve was expected to run out of helium
in 2018. Despite that, a proposed bill in the United States Senate
would allow the reserve to continue to sell the gas. Other large
reserves were in the Hugoton in Kansas, United States, and nearby gas
fields of Kansas and the panhandles of Texas and Oklahoma. New helium
plants were scheduled to open in 2012 in Qatar, Russia, and the US
state of Wyoming, but they were not expected to ease the shortage.

In 2013, Qatar started up the world's largest helium unit, although
the 2017 Qatar diplomatic crisis severely affected helium production
there. 2014 was widely acknowledged to be a year of over-supply in the
helium business, following years of renowned shortages. Nasdaq
reported (2015) that for Air Products, an international corporation
that sells gases for industrial use, helium volumes remain under
economic pressure due to feedstock supply constraints.


In quantum mechanics
======================
In the perspective of quantum mechanics, helium is the second simplest
atom to model, following the hydrogen atom. Helium is composed of two
electrons in atomic orbitals surrounding a nucleus containing two
protons and (usually) two neutrons. As in Newtonian mechanics, no
system that consists of more than two particles can be solved with an
exact analytical mathematical approach (see 3-body problem) and helium
is no exception. Thus, numerical mathematical methods are required,
even to solve the system of one nucleus and two electrons. Such
computational chemistry methods have been used to create a quantum
mechanical picture of helium electron binding which is accurate to
within < 2% of the correct value, in a few computational steps.
Such models show that each electron in helium partly screens the
nucleus from the other, so that the effective nuclear charge 'Z'eff
which each electron sees is about 1.69 units, not the 2 charges of a
classic "bare" helium nucleus.


Related stability of the helium-4 nucleus and electron shell
==============================================================
The nucleus of the helium-4 atom is identical with an alpha particle.
High-energy electron-scattering experiments show its charge to
decrease exponentially from a maximum at a central point, exactly as
does the charge density of helium's own electron cloud. This symmetry
reflects similar underlying physics: the pair of neutrons and the pair
of protons in helium's nucleus obey the same quantum mechanical rules
as do helium's pair of electrons (although the nuclear particles are
subject to a different nuclear binding potential), so that all these
fermions fully occupy 1s orbitals in pairs, none of them possessing
orbital angular momentum, and each cancelling the other's intrinsic
spin. This arrangement is thus energetically extremely stable for all
these particles and has astrophysical implications. Namely, adding
another particle - proton, neutron, or alpha particle - would consume
rather than release energy; all systems with mass number 5, as well as
beryllium-8 (comprising two alpha particles), are unbound.

For example, the stability and low energy of the electron cloud state
in helium accounts for the element's chemical inertness, and also the
lack of interaction of helium atoms with each other, producing the
lowest melting and boiling points of all the elements. In a similar
way, the particular energetic stability of the helium-4 nucleus,
produced by similar effects, accounts for the ease of helium-4
production in atomic reactions that involve either heavy-particle
emission or fusion. Some stable helium-3 (two protons and one neutron)
is produced in fusion reactions from hydrogen, though its estimated
abundance in the universe is about  relative to helium-4.

The unusual stability of the helium-4 nucleus is also important
cosmologically: it explains the fact that in the first few minutes
after the Big Bang, as the "soup" of free protons and neutrons which
had initially been created in about 6:1 ratio cooled to the point that
nuclear binding was possible, almost all first compound atomic nuclei
to form were helium-4 nuclei. Owing to the relatively tight binding of
helium-4 nuclei, its production consumed nearly all of the free
neutrons in a few minutes, before they could beta-decay, and thus few
neutrons were available to form heavier atoms such as lithium,
beryllium, or boron. Helium-4 nuclear binding per nucleon is stronger
than in any of these elements (see nucleogenesis and binding energy)
and thus, once helium had been formed, no energetic drive was
available to make elements 3, 4 and 5. It is barely energetically
favorable for helium to fuse into the next element with a lower energy
per nucleon, carbon. However, due to the short lifetime of the
intermediate beryllium-8, this process requires three helium nuclei
striking each other nearly simultaneously (see triple-alpha process).
There was thus no time for significant carbon to be formed in the few
minutes after the Big Bang, before the early expanding universe cooled
to the temperature and pressure point where helium fusion to carbon
was no longer possible. This left the early universe with a very
similar ratio of hydrogen/helium as is observed today (3 parts
hydrogen to 1 part helium-4 by mass), with nearly all the neutrons in
the universe trapped in helium-4.

