Editing Radon (section)

=== Daughters ===
{{Main|Decay chain#Uranium series}}
{{Sup|222}}Rn belongs to the radium and uranium-238 decay chain, and has a half-life of 3.8235 days. Its first four products (excluding marginal [[decay scheme]]s) are very short-lived, meaning that the corresponding disintegrations are indicative of the initial radon distribution. Its decay goes through the following sequence:<ref name="Sonzogni-2011" />
* {{Sup|222}}Rn, 3.82 days, [[alpha decay]]ing to...
* {{Sup|218}}[[Polonium|Po]], 3.10 minutes, alpha decaying to...
* {{Sup|214}}[[Lead|Pb]], 26.8 minutes, [[beta decay]]ing to...
* {{Sup|214}}[[Bismuth|Bi]], 19.9 minutes, beta decaying to...
* {{Sup|214}}Po, 0.1643&nbsp;ms, alpha decaying to...
* {{Sup|210}}Pb, which has a much longer half-life of 22.3 years, beta decaying to...
* {{Sup|210}}Bi, 5.013 days, beta decaying to...
* {{Sup|210}}Po, 138.376 days, alpha decaying to...
* {{Sup|206}}Pb, stable.

The radon equilibrium factor<ref>{{cite web |access-date=2009-07-07 |url=http://progenygrp.com/why_measure_rdps.htm |title=Why Measure RDPs? |url-status=dead |archive-url=https://web.archive.org/web/20150225020349/http://progenygrp.com/why_measure_rdps.htm |archive-date=2015-02-25}}</ref> is the ratio between the activity of all short-period radon progenies (which are responsible for most of radon's biological effects), and the activity that would be at equilibrium with the radon parent.

If a closed volume is constantly supplied with radon, the concentration of short-lived isotopes will increase until an equilibrium is reached where the overall decay rate of the decay products equals that of the radon itself. The equilibrium factor is 1 when both activities are equal, meaning that the decay products have stayed close to the radon parent long enough for the equilibrium to be reached, within a couple of hours. Under these conditions, each additional pCi/L of radon will increase exposure by 0.01&nbsp;''[[working level]]'' (WL, a measure of radioactivity commonly used in mining). These conditions are not always met; in many homes, the equilibrium factor is typically 40%; that is, there will be 0.004&nbsp;WL of daughters for each pCi/L of radon in the air.<ref name="EPA03" /> {{Sup|210}}Pb takes much longer to come in equilibrium with radon, dependent on environmental factors,<ref>{{Cite journal |last1=Joshi |first1=L. U. |last2=Rangarajan |first2=C. |last3=Sarada Gopalakrishnan |first3=Smt. |date=1969 |title=Measurement of lead-210 in surface air and precipitation |url=https://a.tellusjournals.se/articles/2832/files/submission/proof/2832-1-46460-1-10-20221018.pdf |journal=Tellus |volume=21 |issue=1|page=107 |doi=10.1111/j.2153-3490.1969.tb00423.x |bibcode=1969Tell...21..107J }}</ref> but if the environment permits accumulation of dust over extended periods of time, <sup>210</sup>Pb and its decay products may contribute to overall radiation levels as well. Several studies on the radioactive equilibrium of elements in the environment find it more useful to use the ratio of other {{Sup|222}}Rn decay products with {{Sup|210}}Pb, such as {{Sup|210}}Po, in measuring overall radiation levels.<ref>{{Unbulleted list citebundle|{{Cite journal|url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/53/079/53079681.pdf |title=Radioactive lead in the environment and in the human body |last=Jaworowski |first=Z. |publisher=Institute of Nuclear Research |location=Warsaw, Poland |journal=At. Energy Rev. |date= 1969 |volume=7 |issue=1 }}|{{Cite journal|title=Polonium-210 and Lead-210 in the Terrestrial environment: A historical review |first1=Bertil R.R. |last1=Persson |first2=Elis |last2=Holm |doi=10.1016/j.jenvrad.2011.01.005 |pmid=21377252 |journal= J Environ Radioact |date=May 2011 |volume=102 |issue=5 |pages=420–9|bibcode=2011JEnvR.102..420P }}}}</ref>

Because of their [[electrostatic charge]], radon progenies adhere to surfaces or dust particles, whereas gaseous radon does not. Attachment removes them from the air, usually causing the equilibrium factor in the atmosphere to be less than 1. The equilibrium factor is also lowered by air circulation or air filtration devices, and is increased by airborne dust particles, including cigarette smoke. The equilibrium factor found in epidemiological studies is 0.4.<ref>{{cite book|url=https://books.google.com/books?id=YDRCCNibEqYC&pg=PA179|page=179|title=Health effects of exposure to radon, Volume 6 of BEIR (Series)|publisher=National Academies Press|date=1999|isbn=978-0-309-05645-8}}</ref>