Analysis of Factors Affecting Aerosol, Unattached Fraction and Radon Progeny Measurements in Mines

摘要

Data from measurements of unattached fractions and aerosol and activity size distributions obtained in Elliot Lake uranium mines in Jan/Feb 1985 are analyzed in detail. Approximating the bimodal activity size distribution - one mode is the unattached fraction, the other mode is the attached fraction - by a unimodal distribution (for the attached fraction) is justified for up to at least an assumed 10% unattached fraction. This assumed unattached fraction is substracted from the counts on the reference filter in the procedure for examining the validity of the approximation. The effect of the approximation on the median diameter of the aerosol is negligible. The unattached fraction determined from the difference in reference and back-up filter activities is much more accurate when based on gross alpha counts than when based on radionuclide concentrations calculated from the filter activities. Calculation of the unattached fraction from counts on the wire screen and on the reference filter yields smaller unattached fractions than from counts on the reference and on the back-up filter, for reasons not understood. The overall precision of measurement for the wire screen method, however, is much poorer than for the reference-back-up method. Theoretical determination of the unattached fraction is very sensitive to the age of the air, especially for relatively young air (age<20min). The hybrid theory of attachment describes the attachment mechanism. Unattached fractions determined by this theory are consistent with those calculated from the reference and back-up filter measurements. The use of a single count median diameter rather than the complete size spectrum of aerosols introduces large errors in the theoretical determination of unattached fraction, especially for Pb-214 and Bi-214. The measurement methodology, mine data, details of the data analysis techniques, and the results are all presented in this report. (Atomindex citation 20:011483)