All heavier elements (including those necessary for rocky planets like
the Earth, and for carbon-based or other life) have thus been created
since the Big Bang in stars which were hot enough to fuse helium
itself. All elements other than hydrogen and helium today account for
only 2% of the mass of atomic matter in the universe. Helium-4, by
contrast, comprises about 24% of the mass of the universe's ordinary
matter--nearly all the ordinary matter that is not hydrogen.


Gas and plasma phases
=======================
Helium is the second least reactive noble gas after neon, and thus the
second least reactive of all elements. It is chemically inert and
monatomic in all standard conditions. Because of helium's relatively
low molar (atomic) mass, its thermal conductivity, specific heat, and
sound speed in the gas phase are all greater than any other gas except
hydrogen. For these reasons and the small size of helium monatomic
molecules, helium diffuses through solids at a rate three times that
of air and around 65% that of hydrogen.

Helium is the least water-soluble monatomic gas, and one of the least
water-soluble of any gas (CF4, SF6, and C4F8 have lower mole fraction
solubilities: 0.3802, 0.4394, and 0.2372 x2/10−5, respectively, versus
helium's 0.70797 x2/10−5), and helium's index of refraction is closer
to unity than that of any other gas. Helium has a negative
Joule-Thomson coefficient at normal ambient temperatures, meaning it
heats up when allowed to freely expand. Only below its Joule-Thomson
inversion temperature (of about 32 to 50 K at 1 atmosphere) does it
cool upon free expansion. Once precooled below this temperature,
helium can be liquefied through expansion cooling.

Most extraterrestrial helium is plasma in stars, with properties quite
different from those of atomic helium. In a plasma, helium's electrons
are not bound to its nucleus, resulting in very high electrical
conductivity, even when the gas is only partially ionized. The charged
particles are highly influenced by magnetic and electric fields. For
example, in the solar wind together with ionized hydrogen, the
particles interact with the Earth's magnetosphere, giving rise to
Birkeland currents and the aurora.


Liquid phase
==============
Helium liquifies when cooled below 4.2 K at atmospheric pressure.
Unlike any other element, however, helium remains liquid down to a
temperature of absolute zero. This is a direct effect of quantum
mechanics: specifically, the zero point energy of the system is too
high to allow freezing. Pressures above about 25 atmospheres are
required to freeze it. There are two liquid phases: Helium I is a
conventional liquid, and Helium II, which occurs at a lower
temperature, is a superfluid.


Helium I
==========
Below its boiling point of 4.22 K and above the lambda point of 2.1768
K, the isotope helium-4 exists in a normal colorless liquid state,
called 'helium I'. Like other cryogenic liquids, helium I boils when
it is heated and contracts when its temperature is lowered. Below the
lambda point, however, helium does not boil, and it expands as the
temperature is lowered further.

Helium I has a gas-like index of refraction of 1.026 which makes its
surface so hard to see that floats of Styrofoam are often used to show
where the surface is. This colorless liquid has a very low viscosity
and a density of 0.145-0.125 g/mL (between about 0 and 4 K), which is
only one-fourth the value expected from classical physics. Quantum
mechanics is needed to explain this property and thus both states of
liquid helium (helium I and helium II) are called 'quantum fluids',
meaning they display atomic properties on a macroscopic scale. This
may be an effect of its boiling point being so close to absolute zero,
preventing random molecular motion (thermal energy) from masking the
atomic properties.


Helium II
===========
Liquid helium below its lambda point (called 'helium II') exhibits
very unusual characteristics. Due to its high thermal conductivity,
when it boils, it does not bubble but rather evaporates directly from
its surface. Helium-3 also has a superfluid phase, but only at much
lower temperatures; as a result, less is known about the properties of
the isotope.

Helium II is a superfluid, a quantum mechanical state of matter with
strange properties. For example, when it flows through capillaries as
thin as 10 to 100 nm it has no measurable viscosity. However, when
measurements were done between two moving discs, a viscosity
comparable to that of gaseous helium was observed. Existing theory
explains this using the 'two-fluid model' for helium II. In this
model, liquid helium below the lambda point is viewed as containing a
proportion of helium atoms in a ground state, which are superfluid and
flow with exactly zero viscosity, and a proportion of helium atoms in
an excited state, which behave more like an ordinary fluid.

In the 'fountain effect', a chamber is constructed which is connected
to a reservoir of helium II by a sintered disc through which
superfluid helium leaks easily but through which non-superfluid helium
cannot pass. If the interior of the container is heated, the
superfluid helium changes to non-superfluid helium. In order to
maintain the equilibrium fraction of superfluid helium, superfluid
helium leaks through and increases the pressure, causing liquid to
fountain out of the container.

