On the determination of the average radon concentration from few-day measurements in buildings

Radon concentration in outdoor air and in buildings is very variable, showing diurnal and seasonalvariations. Long term measurements with track etch detectors lasting up to one year give the mostprecise one year averages. It arrives, however, that we are obliged to get results much sooner e.g. forscreening measurements. How long should we measure radon concentration to get proper results? Wehave studied the problem of selecting proper time interval on the basis of our six long-termmeasurements in Krakw using AlphaGUARD PQ-2000 ionization chamber. The mean radonconcentration ranged from 543 to 1107 Bq/m3. It was found that the relative error of k-day averagewas decreasing exponentially with a time constant of 4 days. Therefore we would recommend aminimal measuring time of four (k=4) days for a single measurement