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

A two-screen sampler tan effective dosimeter), with a collection efficiency matched to the particle size response of the radon progeny dose conversion factors (DCF), obtained from the ICRP respiratory tract model as implement ed in the computer code RADEP, has been developed to assess the inhalation dose from exposure to radon progeny. In order to evaluate the performance o f this sampler, the second stage of a six-stage wire screen diffusion batte ry was designed to operate as an Effective Dosimeter. This hybrid system al lowed two methods for the determination of the radon progeny DCF. For the f irst method, the activity size distributions, measured using the diffusion battery, were used to obtain a size-weighted DCF. A second determination of DCF was obtained directly from the fraction collected by the Effective Dos imeter. The hybrid diffusion battery was used to measure radon progeny in t he Fairy Cave, Buchan, Victoria at 20-min intervals over a 30-h period. Thi s cave had radon concentrations exceeding 2000 Bq m(-3), with low aerosol c oncentration and low ventilation rates. The measurements were analysed for the radon progeny PAEC, the activity size distribution, the size-weighted D CF and the effective dosimeter collected fraction. The Effective Dosimeter DCFs were determined from the collected fraction using firstly a simple lin ear function and then using a more complex polynomial function to correct f or residual errors. For the linear factor alone, the calculated Effective D osimeter DCFs were on average 11% lower than the equivalent size-weighted D CF values. The agreement using the polynomial function was improved markedl y, with a linear regression of the DCF yielding a fitted ratio of 0.965, wi th an R value of 0.99. For this study, the use of the ICRP conversion conve ntion to estimate the occupational exposure to the tour guides working in t he Fairy Cave would under estimate the effective dose by up to a factor of 2. Crown Copyright (C) 2001 Published by Elsevier Science B.V.