As usual the radon (Rn-222) gas concentrations unit in air is Bequerel per cubic meter.
The decay of radon results in a decay chain with the short-living radioactive nuclides
Decay products concentration often is described with a special unit: The Potential Alpha Energy Concentration (PAEC). This unit origins from uranium ore mining and quantifies the biological influence of a decay products mixture. It describes the resulting a-Energy of all decay products in a distinct volume until their total decay. Common units are: MeV/l or Working Level (1 WL = 130000 MeV/l).
|Data of radon decay products|
|Halflife||3.05 min||26.8 min||19.7 min||1.6·10-4 sec|
|a-Energy||6.00 MeV||0||0||7.68 MeV|
|pot. a-Energy/atom||13.68 MeV||7.68 MeV||7.68 MeV||7.68 MeV|
|pot. a-Energy/Bq||3612 MeV||17820 MeV||13130 MeV||1.8·10-3 MeV|
|pot. a-Energy/100pCi||13350 MeV||65890 MeV||48460 MeV||6.6·10-3 MeV|
In the case of equilibrium between radon and its progenies exist a stationary relation between radon gas concentration and the PAEC.
13350 MeV/l + 65890 MeV/l + 48460 MeV/l = 127700 MeV/l
1.3·105 MeV/l = 1 Working Level (WL)
The PAEC often is expressed as Equivalent Equilibrium Concentration (EC or EEC) with:
1 WL = 3700 Bq/m³ (EC)
The EC value is in most cases lower than the real radon gas concentration. The relation between EC and radon gas concentration CRn is called Equilibrium Factor F.
F = EC / CRn
The value of the Equilibrium Factor is F = 0...1 - in buildings about F = 0.5 as mean value.