Helium

Helium

Overview
Helium is the chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

 with atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

 2 and an atomic weight of 4.002602, which is represented by the symbol
Chemical symbol
A chemical symbol is a 1- or 2-letter internationally agreed code for a chemical element, usually derived from the name of the element, often in Latin. Only the first letter is capitalised...

 He. It is a colorless, odorless, tasteless, non-toxic, inert
Inert
-Chemistry:In chemistry, the term inert is used to describe a substance that is not chemically reactive.The noble gases were previously known as inert gases because of their perceived lack of participation in any chemical reactions...

, monatomic gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

 that heads the noble gas
Noble gas
The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity...

 group in the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...

. Its boiling
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

 and melting
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...

 points are the lowest among the elements and it exists only as a gas except in extreme conditions.

Helium is the second lightest element and is the second most abundant element
Abundance of the chemical elements
The abundance of a chemical element measures how relatively common the element is, or how much of the element is present in a given environment by comparison to all other elements...

 in the observable universe
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...

, being present at about 24% of the total elemental mass, which is more than 12 times the mass of all the heavier elements combined.
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Encyclopedia
Helium is the chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

 with atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

 2 and an atomic weight of 4.002602, which is represented by the symbol
Chemical symbol
A chemical symbol is a 1- or 2-letter internationally agreed code for a chemical element, usually derived from the name of the element, often in Latin. Only the first letter is capitalised...

 He. It is a colorless, odorless, tasteless, non-toxic, inert
Inert
-Chemistry:In chemistry, the term inert is used to describe a substance that is not chemically reactive.The noble gases were previously known as inert gases because of their perceived lack of participation in any chemical reactions...

, monatomic gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

 that heads the noble gas
Noble gas
The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity...

 group in the periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...

. Its boiling
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

 and melting
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...

 points are the lowest among the elements and it exists only as a gas except in extreme conditions.

Helium is the second lightest element and is the second most abundant element
Abundance of the chemical elements
The abundance of a chemical element measures how relatively common the element is, or how much of the element is present in a given environment by comparison to all other elements...

 in the observable universe
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...

, being 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 figure in our own Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 and in Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

. This is due to the very high binding energy (per nucleon
Nucleon
In physics, a nucleon is a collective name for two particles: the neutron and the proton. These are the two constituents of the atomic nucleus. Until the 1960s, the nucleons were thought to be elementary particles...

) of helium-4 with respect to the next three elements after helium. This helium-4 binding energy also accounts for its commonality as a product in both nuclear fusion and radioactive decay. Most helium in the universe is helium-4, and is believed to have been formed during the Big Bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...

. Some new helium is being created currently as a result of the nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

 of hydrogen in stars.

Helium is named for the Greek God of the Sun, Helios
Helios
Helios was the personification of the Sun in Greek mythology. Homer often calls him simply Titan or Hyperion, while Hesiod and the Homeric Hymn separate him as a son of the Titans Hyperion and Theia or Euryphaessa and brother of the goddesses Selene, the moon, and Eos, the dawn...

. It was first detected as an unknown yellow spectral line
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...

 signature in sunlight during a solar eclipse in 1868
Solar eclipse of August 18, 1868
A total solar eclipse occurred on August 18, 1868. - Observations :Captain Bullock observed from the Celebes sea, sketching the appearance of the corona, while Gustav Fritsch accompanied an expedition to Aden. -Discovery of helium:...

 by French astronomer Jules Janssen. Janssen is jointly credited with the discovery of the element with Norman Lockyer, who observed the same eclipse and was the first to propose that the line was due to a new element, which he named. In 1903, large reserves of helium were found in natural gas field
Natural gas field
Oil and natural gas are produced by the same geological process according fossil fuel suggestion: anaerobic decay of organic matter deep under the Earth's surface. As a consequence, oil and natural gas are often found together...

s in parts of the United States, which is by far the largest supplier of the gas today.

Helium is used in cryogenics
Cryogenics
In physics, cryogenics is the study of the production of very low temperature and the behavior of materials at those temperatures. A person who studies elements under extremely cold temperature is called a cryogenicist. Rather than the relative temperature scales of Celsius and Fahrenheit,...

 (its largest single use, absorbing about a quarter of production), particularly in the cooling of superconducting magnet
Superconducting magnet
A superconducting magnet is an electromagnet made from coils of superconducting wire. They must be cooled to cryogenic temperatures during operation. In its superconducting state the wire can conduct much larger electric currents than ordinary wire, creating intense magnetic fields...

s, with the main commercial application being in MRI scanners. Helium's other industrial uses- as a pressurizing and purge gas, as a protective atmosphere for arc welding
Arc welding
Arc welding is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct or alternating current, and consumable or non-consumable electrodes...

 and in processes such as growing crystals to make silicon wafers- account for half of the gas produced. A well-known but minor use is as a lifting gas in balloons and airship
Airship
An airship or dirigible is a type of aerostat or "lighter-than-air aircraft" that can be steered and propelled through the air using rudders and propellers or other thrust mechanisms...

s. As with any gas with differing density from 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
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...

 (in particular the property of superfluidity) and to those looking at the phenomena, such as superconductivity
Superconductivity
Superconductivity is a phenomenon of exactly zero electrical resistance occurring in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum...

, that temperatures near absolute zero
Absolute zero
Absolute zero is the theoretical temperature at which entropy reaches its minimum value. The laws of thermodynamics state that absolute zero cannot be reached using only thermodynamic means....

 produce in matter
Matter
Matter is a general term for the substance of which all physical objects consist. Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume...

.

On Earth, the lightness of helium has caused its evaporation from the gas and dust cloud from which the planet condensed, and it is thus relatively rare—0.00052% by volume in the atmosphere. Most terrestrial helium present today is created by the natural radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...

 of heavy radioactive elements (thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

 and uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

), as the alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...

s emitted by such decays consist of helium-4 nuclei
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...

. This radiogenic helium is trapped with natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

 in concentrations up to 7% by volume, from which it is extracted commercially by a low-temperature separation process called fractional distillation
Fractional distillation
Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation...

.

Scientific discoveries


The first evidence of helium was observed on August 18, 1868 as a bright yellow line with a wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

 of 587.49 nanometers in the spectrum
Emission spectrum
The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted by the element's atoms or the compound's molecules when they are returned to a lower energy state....

 of the chromosphere
Chromosphere
The chromosphere is a thin layer of the Sun's atmosphere just above the photosphere, roughly 2,000 kilometers deep....

 of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

. The line was detected by French astronomer Jules Janssen during a total solar eclipse
Solar eclipse
As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially blocks the Sun as viewed from a location on Earth. This can happen only during a new moon, when the Sun and the Moon are in conjunction as seen from Earth. At least...

 in Guntur
Guntur
Guntur , is a city and a municipal corporation in the Indian state of Andhra Pradesh, located to the north and west of the Bay of Bengal. It is approximately to the south of the national capital, New Delhi and south east of state capital, Hyderabad. Guntur is the fourth largest city in Andhra...

, India
British Raj
British Raj was the British rule in the Indian subcontinent between 1858 and 1947; The term can also refer to the period of dominion...

