Natural radioactivity levels and evaluation of radiological hazards in Usakos marble, Erongo region, Namibia

Background : Most parts of the Erongo region of Namibia have shown high background radiation. The aim and objective of this study is to determine the natural radioactivity levels and evaluate the radiological hazards in Usakos marble dome in the Erongo region. Materials and Methods : A high purity germanium (HPGe) detector was used in this study to measure the activity concentrations 226 Ra, 232 Th, and 40 K in marble samples from 20 different points in Usakos marble dome in the Erongo region, Namibia. Result : The mean activity concentrations were found in the range of 0.37 to 339.60 Bq kg - 1 for 226 Ra, 0.20 to 210.30 Bq kg - 1 for 232 Th, and 2.96 to 928.70 Bq kg - 1 for 40 K, respectively. The activity concentrations of 226 Ra, 232 Th, and 40 K were used to estimate values of radium equivalent activity (Ra eq ), Absorbed dose rate (Dr), internal and external hazard indices (H ex & H in ) and the activity utilization index (I γ ). The calculated mean values were Ra eq (226.75 Bq kg - 1 ), (Dr) (102.99 nGyh - 1 ), H ex (0.61), H in (0.95) and I γ (1.59). Conclusion : From a radiological point, the results of (Dr) and (I γ ) were found above the world recommended average and the performed correlation analysis showed strong positive correlation amongst 232 Th and 226 Ra, which confirms these radionuclides as the main contributors to gamma radiation in the Usakos marble dome. The high activity concentrations at some sampling points higher than the world average value pose possible radiological hazards for the marble samples usage for building materials.