Evaluation of natural radioactivity and radiological hazards in concrete aggregates for radiation shielding applications

This study assessed the natural radioactivity and associated radiological hazards in selected concrete aggregates barite, magnetite, hematite, river sand, and Dangote cement intended for radiation shielding applications. The activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K were measured using a NaI (Tl) gamma-ray spectrometer at the Centre for Energy Research and Training, Ahmadu Bello University, Zaria. The corresponding radiological hazard indices were subsequently evaluated using standard models. The mean activity concentrations ranged from 15.8 ± 0.3 to 217.5 ± 2.8 Bq kg⁻¹ for ²²⁶Ra, 27.2 ± 4.5 to 101.4 ± 1.0 Bq kg⁻¹ for ²³²Th, and 46.9 ± 0.4 to 334.5 ± 6.6 Bq kg⁻¹ for ⁴⁰K. The highest ²²⁶Ra and ²³²Th activities were recorded in magnetite (217.5 ± 2.8 Bq kg⁻¹ and 101.4 ± 1.0 Bq kg⁻¹, respectively), while the maximum ⁴⁰K concentration (334.5 ± 6.6 Bq kg⁻¹) occurred in river sand. These values generally fall within or below global averages of 32 Bqkg^{- 1}, 45 Bqkg^{- 1}, and 412 Bqkg^{- 1} set by UNSCAER except for magnetite, which exhibited elevated ²²⁶Ra and ²³²Th levels. The calculated radium equivalent activity (Ra_eq) varied from 92.45 ± 21.19 Bq kg⁻¹ (cement) to 366.11 ± 2.19 Bq kg⁻¹ (magnetite), remaining below the recommended limit of 370 Bq kg⁻¹. The absorbed dose rates ranged from 40.21 ± 4.06 to 163.69 ± 0.43 nGy h⁻¹, mostly within the global range (20-200 nGy h⁻¹). The annual effective dose values were below the ICRP recommended limit of 1 mSv y⁻¹ for all materials except magnetite. The gamma activity index (Iγ) ranged between 0.5 and 1 for most samples, with magnetite slightly exceeding the upper limit (1.25 ± 0.01), indicating potential radiological concern for indoor use. Both external (Hₑₓ) and internal (H_iₙ) hazard indices were below unity for all samples except magnetite. Overall, the results confirm that cement, river sand, hematite, and barite are radiologically safe for construction applications, while magnetite requires cautious use in indoor environments due to its elevated natural radioactivity.