Determination of Dose Factors for External Gamma Radiation in Dwellings

INTRODUCTION The largest contribution for the global population exposure to ionizing radiation arises from natural sources, especially from radionuclides present in terrestrial crust. Certain human activities may eventually increase such exposure to significant levels, from the point of view of radiological protection (1, 2). The presence of natural radionuclides in building materials may lead to an increment of both external and internal radiation exposure of the inhabitants of dwellings built with such materials (3). External exposure inside dwellings arises from gamma-emitter radionuclides existing in the walls, floor and ceiling of the building. Mathematical models can be used to predict external dose rates inside the room, provided the radionuclide concentration activities in dwelling constituents are known (4, 5, 6). This paper presents a methodology for theoretical evaluation of external gamma doses due to radionuclides present in the walls of an hypothetical dwelling. Assuming the dwelling as one compartment of rectangular section and the radionuclides uniformly distributed within each wall, the most commonly cited expression in the literature for the evaluation of the dose is expressed as a linear combination of values of radionuclide concentrations and corresponding dose factors. Evaluation of dose factors is carried out by varying parameters of the model within a physically reasonable range. Results are presented in a graphical form.