Editing Helium (section)

==Applications==
[[File:Modern 3T MRI.JPG|thumb|The largest single use of liquid helium is to cool the superconducting magnets in modern [[MRI Scanner|MRI scanners]].|alt=A large solid cylinder with a hole in its center and a rail attached to its side.]]

{{Pie chart
 | caption=Estimated 2014 U.S. fractional helium use by category. Total use is 34 million cubic meters.<ref name="usgs-helium">{{cite book |author= U.S. Department of the Interior, U.S. Geological Survey |date= 2015 |title= Mineral Commodity Summaries 2014 |chapter= Helium |pages= 72–73 |chapter-url= http://minerals.usgs.gov/minerals/pubs/commodity/helium/mcs-2015-heliu.pdf |url= http://minerals.usgs.gov/minerals/pubs/mcs/index.html |access-date= 2014-05-31 |archive-url= https://web.archive.org/web/20140404122859/http://minerals.usgs.gov/minerals/pubs/mcs/index.html |archive-date= 2014-04-04 |url-status= live }}</ref>
 | other = yes
 | label1 = Cryogenics
 | value1 = 32
 | label2 = Pressurizing and purging
 | value2 = 18
 | label4 = Controlled atmospheres
 | value4 = 18
 | label3 = Welding
 | value3 = 13
 | label5 = Leak detection
 | value5 = 4
 | label6 = Breathing mixtures
 | value6 = 2
}}

While balloons are perhaps the best-known use of helium, they are a minor part of all helium use.<ref name="stwertka" /> Helium is used for many purposes that require some of its unique properties, such as its low [[boiling point]], low [[density]], low [[solubility]], high [[thermal conductivity]], or [[Chemically inert|inertness]]. Of the 2014 world helium total production of about 32 million kg (180 million standard cubic meters) helium per year, the largest use (about 32% of the total in 2014) is in cryogenic applications, most of which involves cooling the superconducting magnets in medical [[MRI]] scanners and [[NMR]] spectrometers.<ref>[http://physicsworld.com/cws/article/news/2010/jan/27/helium-sell-off-risks-future-supply Helium sell-off risks future supply] {{Webarchive|url=https://web.archive.org/web/20120610175902/http://physicsworld.com/cws/article/news/2010/jan/27/helium-sell-off-risks-future-supply |date=2012-06-10 }}, Michael Banks, ''Physics World'', 27 January 2010. accessed February 27, 2010.</ref> Other major uses were pressurizing and purging systems, welding, maintenance of controlled atmospheres, and leak detection. Other uses by category were relatively minor fractions.<ref name="usgs-helium" />

=== Controlled atmospheres ===
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|last1 = Beckwith|first1=I. E.|last2 = Miller|first2=C. G.|title = Aerothermodynamics and Transition in High-Speed Wind Tunnels at Nasa Langley |journal = Annual Review of Fluid Mechanics |volume = 22|issue = 1 |pages = 419–439 |date= 1990 |doi = 10.1146/annurev.fl.22.010190.002223|bibcode = 1990AnRFM..22..419B }}</ref> and [[impulse facility|impulse facilities]].<ref>{{Cite book|author = Morris, C.I. |title = Shock Induced Combustion in High Speed Wedge Flows |date= 2001 |series = Stanford University Thesis |url = http://thermosciences.stanford.edu/pdf/TSD-143.pdf|archive-url = https://web.archive.org/web/20090304210445/http://thermosciences.stanford.edu/pdf/TSD-143.pdf|archive-date = 2009-03-04}}</ref>

=== Gas tungsten arc welding ===
{{main|Gas tungsten arc welding}}
Helium is used as a [[shielding gas]] in [[arc welding]] processes on materials that, at welding temperatures are contaminated and weakened by air or nitrogen.<ref name="nbb" /> A number of inert shielding gases are used in gas tungsten arc welding, but helium is used instead of cheaper [[argon]] especially for welding materials that have higher [[heat conductivity]], like [[aluminium]] or [[copper]].

=== Minor uses ===

==== Industrial leak detection ====
[[File:Ac-system 2.jpg|thumb|left|A dual chamber helium leak detection machine|alt=Photo of a large, metal-framed device (about 3×1×1.5 m) standing in a room.]]