. This line was initially assumed to be sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

. On October 20 of the same year, English astronomer Norman Lockyer observed a yellow line in the solar spectrum, which he named the D3 Fraunhofer line because it was near the known D1 and D2 lines of sodium. He concluded that it was caused by an element in the Sun unknown on Earth. Lockyer and English chemist Edward Frankland
Edward Frankland
Sir Edward Frankland, KCB, FRS was a chemist, one of the foremost of his day. He was an expert in water quality and analysis, and originated the concept of combining power, or valence, in chemistry. He was also one of the originators of organometallic chemistry.-Biography:Edward Frankland was born...

 named the element with the Greek word for the Sun, ἥλιος (helios
Helios
Helios was the personification of the Sun in Greek mythology. Homer often calls him simply Titan or Hyperion, while Hesiod and the Homeric Hymn separate him as a son of the Titans Hyperion and Theia or Euryphaessa and brother of the goddesses Selene, the moon, and Eos, the dawn...

)."

In 1882, Italian physicist Luigi Palmieri
Luigi Palmieri
Luigi Palmieri was an Italian physicist and meteorologist. He was famous for his scientific studies of the eruptions of Mount Vesuvius, for his researches on earthquakes and meteorological phenomena and for improving the seismographer of the time.- Biography :Palmieri was born in Faicchio,...

 detected helium on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

, for the first time, through its D3 spectral line, when he analyzed the lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

 of Mount Vesuvius
Mount Vesuvius
Mount Vesuvius is a stratovolcano in the Gulf of Naples, Italy, about east of Naples and a short distance from the shore. It is the only volcano on the European mainland to have erupted within the last hundred years, although it is not currently erupting...

.

On March 26, 1895, Scottish chemist Sir William Ramsay
William Ramsay
Sir William Ramsay 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 in air" .-Early years:Ramsay was born in Glasgow on 2...

 isolated helium on Earth by treating the mineral cleveite
Cleveite
Cleveite is a radioactive mineral containing uranium and found in Norway. It is an impure variety of uraninite, and has the composition UO2 with about 10% of the uranium substituted by rare earth elements...

 (a variety of uraninite
Uraninite
Uraninite is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2, but also contains UO3 and oxides of lead, thorium, and rare earth elements...

 with at least 10% rare earth elements) with mineral acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

s. Ramsay was looking for argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

 but, after separating nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 from the gas liberated by sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

, 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
William Crookes
Sir William Crookes, OM, FRS was a British chemist and physicist who attended the Royal College of Chemistry, London, and worked on spectroscopy...

. It was independently isolated from cleveite in the same year by chemists Per Teodor Cleve
Per Teodor Cleve
Per Teodor Cleve was a Swedish chemist and geologist.After graduating from the Stockholm Gymnasium in 1858, Cleve matriculated at Uppsala University in May 1858, where he received his PhD in 1863...

 and Abraham Langlet
Abraham Langlet
Nils Abraham Langlet was a Swedish chemist.Langlet was born in Södertälje. From 1886 to 1896, he studied chemistry under Per Teodor Cleve at Uppsala University, where he obtained a doctorate in 1896, and was made docent in the same year...

 in Uppsala, Sweden, who collected enough of the gas to accurately determine its atomic weight
Atomic weight
Atomic weight is a dimensionless physical quantity, the ratio of the average mass of atoms of an element to 1/12 of the mass of an atom of carbon-12...

. Helium was also isolated by the American geochemist William Francis Hillebrand
William Francis Hillebrand
William Francis Hillebrand was an American chemist.-Biography:He was the son of the renowned botanist William 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
Ernest Rutherford, 1st Baron Rutherford of Nelson OM, FRS was a New Zealand-born British chemist and physicist who became known as the father of nuclear physics...

 and Thomas Royds demonstrated that alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...

s are helium nuclei
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...

 by allowing the particles to penetrate the thin glass wall of an evacuated tube, then creating a discharge in the tube to study the spectra of the new gas inside. In 1908, helium was first liquefied by Dutch physicist Heike Kamerlingh Onnes
Heike Kamerlingh Onnes
Heike Kamerlingh Onnes was a Dutch physicist and Nobel laureate. He pioneered refrigeration techniques, and he explored how materials behaved when cooled to nearly absolute zero. He was the first to liquify helium...

 by cooling the gas to less than one kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

. He tried to solidify it by further reducing the temperature but failed because helium does not have a triple point
Triple point
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases of that substance coexist in thermodynamic equilibrium...

 temperature at which the solid, liquid, and gas phases are at equilibrium. Onnes' student Willem Hendrik Keesom
Willem Hendrik Keesom
Willem Hendrik Keesom was a Dutch physicist who, in 1926, invented a method to freeze liquid helium.He also developed the first mathematical description of dipole-dipole interactions in 1921...

 was eventually able to solidify 1 cm3 of helium in 1926 by applying additional external pressure.

In 1938, Russian physicist Pyotr Leonidovich Kapitsa discovered that helium-4
Helium-4
Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...

 has almost no viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 at temperatures near absolute zero
Absolute zero
Absolute zero is the theoretical temperature at which entropy reaches its minimum value. The laws of thermodynamics state that absolute zero cannot be reached using only thermodynamic means....

, a phenomenon now called superfluidity. This phenomenon is related to Bose-Einstein condensation. In 1972, the same phenomenon was observed in helium-3
Helium-3
Helium-3 is a light, non-radioactive isotope of helium with two protons and one neutron. It is rare on Earth, and is sought for use in nuclear fusion research...

, but at temperatures much closer to absolute zero, by American physicists Douglas D. Osheroff
Douglas D. Osheroff
Douglas Dean Osheroff is an American physicist known for his work in experimental condensed matter physics, in particular for his co-discovery of superfluidity in Helium-3. For his contributions he shared the 1996 Nobel Prize in Physics along with David Lee and Robert C...

, David M. Lee, and Robert C. Richardson
Robert Coleman Richardson
Robert Coleman Richardson is an American experimental physicist whose area of research includes sub-millikelvin temperature studies of helium-3...

. The phenomenon in helium-3 is thought to be related to pairing of helium-3 fermion
Fermion
In particle physics, a fermion is any particle which obeys the Fermi–Dirac statistics . Fermions contrast with bosons which obey Bose–Einstein statistics....

s to make boson
Boson
In particle physics, bosons are subatomic particles that obey Bose–Einstein statistics. Several bosons can occupy the same quantum state. The word boson derives from the name of Satyendra Nath Bose....

s, in analogy to Cooper pairs of electrons producing superconductivity
Superconductivity
Superconductivity is a phenomenon of exactly zero electrical resistance occurring in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum...

.

Extraction and use


After an oil drilling operation in 1903 in Dexter, Kansas
Dexter, Kansas
Dexter is a city in Cowley County, Kansas, United States. As of the 2010 census, the city population was 278.-History:Early in the 20th century Dexter became the focus of research that would confirm the existence of an abundance of naturally occurring and readily available helium. In May 1903, a...