The thermal conductivity of helium II is greater than that of any
other known substance, a million times that of helium I and several
hundred times that of copper. This is because heat conduction occurs
by an exceptional quantum mechanism. Most materials that conduct heat
well have a valence band of free electrons which serve to transfer the
heat. Helium II has no such valence band but nevertheless conducts
heat well. The flow of heat is governed by equations that are similar
to the wave equation used to characterize sound propagation in air.
When heat is introduced, it moves at 20 meters per second at 1.8 K
through helium II as waves in a phenomenon known as 'second sound'.

Helium II also exhibits a creeping effect. When a surface extends past
the level of helium II, the helium II moves along the surface, against
the force of gravity. Helium II will escape from a vessel that is not
sealed by creeping along the sides until it reaches a warmer region
where it evaporates. It moves in a 30 nm-thick film regardless of
surface material. This film is called a Rollin film and is named after
the man who first characterized this trait, Bernard V. Rollin. As a
result of this creeping behavior and helium II's ability to leak
rapidly through tiny openings, it is very difficult to confine. Unless
the container is carefully constructed, the helium II will creep along
the surfaces and through valves until it reaches somewhere warmer,
where it will evaporate. Waves propagating across a Rollin film are
governed by the same equation as gravity waves in shallow water, but
rather than gravity, the restoring force is the van der Waals force.
These waves are known as 'third sound'.


Solid phases
==============
Helium remains liquid down to absolute zero at atmospheric pressure,
but it freezes at high pressure. Solid helium requires a temperature
of 1-1.5 K (about −272 °C or −457 °F) at about 25 bar (2.5 MPa) of
pressure. It is often hard to distinguish solid from liquid helium
since the refractive index of the two phases are nearly the same. The
solid has a sharp melting point and has a crystalline structure, but
it is highly compressible; applying pressure in a laboratory can
decrease its volume by more than 30%. With a bulk modulus of about 27
MPa it is ~100 times more compressible than water. Solid helium has a
density of  at 1.15 K and 66 atm; the projected density at 0 K and 25
bar (2.5 MPa) is . At higher temperatures, helium will solidify with
sufficient pressure. At room temperature, this requires about 114,000
atm.

Helium-4 and helium-3 both form several crystalline solid phases, all
requiring at least 25 bar. They both form an α phase, which has a
hexagonal close-packed (hcp) crystal structure, a β phase, which is
face-centered cubic (fcc), and a γ phase, which is body-centered cubic
(bcc).


Isotopes
==========
There are nine known isotopes of helium of which two, helium-3 and
helium-4, are stable. In the Earth's atmosphere, one atom is  for
every million that are . Unlike most elements, helium's isotopic
abundance varies greatly by origin, due to the different formation
processes. The most common isotope, helium-4, is produced on Earth by
alpha decay of heavier radioactive elements; the alpha particles that
emerge are fully ionized helium-4 nuclei. Helium-4 is an unusually
stable nucleus because its nucleons are arranged into complete shells.
It was also formed in enormous quantities during Big Bang
nucleosynthesis.

Helium-3 is present on Earth only in trace amounts. Most of it has
been present since Earth's formation, though some falls to Earth
trapped in cosmic dust. Trace amounts are also produced by the beta
decay of tritium. Rocks from the Earth's crust have isotope ratios
varying by as much as a factor of ten, and these ratios can be used to
investigate the origin of rocks and the composition of the Earth's
mantle.  is much more abundant in stars as a product of nuclear
fusion. Thus in the interstellar medium, the proportion of  to  is
about 100 times higher than on Earth. Extraplanetary material, such as
lunar and asteroid regolith, have trace amounts of helium-3 from being
bombarded by solar winds. The Moon's surface contains helium-3 at
concentrations on the order of 10 ppb, much higher than the
approximately 5 ppt found in the Earth's atmosphere. A number of
people, starting with Gerald Kulcinski in 1986, have proposed to
explore the Moon, mine lunar regolith, and use the helium-3 for
fusion.

Liquid helium-4 can be cooled to about 1 K using evaporative cooling
in a 1-K pot. Similar cooling of helium-3, which has a lower boiling
point, can achieve about  in a helium-3 refrigerator. Equal mixtures
of liquid  and  below  separate into two immiscible phases due to
their dissimilarity (they follow different quantum statistics:
helium-4 atoms are bosons while helium-3 atoms are fermions). Dilution
refrigerators use this immiscibility to achieve temperatures of a few
millikelvins.

It is possible to produce exotic helium isotopes, which rapidly decay
into other substances. The shortest-lived heavy helium isotope is the
unbound helium-10 with a half-life of . Helium-6 decays by emitting a
beta particle and has a half-life of 0.8 second. Helium-7 and helium-8
are created in certain nuclear reactions. Helium-6 and helium-8 are
known to exhibit a nuclear halo.


