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| :''For other uses of this term, see ].'' | |||
| {{Infobox helium}} | |||
| '''Helium''' ('''He''') is a colorless, odorless, tasteless, non-toxic, ] ] ] that heads the ] series in the ] and whose ] is 2. Its ] and ] points are the lowest among the elements and it exists only as a ] except in extreme conditions. Extreme conditions are also needed to create the small handful of helium ]s, which are all unstable at ]. It has a second, rare, ] which is called ]. The behavior of liquid ]'s two fluid phases, helium I and helium II, is important to researchers studying ] (in particular the phenomenon of ]) and to those looking at the effects that temperatures near ] have on ] (such as ]). | |||
| Helium is named for the Sun since it was first detected as a new element in 1868 by a French astronomer, as an unknown yellow ] signature in light from a ]. | |||
| Helium is the second most ] and second lightest element in the known universe, and is one of the elements believed to have been created in the ]. In the modern universe almost all new helium is created as a result of the ] of hydrogen in ]s. On ] helium is rare, and almost all of that which exists was created by the ] of much heavier elements (]s are helium nuclei). After its creation, part of it was trapped with ] in concentrations up to 7% by volume, from which it is extracted commercially by ]. Large reserves of helium have been found in the ]s of the United States (the largest supplier) but helium is known in gas reserves of a few other countries. | |||
| Helium is used in ], in deep-sea breathing systems, in ], to cool ]s (the largest liquid helium use is presently ] machines), for inflating balloons, for providing lift in ]s and as a protective gas for many industrial uses (such as ] and growing ] wafers). | |||
| ==Notable characteristics== | |||
| ===Gas and plasma phases=== | |||
| Helium is the least reactive member of the ] elements, and thus also the least reactive of all elements; it is ] and ] in virtually all conditions. Due to helium's relatively low molar (molecular) mass, in the gas phase it has a ], ], and ] that are all greater than any gas, except ]. For similar reasons, and also due to the small size of its molecules, helium's ] rate through ]s is three times that of air and around 65% that of hydrogen.<ref name="Encyc 261">''The Encyclopedia of the Chemical Elements'', edited by Cifford A. Hampel, "Helium" entry by L. W. Brandt (New York; Reinhold Book Corporation; 1968; page 261) Library of Congress Catalog Card Number: 68-29938</ref> | |||
| Helium is less water ] than any other gas known{{Fact|date=November 2007}}, and helium's ] is closer to unity than that of any other gas{{Fact|date=November 2007}}. Helium has a negative ] at normal ambient temperatures, meaning it heats up when allowed to freely expand. Only below its ] (of about 40 ] at 1 atmosphere) does it cool upon free expansion. Once precooled below this temperature, helium can be liquefied through expansion cooling. | |||
| ] | |||
| Throughout the universe, helium is found mostly in a ] state whose properties are quite different from atomic helium. In a plasma, helium's electrons and protons are not bound together, 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 ] together with ionized hydrogen, they interact with the Earth's ] giving rise to ]s and the ]. | |||
| ===Solid and liquid phases=== | |||
| {{Main article|Liquid helium}} | |||
| Helium solidifies only under great pressure. The resulting colorless, almost invisible ] is highly ]; applying pressure in a laboratory can decrease its volume by more than 30%.<ref name="LANL.gov">Los Alamos National Laboratory (LANL.gov): Periodic Table, "" (viewed ] ] and ] ])</ref> With a ] on the order of 5×10<sup>7</sup> ]<ref>{{cite journal | author = C. Malinowska-Adamska, 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}}</ref> it is 50 times more compressible than water. Unlike any other element, helium will fail to solidify and remain a liquid down to ] at normal pressures. This is a direct effect of quantum mechanics: specifically, the ] of the system is too high to allow freezing. Solid helium requires a temperature of 1–1.5 K (about −272 °C or −457 °F) and about 25 bar (2.5 MPa) of pressure.<ref>'''', at the University of Alberta</ref> It is often hard to distinguish solid from liquid helium since the ] of the two phases are nearly the same. The solid has a sharp ] and has a ]line structure. | |||
