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Helium (from el, ἥλιος,
helios Helios; Homeric Greek: ), Latinized as Helius; Hyperion and Phaethon are also the names of his father and son respectively. often given the epithets Hyperion ("the one above") and Phaethon ("the shining"), is the deity, god and personification o ...

helios
, lit=sun) is a
chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elements cannot be broken down into simp ...
with the
symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning (linguistics), m ...
He and
atomic number 300px, The Rutherford–Bohr model of the hydrogen atom () or a hydrogen-like ion (). In this model it is an essential feature that the photon energy (or frequency) of the electromagnetic radiation emitted (shown) when an electron jumps from one ...
2. It is a colorless, odorless, tasteless, non-toxic, inert,
monatomic In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "Phy ...
gas Gas is one of the four fundamental states of matter In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space ...

gas
, the first in the
noble gas The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under Standard conditions for temperature and pressure, standard conditions, they are all odorl ...
group in the
periodic table The periodic table, also known as the periodic table of (the) chemical elements, is a tabular display of the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is ...

periodic table
. Its boiling and melting point are the lowest among all the elements. Helium is the second lightest and second most abundant element in the observable
universe The universe ( la, universus) is all of space and time and their contents, including planets, stars, galaxy, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development ...

universe
(
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
is the lightest and most abundant). 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 The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
and in
Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant A gas giant is a giant planet composed mainly of hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and at ...

Jupiter
. This is due to the very high
nuclear binding energy Nuclear binding energy in experimental physics is the minimum energy that is required to disassemble the atomic nucleus, nucleus of an atom into its constituent protons and neutrons, known collectively as nucleons. The binding energy for stable n ...
(per
nucleon In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
) of
helium-4 Helium-4 () is a stable isotope of the element helium. It is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consists ...

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 Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products ...

nuclear fusion
and
radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

radioactive decay
. Most helium in the universe is helium-4, the vast majority of which was formed during the
Big Bang The Big Bang is the prevailing of the from the through its subsequent large-scale evolution. The model describes how the from an initial state of high and , and offers a comprehensive explanation for a broad range of observed phenomen ...

Big Bang
. Large amounts of new helium are being created by nuclear fusion of hydrogen in
stars A star is an astronomical object consisting of a luminous spheroid of plasma held together by its own gravity. The nearest star to Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. ...

stars
. Helium was first detected as an unknown, yellow
spectral line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spect ...
signature in sunlight, during a solar eclipse in 1868 by
Georges Rayet Image:Rayet Georges A Pons.jpg, Georges Antoine Pons Rayet Georges-Antoine-Pons Rayet (12 December 1839 – 14 June 1906) was a France, French astronomer. He was born in Bordeaux, France. He began working at the Paris Observatory in 1863. He ...
, Captain C. T. Haig, Norman R. Pogson, and Lieutenant John Herschel, and was subsequently confirmed by French astronomer,
Jules Janssen Pierre Jules César Janssen (22 February 1824 – 23 December 1907), also known as Jules Janssen, was a French astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outsi ...

Jules Janssen
. Janssen is often jointly credited with detecting the element, along with
Norman Lockyer Sir Joseph Norman Lockyer (17 May 1836 – 16 August 1920) was an English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, ...
. Janssen recorded the helium spectral line during the solar eclipse of 1868, while Lockyer observed it from Britain. Lockyer was the first to propose that the line was due to a new element, which he named. The formal discovery of the element was made in 1895 by chemists
Sir William Ramsay Sir William Ramsay (; 2 October 1852 – 23 July 1916) was a Scottish chemist who discovered the noble gases and received the Nobel Prize in Chemistry in 1904 "in recognition of his services in the discovery of the inert gaseous elements ...
,
Per Teodor Cleve Per Teodor Cleve (10 February 1840 – 18 June 1905) was a Swedish chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist A scientist is a person who conducts Scientific ...

