Test of methods for retrospective activity size distribution determination from filter samples

• Activity size distributions can be recovered after aerosol sampling on filters.
• Extraction into a carrier liquid and subsequent nebulisation is appropriate.
• This facilitates the determination of activity size distributions for individuals.
• Size distributions from this method can be used for individual dose coefficients.
• Dose coefficients were calculated for the workers at the new Chernobyl shelter.

Determining the activity size distribution of radioactive aerosol particles requires sophisticated and heavy equipment, which makes measurements at large number of sites difficult and expensive. Therefore three methods for a retrospective determination of size distributions from aerosol filter samples in the laboratory were tested for their applicability. Extraction into a carrier liquid with subsequent nebulisation showed size distributions with a slight but correctable bias towards larger diameters compared with the original size distribution. Yields in the order of magnitude of 1% could be achieved. Sonication-assisted extraction into a carrier liquid caused a coagulation mode to appear in the size distribution. Sonication-assisted extraction into the air did not show acceptable results due to small yields. The method of extraction into a carrier liquid without sonication was applied to aerosol samples from Chernobyl in order to calculate inhalation dose coefficients for 137Cs based on the individual size distribution. The effective dose coefficient is about half of that calculated with a default reference size distribution.