| Solid helium has a density of 0.214 ±0.006 g/ml (1.15 K, 66 atm) with a mean isothermal compressibility of the solid at 1.15 K between the solidus and 66 atm of 0.0031 ±0.0008/atm. Also, no difference in density was noted between 1.8 K and 1.5 K. This data projects that ''T''=0 solid helium under 25 bar of pressure (the minimum required to freeze helium) has a density of 0.187 ±0.009 g/ml.<ref>''Structure of Solid Helium by Neutron Diffraction'', D. G. Henshaw, Physical Review Letters '''109''', Pg. 328 – 330 (Issue 2 – January 1958)</ref> | |||
| ====Helium I state==== | |||
| Below its ] of 4.22 ] and above the ] of 2.1768 kelvin, the ] helium-4 exists in a normal colorless ] state, called ''helium I''. Like other ] liquids, helium I boils when it is heated. It also contracts when its temperature is lowered until it reaches the ], when it stops boiling and suddenly expands. The rate of expansion decreases below the lambda point until about 1 K is reached; at which point expansion completely stops and helium I starts to contract again. | |||
| Helium I has a gas-like ] of 1.026 which makes its surface so hard to see that floats of ] are often used to show where the surface is.<ref name="Encyc Chem Elem">''The Encyclopedia of the Chemical Elements'', page 262</ref> This colorless liquid has a very low ] and a ] one-eighth that of water, which is only one-fourth the value expected from ].<ref name="Encyc Chem Elem"/> ] 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 is probably due to its boiling point being so close to absolute zero, which prevents random molecular motion (]) from masking the atomic properties.<ref name="Encyc Chem Elem"/> | |||
| ====Helium II state==== | |||
| Liquid helium below its lambda point begins to exhibit very unusual characteristics, in a state called ''helium II''. Boiling of helium II is not possible due to its high ]; heat input instead causes ] of the liquid directly to gas. The isotope helium-3 also has a ] phase, but only at much lower temperatures; as a result, less is known about such properties in the isotope helium-3. | |||
| ] also covers the interior of the larger container; if it were not sealed, the helium II would creep out and escape.]] | |||
| Helium II is a ], a quantum-mechanical state of matter with strange properties. For example, when it flows through even capillaries of 10<sup>−7</sup> to 10<sup>−8</sup> m width it has no measurable ]. 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 ], 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>Yuan, Sidney. Yutiopian.com. Retrieved on 5 January 2007.</ref> | |||
| Helium II also exhibits a creeping effect. When a surface extends past the level of helium II, the helium II moves along the surface, seemingly against the force of ]. Helium II will escape from a vessel that is not sealed by creeping along the sides until it reaches a warmer region where it evaporates. It moves in a 30 ]-thick film regardless of surface material. This film is called a ] and is named after the man who first characterized this trait, Bernard V. Rollin.<ref name="Encyc 263">''The Encyclopedia of the Chemical Elements'', page 263</ref><ref>{{cite journal |authors=Fairbank H.A.; Lane C.T. | doi = 10.1103/PhysRev.76.1209 |title=Rollin Film Rates in Liquid Helium |journal=Physical Review |volume=76 |issue=8 |year=1949 |month=October |pages=1209–1211 |date=October 1949}}</ref> As a result of this creeping behavior and helium II's ability to leak rapidly through tiny openings, it is very difficult to confine liquid helium. Unless the container is carefully constructed, the helium II will creep along the surfaces and through valves until it reaches somewhere warmer, where it will evaporate. Waves propagating across a Rollin film are governed by the same equation as ]s in shallow water, but rather than gravity, the restoring force is the ].<ref>Ellis, Fred M. . Wesleyan Quantum Fluids Laboratory. Retrieved on ].</ref> These waves are known as ''third sound''. | |||