Properties
============
Table of thermal and physical properties of helium gas at atmospheric
pressure:
|Temperature (K)        |Density (kg/m^3)       |Specific heat (kJ/kg °C)      |Dynamic
viscosity (kg/m s)      |Kinematic viscosity (m^2/s)    |Thermal conductivity
(W/m °C)       |Thermal diffusivity (m^2/s)    |Prandtl number
|100    |5.193  |9.63E-06       |1.98E-05       |0.073  |2.89E-05       |0.686
|120    |0.406  |5.193  |1.07E-05       |2.64E-05       |0.0819 |3.88E-05       |0.679
|144    |0.3379 |5.193  |1.26E-05       |3.71E-05       |0.0928 |5.28E-05       |0.7
|200    |0.2435 |5.193  |1.57E-05       |6.44E-05       |0.1177 |9.29E-05       |0.69
|255    |0.1906 |5.193  |1.82E-05       |9.55E-05       |0.1357 |1.37E-04       |0.7
|366    |0.1328 |5.193  |2.31E-05       |1.74E-04       |0.1691 |2.45E-04       |0.71
|477    |0.10204        |5.193  |2.75E-05       |2.69E-04       |0.197  |3.72E-04       |0.72
|589    |0.08282        |5.193  |3.11E-05       |3.76E-04       |0.225  |5.22E-04       |0.72
|700    |0.07032        |5.193  |3.48E-05       |4.94E-04       |0.251  |6.66E-04       |0.72
|800    |0.06023        |5.193  |3.82E-05       |6.34E-04       |0.275  |8.77E-04       |0.72
|900    |0.05451        |5.193  |4.14E-05       |7.59E-04       |0.33   |1.14E-03       |0.687
|1000   |5.193  |4.46E-05       |9.14E-04       |0.354  |1.40E-03       |0.654


                             Compounds
======================================================================
Helium has a valence of zero and is chemically unreactive under all
normal conditions. It is an electrical insulator unless ionized. As
with the other noble gases, helium has metastable energy levels that
allow it to remain ionized in an electrical discharge with a voltage
below its ionization potential. Helium can form unstable compounds,
known as excimers, with tungsten, iodine, fluorine, sulfur, and
phosphorus when it is subjected to a glow discharge, to electron
bombardment, or reduced to plasma by other means. The molecular
compounds HeNe, HgHe10, and WHe2, and the molecular ions , , , and
have been created this way. HeH+ is also stable in its ground state
but is extremely reactive--it is the strongest Brønsted acid known,
and therefore can exist only in isolation, as it will protonate any
molecule or counteranion it contacts. This technique has also produced
the neutral molecule He2, which has a large number of band systems,
and HgHe, which is apparently held together only by polarization
forces.

Van der Waals compounds of helium can also be formed with cryogenic
helium gas and atoms of some other substance, such as LiHe and He2.

Theoretically, other true compounds may be possible, such as helium
fluorohydride (HHeF), which would be analogous to HArF, discovered in
2000. Calculations show that two new compounds containing a
helium-oxygen bond could be stable. Two new molecular species,
predicted using theory, CsFHeO and N(CH3)4FHeO, are derivatives of a
metastable FHeO− anion first theorized in 2005 by a group from Taiwan.

Helium atoms have been inserted into the hollow carbon cage molecules
(the fullerenes) by heating under high pressure. The endohedral
fullerene molecules formed are stable at high temperatures. When
chemical derivatives of these fullerenes are formed, the helium stays
inside. If helium-3 is used, it can be readily observed by helium
nuclear magnetic resonance spectroscopy. Many fullerenes containing
helium-3 have been reported. Although the helium atoms are not
attached by covalent or ionic bonds, these substances have distinct
properties and a definite composition, like all stoichiometric
chemical compounds.

Under high pressures helium can form compounds with various other
elements. Helium-nitrogen clathrate (He(N2)11) crystals have been
grown at room temperature at pressures ca. 10 GPa in a diamond anvil
cell. The insulating electride Na2He has been shown to be
thermodynamically stable at pressures above 113 GPa. It has a fluorite
structure.


Natural abundance
===================
Although it is rare on Earth, helium is the second most abundant
element in the known Universe, constituting 23% of its baryonic mass.
Only hydrogen is more abundant. The vast majority of helium was formed
by Big Bang nucleosynthesis one to three minutes after the Big Bang.
As such, measurements of its abundance contribute to cosmological
models. In stars, it is formed by the nuclear fusion of hydrogen in
proton-proton chain reactions and the CNO cycle, part of stellar
nucleosynthesis.

