A methodology to determine Pb, Bi, Pb and Bi in atmospheric aerosols; Application to precisely obtain aerosol residence times and Rn-daughters' equilibrium factors.

Progeny of Rn and Rn, (Pb, Bi, Pb and Bi) are essential to assess radiological hazard, external and internal doses, residence times and equilibrium factors. Precise measurements of these nuclides are quite complex due to their very short half-lives. This study outlines a new and precise methodology to measure these nuclides. Radon-222 and Rn were measured using a radon monitoring system, while their respective progenies were collected in an atmospheric filter using an ASS-500 sampler and measured by gamma-ray spectrometry. The Pb concentrations were very similar to the thoron ones, where all Bi/Pb ratios were consistently less than 1. The relative uncertainties, σ, of the Pb and Bi activity concentrations, and Bi/Pb activity ratio are generally less than 10%. Moreover, Pb/Rn ratios were about 0.7, agreeing well with previous works. The σ for Pb, Bi and Bi/Pb were generally less than 6%. This methodology was applied to estimate aerosol residence times using the Pb/Rn and Bi/Pb activity ratios, and to obtain equilibrium factors, achieving consistent results. Furthermore, the methodology consistency and validity range were studied with time elapsed between sampling end and counting start, and the sampling durations, finding the optimum times to precisely determine Pb, Bi, Pb and Bi.