One industrial application for helium is [[leak detection]]. Because helium [[diffusion|diffuses]] through solids three times faster than air, it is used as a tracer gas to detect [[leak]]s in high-vacuum equipment (such as cryogenic tanks) 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|date = 2005|isbn = 978-0-471-61525-5}}</ref> The tested object is placed in a chamber, which is then evacuated and filled with helium. The helium that escapes through the leaks is detected by a sensitive device ([[helium mass spectrometer]]), even at the leak rates as small as 10<sup>−9</sup> mbar·L/s (10<sup>−10</sup> Pa·m<sup>3</sup>/s). The measurement procedure is normally automatic and is called helium integral test. A simpler procedure is to fill the tested object with helium and to manually search for leaks with a hand-held device.<ref>{{Cite book|url=https://books.google.com/books?id=5L8uIAFm4SoC&pg=PA493|page=493|title=High-vacuum technology: a practical guide|author=Hablanian, M. H.|publisher=CRC Press|date=1997|isbn=978-0-8247-9834-5}}</ref>

Helium leaks through cracks should not be confused with gas permeation through a bulk material. While helium has documented permeation constants (thus a calculable permeation rate) through glasses, ceramics, and synthetic materials, inert gases such as helium will not permeate most bulk metals.<ref>{{Cite book|author=Ekin, Jack W.|title=Experimental Techniques for Low-Temperature measurements|url=https://archive.org/details/experimentaltech0000ekin|url-access=registration|publisher=Oxford University Press|date=2006|isbn=978-0-19-857054-7}}</ref>

==== Flight ====
[[File: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=The Good Year Blimp]]
Because it is [[lighter than air]], [[airship]]s and balloons are inflated with helium for [[Lifting gas|lift]]. While hydrogen gas is more buoyant and escapes permeating through a membrane at a lower rate, helium has the advantage of being non-flammable, and indeed [[fire-retardant]]. Another minor use is in [[rocket]]ry, where helium is used as an [[ullage]] medium to backfill rocket propellant tanks in flight 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]] rocket used in the [[Apollo program]] needed about {{convert|370,000|m3|e6ft3|abbr=off}} of helium to launch.<ref name="LANL.gov" />

==== Minor commercial and recreational uses ====
Helium as a breathing gas has no [[Nitrogen narcosis|narcotic properties]], so helium mixtures such as [[Trimix (breathing gas)|trimix]], [[heliox]] and [[Trimix (breathing gas)#Heliair|heliair]] are used for [[deep diving]] to reduce the effects of narcosis, which worsen with increasing depth.<ref>{{Cite journal |last1=Fowler |first1=B. |last2=Ackles |first2=K. N. |first3=Porlier |last3=G |date=1985 |title=Effects of inert gas narcosis on behavior—a critical review |journal=Undersea Biomedical Research |pmid=4082343 |url=http://archive.rubicon-foundation.org/3019 |access-date=2008-06-27 |volume=12 |issue=4 |pages=369–402 |archive-url=https://web.archive.org/web/20101225052236/http://archive.rubicon-foundation.org/3019 |archive-date=2010-12-25 |url-status=usurped }}</ref><ref name="thomas">{{Cite journal |author=Thomas, J. R. |date=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 |access-date=2008-08-06 |archive-url=https://web.archive.org/web/20081206035952/http://archive.rubicon-foundation.org/2771 |archive-date=2008-12-06 |url-status=usurped }}</ref> As pressure increases with depth, the density of the breathing gas also increases, and the low molecular weight of helium is found to considerably reduce the effort of breathing by lowering the density of the mixture. This reduces the [[Reynolds number]] of flow, leading to a reduction of [[turbulent flow]] and an increase in [[laminar flow]], which requires less breathing.<ref>{{Cite journal| author = Butcher, Scott J.| author2 = Jones, Richard L.| author3 = Mayne, Jonathan R.| author4 = Hartley, Timothy C.| author5 = Petersen, Stewart R.| 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|date = 2007| doi = 10.1007/s00421-007-0541-5| pmid = 17701048| pages = 659–69| s2cid = 7311649}}</ref><ref name="BOCheox21">{{cite web |url=http://www.bochealthcare.co.uk/en/products/heliox/index.shtml |title=Heliox21 |publisher=Linde Gas Therapeutics |date=27 January 2009 |access-date=13 April 2011 |archive-url=https://web.archive.org/web/20110910232729/http://www.bochealthcare.co.uk/en/products/heliox/index.shtml |archive-date=10 September 2011 |url-status=live }}</ref> At depths below {{convert|150|m|ft}} divers breathing helium-oxygen mixtures begin to experience tremors and a decrease in psychomotor function, symptoms of [[high-pressure nervous syndrome]].<ref name="HungerBennett">{{cite journal |last1=Hunger | first1=W. L. Jr. |first2=P. B. |last2=Bennett |title=The causes, mechanisms and prevention of the high pressure nervous syndrome |journal=Undersea Biomed. Res. |volume=1 |issue=1 |pages=1–28 |date=1974 |issn=0093-5387 |oclc=2068005 |pmid=4619860 |url=http://archive.rubicon-foundation.org/2661 |access-date=2008-04-07 |archive-url=https://web.archive.org/web/20101225053451/http://archive.rubicon-foundation.org/2661 |archive-date=2010-12-25 |url-status=usurped }}</ref> This effect may be countered to some extent by adding an amount of narcotic gas such as hydrogen or nitrogen to a helium–oxygen mixture.<ref>{{Cite journal |author=Rostain, J. C. |author2=Gardette-Chauffour, M. C. |author3=Lemaire, C. |author4=Naquet, R. |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 |date=1988 |oclc=2068005 |pmid=3212843 |url=http://archive.rubicon-foundation.org/2487 |access-date=2008-06-24 |archive-url=https://web.archive.org/web/20081206035912/http://archive.rubicon-foundation.org/2487 |archive-date=2008-12-06 |url-status=usurped }}</ref>

