An overview of background radiation level and spatial distribution of NORM in Bangladesh

This study presents the first comprehensive spatial analysis of activity concentrations of naturally occurring radioactive material (NORM) and absorbed dose rates across Bangladesh. Utilising a database compiled from 56 published studies and 40 unpublished theses (1990-present), environmental sample data were mapped onto a systematic grid system comprising 2094 cells (8.05 km × 8.05 km) from which measured and unmeasured locations were revealed across the country. Ordinary Kriging interpolation was applied to visualize nationwide distributions. The analysis revealed significant spatial heterogeneity primarily driven by differences in geology, rock structures, and soil types. Activity concentrations of Ra-226, Th-232, and K-40 ranged from 0.01 to 647.5 Bq kg^-1, 0.2-1230.0 Bq kg^-1, and 0.04-2352.0 Bq kg^-1, respectively. Consequently, the absorbed dose rates varied widely from 0.02 to 745.86 nGy h^-1, yielding a national average of 64.16 nGy h^-1. Furthermore, the gridded mapping exposed severe sampling imbalances: while some localized regions were measured up to 13 times, vast areas remain entirely unsampled. By establishing this pre-operational national baseline, this study successfully distinguishes natural background levels from potential technologically enhanced NORM. The findings provide a critical reference for ongoing environmental monitoring particularly to assess radiation levels around the soon-to-be-operational Rooppur nuclear power plant and offer a strategic framework to guide future targeted sampling in unmeasured regions.