Contribution of building materials to indoor external exposure: Development of a novel comprehensive evaluation tool and results

• Indoor effective dose by gamma radiation is regulated by European Commission • Standardized dose assessment approaches are based on simplifying assumptions • A novel tool was developed to evaluate the indoor effective dose • The tool allows site-specific evaluations including wall density and thickness • The tool provides more accurate and always conservative dose assessment This study presents a novel computational tool developed to evaluate the indoor effective dose from external exposure to gamma radiation emitted by building materials. For maximum user accessibility, the computational results are integrated into a data processing spreadsheet, allowing for near-instantaneous evaluations on basic devices. The tool was extensively validated and offers two primary advantages over existing standardized approaches: significantly higher accuracy obtained by removing simplifying assumptions currently adopted and a broader application range regarding building material density, wall thickness, and room dimensions. The indoor effective dose evaluations performed by the tool demonstrate that some of the assumptions currently adopted by the international regulations and standards are non-conservative. Specifically, results show that indoor effective dose does not saturate at a wall thickness of 20 cm as commonly assumed (e.g., CEN/TR 17113), but increases by 13% when it is extended to 50 cm. Furthermore, the findings reveal that larger rooms lead to higher effective dose estimations, contradicting assumptions inherent in the standard computational approach. While not intended to replace existing regulatory frameworks, the software developed serves as an open-access tool for a more accessible and reliable implementation of the graded approach in radiation protection relative to existing exposure scenarios indoors. By providing more accurate assessments, it facilitates the safe use of building materials that might be deemed unsuitable under conventional screening. This methodology fills the gap between basic screening indices and resource-intensive simulations (by deterministic and Monte Carlo codes), offering a valuable resource for optimized exposure management.