The FAG FHT59S airborne gross-alpha/beta activity monitor applied to time-resolved measurements of Rn-222 progeny concentrations in air

Abstract

Automated monitors for the determination of airborne radioactivity are widely in use as 'early warning' systems for nuclear emergencies, but seldom applied in quantitative studies to the appearance of natural radioactivity (especially radon and short-lived decay-products). This report describes how a specific type of airborne gross-alpha/beta monitor (FAG FHT59S), which is used by the Dutch National Radioactivity Monitoring Network (NRM) for the surveillance of the inhalation pathway, can be applied for this purpose. The main focus is on the performance of the applied algorithm which recalculates actual air activity concentrations from primary measurements, especially for circumstances contradicting assumptions made by the manufacturer. Furthermore, a complete uncertainty analysis has been carried out. As a result, a formula has been derived which converts, within a reasonable degree of uncertainty, the monitor recordings to the equilibrium-equivalent decay-product concentration (EEDC) of Rn-222. NRM-data of Rn-222 (progeny) obtained in this way agree with results of previous radon surveys carried out in the Netherlands.