BETA – Radon professional Training Center
BETA – Radon professional Training Center


The equilibrium equation is a simple formula that defines the relationship between the concentration of radon in the air and the fraction of its decay products that remain suspended in the air. The pie diagram shown below is a useful tool for remembering and manipulating the equation (WL*3700/EF*Rn =1).


Equilibrium equation pie chart

In order to do the calculations via AppoRad, after arriving at the calculator page:           Apporad -> Radon Tools -> Equilibrium equation
First, choose the quantity you want to calculate from the top bar

#1 -▶️ for the Radon concentration,
#2 -▶️ for the Working Level,
#3 -▶️ for the Equilibrium Factor.

Then choose two other asked parameters and click on the calculate button. You may repeat these steps as much as you wish. The default values are equal to 148 Bq/m3 for radon concentration, 0.5 for the Equilibrium factor, and 0.020 for the working level.

Equilibrium equation on AppoRad

In the case where the value of the equilibrium factor is not known, it is possible to use a value equal to 0.4 conventionally. It means that only 40% of radon’s decay products are suspended in the air. It is a good practice to play with this tool by putting different values for one parameter and changing the others to understand better how changing that parameter can influence the other ones.

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