In the Earth's atmosphere, the concentration of helium by volume is
only 5.2 parts per million. The concentration is low and fairly
constant despite the continuous production of new helium because most
helium in the Earth's atmosphere escapes into space by several
processes. In the Earth's heterosphere, a part of the upper
atmosphere, helium and hydrogen are the most abundant elements.

Most helium on Earth is a result of radioactive decay. Helium is found
in large amounts in minerals of uranium and thorium, including
uraninite and its varieties cleveite and pitchblende, carnotite and
monazite (a group name; "monazite" usually refers to monazite-(Ce)),
because they emit alpha particles (helium nuclei, He2+) to which
electrons immediately combine as soon as the particle is stopped by
the rock. In this way an estimated 3000 metric tons of helium are
generated per year throughout the lithosphere. In the Earth's crust,
the concentration of helium is 8 parts per billion. In seawater, the
concentration is only 4 parts per trillion. There are also small
amounts in mineral springs, volcanic gas, and meteoric iron. Because
helium is trapped in the subsurface under conditions that also trap
natural gas, the greatest natural concentrations of helium on the
planet are found in natural gas, from which most commercial helium is
extracted. The concentration varies in a broad range from a few ppm to
more than 7% in a small gas field in San Juan County, New Mexico.

, the world's helium reserves were estimated at 31 billion cubic
meters, with a third of that being in Qatar. In 2015 and 2016
additional probable reserves were announced to be under the Rocky
Mountains in North America and in the East African Rift.

The Bureau of Land Management (BLM) has proposed an October 2024 plan
for managing natural resources in western Colorado. The plan involves
closing 543,000 acres to oil and gas leasing while keeping 692,300
acres open. Among the open areas, 165,700 acres have been identified
as suitable for helium recovery. The United States possesses an
estimated 306 billion cubic feet of recoverable helium, sufficient to
meet current consumption rates of 2.15 billion cubic feet per year for
approximately 150 years.


Modern extraction and distribution
====================================
For large-scale use, helium is extracted by fractional distillation
from natural gas, which can contain as much as 7% helium. Since helium
has a lower boiling point than any other element, low temperatures and
high pressure are used to liquefy nearly all the other gases (mostly
nitrogen and methane). The resulting crude helium gas is purified by
successive exposures to lowering temperatures, in which almost all of
the remaining nitrogen and other gases are precipitated out of the
gaseous mixture. Activated charcoal is used as a final purification
step, usually resulting in 99.995% pure Grade-A helium. The principal
impurity in Grade-A helium is neon. In a final production step, most
of the helium that is produced is liquefied via a cryogenic process.
This is necessary for applications requiring liquid helium and also
allows helium suppliers to reduce the cost of long-distance
transportation, as the largest liquid helium containers have more than
five times the capacity of the largest gaseous helium tube trailers.

In 2008, approximately 169 million standard cubic meters (SCM) of
helium were extracted from natural gas or withdrawn from helium
reserves, with approximately 78% from the United States, 10% from
Algeria, and most of the remainder from Russia, Poland, and Qatar. By
2013, increases in helium production in Qatar (under the company
Qatargas managed by Air Liquide) had increased Qatar's fraction of
world helium production to 25%, making it the second largest exporter
after the United States.
An estimated 54 e9ft3 deposit of helium was found in Tanzania in 2016.
A large-scale helium plant was opened in Ningxia, China in 2020.

In the United States, most helium is extracted from the natural gas of
the Hugoton and nearby gas fields in Kansas, Oklahoma, and the
Panhandle Field in Texas. Much of this gas was once sent by pipeline
to the National Helium Reserve, but since 2005, this reserve has been
depleted and sold off, and it is expected to be largely depleted by
2021 under the October 2013 'Responsible Helium Administration and
Stewardship Act' (H.R. 527). The helium fields of the western United
States are emerging as an alternate source of helium supply,
particularly those of the "Four Corners" region (the states of
Arizona, Colorado, New Mexico and Utah).

Diffusion of crude natural gas through special semipermeable membranes
and other barriers is another method to recover and purify helium. In
1996, the U.S. had 'proven' helium reserves in such gas well complexes
of about 147 billion standard cubic feet (4.2 billion SCM). At rates
of use at that time (72 million SCM per year in the U.S.; see pie
chart below) this would have been enough helium for about 58 years of
U.S. use, and less than this (perhaps 80% of the time) at world use
rates, although factors in saving and processing impact effective
reserve numbers.

