Geant4-based assessment of indoor radiation exposure in Saudi dwellings

This study presents a Geant4-based Monte Carlo framework for assessing indoor gamma radiation in Saudi residential environments. Specific absorbed dose rate conversion factors in air (nGy h^-1 per Bq kg^-1) were calculated using Geant4 simulations for realistic Saudi room geometries, considering gamma emissions from the ²³⁸U and ²³² Th day series and from ⁴⁰K. These conversion factors were then applied to experimentally measured activity concentrations of Saudi building materials compiled from the literature to evaluate absorbed dose rates (nGy h^-1) and corresponding annual effective doses (mSv y^-1). For mean activity values, the absorbed dose rates range from 57.6 to 59.6 nGy h^-1, corresponding to 0.282-0.292 mSv y^-1. A combined deterministic and Gaussian modeling approach was developed to enable rapid dose estimation and to quantify uncertainty associated with geometric variability. The agreement between both approaches is within 1%, and the corresponding geometry-related uncertainty is approximately 1%. When considering the full variability of activity concentrations, the dose rates span a wider range (∼20-110 nGy h^-1), indicating that material composition is the dominant factor controlling indoor gamma exposure, while geometrical effects remain secondary. All predicted doses remain below the recommended public exposure limits, both in terms of total dose and after background correction (excess dose). The proposed framework provides a robust and practical tool for indoor dose assessment applicable to research and regulatory use.