Editing Radon (section)

=== Natural ===
[[Image:Radon Concentration next to Uranium Mine.PNG|thumb|upright=1.1|Radon concentration next to a uranium mine]]

Radon is produced by the radioactive decay of radium-226, which is found in uranium ores, phosphate rock, shales, igneous and metamorphic rocks such as granite, gneiss, and schist, and to a lesser degree, in common rocks such as limestone.<ref name="Kusky" /><ref name="Thad. Godish 2001">{{cite book |author=Godish, Thad |title=Indoor Environmental Quality |date=2001 |publisher=CRC Press |isbn=978-1-56670-402-1}}</ref> Every square mile of surface soil, to a depth of 6&nbsp;inches (2.6&nbsp;km{{sup|2}} to a depth of 15&nbsp;cm), contains about 1&nbsp;gram of radium, which releases radon in small amounts to the atmosphere.<ref name="USPHS90" /> It is estimated that 2.4 billion curies (90 EBq) of radon are released from soil annually worldwide.<ref name="StanleyMoghissi1975">Harley, J. H. in {{cite book |author1=Richard Edward Stanley |author2=A. Alan Moghissi |title=Noble Gases |url=https://books.google.com/books?id=RCxRAAAAMAAJ&q=%221600+pCi%2Fcm2%22&pg=PA659 |year=1975 |publisher=U.S. Environmental Protection Agency |page=111}}<!-- URL was: nepis.epa.gov/Exe/ZyNET.exe/9101F2OM.TXT --></ref> This is equivalent to some {{convert|15.3|kg}}.

Radon concentration can differ widely from place to place. In the open air, it ranges from 1 to 100&nbsp;Bq/m{{sup|3}}, even less (0.1&nbsp;Bq/m{{sup|3}}) above the ocean. In caves or ventilated mines, or poorly ventilated houses, its concentration climbs to 20–2,000&nbsp;Bq/m{{sup|3}}.<ref>{{cite journal |author=Sperrin, Malcolm |author2=Gillmore, Gavin |author3=Denman, Tony |date=2001 |title=Radon concentration variations in a Mendip cave cluster |journal=Environmental Management and Health |volume=12 |page=476 |doi=10.1108/09566160110404881 |issue=5 |url=http://eprints.kingston.ac.uk/1666/}}</ref>

Radon concentration can be much higher in mining contexts. Ventilation regulations instruct to maintain radon concentration in uranium mines under the "working level", with 95th percentile levels ranging up to nearly 3&nbsp;WL (546&nbsp;pCi {{sup|222}}Rn per liter of air; 20.2&nbsp;kBq/m{{sup|3}}, measured from 1976 to 1985).<ref name="USPHS90" />
The concentration in the air at the (unventilated) [[Bad Gastein|Gastein]] Healing Gallery averages 43&nbsp;kBq/m{{sup|3}} (1.2&nbsp;nCi/L) with maximal value of 160&nbsp;kBq/m{{sup|3}} (4.3&nbsp;nCi/L).<ref name="zdo">{{cite journal |doi=10.2203/dose-response.05-025.Zdrojewicz |pmc=2477672 |pmid=18648641 |title=Radon Treatment Controversy, Dose Response |date=2006 |volume=4 |issue=2 |author=Zdrojewicz, Zygmunt |journal=[[Dose-Response]] |last2=Strzelczyk |first2=Jadwiga (Jodi) |pages=106–18}}</ref>

Radon mostly appears with the radium/[[uranium]] series (decay chain) ({{sup|222}}Rn), and marginally with the thorium series ({{sup|220}}Rn). The element emanates naturally from the ground, and some building materials, all over the world, wherever traces of uranium or thorium are found, and particularly in regions with soils containing [[granite]] or [[shale]], which have a higher concentration of uranium. Not all granitic regions are prone to high emissions of radon. Being a rare gas, it usually migrates freely through faults and fragmented soils, and may accumulate in caves or water. Owing to its very short half-life (four days for {{sup|222}}Rn), radon concentration decreases very quickly when the distance from the production area increases. Radon concentration varies greatly with season and atmospheric conditions. For instance, it has been shown to accumulate in the air if there is a [[Inversion (meteorology)|meteorological inversion]] and little wind.<ref name="ehp.niehs.nih.gov">{{Cite journal |last1=Steck |first1=D. J. |last2=Field |first2=R. W. |last3=Lynch |first3=C. F. |year=1999 |title=Exposure to atmospheric radon |journal=Environmental Health Perspectives |volume=107 |issue=2 |pages=123–127 |doi=10.1289/ehp.99107123 |pmc=1566320 |pmid=9924007 |s2cid=1767956 |doi-access=free|bibcode=1999EnvHP.107..123S }}</ref>

