Radioactive aerosols aerodynamic size distributions

Aerodynamic Size Distributions of Naturally-Radioactive Aerosols. Measurements of radionuclide distributions using cascade impactors indicate that Be-7 and Pb-210 are associated with larger aerosols than Pb-212 and Pb-214 (Robig et al., 1980 Papastefanou and Bondietti, 1986). Measurements of Pb-210 associations over oceans indicated activity median aerodynamic diameters (AMAD) near 0.6 pm (Sanak et al., 1981). The impactor measurements of Moore et al. (1980) on Pb-210, Bi-210, and Sr-90 sizes in continental air indicated that about 80% of the activity from all three nuclides was associated with aerosols below 0.3 pm. That work also determined that the mean age of aerosol Pb-210 was about a week. Knuth et al. (1983) compared Pb-210 and stable Pb sizes at a continental location and found that 78% of the Pb-210 found below 1.73 pm was smaller than 0.58 pm. Young (1974) reported that the most of the Be-7 in the atmosphere was associated with submicron aerosols. 

This paper summarizes part of the results of an investigation designed to characterize the aerodynamic size distributions of natural radioactivity and to evaluate the results in the context of sulfate distributions and recent advances in the understanding of aerosol growth mechanisms. This paper, while emphasizing our results on Pb-212 and Pb-214, also summarizes our initial data for longer-lived radionuclides. 

The subject of this particular volume relates to aerosol particle physics including aerosol characterisation, the formation mechanism, the aerodynamic size distribution of the activity and aerosol residence time, instrumentation techniques, aerosol collection and sampling, various kinds of environmental (atmospheric aerosols), particularly radioactive aerosols and the special case of radon decay product aerosols (indoors and outdoors) and the unattached fl ac-tion, thoron decay product aerosols, the deposition patterns of aerosol particles in the lung and the subsequent uptake into human subjects and risk assessment. 

Aerodynamic size distribution of radionuclide-associated aerosol particles (radioactive aerosols)... 

The use of an impactor with a single circular orifice for each jet provides a convenient method for determining the aerodynamic size distribution of an easily assayed aerosol, such as of a radioactive aerosol. This type of impactor is preferred when small sample rates and short sampling periods are desired since the stage characteristics can be accurately prescribed and particle bounce or re-entrainment can be minimised with the use of an appropriate liquid film on the collectors. 

Fig. 5.23. ICRP dust deposition model. The radioactive or mass fraction of an aerosol which is deposited in the N-P, T-B and P regions is given in relation to the activity or mass median aerodynamic diameter (AMAD or MMAD) of the aerosol size distribution. The model is intended for use with aerosol size distributions having an AMAD or MMAD between 0.2 and 10 pm and whose geometric standard deviations are less than 4.5. Provisional deposition estimates further extending the size range are given by the dashed lines. For the unusual aerosol size distributions having an AMAD or MMAD greater than 20 jm, complete N-P deposition can be assumed. The model does not apply to aerosols with AMAD or MMAD below 0.1 jm.

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