Editing Noble gas (section)

==Occurrence==
The abundances of the noble gases in the universe decrease as their [[atomic number]]s increase. Helium is the most common element in the [[universe]] after hydrogen, with a mass fraction of about 24%. Most of the helium in the universe was formed during [[Big Bang nucleosynthesis]], but the amount of helium is steadily increasing due to the fusion of hydrogen in [[stellar nucleosynthesis]] (and, to a very slight degree, the [[alpha decay]] of heavy elements).<ref>{{cite web|last=Weiss|first=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]]|access-date=23 June 2008|archive-url=https://web.archive.org/web/20070208212728/http://www.einstein-online.info/en/spotlights/BBN_obs/index.html|archive-date=8 February 2007|url-status=dead}}</ref><ref>{{cite journal|author=Coc, A.|title=Updated Big Bang Nucleosynthesis confronted to WMAP observations and to the Abundance of Light Elements|journal=[[Astrophysical Journal]]|volume=600|year=2004|pages=544–552|doi=10.1086/380121|bibcode=2004ApJ...600..544C|issue=2|arxiv= astro-ph/0309480 |s2cid=16276658|display-authors=etal}}</ref> 

Abundances on Earth follow different trends; for example, helium is only the third most abundant noble gas in the atmosphere. The reason is that there is no [[primordial element|primordial]] helium in the atmosphere; due to the small mass of the atom, helium cannot be retained by the Earth's [[gravitational field]].<ref name=morrison>{{cite journal|first1=P.|last1=Morrison|last2=Pine|first2=J.|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|bibcode= 1955NYASA..62...71M |s2cid=85015694}}</ref> Helium on Earth comes from the [[alpha decay]] of heavy elements such as [[uranium]] and [[thorium]] found in the Earth's [[Crust (geology)|crust]], and tends to accumulate in [[Natural gas field|natural gas deposit]]s.<ref name=morrison /> The abundance of argon, on the other hand, is increased as a result of the [[beta decay]] of [[potassium-40]], also found in the Earth's crust, to form [[argon-40]], which is the most abundant isotope of argon on Earth despite being relatively rare in the [[Solar System]]. This process is the basis for the [[potassium-argon dating]] method.<ref>{{cite web|url=http://www.geoberg.de/text/geology/07011601.php|title=<sup>40</sup>Ar/<sup>39</sup>Ar dating and errors|access-date=26 June 2008|publisher=[[Technische Universität Bergakademie Freiberg]]|date=16 January 2007|last=Scherer|first=Alexandra |archive-url= https://web.archive.org/web/20071014042248/http://geoberg.de/text/geology/07011601.php |archive-date=14 October 2007}}</ref> 

Xenon has an unexpectedly low abundance in the atmosphere, in what has been called the ''missing xenon problem''; one theory is that the missing xenon may be trapped in minerals inside the Earth's crust.<ref>{{cite journal |first1=Chrystèle|last1=Sanloup |first2=Burkhard C. |last2=Schmidt |first3=Eva Maria Chamorro|last3=Perez |first4=Albert |last4=Jambon |first5=Eugene |last5=Gregoryanz |first6=Mohamed |last6=Mezouar |display-authors=2 |title=Retention of Xenon in Quartz and Earth's Missing Xenon|journal=Science|year=2005|volume=310|issue=5751|pages=1174–1177|doi= 10.1126/science.1119070|pmid=16293758|bibcode= 2005Sci...310.1174S |s2cid=31226092 }}</ref><ref>{{Cite journal |last=Zhu |first=Li |last2=Liu |first2=Hanyu |last3=Pickard |first3=Chris J. |last4=Zou |first4=Guangtian |last5=Ma |first5=Yanming |date=July 2014 |title=Reactions of xenon with iron and nickel are predicted in the Earth's inner core |url=https://www.nature.com/articles/nchem.1925 |journal=Nature Chemistry |language=en |volume=6 |issue=7 |pages=644–648 |doi=10.1038/nchem.1925 |issn=1755-4349|arxiv=1309.2169 }}</ref> Radon is formed in the [[lithosphere]] by the [[alpha decay]] of radium. It can seep into buildings through cracks in their foundation and accumulate in areas that are not well ventilated. Due to its high radioactivity, radon presents a significant health hazard; it is implicated in an estimated 21,000 [[lung cancer]] deaths per year in the United States alone.<ref>{{cite web| title= A Citizen's Guide to Radon| publisher= U.S. Environmental Protection Agency| date= 26 November 2007| url= http://www.epa.gov/radon/pubs/citguide.html| access-date= 26 June 2008}}</ref> Oganesson does not occur in nature and is instead created manually by scientists.
{| class="wikitable" style="text-align: center; margin-left: auto; margin-right: auto; border: none;"
! Abundance ||Helium||Neon||Argon||Krypton||Xenon||Radon
|-
|align="left"|Solar System (for each atom of silicon)<ref>{{cite journal| doi = 10.1086/375492| last = Lodders| first = Katharina|author-link=Katharina Lodders| date = 10 July 2003| title = Solar System Abundances and Condensation Temperatures of the Elements| journal = The Astrophysical Journal| publisher = The American Astronomical Society| volume = 591| issue = 2| pages = 1220–1247| url = http://weft.astro.washington.edu/courses/astro557/LODDERS.pdf| bibcode = 2003ApJ...591.1220L| s2cid = 42498829| access-date = 1 September 2015| archive-url = https://web.archive.org/web/20151107043527/http://weft.astro.washington.edu/courses/astro557/LODDERS.pdf| archive-date = 7 November 2015| url-status = dead}}</ref>|| 2343 || 2.148 || 0.1025 || 5.515 × 10<sup>−5</sup> || 5.391 × 10<sup>−6</sup> || –
|-
|align="left"|Earth's atmosphere (volume fraction in [[parts per million|ppm]])<ref>{{cite web|access-date=1 June 2008|url=http://www.srh.noaa.gov/jetstream//atmos/atmos_intro.htm|title=The Atmosphere |publisher=[[National Weather Service]]}}</ref> || 5.20 || 18.20 || 9340.00 || 1.10 || 0.09 || (0.06–18) × 10<sup>−19</sup><ref name=ullmann/>
|-
|align="left"|Igneous rock (mass fraction in ppm)<ref name="greenwood891"/> || 3 × 10<sup>−3</sup> || 7 × 10<sup>−5</sup> || 4 × 10<sup>−2</sup> || – || – || 1.7 × 10<sup>−10</sup>
|}

<div style="float: right; padding-left: 10px;">
{| class="wikitable" style="text-align: center;"
! Gas || 2004 price ([[United States dollar|USD]]/m<sup>3</sup>)<ref name=kirk>{{cite book |title=Kirk Othmer Encyclopedia of Chemical Technology |author1=Hwang, Shuen-Chen |author2=Lein, Robert D. |author3=Morgan, Daniel A. |chapter=Noble Gases |doi=10.1002/0471238961.0701190508230114.a01 |pages=343–383 |year=2005 |publisher=Wiley}}</ref>
|-
|align=left| Helium (industrial grade) || 4.20–4.90
|-
|align=left| Helium (laboratory grade) || 22.30–44.90
|-
|align=left| Argon || 2.70–8.50
|-
|align=left| Neon || 60–120
|-
|align=left| Krypton || 400–500
|-
|align=left| Xenon || 4000–5000
|}
</div>
For large-scale use, helium is extracted by [[fractional distillation]] from natural gas, which can contain 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/| access-date = 14 July 2008}}</ref>