2026-09-22T02:18:08Zhttps://repository.unam.edu.na/server/oai/requestoai:repository.unam.edu.na:11070/37962024-03-16T22:00:19Zcom_11070_3408com_11070_3311com_11070_3304col_11070_642
Kapofi, Naeman Tuyoleni
2024-03-11T10:30:06Z
2024-03-11T10:30:06Z
2020
http://hdl.handle.net/11070/3796
A mini-thesis submitted in partial fulfilment of the requirements for the degree of master of science in nuclear science
The natural radioactivity and associated hazards in soil samples collected from the
town of Otjiwarongo, Namibia, have been studied by gamma ray spectroscopy. The
town was divided into ten geographical areas and five soil samples were collected
across each area. The samples were dried, homogenized and 500 g of each sample was
placed in a clearly-labelled 500 mL polythene bottle and sealed for four weeks. HPGe
detector was subsequently used to obtain gamma ray spectra of the samples. The
intensities of selected gamma lines were used to determine the activity concentrations
of the primordial radionuclides 238U, 232Th, and 40K in the soil samples. The mean
activity concentrations of the radionuclides in the ten geographical areas vary from
37.6 ± 7.4 to a high of 97.8 ± 46.2 Bq/kg for 238U, from 81.9 ± 16.7 to a very high of
852.8 ± 533.0 Bq/kg for 232Th and from 498.7 ± 55.7 to 807.1 ± 94.5 Bq/kg for 40K.
All these mean activity concentrations are higher than the corresponding world-wide
average values of 33.0 Bq/kg, 45.0 Bq/ kg and 420.0 Bq/kg for 238U, 232Th and 40K
respectively, according to United Nations Scientific Committee on the Effects of
Atomic Radiation (UNSCEAR) 2000 report. Furthermore, the mean activity
concentrations of some of the radionuclides in some areas are more than double those
of the other areas thus indicating that the distribution of radionuclides in the soil of the
town is not uniform. In order to assess the hazards associated with the radionuclides,
different radiation hazard parameters such as absorbed dose rate, effective dose rate,
radium equivalent activity (Raeq), and external radiation hazard index (Hex), were
calculated from the activity concentrations of the radionuclides.
The mean absorbed dose rates in the ten areas vary from 90.0 ± 13.7 to 593.9 ± 347.2
nGy h-1
and are all higher than the world average value of 60.0 nGy h-1
. However, the
ii
corresponding mean effective dose rates vary from 0.11 ± 0.01 to 0.73 ± 0.43 mSv/y
which are all below the maximum permissible limit of 1 mSv/y, according to the
International Commission on Radiological Protection (ICRP) reference level for
public exposure control. Furthermore, the mean effective dose rates in seven of the
areas are relatively low and below 0.2 mSv/y while those in the other three areas are
relatively high and above 0.2 mSv/y. These results indicate that the level of radiation
varies across the town and it is low in seven geographical areas but higher in three
areas. The mean values of the radium equivalent activity in the ten areas vary from
197.9 ± 31.5 to a very high value of 1379.5 ± 815.7 Bq/kg. Again, the mean Raeq in
the seven geographical areas are low and below the maximum permissible limit of 370
Bq/kg while they are high and above the permissible limit in the other three areas.
Similarly, the mean values of Hex in the seven geographical areas are below the
maximum permissible limit of unity but they are above the permissible limit in the
other three areas. These results confirm that the level of ionizing radiation in most
areas of Otjiwarongo is well-below the maximum permissible limit while the level in
three other areas of the town is high and the hazard indices are above the maximum
permissible limit
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University of Namibia
Natural radioactivity
Soil samples
Otjiwarongo
Namibia
Gamma ray spectroscopy
Radiation hazard assessment
Radionuclide concentrations
Radionuclide concentrations and radiation hazard assessment in the soil of Otjiwarongo, Namibia
Thesisopen.access