Difference between revisions of "Helium"

Atomic properties
Atomic number	2
Standard atomic weight	4.002 602(2)
Electron configuration	1s2
Physical properties
Melting point	see text
Boiling point	4.22 K (−268.93 °C)
Critical point	5.2 K, 2.274 bar
Density	0.169 kg m−3 (1 atm, 15 °C); 16.891 kg m−3 (1 atm, 4.2 K); 0.12496 g cm−3 (l, 4.2 K)
Chemical properties
Solubility in water	8.9 cm3 kg−1 (1 atm, 20 °C)
Ionization energies
1st	24.587 3985(14) eV; 2360.634 56(12) kJ mol−1
2nd	54.416 eV; 5250.5 kJ mol−1
Total	79.003 eV; 7622.8 kJ mol−1
Thermodynamic properties
Standard entropy	126.153(2) J K−1 mol−1
Enthalpy change of vaporization	0.08 kJ mol−1
Molar heat capacity (Cp)	20 J K−1 mol−1
Miscellaneous
CAS number	7440-59-7
EC number	231-168-5
	Where appropriate, and unless otherwise stated, data are given for 100 kPa (1 bar) and 298.15 K (25 °C).
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Latest revision as of 18:41, 21 September 2010

hydrogen ← helium → lithium

–
↑
He
↓
Ne

Helium (symbol: He) is a chemical element, the lightest of the noble gases.

History

Helium is the only element to have been discovered extraterrestrially before being found on Earth, specifically in the Sun.^[5] A bright yellow spectral line (λ = 587.49 nm) was first observed by French astronomer Jules Janssen during the eclipse of 18 August 1868, which Janssen observed from Guntur in India, and independently by Norman Lockyer in London on 20 October 1868.^[6]^[7]^[8] Lockyer, together with English chemist Edward Frankland, showed that the line could not be explained by any known element, and proposed the name helium, from the Greek ἥλιος (helios; the Sun).^[9]^[10]

The first isolation of helium from a terrestrial source is usually credited to the British chemist William Ramsey, who isolated the helium that was occluded in the mineral cleveite (a uranium-containing mineral) and identified it by its spectrum.^[11] The occluded gas had been noticed previously by American geochemist William Francis Hillebrand, but had been misidentified as nitrogen.^[12] Helium had been identified (through its spectrum) on Earth as early as 1881 by Italian physicist Luigi Palmieri,^[5] but Palmieri could not isolate a sample of the element. Finally, helium was isolated independently in 1895 by Per Teodor Cleve and Abraham Langlet in Uppsala, Sweden, who collected enough of the gas to accurately determine its atomic weight.^[13] Nevertheless, it was Ramsey who was awarded the Nobel Prize in Chemistry (in 1904),^[14] and who is usually credited with the discovery.

The first significant quantities of helium on Earth were discovered in the natural gas from a well in Kansas, USA, in 1903–6:^[15]^[16] the discovery was designated a National Historic Chemical Landmark by the American Chemical Society in 2000.^[17] At the same time, New Zealander Ernest Rutherford was speculating that one type of radioactivity, known as α-decay, was caused by the emission of a form of helium.^[18] Rutherford was able to prove that α-particles are He²⁺ ions,^[19] for which he was awarded the Nobel Prize In Chemistry in 1908.^[20] Rutherford's elegant proof, coupled with many more circumstantial results from other workers, explained why helium was found in association with uranium and thorium minerals.^{[note 1]}

Helium was first liquified by Dutch physicist Heike Kamerlingh Onnes in 1908, a feat for which he would receive the Nobel Prize in Physics (1913),^[21] but was not solidified until 1926 (by Kamerlingh Onnes' student Willem Hendrik Keesom). Yet another Nobel Prize (again in physics) was awarded to Lev Landau in 1962 for his explanation of the extraordinary proporties of liquid helium at low temperatures, known as superfluidity.^[22]

Occurrence and production

Country	Production 10⁶ m³ ^{[note 2]}
United States	122*
Algeria	24
Qatar	15
Russia	7
Poland	2.5
Estimates for 2009 from the U.S. Geological Survey^[23]
*U.S. figure includes 42 million cubic metres withdrawn from the federal government stockpile.

Helium is the second most common element in the Universe (after hydrogen), accounting for 23% of all atoms. However, the Earth's gravitational field is not strong enough to retain helium in the atmosphere for long periods, and almost all the Earth's primordial helium is believed to have escaped.^[24] The helium currently present on Earth has been formed from the α-decay of radioactive nuclides:^{[note 3]} most of this helium escapes to the atmosphere, where the current volume fraction is 5.24 ppm,^[25] and then into space: some of it, however, can be trapped underground by impermeable rock formations, often associated with natural gas deposits.

The commercial production of helium is based around its extraction from natural gas, which is economically viable when the helium fraction is greater than about 0.3%.^[5] The United States has historically been the predominant producer, although its de novo production is declining and Algeria and Qatar are gaining importance.

The U.S. Bureau of Land Management operates a stockpile of crude (~80%) helium, the National Helium Reserve at Cliffside Field, Potter County, Texas, and a crude-helium pipeline from Bushton, Kansas, passing through the Reichel Field (Kansas) and the Keyes Field (Oklahoma) to the Cliffside Field.^[26] The National Helium Reserve reached its peak in 1980, with 194,000 tonnes (1150 million cubic metres) stored,^[27] but it is being run down under the terms of the Helium Privatization Act of 1996 (Pub. L. 104–273), and will eventually be just 600 million cubic feet (16.6 million cubic metres). About one third of the helium produced in the United States is refined from stored helium rather than being extracted from natural gas,^[23] and the National Helium Reserve held 561 million cubic metres of crude helium at the end of 2008.^[26]

The refinement of crude helium to the normal commercial grade ("Grade I", about 99.995%) requires cooling with liquid hydrogen to below 27 K (−246 °C, −411 °F) to condense out the neon present: liquid hydrogen is required, as helium gas cannot be cooled by the Joule–Thomson effect until its temperature is below about 40 K.^[28]^[29] Commercial helium is usually shipped in bulk as a liquid.^[26]

Use

Total U.S. consumpton (2009) 52.1 million cubic metres
Cryogenics	32%
Pressurizing and purging	18%
Controlled atmospheres	18%
Welding cover gas	13%
Leak detection	4%
Breathing mixtures	2%
Other uses	13%
Estimates for 2009 from the U.S. Geological Survey^[23] The breakdown of usage in other countries may be significantly different: see text.

The main use of helium is in cryogenics, where helium is essential for temperatures below −256 °C (−429 °F),^[23] the approximate boiling point of liquid hydrogen. Cooling with liquid helium allows an operating temperature of around −269 °C (−452 °F), just four kelvins. Such low temperatures are required for superconducting magnets to operate; these are used in a variety of applications, including NMR spectrometers and magnetic resonance imaging (MRI) scanners.

Uses for pressurizing and purging, in controlled atmospheres (e.g., glove boxes) and as a welding cover gas are only important in the United States, where helium is relatively cheap, and are declining even there along with a general fall in U.S. helium consumption (−42% over the period 2000–2009).^[27]^[30]^{[note 4]} In other countries, argon is used for these purposes.

There are several niche uses of helium, including:^[5]

as a means of detecting small leaks of gas in otherwise closed systems using the helium mass spectrometer approach, usually for leaks of 10⁻⁵–10⁻¹³ Pa m³ s⁻¹ (from about 1 ml/min to less than 3 ml per century)
as a replacement for nitrogen in breathing mixtures which are to be delivered to humans at high pressure, such as in deep-sea diving, and also in some medical uses;
as a flow gas in gas chromatography, particularly when using a katharometer, a helium ionization detector (HID) or in GC–MS;
as a lifting gas for meteorological balloons and airships;
as a heat transfer agent, particularly in VHTR nuclear reactors.

Physical properties

Helium has a number of unique physical properties. It is the chemical substance with the lowest boiling point (4.22 K) and the only substance that cannot be solidified by cooling alone at atmospheric pressure. It is also the only substance without a triple point, a temperature and pressure at which solid, liquid and gas are all in equilibrium.^[5]

Helium has an extremely high specific heat capacity (C_p = 5.19 kJ K⁻¹ kg⁻¹ at 25 °C)^[31] and, for a gas, a relatively high thermal conductivity (0.1430 W m⁻¹ K⁻¹ at 0 °C):^[5] both of these are due to the low mass of the atoms which make up helium gas (H₂ is even more exceptional on both counts), and are important in its uses in gas chromatography and as a heat transfer agent.

Helium at low pressures and ambient temperatures is the nearest practical model to an ideal gas, one in which the attractive forces between atoms are negligible, as is the volume of the atoms compared with the volume occupied by the gas. It has an extremely low Joule–Thomson inversion temperature of about 40–45 K:^[29]^[32] above this temperature, the Joule–Thomson coefficient is negative and so helium will warm up as it expands.

Liquid helium

	⁴He		³He
	T	p	T	p
Critical point	5.2 K		3.3 K
Boiling point	4.2 K	1 atm	3.2 K	1 atm
Melting point at minimum freezing pressure	1.0 K	25 bar	0.3 K	29 bar
λ point at saturated vapour pressure	2.17K		1 mK

Main articles: Helium I and helium II

Liquid helium-4 can be condensed at 4.22 K to a liquid phase now known as helium I. If cooling is continued (by allowing some of the liquid to evaporate), the physical properties of the liquid change drastically at about 2.2 K (the exact value depends on the pressure). For a start, the visible bubbling of a boiling liquid disappears, although evaporation continues: the heat capacity increases ten-fold, the thermal conductivity increases a million-fold and the viscosity drops to virtually zero.

The low-temperature liquid phase is known as helium II, and is a superfluid similar in nature to a Bose–Einstein condensate, first discovered in 1938. The transition between the two liquid phases is a second-order phase transition, and the transition temperature is known as the λ point after the shape of the plot of heat capacity vs. temperature, which resembles a Greek letter lambda. Perhaps the best known property of helium II is its propensity to form Rollin films, layers approximately 30 nm thick that will climb up surfaces cool enough to support helium II even against the force of gravity: as such, the confinement of liquid helium below the λ point is particularly difficult.

Helium-3 also forms a superfluid phase, discovered in 1972, but only at temperatures of one millikelvin or less. The difference in behaviour between the two isotopes is due to their nuclear spin: helium-4 atoms are bosons, with zero spin, while helium-3 atoms are spin-½ fermions, and the two types of particle obey different exclusion principles. For similar reasons, liquid helium-4 and liquid helium-3 are no longer miscible below about 0.9 K.

Neither isotope can be solidified at pressures of 1 atm. By raising the pressure to 25 atm or higher, helium can be can be solidified at 1–1.5 K. The solid form is unusually compressible, with a bulk modulus of around 50 MPa (fifty-times more compressible than liquid water). Liquid and solid phases of helium have extremely low refractive indexes, which makes it difficult to distinguish phase changes by visual means.

Chemical properties

Helium has the highest first ionization energy of any element (2372.3 kJ mol⁻¹) and has almost unprecedented chemical inertness. No chemical compounds of helium are known in condensed phases, although the [HeH]⁺ cation (the protonation product of a helium atom) was first observed in 1925,^[33] and its neutral analogue is also known in the gas phase.

The low solubility of helium in water (8.61 cm³ kg⁻¹ at 101.325 kPa, 20 °C)^[5]^[34] is important in its use as a component of breathing mixtures: helium, unlike nitrogen at high pressure, will not dissolve in blood serum, and so poses fewer problems of degassing of the blood stream during decompression.

Notes and references

Notes

↑ See Rutherford's Nobel lecture for a description of the many pieces of evidence which were put together between 1903 and 1908 before Rutherford's final conclusive experiment.
↑ Most U.S. Geological Survey sources quote amounts of helium in millions of cubic metres, measured at 101.325 kPa and 15 °C. Older U.S. sources may quote values in cubic feet, measured at 14.7 psi and 70 °F: one cubic metre (101.325 kPa, 15 °C) = 36.053 cubic feet (14.7 psi, 70 °F). 10⁶ m³ (101.325 kPa, 15 °C) = 169.29 tonnes.
↑ The helium-3 isotope (x = 1.34(3) ppm in the atmosphere) is formed from the β-decay of tritium (31H): the existence of helium from volcanic rocks or associated geothermal springs and gases with x(³He) > 10 ppm indicates that at least some of this helium-3 is primordial.
↑ U.S. consumption of helium in 2000 was 89.8 million cubic metres, of which: cryogenics 24%, pressurizing and purging 20%, welding cover gas 18%, controlled atmospheres 16%, leak detection 6%, breathing mixtures 3%, other uses (chromatography/lifting gas/heat transfer) 13%.

