Editing Radon (section)

=== Concentration units ===
[[Image:Lead210inairatjapan.png|thumb|upright=1.55|<sup>210</sup>Pb is formed from the decay of <sup>222</sup>Rn. Here is a typical deposition rate of <sup>210</sup>Pb as observed in Japan as a function of time, due to variations in radon concentration.<ref>{{cite journal |title=Radon |author= Yamamoto, M. |journal=[[Journal of Environmental Radioactivity]] |date=2006 |pmid=16181712 |issue=1 |doi=10.1016/j.jenvrad.2005.08.001 |volume=86 |last2=Sakaguchi |first2=A. |last3=Sasaki |first3=K. |last4=Hirose |first4=K. |last5=Igarashi |first5=Y. |last6=Kim |first6=C. |pages=110–31}}</ref>]]

Discussions of radon concentrations in the environment refer to <sup>222</sup>Rn, the decay product of uranium and radium. While the average rate of production of <sup>220</sup>Rn (from the thorium decay series) is about the same as that of <sup>222</sup>Rn, the amount of <sup>220</sup>Rn in the environment is much less than that of <sup>222</sup>Rn because of the short half-life of <sup>220</sup>Rn (55 seconds, versus 3.8 days respectively).<ref name="USPHS90" />

Radon concentration in the atmosphere is usually measured in [[becquerel]] per cubic meter (Bq/m<sup>3</sup>), the [[SI derived unit]]. Another unit of measurement common in the US is [[Curie (unit)|picocurie]]s per liter (pCi/L); 1&nbsp;pCi/L = 37&nbsp;Bq/m<sup>3</sup>.<ref name="EPA03">{{cite news|url=http://www.epa.gov/radon/pdfs/402-r-03-003.pdf |archive-url=https://web.archive.org/web/20080227074413/http://www.epa.gov/radon/pdfs/402-r-03-003.pdf |archive-date=2008-02-27 |title=EPA Assessment of Risks from Radon in Homes|publisher= Office of Radiation and Indoor Air, US Environmental Protection Agency|date=June 2003}}</ref> Typical domestic exposures average about 48&nbsp;Bq/m<sup>3</sup> indoors, though this varies widely, and 15&nbsp;Bq/m<sup>3</sup> outdoors.<ref name="EPA radon" /><!-- values converted from pCi/L values in ref -->

In the mining industry, the exposure is traditionally measured in ''[[working level]]'' (WL), and the cumulative exposure in ''working level month'' (WLM); 1&nbsp;WL equals any combination of short-lived <sup>222</sup>Rn daughters (<sup>218</sup>Po, <sup>214</sup>Pb, <sup>214</sup>Bi, and <sup>214</sup>Po) in 1 liter of air that releases 1.3&nbsp;×&nbsp;10<sup>5</sup>&nbsp;MeV of potential alpha energy;<ref name="EPA03" /> 1 WL is equivalent to 2.08&nbsp;×&nbsp;10<sup>−5</sup> joules per cubic meter of air (J/m<sup>3</sup>).<ref name="USPHS90" /> The SI unit of cumulative exposure is expressed in joule-hours per cubic meter (J·h/m<sup>3</sup>). One WLM is equivalent to 3.6&nbsp;×&nbsp;10<sup>−3</sup> J·h/m<sup>3</sup>. An exposure to 1&nbsp;WL for 1 working-month (170 hours) equals 1&nbsp;WLM cumulative exposure. The [[International Commission on Radiological Protection]] recommends an annual limit of 4.8WLM for miners.<ref>{{Cite journal |last1=Vaillant |first1=Ludovic |last2=Bataille |first2=Céline |date=2012-07-19 |title=Management of radon: a review of ICRP recommendations |journal=Journal of Radiological Protection |volume=32 |issue=3 |pages=R1–R12 |doi=10.1088/0952-4746/32/3/r1 |pmid=22809956 |bibcode=2012JRP....32R...1V |issn=0952-4746}}</ref>{{rp|R5}} Assuming 2000 hours of work per year, this corresponds to a concentration of 1500 &nbsp;Bq/m<sup>3</sup>.

<sup>222</sup>Rn decays to <sup>210</sup>Pb and other radioisotopes. The levels of <sup>210</sup>Pb can be measured. The rate of deposition of this radioisotope is weather-dependent.<ref>{{Cite journal |last1=Yang |first1=Handong |last2=Appleby |first2=Peter G. |date=2016-02-22 |title=Use of lead-210 as a novel tracer for lead (Pb) sources in plants |journal=Scientific Reports |volume=6 |pages=21707 |doi=10.1038/srep21707 |issn=2045-2322 |pmc=4761987 |pmid=26898637|bibcode=2016NatSR...621707Y }}</ref>

Radon concentrations found in natural environments are much too low to be detected by chemical means. A 1,000&nbsp;Bq/m<sup>3</sup> (relatively high) concentration corresponds to 0.17&nbsp;[[pico-|picogram]] per cubic meter (pg/m<sup>3</sup>). The average concentration of radon in the atmosphere is about 6{{e|-18}} [[molar percent]], or about 150 atoms in each milliliter of air.<ref>{{cite web |url=http://www.us.lindegas.com/International/Web/LG/US/MSDS.nsf/NotesMSDS/Air+002/$file/Air+002.pdf |title=Health hazard data |publisher=[[The Linde Group]] |archive-url=https://web.archive.org/web/20130625060223/http://www.us.lindegas.com/International/Web/LG/US/MSDS.nsf/NotesMSDS/Air+002/$file/Air+002.pdf |archive-date=2013-06-25}}</ref> The radon activity of the entire Earth's atmosphere originates from only a few tens of grams of radon, consistently replaced by decay of larger amounts of radium, thorium, and uranium.<ref>{{cite web |access-date=2009-07-07 |url=http://www.laradioactivite.com/fr/site/pages/radon.htm |title=Le Radon. Un gaz radioactif naturel |language=fr |archive-date=2011-01-13 |archive-url=https://web.archive.org/web/20110113025038/http://www.laradioactivite.com/fr/site/pages/radon.htm |url-status=dead }}</ref>