Determination of natural radioactivity levels of ²³⁸U, ²³²TH and ⁴⁰K in rocks around Gondar city, Northwest Ethiopia

The aim of the present work was to assess the terrestrial radionuclides distribution and their radiological health related risks in rocks around Gondar city using NaI (Tl) detector gamma-ray spectrometry. The samples were dried, pulverized, homogenized and then on average 300g from each rocks were packed in polyethylene containers. The polyethylene containers were tightly sealed for 4 weeks until the parent radionuclides ²³⁸U, ²³²TH and their daughter products in the rock samples attained in secular equilibrium. Based on the characteristic spectral peaks produced by daughter nuclides of ²⁰⁸Tl (in ²³⁸U series) at 2614.4kev, 214Bi (in ²³²Th) at 1764.4kev and the singly decaying 40K at 1460.8kev, the activity concentrations were determined for 226Ra (238U) from 18.06 ± 5.59 BqKg⁻¹ to 27.05 ± 4.60 BqKg⁻¹ with an average value of 21.36 BqKg⁻¹; for ²³²Th from 54.57 ± 1.42 BqKg⁻¹ to 106.32 ± 1.65 BqKg⁻¹ with mean activity 59.60 ± 2.34 BqKg⁻¹ and for 40K from 152.68 ± 14.10 BqKg⁻¹ to 873.01 ± 13.08 BqKg⁻¹. The calculated absorbed dose rate and the annual effective dose rates were varied from 49.98±1.99 to 102.26±2.84 and from 0.061 to 0.126 μSvy⁻¹ respectively. The result of the finding showed that the activity concentration, radium equivalent activity, absorbed dose rate, annual effective equivalent dose, and external and internal hazard indices of the rocks were obtained below the world recommended values. However, higher activity concentrations of ²³²Th and ⁴⁰K above the world range and mean values were absorbed in rock areas of Dabecha Rufauel and Gondar air port.