Determination of atmospheric lead-210 by alpha-scintillation counting of air filters


Alpha-counting of filters used to sample large volumes of air provides a convenient way of determining atmospheric concentrations of210Pb. Following decay of short-lived222Rn and220Rn progeny, alpha activity of the filters increases as210Pb decays to210Po. After transient equilibrium is reached at about 3 y, alpha activity diminishes with the 22.3 y halflife of210Pb. The degree of equilibrium between210Pb and210Po can be calculated subsequent to sampling, and the average concentration of210Pb in the air during the sampling period can be computed. Contributions to the total210Pb from ambient short-lived radon progeny are small, typically 2-4%. Using high volume air samplers with collection rates of 1.1-1.7 m3/min for 24 h periods, and using counting times of 2 h for 20 cm2 filter sections, we measured alpha counts ranging from 0.0100±0.0050 to 0.200±0.0200 dps. Periodic measurements on 100 of these filters over a 4 y period yielded mean210Pb levels with standard deviations less than ±15%. The method requires minimal sample preparation and can be used to determine past atmospheric210Pb concentrations on filters stored for up to 20 y and more. © 1994 Akadémiai Kiadó.

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Journal of Radioanalytical and Nuclear Chemistry Articles