Further development of a computational method to evaluate indoor gamma dose - rate from building materials using external wall measurements

Sometimes, when it is impossible to perform a direct measurement, it is critical to obtain an estimate of the indoor gamma dose rate with adequate accuracy and precision. With a method we set up – the IN-OUT method – it is possible to estimate the indoor gamma dose rate attributable to building materials. Gamma dose rates are measured in contact with an external wall of a dwelling, and then a “room model” elaboration accounts for the geometrical and structural characteristics of the dwelling. The method was validated over more than 200 dwellings in three Italian regions within the “SETIL” project, the Italian epidemiological study on the aetiology of childhood leukaemia, lymphoma and neuroblastoma. In a first phase, indoor gamma dose rate estimates were obtained using the detailed dwelling information contained in questionnaires filled-in and collected during the indoor measurements. These estimates were very close to the measured values. A more general, less site-dependent approach has now been implemented for 74 dwellings of one region (Latium); by assuming average values for many indoor parameters instead of using the detailed data from the questionnaires, we evaluated the predictive characteristics of this method in situations where detailed data are not available. The ratio between estimated and measured indoor values has an overall average of 1.00 and 20% coefficient of variation. The results are very similar for tuff and concrete dwellings and support the usefulness of the IN-OUT method to obtain an estimate of the indoor gamma dose rate.