Per Teodor Cleve
, and
Nils Abraham Langlet Nils Abraham Langlet (9 July 1868 – 30 March 1936; known by his second given name) was a Sweden, Swedish chemistry, chemist. Biography Langlet was born in Södertälje, Sweden. He was the son of architect Emil Victor Langlet (1824–1898) and hi ...
, who found helium emanating from the
uranium Uranium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

uranium
ore ore – psilomelane Psilomelane is a group name for hard black manganese oxides including hollandite and romanechite. Psilomelane consists of hydrous manganese Manganese is a chemical element Image:Simple Periodic Table Chart- ...

ore
, ''
cleveite Cleveite is an impure radioactivity, radioactive variety of uraninite containing uranium, found in Norway. It has the composition Uranium dioxide, UO2 with about 10% of the uranium substituted by rare-earth elements. It was named after Swedish chemi ...
'', 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 field A petroleum reservoir or oil and gas reservoir is a subsurface pool of hydrocarbon In organic chemistry, a hydrocarbon is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any che ...
s in parts of the United States, which is by far the largest supplier of the gas today. Liquid helium is used in
cryogenics In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regula ...
(its largest single use, absorbing about a quarter of production), and in the
cooling Cooling is removal of heat, usually resulting in a lower temperature and/or phase change. Temperature lowering achieved by any other means may also be called cooling.ASHRAE Terminology, https://www.ashrae.org/technical-resources/free-resources/ashra ...
of
superconducting magnet A superconducting magnet is an electromagnet An electromagnet is a type of magnet A magnet is a material or object that produces a magnetic field A magnetic field is a vector field In vector calculus and physics, a vector f ...
s, with the main commercial application being in
MRI Magnetic resonance imaging (MRI) is a medical imaging Medical imaging is the technique and process of imaging Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of a ...

MRI
scanners. Helium's other industrial uses—as a pressurizing and purge gas, as a protective atmosphere for
arc welding Arc welding is a welding Welding is a process that joins materials, usually s or s, by using high to melt the parts together and allowing them to cool, causing . Welding is distinct from lower temperature metal-joining techniques such as ...
, and in processes such as growing crystals to make
silicon wafer In electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses active devices to control electron flow by amplifier, amplificat ...

silicon wafer
s—account for half of the gas produced. A well-known but minor use is as a
lifting gas A lifting gas or lighter than air gas is a gas that has a lower density than normal atmospheric gases and rises above them as a result. It is required for aerostats An aerostat (From Greek Greek may refer to: Greece Anything of, from, or rel ...
in
balloon A balloon is a flexible bag that can be inflated with a gas, such as helium Helium (from el, ἥλιος, helios Helios; Homeric Greek: ), Latinized as Helius; Hyperion and Phaethon are also the names of his father and son respectiv ...

balloon
s and
airship An airship, dirigible balloon or blimp is a type of aerostat An aerostat (From greek language, Greek ἀήρ ''aer'' (air) + στατός ''statos'' (standing) through French) is a lighter than air aircraft that gains its lift through the ...

airship
s. 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 The human voice consists of sound In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such ...
. 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 Quantum mechanics is a fundamental theory A theory is a reason, rational type of abstraction, abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with ...
(in particular the property of
superfluidity File:Liquid helium Rollin film.jpg, The liquid helium is in the superfluid phase. A thin invisible film creeps up the inside wall of the bowl and down on the outside. A drop forms. It will fall off into the liquid helium below. This will repeat unt ...
) and to those looking at the phenomena, such as
superconductivity Superconductivity is a set of physical properties observed in certain materials where electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current An electric current is a st ...

superconductivity
, produced in
matter In classical physics Classical physics is a group of physics theories that predate modern, more complete, or more widely applicable theories. If a currently accepted theory is considered to be modern, and its introduction represented a major ...
near
absolute zero Absolute zero is the lowest limit of the thermodynamic temperature Thermodynamic temperature is the measure of ''absolute temperature'' and is one of the principal parameters of thermodynamics. A thermodynamic temperature reading of zero deno ...
. On Earth, it is relatively rare—5.2 ppm by volume in the
atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gases surrounding a planet or other material body, that is held in ...

atmosphere
. Most terrestrial helium present today is created by the natural
radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

radioactive decay
of heavy radioactive elements (
thorium Thorium is a weakly radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nucleus is the sma ...

thorium
and
uranium Uranium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

uranium
, although there are other examples), as the
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Proto ...

alpha particle
s emitted by such decays consist of helium-4
nuclei ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...
. This
radiogenic A radiogenic nuclide is a nuclide A nuclide (or nucleide, from nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a ...
helium is trapped with
natural gas Natural gas (also called fossil gas; sometimes just gas) is a naturally occurring hydrocarbon gas mixture consisting of methane and commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxid ...

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 Fractional distillation is the separation of a mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matt ...
. Previously, terrestrial helium—a non-renewable resource because once released into the atmosphere, it promptly escapes into space—was thought to be in increasingly short supply. However, recent 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.