| In the ''fountain effect'', a chamber is constructed which is connected to a reservoir of helium II by a ] 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 II is greater than that of any other known substance, a million times that of helium I and several hundred times that of ]. This is because heat conduction occurs by an exceptional quantum-mechanical mechanism. Most materials that conduct heat well have a ] of free electrons which serve to transfer the heat. Helium II has no such valence band but nevertheless conducts heat well. The ] is governed by equations that are similar to the ] used to characterize sound propagation in air. So when heat is introduced, it will move at 20 meters per second at 1.8 K through helium II as waves in a phenomenon called '']''.<ref name="Encyc 263"/> | |||
| ==Applications== | |||
| ]s such as the ], as opposed to ]]] | |||
| Helium is used for many purposes that require some of its unique properties, such as its low ], low ], low ], high ], or ]ness. Helium is commercially available in either liquid or gaseous form. As a liquid, it can be supplied in small containers called dewars which hold up to 1,000 liters of helium, or in large ISO containers which have nominal capacities as large as 11,000 gallons (41,637 liters). 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. | |||
| *Because it is ], ]s and ]s are inflated with helium for lift. In airships, helium is preferred over hydrogen because it is not flammable and has 92.64% of the ] (or lifting power) of the alternative ] (see ].) | |||
| *For its low solubility in water, the major part of human ], mixtures of helium with ] and ] ('']''), with oxygen only ('']''), with common air ('']''), and with ] and oxygen ('']''), are used in deep-sea breathing systems to reduce the high-pressure risk of ]. | |||
| *At extremely low temperatures, liquid helium is used to cool certain metals to produce ], such as in ]s used in ]. Helium at low temperatures is also used in ]. | |||
| *For its inertness and high ], ] transparency, and because it does not form radioactive isotopes under reactor conditions, helium is used as a coolant in some ], such as ]s. | |||
| *Helium is used as a ] in ] processes on materials that are contaminated easily by air. It is especially useful in ], because it is lighter than air and thus floats, whereas other shielding gases sink. | |||
| *Because it is inert, helium is used as a protective gas in growing ] and ] crystals, in ] and ] production, in ], and as an atmosphere for protecting historical documents. This property also makes it useful in supersonic ]s. | |||
| *In ], helium is used as an ] medium to displace fuel and oxidizers in storage tanks and to condense ] and ] to make ]. It is also used to purge fuel and oxidizer from ground support equipment prior to launch and to pre-cool liquid hydrogen in ]s. For example, the ] booster used in the ] needed about 13 million cubic feet (370,000 m³) of helium to launch.<ref name="LANL.gov"/> | |||
| *The ] of the ] is a mixture of helium and ]. | |||
| *Because it ] through solids at a rate three times that of air, helium is used as a tracer gas to detect leaks in high-vacuum equipment and high-pressure containers, as well as in other applications with less stringent requirements such as heat exchangers, valves, gas panels, etc. | |||
| *Because of its extremely low ], the use of helium reduces the distorting effects of temperature variations in the space between ]es in some ]s. | |||
| *The age of ] and ]s that contain ] and ], ] elements that emit helium nuclei called ]s, can be discovered by measuring the level of helium with a process known as ]. | |||
| *The high thermal conductivity and sound velocity of helium is also desirable in ]. The inertness of helium adds to the environmental advantage of this technology over conventional refrigeration systems which may contribute to ozone depleting and global warming effects. | |||
