Assessment of natural radioactivity in the soils of the Ohorongo Cement plant and the town of Otavi, Namibia
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Date
2020
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Publisher
University of Namibia
Abstract
The activity concentrations of the naturally occurring radionuclides 238U, 232Th, and
40K in soil samples collected from the Ohorongo Cement plant and the town of Otavi,
Namibia have been determined using a High-Purity Germanium (HPGe) detector. In
addition, an assessment of the radiological hazards due to these natural radionuclides
in the soils of the plant and town was carried out. The plant was divided into three
geographical areas, and fifty soil samples were collected across the areas. Also, the
town of Otavi was divided into ten geographical areas, and fifty soil samples were
collected across the areas. These soil samples were processed and 500 g of each sample was placed in a well-labelled 500 ml polythene bottle and analyzed using an HPGe detector. The average activity concentrations of the radionuclides 238U, 232Th, and 40K in the soil samples from the Ohorongo Cement plant were 15.0 ± 4.7 Bq/kg, 25.1 ± 9.9 Bq/kg, and 310.7 ± 97.2 Bq/kg respectively. Similarly, the average activity concentrations of the radionuclides in the soil samples from Otavi were 21.6 ± 7.2 Bq/kg for 238U, 20.3 ± 8.5 Bq/kg for 232Th, and 256.4 ± 113.7 Bq/kg for 40K. The average activity concentrations of 232Th and 40K were found to be higher in the Ohorongo Cement plant than in Otavi. In contrast, the average activity concentration of 238U was higher in Otavi than in the Cement plant. These concentrations were used to calculate the absorbed dose rates and the effective dose rates in air across the different geographical areas in the plant and town. The values of (4.3 ± 1.5) × 10−2 mSv/y and (4.0 ±1.5) × 10−2 mSv/y obtained respectively for the mean effective dose rates in the Cement plant and town are both less than the maximum permissible effective dose rate of 1.0 mSv/y recommended for the public by the International Commission on Radiological Protection. In order to evaluate the associated health hazard, the concentrations were also used to calculate the mean Radium equivalent activity (Raeq) and the mean external hazard index (Hex) for the plant and for the town. The values obtained for Raeq in the Cement plant and town were 74.9 ± 25.6 Bq/kg and 70.4 ± 26.7 Bq/kg, respectively. These values are below the maximum permissible limit of 370 Bq/kg. Furthermore, the values of 0.20 and 0.19 obtained respectively for Hex in the Cement plant and town are again below the maximum permissible limit of 1.0. It is therefore concluded that radiation hazards are negligible in the plant and town and hence the plant and town have normal background radiation. The data generated in this study will contribute to the baseline data on radiological hazards in Namibia.
Description
A mini thesis submitted in partial fulfilment of the requirements for the Degree of Master of Science in Nuclear Science
Keywords
Radioactivity, Ohorongo Cement