History


Scientific discoveries

The first evidence of helium was observed on August 18, 1868, as a bright yellow line with a
wavelength In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular su ...

wavelength
of 587.49 nanometers in the
spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum Continuum may refer to: * Continuum (measurement) Continuum theories or models expla ...
of the
chromosphere The chromosphere ("sphere of color") is the second of the three main layers in the Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gra ...

chromosphere
of the
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
. The line was detected by French astronomer
Jules Janssen Pierre Jules César Janssen (22 February 1824 – 23 December 1907), also known as Jules Janssen, was a French astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outsi ...

Jules Janssen
during a total solar eclipse in
Guntur Guntur () is a city and the administrative headquarters of Guntur district Guntur district is one of the nine districts in the Coastal Andhra Coastal Andhra (') is a region in the state of Andhra Pradesh, India. It was part of Madra ...

Guntur
, India. This line was initially assumed to be
sodium Sodium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical eleme ...

sodium
. On October 20 of the same year, English astronomer,
Norman Lockyer Sir Joseph Norman Lockyer (17 May 1836 – 16 August 1920) was an English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, ...
, observed a yellow line in the solar spectrum, which, he named the D3 because it was near the known D1 and D2
Fraunhofer line (nm). Dips in intensity are observed as dark lines (absorption) at the wavelengths of the Fraunhofer lines, (e.g., the features G, F, b, E, B). The "spectrum of ''blue sky''" presents across 450 – 485 nm, the wavelengths of the color ''blue''. In ...
lines of sodium. He concluded that it was caused by an element in the Sun unknown on Earth. Lockyer and English chemist
Edward Frankland Sir Edward Frankland, (18 January 18259 August 1899) was an United Kingdom of Great Britain and Ireland, English chemist. He was one of the originators of organometallic chemistry and introduced the concept of combining power or valence (chemi ...

Edward Frankland
named the element with the Greek word for the Sun, ἥλιος (''
helios Helios; Homeric Greek: ), Latinized as Helius; Hyperion and Phaethon are also the names of his father and son respectively. often given the epithets Hyperion ("the one above") and Phaethon ("the shining"), is the deity, god and personification o ...

helios
''). In 1881, Italian physicist
Luigi Palmieri Luigi Palmieri (22 April 1807 – 9 September 1896) was an Italian physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branches of science, area of inte ...

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 Mount Vesuvius ( ; it, Vesuvio ; nap, 'O Vesuvio , also or ; la, Vesuvius , also , or ) is a somma A somma volcano (also known as a sommian) is a volcano, volcanic caldera that has been partially filled by a new central volcanic cone, ...
. On March 26, 1895, Scottish chemist
Sir William Ramsay Sir William Ramsay (; 2 October 1852 – 23 July 1916) was a Scottish chemist who discovered the noble gases and received the Nobel Prize in Chemistry in 1904 "in recognition of his services in the discovery of the inert gaseous elements ...

Sir William Ramsay
isolated helium on Earth by treating the mineral
cleveite Cleveite is an impure radioactivity, radioactive variety of uraninite containing uranium, found in Norway. It has the composition Uranium dioxide, UO2 with about 10% of the uranium substituted by rare-earth elements. It was named after Swedish chemi ...
(a variety of
uraninite Uraninite, formerly pitchblende, is a radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nuc ...
with at least 10%
rare-earth elements The rare-earth elements, also called the rare-earth metals or (in context) rare-earth oxides, or the lanthanide The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical element Image:Simple Period ...
) with mineral
acid An acid is a or capable of donating a (hydrogen ion H+) (a ), or, alternatively, capable of forming a with an (a ). The first category of acids are the proton donors, or s. In the special case of , proton donors form the H3O+ and are ...
s. Ramsay was looking for
argon Argon is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

argon
but, after separating
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
and
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
from the gas, liberated by
sulfuric acid Sulfuric acid (American spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography English orthogra ...

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 Sir William Crookes (; 17 June 1832 – 4 April 1919) was a English people, British chemist and physicist who attended the Royal College of Chemistry in London, and worked on spectroscopy. He was a pioneer of vacuum tubes, inventing the Crookes t ...
. It was independently isolated from cleveite, in the same year, by chemists,
Per Teodor Cleve Per Teodor Cleve (10 February 1840 – 18 June 1905) was a Swedish chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist A scientist is a person who conducts Scientific ...

