The adjacent nuclear reaction is the portion of the decay of Uranium 238 into Lead 206 that produces Radon 222 gas.
Rn 222 is the most abundant of the radon isotopes and the only isotope that the name "radon" formally applies to, although in practice they are all usually lumped together under this name. |
Both uranium (U) and thorium (Th) readily substitute for the calcium (Ca) atoms found within mineral structures, and even though these two elements are found at very low levels in most rocks, enough radon is produced thereby to keep the background atmospheric concentration at about 6 x 10-16 moles/liter.
The equivalent to this chemical concentration is usually expressed as a radiochemical dosage when radon measurements are reported, however. Here in the U.S., this value equates to 0.4 pCi /L (picocuries/liter); elsewhere in the world, it is expressed as 0.0148 Bq/m3 (Becquerels per cubic meter). |
For those interested in the numbers, a picocurie is just 0.000,000,000,001 (one-trillionth) of a Curie, which is one of several internationally used units of radioactivity measurement.
A concentration of 1.0 pCi/L means that in one liter of air at that at level there will be about 2.2 radioactive disintegrations per minute. At a level of 4.0 pCi/l, therefore, approximately 9-10 radioactive disintegrations will occur each minute per liter of air (see radon reference level below). This amounts to about 1 per second within the average human lung volume of 6 liters. |
The National Park Service (NPS) has done numerous long term radon monitoring studies in several of the nation’s largest cave systems which has looked at cumulative radon dosages over time for both its employees and visitors.
The EPA has done a similar analysis that also included recreational cavers. These studies concluded that neither employees nor frequent visitors or recreational cavers experienced significant increases in lifetime exposure levels, considering the short duration of most of their visits. |
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