| *Because helium alone is less dense than atmospheric air, it will change the ] (not ]<ref name="Wolfe">, phys.unsw.edu.au. Retrieved on ] ]. </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 ] 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. | |||
| ==History== | |||
| ===Scientific discoveries=== | |||
| Evidence of helium was first detected on ], ] as a bright yellow line with a ] of 587.49 nanometres in the ] of the ] of the ], by French astronomer ] during a total ] in ], ]. This line was initially assumed to be ]. On October 20 of the same year, English astronomer ] observed a yellow line in the solar spectrum, which he named the D<sub>3</sub> ], for it was near the known D<sub>1</sub> and D<sub>2</sub> lines of sodium,<ref>''The Encyclopedia of the Chemical Elements'', page 256</ref> and concluded that it was caused by an element in the Sun unknown on Earth. He and English chemist ] named the element with the Greek word for the Sun, ἥλιος (''helios'')<ref>''Oxford English Dictionary'' (1989), s.v. "helium". Retrieved on December 16, 2006, from Oxford English Dictionary Online. Also, from quotation there: Thomson, W. (1872). ''Rep. Brit. Assoc.'' xcix: "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> | |||
| On ] ] British chemist ] isolated helium on Earth by treating the mineral ] with mineral ]s. Ramsay was looking for ] but, after separating ] and ] from the gas liberated by ], noticed a bright-yellow line that matched the D<sub>3</sub> line observed in the spectrum of the Sun.<ref name="Encyc 257">''The Encyclopedia of the Chemical Elements'', page 257</ref><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 = ] | journal = Proceedings of the Royal Society of London | volume = 58 | issue = | pages = 65-67 | year = 1895}}</ref><ref>{{cite journal | title = Helium, a Gaseous Constituent of Certain Minerals. Part I | author = ] | journal = Proceedings of the Royal Society of London | volume = 58 | pages = 80-89 | year = 1895}}</ref><ref>{{cite journal | title = Helium, a Gaseous Constituent of Certain Minerals. Part II-- | author = ] | journal = Proceedings of the Royal Society of London | volume = 59 | issue = | pages = 325-330 | year = 1895}}</ref><ref name="Encyc 257"/> These samples were identified as helium by Lockyer and British physicist ]. It was independently isolated from cleveite the same year by chemists ] and ] in ], who collected enough of the gas to accurately determine its ].<ref name="Nature's 177">Emsley, ''Nature's Building Blocks'', 177</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 ]. 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> ] (1999). Biographical entry for W.F. Hillebrand (1853–1925), geochemist and US Bureau of Standards administrator in , ed. John A. Garraty and Mark C. Carnes, 24 vols. (Oxford University Press: 1999): v. 10, pp. 808–9; v. 11, pp. 227-8. </ref> | |||
| In 1907, ] and ] demonstrated that ]s are helium ], by allowing them to penetrate the thin glass wall of a 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 ] by cooling the gas to less than one ]. He tried to solidify it by further reducing the temperature but failed, because helium does not have a ] temperature where the solid, liquid, and gas phases are at equilibrium. It was first solidified in 1926 by his student ] by subjecting helium to 25 ] of pressure. | |||
| In 1938, Russian physicist ] discovered that ] (a boson) has almost no ] at temperatures near ], a phenomenon now called ]. This phenomenon is related to ]. In 1972, the same phenomenon was observed in ], but at temperatures much closer to ], by American physicists ], ], and ]. The phenomenon in helium-3 is thought to be related to pairing of helium-3 ]s to make ]s, in analogy to ] of electrons producing ]. | |||
| ===Extraction and uses=== | |||