Per Teodor Cleve
and
Abraham Langlet Nils Abraham Langlet (9 July 1868 – 30 March 1936; known by his second given name) was a Swedish chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist A scientist is a ...
, in
Uppsala Uppsala (, or all ending in , ; archaically spelled ''Upsala'') is the county seat of Uppsala County Uppsala County ( sv, Uppsala län) is a county A county is a geographical region of a country used for administrative or other purposesC ...

Uppsala
, Sweden, who collected enough of the gas to accurately determine its
atomic weight Relative atomic mass (symbol: ''A'') or atomic weight is a dimensionless physical quantity A physical quantity is a physical property of a material or system that can be Quantification (science), quantified by measurement. A physical quantity ...
. Helium was also isolated by the 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 Ernest Rutherford, 1st Baron Rutherford of Nelson, (30 August 1871 – 19 October 1937) was a New Zealand-born British physicist A physicist is a scientist A scientist is a person who conducts scientific research The sci ...
and Thomas Royds demonstrated that
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Proto ...

alpha particle
s are helium
nuclei ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...
, 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 Heike Kamerlingh Onnes (21 September 1853 – 21 February 1926) was a Dutch physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branches of science, are ...
by cooling the gas to less than . 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 Willem Hendrik Keesom () (21 June 1876, Texel Texel (; Texels dialect: ) is a municipality A municipality is usually a single administrative division having Municipal corporation, corporate status and powers of self-government or jurisdic ...
was eventually able to solidify 1 cm3 of helium in 1926 by applying additional external pressure. In 1913,
Niels Bohr Niels Henrik David Bohr (; 7 October 1885 – 18 November 1962) was a Danish Danish may refer to: * Something of, from, or related to the country of Denmark * A national or citizen of Denmark, also called a "Dane", see Demographics of D ...

Niels Bohr
published his "trilogy" on atomic structure that included a reconsideration of the Pickering–Fowler series as central evidence in support of his . This series is named for
Edward Charles Pickering Edward Charles Pickering (July 19, 1846 – February 3, 1919) was an American astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe ...

Edward Charles Pickering
, who in 1896 published observations of previously unknown lines in the spectrum of the star (these are now known to occur with Wolf–Rayet and other hot stars). Pickering attributed the observation (lines at 4551, 5411, and 10123 ) to a new form of hydrogen with half-integer transition levels. In 1912,
Alfred Fowler Alfred Fowler, CBE FRS (22 March 1868, in Yorkshire Yorkshire (; abbreviated Yorks), formally known as the County of York, is a Historic counties of England, historic county of Northern England and the largest in the United Kingdom. Becau ...

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 he Pickering–Fowler seriesdefinitively rom hydrogento 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 Helium-4 () is a stable isotope of the element helium. It is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consists ...

helium-4
has almost no
viscosity The viscosity of a fluid In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, ...

viscosity
at temperatures near
absolute zero Absolute zero is the lowest limit of the thermodynamic temperature Thermodynamic temperature is the measure of ''absolute temperature'' and is one of the principal parameters of thermodynamics. A thermodynamic temperature reading of zero deno ...
, a phenomenon now called
superfluidity File:Liquid helium Rollin film.jpg, The liquid helium is in the superfluid phase. A thin invisible film creeps up the inside wall of the bowl and down on the outside. A drop forms. It will fall off into the liquid helium below. This will repeat unt ...
. This phenomenon is related to
Bose–Einstein condensationBose–Einstein may refer to any of the following related topics: *Bose–Einstein condensate **Bose–Einstein condensation (network theory) *Bose–Einstein correlations *Bose–Einstein statistics {{disambiguation ...
. In 1972, the same phenomenon was observed in
helium-3 Helium-3 (3He see also helion) is a light, stable isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons A proton is a subatomic particle, symbol or , with a positive electric charge Ele ...

helium-3
, but at temperatures much closer to absolute zero, by American physicists Douglas D. Osheroff, David M. Lee, and . The phenomenon in helium-3 is thought to be related to pairing of helium-3
fermion In particle physics, a fermion is a particle that follows Fermi–Dirac statistics and generally has half odd integer spin: spin 1/2, Spin (physics)#Higher spins, spin 3/2, etc. These particles obey the Pauli exclusion principle. Fermions include ...
s to make
boson In quantum mechanics Quantum mechanics is a fundamental theory A theory is a reason, rational type of abstraction, abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinkin ...

boson
s, in analogy to
Cooper pairs In condensed matter physics Condensed matter physics is the field of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that s ...

