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| {{Elementbox_header | number=2 | symbol=He | name=helium | left=] | right=] | above=- | below=] | color1=#c0ffff | color2=green }} | |||
| ] | |||
| {{Elementbox_series | ]es }} | |||
| ] | |||
| {{Elementbox_groupperiodblock | group=18 | period=1 | block=s }} | |||
| ]Thank you, come again, fuck you | |||
| {{Elementbox_appearance_img | He,2| colorless }} | |||
| {{Elementbox_atomicmass_gpm | ]] }} | |||
| {{Elementbox_econfig | 1s<sup>2</sup> }} | |||
| {{Elementbox_epershell | 2 }} | |||
| {{Elementbox_section_physicalprop | color1=#c0ffff | color2=green }} | |||
| {{Elementbox_phase | ] }} | |||
| {{Elementbox_density_gplstp | 0.1786 }} | |||
| {{Elementbox_meltingpoint | k=(at 2.5 MPa) 0.95 | c=-272.2 | f=-458.0 }} | |||
| {{Elementbox_boilingpoint | k=4.22 | c=-268.93 | f=-452.07 }} | |||
| {{Elementbox_criticalpoint | k=5.19 | mpa=0.227 }} | |||
| {{Elementbox_heatfusion_kjpmol | 0.0138 }} | |||
| {{Elementbox_heatvaporiz_kjpmol | 0.0829 }} | |||
| {{Elementbox_heatcapacity_jpmolkat25 | 20.786 }} | |||
| {{Elementbox_vaporpressure_katpa | | | | | 3 | 4 | comment= }} | |||
| {{Elementbox_section_atomicprop | color1=#c0ffff | color2=green }} | |||
| {{Elementbox_crystalstruct | hexagonal or bcc }} | |||
| {{Elementbox_ionizationenergies2 | 2372.3 | 5250.5 }} | |||
| {{Elementbox_atomicradiuscalc_pm | ] }} | |||
| {{Elementbox_covalentradius_pm | ] }} | |||
| {{Elementbox_vanderwaalsrad_pm | ] }} | |||
| {{Elementbox_section_miscellaneous | color1=#c0ffff | color2=green }} | |||
| {{Elementbox_thermalcond_wpmkat300k | 151.3 m}} | |||
| {{Elementbox_cas_number | 7440-59-7 }} | |||
| {{Elementbox_isotopes_begin | isotopesof=helium | color1=#c0ffff | color2=green }} | |||
| |- | |||
| | <sup>3</sup>He || 0.000137%* || colspan="4" | He is ] with 1 ] | |||
| {{Elementbox_isotopes_stable | mn=4 | sym=He | na=99.999863%* | n=2 }} | |||
| |- | |||
| | colspan="6" align="center" | *<small>Atmospheric value, abundance may differ elsewhere.</small> | |||
| {{Elementbox_isotopes_end}} | |||
| {{Elementbox_footer | color1=#c0ffff | color2=green }} | |||
| :''For other uses of this term, see ].'' | |||
| '''Helium''' (symbol '''He''') is a colorless, odorless, tasteless ], one of the nearly inert ]es of the ]. Its ] and ] points are the lowest among the elements; except in extreme conditions, it exists only as a ]. At temperatures near ], it is a '']'', a nearly frictionless phase of matter with unusual properties. | |||
| After ], helium is the second lightest element and the second most abundant element in the ], created during ] and to a lesser extent from ] of hydrogen in ]s. On Earth, helium is primarily a product of the ] of much heavier elements, which emit helium nuclei called ]s; it is found in significant amounts only in ], from which it is extracted at low temperatures by ]. | |||
| First detected in 1868 by French astronomer ] as an unknown yellow ] signature in the light of a ], helium was separately identified as a new element later that year by English astronomer ]. Its presence in natural gas in large, useable amounts was identified in 1905<!--Date of identification-->. Helium is used in ], as a deep-sea ], for inflating ]s and ]s, and as a protective gas for many industrial purposes, such as ]. Inhaling a small amount of the gas temporarily changes the quality of a person's voice; however, caution must be exercised as helium is a simple ]. | |||
| ==Notable characteristics== | |||
| ===Gas and plasma phases=== | |||
| Helium is a colorless, odorless, and non-toxic gas. It is the least reactive member of group 18 (the ]es) of the periodic table and is ] and ] in virtually all conditions. Under ] helium behaves very much like an ]. It has a ] that is greater than any gas except ] and its ] is unusually high. Helium is also less water ] than any other gas known and its ] 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's ] is closer to unity than any other gas. 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. | |||
| ] | |||
| 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 ] 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>++</sup>, HeH<sup>+</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 ]s, and HgHe, which is apparently only held together by polarization forces.<ref name="Encyc 261"/> Theoretically, other compounds, like helium fluorohydride (HHeF), may also be possible. | |||
| Throughout the universe, helium is found mostly in a ] state whose properties are quite different to molecular helium. As 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=== | |||