Helium is generally extracted from natural gas because it is present
in air at only a fraction of that of neon, yet the demand for it is
far higher. It is estimated that if all neon production were retooled
to save helium, 0.1% of the world's helium demands would be satisfied.
Similarly, only 1% of the world's helium demands could be satisfied by
re-tooling all air distillation plants. Helium can be synthesized by
bombardment of lithium or boron with high-velocity protons, or by
bombardment of lithium with deuterons, but these processes are a
completely uneconomical method of production.

Helium is commercially available in either liquid or gaseous form. As
a liquid, it can be supplied in small insulated containers called
dewars which hold as much as 1,000 liters of helium, or in large ISO
containers, which have nominal capacities as large as 42 m3 (around
11,000 U.S. gallons). In gaseous form, small quantities of helium are
supplied in high-pressure cylinders holding as much as 8 m3
(approximately . 282 standard cubic feet), while large quantities of
high-pressure gas are supplied in tube trailers, which have capacities
of as much as 4,860 m3 (approx. 172,000 standard cubic feet).


Conservation advocates
========================
According to helium conservationists like Nobel laureate physicist
Robert Coleman Richardson, writing in 2010, the free market price of
helium has contributed to "wasteful" usage (e.g. for helium balloons).
Prices in the 2000s had been lowered by the decision of the U.S.
Congress to sell off the country's large helium stockpile by 2015.
According to Richardson, the price needed to be multiplied by 20 to
eliminate the excessive wasting of helium. In the 2012 Nuttall et al.
paper titled "Stop squandering helium", it was also proposed to create
an International Helium Agency that would build a sustainable market
for "this precious commodity".


                            Applications
======================================================================
While balloons are perhaps the best-known use of helium, they are a
minor part of all helium use. Helium is used for many purposes that
require some of its unique properties, such as its low boiling point,
low density, low solubility, high thermal conductivity, or inertness.
Of the 2014 world helium total production of about 32 million kg (180
million standard cubic meters) helium per year, the largest use (about
32% of the total in 2014) is in cryogenic applications, most of which
involves cooling the superconducting magnets in medical MRI scanners
and NMR spectrometers. Other major uses were pressurizing and purging
systems, welding, maintenance of controlled atmospheres, and leak
detection. Other uses by category were relatively minor fractions.


Controlled atmospheres
========================
Helium is used as a protective gas in growing silicon and germanium
crystals, in titanium and zirconium production, and in gas
chromatography, because it is inert. Because of its inertness,
thermally and calorically perfect nature, high speed of sound, and
high value of the heat capacity ratio, it is also useful in supersonic
wind tunnels and impulse facilities.


Gas tungsten arc welding
==========================
Helium is used as a shielding gas in arc welding processes on
materials that are contaminated and weakened by air or nitrogen at
welding temperatures. A number of inert shielding gases are used in
gas tungsten arc welding, but helium is used instead of cheaper argon
especially for welding materials that have higher heat conductivity,
like aluminium or copper.


Industrial leak detection
===========================
One industrial application for helium is leak detection. Because
helium diffuses through solids three times faster than air, it is used
as a tracer gas to detect leaks in high-vacuum equipment (such as
cryogenic tanks) and high-pressure containers. The tested object is
placed in a chamber, which is then evacuated and filled with helium.
The helium that escapes through the leaks is detected by a sensitive
device (helium mass spectrometer), even at the leak rates as small as
10−9 mbar·L/s (10−10 Pa·m3/s). The measurement procedure is normally
automatic and is called helium integral test. A simpler procedure is
to fill the tested object with helium and to manually search for leaks
with a hand-held device.

Helium leaks through cracks should not be confused with gas permeation
through a bulk material. While helium has documented permeation
constants (thus a calculable permeation rate) through glasses,
ceramics, and synthetic materials, inert gases such as helium will not
permeate most bulk metals.


Flight
========
Because it is lighter than air, airships and balloons are inflated
with helium for lift. While hydrogen gas is more buoyant and escapes
permeating through a membrane at a lower rate, helium has the
advantage of being non-flammable, and indeed fire-retardant. Another
minor use is in rocketry, where helium is used as an ullage medium to
backfill rocket propellant tanks in flight and to condense hydrogen
and oxygen to make rocket fuel. It is also used to purge fuel and
oxidizer from ground support equipment prior to launch and to pre-cool
liquid hydrogen in space vehicles. For example, the Saturn V rocket
used in the Apollo program needed about 370,000 m3 of helium to
launch.


