Source strength of thick, continuously deposited alpha sources

In the presence of sizable amounts of background aerosols, detection and quantitation of airborne alpha emitters becomes difficult. The interaction of alpha particles with the material of the background aerosol in the source leads to a deterioration of alpha spectra and a saturation of count rates. As stopping powers and ranges for alpha particles are not well-known for most substances, a determination of the specific source strength and of the airborne radioactivity concentration is difficult and beset by considerable systematic uncertainties. It is shown here, that for emitters with a half-life long compared to the accumulation time of that thick source, simple relationships can be obtained for the source strength at saturation, and thus also for specific activity of the source and the airborne activity concentration. 1 reference, 2 figures