Determination of 210Po and 210Pb in rainwater using measurement of 210Po and 210Bi Original Research Article

A method for determination of 210Po and 210Pb 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 m2) and to give results with the minimum delay. This was achieved by estimating 210Pb from counts of the daughter 210Bi after allowing 30 days for ingrowth. 210Po was measured directly by α-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. 210Po 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, 210Bi was separated from the 210Pb by extraction into 0.2% DDTC in chloroform and precipitated as bismuth oxychloride. The bismuth oxychloride was collected by filtration and the 210Bi counted using a gas-flow proportional counter. 210Pb activity was inferred from the 210Bi activity. This procedure allowed rapid, sensitive and cost effective measurement of 210Bi 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.