Minor commercial and recreational uses
========================================
Helium as a breathing gas has no narcotic properties, so helium
mixtures such as trimix, heliox and heliair are used for deep diving
to reduce the effects of narcosis, which worsen with increasing depth.
As pressure increases with depth, the density of the breathing gas
also increases, and the low molecular weight of helium is found to
considerably reduce the effort of breathing by lowering the density of
the mixture. This reduces the Reynolds number of flow, leading to a
reduction of turbulent flow and an increase in laminar flow, which
requires less breathing. At depths below 150 m divers breathing
helium-oxygen mixtures begin to experience tremors and a decrease in
psychomotor function, symptoms of high-pressure nervous syndrome. This
effect may be countered to some extent by adding an amount of narcotic
gas such as hydrogen or nitrogen to a helium-oxygen mixture.

Helium-neon lasers, a type of low-powered gas laser producing a red
beam, had various practical applications which included barcode
readers and laser pointers, before they were almost universally
replaced by cheaper diode lasers.

For its inertness and high thermal conductivity, neutron transparency,
and because it does not form radioactive isotopes under reactor
conditions, helium is used as a heat-transfer medium in some
gas-cooled nuclear reactors.

Helium, mixed with a heavier gas such as xenon, is useful for
thermoacoustic refrigeration due to the resulting high heat capacity
ratio and low Prandtl number. The inertness of helium has
environmental advantages over conventional refrigeration systems which
contribute to ozone depletion or global warming.

Helium is also used in some hard disk drives.


Scientific uses
=================
The use of helium reduces the distorting effects of temperature
variations in the space between lenses in some telescopes due to its
extremely low index of refraction. This method is especially used in
solar telescopes where a vacuum tight telescope tube would be too
heavy.

Helium is a commonly used carrier gas for gas chromatography.

The age of rocks and minerals that contain uranium and thorium can be
estimated by measuring the level of helium with a process known as
helium dating.

Helium at low temperatures is used in cryogenics and in certain
cryogenic applications. As examples of applications, liquid helium is
used to cool certain metals to the extremely low temperatures required
for superconductivity, such as in superconducting magnets for magnetic
resonance imaging. The Large Hadron Collider at CERN uses 96 metric
tons of liquid helium to maintain the temperature at 1.9 K.


Medical uses
==============
Helium was approved for medical use in the United States in April 2020
for humans and animals.


                          As a contaminant
======================================================================
While chemically inert, helium contamination impairs the operation of
microelectromechanical systems (MEMS) such that iPhones may fail.


Effects
=========
Neutral helium at standard conditions is non-toxic, plays no
biological role and is found in trace amounts in human blood.


The speed of sound in helium is nearly three times the speed of sound
in air. Because the natural resonance frequency of a gas-filled cavity
is proportional to the speed of sound in the gas, when helium is
inhaled, a corresponding increase occurs in the resonant frequencies
of the vocal tract, which is the amplifier of vocal sound. This
increase in the resonant frequency of the amplifier (the vocal tract)
gives increased amplification to the high-frequency components of the
sound wave produced by the direct vibration of the vocal folds,
compared to the case when the voice box is filled with air. When a
person speaks after inhaling helium gas, the muscles that control the
voice box still move in the same way as when the voice box is filled
with air; therefore the fundamental frequency (sometimes called pitch)
produced by direct vibration of the vocal folds does not change.
However, the high-frequency-preferred amplification causes a change in
timbre of the amplified sound, resulting in a reedy, duck-like vocal
quality. The opposite effect, lowering resonant frequencies, can be
obtained by inhaling a dense gas such as sulfur hexafluoride or xenon.


Hazards
=========
Inhaling helium can be dangerous if done to excess, since helium is a
simple asphyxiant and so displaces oxygen needed for normal
respiration. Fatalities have been recorded, including a youth who
suffocated in Vancouver in 2003 and two adults who suffocated in South
Florida in 2006. In 1998, an Australian girl from Victoria fell
unconscious and temporarily turned blue after inhaling the entire
contents of a party balloon.
Inhaling helium directly from pressurized cylinders or even balloon
filling valves is extremely dangerous, as high flow rate and pressure
can result in barotrauma, fatally rupturing lung tissue.

Death caused by helium is rare. The first media-recorded case was that
of a 15-year-old girl from Texas who died in 1998 from helium
inhalation at a friend's party; the exact type of helium death is
unidentified.

In the United States, only two fatalities were reported between 2000
and 2004, including a man who died in North Carolina of barotrauma in
2002. A youth asphyxiated in Vancouver during 2003, and a 27-year-old
man in Australia had an embolism after breathing from a cylinder in
2000. Since then, two adults asphyxiated in South Florida in 2006, and
there were cases in 2009 and 2010, one of whom was a Californian youth
who was found with a bag over his head, attached to a helium tank, and
another teenager in Northern Ireland died of asphyxiation. At Eagle
Point, Oregon a teenage girl died in 2012 from barotrauma at a party.
A girl from Michigan died from hypoxia later in the year.

