Editing Period 6 element (section)

===Radon===
{{main|Radon}}
'''Radon''' is a [[chemical element]] with symbol '''Rn''' and [[atomic number]] 86. It is a [[radioactive decay|radioactive]], colorless, odorless, tasteless<ref>{{Cite book|title=Britannica Concise Encyclopedia|publisher=Encyclopaedia Britannica: Britannica Digital Learning|year=2017|via=Credo Reference}}</ref> [[noble gas]], occurring naturally as the decay product of [[uranium]] or [[thorium]]. Its most stable [[isotope]], [[Radon-222|<sup>222</sup>Rn]], has a [[half-life]] of 3.8 days. Radon is one of the densest substances that remains a [[gas]] under normal conditions. It is also the only gas that is radioactive under normal conditions, and is considered a health hazard due to its radioactivity. Intense radioactivity also hindered chemical studies of radon and only a few compounds are known.

Radon is formed as part of the normal radioactive [[decay chain]] of uranium and thorium. Uranium and thorium have been around since the earth was formed and their [[isotopes of thorium|most common isotope]] has a very long half-life (14.05 billion years). Uranium and thorium, [[radium]], and thus radon, will continue to occur for millions of years at about the same concentrations as they do now.<ref name=USPHS90>[http://www.bvsde.paho.org/bvstox/i/fulltext/toxprofiles/radon.pdf Toxological profile for radon] {{Webarchive|url=https://web.archive.org/web/20160415161629/http://www.bvsde.paho.org/bvstox/i/fulltext/toxprofiles/radon.pdf |date=2016-04-15 }}, [[Agency for Toxic Substances and Disease Registry]], U.S. Public Health Service, In collaboration with U.S. Environmental Protection Agency, December 1990.</ref> As the radioactive gas of radon decays, it produces new radioactive elements called radon daughters or decay products. Radon daughters are solids and stick to surfaces such as dust particles in the air. If contaminated dust is inhaled, these particles can stick to the airways of the lung and increase the risk of developing lung cancer.<ref>{{cite web|url=http://www.mass.gov/eohhs/consumer/community-health/environmental-health/exposure-topics/radiation/radon/public-health-fact-sheet-on-radon.html |title=Public Health Fact Sheet on Radon – Health and Human Services |publisher=Mass.Gov |access-date=2011-12-04}}</ref>

Radon is responsible for the majority of the public exposure to [[ionizing radiation]]. It is often the single largest contributor to an individual's [[background radiation]] dose, and is the most variable from location to location. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as attics and basements. It can also be found in some [[Spring (hydrosphere)|spring waters]] and hot springs.<ref>{{cite web|title=Facts about Radon|publisher=Facts about|url=http://www.facts-about.org.uk/science-element-radon.htm|access-date=2008-09-07|url-status=dead|archive-url=https://web.archive.org/web/20050222004131/http://www.facts-about.org.uk/science-element-radon.htm|archive-date=2005-02-22}}</ref>

[[Epidemiological]] studies have shown a clear link between breathing high concentrations of radon and incidence of [[lung cancer]]. Thus, radon is considered a significant contaminant that affects [[indoor air quality]] worldwide. According to the [[United States Environmental Protection Agency]], radon is the second most frequent cause of lung cancer, after cigarette smoking, causing 21,000 lung cancer deaths per year in the [[United States]]. About 2,900 of these deaths occur among people who have never smoked. While radon is the second most frequent cause of lung cancer, it is the number one cause among non-smokers, according to EPA estimates.<ref name="epa">{{cite web|url=http://www.epa.gov/radon/pubs/citguide.html|title=A Citizen's Guide to Radon|date=October 12, 2010|work=www.epa.gov|publisher=[[United States Environmental Protection Agency]]|access-date=January 29, 2012}}</ref>