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Mapping potential radon‐222 exhalation at the soil surface: An example in Armorica, Brittany Volume 3, issue 1, Janvier-Février 2004

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Institut de radioprotection et de sûreté nucléaire (IRSN), DEI\SARGD\LERAR, BP 17, 92262 Fontenay‐aux‐Roses, <geraldine.ielschirsn.fr> CREGU, UMR G2R 7566 Géologie et gestion des ressources minérales et énergétiques, Université Henri Poincaré, BP 23, 54506 Vandœuvre‐lès‐Nancy cedex

Radon‐222 is a radioactive natural gas produced by the decay of radium‐226, itself produced by the decay of uranium‐238 naturally present in rocks and soil. It can accumulate in buildings, and inhalation of this gas and its decay products is a potential human health risk. Effective risk management needs to determine in advance the areas in which the density of buildings with high radon levels is likely to be highest. Research programs over the past several years have successfully developed a methodology for predicting and mapping the radon exhalation potential at the soil surface. This approach, based on quantification of the radon flux at the surface, starts from a precise characterization of the main local geological and pedological variables that influence the radon source and its transport to the soil\atmosphere interface. The methodology crosses the cartographic analysis into a Geographic Information System (GIS) and a simplified model for vertical transport of radon by diffusion through pores in the soil. This code, called TRACHGEO , calculates the radon flux density as a function of the chemical and physical properties of the rock and the subjacent soil. In this paper, we discuss the results from the application of this approach to an area (3,000 km2) located in Brittany (Western France). We discuss the validity of our forecasts and the use of such predictive maps as guides for radon risk management in existing or future buildings.