Determination of the Fractionation Coefficient of Cesium-137 in an Aqueous Aerosol under Laboratory Condiotions

It is known that the concentration ratio of chemical elements in an aqueous aerosol (AA) can differ significantly from that of the same elements in the aqueous medium (AM) from which this AA was formed. Different accumulation (fractionation) of elements in AA occurs in the surface microlayer of water and is observed only for water-soluble microimpurities, whereas dissolved salts present in macroscopic concentrations undergo no accumulation. For radionuclides, the relative fractionation coefficient F(X/Cs) is defined as the degree of accumulation of the activity of radionuclide X in AA relative to another, reference radionuclide (137Cs). The values of F(X/Cs) were determined previously under natural conditions in the region of V-9 intermediate-level liquid radioactive waste storage reservoir (Lake Karachay) by analyzing the ratio of the volume activities of the radionuclides in water, RW(Cs/X), and in AA (in air), RA(Cs/X): F(X/Cs) = RA(Cs/X)/RW(Cs/X). Attempts to estimate the absolute fractionation coefficient of 137Cs, F(Cs), in AA relative to its content in AM failed. A procedure was suggested for determining the absolute fractionation coefficient of 137Cs, F(Cs), in AA relative to its content in AM under laboratory conditions. The procedure was tested with a model AM with the parameters close to those of V-9 reservoir (137Cs volume activity 0.17 MBq/L, dry residue ~10 g/L). The integral value of F(137Cs) for the model AM (for all the aqueous aerosol particles of size smaller than ~100 μm) varied from 4.4 to 6.5.