UNCERTAINTY ANALYSIS OF THE EFFECTIVE DOSE PER UNIT EXPOSURE FROM RADON PROGENY AND IMPLICATIONS FOR ICRP RISK-WEIGHTING FACTORS

The International Commission on Radiological Protection has recently e ndorsed a new model of the human respiratory tract. This model has bee n used to calculate the effective dose per unit exposure to radon prog eny in mines or homes. The resulting effective dose per unit exposure is between 2 and 3 times that suggested by epidemiological approaches: dosimetry estimates are around 15 mSv per WLM, while epidemiological estimates are around 5 mSv per WLM. In an attempt to reconcile these t wo estimates, a detailed examination of the underlying assumptions mad e in the dosimetric approach has been performed. The sources of uncert ainty in the final estimate of effective dose per unit exposure to rad on progeny, E/P(p), have been divided into uncertainty in (a) aerosol conditions, (b) ICRP respiratory tract model parameters, and (c) other ICRP assumptions used in the calculation. Furthermore, the uncertaint y of E/P(p) to parameters which ICRP had not intended the user of the model to adjust, (d) the cell depths, thicknesses, and sensitivities o f the target cell layers themselves, has been investigated. A sensitiv ity analysis of E/P(p) to parameters in each of these categories has b een performed. Probability distributions of all the parameters that af fect E/P(p) have been generated, and in order to propagate these uncer tainties, a Monte Carlo type simulation based on the Latin Hypercube s ampling method has been performed. The conclusion is that the dosimetr y based estimate of E/P(p) is unlikely to be reconciled with the epide miological estimate of 5 mSv per WLM unless at least one of the values of the risk-weighting factors, currently recommended by ICRP, is reco nsidered.