, produced a gas geyser that would not burn, Kansas state geologist Erasmus Haworth
Erasmus Haworth
Erasmus Haworth was an American geologist.Born on a farm near Indianola, Iowa, he graduated from the University of Kansas with a bachelor of science degree in 1883 and received a master's degree there the following year. He received his doctoral degree from Johns Hopkins University in 1888...

 collected samples of the escaping gas and took them back to the University of Kansas
University of Kansas
The University of Kansas is a public research university and the largest university in the state of Kansas. KU campuses are located in Lawrence, Wichita, Overland Park, and Kansas City, Kansas with the main campus being located in Lawrence on Mount Oread, the highest point in Lawrence. The...

 at Lawrence where, with the help of chemists Hamilton Cady
Hamilton Cady
Hamilton Perkins Cady, , was an American chemist who in 1907 in collaboration with David McFarland discovered that helium could be extracted from natural gas.-Early life:...

 and David McFarland, he discovered that the gas consisted of, by volume, 72% nitrogen, 15% methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 (a combustible percentage only with sufficient oxygen), 1% hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

, 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. The greatest reserves of helium were in the Hugoton
Hugoton Natural Gas Area
Hugoton Natural Gas Area is a combination of large natural gas fields in the U.S. state of Kansas, the largest of which is the Hugoton Field. Its name is derived from the town of Hugoton, Kansas, near which the Hugoton Field was first discovered.-History:...

 and nearby gas fields in southwest Kansas and the panhandles of Texas and Oklahoma.

This enabled the United States to become the world's leading supplier of helium. Following a suggestion by Sir Richard Threlfall
Richard Threlfall
Sir Richard Threlfall FRS was an English chemist and engineer, he established the School of Physics at the University of Sydney and made important contributions to military science during World War I. He was elected a fellow of the Royal Society in 1899, and was created K.B.E. in 1917 and G.B.E...

, the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

 sponsored three small experimental helium plants during World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

. The goal was to supply barrage balloon
Barrage balloon
A barrage balloon is a large balloon tethered with metal cables, used to defend against low-level aircraft attack by damaging the aircraft on collision with the cables, or at least making the attacker's approach more difficult. Some versions carried small explosive charges that would be pulled up...

s with the non-flammable, lighter-than-air gas. A total of 5,700 m3 (200,000 cubic feet) 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-7, which flew its maiden voyage from Hampton Roads, Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...

, to Bolling Field in Washington, D.C.
Washington, D.C.
Washington, D.C., formally the District of Columbia and commonly referred to as Washington, "the District", or simply D.C., is the capital of the United States. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....

, on December 1, 1921.

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
Lifting gas
Because of the Archimedes' principle, a lifting gas is required for aerostats to create buoyancy. Its density is lower than that of air . Only certain lighter than air gases are suitable as lifting gases.- Hot Air :...

 in lighter-than-air craft. This use increased demand during World War II, as well as demands for shielded arc welding
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

. The helium mass spectrometer
Helium mass spectrometer
A helium mass spectrometer is an instrument commonly used to detect and locate small leaks. It was initially developed in the Manhattan Project during World War II to find extremely small leaks in the gas diffusion process of uranium enrichment plants. It typically uses a vacuum chamber in which a...

 was also vital in the atomic bomb Manhattan Project
Manhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...

.

The government of the United States set up the National Helium Reserve
National Helium Reserve
The National Helium Reserve, also known as the Federal Helium Reserve, is a strategic reserve of the United States holding over a billion cubic meter of helium gas. The helium is stored at the Cliffside Storage Facility about northwest of Amarillo, Texas, in a natural geologic gas storage...

 in 1925 at Amarillo, Texas
Amarillo, Texas
Amarillo is the 14th-largest city, by population, in the state of Texas, the largest in the Texas Panhandle, and the seat of Potter County. A portion of the city extends into Randall County. The population was 190,695 at the 2010 census...

, with the goal of supplying military airship
Airship
An airship or dirigible is a type of aerostat or "lighter-than-air aircraft" that can be steered and propelled through the air using rudders and propellers or other thrust mechanisms...

s in time of war and commercial airships in peacetime. Because of a US military embargo against Germany that restricted helium supplies, the Hindenburg
LZ 129 Hindenburg
LZ 129 Hindenburg was a large German commercial passenger-carrying rigid airship, the lead ship of the Hindenburg class, the longest class of flying machine and the largest airship by envelope volume...

, like all German Zeppelins, was forced to use hydrogen as the lift gas. Helium use following World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 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
Space Race
The Space Race was a mid-to-late 20th century competition between the Soviet Union and the United States for supremacy in space exploration. Between 1957 and 1975, Cold War rivalry between the two nations focused on attaining firsts in space exploration, which were seen as necessary for national...

 and Cold War
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...

. 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
United States Bureau of Mines
For most of the 20th century, the U.S. Bureau of Mines was the primary United States Government agency conducting scientific research and disseminating information on the extraction, processing, use, and conservation of mineral resources.- Summary :...

 arranged for five private plants to recover helium from natural gas. For this helium conservation program, the Bureau built a 425 miles (684 km) pipeline from Bushton
Bushton, Kansas
Bushton is a city in Rice County, Kansas, United States. As of the 2010 census, the city population was 279.-Geography:Bushton is located at . According to the United States Census Bureau, the city has a total area of , all of it land.-Demographics:As of the census of 2000, there were 314 people,...

, Kansas
Kansas
Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...

, 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, when it then 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. The resulting "Helium Privatization Act of 1996" (Public Law 104–273) directed the United States Department of the Interior
United States Department of the Interior
The United States Department of the Interior is the United States federal executive department of the U.S. government responsible for the management and conservation of most federal land and natural resources, and the administration of programs relating to Native Americans, Alaska Natives, Native...

 to start emptying the reserve 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 over 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
Arzew
Arzew or Arzeu is a port city in Algeria, from Oran. It is the capital of Arzew District, Oran Province.-Antiquity:Like the rest of North Africa, the site of modern-day Arzew was originally inhabited by the Berbers...

, Algeria
Algeria
Algeria , officially the People's Democratic Republic of Algeria , also formally referred to as the Democratic and Popular Republic of Algeria, is a country in the Maghreb region of Northwest Africa with Algiers as its capital.In terms of land area, it is the largest country in Africa and the Arab...

, 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 above 15 million kg per year. In 2004–2006, two additional plants, one in Ras Laffan
Ras Laffan Industrial City
Ras Laffan Industrial City is an industrial hub located north of Doha, Qatar. It is administrated by Qatar Petroleum.Ras Laffan Industrial City is the Qatar's main site for production of liquefied natural gas and gas-to-liquid...

, Qatar
Qatar
Qatar , also known as the State of Qatar or locally Dawlat Qaṭar, is a sovereign Arab state, located in the Middle East, occupying the small Qatar Peninsula on the northeasterly coast of the much larger Arabian Peninsula. Its sole land border is with Saudi Arabia to the south, with the rest of its...

, and the other in Skikda
Skikda
Skikda is a city in north eastern Algeria and a port on the Gulf of Stora, the ancient Sinus Numidicus. It was known as Philippeville until the end of the Algerian War of Independence in 1962...