Cooper pairs
of electrons producing
superconductivity Superconductivity is a set of physical properties observed in certain materials where electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current An electric current is a st ...

superconductivity
.


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 The University of Kansas (KU) is a with its main campus in , United States, and several satellite campuses, research and educational centers, medical centers, and classes across the state of Kansas. Two branch campuses are in the on the Kans ...
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 Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
, 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 Natural gas (also called fossil gas; sometimes just gas) is a naturally occurring hydrocarbon gas mixture consisting of methane and commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxid ...

natural gas
. This enabled the United States to become the world's leading supplier of helium. 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 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 (ZR-1), ''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 A lifting gas or lighter than air gas is a gas that has a lower density than normal atmospheric gases and rises above them as a result. It is required for aerostats An aerostat (From Greek Greek may refer to: Greece Anything of, from, or rel ...
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
airship An airship, dirigible balloon or blimp is a type of aerostat An aerostat (From greek language, Greek ἀήρ ''aer'' (air) + στατός ''statos'' (standing) through French) is a lighter than air aircraft that gains its lift through the ...

airship
s 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, the LZ 129 Hindenburg, Hindenburg, like all German Zeppelins, was forced to use hydrogen as the lift gas. 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 United States Bureau of Mines, 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 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 phase out the reserve.Stwertka, Albert (1998). ''Guide to the Elements: Revised Edition''. New York; Oxford University Press, p. 24. 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 million cubic meters (600 million cubic feet) 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 Industrial City, 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 National Helium Reserve, 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 Natural Gas Area, 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 & Chemicals, Air Products, an international corporation that sells gases for industrial use, helium volumes remain under economic pressure due to feedstock supply constraints.


Characteristics


The helium atom


Helium in quantum mechanics

In the perspective of
quantum mechanics Quantum mechanics is a fundamental theory A theory is a reason, rational type of abstraction, abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with ...
, 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'' which each electron sees, is about 1.69 units, not the 2 charges of a classic "bare" helium nucleus.


The related stability of the helium-4 nucleus and electron shell

The nucleus of the helium-4 atom is identical with an
alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Proto ...

alpha particle
. 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
fermion In particle physics, a fermion is a particle that follows Fermi–Dirac statistics and generally has half odd integer spin: spin 1/2, Spin (physics)#Higher spins, spin 3/2, etc. These particles obey the Pauli exclusion principle. Fermions include ...
s fully occupy 1s1s, 1s orbitals in pairs, none of them possessing orbital angular momentum, and each cancelling the other's intrinsic spin. Adding another of any of these particles would require angular momentum and would release substantially less energy (in fact, no nucleus with five nucleons is stable). This arrangement is thus energetically extremely stable for all these particles, and this stability accounts for many crucial facts regarding helium in nature. 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 (2 protons and 1 neutron) is produced in fusion reactions from hydrogen, but it is a very small fraction compared to the highly favorable helium-4. The unusual stability of the helium-4 nucleus is also important Cosmology, cosmologically: it explains the fact that in the first few minutes after the
Big Bang The Big Bang is the prevailing of the from the through its subsequent large-scale evolution. The model describes how the from an initial state of high and , and offers a comprehensive explanation for a broad range of observed phenomen ...

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. So tight was helium-4 binding that helium-4 production consumed nearly all of the free neutrons in a few minutes, before they could beta-decay, and also leaving few 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 was barely energetically favorable for helium to fuse into the next element with a lower energy per
nucleon In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
, carbon. However, due to lack of intermediate elements, 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, makes up about 23% 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 Speed of sound, sound speed in the gas phase are all greater than any other gas except
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
. For these reasons and the small size of helium monatomic molecules, helium diffusion, diffuses through solids at a rate three times that of air and around 65% that of hydrogen. Helium is the least water-solubility, soluble monatomic gas, and one of the least water-soluble of any gas (Tetrafluoromethane, CF4, Sulfur hexafluoride, SF6, and Octafluorocyclobutane, 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 found in a plasma (physics), plasma state, 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 helium

Unlike any other element, helium will remain liquid down to
absolute zero Absolute zero is the lowest limit of the thermodynamic temperature Thermodynamic temperature is the measure of ''absolute temperature'' and is one of the principal parameters of thermodynamics. A thermodynamic temperature reading of zero deno ...
at normal pressures. This is a direct effect of quantum mechanics: specifically, the zero point energy of the system is too high to allow freezing. 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 Compressibility, compressible; applying pressure in a laboratory can decrease its volume by more than 30%. With a bulk modulus of about 27 megapascal, 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 I

Below its boiling point of and above the lambda point of , 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 Expanded polystyrene, Styrofoam are often used to show where the surface is. This colorless liquid has a very low
viscosity The viscosity of a fluid In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, ...