| After an oil drilling operation in 1903 in ], ], ] produced a gas geyser that would not burn, Kansas state geologist ] collected samples of the escaping gas and took them back to the University of Kansas at Lawrence where, with the help of chemists ] and ], he discovered that the gas contained, by volume, 72% nitrogen, 15% methane—insufficient to make the gas combustible, 1% hydrogen, and 12% of an unidentifiable gas.<ref name="Emsley 179">Emsley, ''Nature's Building Blocks'', 179</ref> With further analysis, Cady and McFarland discovered that 1.84% of the gas sample was helium.<ref>{{cite web|author=]|date=2004|url=http://acswebcontent.acs.org/landmarks/landmarks/helium/helium.html|title=The Discovery of Helium in Natural Gas|accessdate=2006-05-17}}</ref> Far from being a rare element, helium was present in vast quantities under the American Great Plains, available for extraction from natural gas. | |||
| This put the ] in an excellent position to become the world's leading supplier of helium. Following a suggestion by Sir ], the ] sponsored three small experimental helium production plants during ]. The goal was to supply ]s with the non-flammable lifting gas. A total of 200,000 cubic feet (5700 m³) of 92% helium was produced in the program even though only a few cubic feet (less than 100 liters) of the gas had previously been obtained.<ref name="Encyc 257"/> Some of this gas was used in the world's first helium-filled ], the U.S. Navy's C-7, which flew its maiden voyage from ], ] to ] in ] on ] ].<ref>{{cite book |editor=Eugene M. Emme, 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=] |location=Washington, DC |accessdate=2007-01-05 }}</ref> | |||
| 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 ]. Helium was also vital in the atomic bomb ]. | |||
| The ] set up the ] in 1925 at ], ] with the goal of supplying military ]s in time of ] and commercial airships in peacetime. Due to a US military embargo against Germany that restricted helium supplies, the ] was forced to use ] as the lift gas. Helium use following ] was depressed but the reserve was expanded in the 1950s to ensure a supply of liquid helium as a coolant to create oxygen/hydrogen ] (among other uses) during the ] and ]. Helium use in the United States in 1965 was more than eight times the peak wartime consumption. | |||
| After the "Helium Acts Amendments of 1960" (Public Law 86–777), the ] arranged for five private plants to recover helium from natural gas. For this ''helium conservation'' program, the Bureau built a 425-mile (684 km) pipeline from ], ] to connect those plants with the government's partially depleted Cliffside gas field, near ], ]. This helium-nitrogen mixture was injected and stored in the Cliffside gas field until needed, when it then was further purified. | |||
| By 1995, a billion cubic metres of the gas had been collected and the reserve was US$1.4 billion in debt, prompting the ] in 1996 to phase out the reserve.<ref name="Emsley 179"/><ref>''Guide to the Elements: Revised Edition'', by Albert Stwertka (New York; Oxford University Press; 1998; page 24) ISBN 0-19-512708-0</ref> The resulting "Helium Privatization Act of 1996"<ref>{{cite web |title=Helium Privatization Act of 1996|url=http://www7.nationalacademies.org/ocga/Laws/PL104_273.asp|accessdate=2007-01-05}}</ref> (Public Law 104–273) directed the ] to start liquidating the reserve by 2005.<ref>, nap.edu. Retrieved on ] ].</ref> | |||
| Helium produced before 1945 was about 98% pure (2% ]), 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 99.995% helium were available. | |||
| For many years the United States produced over 90% of commercially usable helium in the world. Extraction plants created in ], ], ], and other nations produced the remaining helium. In the mid 1990s, A new plant in Arzew, Algeria producing 600mmcf came on stream, with enough production to cover all of Europe's demand. Subsequently, 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. Through this time, both helium consumption and the costs of producing helium increased and during 2007 the major suppliers, Air Liquide, Airgas and Praxair all raised prices from 10 to 30%. | |||
| ==Occurrence and production== | |||
| ===Natural abundance=== | |||
| Helium is the second most abundant element in the known Universe after ] and constitutes 23% of the elemental ] of the universe. It is concentrated in stars, where it is formed from ] by the ] of the ] and ]. According to the ] model of the early development of the universe, the vast majority of helium was formed during ], from one to three minutes after the Big Bang. As such, measurements of its abundance contribute to cosmological models. | |||
