Radon decay products equilibrium at different aerosol concentrations.

The influence of aerosol particle concentration on the activity of short-lived radon decay products (RPDs) was investigated inside a standard radon box. The 218Po:214Pb:214Bi activity ratio was determined for unattached and attached fractions of radon decay products at different aerosol concentrations. For the unattached fraction, this ratio was 1:0.31:0.06, while for the attached aerosol fraction the activity ratio was 1:1.4:0.91 at a low aerosol concentration (2000 cm-3) and with the unattached fraction fp = 0.45. In this case, there was no additional aerosol in the standard radon box and the equilibrium shift ratio for the total activity (attached and unattached) was 1:0.55:0.27 for 218Po:214Pb:214Bi. When the aerosol was injected, the unattached fraction nearly disappeared at a high aerosol concentration (80000-90000 cm-3). The equilibrium shift ratio for the total activity at a high aerosol concentration was 1:2:1.5 for 218Po:214Pb:214Bi. This ratio was the same for the attached fraction. For no more than 0.01 of the unattached fractions, this ratio was 1:0.85:0.7. Radioactive equilibrium factors and unattached fractions were also determined at different aerosol particles concentrations. A negative correlation between unattached fraction and the radioactive equilibrium factor, as well as a positive correlation coefficient between the radioactive equilibrium factor and aerosol particle concentration in a standard radon box, has been determined.