References

↑ Helium. In NIST Chemistry WebBook; National Institute for Standards and Technology, <http://webbook.nist.gov/cgi/inchi/InChI%3D1S/He>. (accessed 19 March 2010).
↑ ^2.0 ^2.1 ^2.2 Helium. In Gas Encyclopedia; Air Liquide, <http://encyclopedia.airliquide.com/encyclopedia.asp?GasID=32>. (accessed 3 April 2010).
↑ Moore, Charlotte E. Ionization potentials and ionization limits derived from the analyses of optical spectra. Natl. Stand. Ref. Data Ser., (U.S. Natl. Bur. Stand.) 1970, 34, 1–22, <http://www.nist.gov/data/nsrds/NSRDS-NBS34.pdf>.
↑ Cox, J. D.; Wagman, D. D.; Medvedev, V. A. CODATA Key Values for Thermodynamics; Hemisphere: New York, 1989. ISBN 0891167587, <http://www.codata.org/resources/databases/key1.html>.
↑ ^5.0 ^5.1 ^5.2 ^5.3 ^5.4 ^5.5 ^5.6 ^5.7 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; pp 1042–59. ISBN 0-08-022057-6.
↑ Cortie, A. L. Sir Norman Lockyer, 1836–1920. Astrophys. J. 1921, 53 (4), 233–48, <http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1921ApJ....53..233C&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf>.
↑ Leggett, Hadley Aug. 18, 1868: Helium Discovered During Total Solar Eclipse; wired.com, August 18, 2009, <http://www.wired.com/thisdayintech/2009/08/dayintech_0818/>. (accessed 18 March 2010).
↑ C. R. Hebd. Acad. Sci. Paris 1868, 67, 836–41, <http://gallica.bnf.fr/ark:/12148/bpt6k3024c.image.r=comptes-rendus+hebdomadaires+Acad%C3%A9mie+des+Sciences.f836.langFR>.
↑ Helium. In Oxford English Dictionary; Oxford University Press, 2008, <http://dictionary.oed.com/cgi/entry/50104457?>. (accessed 20 July 2008).
↑ "Frankland and Lockyer find the yellow prominences to give a very decided bright line not far from D, but hitherto not identified with any terrestrial flame. It seems to indicate a new substance, which they propose to call Helium." Thomson, W. Rep. Brit. Assoc. 1872, 99.
↑ Ramsay, William On a Gas Showing the Spectrum of Helium, the Reputed Cause of D₃, One of the Lines in the Coronal Spectrum. Preliminary Note. Proc. Roy. Soc. London 1895, 58, 65–67. DOI: 10.1098/rspl.1895.0006. Ramsay, William Helium, a Gaseous Constituent of Certain Minerals. Part I. Proc. Roy. Soc. London 1895, 58, 80–89. DOI: 10.1098/rspl.1895.0010. Ramsay, William Helium, a Gaseous Constituent of Certain Minerals. Part II. Proc. Roy. Soc. London 1895, 59, 325–30. DOI: 10.1098/rspl.1895.0097.
↑ W. F. Hillebrand (1853–1925), geochemist and US Bureau of Standards administrator. In American National Biography; Garraty, John A.; Carnes, Mark C., Eds.; Oxford University Press, 1999; Vol. 10-11, pp 227–28, 808–9.
↑ Langlet, N. A. Das Atomgewicht des Heliums. Z. Anorg. Chem. 1895, 10 (1), 289–92. DOI: 10.1002/zaac.18950100130.
↑ The Nobel Prize in Chemistry 1904; Nobel Foundation, <http://nobelprize.org/nobel_prizes/chemistry/laureates/1904/index.html>. (accessed 2 April 2010).
↑ McFarland, D. F. Composition of Gas from a Well at Dexter, Kan.. Trans. Kansas Acad. Sci. 1903, 19, 60–62. DOI: 10.2307/3624173.
↑ Cady, H.P.; McFarland, D. F. Helium in Natural Gas. Science 1906, 24, 344. DOI: 10.1126/science.24.611.344.
↑ The Discovery of Helium in Natural Gas; American Chemical Society, <http://acswebcontent.acs.org/landmarks/landmarks/helium/helium.html>. (accessed 2 April 2010).
↑ Rutherford, E.; Soddy, F. The Cause and Nature of Radioactivity II. Phil. Mag., Ser. 6 1902, 4, 569–85. Rutherford, E. The Magnetic and Electric Deviation of the Easily Absorbed Rays from Radium. Phil. Mag., Ser. 6 1903, 5, 177–87. Rutherford, E.; Soddy, F. The Radioactivity of Uranium. Phil. Mag., Ser. 6 1903, 5, 441–45. Rutherford, E.; Soddy, F. A Comparative Study of the Radioactivity of Radium and Thorium. Phil. Mag., Ser. 6 1903, 5, 445–57. Rutherford, E. The Amount of Emanation and Helium from Radium. Nature 1903, 68, 366–67.
↑ Rutherford, E.; Royds, T. Spectrum of the Radium Emanation. Nature 1908, 78, 220–21. Rutherford, E.; Royds, T. The Nature of the Alpha Particle. Mem. Manchester Lit. Phil. Soc., Ser. IV 1908, 53 (1), 1–3. Rutherford, E.; Royds, T. The Nature of the Alpha Particle from Radioactive Substances. Phil. Mag., Ser. 6 1909, 17, 281–86.
↑ The Nobel Prize in Chemistry 1908; Nobel Foundation, <http://nobelprize.org/nobel_prizes/chemistry/laureates/1908/index.html>. (accessed 2 April 2010).
↑ The Nobel Prize in Physics 1913; Nobel Foundation, <http://nobelprize.org/nobel_prizes/physics/laureates/1913/>. (accessed 4 April 2010).
↑ The Nobel Prize in Physics 1962; Nobel Foundation, <http://nobelprize.org/nobel_prizes/physics/laureates/1962/>. (accessed 4 April 2010).
↑ ^23.0 ^23.1 ^23.2 ^23.3 Pacheco, Norbert; Thomas, Diedre S. Helium. In Mineral Commodities Summaries; U.S. Geological Survey, January 2010, <http://minerals.usgs.gov/minerals/pubs/commodity/helium/mcs-2010-heliu.pdf>.
↑ Atomic weights of the elements. Review 2000. Pure Appl. Chem., 75 (6), 683–800. DOI: 10.1351/pac200375060683.
↑ U.S. Standard Atmosphere, 1976; National Oceanic and Atmospheric Administration: Washington, D.C., 1976; p 3, <http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770009539_1977009539.pdf>.
↑ ^26.0 ^26.1 ^26.2 Pacheco, Norbert Helium. In 2008 Minerals Yearbook; U.S. Geological Survey, October 2009, <http://minerals.usgs.gov/minerals/pubs/commodity/helium/myb1-2008-heliu.pdf>.
↑ ^27.0 ^27.1 Kelly, T. D.; Matos, G. R. Helium statistics. In Historical statistics for mineral and material commodities in the United States; U.S. Geological Survey, 2008. U.S. Geological Survey Data Series 140, <http://minerals.usgs.gov/ds/2005/140/helium.pdf>. (accessed 19 March 2010).
↑ Ashmead, J. A Joule–Thomson Cascade Liquefier for Helium. Proc. Phys. Soc. B 1950, 63 (7), 504. DOI: 10.1088/0370-1301/63/7/304.
↑ ^29.0 ^29.1 Van Sciver, Steven W. Helium cryogenics; Springer, 1986; pp 286–88. ISBN 0306423359, <http://books.google.co.uk/books?id=bdYsrq2n5YYC>.
↑ Kelly, T. D.; Matos, G. R. Helium statistics. In Historical statistics for mineral and material commodities in the United States; U.S. Geological Survey, 2003. U.S. Geological Survey Data Series 140, <http://minerals.usgs.gov/ds/2005/140/helium-use.pdf>. (accessed 19 March 2010).
↑ CRC Handbook of Chemistry and Physics, 62nd ed.; Weast, Robert C., Ed.; CRC Press: Boca Raton, FL, 1981; p D-155. ISBN 0-8493-0462-8.
↑ Roebuck, J. R.; Osterberg, H. The Joule-Thomson Effect in Helium. Phys. Rev. 1933, 43 (1), 60–69. DOI: 10.1103/PhysRev.43.60.
↑ Hogness, T. R.; Lunn, E. G. The Ionization of Hydrogen by Electron Impact as Interpreted by Positive Ray Analysis. Phys. Rev. 1925, 26, 44–55. DOI: 10.1103/PhysRev.26.44.
↑ Weiss, Ray F. Solubility of helium and neon in water and seawater. J. Chem. Eng. Data 1971, 16 (2), 235–41. DOI: 10.1021/je60049a019.

External links

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[21] See Rutherford's Nobel lecture for a description of the many pieces of evidence which were put together between 1903 and 1908 before Rutherford's final conclusive experiment.

[m3-24] Most U.S. Geological Survey sources quote amounts of helium in millions of cubic metres, measured at 101.325 kPa and 15 °C. Older U.S. sources may quote values in cubic feet, measured at 14.7 psi and 70 °F: one cubic metre (101.325 kPa, 15 °C) = 36.053 cubic feet (14.7 psi, 70 °F). 10⁶ m³ (101.325 kPa, 15 °C) = 169.29 tonnes.

[27] The helium-3 isotope (x = 1.34(3) ppm in the atmosphere) is formed from the β-decay of tritium (31H): the existence of helium from volcanic rocks or associated geothermal springs and gases with x(³He) > 10 ppm indicates that at least some of this helium-3 is primordial.

[34] U.S. consumption of helium in 2000 was 89.8 million cubic metres, of which: cryogenics 24%, pressurizing and purging 20%, welding cover gas 18%, controlled atmospheres 16%, leak detection 6%, breathing mixtures 3%, other uses (chromatography/lifting gas/heat transfer) 13%.

[NIST-1] Helium. In NIST Chemistry WebBook; National Institute for Standards and Technology, <http://webbook.nist.gov/cgi/inchi/InChI%3D1S/He>. (accessed 19 March 2010).

[AirLiquide-2] 2.0 ^2.1 ^2.2 Helium. In Gas Encyclopedia; Air Liquide, <http://encyclopedia.airliquide.com/encyclopedia.asp?GasID=32>. (accessed 3 April 2010).

[3] Moore, Charlotte E. Ionization potentials and ionization limits derived from the analyses of optical spectra. Natl. Stand. Ref. Data Ser., (U.S. Natl. Bur. Stand.) 1970, 34, 1–22, <http://www.nist.gov/data/nsrds/NSRDS-NBS34.pdf>.

[4] Cox, J. D.; Wagman, D. D.; Medvedev, V. A. CODATA Key Values for Thermodynamics; Hemisphere: New York, 1989. ISBN 0891167587, <http://www.codata.org/resources/databases/key1.html>.

[G.26E-5] 5.0 ^5.1 ^5.2 ^5.3 ^5.4 ^5.5 ^5.6 ^5.7 Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; pp 1042–59. ISBN 0-08-022057-6.

[6] Cortie, A. L. Sir Norman Lockyer, 1836–1920. Astrophys. J. 1921, 53 (4), 233–48, <http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1921ApJ....53..233C&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf>.

[7] Leggett, Hadley Aug. 18, 1868: Helium Discovered During Total Solar Eclipse; wired.com, August 18, 2009, <http://www.wired.com/thisdayintech/2009/08/dayintech_0818/>. (accessed 18 March 2010).

[8] C. R. Hebd. Acad. Sci. Paris 1868, 67, 836–41, <http://gallica.bnf.fr/ark:/12148/bpt6k3024c.image.r=comptes-rendus+hebdomadaires+Acad%C3%A9mie+des+Sciences.f836.langFR>.

[9] Helium. In Oxford English Dictionary; Oxford University Press, 2008, <http://dictionary.oed.com/cgi/entry/50104457?>. (accessed 20 July 2008).

[10] "Frankland and Lockyer find the yellow prominences to give a very decided bright line not far from D, but hitherto not identified with any terrestrial flame. It seems to indicate a new substance, which they propose to call Helium." Thomson, W. Rep. Brit. Assoc. 1872, 99.

[11] Ramsay, William On a Gas Showing the Spectrum of Helium, the Reputed Cause of D₃, One of the Lines in the Coronal Spectrum. Preliminary Note. Proc. Roy. Soc. London 1895, 58, 65–67. DOI: 10.1098/rspl.1895.0006. Ramsay, William Helium, a Gaseous Constituent of Certain Minerals. Part I. Proc. Roy. Soc. London 1895, 58, 80–89. DOI: 10.1098/rspl.1895.0010. Ramsay, William Helium, a Gaseous Constituent of Certain Minerals. Part II. Proc. Roy. Soc. London 1895, 59, 325–30. DOI: 10.1098/rspl.1895.0097.

[12] W. F. Hillebrand (1853–1925), geochemist and US Bureau of Standards administrator. In American National Biography; Garraty, John A.; Carnes, Mark C., Eds.; Oxford University Press, 1999; Vol. 10-11, pp 227–28, 808–9.

[13] Langlet, N. A. Das Atomgewicht des Heliums. Z. Anorg. Chem. 1895, 10 (1), 289–92. DOI: 10.1002/zaac.18950100130.

[14] The Nobel Prize in Chemistry 1904; Nobel Foundation, <http://nobelprize.org/nobel_prizes/chemistry/laureates/1904/index.html>. (accessed 2 April 2010).

[15] McFarland, D. F. Composition of Gas from a Well at Dexter, Kan.. Trans. Kansas Acad. Sci. 1903, 19, 60–62. DOI: 10.2307/3624173.

[16] Cady, H.P.; McFarland, D. F. Helium in Natural Gas. Science 1906, 24, 344. DOI: 10.1126/science.24.611.344.

[17] The Discovery of Helium in Natural Gas; American Chemical Society, <http://acswebcontent.acs.org/landmarks/landmarks/helium/helium.html>. (accessed 2 April 2010).

[18] Rutherford, E.; Soddy, F. The Cause and Nature of Radioactivity II. Phil. Mag., Ser. 6 1902, 4, 569–85. Rutherford, E. The Magnetic and Electric Deviation of the Easily Absorbed Rays from Radium. Phil. Mag., Ser. 6 1903, 5, 177–87. Rutherford, E.; Soddy, F. The Radioactivity of Uranium. Phil. Mag., Ser. 6 1903, 5, 441–45. Rutherford, E.; Soddy, F. A Comparative Study of the Radioactivity of Radium and Thorium. Phil. Mag., Ser. 6 1903, 5, 445–57. Rutherford, E. The Amount of Emanation and Helium from Radium. Nature 1903, 68, 366–67.

[19] Rutherford, E.; Royds, T. Spectrum of the Radium Emanation. Nature 1908, 78, 220–21. Rutherford, E.; Royds, T. The Nature of the Alpha Particle. Mem. Manchester Lit. Phil. Soc., Ser. IV 1908, 53 (1), 1–3. Rutherford, E.; Royds, T. The Nature of the Alpha Particle from Radioactive Substances. Phil. Mag., Ser. 6 1909, 17, 281–86.

[20] The Nobel Prize in Chemistry 1908; Nobel Foundation, <http://nobelprize.org/nobel_prizes/chemistry/laureates/1908/index.html>. (accessed 2 April 2010).

[22] The Nobel Prize in Physics 1913; Nobel Foundation, <http://nobelprize.org/nobel_prizes/physics/laureates/1913/>. (accessed 4 April 2010).

[23] The Nobel Prize in Physics 1962; Nobel Foundation, <http://nobelprize.org/nobel_prizes/physics/laureates/1962/>. (accessed 4 April 2010).

[USGS-MCS-25] 23.0 ^23.1 ^23.2 ^23.3 Pacheco, Norbert; Thomas, Diedre S. Helium. In Mineral Commodities Summaries; U.S. Geological Survey, January 2010, <http://minerals.usgs.gov/minerals/pubs/commodity/helium/mcs-2010-heliu.pdf>.

[26] Atomic weights of the elements. Review 2000. Pure Appl. Chem., 75 (6), 683–800. DOI: 10.1351/pac200375060683.

[28] U.S. Standard Atmosphere, 1976; National Oceanic and Atmospheric Administration: Washington, D.C., 1976; p 3, <http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770009539_1977009539.pdf>.

[MYB-29] 26.0 ^26.1 ^26.2 Pacheco, Norbert Helium. In 2008 Minerals Yearbook; U.S. Geological Survey, October 2009, <http://minerals.usgs.gov/minerals/pubs/commodity/helium/myb1-2008-heliu.pdf>.

[UGS-DS-30] 27.0 ^27.1 Kelly, T. D.; Matos, G. R. Helium statistics. In Historical statistics for mineral and material commodities in the United States; U.S. Geological Survey, 2008. U.S. Geological Survey Data Series 140, <http://minerals.usgs.gov/ds/2005/140/helium.pdf>. (accessed 19 March 2010).

[31] Ashmead, J. A Joule–Thomson Cascade Liquefier for Helium. Proc. Phys. Soc. B 1950, 63 (7), 504. DOI: 10.1088/0370-1301/63/7/304.

[VanSciver-32] 29.0 ^29.1 Van Sciver, Steven W. Helium cryogenics; Springer, 1986; pp 286–88. ISBN 0306423359, <http://books.google.co.uk/books?id=bdYsrq2n5YYC>.

[33] Kelly, T. D.; Matos, G. R. Helium statistics. In Historical statistics for mineral and material commodities in the United States; U.S. Geological Survey, 2003. U.S. Geological Survey Data Series 140, <http://minerals.usgs.gov/ds/2005/140/helium-use.pdf>. (accessed 19 March 2010).

[35] CRC Handbook of Chemistry and Physics, 62nd ed.; Weast, Robert C., Ed.; CRC Press: Boca Raton, FL, 1981; p D-155. ISBN 0-8493-0462-8.

[36] Roebuck, J. R.; Osterberg, H. The Joule-Thomson Effect in Helium. Phys. Rev. 1933, 43 (1), 60–69. DOI: 10.1103/PhysRev.43.60.

[37] Hogness, T. R.; Lunn, E. G. The Ionization of Hydrogen by Electron Impact as Interpreted by Positive Ray Analysis. Phys. Rev. 1925, 26, 44–55. DOI: 10.1103/PhysRev.26.44.

[38] Weiss, Ray F. Solubility of helium and neon in water and seawater. J. Chem. Eng. Data 1971, 16 (2), 235–41. DOI: 10.1021/je60049a019.