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 (see: macroscopic quantum phenomena) of matter with strange properties. For example, when it flows through capillaries as thin as 10−7 to 10−8 m it has no measurable
viscosity The viscosity of a fluid In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, ...

viscosity
. However, when measurements were done between two moving discs, a viscosity comparable to that of gaseous helium was observed. Current 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 sintering, 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 heat transfer, 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 nanometre, 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''.


Isotopes

There are nine known isotopes of helium, but only
helium-3 Helium-3 (3He see also helion) is a light, stable isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons A proton is a subatomic particle, symbol or , with a positive electric charge Ele ...

helium-3
and
helium-4 Helium-4 () is a stable isotope of the element helium. It is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consists ...

helium-4
are stable isotope, 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
nucleon In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s are arranged into Nuclear shell model, 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 (geology), 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 Moon, 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 Parts per billion, ppb, much higher than the approximately 5 Parts per trillion, 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 Nuclear fusion, fusion. Liquid helium-4 can be cooled to about 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
boson In quantum mechanics Quantum mechanics is a fundamental theory A theory is a reason, rational type of abstraction, abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinkin ...

boson
s while helium-3 atoms are
fermion In particle physics, a fermion is a particle that follows Fermi–Dirac statistics and generally has half odd integer spin: spin 1/2, Spin (physics)#Higher spins, spin 3/2, etc. These particles obey the Pauli exclusion principle. Fermions include ...
s). 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 helium-5 with a half-life of . Helium-6 decays by emitting a beta particle and has a half-life of 0.8 second. Helium-7 also emits a beta particle as well as a gamma ray. Helium-7 and helium-8 are created in certain nuclear reactions. Helium-6 and helium-8 are known to exhibit a nuclear halo.


Compounds

Helium has a Valence (chemistry), 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 compound (chemistry), 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 physics, 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–Lowry acid–base theory, 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 spectral band, 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 dihelium, He2. Theoretically, other true compounds may be possible, such as helium fluorohydride (HHeF) which would be analogous to Argon fluorohydride, 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. If confirmed by experiment, the only remaining element with no known stable compounds would be neon. Helium atoms have been inserted into the hollow carbon cage molecules (the fullerenes) by heating under high pressure. The endohedral fullerene, endohedral fullerene molecules formed are stable at high temperatures. When chemical derivatives of these fullerenes are formed, the helium stays inside. If
helium-3 Helium-3 (3He see also helion) is a light, stable isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons A proton is a subatomic particle, symbol or , with a positive electric charge Ele ...

helium-3
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 Insulator (electricity), insulating electride Disodium helide, Na2He has been shown to be thermodynamically stable at pressures above 113 GPa. It has a fluorite structure.


Occurrence and production


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 Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
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 Nuclear fusion is a nuclear reaction, reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products ...

nuclear fusion
of hydrogen in proton–proton chain, 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 atmospheric escape, escapes into space by several processes. In the Earth's heterosphere, a part of the upper atmosphere, helium and other lighter gases are the most abundant elements. Most helium on Earth is a result of
radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

radioactive decay
. Helium is found in large amounts in minerals of
uranium Uranium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

uranium
and
thorium Thorium is a weakly radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nucleus is the sma ...

thorium
, including
uraninite Uraninite, formerly pitchblende, is a radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nuc ...
and its varieties
cleveite Cleveite is an impure radioactivity, radioactive variety of uraninite containing uranium, found in Norway. It has the composition Uranium dioxide, UO2 with about 10% of the uranium substituted by rare-earth elements. It was named after Swedish chemi ...
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 spring (hydrosphere), 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 40 billion cubic meters, with a quarter of that being in the South Pars / North Dome Gas-Condensate field owned jointly by Qatar and Iran. In 2015 and 2016 additional probable reserves were announced to be under the Rocky Mountains in North America and in the East African Rift.