[[Helium–neon laser]]s, a type of low-powered gas laser producing a red beam, had various practical applications which included [[barcode reader]]s and [[laser pointer]]s, before they were almost universally replaced by cheaper [[diode laser]]s.<ref name="nbb" />

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 reactor|gas-cooled nuclear reactor]]s.<ref name="nostrand" />

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 |date=1999 |volume=105 |issue=5 |pages=2677–2684 |doi=10.1121/1.426884|author1 = Belcher, James R.|pmid=10335618|bibcode = 1999ASAJ..105.2677B|author2=Slaton, William V.|author3=Raspet, Richard|author4=Bass, Henry E.|author5=Lightfoot, Jay|doi-access=free}}</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 |author2=Gurney, Kevin |publisher=MIT Press |date=1995 |isbn=978-0-262-13308-1}}</ref>

Helium is also used in some [[hard disk drive]]s.<ref>{{Cite web|url=https://arstechnica.com/information-technology/2013/11/hgst-balloons-disk-capacity-with-helium-filled-6tb-drive/|title=HGST balloons disk capacity with helium-filled 6TB drive|first=Sean|last=Gallagher|date=November 4, 2013|website=Ars Technica|access-date=June 14, 2017|archive-url=https://web.archive.org/web/20170707231259/https://arstechnica.com/information-technology/2013/11/hgst-balloons-disk-capacity-with-helium-filled-6tb-drive/|archive-date=July 7, 2017|url-status=live}}</ref>

==== Scientific uses ====
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 |date= 1997 |doi = 10.1080/10556799708208113|bibcode = 1997A&AT...13...35J }}</ref><ref>{{Cite journal|bibcode = 1983ApOpt..22...10E|title = Tests of vacuum VS. helium in a solar telescope|author = Engvold, O.|author2 = Dunn, R.B.|author3 = Smartt, R. N.|author4 = Livingston, W. C.| journal = Applied Optics|date = 1983|pages = 10–12|issue = 1|volume = 22|pmid = 20401118|doi = 10.1364/AO.22.000010}}</ref>

Helium is a commonly used carrier gas for [[gas chromatography]].

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" />

Helium at low temperatures is used in [[cryogenics]] and in certain cryogenic applications. As examples of applications, 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 [[metric ton]]s of liquid helium to maintain the temperature at {{convert|1.9|K|C F}}.<ref name="CERN-LHC">{{cite web|url=http://visits.web.cern.ch/visits/guides/tools/presentation/LHC_booklet-2.pdf |archive-url=https://web.archive.org/web/20110706223231/http://visits.web.cern.ch/visits/guides/tools/presentation/LHC_booklet-2.pdf |archive-date=2011-07-06 |title=LHC: Facts and Figures|publisher=[[CERN]]|access-date=2008-04-30}}</ref>

==== Medical uses ====
Helium was approved for medical use in the United States in April 2020 for humans and animals.<ref>{{cite web | title=Helium, USP: FDA-Approved Drugs | website=U.S. Food and Drug Administration | url=https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=213990 | access-date=30 April 2020}}</ref><ref>{{cite web | url=https://www.accessdata.fda.gov/drugsatfda_docs/appletter/2020/213990orig1s000MGltr.pdf | title=FDA approval letter | date=14 April 2020 | access-date=30 April 2020}}</ref>