Natural Radioactivity Levels and Radiogenic Heat Production in River Sediments from Gulu and Amuru Districts, Northern Uganda

Abstract

The activity concentrations (AC) of ²³⁸U, ²³²Th and ⁴⁰K in sediments from Gulu and Amuru districts, Uganda were determined using NaI(Tl) detector at Physics Department, Makerere University, Kampala to obtain; radioelement concentrations (RC), radiogenic heat production (RHP) and associated heat flow (H_f). The AC varied from (36.1 ± 2.3 - 261.2 ± 15.3) for ²³⁸U, (97.4 ± 13.5 - 334.2 ± 36.6) for ²³²Th, and (47.5 ± 3.9 - 1442.3 ± 58.9) Bq kg^-1 for ⁴⁰K, with averages of 89.6 ± 6.3, 168.6 ± 17.9, and 275.4 ± 14.0 Bq kg^-1, respectively, above the world limits of 35, 30, and 400 Bq kg^-1, for ²³⁸U, ²³²Th and ⁴⁰K. The RC varied from (2.9 ± 0.2 - 20.8 ± 1.2) ppm for ²³⁸U, (23.9 ± 3.3 - 82.0 ± 9.2) ppm for ²³²Th, and (0.2 ± 0.01 - 3.2 ± 0.1) % for ⁴⁰K, with averages of 7.1 ± 0.5 ppm, 41.3 ± 4.3 ppm, and 1.1 ± 0.05%, respectively. The ²³⁸U and ²³²Th averages were above the Earth’s crust values of 3 ppm and 12 ppm, respectively. The ⁴⁰K average is below the Earth’s crust value of 2.33%.  The RHP varied from (2.5 ± 0.6 - 10.2 ± 2.6) µW m^-3 with an average of 4.5 ± 1.1 µW m^-3, above the world average of 4µW m^-3. High and moderate RHP, each account for 50% of the samples. The overall RHP mainly depended on ²³²Th amounts, with 60% contribution. However, an increase in the AC of ²³⁸U, ²³²Th and ⁴⁰K reflected the integrated effect of RHP. The H_f varied from (19.6 ± 1.0 - 80.0 ± 4.0) mW m^-2 with an average of 35.3 ± 1.8 mW m^-2. The high RHP and H_f values indicates feasibility for geothermal exploration. This calls for further studies to validate these findings.