Radionuclide concentrations and radiation hazard assessment in the soil of Otjiwarongo, Namibia

Abstract

The natural radioactivity and associated hazards in soil samples collected from ten geographical areas in the town of Otjiwarongo, Namibia, have been studied by gamma-ray spectroscopy with an HPGe detector. The mean activity concentrations of the primordial radionuclides ²³ᴽU, and ²³²Th,  ⁴⁰K in the ten areas was found to vary from 37.6 ± 7.4 Bq/kg to 97.8 ± 46.2 Bq/kg for ²³ᴽU, from 81.9 ± 16.7 Bq/kg to 852.8 ± 533.0 Bq/kg for ²³²Th and from 498.7 ± 55.7 Bq/kg to 807.1 ± 94.5 Bq/kg for 40K. Most of these mean activity concentrations, especially those of ²³²Th, are much higher than the corresponding worldwide average values. In order to evaluate the associated health hazard, the activity concentrations were used to calculate different radiological parameters. The values obtained for the mean radium equivalent activity (ᴿᵃₑq) in some areas are above the maximum permissible limit. Also, the values obtained for the mean external hazard index (Hₑᵪ) in some areas are above the corresponding maximum permissible limit. However, the mean effective dose rates in the ten areas vary from 0.11 ± 0.01мSν y−¹ to 0.73 ± 0.43мSν y−¹ which are all below the maximum permissible limit of 1.0 mSv y−1 . These results imply that radiation hazard is negligible in the town of Otjiwarongo