, Algeria, were built, but as of early 2007, Ras Laffan is functioning at 50%, and Skikda has yet to start up. Algeria quickly became the second leading producer of helium. Through this time, both helium consumption and the costs of producing helium increased. In the 2002 to 2007 period helium prices doubled.

The helium atom




Helium in quantum mechanics


In the perspective of quantum mechanics
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...

, helium is the second simplest atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...

 to model, following the hydrogen atom
Hydrogen atom
A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positively-charged proton and a single negatively-charged electron bound to the nucleus by the Coulomb force...

. Helium is composed of two electrons in atomic orbital
Atomic orbital
An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...

s surrounding a nucleus containing two protons along with some neutrons. As in Newtonian mechanics, no system consisting 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
Computational chemistry
Computational chemistry is a branch of chemistry that uses principles of computer science to assist in solving chemical problems. It uses the results of theoretical chemistry, incorporated into efficient computer programs, to calculate the structures and properties of molecules and solids...

 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. In such models it is found 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 particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...

. 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
Fermion
In particle physics, a fermion is any particle which obeys the Fermi–Dirac statistics . Fermions contrast with bosons which obey Bose–Einstein statistics....

s fully occupy 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 involving both heavy-particle emission, and fusion. Some stable helium-3 is produced in fusion reactions from hydrogen, but it is a very small fraction, compared with the highly favorable helium-4. The stability of helium-4 is the reason hydrogen is converted to helium-4 (not deuterium or helium-3 or heavier elements) in the Sun. It is also partly responsible for the fact that the alpha particle is by far the most common type of baryonic particle to be ejected from atomic nuclei; in other words, alpha decay
Alpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...

 is far more common than cluster decay
Cluster decay
Cluster decay is a type of nuclear decay in which a parent atomic nucleus with A nucleons and Z protons emits a cluster of Ne neutrons and Ze protons heavier than an alpha particle but lighter than a typical binary fission fragment Cluster decay (also named heavy particle radioactivity or heavy...

.


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
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...

, 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
Binding energy
Binding energy is the mechanical energy required to disassemble a whole into separate parts. A bound system typically has a lower potential energy than its constituent parts; this is what keeps the system together—often this means that energy is released upon the creation of a bound state...

) and thus no energetic drive was available, once helium had been formed, 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
Nucleon
In physics, a nucleon is a collective name for two particles: the neutron and the proton. These are the two constituents of the atomic nucleus. Until the 1960s, the nucleons were thought to be elementary particles...

, 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 least reactive noble gas
Noble gas
The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity...

 after neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...

 and thus the second least reactive of all elements; it is inert
Inert
-Chemistry:In chemistry, the term inert is used to describe a substance that is not chemically reactive.The noble gases were previously known as inert gases because of their perceived lack of participation in any chemical reactions...

 and monatomic in all standard conditions. Because of helium's relatively low molar (atomic) mass, its thermal conductivity
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

, specific heat, and sound speed
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....

 in the gas phase are all greater than any other gas except hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

. For similar reasons, and also due to the small size of helium atoms, helium's diffusion
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

 rate through solids is three times that of air and around 65% that of hydrogen.

Helium is the least water soluble
Solubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...

 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 found in a plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

 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
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

 together with ionized hydrogen, the particles interact with the Earth's magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...

 giving rise to Birkeland current
Birkeland current
A Birkeland current is a set of currents which flow along geomagnetic field line connecting the Earth’s magnetosphere to the Earth's high latitude ionosphere. They are a specific class of magnetic field-aligned currents. Lately, the term Birkeland currents has been expanded by some authors to...

s and the aurora.

Solid and liquid phases



Unlike any other element, helium will remain liquid down to absolute zero
Absolute zero
Absolute zero is the theoretical temperature at which entropy reaches its minimum value. The laws of thermodynamics state that absolute zero cannot be reached using only thermodynamic means....

 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) and about 25 bar (2.5 MPa) of pressure. It is often hard to distinguish solid from liquid helium since the refractive index
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....

 of the two phases are nearly the same. The solid has a sharp melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...

 and has a crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

line structure, but it is highly compressible; applying pressure in a laboratory can decrease its volume by more than 30%. With a bulk modulus
Bulk modulus
The bulk modulus of a substance measures the substance's resistance to uniform compression. It is defined as the pressure increase needed to decrease the volume by a factor of 1/e...

 on the order of 50 MPa it is 50 times more compressible than water. Solid helium has a density of 0.214 ± 0.006 g/cm3 at 1.15 K and 66 atm; the projected density at 0 K and 25 bar (2.5 MPa) is 0.187 ± 0.009 g/cm3.

Helium I state


Below its boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

 of 4.22 kelvins and above the lambda point
Lambda point
The Lambda point is the temperature below which normal fluid helium transitions to superfluid helium II. More precisely, there is a lower lambda point at 2.172 K, 0.0497 atm, and an upper one at 1.76 K, 29.8 atm....

 of 2.1768 kelvins, the isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

 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
Styrofoam
Styrofoam is a trademark of The Dow Chemical Company for closed-cell currently made for thermal insulation and craft applications. In 1941, researchers in Dow's Chemical Physics Lab found a way to make foamed polystyrene...

 are often used to show where the surface is. This colorless liquid has a very low viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 and a density of 0.145–0.125 g/mL (between about 0 and 4 K, respectively), which is only one-fourth the value expected from classical physics
Classical physics
What "classical physics" refers to depends on the context. When discussing special relativity, it refers to the Newtonian physics which preceded relativity, i.e. the branches of physics based on principles developed before the rise of relativity and quantum mechanics...

. Quantum mechanics
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...

 is needed to explain this property and thus both types of liquid helium 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
Thermal energy
Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....

) from masking the atomic properties.

Helium II state


Liquid helium below its lambda point begins to exhibit very unusual characteristics, in a state called helium II. Boiling of helium II is not possible due to its high thermal conductivity
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

; heat input instead causes evaporation
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....

 of the liquid directly to gas. Helium-3
Helium-3
Helium-3 is a light, non-radioactive isotope of helium with two protons and one neutron. It is rare on Earth, and is sought for use in nuclear fusion research...

 also has a superfluid
Superfluid
Superfluidity is a state of matter in which the matter behaves like a fluid without viscosity and with extremely high thermal conductivity. The substance, which appears to be a normal liquid, will flow without friction past any surface, which allows it to continue to circulate over obstructions and...

 phase, but only at much lower temperatures; as a result, less is known about such properties in 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 10−7 to 10−8 m it has no measurable viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher 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
Ground state
The ground state of a quantum mechanical system is its lowest-energy state; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the 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
Sintering
Sintering is a method used to create objects from powders. It is based on atomic diffusion. Diffusion occurs in any material above absolute zero, but it occurs much faster at higher temperatures. In most sintering processes, the powdered material is held in a mold and then heated to a temperature...

 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
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

. This is because heat conduction occurs by an exceptional quantum mechanism. Most materials that conduct heat well have a valence band
Valence band
In solids, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature....

 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
Heat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...

 is governed by equations that are similar to the wave equation
Wave equation
The wave equation is an important second-order linear partial differential equation for the description of waves – as they occur in physics – such as sound waves, light waves and water waves. It arises in fields like acoustics, electromagnetics, and fluid dynamics...