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Difference between revisions of "Helium"

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-'''Helium''' ({{pron-en|ˈhiːliəm}}, {{respell|HEE|lee-əm}}) is the [[chemical element]] with [[atomic number]] 2, and is represented by the symbol '''He'''. It is a colorless, odorless, tasteless, non-toxic, [[inert]] [[monatomic]] [[gas]] that heads the [[noble gas]] group in the [[periodic table]]. Its [[boiling point|boiling]] and [[melting point|melting]] points are the lowest among the elements and it exists only as a gas except in extreme conditions.
+{{Infobox element
+|name = helium
-An unknown yellow [[spectroscopy|spectral line]] signature in sunlight was first observed from a [[solar eclipse]] in 1868 by French astronomer [[Pierre Janssen]]. Janssen is jointly credited with the [[discovery of the chemical elements|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 helium. In 1903, large reserves of helium were found in the [[natural gas field]]s of the [[United States]], which is by far the largest supplier of the gas. Helium is used in [[cryogenics]], in [[Heliox|deep-sea breathing systems]], to cool [[superconducting magnet]]s, in [[helium dating]], for inflating balloons, for providing lift in [[airship]]s and as a protective gas for many industrial uses (such as [[arc welding]] and growing [[silicon wafer]]s). Inhaling a small volume of the gas temporarily changes the timbre and quality of the human voice. The behavior of liquid helium-4's two fluid phases, helium&nbsp;I and helium&nbsp;II, is important to researchers studying [[quantum mechanics]] (in particular the phenomenon of [[superfluidity]]) and to those looking at the effects that temperatures near [[absolute zero]] have on [[matter]] (such as [[superconductivity]]).
+|symbol = He
+|left = [[hydrogen]]
-Helium is the second lightest element and is the second most [[chemical abundance|abundant]] in the observable [[universe]], being present in the universe in masses more than 12 times those of all the other elements heavier than helium combined. Helium's abundance is also similar to this in our own Sun and Jupiter. This high abundance is due to the very high binding energy (per [[nucleon]]) of helium-4 with respect to the next three elements after helium (lithium, beryllium, and boron). 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 was formed during the [[Big Bang]]. Some new helium is being created presently as a result of the [[nuclear fusion]] of hydrogen, in all but the very heaviest [[star]]s, which fuse helium into heavier elements at the extreme ends of their lives.
+|right = [[lithium]]
+|above = –
-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. What helium is present today has been mostly created by the natural [[radioactive decay]] of heavy radioactive elements ([[thorium]] and [[uranium]]), as the [[alpha particle]]s that are emitted by such decays consist of helium-4 [[atomic nucleus|nuclei]]. This radiogenic helium is trapped with [[natural gas]] in concentrations up to seven percent by volume, from which it is extracted commercially by a low-temperature separation process called [[fractional distillation]].
+|below = [[Neon|Ne]]
+|atomic-number = 2
+|atomic-weight = 4.002 602(2)
+|configuration = 1s<sup>2</sup>
+|phys-ref = <ref name="NIST">{{NIST chemistry | name = Helium | id = 1S/He | accessdate = 2010-03-19}}.</ref><ref name="AirLiquide">{{AirLiquide | name = Helium | id = 32 | accessdate = 2010-04-03}}.</ref>
+|melting-point = ''see text''
+|boiling-point = 4.22 K (−268.93&nbsp;°C)
+|critical-point = 5.2 K, 2.274 bar
+|density = 0.169 kg m<sup>−3</sup> (1 atm, 15&nbsp;°C)<br/>16.891 kg m<sup>−3</sup> (1 atm, 4.2&nbsp;K)<br/>0.12496 g cm<sup>−3</sup> (l, 4.2&nbsp;K)
+|chem-ref = <ref name="AirLiquide"/>
+|solubility = 8.9 cm<sup>3</sup> kg<sup>−1</sup> (1 atm, 20&nbsp;°C)
+|IE-ref = <ref>{{NSRDS-NBS 34}}.</ref>
+|IE1 = 24.587 3985(14) eV<br/>2360.634 56(12) kJ mol<sup>−1</sup>
+|IE2 = 54.416 eV<br/>5250.5 kJ mol<sup>−1</sup>
+|IE-total = 79.003 eV<br/>7622.8 kJ mol<sup>−1</sup>
+|thermo-ref = <ref name="AirLiquide"/><ref>{{CODATA thermo}}.</ref><ref name="G&E">{{Greenwood&Earnshaw1st|pages=1042–59}}.</ref>
+|entropy = 126.153(2) J K<sup>−1</sup> mol<sup>−1</sup>
+|enthalpy-vaporization = 0.08 kJ mol<sup>−1</sup>
+|heat-capacity = 20 J K<sup>−1</sup> mol<sup>−1</sup>
+|CAS-number = 7440-59-7
+|EC-number = 231-168-5
+}}
+'''Helium''' (symbol: '''He''') is a [[chemical element]], the lightest of the [[noble gas]]es.
 ==History==
-===Scientific discoveries===
+Helium is the only element to have been discovered extraterrestrially before being found on Earth, specifically in the Sun.<ref name="G&E"/> A bright yellow spectral line (''λ''&nbsp;= 587.49&nbsp;nm) was first observed by French astronomer [[Jules Janssen]] during the eclipse of 18&nbsp;August 1868, which Janssen observed from Guntur in India, and independently by [[Norman Lockyer]] in London on 20&nbsp;October 1868.<ref>{{citation | title = Sir Norman Lockyer, 1836–1920 | url = http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1921ApJ....53..233C&amp;data_type=PDF_HIGH&amp;whole_paper=YES&amp;type=PRINTER&amp;filetype=.pdf | last = Cortie | first = A. L. | journal = Astrophys. J. | year = 1921 | volume = 53 | issue = 4 | pages = 233–48}}.</ref><ref>{{citation | url = http://www.wired.com/thisdayintech/2009/08/dayintech_0818/  | publisher = wired.com | accessdate = 2010-03-18 | title = Aug. 18, 1868: Helium Discovered During Total Solar Eclipse | date = August 18, 2009 | first = Hadley | last = Leggett}}.</ref><ref>{{citation | journal = C. R. Hebd. Acad. Sci. Paris | volume = 67 | year = 1868 | pages = 836–41 | url = http://gallica.bnf.fr/ark:/12148/bpt6k3024c.image.r=comptes-rendus+hebdomadaires+Acad%C3%A9mie+des+Sciences.f836.langFR}}.</ref> Lockyer, together with English chemist [[Edward Frankland]], showed that the line could not be explained by any known element, and proposed the name helium, from the Greek {{Polytonic|ἥλιος}} (''helios''; the Sun).<ref>{{citation | contribution = Helium | title = Oxford English Dictionary | year = 2008 | url = http://dictionary.oed.com/cgi/entry/50104457? | publisher = Oxford University Press | accessdate = 2008-07-20}}.</ref><ref>"Frankland and Lockyer find the yellow prominences to give a very decided bright line not far from D, but hitherto not identified with any terrestrial flame. It seems to indicate a new substance, which they propose to call Helium." {{citation| last = Thomson | first = W. | year = 1872 | journal = Rep. Brit. Assoc. | page = 99}}.</ref>
-The first evidence of helium was observed on August 18, 1868 as a bright yellow line with a [[wavelength]] of 587.49&nbsp;nanometers in the [[Emission spectrum|spectrum]] of the [[chromosphere]] of the [[Sun]]. The line was detected by French astronomer [[Pierre Janssen]] during a total [[solar eclipse]] in [[Guntur]], [[British Raj|India]].<ref name="frnch">{{cite journal|title = French astronomers in India during the 17th - 19th centuries |journal = Journal of the British Astronomical Association|volume =101|issue = 2|pages = 95–100|url = http://articles.adsabs.harvard.edu//full/1991JBAA..101...95K/0000100.000.html|author = Kochhar, R. K. |accessdate=2008-07-27|year=1991}}</ref><ref name="nbb"/> This line was initially assumed to be [[sodium]]. On October 20 of the same year, English astronomer [[Norman Lockyer]] observed a yellow line in the solar spectrum, which he named the D<sub>3</sub> [[Fraunhofer line]] because it was near the known D<sub>1</sub> and D<sub>2</sub> lines of sodium.<ref name=enc>{{cite book |title= The Encyclopedia of the Chemical Elements |pages =256-268 |author = Clifford A. Hampel |location=New York |isbn = 0442155980 |year = 1968 |publisher =Van Nostrand Reinhold}}</ref>  He concluded that it was caused by an element in the Sun unknown on Earth. Lockyer and English chemist [[Edward Frankland]] named the element with the Greek word for the Sun, ἥλιος (''[[helios]]'')."<ref>[http://balloonprofessional.co.uk/decoration_balloons/balloon-helium-gas/ Sir Norman Lockyer - discovery of the element that he named helium]" ''Balloon Professional Magazine'', 07 Aug 2009.</ref><ref>{{cite web| title=Helium|publisher = Oxford English Dictionary| year = 2008| url = http://dictionary.oed.com/cgi/entry/50104457?| accessdate = 2008-07-20}}</ref><ref>{{cite book|author=Thomson, W.|year=1872|publisher=Rep. Brit. Assoc. xcix|title=Frankland and Lockyer find the yellow prominences to give a very decided bright line not far from D, but hitherto not identified with any terrestrial flame. It seems to indicate a new substance, which they propose to call Helium}}</ref>
-[[Image:Helium spectrum.jpg|left|200px|thumb|Spectral lines of helium|alt=Picture of visible spectrum with superimposed sharp yellow and blue and violet lines.]]
-On March 26, 1895 British chemist [[William Ramsay|Sir William Ramsay]] isolated helium on Earth by treating the mineral [[cleveite]] (a variety of [[uraninite]] with at least 10% [[rare earth elements]]) with mineral [[acid]]s. Ramsay was looking for [[argon]] but, after separating [[nitrogen]] and [[oxygen]] from the gas liberated by [[sulfuric acid]], he noticed a bright yellow line that matched the D<sub>3</sub> line observed in the spectrum of the Sun.<ref name=enc/><ref>{{cite journal|title = On a Gas Showing the Spectrum of Helium, the Reputed Cause of D3 , One of the Lines in the Coronal Spectrum. Preliminary Note|author = [[William Ramsay|Ramsay, William]]|journal = Proceedings of the Royal Society of London|volume = 58|pages = 65–67|year = 1895|doi = 10.1098/rspl.1895.0006}}</ref><ref>{{cite journal|title = Helium, a Gaseous Constituent of Certain Minerals. Part I|author = Ramsay, William|journal = Proceedings of the Royal Society of London|volume = 58|pages = 80–89|year = 1895|doi = 10.1098/rspl.1895.0010}}</ref><ref>{{cite journal|title = Helium, a Gaseous Constituent of Certain Minerals. Part II--|author = Ramsay, William|journal = Proceedings of the Royal Society of London|volume = 59|pages = 325–330|year = 1895|doi = 10.1098/rspl.1895.0097}}</ref> These samples were identified as helium by Lockyer and British physicist [[William Crookes]]. It was independently isolated from cleveite in the same year by chemists [[Per Teodor Cleve]] and [[Abraham Langlet]] in [[Uppsala, Sweden]], who collected enough of the gas to accurately determine its [[atomic weight]].<ref name="nbb"/><ref>{{de icon}} {{cite journal|title = Das Atomgewicht des Heliums|author = Langlet, N. A.|journal = Zeitschrift für anorganische Chemie|volume = 10|issue = 1| pages = 289–292|year = 1895|doi =10.1002/zaac.18950100130|language= German}}</ref><ref>{{cite book| chapter= Bibliography of Helium Literature|author =Weaver, E.R.| title=Industrial & Engineering Chemistry|year=1919}}</ref> Helium was also isolated by the American geochemist [[William Francis Hillebrand]] prior to Ramsay's discovery when he noticed unusual spectral lines while testing a sample of the mineral uraninite. Hillebrand, however, attributed the lines to nitrogen. His letter of congratulations to Ramsay offers an interesting case of discovery and near-discovery in science.<ref>{{cite book|author=[[Pat Munday|Munday, Pat]]|year=1999|title=Biographical entry for W.F. Hillebrand (1853–1925), geochemist and US Bureau of Standards administrator in [[American National Biography]]|editor=John A. Garraty and Mark C. Carnes|volume=10-11|publisher=Oxford University Press|pages= 808–9; pp. 227–8}}</ref>
-In 1907, [[Ernest Rutherford]] and Thomas Royds demonstrated that [[alpha particle]]s are helium [[atomic nucleus|nuclei]] by allowing the particles to penetrate the thin glass wall of an evacuated tube, then creating a discharge in the tube to study the spectra of the new gas inside. In 1908, helium was first liquefied by Dutch physicist [[Heike Kamerlingh Onnes]] by cooling the gas to less than one [[kelvin]].<ref>{{cite journal |title = Little cup of Helium, big Science |author = van Delft, Dirk |journal = Physics today |url = http://www-lorentz.leidenuniv.nl/history/cold/VanDelftHKO_PT.pdf |format=PDF|pages = 36–42 |year = 2008 |accessdate = 2008-07-20}}</ref> He tried to solidify it by further reducing the temperature but failed because helium does not have a [[triple point]] temperature at which the solid, liquid, and gas phases are at equilibrium. Onnes' student [[Willem Hendrik Keesom]] was eventually able to solidify 1&nbsp;cm<sup>3</sup> of helium in 1926.<ref>{{cite news|title = Coldest Cold| publisher = Time Inc.| date = 1929-06-10| url = http://www.time.com/time/magazine/article/0,9171,751945,00.html| accessdate = 2008-07-27}}</ref>
+The first isolation of helium from a terrestrial source is usually credited to the British chemist [[William Ramsey]], who isolated the helium that was occluded in the mineral [[cleveite]] (a [[uranium]]-containing mineral) and identified it by its spectrum.<ref>{{citation | title = On a Gas Showing the Spectrum of Helium, the Reputed Cause of D<sub>3</sub>, One of the Lines in the Coronal Spectrum. Preliminary Note | last = Ramsay | first = William | authorlink = William Ramsay | journal = Proc. Roy. Soc. London | volume = 58 | pages = 65–67 | year = 1895 | doi = 10.1098/rspl.1895.0006}}. {{citation | title = Helium, a Gaseous Constituent of Certain Minerals. Part I | last = Ramsay | first = William | authorlink = William Ramsay | journal = Proc. Roy. Soc. London | volume = 58 | pages = 80–89 | year = 1895 | doi = 10.1098/rspl.1895.0010}}. {{citation | title = Helium, a Gaseous Constituent of Certain Minerals. Part II | last = Ramsay | first = William | authorlink = William Ramsay | journal = Proc. Roy. Soc. London | volume = 59 | pages = 325–30 | year = 1895 | doi = 10.1098/rspl.1895.0097}}.</ref> The occluded gas had been noticed previously by American geochemist [[William Francis Hillebrand]], but had been misidentified as nitrogen.<ref>{{citation | year = 1999 | contribution = W. F. Hillebrand (1853–1925), geochemist and US Bureau of Standards administrator | title = American National Biography | editor1-first = John A. | editor1-last = Garraty | editor2-first = Mark C. | editor2-last = Carnes | volume = 10-11 | publisher=Oxford University Press | pages = 227–28, 808–9}}.</ref> Helium had been identified (through its spectrum) on Earth as early as 1881 by Italian physicist [[Luigi Palmieri]],<ref name="G&E"/> but Palmieri could not isolate a sample of the element. Finally, helium was isolated independently in 1895 by [[Per Teodor Cleve]]  and [[Abraham Langlet]]  in [[Uppsala]], [[Sweden]], who collected enough of the gas to accurately determine its [[atomic weight]].<ref>{{citation | title = Das Atomgewicht des Heliums | last = Langlet | first = N. A. | authorlink = Abraham Langlet | journal = Z. Anorg. Chem. | volume = 10 | issue = 1 | pages = 289–92 | year = 1895 | doi =10.1002/zaac.18950100130}}.</ref> Nevertheless, it was Ramsey who was awarded the [[Nobel Prize in Chemistry]] (in 1904),<ref>{{citation | title = The Nobel Prize in Chemistry 1904 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1904/index.html | publisher = Nobel Foundation | accessdate = 2010-04-02}}.</ref> and who is usually credited with the discovery.
-In 1938, Russian physicist [[Pyotr Leonidovich Kapitsa]] discovered that [[helium-4]] has almost no [[viscosity]] at temperatures near [[absolute zero]], a phenomenon now called [[superfluidity]].<ref>{{cite journal |title = Viscosity of Liquid Helium below the λ-Point |author = [[Pyotr Leonidovich Kapitsa|Kapitza, P.]] |journal = [[Nature]] |volume = 141 |pages = 74 |doi = 10.1038/141074a0 |year = 1938}}</ref> This phenomenon is related to [[Bose-Einstein condensation]]. In 1972, the same phenomenon was observed in [[helium-3]], but at temperatures much closer to absolute zero, by American physicists [[Douglas D. Osheroff]], [[David M. Lee]], and [[Robert Coleman Richardson|Robert C. Richardson]]. The phenomenon in helium-3 is thought to be related to pairing of helium-3 [[fermion]]s to make [[boson]]s, in analogy to [[Cooper pairs]] of electrons producing [[superconductivity]].<ref>{{cite journal |title = Evidence for a New Phase of Solid He<sup>3</sup> |author = Osheroff, D. D. |coauthors = R. C. Richardson, D. M. Lee |journal = Phys. Rev. Lett. |volume = 28 |issue = 14 |pages = 885–888 |doi = 10.1103/PhysRevLett.28.885 |year = 1972}}</ref>
