Determination of 210Po and 210Pb in rainwater using measurement of 210Po and 210Bi

A method for determination of Po-210 and Pb-210 in rainwater samples is described. This method was developed to permit measurement of the radionuclides in rainwater samples collected at short time intervals (2 weeks) on a small area (0.5 m(2)) and to give results with the minimum delay. This was achieved by estimating Pb-210 from counts of the daughter Bi-210 after allowing 30 days for ingrowth. Po-210 was measured directly by alpha-spectrometry. The radionuclides were collected from rainwater samples by co-precipitation with manganese dioxide then the precipitate was dissolved in a small volume of HCl/H2O2. Po-210 was plated onto silver and counted immediately and stable Bi was added to the solution which was allowed to stand for 30 days. After this time, Bi-210 was separated from the Pb-210 by extraction into 0.2% DDTC in chloroform and precipitated as bismuth oxychloride. The bismuth oxychloride was collected by filtration and the Bi-210 counted using a gas-flow proportional counter. Pb-210 activity was inferred from the Bi-210 activity. This procedure allowed rapid, sensitive and cost effective measurement of Bi-210 in rain water with a limit of detection 4.2 mBq and a coefficient of variation of 2% for four replicate analyses at the 1.0 Bq level. (C) 2000 Published by Elsevier Science B.V.