 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
Second sound
Second sound is a quantum mechanical phenomenon in which heat transfer occurs by wave-like motion, rather than by the more usual mechanism of diffusion. Heat takes the place of pressure in normal sound waves. This leads to a very high thermal conductivity...

.

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
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...

-thick film regardless of surface material. This film is called a Rollin film
Rollin film
A Rollin film, named after Bernard V. Rollin, is a 30 nm-thick liquid film of helium in the helium II state. It exhibits a "creeping" effect in response to surfaces extending past the film's level...

 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 liquid helium. 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 wave
Gravity wave
In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media which has the restoring force of gravity or buoyancy....

s in shallow water, but rather than gravity, the restoring force is the van der Waals force
Van der Waals force
In physical chemistry, the van der Waals force , named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral...

. These waves are known as third sound.

Isotopes



There are eight known isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

s of helium, but only helium-3
Helium-3
Helium-3 is a light, non-radioactive isotope of helium with two protons and one neutron. It is rare on Earth, and is sought for use in nuclear fusion research...

 and helium-4
Helium-4
Helium-4 is a non-radioactive isotope of helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is the same as an alpha particle, consisting of two protons and two neutrons. Alpha decay of heavy...

 are stable
Stable isotope
Stable isotopes are chemical isotopes that may or may not be radioactive, but if radioactive, have half-lives too long to be measured.Only 90 nuclides from the first 40 elements are energetically stable to any kind of decay save proton decay, in theory...

. In the Earth's atmosphere, there is one atom for every million atoms. 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
Alpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...

 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
Nucleon
In physics, a nucleon is a collective name for two particles: the neutron and the proton. These are the two constituents of the atomic nucleus. Until the 1960s, the nucleons were thought to be elementary particles...

s are arranged into complete shells. It was also formed in enormous quantities during Big Bang nucleosynthesis
Big Bang nucleosynthesis
In physical cosmology, Big Bang nucleosynthesis refers to the production of nuclei other than those of H-1 during the early phases of the universe...

.

Helium-3 is present on Earth only in trace amounts; most of it since Earth's formation, though some falls to Earth trapped in cosmic dust
Cosmic dust
Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...

. Trace amounts are also produced by the beta decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...

 of tritium
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...

. 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
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....

. is much more abundant in stars, as a product of nuclear fusion. Thus in the interstellar medium
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...

, the proportion of to is around 100 times higher than on Earth. Extraplanetary material, such as lunar and asteroid regolith
Regolith
Regolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...

, have trace amounts of helium-3 from being bombarded by solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

s. The Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

's surface contains helium-3 at concentrations on the order of 0.01 ppm, a lot higher than the ca. 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
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

.

Liquid helium-4 can be cooled to about 1 kelvin using evaporative cooling in a 1-K pot
1-K pot
A 1-K pot is a cryogenic device used to attain temperatures down to approximately 1 kelvin.The 1-K pot is a small vessel in a cryogenic system that is filled with liquid helium. Usually it is a few cubic centimeters in size with a pickup-tube extending into the primary liquid helium bath of the...

. Similar cooling of helium-3, which has a lower boiling point, can achieve about in a helium-3 refrigerator
Helium-3 refrigerator
A helium-3 refrigerator is a simple device used in experimental physics for obtaining temperatures down to about 0.2 kelvins. By evaporative cooling of helium-4 , a 1-K pot liquefies a small amount of helium-3 in a small vessel called a helium-3 pot...

. 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
Boson
In particle physics, bosons are subatomic particles that obey Bose–Einstein statistics. Several bosons can occupy the same quantum state. The word boson derives from the name of Satyendra Nath Bose....

s while helium-3 atoms are fermion
Fermion
In particle physics, a fermion is any particle which obeys the Fermi–Dirac statistics . Fermions contrast with bosons which obey Bose–Einstein statistics....

s). Dilution refrigerator
Dilution refrigerator
A dilution refrigerator is a cryogenic device first proposed by Heinz London. Its refrigeration process uses a mixture of two isotopes of helium: helium-3 and helium-4...

s 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
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 of . Helium-6 decays by emitting a beta particle
Beta particle
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...

 and has a half-life of 0.8 second. Helium-7 also emits a beta particle as well as a gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...

. Helium-7 and helium-8 are created in certain nuclear reaction
Nuclear reaction
In nuclear physics and nuclear chemistry, a nuclear reaction is semantically considered to be the process in which two nuclei, or else a nucleus of an atom and a subatomic particle from outside the atom, collide to produce products different from the initial particles...

s. Helium-6 and helium-8 are known to exhibit a nuclear halo
Nuclear halo
In nuclear physics, an atomic nucleus is called a halo nucleus or is said to have a nuclear halo if its radius is appreciably larger than that predicted by the liquid drop model, wherein the nucleus is assumed to be a sphere of constant density....

. Helium-2 (two protons, no neutrons) is a radioisotope that decays by proton emission
Proton emission
Proton emission is a type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case the process is known as beta-delayed proton emission, or can occur from the ground state of very...

 into protium (hydrogen), with a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 of .

Compounds



Helium has a valence
Valence (chemistry)
In chemistry, valence, also known as valency or valence number, is a measure of the number of bonds formed by an atom of a given element. "Valence" can be defined as the number of valence bonds...

 of zero and is chemically unreactive under all normal conditions. It is an electrical insulator unless ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

ized. As with the other noble gases, helium has metastable energy level
Energy level
A quantum mechanical system or particle that is bound -- that is, confined spatially—can only take on certain discrete values of energy. This contrasts with classical particles, which can have any energy. These discrete values are called energy levels...

s that allow it to remain ionized in an electrical discharge with a voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

 below its ionization potential
Ionization potential
The ionization energy of a chemical species, i.e. an atom or molecule, is the energy required to remove an electron from the species to a practically infinite distance. Large atoms or molecules have a low ionization energy, while small molecules tend to have higher ionization energies.The property...

. Helium can form unstable compounds, known as excimer
Excimer
An excimer is a short-lived dimeric or heterodimeric molecule formed from two species, at least one of which is in an electronic excited state. Excimers are often diatomic and are composed of two atoms or molecules that would not bond if both were in the ground state. The lifetime of an excimer is...

s, with tungsten, iodine, fluorine, sulfur and phosphorus when it is subjected to an electric glow discharge
Electric glow discharge
An electric glow discharge is a plasma formed by the passage of current at 100 V to several kV through a gas, often argon or another noble gas. It is found in products such as neon lamps and plasma-screen televisions, and is used in plasma physics and analytical chemistry.-Basic operating...

, to electron bombardment, or else is a plasma for another reason. The molecular compounds HeNe, HgHe10, and WHe2, and the molecular ions , , , and have been created this way. This technique has also allowed the production of the neutral molecule He2, which has a large number of band systems, and HgHe, which is apparently held together only by polarization forces. Theoretically, other true compounds may also be possible, such as helium fluorohydride (HHeF) which would be analogous to HArF
Argon fluorohydride
Argon fluorohydride is the first known compound of the chemical element argon.-Discovery:The discovery of this first argon compound is credited to a group of Finnish scientists, led by Markku Räsänen...

