Aerosols: unexpected disequilibrium phenomena between airborne radio activities of lead-210 and its progenies bismuth-210 and polonium-210

摘要

For the first time, concentrations of the long lived radon progenies ~(210)Pb, ~(210)Bi and ~(210)Po were measured in the mine atmosphere of the so called "healing gallery" in Badgastein, Austria, a region famous for its radioactive springs. These investigations were performed in order to study the radioactive equilibrium between the ~(210)Pb-~(210)Bi and the ~(210)Pb-~(210)Po pairs so as to gain more information about the aerosol-forming processes in the mine. The particle size distribution of the aerosols was determined under different ventilation conditions. Six-stage and eight-stage cascade impactors with working ranges from 0.15 to5 μm and from 0.063 to 8 μm, respectively, were used to collect the mine aerosols. These samples were analysed in the laboratory and measured by liquid scintillation spectrometry. The most surprising results were found under full ventilation, when the total activity concentrations of ~(210)Pb, ~(210)Bi and ~(210)Po were 4.6, 2.0 and 16.5 mBq/m~3, respectively. In this case ~(210)Po/~(210)Pb activity ratios ranged between 1.8 +- 0.3 and 4.3 +- 0.3. These unexpected results were confirmed by the eight-stage impactor samples. For the smallest particles, between 0.062 and 0.125 μm, an even higher value of 7.5 was observed. As outside sources could be excluded, such ~(210)Po enrichments must occur during the aerosol-forming process itself inside the mine.