| Helium solidifies only under great pressure. The resulting colorless, almost invisible ] is highly ]; applying pressure in the 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>http://www3.interscience.wiley.com/cgi-bin/abstract/105558571/ABSTRACT</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. Solid helium requires a temperature of 1–1.5 K (about −272 °C or −457 °F) and about 26 standard atmospheres (2.6 MPa) of pressure.<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> It is often hard to distinguish solid from '']'' since the ] of the two phases are nearly the same. The solid has a sharp ] and has a ]line structure. | |||
| ====Helium I state==== | |||
| Below its ] of 4.22 ]s and above the ] of 2.1768 kelvins, the ] helium-4 exists in a normal colorless ] state, called ''helium I''. Like other cryogenic liquids, helium I boils when heat is added to it. 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 ] 1/8th that of ], which is only 1/4th 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 superfluid 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>http://www.yutopian.com/Yuan/TFM.html</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, ].<ref name="Encyc 263">''The Encyclopedia of the Chemical Elements'', page 263</ref><ref>http://prola.aps.org/abstract/PR/v76/i8/p1209_1</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. | |||
| 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>http://cryowwwebber.gsfc.nasa.gov/introduction/liquid_helium.html</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 ]s that are similar to the ] used to characterize ] 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"/> | |||
| ==Helium Voice== | |||
| It is a common misconception that Helium's effects on the voice are related to its density. The real explanation is slightly more complicated. Because Helium is ] (earth's atmosphere consists of over 95% ] molecules), its ] differs from that of air. This means that the speed of sound in helium is faster, and sound of the same frequency has a longer wavelength compared to in air. This difference results in the ] of the larynx corresponding to higher frequencies, and thus a higher pitched voice. An audio source which does not rely on a resonant air cavity (such as computer speaker) will not change pitch in a Helium atmosphere. If you took an orchestra to jupiter (whose atmosphere is primarily Helium and Hydrogen), the winds would be out of tune but the strings would remain unchanged. | |||
| ==Applications== | |||
| ]s such as the USGS blimp.]] | |||
| Helium is used for many purposes that require some of its unique properties, such as its low ], low ], low ], high ], or ]ness. Pressurized helium is commercially available in large quantities. | |||
| *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 lifting power of the alternative ]. | |||
| *For its low solubility in water, the major part of human ], air 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 ], decompression sickness, and ]. | |||
| *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 ], helium is used as a coolant in some ], such as ]s, and in ] air-sensitive metals. | |||
| *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 to detect leaks in high-vacuum equipment and high-pressure containers. | |||
| *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 the level of helium there. | |||
| *As explained above, inhaling Helium can change the pitch of a person's voice. However, inhaling it from a typical commercial source, such as that used to fill balloons, can be dangerous due to the number of contaminants that may be present. These could include trace amount of other gases, in addition to aerosolized lubricating oil. | |||
| *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. | |||
| ==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''). | |||
| 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> 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> | |||
| In 1907, ] and ] demonstrated that an ] is a helium ]. 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 Pyotr Leonidovich Kapitsa discovered that helium-4 has almost no ] at temperatures near ], a phenomenon now called ]. In 1972, the same phenomenon was observed in helium-3 by American physicists ], ], and ]. | |||
| ===Production and use=== | |||
| 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 ], ]. | |||
