SIZE DISTRIBUTION OF RADON PROGENY AEROSOL IN THE WORKING AREA OF A DRY FORMER URANIUM-MINE

To provide improved particle size data for reconstructing the radiatio n dose incurred by Colorado plateau uranium miners, sampling exercises were made in 1988 and 1994 at Twilight Mine in western Colorado, a fo rmer uranium mine that is now used as a research and training facility . The strategy was to simulate or approximate some of the conditions t o which the miners were exposed, then sample the aerosol with modern i nstrumentation. By combining data from an impactor with data from a di ffusion-based sampler, it was possible to cover the particle size rang e from 0.5 to 5000 nm. The major new finding of these sampling exercis es was that, with or without diesel operation, 5 to 30% of the potenti al alpha energy was bound to particles larger than 1000 nm. These part icles formed a well-defined mode (the coarse-particle mode) in the par ticle size distribution. Current lung models show that tracheobronchia l deposition increases with increasing particle size above 1000 nm. Co nsequently, the existence of coarse particles implies that the lung do se incurred by uranium miners was larger than previously thought. An a pproximate calculation based on the new data indicates a 40% increase in dose. Copyright (C) 1996 Elsevier Science Ltd.