 Occurrence
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| On average, there is one atom of radon in 1 x 1021 molecules of air. Radon can be found in some spring waters and hot springs. The towns of Misasa, Japan, and Bad Kreuznach, Germany boast radium-rich springs which emit radon.
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| Radon emanates naturally from the ground, particularly in certain regions, especially (but not only) regions with granitic
soils. However, not all granitic regions are prone to high emissions of radon. Depending on how houses are built and ventilated,
radon may accumulate in basements and dwellings. The highest average radon concentrations in counties in the US are found
in Iowa and in the Appalachian Mountains areas in south-eastern Pennsylvania.
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| Radon, along with other noble gases krypton and xenon, is also produced during the operation of nuclear power plants. A small fraction of it leaks out of the fuel, through the
cladding and into the cooling water, from which it is scavenged. It is then routed to a holdup tank where it remains for a
large number of half-lives. It is finally purged to the open air through a tall stack which is carefully monitored for radiation level.
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| The European Union recommends that action should be taken starting from concentrations of 400 Bq/m3 for old houses and 200 Bq/m3 for new ones. After publication of the North American and European Pooling Studies, Health Canada has proposed a new guideline
that lowers their action level from 800 to 200 Bq/m3. The United States Environmental Protection Agency (EPA) strongly recommends action for any house with a concentration higher
than 148 Bq/m3 (given as 4 pCi/L), and encourages action starting at 74 Bq/m3 (given as 2 pCi/L). EPA radon risk level tables including comparisons to other risks encountered in life are available in
their citizen's guide. Nearly one in 15 homes in the U.S. has a high level of indoor radon according to their statistics.
The U.S. Surgeon General and EPA recommend all homes be tested for radon. Since 1985, millions of homes have been tested for
radon in the U.S.
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