MODELLING OF GEOGENIC RADON IN SARDINIA AND HEALTH RISK ASSESSMENT

Enhanced level of radon in indoor environments such as homes, schools, public buildings and workplaces is considered an important health issue. Provided that radon is responsible for about 3–14 percent of all lung cancers, governments and inter-governmental institutions have issued several rules in the field of radioprotection of people from exposure to radon and its progenies. As one of the main preventive measures in Europe, the 2013/59/EURATOM BSS Directive requires the member states countries to prepare an action plan to address the radon potential source and identify Radon Prone Areas (RPAs), where the radon concentration is expected to exceed the national threshold level (as annual average of 300 Bq m-3 for both residential and workplaces). Following this directive, the work to be discussed here focuses on the preparation of a radon potential map of Sardinia according to the “Vast Area” approach and based on the use of literature derived geogenic data (e.g. lithological and geological types, U and Ra content, soil-gas radon, permeability and tectonics). As one of the main results of this thesis work, a predictive Geogenic Radon Potential (GRP) map expressing the radon potentials in ordinal categories was developed. The produced GRP map has merit because 1) it doesn't depend on the anthropogenic factors (e.g. building material, ventilation rate and living habits); 2) it can be used for the estimation of the radon hazard of both existing buildings and future construction sites, thus for the land-use planning. Complementary field and laboratory-based experiments were conducted to examine the predictive power of the proposed GRP map. Through the validation tests, we tried to answer three main questions; 1) considering the effect of radon anthropogenic factors, is it possible to use the GRP levels to estimate the indoor radon concentration for an area? 2) Do the results of real-time pilot tests in an area identified as RPA correlate with the category of radon potential predicted by the GRP map? And 3) is it possible to use the GRP map to justify the occurrence of enhanced levels of radon in closed spaces? In general, the correlations between examination test results and the predicted radon potential by the GRP map showed that the proposed map can address the major source of indoor radon in Sardinia. Besides, the radon emanation potential and natural radioactivity of the building material, the second major contributor to the indoor radon activity, was also investigated in detail parallel to the GRP mapping. The application of radon is not limited to addressing the health hazard. Radon monitoring coupled with natural radioactivity detection can be used as a tool for radiogenic assessments. This application was investigated in an area that consists of heavy mineral placer deposits in South-Eastern Sardinia. Through this experiment, the natural radioactive characteristics and radon-related behaviors of studied formations were well-distinguished The last year of the Ph.D. programme was carried out at Trinity College of Dublin, where the primary purpose of the study was to evaluate in detail the radon and thoron potential in an area with complex geology. Data obtained from radiometric surveys, geochemical measurements and indoor radon concentrations were used to distinguish radon and thoron release from different geo formations and soil types. To aim this, a set of samples were collected from selected geo types and radon/thoron exhalation rates were estimated through laboratory experiments. As a result, radon and thoron potential maps were developed. In the next step, a detailed investigation of soil gas radon concentrations was considered in a radon priority area identified through the potential maps. As a result of the second investigation, a geostatistical model was built to estimate the GRPs with higher accuracy.