Radionuclide analysis of soil samples taken from Outjo, Namibia
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Date
2019
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Publisher
University of Namibia
Abstract
Naturally occurring radionuclides such as Uranium (238U), Thorium (232Th) and
Potassium (40K), exist in the soil where they continuously disintegrate and emit
ionising radiation which could pose health hazards to the inhabitants of a given
location if the concentrations of the radionuclides are very high. In this work, the
concentrations of the radionuclides 238U, 232Th and 40K in the soil samples taken from Outjo have been studied by gamma spectrometry. The town of Outjo was divided into ten geographical areas and five samples were collected across each area. These samples were dried under laboratory temperature, passed through a 2 mm mesh screen and sealed in 500 ml polythene bottles. The samples were analysed using a liquid nitrogen cooled High Purity Germanium (HPGe) detector (by Canberra). The Python Code was used to calculate the activity concentrations of- and Hazard indices due tothe radionuclides 238U, 232Th and 40K from the intensities of the gamma lines emitted. The results obtained show that the concentrations of radionuclides in the soils of the town of Outjo vary from 11. 7 ± 1.6 to 29. 8 ± 2.0 Bq kg-1 with an average of 20.5 ± 3.5 Bq kg-1 for 238U, 15.2 ± 1.8 to 58.3 ± 4.2 Bq kg-1 with an average of 31.4 ± 8.9 Bq kg-1 for 232Th and 206.2 ± 12.9 to 819.6 ± 31.9 Bq kg-1 with an average of 350.6 ± 124.6 Bq kg-1 for 40K. The average concentrations for 238U and 40K are lower than the worldwide averages of 35.0 Bq kg-1 and 400.0 Bq kg-1 respectively. In contrast, the average concentration for 232Th is slightly higher than the worldwide average of 30.0Bq kg-1.
The average outdoor air absorbed dose rate due to terrestrial gamma rays at 1m abovethe ground was found to be 43.0 ± 10.6 nGyh-1 which is below the worldwide averagevalue of 58.0 nGyh-1. Also, the corresponding average effective dose was found to be0.05 ± 0.01 mSvy-1 which is below the maximum permissible limit of 1.0 mSvy-1. These results imply that the background radiation in the town is not high. The average
values of Raeq and Hex are 92.4 ± 22.5 Bq kg-1 and 0.25 ± 0.06 which are below the
recommended maximum limit of 370.0 Bq kg-1 and 1 respectively. Furthermore, the
average values obtained for the other hazard parameters are all below the
recommended maximum values, thus confirming that the town have normal
background radiation so that radiation hazard is negligible in the town. All the results
obtained in this study will contribute to the national baseline data of activity
concentrations of radionuclides in the soils of Namibia.
Description
A mini theses submitted in partial fulfilment of the requirements for the degree of Master of Science (Nuclear Science)
Keywords
Soils of Namibia, Radionuclides