, 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 [F– HeO] anion first theorized in 2005 by a group from Taiwan. If confirmed by experiment, such compounds will end helium's chemical inertness, and the only remaining inert element will be neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...

.

Helium has been put inside the hollow carbon cage molecules (the fullerene
Fullerene
A fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and they resemble the balls used in association football. Cylindrical ones are called carbon nanotubes or buckytubes...

s) by heating under high pressure. The endohedral fullerene molecules formed are stable up to high temperatures. When chemical derivatives of these fullerenes are formed, the helium stays inside. If helium-3
Helium-3
Helium-3 is a light, non-radioactive isotope of helium with two protons and one neutron. It is rare on Earth, and is sought for use in nuclear fusion research...

 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.

Natural abundance


Helium is the second most abundant element in the known Universe (after hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

), constituting 23% of its baryon
Baryon
A baryon is a composite particle made up of three quarks . Baryons and mesons belong to the hadron family, which are the quark-based particles...

ic mass. The vast majority of helium was formed by Big Bang nucleosynthesis
Big Bang nucleosynthesis
In physical cosmology, Big Bang nucleosynthesis refers to the production of nuclei other than those of H-1 during the early phases of the universe...

 one to three minutes after the Big Bang. As such, measurements of its abundance contribute to cosmological models. In star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

s, it is formed by the nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...

 of hydrogen in proton-proton chain reaction
Proton-proton chain reaction
The proton–proton chain reaction is one of several fusion reactions by which stars convert hydrogen to helium, the primary alternative being the CNO cycle. The proton–proton chain dominates in stars the size of the Sun or smaller....

s and the CNO cycle
CNO cycle
The CNO cycle is one of two sets of fusion reactions by which stars convert hydrogen to helium, the other being the proton–proton chain. Unlike the proton–proton chain reaction, the CNO cycle is a catalytic cycle. Theoretical models show that the CNO cycle is the dominant source of energy in stars...

, part of stellar nucleosynthesis
Stellar nucleosynthesis
Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the elements heavier than hydrogen. Some small quantity of these reactions also occur on the stellar surface under various circumstances...

.

In the Earth's atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

, 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
Atmospheric escape
Atmospheric escape is the loss of planetary atmospheric gases to outer space.- Thermal escape mechanisms :One classical thermal escape mechanism is Jeans escape. In a quantity of gas, the average velocity of a molecule is determined by temperature, but the velocity of individual molecules varies...

 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.

Nearly all helium on Earth is a result of radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...

, and thus an Earthly helium balloon is essentially a bag of retired alpha particles. Helium is found in large amounts in minerals of uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 and thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

, including cleveite
Cleveite
Cleveite is a radioactive mineral containing uranium and found in Norway. It is an impure variety of uraninite, and has the composition UO2 with about 10% of the uranium substituted by rare earth elements...

, pitchblende, carnotite
Carnotite
Carnotite is a potassium uranium vanadate radioactive mineral with chemical formula: K222·3H2O. The water content can vary and small amounts of calcium, barium, magnesium, iron, and sodium are often present.-Occurrence:...

 and monazite
Monazite
Monazite is a reddish-brown phosphate mineral containing rare earth metals. It occurs usually in small isolated crystals. There are actually at least four different kinds of monazite, depending on relative elemental composition of the mineral:...

, 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
Lithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's 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
Spring (hydrosphere)
A spring—also known as a rising or resurgence—is a component of the hydrosphere. Specifically, it is any natural situation where water flows to the surface of the earth from underground...

, 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 up to over 7% in a small gas field in San Juan County, New Mexico
San Juan County, New Mexico
-2010:Whereas according to the 2010 U.S. Census Bureau:*51.6% White*0.6% Black*36.6% Native American*0.4% Asian*0.1% Native Hawaiian or Pacific Islander*3.5% Two or more races*7.2% Other races*19.1% Hispanic or Latino -2000:...

.

Modern extraction and distribution


For large-scale use, helium is extracted by fractional distillation
Fractional distillation
Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation...

 from natural gas, which contains up to 7% helium. Since helium has a lower boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

 than any other element, low temperature and high pressure are used to liquefy nearly all the other gases (mostly nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 and methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

). 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
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...

. 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. In the United States, most helium is extracted from natural gas of the Hugoton
Hugoton Natural Gas Area
Hugoton Natural Gas Area is a combination of large natural gas fields in the U.S. state of Kansas, the largest of which is the Hugoton Field. Its name is derived from the town of Hugoton, Kansas, near which the Hugoton Field was first discovered.-History:...

 and nearby gas fields in Kansas, Oklahoma, and Texas. Much of this gas was once sent by pipeline to the National Helium Reserve
National Helium Reserve
The National Helium Reserve, also known as the Federal Helium Reserve, is a strategic reserve of the United States holding over a billion cubic meter of helium gas. The helium is stored at the Cliffside Storage Facility about northwest of Amarillo, Texas, in a natural geologic gas storage...

, but since 2005 this reserve is presently being depleted and sold off.

Diffusion of crude natural gas through special semipermeable membrane
Semipermeable membrane
A semipermeable membrane, also termed a selectively permeable membrane, a partially permeable membrane or a differentially permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized "facilitated diffusion".The rate of...

s and other barriers is another method to recover and purify helium. , 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 is 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. It is estimated that the resource base for yet-unproven helium in natural gas in the U.S. is 31–53 trillion SCM, about 1000 times the proven reserves.

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, that 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
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...

 or boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...

 with high-velocity protons, but economically, this is a completely non-viable method of production.

Helium is commercially available in either liquid or gaseous form. As a liquid, it can be supplied in small containers called Dewars
Dewar flask
A Dewar flask is a vessel designed to provide very good thermal insulation. For instance, when filled with a hot liquid, the vessel will not allow the heat to easily escape, and the liquid will stay hot for far longer than in a typical container...

 which hold up to 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 up to 8 m3 (approx. 282 standard cubic feet), while large quantities of high pressure gas are supplied in tube trailers which have capacities of up to 4,860 m3 (approx. 172,000 standard cubic feet).

Conservation advocates


According to helium conservationists like Robert Coleman Richardson
Robert Coleman Richardson
Robert Coleman Richardson is an American experimental physicist whose area of research includes sub-millikelvin temperature studies of helium-3...

, the free market price of helium has contributed to "wasteful" usage (e.g. for helium balloons
Tethered helium balloon
A tethered helium balloon is a helium-filled gas balloon which is tethered to the ground, or to a road vehicle, by a steel rope and raised and lowered by a winch.- Tethered or Static Helium Balloon:...

). Prices in the 2000s have been lowered by U.S. Congress' decision to sell off the country's large helium stockpile by 2015. According to Richardson, the current price needs to be multiplied by 20 to eliminate the excessive wasting of helium.

Applications



Helium is used for many purposes that require some of its unique properties, such as its low boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

, low density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

, low solubility
Solubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...