Modern extraction and distribution

For large-scale use, helium is extracted by
fractional distillation Fractional distillation is the separation of a mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matt ...
from natural gas, which can contain as much as 7% helium. Since helium has a lower boiling point than any other element, low temperature and high pressure are used to liquefy nearly all the other gases (mostly
nitrogen Nitrogen is the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

nitrogen
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 RasGas managed by Air Liquide) had increased Qatar's fraction of world helium production to 25%, and made it the second largest exporter after the United States. An estimated 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 natural gas of the Hugoton Natural Gas Area, 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 is being depleted and sold off, and is expected to be largely depleted by 2021, under the October 2013 ''Responsible Helium Administration and Stewardship Act'' (H.R. 527). 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 must be 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 Dewar flask, 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 (approx. 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 Tethered helium balloon, 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 their book, the ''Future of helium as a natural resource'' (Routledge, 2012), Nuttall, Clarke & Glowacki (2012) also proposed to create an International Helium Agency (IHA) to 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 Chemically inert, 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 Magnetic resonance imaging (MRI) is a medical imaging Medical imaging is the technique and process of imaging Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of a ...

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, ideal gas, 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 facility, impulse facilities.


Gas tungsten arc welding

Helium is used as a shielding gas in
arc welding Arc welding is a welding Welding is a process that joins materials, usually s or s, by using high to melt the parts together and allowing them to cool, causing . Welding is distinct from lower temperature metal-joining techniques such as ...
processes on materials that at welding temperatures are contaminated and weakened by air or nitrogen. A number of inert shielding gases are used in gas tungsten arc welding, but helium is used instead of cheaper
argon Argon is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

argon
especially for welding materials that have higher heat conductivity, like aluminium or copper.


Minor uses


Industrial leak detection

One industrial application for helium is leak detection. Because helium diffusion, 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,
airship An airship, dirigible balloon or blimp is a type of aerostat An aerostat (From greek language, Greek ἀήρ ''aer'' (air) + στατός ''statos'' (standing) through French) is a lighter than air aircraft that gains its lift through the ...

airship
s and balloons are inflated with helium for Lifting gas, 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 displace fuel and oxidizers in storage tanks 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 (13 million cubic feet) of helium to launch.


Minor commercial and recreational uses

Helium as a breathing gas has no Nitrogen narcosis, narcotic properties, so helium mixtures such as Trimix (breathing gas), trimix, heliox and Trimix (breathing gas)#Heliair, 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 work of breathing. At depths below 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 lens (optics), 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 Uranium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

uranium
and
thorium Thorium is a weakly radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus The atomic nucleus is the sma ...

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 cryogenics applications. As examples of applications, liquid helium is used to cool certain metals to the extremely low temperatures required for
superconductivity Superconductivity is a set of physical properties observed in certain materials where electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current An electric current is a st ...

superconductivity
, such as in
superconducting magnet A superconducting magnet is an electromagnet An electromagnet is a type of magnet A magnet is a material or object that produces a magnetic field A magnetic field is a vector field In vector calculus and physics, a vector f ...
s for magnetic resonance imaging. The Large Hadron Collider at CERN uses 96 metric tons of liquid helium to maintain the temperature at .


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 will impair the operation of microelectromechanical systems (MEMS) such that iPhones may fail.


Inhalation and safety


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 fundamental frequency, 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 frequency, 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 an 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 (music), 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 gas, 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 cyanosis, 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 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 frostbite, 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


Notes


References


Bibliography

* * * *


External links

General
U.S. Government's Bureau of Land Management: Sources, Refinement, and Shortage.
With some history of helium.
U.S. Geological Survey publications on helium
beginning 1996
Helium

Where is all the helium?
Aga website


Chemistry in its element podcast
(MP3) from the Royal Society of Chemistry's Chemistry World
Helium


includes health and safety information regarding accidental exposures to helium More detail

at ''The Periodic Table of Videos'' (University of Nottingham)
Helium
at the Helsinki University of Technology; includes pressure-temperature phase diagrams for helium-3 and helium-4
Lancaster University, Ultra Low Temperature Physics
nbsp;– includes a summary of some low temperature techniques *Video

(Alfred Leitner, 1963, 38 min.) Miscellaneous

with audio samples that demonstrate the unchanged voice pitch

Helium shortage
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

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 * * {{Featured article Airship technology Helium, Chemical elements Noble gases Quantum phases Coolants Nuclear reactor coolants Diving equipment E-number additives