REANALYSIS OF 1973 ACTIVITY-WEIGHTED PARTICLE-SIZE DISTRIBUTION MEASUREMENTS IN ACTIVE US URANIUM MINES

Activity-weighted particle size distribution data taken with a low-pre ssure impactor in two working uranium mines have been reanalyzed using modern unfolding techniques. Both mines used diesel engines and tr er e located in the southwestern United States at an elevation of 2120 m; 14 measurements were made in the winter of 1973 at several mine locat ions and during typical mining activities. The activity median diamete r for the principal mode of the distribution determined using these be tter methods ranged between a minimum of 72 nm and a maximum of 303 nm ; the average value was 169 nm (average geometric standard deviation: 2.42), which is significantly smaller than the estimate of 250 nm (geo metric standard deviation: 2.5) obtained originally using graphical me thods and currently used in some dosimetric calculations. Four samples had secondary modes with more than 20% of the total activity at diame ters less than 60 nm; this was possibly a consequence of bimodal diese l emission and/or aerosols generated by propane combustion. (C) 1998 A merican Association for Aerosol Research.