, high thermal conductivity
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

, or inert
Inert
-Chemistry:In chemistry, the term inert is used to describe a substance that is not chemically reactive.The noble gases were previously known as inert gases because of their perceived lack of participation in any chemical reactions...

ness. Of the 2008 world helium total production of about 32 million kg (193 million standard cubic meters) helium per year, the largest use (about 22% of the total in 2008) is in cryogenic applications, most of which involves cooling the superconducting magnets in medical MRI scanners. Other major uses (totalling to about 78% of use in 1996) were pressurizing and purging systems, maintenance of controlled atmospheres, and welding. Other uses by category were relatively minor fractions.

Controlled atmospheres


Helium is used as a protective gas in growing silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 and germanium
Germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....

 crystals, in titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

 and zirconium
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, grey-white, strong transition metal that resembles titanium...

 production, and in gas chromatography, because it is inert. Because of its inertness, thermally and calorically perfect
Ideal gas
An ideal gas is a theoretical gas composed of a set of randomly-moving, non-interacting point particles. The ideal gas concept is useful because it obeys the ideal gas law, a simplified equation of state, and is amenable to analysis under statistical mechanics.At normal conditions such as...

 nature, high speed of sound
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....

, and high value of the heat capacity ratio
Heat capacity ratio
The heat capacity ratio or adiabatic index or ratio of specific heats, is the ratio of the heat capacity at constant pressure to heat capacity at constant volume . It is sometimes also known as the isentropic expansion factor and is denoted by \gamma or \kappa . The latter symbol kappa is...

, it is also useful in supersonic wind tunnel
Wind tunnel
A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...

s and impulse facilities
Impulse facility
A testing facility that relies on rapid release of stored energy to generate a short period of high enthalpy test conditions for testing of aerodynamic flow, aerodynamic heating and atmospheric reentry, combustion, chemical kinetics, ballistics, and other effects...

.

Gas tungsten arc welding



Helium is used as a shielding gas
Shielding gas
Shielding gases are inert or semi-inert gases that are commonly used in several welding processes, most notably gas metal arc welding and gas tungsten arc welding . Their purpose is to protect the weld area from atmospheric gases, such as oxygen, nitrogen, carbon dioxide, and water vapour...

 in arc welding
Arc welding
Arc welding is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct or alternating current, and consumable or non-consumable electrodes...

 processes on materials that at welding temperatures are contaminated and weakened by air or nitrogen. A number of inert shelding gases are used in gas tungsten arc welding, but helium is used instead of cheaper argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

 especially for welding materials that have higher heat conductivity, like aluminum or copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

.

Industrial leak detection


One industrial application for helium is leak detection. Because helium diffuses
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

 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
Helium mass spectrometer
A helium mass spectrometer is an instrument commonly used to detect and locate small leaks. It was initially developed in the Manhattan Project during World War II to find extremely small leaks in the gas diffusion process of uranium enrichment plants. It typically uses a vacuum chamber in which a...

), 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
Lighter than air
Lighter than air refers to gases that are buoyant in air because they have densities lower than that of air .Some of these gases are used as lifting gases in lighter-than-air aircraft, which include free balloons, moored balloons, and airships, to make the whole craft, on average, lighter than air...

, airship
Airship
An airship or dirigible is a type of aerostat or "lighter-than-air aircraft" that can be steered and propelled through the air using rudders and propellers or other thrust mechanisms...

s and balloons are inflated with helium for lift. While hydrogen gas is approximately 7% more buoyant, helium has the advantage of being non-flammable (in addition to being fire retardant). While balloons are perhaps the most well-known use of helium, they are a minor part of all helium use. Another minor use is in rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...

ry, where helium is used as an ullage
Ullage
Ullage or Headspace refers to the unfilled space in a container, particularly with a liquid.-Etymology:The word comes ultimately from the Latin oculus, “eye”, which was used in a figurative sense by the Romans for the bung hole of a barrel...

 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
Saturn V
The Saturn V was an American human-rated expendable rocket used by NASA's Apollo and Skylab programs from 1967 until 1973. A multistage liquid-fueled launch vehicle, NASA launched 13 Saturn Vs from the Kennedy Space Center, Florida with no loss of crew or payload...

 booster used in the Apollo program needed about 370,000 m3 (13 million cubic feet) of helium to launch.

Minor commercial and recreational uses


For its low solubility in nervous tissue
Nervous tissue
Nervous tissue is one of four major classes of vertebrate tissue.Nervous tissue is the main component of the nervous system - the brain, spinal cord, and nerves-which regulates and controls body functions...

, helium mixtures such as trimix, heliox
Heliox
Heliox is a breathing gas composed of a mixture of helium and oxygen .Heliox has been used medically since the 1930s, and although the medical community adopted it initially to alleviate symptoms of upper airway obstruction, its range of medical uses has since expanded greatly, mostly because of...

 and heliair
Heliair
Heliair is a breathing gas consisting of mixture of oxygen, nitrogen and helium and is often used during the deep phase of dives carried out using technical diving techniques...

 are used for deep diving
Deep diving
The meaning of the term deep diving is a form of technical diving. It is defined by the level of the diver's diver training, diving equipment, breathing gas, and surface support:...

 to reduce the effects of narcosis
Nitrogen narcosis
Narcosis while diving , is a reversible alteration in consciousness that occurs while scuba diving at depth. The Greek word ναρκωσις is derived from narke, "temporary decline or loss of senses and movement, numbness", a term used by Homer and Hippocrates...

. At depths below 150 metres (492.1 ft) small amounts of hydrogen are added to a helium-oxygen mixture to counter the effects of high pressure nervous syndrome
High pressure nervous syndrome
High-pressure nervous syndrome is a neurological and physiological diving disorder that results when a commercial diver or scuba diver descends below about while breathing a helium–oxygen mixture. The effects depend on the rate of descent and the depth...

. At these depths the low density of helium is found to considerably reduce the effort of breathing.

Helium-neon laser
Helium-neon laser
A helium–neon laser or HeNe laser, is a type of gas laser whose gain medium consists of a mixture of helium and neon inside of a small bore capillary tube, usually excited by a DC electrical discharge.- History of HeNe laser development:...

s, a type of low-powered gas laser producing a red beam, had various practical applications which included barcode reader
Barcode reader
A barcode reader is an electronic device for reading printed barcodes. Like a flatbed scanner, it consists of a light source, a lens and a light sensor translating optical impulses into electrical ones...

s and laser pointer
Laser pointer
A laser pointer or laser pen is a small portable device with a power source and a laser emitting a very narrow coherent low-powered beam of visible light, intended to be used to highlight something of interest by illuminating it with a small bright spot of colored light...

s, before they were almost universally replaced by cheaper diode lasers.

For its inertness and high thermal conductivity
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

, 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
Thermoacoustic refrigeration
Thermoacoustic engines are thermoacoustic devices which use high-amplitude sound waves to pump heat from one place to another, or conversely use a heat difference to induce high-amplitude sound waves. In general, thermoacoustic engines can be divided into standing wave and travelling wave devices...

 due to the resulting high heat capacity ratio
Heat capacity ratio
The heat capacity ratio or adiabatic index or ratio of specific heats, is the ratio of the heat capacity at constant pressure to heat capacity at constant volume . It is sometimes also known as the isentropic expansion factor and is denoted by \gamma or \kappa . The latter symbol kappa is...

 and low Prandtl number. The inertness of helium has environmental advantages over conventional refrigeration systems which contribute to ozone depletion or global warming.