+The first significant quantities of helium on Earth were discovered in the [[natural gas]] from a well in Kansas, USA, in 1903–6:<ref>{{citation | last = McFarland | first = D. F. | title = Composition of Gas from a Well at Dexter, Kan. | volume = 19 | pages = 60–62 | | year = 1903 | journal = Trans. Kansas Acad. Sci. | doi = 10.2307/3624173}}.</ref><ref>{{citation | last1 = Cady | first1 = H.P. | last2 = McFarland | first2 = D. F. | title = Helium in Natural Gas | journal = Science | volume = 24 | page = 344 | doi = 10.1126/science.24.611.344 | year = 1906}}.</ref> the discovery was designated a [[National Historic Chemical Landmark]] by the [[American Chemical Society]] in 2000.<ref>{{citation | title = The Discovery of Helium in Natural Gas | url = http://acswebcontent.acs.org/landmarks/landmarks/helium/helium.html | publisher = American Chemical Society | accessdate = 2010-04-02}}.</ref> At the same time, New Zealander [[Ernest Rutherford]] was speculating that one type of [[radioactivity]], known as [[α-decay]], was caused by the emission of a form of helium.<ref>{{citation | first1 = E. | last1 = Rutherford | authorlink1 = Ernest Rutherford | first2 = F. | last2 = Soddy | authorlink2 = Frederick Soddy | title = The Cause and Nature of Radioactivity II | journal = Phil. Mag., Ser. 6 | volume = 4 | year = 1902 | pages = 569–85}}. {{citation | first = E. | last = Rutherford | authorlink1 = Ernest Rutherford | title = The Magnetic and Electric Deviation of the Easily Absorbed Rays from Radium | journal = Phil. Mag., Ser. 6 | volume = 5 | year = 1903 | pages = 177–87}}. {{citation | first1 = E. | last1 = Rutherford | authorlink = Ernest Rutherford | first2 = F. | last2 = Soddy | authorlink2 = Frederick Soddy | title = The Radioactivity of Uranium | journal = Phil. Mag., Ser. 6 | volume = 5 | year = 1903 | pages = 441–45}}. {{citation | first1 = E. | last1 = Rutherford | authorlink1 = Ernest Rutherford | first2 = F. | last2 = Soddy | authorlink2 = Frederick Soddy | title = A Comparative Study of the Radioactivity of Radium and Thorium | journal = Phil. Mag., Ser. 6 | volume = 5 | year = 1903 | pages = 445–57}}. {{citation | first = E. | last = Rutherford | authorlink1 = Ernest Rutherford | title = The Amount of Emanation and Helium from Radium | journal = Nature | volume = 68 | pages = 366–67 | year = 1903}}.</ref> Rutherford was able to prove that α-particles are He<sup>2+</sup> ions,<ref>{{citation | first1 = E. | last1 = Rutherford | authorlink1 = Ernest Rutherford | first2 = T. | last2 = Royds | title = Spectrum of the Radium Emanation | journal = Nature | volume = 78 | pages = 220–21 | year = 1908}}. {{citation | first1 = E. | last1 = Rutherford | authorlink1 = Ernest Rutherford | first2 = T. | last2 = Royds | title = The Nature of the Alpha Particle | journal = Mem. Manchester Lit. Phil. Soc., Ser. IV | volume = 53 | issue = 1 | pages = 1–3 | year = 1908}}. {{citation | first1 = E. | last1 = Rutherford | authorlink1 = Ernest Rutherford | first2 = T. | last2 = Royds | title = The Nature of the Alpha Particle from Radioactive Substances | journal = Phil. Mag., Ser. 6 | volume = 17 | pages = 281–86 | year = 1909}}.</ref> for which he was awarded the Nobel Prize In Chemistry in 1908.<ref>{{citation | title = The Nobel Prize in Chemistry 1908 | url = http://nobelprize.org/nobel_prizes/chemistry/laureates/1908/index.html | publisher = Nobel Foundation | accessdate = 2010-04-02}}.</ref> Rutherford's elegant proof, coupled with many more circumstantial results from other workers, explained why helium was found in association with [[Uranium minerals|uranium]] and [[thorium minerals]].<ref group="note">See [http://nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-lecture.html Rutherford's Nobel lecture] for a description of the many pieces of evidence which were put together between 1903 and 1908 before Rutherford's final conclusive experiment.</ref>
-===Extraction and use===
+Helium was first liquified by Dutch physicist [[Heike Kamerlingh Onnes]] in 1908, a feat for which he would receive the [[Nobel Prize in Physics]] (1913),<ref>{{citation | title = The Nobel Prize in Physics 1913 | url = http://nobelprize.org/nobel_prizes/physics/laureates/1913/ | publisher = Nobel Foundation | accessdate = 2010-04-04}}.</ref> but was not solidified until 1926 (by Kamerlingh Onnes' student [[Willem Hendrik Keesom]]). Yet another Nobel Prize (again in physics) was awarded to [[Lev Landau]] in 1962 for his explanation of the extraordinary proporties of liquid helium at low temperatures, known as [[superfluidity]].<ref>{{citation | title = The Nobel Prize in Physics 1962 | url = http://nobelprize.org/nobel_prizes/physics/laureates/1962/ | publisher = Nobel Foundation | accessdate = 2010-04-04}}.</ref>
-After an oil drilling operation in 1903 in [[Dexter, Kansas|Dexter]], [[Kansas]] produced a gas geyser that would not burn, Kansas state geologist [[Erasmus Haworth]] collected samples of the escaping gas and took them back to the [[University of Kansas]] at Lawrence where, with the help of chemists [[Hamilton Cady]] and David McFarland, he discovered that the gas consisted of, by volume, 72% nitrogen, 15% [[methane]] (a [[combustible]] percentage only with sufficient oxygen), 1% [[hydrogen]], and 12% an unidentifiable gas.<ref name="nbb"/><ref>{{cite journal |author = McFarland, D. F. |title = Composition of Gas from a Well at Dexter, Kan |volume = 19|issue = |pages = 60–62 |url = http://www.jstor.org/stable/3624173 |year = 1903 |accessdate=2008-07-22 |journal = Transactions of the Kansas Academy of Science |doi = 10.2307/3624173}}</ref> With further analysis, Cady and McFarland discovered that 1.84% of the gas sample was helium.<ref>{{cite web|publisher=[[American Chemical Society]]|year=2004|url=http://acswebcontent.acs.org/landmarks/landmarks/helium/helium.html|title=The Discovery of Helium in Natural Gas|accessdate=2008-07-20}}</ref><ref>{{cite journal |author = Cady, H.P. |coauthors = D. F. McFarland |title = Helium in Natural Gas |journal = Science |volume = 24 |issue = |pages = 344 |doi = 10.1126/science.24.611.344 |year = 1906 |pmid = 17772798}}</ref> 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.<ref>{{cite journal |author = Cady, H.P. |coauthors = D. F. McFarland |title = Helium in Kansas Natural Gas |journal = Transactions of the Kansas Academy of Science |volume = 20 |issue = |pages = 80–81 |url = http://mc1litvip.jstor.org/stable/3624645 |year = 1906|accessdate=2008-07-20 |doi = 10.2307/3624645}}</ref> The greatest reserves of helium were in the [[Hugoton Natural Gas Area|Hugoton]] 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]], the [[United States Navy]] sponsored three small experimental helium production plants during [[World War I]]. The goal was to supply [[barrage balloon]]s with the non-flammable, lighter-than-air gas. A total of 200 thousand cubic feet (5,700&nbsp;m<sup>3</sup>) of 92% helium was produced in the program even though only a few cubic feet (less than 100&nbsp;liters) of the gas had previously been obtained.<ref name=enc/> 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|Hampton Roads]], [[Virginia]] to [[Bolling Field]] in [[Washington, D.C.]] on December 1, 1921.<ref>{{cite book |editor=Emme, Eugene M. comp. |title=Aeronautics and Astronautics: An American Chronology of Science and Technology in the Exploration of Space, 1915–1960 |year=1961 |pages=11–19 |chapter=Aeronautics and Astronautics Chronology, 1920–1924 |chapterurl=http://www.hq.nasa.gov/office/pao/History/Timeline/1920-24.html |publisher=[[NASA]] |location=Washington, D.C. |accessdate=2008-07-20}}</ref>
+==Occurrence and production==
+{| class="wikitable" align=left style="margin:0 0.5em 0 0; width:14em;"
+|-
+! Country
+! <u>Production</u><br/>10<sup>6</sup>&nbsp;m<sup>3</sup><br/><ref group="note" name="m3">Most U.S. Geological Survey sources quote amounts of helium in millions of cubic metres, measured at 101.325&nbsp;kPa and 15&nbsp;°C. Older U.S. sources may quote values in cubic feet, measured at 14.7&nbsp;psi and 70&nbsp;°F: one cubic metre (101.325&nbsp;kPa, 15&nbsp;°C) = 36.053 cubic feet (14.7&nbsp;psi, 70&nbsp;°F). 10<sup>6</sup>&nbsp;m<sup>3</sup> (101.325&nbsp;kPa, 15&nbsp;°C) = 169.29&nbsp;tonnes.</ref>
+|-
+| [[United States]]
+| align=right | 122*
+|-
+| [[Algeria]]
+| align=right | 24
+|-
+| [[Qatar]]
+| align=right | 15
+|-
+| [[Russia]]
+| align=right | 7
+|-
+| [[Poland]]
+| align=right | 2.5
+|-
+| colspan=2 | Estimates for 2009 from the<br/>U.S. Geological Survey<ref name="USGS-MCS">{{citation | first1 = Norbert | last1 = Pacheco | first2 = Diedre S. | last2 = Thomas | url = http://minerals.usgs.gov/minerals/pubs/commodity/helium/mcs-2010-heliu.pdf | title = Mineral Commodities Summaries | contribution = Helium | date = January 2010 | publisher = U.S. Geological Survey}}.</ref>
+|-
+| colspan=2 | <small>*U.S. figure includes 42 million<br/>cubic metres withdrawn from the<br/>federal government stockpile.</small>
+|-
+|}
+Helium is the second most common element in the Universe (after [[hydrogen]]), accounting for 23% of all atoms. However, the Earth's gravitational field is not strong enough to retain helium in the atmosphere for long periods, and almost all the Earth's primordial helium is believed to have escaped.<ref>{{IUPAC atomic weight review 2000}}.</ref> The helium currently present on Earth has been formed from the [[α-decay]] of radioactive nuclides:<ref group="note">The [[helium-3]] isotope (''x''&nbsp;= 1.34(3)&nbsp;ppm in the atmosphere) is formed from the [[β-decay]] of [[tritium]] ({{Nuclide|Z=1|A=3}}): the existence of helium from volcanic rocks or associated geothermal springs and gases with ''x''(<sup>3</sup>He)&nbsp;> 10&nbsp;ppm indicates that at least some of this helium-3 is primordial.</ref> most of this helium escapes to the atmosphere, where the current [[volume fraction]] is 5.24&nbsp;ppm,<ref>{{citation | title = U.S. Standard Atmosphere, 1976 | url = http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770009539_1977009539.pdf | publisher = National Oceanic and Atmospheric Administration | location = Washington, D.C. | year = 1976 | page = 3}}.</ref> and then into space: some of it, however, can be trapped underground by impermeable rock formations, often associated with [[natural gas]] deposits.
-Although the extraction process, using low-temperature gas liquefaction, was not developed in time to be significant during World War I, production continued. Helium was primarily used as a [[lifting gas]] in lighter-than-air craft. This use increased demand during World War II, as well as demands for shielded arc [[welding]]. The [[helium mass spectrometer]] was also vital in the atomic bomb [[Manhattan Project]].<ref>{{cite book|chapter=Leak Detection|author=Hilleret, N.|publisher=[[CERN]]|title=CERN Accelerator School, vacuum technology: proceedings: Scanticon Conference Centre, Snekersten, Denmark, 28 May – 3 June 1999 |editor=S. Turner |location=Geneva, Switzerland|url=http://doc.cern.ch/yellowrep/1999/99-05/p203.pdf |format=PDF| year=1999 |pages=203–212 |quote=At the origin of the helium leak detection method was the Manhattan Project and the unprecedented leak-tightness requirements needed by the uranium enrichment plants. The required sensitivity needed for the leak checking led to the choice of a mass spectrometer designed by Dr. A.O.C. Nier tuned on the helium mass.}}</ref>
+The commercial production of helium is based around its extraction from natural gas, which is economically viable when the helium fraction is greater than about 0.3%.<ref name="G&E"/> The [[United States]] has historically been the predominant producer, although its ''de novo'' production is declining and [[Algeria]] and [[Qatar]] are gaining importance.
-The [[government of the United States]] set up the [[National Helium Reserve]] in 1925 at [[Amarillo, Texas|Amarillo]], [[Texas]] with the goal of supplying military [[airship]]s in time of war and commercial airships in peacetime.<ref name=enc/> Due to a US military embargo against Germany that restricted helium supplies, the [[LZ 129 Hindenburg|Hindenburg]] was forced to use hydrogen as the lift gas. Helium use following [[World War II]] was depressed but the reserve was expanded in the 1950s to ensure a supply of liquid helium as a coolant to create oxygen/hydrogen [[rocket fuel]] (among other uses) during the [[Space Race]] and [[Cold War]]. Helium use in the United States in 1965 was more than eight times the peak wartime consumption.<ref>{{cite journal| author = Williamson, John G.| title = Energy for Kansas| journal = Transactions of the Kansas Academy of Science| volume = 71| issue = 4| pages = 432–438| publisher = Kansas Academy of Science|date =1968| url = http://www.jstor.org/pss/3627447| accessdate = 2008-07-27}}</ref>
+The U.S. Bureau of Land Management operates a stockpile of crude (~80%) helium, the [[National Helium Reserve]] at Cliffside Field, Potter County, Texas, and a crude-helium pipeline from Bushton, Kansas, passing through the Reichel Field (Kansas) and the Keyes Field (Oklahoma) to the Cliffside Field.<ref name="MYB">{{citation | first = Norbert | last = Pacheco | url = http://minerals.usgs.gov/minerals/pubs/commodity/helium/myb1-2008-heliu.pdf | contribution = Helium | title = 2008 Minerals Yearbook | publisher = U.S. Geological Survey | date = October 2009}}.</ref> The National Helium Reserve reached its peak in 1980, with 194,000&nbsp;tonnes (1150&nbsp;million cubic metres) stored,<ref name="UGS-DS">{{citation | publisher = U.S. Geological Survey | year = 2008 | contribution = Helium statistics | last1 = Kelly | first1 = T. D. | last2 = Matos | first2 = G. R. | title = Historical statistics for mineral and material commodities in the United States | id = U.S. Geological Survey Data Series 140 | url = http://minerals.usgs.gov/ds/2005/140/helium.pdf | accessdate = 2010-03-19}}.</ref> but it is being run down under the terms of the [[Helium Privatization Act of 1996]]  (Pub.&nbsp;L. 104–273), and will eventually be just 600&nbsp;million cubic feet (16.6&nbsp;million cubic metres). About one third of the helium produced in the United States is refined from stored helium rather than being extracted from natural gas,<ref name="USGS-MCS"/> and the National Helium Reserve held 561&nbsp;million cubic metres of crude helium at the end of 2008.<ref name="MYB"/>
-After the "Helium Acts Amendments of 1960" (Public Law 86–777), the [[United States Bureau of Mines|U.S. Bureau of Mines]] arranged for five private plants to recover helium from natural gas. For this ''helium conservation'' program, the Bureau built a 425&nbsp;mile (684&nbsp;km) pipeline from [[Bushton, Kansas|Bushton]], [[Kansas]] to connect those plants with the government's partially depleted Cliffside gas field, near Amarillo, Texas. This helium-nitrogen mixture was injected and stored in the Cliffside gas field until needed, when it then was further purified.<ref>{{cite journal|journal = Federal Register|date = 2005-10-06|volume = 70|issue = 193|pages = 58464|url = http://edocket.access.gpo.gov/2005/pdf/05-20084.pdf|format=PDF| title = Conservation Helium Sale |accessdate=2008-07-20}}</ref>
+The refinement of crude helium to the normal commercial grade ("Grade&nbsp;I", about 99.995%) requires cooling with liquid [[hydrogen]] to below 27&nbsp;K (−246&nbsp;°C, −411&nbsp;°F) to condense out the [[neon]] present: liquid hydrogen is required, as helium gas cannot be cooled by the [[Joule–Thomson effect]] until its temperature is below about 40&nbsp;K.<ref>{{citation | first = J. | last = Ashmead | year = 1950 | | title = A Joule–Thomson Cascade Liquefier for Helium  | journal = Proc. Phys. Soc. B | volume = 63 | issue = 7 | pages = 504 | doi = 10.1088/0370-1301/63/7/304}}.</ref><ref name="VanSciver">{{citation | title = Helium cryogenics | first = Steven W. | last = Van Sciver | url = http://books.google.co.uk/books?id=bdYsrq2n5YYC | pages = 286–88 | publisher = Springer | year = 1986 | isbn = 0306423359}}.</ref> Commercial helium is usually shipped in bulk as a liquid.<ref name="MYB"/>
