CHARACTERIZATION OF INDOOR AIRBORNE RADIOACTIVITY

A programme of measurements of indoor atmospheric parameters appropriate to Australian building practice and the estimation of radiation dose from inhaled radioactivity has been commenced. Preliminary measurements, using both grab-sampling (seven samples) and continuous methods (63 1 h samples), have been carried out in a typical Australian home. Good agreement was obtained between the two sampling methodologies. The measured radon-radon daughter equilibrium ratios were in the range 0. 1 7-0.49, with values for the mean and the standard deviation for the grab-samples and the continuous sampling of 0.28 +/- 0.06 and 0.32 +/- 0.09, respectively. The values of the unattached fraction (f(p)) of potential alpha energy concentration (PAEC) were in the range of 0-80%. The daytime mean value of f(p) was 14% for both methods, compared with the 24 h average value, derived from the continuous method, of 20%. The measured PAEC size distributions were either single-peaked or bimodal, with the geometric mean of the lower mode between 0.5 and 1.2 nm and the upper mode between 85 and 200 nm. Factors for conversion to effective dose were calculated from the average of the results of the James-Birchall and Jacobi-Eisfeld dosimetric models(1). The distribution of factors for the three days sampling period was found to be log-normally distributed, with a mean and geometric mean of 22.5 Bq.m-3.mSv-1 and 19.5 Bq.m-3.mSv-1, respectively. These results are consistent with similar measurements in European homeS(2).