Dosimetric models used in the Alpha-Risk project to quantify exposure of uranium miners
Titre du congrès :5th Conference on Protection Against Radon at Home and at Work
Ville du congrès :Prague
Date du congrès :09/09/2007
Titre de la revue: Radiation Protection Dosimetry Volume 130 Issue 1
Radon, Rn-222, is a radioactive noble gas and decays with a half-life of 3.82 d by mainly alpha emission. Its progeny includes four short lived radioisotopes of Po, Pb and Bi which finally decay into the 22 y half-life Pb-210. The exposure to radon is generally quantified by the working level month (WLM) which is related to the potential alpha energy concentration of its short lived progeny. The exposure can also be quantified in terms of the activity concentration of the radon gas in h Bq m-3. The two units are related via the equilibrium factor, F, which is a measure of the degree of disequilibrium between the radon gas and its progeny.
The dose received by the radiosensitive cells of the respiratory airways arising from the inhalation of radon progeny depends on the activity size distribution of the radon progeny aerosol, physiological parameters such as breathing rate, and on morphometric parameters such as the depth of the target cells of the epithelia. Two consistent approaches are presented here to evaluate this dose. One is based on the Human Respiratory Tract Model developed by the International Commission on Radiological Protection (ICRP) and the other makes use of a stochastic aerosol deposition model coupled to a microdosimetric calculation.
After inhalation and deposition in the airways of the radon progeny, a fraction of the activity is absorbed into blood and distributed in tissues including the liver, kidney and hematopoetic stem cells of the bone marrow. The dose received by these tissues is evaluated using the systemic models of the ICRP.
The European project Alpha-Risk aims at quantifying the cancer and non-cancer risks associated with multiple chronic radiation exposures by epidemiological studies, organ dose calculation and risk assessment. In the frame of this project, we have applied the models to the organ dosimetry of uranium miners who are internally exposed to radon and its progeny as well as to long-lived radionuclides present in the uranium ore. The choice of parameter values adapted to specific scenarios and the results of preliminary dose calculation are presented for both sources of exposure. The organ doses arising from the inhalation of radon gas alone have been evaluated using published dose coefficients that had been calculated with a pharmacokinetic model specific for the radon gas.
Acknowledgement: This work is supported by the European contract Alpha-Risk (FP6-516483)