-By 1995, a billion cubic meters of the gas had been collected and the reserve was US$1.4&nbsp;billion in debt, prompting the [[Congress of the United States]] in 1996 to phase out the reserve.<ref name="nbb"/><ref name="stwertka">Stwertka, Albert (1998). ''Guide to the Elements: Revised Edition''. New York; Oxford University Press, p. 24. ISBN 0-19-512708-0</ref> The resulting "Helium Privatization Act of 1996"<ref>Helium Privatization Act of 1996 {{USPL|104|273}}</ref> (Public Law 104–273) directed the [[United States Department of the Interior]] to start emptying the reserve by 2005.<ref>{{cite web| url = http://www.nap.edu/openbook/0309070384/html/index.html|title = Executive Summary |publisher = nap.edu |accessdate=2008-07-20}}</ref>
+==Use==
+{| class="wikitable"  align=right style="margin:0 0 0 0.5em; width:18em;"
-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.<ref>{{cite book|publisher=Bureau of Mines / Minerals yearbook 1949|year=1951|author=Mullins, P.V. |coauthors = R. M. Goodling| title = Helium|pages = 599–602 |url = http://digicoll.library.wisc.edu/cgi-bin/EcoNatRes/EcoNatRes-idx?type=div&did=ECONATRES.MINYB1949.PVMULLINS&isize=text|accessdate=2008-07-20}}</ref>
+|-
+! colspan=2 | Total U.S. consumpton (2009)<br/>52.1 million cubic metres
-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]], [[Algeria]] producing 600&nbsp;million cubic feet (17 million cubic meters) began operation, with enough production to cover all of Europe's demand. Meanwhile, by 2000, the consumption of helium within the US had risen to above 15,000&nbsp;[[tonne|metric tons]].<ref>{{cite web|url=http://minerals.usgs.gov/ds/2005/140/helium-use.pdf|format=PDF| title= Helium End User Statistic|accessdate = 2008-07-12|publisher = U.S. Geological Survey|accessdate=2008-07-20}}</ref> In 2004–2006, two additional plants, one in Ras Laffen, [[Qatar]] and the other in [[Skikda]], Algeria were built, but as of early 2007, Ras Laffen is functioning at 50%, and Skikda has yet to start up. Algeria quickly became the second leading producer of helium.<ref name="wwsupply">{{cite journal
+|-
- |title=Challenges to the Worldwide Supply of Helium in the Next Decade |author=Smith, E.M.
+| Cryogenics
- |coauthors=T.W. Goodwin, J. Schillinger |journal=Advances in Cryogenic Engineering |volume=49 A |issue=710 |pages=119–138
+| align=right | 32%
- |year=2003 |doi=10.1063/1.1774674 |format=PDF |accessdate=2008-07-20
+|-
- |url=https://www.airproducts.com/NR/rdonlyres/E44F8293-1CEE-4D80-86EA-F9815927BE7E/0/ChallengestoHeliumSupply111003.pdf
+| Pressurizing and purging
-}}</ref> Through this time, both helium consumption and the costs of producing helium increased.<ref name="Kaplan2007">{{Citation
+| align=right | 18%
- |last=Kaplan |first=Karen H. |date=June 2007 |title=Helium shortage hampers research and industry
+|-
- |periodical=[[Physics Today]] |publisher=[[American Institute of Physics]]
+| Controlled atmospheres
- |volume=60 |issue=6 |pages=31–32 |accessdate=2008-07-20
+| align=right | 18%
- |url=http://ptonline.aip.org/journals/doc/PHTOAD-ft/vol_60/iss_6/31_1.shtml
+|-
- |doi=10.1063/1.2754594
+| Welding cover gas
-}}</ref> In the 2002 to 2007 period helium prices doubled,<ref name="Basu2007">{{Citation
+| align=right | 13%
- |last=Basu |first=Sourish |editor-last=Yam |editor-first=Philip
+|-
- |date=October 2007 |title=Updates: Into Thin Air |accessdate=2008-08-04
+| Leak detection
- |periodical=Scientific American |publisher=Scientific American, Inc. |volume=297 |issue=4 |pages=18
+| align=right | 4%
- |url=http://www.sciamdigital.com/index.cfm?fa=Products.ViewIssuePreview&ARTICLEID_CHAR=E0D18FB2-3048-8A5E-104115527CB01ADB
-}}</ref> and during 2008 alone the major suppliers raised prices about 50%.{{citation needed|date=August 2008}}
-==Characteristics==
-===The helium atom===
-{{main|Helium atom}}
-{| border="1" cellspacing="0" align="right" cellpadding="2" style="margin-left:1em" width=300
 |-
-! bgcolor=gray|'''''Helium atom'''''
+| Breathing mixtures
+| align=right | 2%
 |-
-| align="center"|[[Image:Helium atom QM.svg|300px|right|Helium atom ground state.|alt=Picture of a diffuse gray sphere with grayscale density decreasing from the center. Length scale about 1 Angstrom. An inset outlines the structure of the core, with two red and two blue atoms at the length scale of 1 femtometer.]]
+| Other uses
+| align=right | 13%
 |-
-| style="font-size: smaller; text-align: justify;"|An illustration of the helium atom, depicting the [[atomic nucleus|nucleus]] (pink) and the [[electron cloud]] distribution (black). The nucleus (upper right) in helium-4 is in reality spherically symmetric and closely resembles the electron cloud, although for more complicated nuclei this is not always the case. The black bar is one [[ångström]], equal to 10<sup>−10</sup>&nbsp;[[metre|m]] or 100,000&nbsp;[[Femtometre|fm]].
+| colspan=2 | Estimates for 2009 from the U.S. Geological Survey<ref name="USGS-MCS"/><br/>The breakdown of usage in other countries may be significantly different: ''see text''.
 |-
 |}
+The main use of helium is in cryogenics, where helium is essential for temperatures below −256&nbsp;°C (−429&nbsp;°F),<ref name="USGS-MCS"/> the approximate boiling point of liquid [[hydrogen]]. Cooling with liquid helium allows an operating temperature of around −269&nbsp;°C (−452&nbsp;°F), just four [[kelvin]]s. Such low temperatures are required for [[superconducting magnet]]s to operate; these are used in a variety of applications, including [[NMR spectrometer]]s and [[magnetic resonance imaging]] (MRI) scanners.
-==== Helium in quantum mechanics ====
+Uses for pressurizing and purging, in controlled atmospheres (e.g., [[glove box]]es) and as a welding cover gas are only important in the United States, where helium is relatively cheap, and are declining even there along with a general fall in U.S. helium consumption (−42% over the period 2000–2009).<ref name="UGS-DS"/><ref>{{citation | publisher = U.S. Geological Survey | year = 2003 | contribution = Helium statistics | last1 = Kelly | first1 = T. D. | last2 = Matos | first2 = G. R. | title = Historical statistics for mineral and material commodities in the United States | id = U.S. Geological Survey Data Series 140 | url = http://minerals.usgs.gov/ds/2005/140/helium-use.pdf | accessdate = 2010-03-19}}.</ref><ref group="note">U.S. consumption of helium in 2000 was 89.8 million cubic metres, of which: cryogenics 24%, pressurizing and purging 20%, welding cover gas 18%, controlled atmospheres 16%, leak detection 6%, breathing mixtures 3%, other uses (chromatography/lifting gas/heat transfer) 13%.</ref> In other countries, [[argon]] is used for these purposes.
-Helium is the next simplest [[atom]] to solve using the rules of quantum mechanics, after the [[hydrogen atom]]. Helium is composed of two electrons in orbit around a nucleus containing two protons along with some neutrons. However, 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. However, numerical [[computational chemistry]] methods have been used to create a quantum mechanical picture of helium electron binding which is accurate to within &lt; 2% of the correct value, in a few computational steps.<ref>http://www.sjsu.edu/faculty/watkins/helium.htm</ref> 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 ====
+There are several niche uses of helium, including:<ref name="G&E"/>
+*as a means of detecting small leaks of gas in otherwise closed systems using the [[helium mass spectrometer]] approach, usually for leaks of {{nowrap|10<sup>−5</sup>–10<sup>−13</sup>&nbsp;Pa m<sup>3</sup> s<sup>−1</sup>}} (from about 1&nbsp;ml/min to less than 3&nbsp;ml per century)
+*as a replacement for [[nitrogen]] in [[breathing mixture]]s which are to be delivered to humans at high pressure, such as in deep-sea diving, and also in some medical uses;
+*as a flow gas in [[gas chromatography]], particularly when using a [[katharometer]], a [[helium ionization detector]] (HID) or in [[GC–MS]];
+*as a lifting gas for meteorological balloons and airships;
+*as a heat transfer agent, particularly in [[Very high temperature reactor|VHTR]] [[nuclear reactor]]s.
-The nucleus of the helium-4 atom, which is identical with an [[alpha particle]] is particularly interesting, inasmuch as 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]]. The reason for this symmetry is elegant: the pair of neutrons and pair of protons in helium's nucleus both obey exactly 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]]s fully occupy 1s orbitals in pairs, none of them possessing orbital angular momentum, and each cancelling the other's intrinsic spin. This arrangement is energetically extremely stable for all these particles, and this stability accounts for many crucial facts regarding helium in nature.
+==Physical properties==
+Helium has a number of unique physical properties. It is the [[chemical substance]] with the lowest [[boiling point]] (4.22&nbsp;K) and the only substance that cannot be solidified by cooling alone at atmospheric pressure. It is also the only substance without a [[triple point]], a temperature and pressure at which solid, liquid and gas are all in equilibrium.<ref name="G&E"/>
-For example, the stability and low energy of the electron cloud state in helium accounts for the element's chemical inertness (the most extreme of all the elements), and also the lack of interaction of helium atoms with themselves, producing the lowest melting and boiling points of all the elements.
+Helium has an extremely high [[specific heat capacity]] (''C<sub>p</sub>''&nbsp;= {{nowrap|5.19&nbsp;kJ K<sup>−1</sup> kg<sup>−1</sup>}} at 25&nbsp;°C)<ref>{{RubberBible62nd|page=D-155}}.</ref> and, for a gas, a relatively high [[thermal conductivity]] ({{nowrap|0.1430&nbsp;W m<sup>−1</sup> K<sup>−1</sup>}} at 0&nbsp;°C):<ref name="G&E"/> both of these are due to the low mass of the atoms which make up helium gas (H<sub>2</sub> is even more exceptional on both counts), and are important in its uses in [[gas chromatography]] and as a heat transfer agent.
-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. 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 responsible for the fact the alpha particle is by far the most common type of baryonic particle to be ejected from atomic nuclei—that is, ([[alpha decay]] is far more common than [[cluster decay]]).
+Helium at low pressures and ambient temperatures is the nearest practical model to an [[ideal gas]], one in which the attractive forces between atoms are negligible, as is the volume of the atoms compared with the volume occupied by the gas. It has an extremely low [[Joule–Thomson inversion temperature]] of about 40–45&nbsp;K:<ref name="VanSciver"/><ref>{{citation | journal = Phys. Rev. | volume = 43 | issue = 1 | pages = 60–69 | year = 1933 | title = The Joule-Thomson Effect in Helium | first1 = J. R. | last1 = Roebuck | first2 = H. | last2 = Osterberg | doi = 10.1103/PhysRev.43.60}}.</ref> above this temperature, the Joule–Thomson coefficient is negative and so helium will warm up as it expands.
-The unusual stability of the helium-4 nucleus is also important cosmologically—it explains the fact that in the first few minutes after the [[Big Bang]], as the soup of free protons and neutrons which had been created in about 6:1 ratio, cooled to the point that nuclear binding was possible, the first nuclei to form were helium-4 nuclei. So tight was helium-4 binding, in fact, than it consumed nearly all of the free neutrons before they could beta-decay, leaving very few left to form any lithium, beryllium, or boron. Helium-4 nuclear binding is stronger than in any of these elements (see [[nucleogenesis]] and [[binding energy]]) 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]], carbon. However, due to lack of intermediate elements, this process would take 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 Big Bang, before the early expanding universe cooled in a matter of minutes 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 to helium as is seen today (3 parts hydrogen to 1 part helium-4 by mass), with nearly all the neutrons in the universe (even as it exists today) trapped in the helium-4.
+===Liquid helium===
+{| class="wikitable" align=right style="margin:0 0 0 0.5em;"
+|-
+! rowspan=2 | &nbsp;
+! colspan=2 | [[Helium-4|<sup>4</sup>He]]
+! colspan=2 | [[Helium-3|<sup>3</sup>He]]
+|-
+! ''T''
+! ''p''
+! ''T''
+! ''p''
+|-
+| [[Critical point]]
+| 5.2 K
+|
+| 3.3 K
+|
+|-
+| [[Boiling point]]
+| 4.2 K
+| 1 atm
+| 3.2 K
+| 1 atm
+|-
+| [[Melting point]] at<br/>minimum freezing pressure
+| 1.0 K
+| 25 bar
+| 0.3 K
+| 29 bar
+|-
+| [[λ point]] at<br/>saturated vapour pressure
+| 2.17K
+|
+| 1 mK
+|
+|-
+|}
+{{main|Helium I|helium II}}
+Liquid helium-4 can be condensed at 4.22&nbsp;K to a liquid phase now known as [[helium I]]. If cooling is continued (by allowing some of the liquid to evaporate), the physical properties of the liquid change drastically at about 2.2&nbsp;K (the exact value depends on the pressure). For a start, the visible bubbling of a boiling liquid disappears, although [[evaporation]] continues: the [[heat capacity]] increases ten-fold, the [[thermal conductivity]] increases a ''million-fold'' and the [[viscosity]] drops to virtually zero.
-All heavier elements (including those necessary for rocky planets like the Earth, and for carbon-based or other life), have thus had to be created since the Big Bang, in stars which were hot enough to burn not just hydrogen (for this produces only more helium), but hot enough to burn helium itself. Such stars are massive and therefore rare, and this fact accounts for the fact that all other chemical elements after 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 which isn't hydrogen.
+The low-temperature liquid phase is known as [[helium II]], and is a [[superfluid]] similar in nature to a [[Bose–Einstein condensate]], first discovered in 1938. The transition between the two liquid phases is a [[second-order phase transition]], and the transition temperature is known as the [[λ point]] after the shape of the plot of heat capacity vs. temperature, which resembles a Greek letter lambda. Perhaps the best known property of helium&nbsp;II is its propensity to form Rollin films, layers approximately 30&nbsp;nm thick that will climb up surfaces cool enough to support helium&nbsp;II even against the force of gravity: as such, the confinement of liquid helium below the λ&nbsp;point is particularly difficult.
-===Gas and plasma phases===
+[[Helium-3]] also forms a superfluid phase, discovered in 1972, but only at temperatures of one millikelvin or less. The difference in behaviour between the two isotopes is due to their nuclear spin: helium-4 atoms are [[boson]]s, with zero [[spin]], while helium-3 atoms are spin-½ [[fermion]]s, and the two types of particle obey different exclusion principles. For similar reasons, liquid helium-4 and liquid helium-3 are no longer miscible below about 0.9&nbsp;K.
-Helium is the least reactive [[noble gas]] after [[neon]] and thus the second least reactive of all elements; it is [[inert]] and [[monatomic]] in all standard conditions. Due to helium's relatively low molar (atomic) mass, in the gas phase its [[thermal conductivity]], [[specific heat]], and [[Speed of sound|sound speed]] are all greater than any other gas except [[hydrogen]]. For similar reasons, and also due to the small size of helium atoms, helium's [[diffusion]] rate through solids is three times that of air and around 65% that of hydrogen.<ref name=enc/>
-[[Image:HeTube.jpg|thumb|left|Helium discharge tube shaped like the element's atomic symbol|alt=Illuminated light red gas discharge tubes shaped as letters H and e.]]
