Browsing by Author "Shimboyo, Simon A."

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Determination of natural radioactivity in soils of Henties Bay, Namibia
    (University of Namibia, 2015) Shimboyo, Simon A.; Oyedele, James
    The concentrations of naturally occurring radionuclides 40K, 238U and 232Th in soil samples collected across the town of Henties Bay in Western Namibia have been determined and used to estimate a baseline natural radiation level in the town. These concentrations were measured using an HPGe detector and found to vary from 790.2±31.6 Bq kg−1 to 1039.0±38.7 Bq kg−1 with a mean of 936.1±68.5 Bq kg−1 for 40K, 36.2±2.6 Bq kg−1 to 153.4±4.8 Bq kg−1 with a mean of 62.2±20.0 Bq kg−1 for 238U and 50.4±4.5 Bq kg−1 to 323.6±12.7 Bq kg−1 with a mean of 97.1±44.7 Bq kg−1 for 232Th. The corresponding effective dose rate obtained from the radionuclides is 0.16±0.04 mSv y−1. This dose rate is well below the limit of 1.0 mSv y−1 recommended for the public by the International Commission on Radiological Protection (ICRP) and indicates that the town has a normal background radiation.
  • Thumbnail Image
    Item
    Measurement of natural radioactivity and dose rate assessment of terrestrial gamma radiation in the soils of Karibib and Okahandja, Namibia
    (University of Namibia, 2019) Midzi, Wilfred; Oyedele, James; Shimboyo, Simon A.; Taapopi, Erastus E.
    The activity concentrations of the naturally occurring radionuclides 238U, 232Th and 40K in soil samples taken from the towns of Okahandja and Karibib in Namibia have been determined by gamma-ray spectroscopy using an HPGe detector. The average activity concentrations of 238U, 232Th and 40K in Karibib are 29.4±5.8Bq/kg, 49.0±8.6Bq/kg, and 824.3±153.5Bq/kg while they are 40.9±8.6Bq/kg, 57.9±19.4Bq/kg, and 562.4±125.4Bq/kg respectively in Okahandja. Most of these values are much higher than the corresponding worldwide average values. These activity concentrations were used to calculate different radiological parameters in order to evaluate the associated health hazard. The value of 9.5×10−2 mSv/y obtained for the mean effective dose rate in both towns is far below the permissible limit of 1.0mSv/y recommended by the ICRP and implies that there is no significant radiation hazard in the towns. Also, the values of 163.0Bq/kg and 167.1Bq/kg obtained for the average radium equivalent activity (Raeq) in the towns and the corresponding values obtained for the average external hazard index (Hex) are much below their maximum permissible limits thus confirming that radiological hazard is negligible in the towns.
  • Thumbnail Image
    Item
    Natural radioactivity in soils of the Walvis Bay - Henties Bay coastal area, Namibia
    (2013) Shimboyo, Simon A.
    Naturally occurring radionuclides such as 238U, 232Th and 40K are present in the soil where they disintegrate spontaneously releasing ionizing radiation which could pose health hazards to the inhabitants of a given location especially when the concentrations of the radionuclides are high. In Namibia, the Walvis Bay – Henties Bay coastal area is known to have many mineral resources including uranium and therefore the concentrations of the radionuclides in the soils and the associated radioactivity may be high in some towns in the area. It is therefore important to study the concentrations of radionuclides and the radioactivity in the soils of the major towns in the area. In this study, the concentrations of the radionuclides 238U, 232Th and 40K and their progeny, and their contribution to natural radioactivity in the soils of six major towns in the Walvis Bay – Henties Bay coastal area have been determined. These towns are Usakos, Arandis, Swakopmund, Walvis Bay, Wlotzkasbaken and Henties Bay. A total of 305 soil samples were collected across the six towns and dried under laboratory temperature for 72 hours. These samples were pulverised and passed through a 2 mm mesh screen and sealed in 500 ml polythene bottles. The specific activities of the radionuclides 238U, 232Th and 40K in the samples were subsequently analysed using a well-shielded high-purity germanium (HPGe) detector. The average concentration for 238U varies from a minimum of 14.5 ± 2.5 Bq kg-1 in Walvis Bay to a maximum of 104.1 ± 28.1 Bq kg-1 in Wlotzkasbaken, with a mean of 52.6 ± 24.5 Bq kg-1 for the six towns. Also, the average concentration for 232Th varies from a minimum of 18.0 ± 3.0 Bq kg-1 in Walvis Bay to a maximum of 334.4 ± 86.9 Bq kg-1 in Arandis, with a mean of 104.3 ± 85.9 Bq kg-1 while the average concentration for 40K varies from a minimum of 363.3 ± 41.3 Bq kg-1 in Walvis Bay to a maximum of 1336.5 ± 142.0 Bq kg-1 in Usakos, with a mean of 778.7 ± 204.6 Bq kg-1 for the six towns. These values were used to calculate the mean absorbed dose rate and the annual effective dose. The average annual effective dose varies from a minimum of 0.04 ± 0.01 mSv in Walvis Bay to a maximum of 0.35 ± 0.07 mSv in Arandis, with a mean of 0.15 ± 0.08 mSv for the six towns. These values are lower than the maximum permissible limit of 1.0 mSv recommended by the International Commission on Radiological Protection (ICRP) for the public so that the towns do not have high natural radioactivity.
  • Thumbnail Image
    Item
    Soil radioactivity levels and associated hazards in selected towns in uranium-rich western Namibia
    (University of Namibia, 2016) Shimboyo, Simon A.; Oyedele, James; Sitoka, S.S.
    Soil samples from three major towns and a holiday settlement in uranium-rich western Namibia have been analysed using a HPGe detector for radioactivity due to 238U, 232Th and 40K. The average activity concentrations of the radionuclides in the towns and settlement vary from a low of 18.6 ± 4.6 to a high of 69.6 ± 26.3 Bq kg−1 for 238U, 23.8 ± 8.4 to 91.1 ± 41.0 Bq kg−1 for 232Th and 460.3 ± 76.2 to 959.5 ± 194.7 Bq kg−1 for 40K. In order to evaluate the associated health hazard, the concentrations were used to calculate the mean annual effective dose, radium equivalent activity (Raeq) and external hazard index (Hex) for the towns and settlement. The values of 0.11 mSv, 195.3 Bq kg−1 and 0.53 obtained respectively for the mean annual effective dose, Raeq and Hex are, however, below their permissible limits thus implying that radiation hazard is negligible.