On February 4, 2015, it was revealed that, during the recording of
their main TV show on January 28, a 12-year-old member (name withheld)
of Japanese all-girl singing group 3B Junior suffered from air
embolism, losing consciousness and falling into a coma as a result of
air bubbles blocking the flow of blood to the brain after inhaling
huge quantities of helium as part of a game. The incident was not made
public until a week later. The staff of TV Asahi held an emergency
press conference to communicate that the member had been taken to the
hospital and is showing signs of rehabilitation such as moving eyes
and limbs, but her consciousness has not yet been sufficiently
recovered. Police have launched an investigation due to a neglect of
safety measures.

The safety issues for cryogenic helium are similar to those of liquid
nitrogen; its extremely low temperatures can result in cold burns, and
the liquid-to-gas expansion ratio can cause explosions if no
pressure-relief devices are installed. Containers of helium gas at 5
to 10 K should be handled as if they contain liquid helium due to the
rapid and significant thermal expansion that occurs when helium gas at
less than 10 K is warmed to room temperature.

At high pressures (more than about 20 atm or two MPa), a mixture of
helium and oxygen (heliox) can lead to high-pressure nervous syndrome,
a sort of reverse-anesthetic effect; adding a small amount of nitrogen
to the mixture can alleviate the problem.


                              See also
======================================================================
* Abiogenic petroleum origin
* Helium-3 propulsion
* Leidenfrost effect
* Superfluid
* Tracer-gas leak testing method
* Hamilton Cady


                           External links
======================================================================
General
*
[https://web.archive.org/web/20080725060842/http://www.blm.gov/wo/st/en/info/newsroom/2007/january/NR0701_2.html
U.S. Government's Bureau of Land Management: Sources, Refinement, and
Shortage.] With some history of helium.
* [http://minerals.usgs.gov/minerals/pubs/commodity/helium/ U.S.
Geological Survey publications on helium] beginning 1996:
[http://minerals.usgs.gov/minerals/pubs/commodity/helium/mcs-2012-heliu.pdf
Helium]
*
[https://web.archive.org/web/20121110030719/http://www.aga.com/international/web/lg/aga/like35agacom.nsf/0/BEF74B49AFC3099DC1257A2200473157
Where is all the helium?] Aga website
* [http://education.jlab.org/itselemental/ele002.html It's Elemental -
Helium]
* [http://www.rsc.org/chemistryworld/podcast/element.asp Chemistry in
its element podcast] (MP3) from the Royal Society of Chemistry's
Chemistry World:
[http://www.rsc.org/images/CIIE_Helium_48kbps_tcm18-133173.mp3 Helium]
*
[https://web.archive.org/web/20170709192820/https://www.cdc.gov/niosh/ipcsneng/neng0603.html
International Chemical Safety Cards - Helium] includes health and
safety information regarding accidental exposures to helium

More detail
* [http://www.periodicvideos.com/videos/002.htm Helium] at 'The
Periodic Table of Videos' (University of Nottingham)
* [http://boojum.hut.fi/research/theory/helium.html Helium]  at the
Helsinki University of Technology; includes pressure-temperature phase
diagrams for helium-3 and helium-4
* [http://www.physics.lancs.ac.uk/research/condmatt/ult/index.htm
Lancaster University, Ultra Low Temperature Physics] - includes a
summary of some low temperature techniques
*Video: [http://www.alfredleitner.com/p/liquid-helium.html
Demonstration of superfluid helium] (Alfred Leitner, 1963, 38 min.)

Miscellaneous
*
[https://web.archive.org/web/20041210113812/http://www.phys.unsw.edu.au/PHYSICS_!/SPEECH_HELIUM/speech.html
Physics in Speech] with audio samples that demonstrate the unchanged
voice pitch
*
[https://web.archive.org/web/20050904191641/http://du.edu/~jcalvert/phys/helium.htm
Article about helium and other noble gases]

Helium shortage
* [https://purl.fdlp.gov/GPO/gpo41438 America's Helium Supply: Options
for Producing More Helium from Federal Land: Oversight Hearing before
the Subcommittee on Energy and Mineral Resources of the Committee on
Natural Resources, U.S. House Of Representatives, One Hundred
Thirteenth Congress, First Session, Thursday, July 11, 2013]
* [https://purl.fdlp.gov/GPO/gpo35149 Helium Program: Urgent Issues
Facing BLM's Storage and Sale of Helium Reserves: Testimony before the
Committee on Natural Resources, House of Representatives] Government
Accountability Office
*
*


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