General Information on Radon

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What is Radon?

Radon PTable.jpg

Radon (chemical symbol: Rn) is a natural part of the environment. It is a radioactive gas that comes mainly from soil and rock, and is a normal part of the air we breathe.

Radon can also come from water and building materials, but the amount is usually very small. Radon cannot be seen, and has no smell. The only way to know how much radon is in the air is to measure it.

Radon makes up the largest part of natural Sources of Radiation Exposure.

There is usually less radon outdoors than indoors, since radon can concentrate in enclosed spaces. Exposure to radon outdoors is generally not an issue, so we normally focus on Exposure to Radon at Home and in indoor workplaces.

Radon is the second leading cause of lung cancer after smoking. Exposure to higher levels of radon for a long time can increase your risk of lung cancer.

Information on measuring and, if necessary, reducing radon levels, is available for homeowners, businesses, and government authorities.

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Risk of Exposure to Radon


There is strong evidence that exposure to radon can cause lung cancer. Radon exposure is the second leading cause of lung cancer after smoking.

Smokers are more at risk from radon exposure than non-smokers. A lifetime of exposure to radon at 100 Bq/m3 increases the risk of lung cancer by 0.1% for non-smokers, and 2% for smokers.

More precisely, for an average radon concentration of 100 Bq/m3, the lifetime risk of lung cancer for non-smokers is 0.5% (compared with a risk of 0.4% in the absence of radon). For lifelong smokers, the risk is 12% (compared with a risk of 10% in the absence of radon).

From the WHO Factsheet on Indoor Radon

"Radon is the most important cause of lung cancer after smoking. It is estimated that radon causes between 3–14% of all lung cancers in a country, depending on the average radon level and the smoking prevalence in a country.”

“… the risk of lung cancer increases … with increasing radon exposure.”

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) is the leading international body on radiation levels and effects. Visit the UNSCEAR website or read the UNEP report on "Radiation Effects and Sources" based on UNSCEAR work to learn more

Quotes from Publications

Lung Cancer: Publication 115[1] paragraph 55

… There is compelling evidence from cohort studies of underground miners and from case–control studies of residential radon exposures that radon and its progeny can cause lung cancer…

… The cumulative risk of lung cancer up to 75 years of age for lifelong non-smokers is estimated to be 0.4%, 0.5%, and 0.7% for radon activity concentrations of 0, 100, and 400 Bq/m3, respectively…

…The cumulative risks of lung cancer for lifelong smokers by 75 years of age are close to 10%, 12%, and 16% for radon activity concentrations of 0, 100, and 400 Bq/m3, respectively…

… Cigarette smoking remains the most important cause of lung cancer…

Other Cancers: Publication 115[1] paragraph 39

… review of the available epidemiological evidence shows no consistent evidence for an association between radon concentration and cancer, other than lung cancer.

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Units of Measure

Radon Measurements

A becquerel is a measure of radioactivity. One becquerel (Bq) is equal to one radioactive decay per second.

Radon concentrations in air are usually measured in becquerels per cubic meter (Bq/m3). That’s the amount of radon (becquerels) in a volume of air (cubic metre).

Worldwide, the average radon concentration in outdoor air is around 10 Bq/m3.

Some countries still use older units of picocuries per litre (pCi/L). 10 Bq/m3 = 0.27 pCi/L.

Potential Alpha Energy Concentration

In some circumstances, it’s more important to measure the level of radon progeny instead of the radon itself, specifically the Potential Alpha Energy Concentration (PAEC). This is the sum of the alpha particle decay energy of all the short-lived progeny of radon in a volume of air. The SI unit is joule per cubic metre (J m-3).

Historically, PAEC was measured in units of Working Levels (WL). 1 WL= 2.08 x 10-5J m-3

Quotes from ICRP

Publication 65[2] paragraphs 15-22

The potential alpha energy … of an atom in the decay chain of radon is the total alpha energy emitted during the decay of this atom to stable 210Pb…. The potential alpha energy concentration…of any mixture of short-lived radon progeny in air is the sum of the potential alpha energy of these atoms present per unit volume of air.… This quantity is expressed in the SI unit J m-3….

The potential alpha energy concentration … can be also expressed in terms of the so-called equilibrium equivalent concentration of … radon. The equilibrium equivalent concentration, corresponding to a non-equilibrium mixture of radon progeny in air, is the activity concentration of radon in radioactive equilibrium with its short-lived progeny that has the same potential alpha energy concentration … as the actual non-equilibrium mixture. The SI unit of the equilibrium equivalent concentration is Bq m-3….

… exposure … to radon progeny is defined as the time integral of the potential alpha energy concentration in air… The unit … is J h m-3 … [or] the historical unit Working Level Month (WLM) … 1 WLM = 3.54 mJ h m-3

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More In-Depth Information

If you are looking for something more extensive look no further below are a collection of related links and articles that can provide more information on this topic!

Risk of Exposure to Radon

Expert Summary of ICRP Recommendations on Radon ICRP Radon Summary
Lung Cancer Risk from Radon and Progeny and Statement on Radon ICRP Publication 115
Radiological Protection against Radon Exposure ICRP Publication 126
WHO Factsheet on Indoor Radon
WHO Handbook on Indoor Radon Handbook
UNEP report on Radiation Effects and Sources

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  1. 1.0 1.1 ICRP Publication 115 Lung Cancer Risk from Radon and Progeny and Statement on Radon Ann ICRP 40(1) 2010.
  2. ICRP Publication 65 Protection Against Radon-222 at Home and at Work - Ann ICRP 23(2) 1993.