Assessment of radiation dose from exposure to radon and thoron progeny

The assessment of exposure to radon and thoron is usually derived from measurements of the airborne concentrations of the radioactive gases or their decay products. Monitoring programmes and surveys can provide detailed information about temporal and spatial variations in these airborne concentrations. The international Commission on Radiological protection (ICRP) recommends that the calculation of the inhalation dose for an individual exposed to radon progeny should be based on a single conversion factor derived from epidemiological studies of uranium mine exposure. This approach does not take into account differences in aerosol characteristics, particularly the fraction and diameter of any ultrafine (unattached) mode. The Australian Radiation Laboratory (ARL) has developed a number of systems for assessing the aerosol parameters required by the dosimetric models of radon progeny inhalation, These systems include a practical dichotomous-sampling field device and computational algorithm which has a measurement characteristic as a function of particle size that closely simulates the dependence of effective dose on aerosol size. This device can be used as a radon or thoron progeny Effective Dosimeter. This paper describes the application of the ARL systems to the assessment of radon progeny radiation dose in a range of Australian exposure situations and examines the applicability of the ICRP conversion convention. The quality of radon and radon progeny measurements can be optimised by proper calibration methods, supported by intercomparison exercises such as those organised within the International Radon Metrology Programme (IRMP). There is a need for a similar programme to intercompare radon progeny dose assessment methods.