| In the ], the concentration of helium by volume is only 5.2 parts per million.<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=] }}</ref> The concentration is low and fairly constant despite the continuous production of new helium because most helium in the Earth's atmosphere ] into space by several processes.<ref>{{cite journal |author=Lie-Svendsen, Ø.; Rees, M. H. |year=1996 |title=Helium escape from the terrestrial atmosphere: The ion outflow mechanism |journal=] |volume=101 |issue=A2 |pages=2435–2444 |doi=10.1029/95JA02208}}</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|last=Strobel|first=Nick}}</ref> | |||
| In the Earth's ], 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 ]. The ] is primarily found in minerals of ] and ], including ]s, ], ] and ], because they emit ]s, which consist of helium nuclei (He<sup>2+</sup>) to which electrons readily combine. In this way an estimated 3.4 litres of helium per year are generated per cubic kilometer of the Earth's crust. 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 ], ] gas, and meteoric iron. The greatest concentrations on the planet are in ], from which most commercial helium is derived. | |||
| The world's helium supply may be in danger, according to ] ] Lee Sobotka. The largest reserve is in Texas and would run out in eight years if consumed at the current pace.<ref name="WUSTL"></ref> Helium is non-renewable and irreplaceable by conventional methods. | |||
| ===Modern extraction=== | |||
| For large-scale use, helium is extracted by ] from ], which contains up to 7% helium.<ref></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 ] and ]). 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. ] is used as a final purification step, usually resulting in 99.995% pure, Grade-A, helium.<ref>''The Encyclopedia of the Chemical Elements'', page 258</ref> The principal impurity in Grade-A helium is ]. In a final production step, most of the helium that is produced is liquefied via a ] process. This is necessary for applications requiring liquid helium and also allows helium suppliers to reduce the cost of long distance transportation, as the largest liquid helium containers have more than five times the capacity of the largest gaseous helium tube trailers. | |||
| In 2005, approximately one hundred and sixty 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. In the United States, most helium is extracted from natural gas in Kansas and Texas. | |||
| Diffusion of crude natural gas through special ]s and other barriers is another method to recover and purify helium. Helium can be synthesized by bombardment of ] or ] with high-velocity ]s, but this is not an economically viable method of production. | |||
| ==Isotopes== | |||
| {{Main article|Isotopes of helium}} | |||
| Although there are eight known ]s of helium, only ] and ] are ]. In the Earth's atmosphere, there is one He-3 atom for every million He-4 atoms.<ref name="Nature's 178">Emsley, John. ''Nature's Building Blocks: An A-Z Guide to the Elements''. Oxford: Oxford University Press, 2001. Page 178. ISBN 0-19-850340-7</ref> However, helium is unusual in that its isotopic abundance varies greatly depending on its origin. In the ], the proportion of He-3 is around a hundred times higher.<ref>{{cite journal | title=Isotopic Composition and Abundance of Interstellar Neutral Helium Based on Direct Measurements |authors=Zastenker G.N.; Salerno E.; Buehler F.; Bochsler P.; Bassi M.; Agafonov Y.N.; Eismont N.A.; Khrapchenkov V.V.; Busemann H.|journal=Astrophysics|volume=45|issue=2|date=April 2002|pages=131–142|url=http://www.ingentaconnect.com/content/klu/asys/2002/00000045/00000002/00378626|accessdate=2007-01-05 }}</ref> Rocks from the Earth's crust have isotope ratios varying by as much as a factor of ten; this is used in ] to study the origin of such rocks. | |||
