Editing Background radiation (section)

===Airborne sources===
The biggest source of natural background radiation is airborne [[radon]], a radioactive gas that emanates from the ground. Radon and its [[isotope]]s, parent [[radionuclide]]s, and [[decay product]]s all contribute to an average inhaled dose of 1.26&nbsp;[[Sievert#Common SI usage|mSv/a]] (millisievert [[wikt:per annum|per year]]). Radon is unevenly distributed and varies with weather, such that much higher doses apply to many areas of the world, where it represents a [[Health effects of radon|significant health hazard]]. Concentrations over 500 times the world average have been found inside buildings in Scandinavia, the United States, Iran, and the Czech Republic.<ref name="UNSCEAR2006E">{{cite book|author=United Nations Scientific Committee on the Effects of Atomic Radiation|title=Effects of Ionizing Radiation |date=2006 |publication-date=2008 |publisher=United Nations|location=New York|isbn=978-92-1-142263-4|volume=II|chapter=Annex E: Sources-to-effects assessment for radon in homes and workplaces|chapter-url=http://www.unscear.org/docs/reports/2006/09-81160_Report_Annex_E_2006_Web.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.unscear.org/docs/reports/2006/09-81160_Report_Annex_E_2006_Web.pdf |archive-date=2022-10-09 |url-status=live|access-date=2 December 2012}}</ref> Radon is a decay product of uranium, which is relatively common in the Earth's crust, but more concentrated in ore-bearing rocks scattered around the world. Radon seeps out of these [[ores]] into the atmosphere or into ground water or infiltrates into buildings. It can be inhaled into the lungs, along with its [[decay product]]s, where they will reside for a period of time after exposure.

Although radon is naturally occurring, exposure can be enhanced or diminished by human activity, notably house construction. A poorly sealed dwelling floor, or poor basement ventilation, in an otherwise well insulated house can result in the accumulation of radon within the dwelling, exposing its residents to high concentrations. The widespread construction of well insulated and sealed homes in the northern industrialized world has led to radon becoming the primary source of background radiation in some localities in northern North America and Europe.{{citation needed|date=December 2012}} Basement sealing and suction ventilation reduce exposure. Some building materials, for example [[lightweight concrete]] with [[alum shale]], [[phosphogypsum]] and Italian [[tuff]], may emanate radon if they contain [[radium]] and are porous to gas.<ref name=UNSCEAR2006E />

Radiation exposure from radon is indirect. Radon has a short half-life (4 days) and decays into other solid particulate [[Decay chain#Radium series|radium-series]] radioactive nuclides. These radioactive particles are inhaled and remain lodged in the lungs, causing continued exposure. Radon is thus assumed to be the second leading cause of [[lung cancer]] after [[tobacco smoking|smoking]], and accounts for 15,000 to 22,000 cancer deaths per year in the US alone.<ref>{{cite web| url = http://www.cancer.gov/cancertopics/factsheet/Risk/radon| title = Radon and Cancer: Questions and Answers – National Cancer Institute (USA)| date = 6 December 2011}}</ref>{{better source needed|date=December 2012}}<!--Radon may also dissolve in groundwater and be ingested, producing a dose to the stomach and the foetus. But this section is about air, inhalation only--> However, the discussion about the opposite experimental results is still going on.<ref>{{cite journal |last=Fornalski |first=K. W. |author2=Adams, R. |author3=Allison, W. |author4=Corrice, L. E. |author5=Cuttler, J. M. |author6=Davey, Ch. |author7=Dobrzyński, L. |author8=Esposito, V. J. |author9=Feinendegen, L. E. |author10=Gomez, L. S. |author11=Lewis, P. |author12=Mahn, J. |author13=Miller, M. L. |author14=Pennington, Ch. W. |author15=Sacks, B. |author16=Sutou, S. |author17=Welsh, J. S. |pmid=26223888 |title=The assumption of radon-induced cancer risk |year=2015 |journal=Cancer Causes & Control |doi=10.1007/s10552-015-0638-9 |issue=26 |volume=10 |pages=1517–18|s2cid=15952263 }}</ref>

About 100,000&nbsp;Bq/m<sup>3</sup> of radon was found in [[Health effects of radon#Accumulation in dwellings|Stanley Watras's]] basement in 1984.<ref>{{cite conference |url=http://wpb-radon.com/Radon_research_papers/1995%20Nashville,%20TN/1995_14_Indoor%20Radon%20Concentration%20Data--Geographic%20and%20Geologic%20Distribution,%20Captial%20District,%20NY.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://wpb-radon.com/Radon_research_papers/1995%20Nashville,%20TN/1995_14_Indoor%20Radon%20Concentration%20Data--Geographic%20and%20Geologic%20Distribution,%20Captial%20District,%20NY.pdf |archive-date=2022-10-09 |url-status=live |title=Indoor Radon Concentration Data: Its Geographic and Geologic Distribution, an Example from the Capital District, NY |first1=John J. |last1=Thomas |first2=Barbara R. |last2=Thomas |first3=Helen M. |last3=Overeynder |date= 27–30 September 1995  |conference=International Radon Symposium |conference-url=http://internationalradonsymposium.org/ |publisher=American Association of Radon Scientists and Technologists |location=Nashville, TN |access-date=2012-11-28}}</ref><ref>{{cite book|last1=Upfal |first1=Mark J. |last2=Johnson |first2=Christine |title=Occupational, industrial, and environmental toxicology|year=2003|publisher=Mosby|location=St Louis, Missouri|isbn=9780323013406|chapter-url=http://toxicology.ws/Greenberg/Chapter%2065%20-%20Residential%20Radon.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://toxicology.ws/Greenberg/Chapter%2065%20-%20Residential%20Radon.pdf |archive-date=2022-10-09 |url-status=live|edition=2nd|chapter=65 Residential Radon|editor1-first=Michael I. |editor1-last=Greenberg |editor2-first=Richard J. |editor2-last=Hamilton |editor3-first=Scott D. |editor3-last=Phillips |editor4-first=Gayla J. |editor4-last=McCluskey|access-date=28 November 2012}}</ref> He and his neighbours in [[Boyertown, Pennsylvania]], United States may hold the record for the most radioactive dwellings in the world. International radiation protection organizations estimate that a [[committed dose]] may be calculated by multiplying the [[equilibrium equivalent concentration]] (EEC) of radon by a factor of 8 to 9 {{sfrac|nSv·m<sup>3</sup>|Bq·h}} and the EEC of [[thoron]] by a factor of 40 {{sfrac|nSv·m<sup>3</sup>|Bq·h}}.<ref name=UNSCEAR2008 /><!-- The 8 is from ICRP, noted by UNSCEAR along with their own value of 9-->

Most of the atmospheric background is caused by radon and its decay products. The [[gamma spectroscopy|gamma spectrum]] shows prominent peaks at 609, 1120, and 1764&nbsp;[[keV]], belonging to [[bismuth-214]], a radon decay product. The atmospheric background varies greatly with wind direction and meteorological conditions. Radon also can be released from the ground in bursts and then form "radon clouds" capable of traveling tens of kilometers.<ref name="DetNuc">Gary W. Philips, David J. Nagel, Timothy Coffey – [http://large.stanford.edu/courses/2011/ph241/keller1/docs/phillips.pdf A Primer on the Detection of Nuclear and Radiological Weapons], Center for Technology and National Security Policy, National Defense University, May 2005</ref>