General information 

During an exhalation measurement the values of radon will increase over the time because of physical properties of
decay as long as there is no saturation in the detection chamber.
For the evaluation of the exhalation rate a calculation program ERSEval (Data view 

Typical sample spectrum 

Linear fit calculation 

Linear regression leads to the equation: C(t) = Slope · t + Intercept (Linearfunction) with C(t) as a function of t (time). The two constants Slope and Intercept will be calculated so that square of deviation is a minimum. The constant Slope is the average slope and necessary to calculate the exhalationrate (Flux). 

Evaluation of flux by linear fit 

Geometric constants 

Volume of a halfsphere with D = 160 mm is V = 0.00155 m³ With the measuring interval t[s] and the average Slope the exhalation rate (Flux) F can be determined to: F = Slope · V / A [Bq/m²s] 

Exponential fit calculation 

Exponential regression leads to the equation: C(t) = Cmax · (1exp^{(l · t)}) (Exponential growth) with Cmax as saturation or plateau concentration and l as sum of radon decay constant l_{Rn} and ventilation rate l_{v}. This equation contains the two unknown variables Cmax and l_{v}. By a numerical iteration process the ventilation rate of the chamber l_{v} can be determined with good accuracy as well as the saturation concentration to calculate the exponential fit by the least squares method. 

Evaluation of flux by exponential fit 

With the calculated values exhalation rate (Flux) F can be determined to: F = Cmax · l ·V / A [Bq/m²s] 