Field tests of a radon progeny sampler for the determination of effective dose

The International Commission on Radiological Protection (ICRP) recommends the use of a singleconversion factor, derived from epidemiological studies of exposure to uranium miners, for thedetermination of the effective dose from inhalation of radon progeny. Dosimetric models of radonprogeny inhalation predict that the dose conversion factors (DCF) are dependent upon the form ofthe radon progeny activity size distribution. The measurement of these activity size distributions isdifficult and an alternative approach has been proposed. The so-called Effective Dosimeter uses atwo-screen sampler with a collection efficiency matched to the particle size behaviour of the radonprogeny DCF, as determined from the ICRP Human Respiratory Tract Model. For this presentwork an Effective Dosimeter was constructed as the second stage of a six-stage wire screendiffusion battery. This diffusion battery was operated at a continuous sampling rate of 0.8 lpm,with in-situ counting of the alpha particle activity from the progeny deposited on the filtersproviding an estimate of the radon progeny potential alpha energy concentration (PAEC). Thishybrid system allowed two methods for the determination of the radon progeny DCF. The activitysize distributions, measured using the diffusion battery, were combined with the values of the DCFas a function of particle size to obtain a size-weighted DCF. The DCF values were obtained fromthe ICRP respiratory tract model, as implemented in the computer code RADEP. The seconddetermination of DCF was obtained directly from the fraction collected by the EffectiveDosimeter. The hybrid diffusion battery was used to measure radon progeny in the Fairy Cave,Buchan, Victoria at 20-minute intervals over 30 hour period. This cave had radon concentrationsexceeding 2000 Bq m-3, with low aerosol concentration and ventilation rate. The measurementswere analysed to determine the radon progeny PAEC, the activity size distribution, the sizeweightedDCF and the Effective Dosimeter collected fraction. The Effective Dosimeter DCFswere determined from the collected fraction using firstly a simple linear function and then using amore complex polynomial function to correct for residual errors. For the linear factor alone, thecalculated Effective Dosimeter DCFs were on average 11% lower than the equivalent sizeweightedDCF values. The agreement using the polynomial function was improved markedly, witha with a linear regression of the DCF yielding a fitted ratio of 0.965, with a R value of 0.99.