Rapid determination of atmospheric alpha contamination by using the Frisch grid ionization chamber

In a radiation emergency situation, the majority of radionuclides is dispersed in the form of aerosols and can be captured on aerosol filters. Alpha-spectrometric analysis is necessary for alpha radionuclides emitting no gamma radiation. A Frisch grid ionization chamber has been tested for this purpose. Three types of filters were tested: Millipore membrane filters, Synpor membrane filters, and glass-fiber Whatman filters. Aerosols from the radon chamber were deposited on the filter by means of an aerosol sampler, the alpha-spectrum was measured and its quality was evaluated. For the next tests, the glass-fiber Whatman filter was chosen. The aim of the experiments that followed was to determine the limits of detection (LDs) for some radionuclides. Outdoor air samples were prepared using filters 10 cm in diameter. The interval between the end of sampling and the start of counting was different for each sample, owing to which the time dependence of the LD levels. The average LD shortly after sampling was about 1.1 Bq/filter and decreased to about 0.5 Bq/filter in 3 hours. (orig.)