Scientific uses


The use of helium reduces the distorting effects of temperature variations in the space between lenses
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...

 in some telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

s, 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
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 and thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

 can be estimated by measuring the level of helium with a process known as helium dating
Helium dating
Helium dating may refer to the traditional uranium-thorium dating or uranium-thorium/helium dating.A relatively new dating method, tritium-helium dating has been developed for determining rates of oxygen utilization in the ocean....

.

Helium at low temperatures is used in cryogenics
Cryogenics
In physics, cryogenics is the study of the production of very low temperature and the behavior of materials at those temperatures. A person who studies elements under extremely cold temperature is called a cryogenicist. Rather than the relative temperature scales of Celsius and Fahrenheit,...

, and in certain crygenics applications. As examples of applications, liquid helium is used to cool certain metals to the extremely low temperatures required for superconductivity
Superconductivity
Superconductivity is a phenomenon of exactly zero electrical resistance occurring in certain materials below a characteristic temperature. It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum...

, such as in superconducting magnet
Superconducting magnet
A superconducting magnet is an electromagnet made from coils of superconducting wire. They must be cooled to cryogenic temperatures during operation. In its superconducting state the wire can conduct much larger electric currents than ordinary wire, creating intense magnetic fields...

s for magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...

. The Large Hadron Collider
Large Hadron Collider
The Large Hadron Collider is the world's largest and highest-energy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature....

 at CERN
CERN
The European Organization for Nuclear Research , known as CERN , is an international organization whose purpose is to operate the world's largest particle physics laboratory, which is situated in the northwest suburbs of Geneva on the Franco–Swiss border...

 uses 96 metric tons of liquid helium to maintain the temperature at 1.9 kelvin.

Safety


Neutral helium at standard conditions is non-toxic, plays no biological role and is found in trace amounts in human blood. If enough helium is inhaled that oxygen needed for normal respiration
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...

 is replaced, asphyxia
Asphyxia
Asphyxia or asphyxiation is a condition of severely deficient supply of oxygen to the body that arises from being unable to breathe normally. An example of asphyxia is choking. Asphyxia causes generalized hypoxia, which primarily affects the tissues and organs...

 is possible. The safety issues for cryogenic helium are similar to those of liquid nitrogen
Liquid nitrogen
Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4...

; its extremely low temperatures can result in cold burns
Frostbite
Frostbite is the medical condition where localized damage is caused to skin and other tissues due to extreme cold. Frostbite is most likely to happen in body parts farthest from the heart and those with large exposed areas...

 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
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...

 that occurs when helium gas at less than 10 K is warmed to room temperature
Room temperature
-Comfort levels:The American Society of Heating, Refrigerating and Air-Conditioning Engineers has listings for suggested temperatures and air flow rates in different types of buildings and different environmental circumstances. For example, a single office in a building has an occupancy ratio per...

.

Biological effects



The speed of sound
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....

 in helium is nearly three times the speed of sound in air. Because the fundamental frequency
Fundamental frequency
The fundamental frequency, often referred to simply as the fundamental and abbreviated f0, is defined as the lowest frequency of a periodic waveform. In terms of a superposition of sinusoids The fundamental frequency, often referred to simply as the fundamental and abbreviated f0, is defined as the...

 of a gas-filled cavity is proportional to the speed of sound in the gas, when helium is inhaled there is a corresponding increase in the pitches of the resonant frequencies of the vocal tract
Vocal tract
The vocal tract is the cavity in human beings and in animals where sound that is produced at the sound source is filtered....

. This causes a reedy, duck-like vocal quality. (The opposite effect, lowering frequencies, can be obtained by inhaling a dense gas such as sulfur hexafluoride
Sulfur hexafluoride
Sulfur hexafluoride is an inorganic, colorless, odorless, and non-flammable greenhouse gas. has an octahedral geometry, consisting of six fluorine atoms attached to a central sulfur atom. It is a hypervalent molecule. Typical for a nonpolar gas, it is poorly soluble in water but soluble in...

 or xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...

.)

Inhaling helium can be dangerous if done to excess, since helium is a simple asphyxiant
Asphyxiant gas
An asphyxiant gas is a non-toxic or minimally toxic gas which reduces or diplaces the normal oxygen concentration in breathing air. Prolonged breathing of oxygen depleted air can lead to death by asphyxiation...

 and so displaces oxygen needed for normal respiration. Breathing pure helium continuously causes death by asphyxia
Asphyxia
Asphyxia or asphyxiation is a condition of severely deficient supply of oxygen to the body that arises from being unable to breathe normally. An example of asphyxia is choking. Asphyxia causes generalized hypoxia, which primarily affects the tissues and organs...

tion within minutes. Inhaling helium directly from pressurized cylinders is extremely dangerous, as the high flow rate can result in barotrauma
Barotrauma
Barotrauma is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding fluid...

, fatally rupturing lung tissue. However, death caused by helium is rare, with only two fatalities reported between 2000 and 2004 in the United States. However, there were two cases in 2010, one in the USA in January and another in Northern Ireland in November.

At high pressures (more than about 20 atm or two MPa
MPA
-Academic degrees:* Master of Professional Accountancy* Master of Public Administration* Master of Public Affairs* Master of Physician's Assistant-Chemicals:* Medroxyprogesterone acetate, also known by the brand name Depo-Provera* Morpholide of pelargonic acid...

), a mixture of helium and oxygen (heliox
Heliox
Heliox is a breathing gas composed of a mixture of helium and oxygen .Heliox has been used medically since the 1930s, and although the medical community adopted it initially to alleviate symptoms of upper airway obstruction, its range of medical uses has since expanded greatly, mostly because of...

) 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
    Abiogenic petroleum origin
    Abiogenic petroleum origin is a largely abandoned hypothesis that was proposed as an alternative to theory of biological petroleum origin. It was relatively popular in the past, but it went largely forgotten at the end of the 20th century after it failed to predict the location of new wells.The...

  • Helium-3 propulsion
  • Leidenfrost effect
    Leidenfrost effect
    The Leidenfrost effect is a phenomenon in which a liquid, in near contact with a mass significantly hotter than the liquid's boiling point, produces an insulating vapor layer which keeps that liquid from boiling rapidly...

  • Quantum solid
    Quantum solid
    In physics, a quantum solid is a type of solid that is "intrinsically restless", in the sense that atoms continuously vibrate about their position and exchange places even at the absolute zero of temperature. The archetypal quantum solid is low density solid helium.-References:*E.Polturak and...

  • Superfluid
    Superfluid
    Superfluidity is a state of matter in which the matter behaves like a fluid without viscosity and with extremely high thermal conductivity. The substance, which appears to be a normal liquid, will flow without friction past any surface, which allows it to continue to circulate over obstructions and...

  • Tracer-gas leak testing method
    Tracer-gas leak testing method
    Tracer-gas leak testing method is a nondestructive testing method.-Types:Several tracer-gas leak testing methods exist among which the methods of choice are:* Helium mass spectrometer or helium leak detection, providing the highest sensitivity...


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