Georadiological Assessment and Radiological Hazard Mapping of Uranium-Enriched Formations in El Sheikh Soliman Area, Southwestern Sinai, Egypt

Abstract

High-resolution georadiological assessment of 66 stratigraphically and lithologically varied rock samples from El Sheikh Soliman region (selected as the area of ground magnetic survey) was performed using gamma-ray spectrometry and multivariate statistical tools. The concentrations and distribution of natural radionuclides ²³⁸U, ²³⁸Ra, ²³²Th, and ⁴⁰K were measured, and the associated radiological hazards were evaluated. The activity levels of ²³⁸U ranged from 45.1 to 1073.2 Bq/kg (mean = 316.4 Bq/kg), with peak values in ferruginous siltstones (Um Bogma formation), organic-rich shales (Adedia formation), and micaceous shales (Abu Hamata formation). Over 70% of samples exhibited uranium-series disequilibrium (U/Ra >1.5), suggesting recent uranium remobilization under oxidizing-suboxic conditions. Radiological indices such as radium equivalent activity (Ra_eq), absorbed dose rate (D_r), and annual effective dose equivalent (AEDE) indicated that 36% of samples exceeded the Ra_eq safety limit of 370 Bq/kg, and 41% surpassed the global AEDE average (0.07 mSv/year), with strong correlations (r > 0.85) between ²³⁸U and hazard indicators. Although ²³²Th concentrations were lower (22.4–186.1 Bq/kg), significant contributions were found in felsic and metavolcanic rocks due to accessory minerals like monazite and zircon. The ⁴⁰K levels (54.3–1420.5 Bq/kg) were higher in granitic and clay-rich samples containing K-feldspar and muscovite. While ²³²Th and ⁴⁰K posed lower direct risks, their cumulative effects influenced Ra_eq and H_ex indices. Principal component analysis explained 87.3% of total variance, with uranium being the dominant factor. Hierarchical cluster analysis revealed four geochemically distinct groups, reflecting variations in lithology, mineralogy, and redox behavior. The study highlights the value of integrating radiometric and statistical data for effective radiological hazard mapping and environmental monitoring in uranium-rich arid zones.