+Neither isotope can be solidified at pressures of 1&nbsp;atm. By raising the pressure to 25&nbsp;atm or higher, helium can be can be solidified at 1–1.5&nbsp;K. The solid form is unusually compressible, with a bulk modulus of around 50&nbsp;MPa (fifty-times more compressible than liquid water). Liquid and solid phases of helium have extremely low [[refractive index]]es, which makes it difficult to distinguish phase changes by visual means.
-Helium is less water [[solubility|soluble]] than any other gas known,<ref>{{cite journal|title = Solubility of helium and neon in water and seawater|author = Weiss, Ray F.| year = 1971| journal = J. Chem. Eng. Data|volume = 16|issue = 2|pages = 235–241 |doi = 10.1021/je60049a019}}</ref> and helium's [[index of refraction]] is closer to unity than that of any other gas.<ref>{{cite journal|title = Using helium as a standard of refractive|author = Stone, Jack A. |coauthors = Alois Stejskal| year = 2004| journal = Metrologia|volume = 41|pages = 189–197 |doi =10.1088/0026-1394/41/3/012}}</ref> 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&nbsp;K at 1&nbsp;atmosphere) does it cool upon free expansion.<ref name=enc/> Once precooled below this temperature, helium can be liquefied through expansion cooling.
-Most extraterrestrial helium is found in a [[Plasma (physics)|plasma]] state, with properties quite different from those of atomic helium. In a plasma, helium's electrons are not bound to its nucleus, resulting in very high electrical conductivity, even when the gas is only partially ionized. The charged particles are highly influenced by magnetic and electric fields. For example, in the [[solar wind]] together with ionized hydrogen, the particles interact with the Earth's [[magnetosphere]] giving rise to [[Birkeland current]]s and the [[Aurora (phenomenon)|aurora]].<ref>{{cite journal|title = Helium isotopes in an aurora|author = Buhler, F. |coauthors = W. I. Axford, H. J. A. Chivers, K. Martin| year = 1976|journal = J. Geophys. Res.|volume = 81|issue = 1|pages = 111–115|doi = 10.1029/JA081i001p00111}}</ref>
+==Chemical properties==
+Helium has the highest first [[ionization energy]] of any element ({{nowrap|2372.3&nbsp;kJ mol<sup>−1</sup>}}) and has almost unprecedented chemical inertness. No [[chemical compound]]s of helium are known in [[condensed phase]]s, although the [HeH]<sup>+</sup> cation (the protonation product of a helium atom) was first observed in 1925,<ref>{{citation | first1 = T. R. | last1 = Hogness | first2 = E. G. | last2 = Lunn | title = The Ionization of Hydrogen by Electron Impact as Interpreted by Positive Ray Analysis | journal = Phys. Rev. | year = 1925 | volume = 26 | pages = 44–55 | doi = 10.1103/PhysRev.26.44}}.</ref> and its neutral analogue is also known in the gas phase.
-===Solid and liquid phases===
+The low solubility of helium in water ({{nowrap|8.61&nbsp;cm<sup>3</sup> kg<sup>−1</sup>}} at 101.325&nbsp;kPa, 20&nbsp;°C)<ref name="G&E"/><ref>{{citation | title = Solubility of helium and neon in water and seawater | first = Ray F. | last = Weiss | journal = J. Chem. Eng. Data | year = 1971 | volume = 16 | issue = 2 | pages = 235–41 | doi = 10.1021/je60049a019}}.</ref> is important in its use as a component of [[breathing mixture]]s: helium, unlike [[nitrogen]] at high pressure, will not dissolve in [[blood serum]], and so poses fewer problems of degassing of the blood stream during decompression.
-{{main|Liquid helium}}
-Unlike any other element, helium will remain liquid down to [[absolute zero]] 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&nbsp;K (about –272&nbsp;°C or –457&nbsp;°F) and about 25&nbsp;bar (2.5&nbsp;MPa) of pressure.<ref>{{cite web |date = 2005-10-05 |url = http://www.phys.ualberta.ca/~therman/lowtemp/projects1.htm |title = Solid Helium |publisher = Department of Physics [[University of Alberta]]|accessdate=2008-07-20}}</ref> It is often hard to distinguish solid from liquid helium since the [[refractive index]] of the two phases are nearly the same. The solid has a sharp [[melting point]] and has a [[crystal]]line structure, but it is highly [[Compressibility|compressible]]; applying pressure in a laboratory can decrease its volume by more than 30%.<ref name="LANL.gov">{{RubberBible86th}}</ref> With a [[bulk modulus]] on the order of 5×10<sup>7</sup> [[Pascal (unit)|Pa]]<ref>{{cite journal |author = Malinowska-Adamska, C. |coauthors = P. Soma, J. Tomaszewski |title = Dynamic and thermodynamic properties of solid helium in the reduced all-neighbours approximation of the self-consistent phonon theory |journal = Physica status solidi (b) |volume = 240 |issue = 1 |pages = 55–67 |doi = 10.1002/pssb.200301871 |year = 2003}}</ref> it is 50 times more compressible than water. Solid helium has a density of 0.214&nbsp;±&nbsp;0.006&nbsp;g/ml at 1.15&nbsp;K and 66&nbsp;atm; the projected density at 0&nbsp;K and 25&nbsp;bar is 0.187&nbsp;±&nbsp;0.009&nbsp;g/ml.<ref>{{cite journal |author = Henshaw, D. B. |title = Structure of Solid Helium by Neutron Diffraction |journal = Physical Review Letters |volume = 109 |issue = 2 |pages = 328–330 |doi = 10.1103/PhysRev.109.328 |year = 1958}}</ref>
+==Notes and references==
+===Notes===
+{{reflist|group=note}}
-====Helium I state====
+===References===
-Below its [[boiling point]] of 4.22&nbsp;kelvin and above the [[lambda point]] of 2.1768&nbsp;kelvin, the [[isotope]] helium-4 exists in a normal colorless liquid state, called ''helium&nbsp;I''.<ref name=enc/> Like other [[cryogenic]] liquids, helium&nbsp;I boils when it is heated and contracts when its temperature is lowered. Below the lambda point, however, helium doesn't boil, and it expands as the temperature is lowered further. <!-- clarifyme / The rate of expansion decreases below the lambda point until about 1&nbsp;K is reached; at which point expansion completely stops and helium&nbsp;I starts to contract again. / if it is below the lambda point, should not it be helium II?-->
-Helium&nbsp;I has a gas-like [[index of refraction]] of 1.026 which makes its surface so hard to see that floats of [[styrofoam]] are often used to show where the surface is.<ref name=enc/> This colorless liquid has a very low [[viscosity]] and a density one-eighth that of water, which is only one-fourth the value expected from [[classical physics]].<ref name=enc/> [[Quantum mechanics]] 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]]) from masking the atomic properties.<ref name=enc/>
-====Helium II state====
-Liquid helium below its lambda point begins to exhibit very unusual characteristics, in a state called ''helium&nbsp;II''. Boiling of helium&nbsp;II is not possible due to its high [[thermal conductivity]]; heat input instead causes [[evaporation]] of the liquid directly to gas. The isotope helium-3 also has a [[superfluid]] phase, but only at much lower temperatures; as a result, less is known about such properties in the isotope helium-3.<ref name=enc/>
-[[Image:helium-II-creep.svg|thumb|right|200px|Unlike ordinary liquids, helium&nbsp;II will creep along surfaces in order to reach an equal level; after a short while, the levels in the two containers will equalize. The [[Rollin film]] also covers the interior of the larger container; if it were not sealed, the helium&nbsp;II would creep out and escape.<ref name=enc/>|alt=A cross-sectional drawing showing one vessel inside another. There is a liquid in the outer vessel, and it tends to flow into the inner vessel over its walls.]]
-Helium&nbsp;II is a superfluid, a quantum-mechanical state of matter with strange properties. For example, when it flows through capillaries as thin as 10<sup>−7</sup> to 10<sup>−8</sup>&nbsp;m it has no measurable [[viscosity]].<ref name="nbb"/> However, when measurements were done between two moving discs, a viscosity comparable to that of gaseous helium was observed. Current theory explains this using the ''two-fluid model'' for helium II. In this model, liquid helium below the lambda point is viewed as containing a proportion of helium atoms in a [[ground state]], which are superfluid and flow with exactly zero viscosity, and a proportion of helium atoms in an excited state, which behave more like an ordinary fluid.<ref>{{cite journal |doi = 10.1006/aphy.2000.6019 |title = Microscopic Theory of Superfluid Helium |journal = Annals of Physics |volume = 281 |issue = 1–2 |year = 2000|pages = 636–705 12091211 |author = Hohenberg, P. C.|coauthors = P. C. Martin}}</ref>
-In the ''fountain effect'', a chamber is constructed which is connected to a reservoir of helium&nbsp;II by a [[sintering|sintered]] disc through which superfluid helium leaks easily but through which non-superfluid helium cannot pass. If the interior of the container is heated, the superfluid helium changes to non-superfluid helium. In order to maintain the equilibrium fraction of superfluid helium, superfluid helium leaks through and increases the pressure, causing liquid to fountain out of the container.<ref>{{cite web |author=Warner, Brent|url=http://cryowwwebber.gsfc.nasa.gov/introduction/liquid_helium.html |title=Introduction to Liquid Helium |publisher=NASA|accessdate=2007-01-05 |archiveurl=http://web.archive.org/web/20050901062951/http://cryowwwebber.gsfc.nasa.gov/introduction/liquid_helium.html |archivedate=2005-09-01}}</ref>
-The thermal conductivity of helium&nbsp;II is greater than that of any other known substance, a million times that of helium&nbsp;I and several hundred times that of [[copper]].<ref name=enc/> This is because heat conduction occurs by an exceptional quantum mechanism. Most materials that conduct heat well have a [[valence band]] of free electrons which serve to transfer the heat. Helium&nbsp;II has no such valence band but nevertheless conducts heat well. The [[heat transfer|flow of heat]] is governed by equations that are similar to the [[wave equation]] used to characterize sound propagation in air. When heat is introduced, it moves at 20&nbsp;meters per second at 1.8&nbsp;K through helium&nbsp;II as waves in a phenomenon known as ''[[second sound]]''.<ref name=enc/>
-Helium&nbsp;II also exhibits a creeping effect. When a surface extends past the level of helium&nbsp;II, the helium&nbsp;II moves along the surface, seemingly against the force of [[gravity]]. Helium&nbsp;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&nbsp;[[nanometre|nm]]-thick film regardless of surface material. This film is called a [[Rollin film]] and is named after the man who first characterized this trait, Bernard V. Rollin.<ref name=enc/><ref>{{cite journal |doi = 10.1103/PhysRev.76.1209 |title = Rollin Film Rates in Liquid Helium |journal = Physical Review |volume = 76 |issue = 8 |pages = 1209–1211|year = 1949 |author = Fairbank, H. A. |coauthors = C. T. Lane}}</ref><ref>{{cite journal |doi = 10.1016/S0031-8914(39)80013-1 |title = On the "film" phenomenon of liquid helium II |journal = Physica |volume = 6 |issue = 2 |year = 1939 |pages = 219–230 |author = Rollin, B. V. |coauthors = F. Simon}}</ref> As a result of this creeping behavior and helium&nbsp;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&nbsp;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]]s in shallow water, but rather than gravity, the restoring force is the [[van der Waals force]].<ref>{{cite web |author = Ellis, Fred M. |url = http://fellis.web.wesleyan.edu/research/thrdsnd.html |title = Third sound |publisher = Wesleyan Quantum Fluids Laboratory|year = 2005|accessdate = 2008-07-23}}</ref> These waves are known as ''[[third sound]]''.<ref>{{cite journal |doi = 10.1103/PhysRev.188.370 |title = Hydrodynamics and Third Sound in Thin He II Films |journal = Physical Review |volume = 188 |issue = 1|year = 1949 |pages = 370–384|author = Bergman, D.}}</ref><!-- "van", see cite itself and [[Talk:Van der Waals#Van should be capitalized unless preceded by first name]] rebuttal -->
-==Isotopes==
-{{main|Isotopes of helium}}
-There are eight known [[isotope]]s of helium, but only [[helium-3]] and [[helium-4]] are [[stable isotope|stable]]. In the Earth's atmosphere, there is one {{chem|3|He}} atom for every million {{chem|4|He}} atoms.<ref name="nbb">{{cite book| author = Emsley, John| title = Nature's Building Blocks| publisher = Oxford University Press| year = 2001| location = Oxford| pages = 175–179| isbn = 0-19-850341-5}}</ref> Unlike most elements, helium's isotopic abundance varies greatly by origin, due to the different formation processes. The most common isotope, helium-4, is produced on Earth by [[alpha decay]] of heavier radioactive elements; the alpha particles that emerge are fully ionized helium-4 nuclei. Helium-4 is an unusually stable nucleus because its [[nucleon]]s are arranged into [[Nuclear shell model|complete shells]]. It was also formed in enormous quantities during [[Big Bang nucleosynthesis]].<ref name="bigbang" />
-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]].<ref name="heliumfundamentals">{{cite web |url = http://www.mantleplumes.org/HeliumFundamentals.html |title = Helium Fundamentals |author = Anderson, Don L. |coauthors = G. R. Foulger, Anders Meibom |date = 2006-09-02 |accessdate = 2008-07-20 |publisher = MantlePlumes.org}}</ref> Trace amounts are also produced by the [[beta decay]] of [[tritium]].<ref>{{cite journal|title= Half-Life of Tritium| journal=Physical Review|volume= 72|year= 1947| pages= 972–972|author= Novick, Aaron| doi=10.1103/PhysRev.72.972.2}}</ref> Rocks from the Earth's crust have isotope ratios varying by as much as a factor of ten, and these ratios can be used to investigate the origin of rocks and the composition of the Earth's [[Mantle (geology)|mantle]].<ref name="heliumfundamentals"/> {{chem|3|He}} is much more abundant in stars, as a product of nuclear fusion. Thus in the [[interstellar medium]], the proportion of {{chem|3|He}} to {{chem|4|He}} is around 100 times higher than on Earth.<ref>{{cite journal|title=Isotopic Composition and Abundance of Interstellar Neutral Helium Based on Direct Measurements| journal=Astrophysics| volume=45| issue=2|year=2002| pages=131–142| url=http://www.ingentaconnect.com/content/klu/asys/2002/00000045/00000002/00378626 |accessdate=2008-07-20 |author=Zastenker G. N. |coauthors = E. Salerno, F. Buehler, P. Bochsler, M. Bassi, Y. N. Agafonov, N. A. Eismont, V. V. Khrapchenkov, H. Busemann| doi=10.1023/A:1016057812964}}</ref> Extraplanetary material, such as lunar and asteroid [[regolith]], have trace amounts of helium-3 from being bombarded by [[solar wind]]s. The [[Moon]]'s surface contains helium-3 at concentrations on the order of 0.01&nbsp;[[Parts per million|ppm]].<ref>{{cite web |url = http://fti.neep.wisc.edu/Research/he3_pubs.html|title = Lunar Mining of Helium-3 |date = 2007-10-19| accessdate = 2008-07-09| publisher = Fusion Technology Institute of the University of Wisconsin-Madison}}</ref><ref>{{ cite web|url= http://www.lpi.usra.edu/meetings/lpsc2007/pdf/2175.pdf|format=PDF| title = The estimation of helium-3 probable reserves in lunar regolith| author= Slyuta, E. N. |coauthors = A. M. Abdrakhimov, E. M. Galimov| work= Lunar and Planetary Science XXXVIII| year=2007|accessdate=2008-07-20}}</ref> A number of people, starting with Gerald Kulcinski in 1986,<ref>{{cite news|url = http://www.thespacereview.com/article/536/1|title = A fascinating hour with Gerald Kulcinski|author=Hedman, Eric R.|date = 2006-01-16|work = The Space Review|accessdate=2008-07-20}}</ref> have proposed to explore the moon, mine lunar regolith and use the helium-3 for [[Nuclear fusion|fusion]].
-Liquid helium-4 can be cooled to about 1&nbsp;kelvin using [[evaporative cooling]] in a [[1-K pot]]. Similar cooling of helium-3, which has a lower boiling point, can achieve about 0.2&nbsp;kelvin in a [[helium-3 refrigerator]]. Equal mixtures of liquid {{chem|3|He}} and {{chem|4|He}} below 0.8&nbsp;K separate into two immiscible phases due to their dissimilarity (they follow different [[quantum statistics]]: helium-4 atoms are [[boson]]s while helium-3 atoms are [[fermion]]s).<ref name = enc/> [[Dilution refrigerator]]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]] of 7.6{{e|–22}} seconds. Helium-6 decays by emitting a [[beta particle]] and has a half life of 0.8&nbsp;seconds. Helium-7 also emits a beta particle as well as a [[gamma ray]]. Helium-7 and helium-8 are created in certain [[nuclear reaction]]s.<ref name=enc/> Helium-6 and helium-8 are known to exhibit a [[nuclear halo]]. Helium-2 (two protons, no neutrons) is a [[radioisotope]] that decays by [[proton emission]] into [[hydrogen-1|protium]], with a [[half-life]] of 3{{e|–27}} seconds.<ref name = enc/>