| The most common isotope, helium-4, is produced on Earth by ] of heavier radioactive elements; the ]s that emerge are fully ionized helium-4 nuclei. Helium-4 is an unusually stable nucleus because its ]s are arranged into ]. It was also formed in enormous quantities during ]. | |||
| ] of liquid helium-4, in a so-called ], cools the liquid to about 1 ]. In a ], similar cooling of helium-3, which has a lower boiling point, reaches a temperature of about 0.2 kelvin. Equal mixtures of liquid helium-3 and helium-4 below 0.8 K will separate into two immiscible phases due to their dissimilarity (they follow different ]: helium-4 atoms are ]s while helium-3 atoms are ]s).<ref>''The Encyclopedia of the Chemical Elements'', page 264</ref> ]s take advantage of the immiscibility of these two isotopes to achieve temperatures of a few millikelvins. | |||
| There is only a trace amount of helium-3 on Earth, primarily present since the formation of the Earth, although some falls to Earth trapped in cosmic dust.<ref name="heliumfundamentals"></ref> Trace amounts are also produced by the ] of ].<ref></ref> In ]s, however, helium-3 is more abundant, a product of ]. Extraplanetary material, such as ] and ] ], have trace amounts of helium-3 from being bombarded by ]s. The ]'s surface contains helium-3 at concentrations on the order of 0.01 ].<ref></ref><ref>{{ cite web | url= http://www.lpi.usra.edu/meetings/lpsc2007/pdf/2175.pdf | title = The estimation of helium-3 probable reserves in lunar regolith | author = E. N. Slyuta and A. M. Abdrakhimov, and E. M. Galimov | work = Lunar and Planetary Science XXXVIII | year=2007}}</ref> A number of people, starting with ] in 1986,<ref>{{cite news | url = http://www.thespacereview.com/article/536/1 | title = A fascinating hour with ] | author=Eric R. Hedman | date = January 16, 2006 | work = The Space Review}}</ref> have proposed to ], mine lunar regolith and use the helium-3 for ]. | |||
| The different formation processes of the two stable isotopes of helium produce the differing isotope abundances. These differing isotope abundances can be used to investigate the origin of rocks and the composition of the Earth's ].<ref name="heliumfundamentals"/> | |||
| It is possible to produce ], which rapidly decay into other substances. The shortest-lived heavy helium isotope is helium-5 with a ] of 7.6×10<sup>−22</sup> second. Helium-6 decays by emitting a ] and has a half life of 0.8 second. Helium-7 also emits a beta particle as well as a ]. Helium-7 and helium-8 are hyperfragments that are created in certain ]s.<ref>''The Encyclopedia of the Chemical Elements'', page 260</ref> | |||
| The exotics helium-6 and helium-8 are known to exhibit a ]. | |||
| Helium-2 (two protons, no neutrons) is a ] of helium that decays by ] into ] (hydrogen) with a ] of 3x10<sup>−27</sup> second.<ref>''The Encyclopedia of the Chemical Elements'', page 264</ref> | |||
| ==Biological effects== | |||
| The voice of a person who has inhaled helium temporarily sounds high-pitched. This is because the ] in helium is nearly three times the speed of sound in air. Because the ] of a gas-filled cavity is proportional to the speed of sound in the gas, when helium is inhaled there is a corresponding increase in the ] of the ].<ref name="Nature's 177"/> (The opposite effect, lowering frequencies, can be obtained by inhaling ]) | |||
| Inhaling helium, e.g. to produce the ], can be dangerous if done to excess since helium is a simple ], thus it displaces ] needed for normal ]. Death by ] will result within minutes if pure helium is breathed continuously. In mammals (with the notable exceptions of ]s and many burrowing animals) the breathing reflex is triggered by excess of ] rather than lack of oxygen, so asphyxiation by helium progresses without the victim experiencing ]. Inhaling helium directly from pressurized cylinders is extremely dangerous as the high flow rate can result in ], fatally rupturing ] tissue.<ref>, Slate.com. Retrieved on ] ].</ref> | |||
| Neutral helium at standard conditions is non-toxic, plays no biological role and is found in trace amounts in human blood. At high pressures (more than about 20 atm or two ]), a mixture of helium and oxygen (]) can lead to ], a sort of reverse-anesthetic effect; adding a small amount of nitrogen to the mixture can alleviate the problem.<ref>, scuba-doc.com. Retrieved on ] ]. </ref> | |||
