A Radon Progeny Sampler for the Determination of Effective Dose

Abstract

The design and simulated performance is described of a two-stage sampler (HE-Sampler) for 222 Rn progeny. This HE-Sampler has a collection efficiency optimised to match the particle size dependency of the radon progeny dose conversion factor (DCF), derived from the latest Respiratory Tract Model of the Intemational Commission on Radiological Protection, as implemented in the computer code RADEP. The HE-Sampler comprises a wire screen pre-separator, matched to the nasal deposition, and a wire screen collector, matched to the respiratory tract collection. This HE-Sampler allows for the estimation of the radiation dose from the inhalation of 222 Rn progeny, derived from two concurrent alpha particle activity measurements, one on the HE-Sampler screen collector and one on a reference filter sample. As a first approximation, the DCF is proportional to the collected fraction. The HE-Sampler response was simulated for a range of radon progeny size distributions to determine the error in the estimated DCF values. For monodispersed radon progeny the DCF errors were up to 35%. For polydispersed radon progeny distributions in the range 1 nm to 1000 nm, the DCF error was in the range ±10% and ±20%, for occupational and environmental exposure, respectively. This error range can be reduced to ±10% between 0.6 nm and 700 nm by using a polynomial fitting function. The simulated response to complex particle size distributions was investigated using a data set of 70 experimental measurements taken as representative of environmental and occupational exposure. For environmental exposure, the derived mean DCF error and the root mean square (RMS) error were +3.6% and ±4.8% for polynomial fitting functions, respectively. The corresponding values for occupational exposure were 0.5% and ±3.1%. The effect of systematic errors in the operating parameters was investigated using a further simulation based on this experimental data set. The simulation results show that the HE-Sampler is relatively insensitive to variations in sampling rate and in the screen parameters, particularly for environmental exposure.