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Comparison measurement of the activity concentration of radon progenies between the Bundesamt für Strahlenschutz (Federal Office for Radiation Protection - BfS) and PTB successful


Within the scope of a comparison measurement between the DAkkS-accredited BfS laboratory and PTB, two radon-222 progeny atmospheres were compared by means of a transfer standard. The comparison took place in PTB’s new radon reference chamber and provided a good agreement within the accuracy required for accreditation.

Two different equilibrium factors of F = 0.4 and F = 1.0, respectively, were generated. The atmospheres were kept stable for a period of at least 5 hours and measured by PTB with the radon progeny measuring set-up (RnF3). BfS’s transfer standard was located in the reference atmosphere and performed measurements every 60 minutes. PTB’s reference value was determined with a relative uncertainty of 6 % - 13 % (k = 2).

When comparing the primary radon progeny atmosphere and the internal calibration of BfS, an agreement within 15 % was found. This corresponds to the requirements for accreditation. Comparison measurements with a high unattached fraction are still difficult and are therefore excluded from the scope of the comparison measurement. The challenge which consists in providing a suitable transfer standard for different equilibrium factors, unattached fractions and activity concentrations remains.