| Containers of helium gas at 5 to 10 K should be handled as if they contain liquid helium due to the rapid and significant ] that occurs when helium gas at less than 10 K is warmed to ].<ref name="LANL.gov"/> | |||
| ==Compounds== | |||
| {{seealso|Noble gas compound}} | |||
| Helium is chemically unreactive under all normal conditions due to its ] of zero. It is an electrical insulator unless ]ized. As with the other noble gases, helium has metastable ]s that allow it to remain ionized in an electrical discharge with a ] below its ]. Helium can form unstable ]s with ], ], ], ] and ] when it is subjected to an ], through electron bombardment or is otherwise a ]. HeNe, HgHe<sub>10</sub>, WHe<sub>2</sub> and the molecular ions He<sub>2</sub><sup>+</sup>, He<sub>2</sub><sup>2+</sup>, ], and HeD<sup>+</sup> have been created this way. This technique has also allowed the production of the neutral molecule He<sub>2</sub>, which has a large number of ], and HgHe, which is apparently only held together by polarization forces.<ref name="Encyc 261"/> Theoretically, other compounds may also be possible, such as helium fluorohydride (HHeF) which would be analogous to ], discovered in 2000. | |||
| Helium has been put inside the hollow carbon cage molecules (the ]s) by heating under high pressure of the gas. The neutral molecules formed are stable up to high temperatures. When chemical derivatives of these fullerenes are formed, the helium stays inside. If ] is used, it can be readily observed by helium NMR spectroscopy. Many fullerenes containing helium-3 have been reported. Although the helium atoms are not attached by covalent or ionic bonds, these substances fit the definition of compounds in the ''Handbook of Chemistry and Physics''. They are the first stable neutral helium compounds to be formed. | |||
| ==References== | |||
| <div class="references-small"> | |||
| ;Prose | |||
| *''The Elements: Third Edition'', by John Emsley (New York; Oxford University Press; 1998; pages 94–95) ISBN 0-19-855818-X | |||
| *United States Geological Survey (usgs.gov): (PDF) (viewed ] ]) | |||
| *'''', by J. Vercheval (viewed ] ]) | |||
| *''Isotopic Composition and Abundance of Interstellar Neutral Helium Based on Direct Measurements'', Zastenker G.N. ''et al.'', , published in , April 2002, vol. 45, no. 2, pp. 131–142(12) | |||
| *'''', C. Malinowska-Adamska, P. Sŀoma, J. Tomaszewski, physica status solidi (b), Volume 240, Issue 1 , Pages 55–67; Published Online: ] ] | |||
| *'''', S. Yuan, (viewed ] ]) | |||
| *''Rollin Film Rates in Liquid Helium'', Henry A. Fairbank and C. T. Lane, Phys. Rev. 76, 1209–1211 (1949), | |||
| *'''', at the NASA Goddard Space Flight Center (viewed ] ]) | |||
| *'''', Engvold, O.; Dunn, R. B.; Smartt, R. N.; Livingston, W. C.. Applied Optics, vol. 22, ] ], p. 10–12 | |||
| *{{cite book | author = Bureau of Mines | title = Minerals yearbook mineral fuels Year 1965, Volume II (1967) | publisher = U. S. Government Printing Office | year = 1967 }} | |||
| *'''', Don L. Anderson, G. R. Foulger & Anders Meibom (viewed ] ]) | |||
| *'''', Diving Medicine Online (viewed ] ]) | |||
| ;Table | |||
| * '' Fourteenth Edition: Chart of the Nuclides'', General Electric Company, 1989 | |||
| *WebElements.com and EnvironmentalChemistry.com per the guidelines at (viewed ] ]) | |||
| </div> | |||
| ==Notes== | |||
| {{reflist}} | |||
| ==See also== | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| ==External links== | |||
| {{Commons|Helium}} | |||
| {{wiktionary|helium}} | |||
| ;General | |||
| * With some History of Helium. | |||
| * | |||
| * | |||
| ;More detail | |||
| * at the ]; includes pressure-temperature phase diagrams for helium-3 and helium-4 | |||
| * - includes a summary of some low temperature techniques | |||
| ;Miscellaneous | |||
| * with audio samples that demonstrate the unchanged voice pitch | |||
| * | |||
| {{E number infobox 930-949}} | |||
| {{Compact periodic table}} | |||
| {{featured article}} | |||
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