-==Compounds==
-{{seealso|Noble gas compound}}
-Helium has a [[Valence (chemistry)|valence]] of zero and is chemically unreactive under all normal conditions.<ref name="LANL.gov" /> It is an electrical insulator unless [[ion]]ized. As with the other noble gases, helium has metastable [[energy level]]s that allow it to remain ionized in an electrical discharge with a [[voltage]] below its [[ionization potential]].<ref name=enc/> Helium can form unstable [[compound (chemistry)|compounds]], known as [[excimer]]s, with tungsten, iodine, fluorine, sulfur and phosphorus when it is subjected to an [[electric glow discharge]], to electron bombardment, or else is a [[Plasma physics|plasma]] for another reason. HeNe, HgHe<sub>10</sub>, WHe<sub>2</sub> and the molecular ions {{chem|He|2|+}}, {{chem|He|2|2+}}, {{chem|link=Hydrohelium(1+) ion|HeH|+}}, and {{chem|HeD|+}} have been created this way.<ref>{{cite journal |title = Massenspektrographische Untersuchungen an Wasserstoff- und Heliumkanalstrahlen ({{chem|H|3|+}}, {{chem|H|2|-}}, {{chem|HeH|+}}, {{chem|HeD|+}}, {{chem|He|-}}) |author = Hiby, Julius W. |journal = [[Annalen der Physik]] |volume = 426 |issue = 5 |pages = 473–487 |year = 1939 |doi = 10.1002/andp.19394260506 |accessdate=2008-07-20}}</ref> This technique has also allowed the production of the neutral molecule He<sub>2</sub>, which has a large number of [[spectral band|band systems]], and HgHe, which is apparently only held together by polarization forces.<ref name=enc/> Theoretically, other true compounds may also be possible, such as helium fluorohydride (HHeF) which would be analogous to [[Argon fluorohydride|HArF]], discovered in 2000.<ref>{{cite journal |title = Prediction of a Metastable Helium Compound: HHeF |author = Ming Wah Wong |journal = [[Journal of the American Chemical Society]] |volume = 122 |issue = 26 |pages = 6289–6290 |year = 2000 |doi = 10.1021/ja9938175}}</ref> Calculations show that two new compounds containing a helium-oxygen bond could be stable.<ref>{{cite journal|title = On Chemical Bonding Between Helium and Oxygen|first = W.|last = Grochala|journal = Polish Journal of Chemistry|volume = 83|pages = 87–122|year =2009}}</ref> The two new molecular species, predicted using theory, CsFHeO and N(CH<sub>3</sub>)<sub>4</sub>FHeO, 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 nobility, and the only remaining noble element will be [[neon]].<ref>{{cite web|url = http://www.uw.edu.pl/en/strony/news/chemist.pdf|title = Collapse of helium’s chemical nobility
-predicted by Polish chemist|accessdate = 2009-05-15}}</ref> {{citation needed|Extraordinary claims require extraordinary evidence.|date=January 2009}}
-Helium has been put inside the hollow carbon cage molecules (the [[fullerene]]s) by heating under high pressure. The [[endohedral fullerene|endohedral fullerene molecules]] formed are stable up to high temperatures. When chemical derivatives of these fullerenes are formed, the helium stays inside.<ref>{{cite journal |title = Stable Compounds of Helium and Neon: He@C<sub>60</sub> and Ne@C<sub>60</sub> |author = Saunders, Martin Hugo |coauthors = A. Jiménez-Vázquez, R. James Cross, Robert J. Poreda |journal = Science |volume = 259 |issue = 5100 |pages = 1428–1430 |year = 1993 |doi = 10.1126/science.259.5100.1428 |pmid = 17801275|accessdate=2008-07-20}}</ref> If [[helium-3]] is used, it can be readily observed by helium [[nuclear magnetic resonance spectroscopy]].<ref>{{cite journal |title = Probing the interior of fullerenes by <sup>3</sup>He NMR spectroscopy of endohedral <sup>3</sup>He@C<sub>60</sub> and <sup>3</sup>He@C<sub>70</sub> |author = Saunders, M.|coauthors = H. A. Jiménez-Vázquez, R. J. Cross, S. Mroczkowski, D. I. Freedberg, F. A. L. Anet|journal = Nature |volume = 367 |issue = |pages = 256–258 |year = 1994 |doi = 10.1038/367256a0 |accessdate=2008-07-20}}</ref> 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.
-==Occurrence and production==
-===Natural abundance===
-Helium is the second most abundant element in the known Universe (after [[hydrogen]]), constituting 23% of the [[baryon]]ic mass of the Universe.<ref name="nbb"/> The vast majority of helium was formed by Big Bang [[nucleosynthesis]] from one to three minutes after the Big Bang. As such, measurements of its abundance contribute to cosmological models. In [[star]]s, it is formed by the [[nuclear fusion]] of hydrogen in [[proton-proton chain reaction]]s and the [[CNO cycle]], part of [[stellar nucleosynthesis]].<ref name="bigbang">{{cite web|author=Weiss, Achim|title=Elements of the past: Big Bang Nucleosynthesis and observation|url=http://www.einstein-online.info/en/spotlights/BBN_obs/index.html|publisher=[[Max Planck Institute for Gravitational Physics]]|accessdate=2008-06-23}}; {{cite journal|author=Coc, A. |coauthors = et al.|title=Updated Big Bang Nucleosynthesis confronted to WMAP observations and to the Abundance of Light Elements|journal=[[Astrophysical Journal]]|volume=600|year=2004|pages=544|doi=10.1086/380121}}</ref>
-In the [[Earth's atmosphere]], the concentration of helium by volume is only 5.2 parts per million.<ref>{{cite journal |author=Oliver, B. M. |coauthors = James G. Bradley, Harry Farrar IV |year=1984 |title= Helium concentration in the Earth's lower atmosphere |journal=Geochimica et Cosmochimica Acta |volume=48 |issue=9 |pages=1759–1767 |doi=10.1016/0016-7037(84)90030-9}}</ref><ref>{{cite web |url=http://www.srh.weather.gov/jetstream/atmos/atmos_intro.htm |title=The Atmosphere: Introduction |work=JetStream - Online School for Weather |publisher=[[National Weather Service]] |date = 2007-08-29 |accessdate = 2008-07-12}}</ref> The concentration is low and fairly constant despite the continuous production of new helium because most helium in the Earth's atmosphere [[atmospheric escape|escapes]] into space by several processes.<ref>{{cite journal |author=Lie-Svendsen, Ø. |coauthors = M. H. Rees |year=1996 |title=Helium escape from the terrestrial atmosphere: The ion outflow mechanism |journal=Journal of Geophysical Research |volume=101 |issue=A2 |pages=2435–2444 |doi=10.1029/95JA02208|accessdate=2008-07-20}}</ref><ref>{{cite web|url=http://www.astronomynotes.com/solarsys/s3.htm|chapter=Atmospheres|title=Nick Strobel's Astronomy Notes|year=2007|accessdate=2007-09-25|author=Strobel, Nick}}</ref> 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]], and thus an Earthly helium balloon is essentially a bag of retired [[alpha particles]]. Helium is found in large amounts in minerals of [[uranium]] and [[thorium]], including [[cleveite]], [[pitchblende]], [[carnotite]] and [[monazite]], because they emit alpha particles (helium nuclei, He<sup>2+</sup>) to which electrons immediately combine as soon as the particle is stopped by the rock. In this way an estimated 3000&nbsp;tonnes of helium are generated per year throughout the [[lithosphere]].<ref name="cook">{{cite journal |author=Cook, Melvine A. |year=1957 |title=Where is the Earth's Radiogenic Helium? |journal= Nature |volume=179 |issue= |pages=213 |doi=10.1038/179213a0}}</ref><ref>{{cite journal |author= Aldrich, L. T. |coauthors = Alfred O. Nier |year=1948 |title=The Occurrence of He<sup>3</sup> in Natural Sources of Helium |journal = Phys. Rev. |volume=74 |issue= |pages= 1590–1594 |doi=10.1103/PhysRev.74.1590|accessdate=2008-07-20}}</ref><ref>{{cite journal |author=Morrison, P. |coauthors = J. Pine |year=1955 |title= Radiogenic Origin of the Helium Isotopes in Rock |journal = Annals of the New York Academy of Sciences |volume=62 |issue=3 |pages=71–92 |doi=10.1111/j.1749-6632.1955.tb35366.x}}</ref> In the Earth's crust, the concentration of helium is 8 parts per billion. In seawater, the concentration is only 4 parts per trillion. There are also small amounts in mineral [[spring (hydrosphere)|springs]], volcanic gas, and meteoric iron. Because helium is trapped in a similar way by non-permeable layer of rock like [[natural gas]] the greatest concentrations on the planet are found in natural gas, from which most commercial helium is derived. 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]].<ref>{{cite journal |author=Zartman, R. E. |year=1961 |title= Helium Argon and Carbon in Natural Gases |journal = Journal of Geophysical Research |volume=66 |issue=1 |pages=277–306 |url=http://www.agu.org/journals/jz/v066/i001/JZ066i001p00277/|accessdate=2008-07-21 |doi=10.1029/JZ066i001p00277}}</ref><ref>{{cite journal |author=Broadhead, Ronald F. |year=2005 |title= Helium in New Mexico – geology distribution resource demand and exploration possibilities |journal = New Mexico Geology |volume=27 |issue=4 |pages=93–101 |url=http://geoinfo.nmt.edu/publications/periodicals/nmg/27/n4/helium.pdf |format=PDF|accessdate=2008-07-21}}</ref>
-===Modern extraction===
-For large-scale use, helium is extracted by [[fractional distillation]] from natural gas, which contains up to 7% helium.<ref>{{cite web| author = Winter, Mark| title = Helium: the essentials| publisher = University of Sheffield|year = 2008| url = http://www.webelements.com/helium/| accessdate = 2008-07-14}}</ref> Since helium has a lower boiling point than any other element, low temperature and high pressure are used to liquefy nearly all the other gases (mostly [[nitrogen]] and [[methane]]). The resulting crude helium gas is purified by successive exposures to lowering temperatures, in which almost all of the remaining nitrogen and other gases are precipitated out of the gaseous mixture. [[Activated charcoal]] is used as a final purification step, usually resulting in 99.995% pure Grade-A helium.<ref name=enc/> The principal impurity in Grade-A helium is [[neon]]. In a final production step, most of the helium that is produced is liquefied via a [[cryogenic]] process. This is necessary for applications requiring liquid helium and also allows helium suppliers to reduce the cost of long distance transportation, as the largest liquid helium containers have more than five times the capacity of the largest gaseous helium tube trailers.<ref name="wwsupply" /><ref>{{cite conference| author = Z. Cai |coauthors = R. Clarke, N. Ward, W. J. Nuttall, B. A. Glowacki|title = Modelling Helium Markets| publisher = University of Cambridge| year = 2007| url = http://www.jbs.cam.ac.uk/programmes/phd/downloads/conference_spring2007/papers/cai.pdf| format=PDF| accessdate = 2008-07-14}}</ref>
-In 2005, approximately 160 million cubic meters of helium were extracted from natural gas or withdrawn from helium reserves, with approximately 83% from the United States, 11% from Algeria, and most of the remainder from Russia and Poland.<ref>{{cite conference| title = Helium| booktitle = Mineral Commodity Summaries| pages = 78–79| publisher = U.S. Geological Survey|year = 2004| url = http://minerals.usgs.gov/minerals/pubs/commodity/helium/heliumcs04.pdf| format = PDF| accessdate = 2008-07-14}}</ref> In the United States, most helium is extracted from natural gas of the [[Hugoton Natural Gas Area|Hugoton]] and nearby gas fields in Kansas, Oklahoma, and Texas.<ref name="wwsupply" /> Diffusion of crude natural gas through special [[semipermeable membrane]]s and other barriers is another method to recover and purify helium.<ref>{{cite journal |title = Membrane technology — A new trend in industrial gas separation |author = Belyakov, V.P. |coauthors= S. G. Durgar'yan, B. A. Mirzoyan, et al. |journal = Chemical and Petroleum Engineering |volume = 17 |issue = 1 |pages = 19–21 |year = 1981 |doi = 10.1007/BF01245721}}</ref>
-Helium can be synthesized by bombardment of [[lithium]] or [[boron]] with high-velocity protons, but this is not an economically viable method of production.<ref>{{cite journal |title = A Photographic Investigation of the Transmutation of Lithium and Boron by Protons and of Lithium by Ions of the Heavy Isotope of Hydrogen |author = Dee, P. I. |coauthors = E. T. S. Walton |journal = [[Proceedings of the Royal Society of London]] |volume = 141 |issue = 845 |pages = 733–742 |year = 1933 |doi = 10.1098/rspa.1933.0151}}</ref>
-===Supply depletion===
-Current reserves of helium are being utilized much faster than they are being replenished. Given this situation, there are major concerns that the supply of helium may be depleted soon; the world's largest reserves, in [[Amarillo, Texas]], are expected to run out within the next eight years. This might be preventable if current users capture and recycle the gas and if oil and gas companies make use of capture techniques when extracting gas.<ref>{{cite web| title = Helium Supplies Endangered, Threatening Science And Technology?|publisher = Science Daily|year = 2008| url = http://www.sciencedaily.com/releases/2008/01/080102093943.htm| accessdate = 2009-08-26}}</ref><ref>{{cite web| author = Jenkins, Emily| title = A Helium Shortage?|publisher = Wired|year = 2000|url = http://www.wired.com/wired/archive/8.08/helium.html| accessdate = 2009-08-26}}</ref>
-==Applications==
-Helium is used for many purposes that require some of its unique properties, such as its low [[boiling point]], low [[density]], low [[solubility]], high [[thermal conductivity]], or [[inert]]ness. Helium is commercially available in either liquid or gaseous form. As a liquid, it can be supplied in small containers called [[Dewar flask|Dewars]] which hold up to 1,000&nbsp;liters of helium, or in large ISO containers which have nominal capacities as large as 11,000 US gallons (42&nbsp;m<sup>3</sup>). In gaseous form, small quantities of helium are supplied in high pressure cylinders holding up to 300 [[standard cubic feet]], while large quantities of high pressure gas are supplied in tube trailers which have capacities of up to 180,000 standard cubic feet.
-[[Image:Goodyear-blimp.jpg|thumb|left|Because of its low density and incombustibility, helium is the gas of choice to fill airships such as the [[Goodyear blimp]].|alt=Cigar-shaped blimp with "Good Year" written on its side.]]
-; Airships, balloons and rocketry
-Because it is [[lighter than air]], [[airship]]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).<ref name="stwertka"/> In [[rocketry]], helium is used as an [[ullage]] medium to displace fuel and oxidizers in storage tanks and to condense hydrogen and oxygen to make [[rocket fuel]]. It is also used to purge fuel and oxidizer from ground support equipment prior to launch and to pre-cool liquid hydrogen in [[space vehicle]]s. For example, the [[Saturn V]] booster used in the [[Apollo program]] needed about 13 million cubic feet (370,000&nbsp;m<sup>3</sup>) of helium to launch.<ref name="LANL.gov"/>
-;Commercial and recreational
-Helium alone is less dense than atmospheric air, so it will change the [[timbre]] (not [[Pitch (music)|pitch]]<ref name="Wolfe">{{cite web|url = http://www.phys.unsw.edu.au/PHYSICS_!/SPEECH_HELIUM/speech.html|title = Physics in speech|publisher = phys.unsw.edu.au. |accessdate=2008-07-20}}</ref>) of a person's voice when inhaled. However, inhaling it from a typical commercial source, such as that used to fill balloons, can be dangerous due to the risk of [[asphyxiation]] from lack of oxygen, and the number of contaminants that may be present. These could include trace amounts of other gases, in addition to aerosolized lubricating oil.
