Radon: Units of Measure

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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.


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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).

If radon progeny are in equilibrium with radon-222 (which is rarely the case):

10 Bq/m3 (radon-222) = 0.27 pCi/L (radon-222) = 5.56 x 10-8 J m-3 (PAEC) = 0.0027 WL (PAEC)

Quotes from ICRP Publications

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Publication 65, 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

See Also