High concentrations of radon can be found in some spring waters and hot springs.<ref>{{cite web |url=http://www.cheec.uiowa.edu/misc/radon_occ.pdf |archive-url=https://web.archive.org/web/20060316062136/http://www.cheec.uiowa.edu/misc/radon_occ.pdf |url-status=dead |archive-date=2006-03-16 |title=Radon Occurrence and Health Risk |author=Field, R. William |publisher=Department of Occupational and Environmental Health, University of Iowa |access-date=2008-02-02}}</ref> The towns of [[Boulder, Montana]]; [[Misasa, Tottori|Misasa]]; [[Bad Kreuznach]], Germany; and the country of Japan have radium-rich springs that emit radon. To be classified as a radon mineral water, radon concentration must be above 2&nbsp;nCi/L (74&nbsp;kBq/m{{sup|3}}).<ref>{{cite web |access-date=2009-07-07 |url=https://www.amtamassage.org/journal/winter03_journal/balneology.html |title=The Clinical Principles Of Balneology & Physical Medicine |url-status=dead |archive-url=https://web.archive.org/web/20080508064535/http://amtamassage.org/journal/winter03_journal/balneology.html |archive-date=May 8, 2008 }}</ref> The activity of radon mineral water reaches 2&nbsp;MBq/m{{sup|3}} in Merano and 4&nbsp;MBq/m{{sup|3}} in Lurisia (Italy).<ref name="zdo" />

Natural radon concentrations in the [[Earth's atmosphere]] are so low that radon-rich water in contact with the atmosphere will continually lose radon by [[volatilization]]. Hence, [[ground water]] has a higher concentration of {{sup|222}}Rn than [[surface water]], because radon is continuously produced by radioactive decay of {{sup|226}}Ra present in rocks. Likewise, the [[aquifer|saturated zone]] of a soil frequently has a higher radon content than the [[vadose zone|unsaturated zone]] because of [[diffusion]]al losses to the atmosphere.<ref>{{Unbulleted list citebundle|{{cite web |access-date=2008-06-28 |title=The Geology of Radon |url=http://energy.cr.usgs.gov/radon/georadon/3.html |publisher=United States Geological Survey |archive-date=2008-05-09 |archive-url=https://web.archive.org/web/20080509185452/http://energy.cr.usgs.gov/radon/georadon/3.html |url-status=dead }}|{{cite web |access-date=2008-06-28 |url=http://www.cosis.net/abstracts/EGU2008/08953/EGU2008-A-08953.pdf?PHPSESSID= |format=PDF |title=Radon-222 as a tracer in groundwater-surface water interactions |publisher=Lancaster University |archive-date=November 8, 2021 |archive-url=https://web.archive.org/web/20211108075203/https://www.cosis.net/abstracts/EGU2008/08953/EGU2008-A-08953.pdf?PHPSESSID= |url-status=dead }}}}</ref>

In 1971, [[Apollo 15]] passed {{Cvt|110|km||abbr=}} above the [[Aristarchus (crater)|Aristarchus plateau]] on the [[Moon]], and detected a significant rise in [[alpha particle]]s thought to be caused by the decay of {{sup|222}}Rn. The presence of {{sup|222}}Rn has been inferred later from data obtained from the [[Lunar Prospector]] alpha particle spectrometer.<ref>{{cite journal |last1=Lawson |first1=S. |last2=Feldman |first2=W. |last3=Lawrence |first3=D. |last4=Moore |first4=K. |last5=Elphic |first5=R. |last6=Belian |first6=R. |title=Recent outgassing from the lunar surface: the Lunar Prospector alpha particle spectrometer |journal=[[J. Geophys. Res.]] |volume=110 |page=1029 |date=2005 |issue=E9 |doi=10.1029/2005JE002433 |bibcode=2005JGRE..110.9009L |doi-access=free }}</ref>

Radon is found in some [[petroleum]]. Because radon has a similar pressure and temperature curve to [[propane]], and [[oil refineries]] separate petrochemicals based on their boiling points, the piping carrying freshly separated propane in oil refineries can become [[radioactive contamination|contaminated]] because of decaying radon and its products.<ref name="neb-one1994">{{cite news |publisher=National Energy Board |access-date=2009-07-07 |url= http://www.neb-one.gc.ca/clf-nsi/rsftyndthnvrnmnt/sfty/sftydvsr/1994/nbs199401-eng.pdf |title=Potential for Elevated Radiation Levels In Propane |date=April 1994}}</ref>

Residues from the petroleum and [[natural gas]] industry often contain radium and its daughters. The sulfate scale from an [[oil well]] can be radium rich, while the water, oil, and gas from a well often contains radon. Radon decays to form solid radioisotopes that form coatings on the inside of pipework.<ref name="neb-one1994" />