Activity size distribution of radioactive aerosol particles

Activity size distribution of radioactive aerosol particles 

There are two methods that can be used to make activity-weighted size distribution measurements screen diffusion batteries (Hopke et al., 1992 Cheng et al., 1994) and all-type cascade impactors. Although screen diffusion batteries have been widely used, the activity size distribution cannot be easily obtained with them due to technical and calculation complexities. Even when conventional equipment and the impactor method are used it is difficult to obtain a result that is not affected by the decay of the radioisotopes. 

The stainless steel collecting plates of the Andersen cascade impactors are leached after the end of the aerosol sampling with a 2-ml solution of 1 M (molar) HNO3 in the case of and Pb. The leachate is rapidly evaporated on 5.08-cm (2-inch) diameter stainless steel plates using a hot plate, and the activity of the radioisotopes is measured by a-, and 3/-counting systems. Less than 30 to 40 min are needed to prepare the samples for counting after sampling is stopped. 

For 2i Pb and the stainless steel plates are leached with 300 cc of 2 N HCl. The solution is then filtered. The high leaching efficiency of 2 N HCl, better than 99%, can be confirmed by counting Pb and Bi in (a) the solution after leaching and (b) the leached filter residue, using Ge y-detectors. The filtrate is then passed through Dowex-1 anion ex- 

For Be measurements with high volume cascade impactors (HVI), even with 1 ACFM cascade impactors, the plates are leached with 0.1 M HCl and the activity of Be is measured with coaxial Ge y-detectors through the gamma photons of energy 477 keV. 

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