| 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. Helium use following ] was depressed but the reserve was expanded in the 1950s to ensure a supply 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 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" (Public Law 104–273) directed the ] to start liquidating the reserve by 2005.<ref>http://www.nap.edu/openbook/0309070384/html/index.html Executive Summary</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 early 2000s, ] and ] were added as well. Algeria quickly became the second leading producer of helium. Through this time, both helium consumption and the costs of producing helium increased. | |||
| ==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 ]s, where it is formed from ] by the ] of the ] and ]. According to the ] model of the early development of the ], 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, largely because most helium in the Earth's atmosphere escapes into space due to its inertness and low mass. In the Earth's ], a part of the upper atmosphere, helium and other lighter gases are the most abundant elements. | |||
| Nearly all helium on ] 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. | |||
| ===Production=== | |||
| 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 ]. | |||
| As of 2004, over one hundred and fifty million cubic metres of helium were extracted from natural gas or withdrawn from helium reserves, annually, with approximately 84% of production from the United States, 10% from Algeria, and most of the remainder from Canada, China, Poland, Qatar, and Russia. In the United States, most helium is produced in Kansas and Texas.<ref>{{web cite|author=]|date=January 2006|url=http://minerals.usgs.gov/minerals/pubs/commodity/helium/|title=Mineral Commodity Summaries: Helium|accessdate=2006-05-22}}</ref> | |||
| Diffusion of crude natural gas through special semi-] membranes 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== | |||
| 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"/> 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>http://www.ingentaconnect.com/content/klu/asys/2002/00000045/00000002/00378626</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 ]. | |||
| 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">http://www.mantleplumes.org/HeliumFundamentals.html</ref> Trace amounts are also produced by the ] of ].<ref>http://environmentalchemistry.com/yogi/periodic/Li-pg2.html</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 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 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> | |||
| ==Precautions== | |||
| The voice of a person who has inhaled helium temporarily sounds high-pitched, resembling those of the ] characters '']'' or '']'' (although these characters' voices were produced by shifting the pitch of normal voices). This is because the ] in helium is nearly three times that in air. As a result, when helium is inhaled there is a corresponding increase in the ] of the ].<ref name="Nature's 177"/> The higher perceived pitch is only due to a different frequency shaping of the voice, the ] of the ] remains more or less the same.<ref>http://www.phys.unsw.edu.au/PHYSICS_!/SPEECH_HELIUM/speech.html</ref> | |||
| Although the vocal effect of inhaling helium may be amusing, it 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 ] (with the notable exception of ]s) 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. | |||
| Neutral helium at standard conditions is non-toxic, plays no biological role and is found in trace amounts in ] ]. At high pressures, a mixture of helium and oxygen (]) can lead to ], however, increasing the proportion of nitrogen can alleviate the problem.<ref>http://www.scuba-doc.com/HPNS.html</ref> | |||
| Containers of helium gas at 5 to 10 K should be handled as if they have liquid helium inside due to the rapid and significant ] that occurs when helium gas at less than 10 K is warmed to ].<ref name="LANL.gov"/> | |||
| ==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== | |||
| <div class="references-small"> | |||
| <references /> | |||
| </div> | |||
| ==External links== | |||
| {{Commons|Helium}} | |||
| {{wiktionary|helium}} | |||
| ;General | |||
| * | |||
| * | |||
| * | |||
| * about liquid Helium-II and low temperature phase diagram | |||
| ;More detail | |||
| * at the ]; includes pressure-temperature phase diagrams for helium-3 and helium-4. | |||
| * - includes a summary of some low temperature techniques. | |||
| ;Miscellaneous | |||
| * regarding inhalation | |||
| * with audio samples that demonstrate the unchanged voice pitch | |||
| * | |||
| * | |||
| {{E number infobox 930-949}} | |||
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Revision as of 15:03, 25 September 2006
Media:Example.oggMedia:Example.oggMedia:Example.oggMedia:Example.oggMedia:Example.oggMedia:Example.ogg Media:Example.ogg Media:Example.ogg Media:Example.ogg Media:Example.oggThank you, come again, fuck you