-For its low solubility in [[nervous tissue]], helium mixtures such as [[Trimix (breathing gas)|trimix]], [[heliox]] and [[heliair]] are used for [[deep diving]] to reduce the effects of [[Nitrogen narcosis|narcosis]].<ref>{{cite journal |last=Fowler |first=B |coauthors=Ackles KN, Porlier G |year=1985 |title=Effects of inert gas narcosis on behavior—a critical review |journal=Undersea Biomedical Research Journal |pmid=4082343 |url=http://archive.rubicon-foundation.org/3019 |accessdate=2008-06-27}}</ref><ref name="thomas">{{cite journal |author= Thomas, J. R. |year=1976 |title=Reversal of nitrogen narcosis in rats by helium pressure |journal=Undersea Biomed Res. |volume=3 |issue=3 |pages=249–59 |pmid=969027 |url=http://archive.rubicon-foundation.org/2771 |accessdate=2008-08-06}}</ref> At depths below {{convert|150|m|ft}} small amounts of hydrogen are added to a helium-oxygen mixture to counter the effects of [[high pressure nervous syndrome]].<ref>{{cite journal |author=Rostain, J. C. |coauthors=M. C. Gardette-Chauffour, C. Lemaire, R. Naquet|title=Effects of a H<sub>2</sub>-He-O<sub>2</sub> mixture on the HPNS up to 450 msw |journal=Undersea Biomed. Res. |volume=15 |issue=4 |pages=257–70 |year=1988|oclc=2068005 |pmid=3212843 |url=http://archive.rubicon-foundation.org/2487 |accessdate=2008-06-24}}</ref> At these depths the low density of helium is found to considerably reduce the effort of breathing.<ref>{{cite journal| author = Butcher, Scott J.| coauthors = Richard L. Jones, Jonathan R. Mayne, Timothy C. Hartley, Stewart R. Petersen| title = Impaired exercise ventilatory mechanics with the self-contained breathing apparatus are improved with heliox| journal = European Journal of Applied Physiology| volume = 101| issue = 6| pages = 659| publisher = Springer| location = Netherlands|year = 2007| doi = 10.1007/s00421-007-0541-5}}</ref>
-[[Helium-neon laser]]s have various applications, including [[barcode reader]]s.<ref name="nbb"/>
-;Industrial leak detection
-One industrial application for helium is leak detection. Because it [[diffusion|diffuses]] through solids at three times the rate of air, helium is used as a tracer gas to detect leaks in high-vacuum equipment and high-pressure containers.<ref name="nostrand">{{cite encyclopedia| title = Helium|editor = Considine, Glenn D.| encyclopedia = Van Nostrand's Encyclopedia of Chemistry| pages = 764–765|publisher = Wiley-Interscience|year = 2005|isbn = 0-471-61525-0}}</ref>
-[[Image:Ac-system 2.jpg|thumb|left|A dual chamber Helium Leak Detection Machine from KONTIKAB.|alt=Photo of a large, metal-framed device (about 3x1x1.5 m) standing in a room.]]
-If one needs to know the total leak rate of the tested product (for example in a heat pumps or an air conditioning system), the object is placed in a test chamber, the air in the chamber is removed with vacuum pumps and the product is filled with helium under specific pressure. The helium that escapes through the leaks is detected by a sensitive device ([[mass spectrometer]]), even at the leak rates as small as 10<sup>−9</sup> mbar L/s. The measurement procedure is normally automatic and is called Helium Integral Test. In a simpler test, the product is filled with helium and an operator is manually searching for the leak with a hand-held device called sniffer.<ref>{{cite book|url=http://books.google.com/books?id=5L8uIAFm4SoC&pg=PA493|page=493|title=High-vacuum technology: a practical guide|author=Hablanian, M. H.|publisher=CRC Press|year=1997|isbn=0824798341}}</ref>
-For its inertness and high [[thermal conductivity]], neutron transparency, and because it does not form radioactive isotopes under reactor conditions, helium is used as a heat-transfer medium in some gas-cooled [[nuclear reactors]].<ref name="nostrand"/> Helium is used as a [[shielding gas]] in [[arc welding]] processes on materials that are contaminated easily by air.<ref name="nbb"/>
-Helium is used as a protective gas in growing [[silicon]] and [[germanium]] crystals, in [[titanium]] and [[zirconium]] production, and in [[gas chromatography]],<ref name="LANL.gov"/> because it is inert. Because of its inertness, [[ideal gas|thermally and calorically perfect]] nature, high [[speed of sound]], and high value of the [[heat capacity ratio]], it is also useful in supersonic [[wind tunnel]]s<ref>{{cite journal |author = Beckwith, I.E. |coauthors = C. G. Miller III |title = Aerothermodynamics and Transition in High-Speed Wind Tunnels at Nasa Langley |journal = Annual Review of Fluid Mechanics |volume = 22 |pages = 419–439 |year= 1990 |doi = 10.1146/annurev.fl.22.010190.002223}}</ref> and [[impulse facility|impulse facilities]]<ref>{{cite book |author = Morris, C.I. |title = Shock Induced Combustion in High Speed Wedge Flows |year= 2001 |series = Stanford University Thesis |url = http://thermosciences.stanford.edu/pdf/TSD-143.pdf|format=PDF}}</ref>.
-Helium, mixed with a heavier gas such as xenon, is useful for [[thermoacoustic refrigeration]] due to the resulting high [[heat capacity ratio]] and low [[Prandtl number]].<ref>{{cite journal |title=Working gases in thermoacoustic engines |journal=The Journal of the Acoustical Society of America |year=1999 |volume=105 |issue=5 |pages=2677–2684 |doi=10.1121/1.426884|author = Belcher, James R. |coauthors = William V. Slaton, Richard Raspet, Henry E. Bass, Jay Lightfoot}}</ref> The inertness of helium has environmental advantages over conventional refrigeration systems which contribute to ozone depletion or global warming.<ref>{{cite book |title=Mending the Ozone Hole: Science, Technology, and Policy |author=Makhijani, Arjun |coauthors = Kevin Gurney |publisher=MIT Press |year=1995 |isbn=0262133083}}</ref>
-[[Image:Modern 3T MRI.JPG|thumb|right|Liquid helium is used to cool the superconducting magnets in modern MRI scanners.|alt=A large solid cylinder with a hole in its center and a rail attached to its side.]]
-;Scientific
-The use of helium reduces the distorting effects of temperature variations in the space between [[lens (optics)|lenses]] in some [[telescope]]s, due to its extremely low [[index of refraction]].<ref name=enc/> This method is especially used in solar telescopes where a vacuum tight telescope tube would be too heavy.<ref>{{cite journal |author = Jakobsson, H. |title = Simulations of the dynamics of the Large Earth-based Solar Telescope |journal = Astronomical & Astrophysical Transactions |volume = 13 |issue = 1 |pages = 35–46 |year= 1997 |doi = 10.1080/10556799708208113}}</ref><ref>{{cite journal|url = http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1983ApOpt..22...10E&amp;db_key=AST|title = Tests of vacuum VS helium in a solar telescope|author = Engvold, O. |coauthors = R.B. Dunn, R. N. Smartt, W. C. Livingston| journal = Applied Optics|year = 1983|pages = 10–12|volume = 22|accessdate=2008-07-27|doi = 10.1364/AO.22.000010}}</ref>
-The age of rocks and minerals that contain [[uranium]] and [[thorium]] can be estimated by measuring the level of helium with a process known as [[helium dating]].<ref name="nbb"/><ref name=enc/>
-Liquid helium is used to cool certain metals to the extremely low temperatures required for [[superconductivity]], such as in [[superconducting magnet]]s for [[magnetic resonance imaging]]. The [[Large Hadron Collider]] at [[CERN]] uses 96&nbsp;tonnes of liquid helium to maintain the temperature at 1.9&nbsp;Kelvin.<ref name="CERN-LHC">{{cite web|url=http://visits.web.cern.ch/visits/guides/tools/presentation/LHC_booklet-2.pdf LHC Guide booklet|title=CERN - LHC: Facts and Figures|publisher=[[CERN]]|accessdate=2008-04-30}}</ref> Helium at low temperatures is also used in [[cryogenics]].
-Helium is a commonly used carrier gas for [[gas chromatography]]. The leak rate of industrial vessels (typically vacuum chambers and cryogenic tanks) is measured using helium because of its small molecular diameter and because it is inert. No other inert substance will leak through micro-cracks or micro-pores in a vessel's wall at a greater rate than helium. A helium leak detector (see [[Helium mass spectrometer]]) is used to find leaks in vessels. 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 syntheic materials, inert gasses such as helium will not permeate most bulk metals.<ref>{{cite book|author=Jack W. Ekin|title=Experimental Techniques for Low-Temperature measurements|url=http://books.google.co.jp/books?id=Q9tmZQTDPiYC|publisher=Oxford University Press|year=2006|isbn=0198570546}}</ref>
-==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 (physiology)|respiration]] is replaced [[asphyxia]] is possible. The safety issues for cryogenic helium are similar to those of [[liquid nitrogen]]; its extremely low temperatures can result in [[frostbite|cold burn]]s and the liquid to gas expansion ratio can cause explosions if no pressure-relief devices are installed.
-Containers of helium gas at 5 to 10 K should be handled as if they contain liquid helium due to the rapid and significant [[thermal expansion]] that occurs when helium gas at less than 10 K is warmed to [[room temperature]].<ref name="LANL.gov"/>
-==Biological effects==
-{{Listen|right|filename=Helium article read with helium.ogg|title=Effect of helium on a human voice|description=The effect of helium on a human voice|format=[[Ogg]]}}
-The human voice is not like a string instrument, in which the a primarily vibrating object completely sets the pitch of the sound. Rather, in a human, the [[vocal folds]] act as a source of polytonic vibration, much like the reed(s) in [[woodwind]] musical instruments. As in a woodwind, the size of the resonant cavity plays a large part in picking out and amplifying a given fundamental or overtone frequency of vibration, during soundmaking. The voice of a person who has inhaled helium temporarily changes in timbre in a way that makes it sound high-pitched, because higher overtones are being amplified. The [[speed of sound]] in helium is nearly three times the speed of sound in air; because the [[fundamental frequency]] 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 pitch of the [[resonant frequency|resonant frequencies]] of the [[vocal tract]].<ref name="nbb"/><ref>{{cite journal |author=Ackerman MJ, Maitland G |title=Calculation of the relative speed of sound in a gas mixture |journal=Undersea Biomed Res |volume=2 |issue=4 |pages=305–10 |year=1975|pmid=1226588|url=http://archive.rubicon-foundation.org/2738 |accessdate=2008-08-09}}</ref> (The opposite effect, lowering frequencies, can be obtained by inhaling a dense gas such as [[sulfur hexafluoride]].)
-Inhaling helium can be dangerous if done to excess, since helium is a simple [[asphyxiant]] and so displaces oxygen needed for normal respiration.<ref name="nbb"/><ref name="Grass">{{de icon}} {{cite journal|title = Suicidal asphyxiation with helium: Report of three cases Suizid mit Helium Gas: Bericht über drei Fälle|journal = Wiener Klinische Wochenschrift| volume = 119|issue =9–10|year = 2007|doi = 10.1007/s00508-007-0785-4|author = Grassberger, Martin |coauthors = Astrid Krauskopf|pages = 323–325 |language=German & English}}</ref> Breathing pure helium continuously causes death by [[asphyxiation]] within minutes. Inhaling helium directly from pressurized cylinders is extremely dangerous, as the high flow rate can result in [[barotrauma]], fatally rupturing lung tissue.<ref name="Grass" /><ref name="slate">{{cite news|author = Engber, Daniel| title = Stay Out of That Balloon!|publisher = Slate.com| date = 2006-06-13| url = http://www.slate.com/id/2143631/| accessdate = 2008-07-14}}</ref> However, death caused by helium is quite rare, with only two fatalities reported between 2000 and 2004 in the United States.<ref name="slate" />
-At high pressures (more than about 20&nbsp;atm or two&nbsp;[[MPa]]), a mixture of helium and oxygen ([[heliox]]) can lead to [[high pressure nervous syndrome]], a sort of reverse-anesthetic effect; adding a small amount of nitrogen to the mixture can alleviate the problem.<!--<ref>{{cite web| last = Campbell| first = Ernest S.| title = High Pressure Nervous Syndrome| work = Physics and Problems With Gases|date = 2008-05-13| url = http://www.scuba-doc.com/HPNS.html| accessdate = 2008-07-16}}</ref>--><ref>{{cite journal |author=Rostain JC, Lemaire C, Gardette-Chauffour MC, Doucet J, Naquet R |title=Estimation of human susceptibility to the high-pressure nervous syndrome |journal=J Appl Physiol |volume=54 |issue=4 |pages=1063–70 |year=1983|pmid=6853282|url=http://jap.physiology.org/cgi/pmidlookup?view=long&pmid=6853282 |accessdate=2008-08-09}}</ref><ref>{{cite journal |last=Hunger Jr |first=W. L. |coauthors=P. B. Bennett. |title=The causes, mechanisms and prevention of the high pressure nervous syndrome |journal=Undersea Biomed. Res. |volume=1 |issue=1 |pages=1–28 |year=1974|oclc=2068005 |pmid=4619860 |url=http://archive.rubicon-foundation.org/2661 |accessdate=2008-08-09}}</ref>
-==See also==
-{{colbegin|3}}
-*[[Abiogenic petroleum origin]]
-*[[Helium-3 propulsion]]
-*[[Leidenfrost effect]]
-*[[Quantum solid]]
-*[[Superfluid]]
-*[[Tracer-gas leak testing method]]
-*[[Helium atom]]
-{{colend}}
-==Notes==
 {{reflist|2}}
-==References==
-<!-- Commented out the already noted references-->
-<div class="references-small">
-*{{cite book|author = Bureau of Mines|title = Minerals yearbook mineral fuels Year 1965, Volume II (1967)|publisher = U. S. Government Printing Office|year = 1967}}<!--Can't find this in worldcat -->
-*{{cite web|url=http://chartofthenuclides.com/default.html|title=Chart of the Nuclides: Fourteenth Edition |publisher= General Electric Company |year=1989}}
-*{{cite book|author=Emsley, John|title=The Elements |edition= 3rd |location= New York |publisher= Oxford University Press |year=1998 |isbn= 978-0198558187}}
-*{{cite web|publisher=United States Geological Survey (usgs.gov)|url=http://minerals.usgs.gov/minerals/pubs/commodity/helium/heliumcs07.pdf |title=Mineral Information for Helium |format=PDF |accessdate=2007-01-05}}
-*{{cite web|url = http://web.archive.org/web/20050101090349/www.oma.be/BIRA-IASB/Public/Research/Thermo/Thermotxt.en.html|title = The thermosphere: a part of the heterosphere|author = Vercheval, J.|year= 2003| accessdate = 2008-07-12|publisher = Belgian Institute for Space Aeronomy}}
-*{{cite journal |title = Isotopic Composition and Abundance of Interstellar Neutral Helium Based on Direct Measurements|author = Zastenker, G. N. |coauthors = E. Salerno, F. Buehler, P. Bochsler, M. Bassi, Y. N. Agafonov, N. A. Eismont, V. V. Khrapchenkov, H. Busemann|journal= Astrophysics|year= 2002 |volume= 45 |issue= 2 |pages= 131–142 |doi= 10.1023/A:1016057812964}}
-</div>
 ==External links==
-{{Commons|Helium}}
+{{wikipedia|Helium}}
-{{wiktionary|helium}}
+*[http://www.webelements.com/helium/ WebElements]
-{{Spoken Wikipedia|Helium.ogg|2009-07-15}}
-;General
-*[http://uk.youtube.com/watch?v=a8FJEiI5e6Q The Periodic Table of Videos - Helium]
-*[http://www.blm.gov/wo/st/en/info/newsroom/2007/january/NR0701_2.html US Government' Bureau of Land Management: Sources, Refinement, and Shortage.] With some History of Helium.
-*[http://minerals.usgs.gov/minerals/pubs/commodity/helium/ U.S. Geological Survey Publicationson Helium] beginning 1996
-*[http://education.jlab.org/itselemental/ele002.html It's Elemental – Helium]
-*[http://www.rsc.org/chemistryworld/podcast/element.asp Chemistry in its element podcast] (MP3) from the [[Royal Society of Chemistry]]'s [[Chemistry World]]: [http://www.rsc.org/images/CIIE_Helium_48kbps_tcm18-133173.mp3 Helium]
-;More detail
-*[http://boojum.hut.fi/research/theory/helium.html Helium] at the [[Helsinki University of Technology]]; includes pressure-temperature phase diagrams for helium-3 and helium-4
-*[http://www.lancs.ac.uk/depts/physics/research/condmatt/ult/index.html Lancaster University, Ultra Low Temperature Physics] - includes a summary of some low temperature techniques
-;Miscellaneous
-*[http://www.phys.unsw.edu.au/PHYSICS_!/SPEECH_HELIUM/speech.html Physics in Speech] with audio samples that demonstrate the unchanged voice pitch
-*[http://www.du.edu/~jcalvert/phys/helium.htm Article about helium and other noble gases]
-{{E number infobox 930-949}}
-{{Compact periodic table}}
-{{featured article}}
+[[Category:Helium| ]]
 [[Category:Chemical elements]]
 [[Category:Noble gases]]
-[[Category:Coolants]]
+[[Category:Packaging gases]]
-[[Category:Helium]]
+[[Category:National Historic Chemical Landmarks]]
-[[Category:Airship technology]]
-[[Category:Nuclear reactor coolants]]
-{{Imported from Wikipedia|name=Helium|id=329382281}}
+{{CC-BY-3.0}}