The influence of geographic factors on the distribution of natural radionuclides

Geyser, Alwyn Petrus (2017-12)

Thesis (MMil)--Stellenbosch Univeristy, 2017.

Thesis

ENGLISH SUMMARY: The primordial radionuclides 40K, 232Th, and 238U have been present in almost all rocks, soils, and minerals since the formation of Earth. These radionuclides emit gamma radiation that is detectable by means of a scintillation detector. By measuring the concentrations of 40K, 232Th, and 238U in an area it is possible to draw radioelement maps. These radioelement maps were then used in a qualitative analysis to establish the influence of local geographic factors on the distribution of natural radionuclides. The research site is a granite outcrop, Baviaansberg, and the immediate area surrounding the outcrop. Baviaansberg is situated in the Saldanha Bay Military Area on the West Coast of South Africa. The available literature on the impact of geographic factors on the distribution of natural radionuclides are limited. Scientific radioelement mapping in military areas in South Africa has only been completed by Bezuidenhout (2012). The research provided the opportunity to study the feasibility of establishing a link between natural radionuclide concentrations and geographic factors within a military area. Hence, the aim of the research was to investigate the relationship between geographic factors and the distribution of natural radionuclides of a particular area. Radioelement maps were used to analyse the impact of the respective geographic factors “geology”, “topography”, “soil type”, “hydrology”, “wind” and “human activity” on the distribution of the concentrations of natural radionuclides. Radiation measurements of the natural radionuclides in the research site were completed by means of in situ measurements using a NaI(Tl) scintillation detector connected to a tablet computer. Once the natural radionuclide concentrations were extracted by means of Full Spectrum Analysis (FSA), radioelement maps were created from the results. Qualitative analysis was performed on the radioelement maps by means of comparing it to the slope raster, slope profiles, a flow accumulation raster, wind data, Google Earth images, a human activities map, a soil type map, Spline vs Kriging raster, Th vs K raster, U vs K raster, and a U vs Th raster. The qualitative analysis aimed to establish the influence of the identified geographic factors on the spread of natural radionuclide concentrations. The results indicated that the geology of an area influences the distribution of natural radionuclides. The highest concentrations of natural radionuclides were found close to the granite outcrops on Baviaansberg. Slope was used to determine the influence of topography. The results revealed that slope influences 40K concentrations to a greater extent than 232Th and 238U concentrations due to the solubility of 40K. The different soil types within Baviaansberg also displayed unique associated natural radionuclide concentrations. According to the research results, the hydrology of Baviaansberg impacted on the spread of 40K, 232Th and 238U concentrations. However, 40K was influenced to a greater extent because of its solubility. The impact of the dry summer winds on the distribution of natural radionuclides became apparent through a comparison of the leeward and windward slopes of Baviaansberg. On the leeward slope higher concentrations of natural radionuclides were recorded than on the windward slope due to small particles that are removed from the windward slope and deposited on the leeward slope. Research results concerning the influence of human activities on the distribution of natural radiation were inconclusive. Further research needs to be conducted in order to confirm a definite relationship, should it in fact exist. True to the aim of the research, the study established that it is feasible to validate the influence of geographic factors on the distribution of natural radionuclides by analysing the natural radionuclide concentrations of an area.

AFRIKAANS OPSOMMING: Die primordiale radioaktiewe nukliëdes 40K, 232Th, en 238U is reeds sedert die ontstaan van die aarde teenwoordig in byna alle rotse, grondtipes, en minerale. Hierdie nukliëdes straal gammastrale uit wat gemeet kan word met ‘n sintillasiedetektor. Deur die konsentrasies van 40K, 232Th, en 238U in ‘n area te meet was dit moontlik om radioelementkaarte te teken. Die radioelementkaarte is dan gebruik gedurende kwalitatiewe-analiese om die invloed van die lokale geografiese faktore op die verspreiding van die natuurlike radioaktiewe nukliëdes te bepaal. Die area geselekteer vir hierdie studie is ‘n granietkop, Baviaansberg, en die onmiddelik omliggende area van die kop. Baviaansberg is geleë in die Saldanhabaai Militêre Area aan die Weskus van Suid-Afrika. The available literature on the impact of geographic factors on the distribution of natural radionuclides are limited. Scientific radioelement mapping in military areas in South Africa has only been completed by Bezuidenhout (2012). The research provided the opportunity to study the feasibility of establishing a link between natural radionuclide concentrations and geographic factors within a military area. Die beskikbare literatuur wat die impak van geografiese faktore op die verspreiding van natuurlike radioaktiewe nukliëdes beskryf is bepark. Wetenskaplike radioelement kartering van militêre areas in Suid Afrika was nog net behartig deur Bezuidenhout (2012). Die navorsing bied die geleentheid om te bepaal of daar wel ‘n verhouding is tussen die natuurlike radioaktiewe nukliëde konsentrasies and gegrafise faktore in a militêre area. Die doel van die navorsing was om die verhouding tussen die geografiese faktore en die verspreiding van natuurlike radioaktiewe nukliëdes van ‘n area te bepaal. Radioelementkaarte is gebruik om die impak van die geografiese faktore, geologie, topografie, grondtipe, hidrologie, wind- en menslike aktiwiteite, op die verspreiding van die konsentrasies van natuurlike radioaktiewe nukliëdes te ontleed. Die stralingmetings van die natuurlike radioaktiewe nukliëdes in die studie area is gedoen via in situ-opmetings deur gebruik te maak van ‘n NaI(Tl) sintillasie detektor wat aan ‘n tabletrekenaar gekoppel was. Die konsentrasies van die natuurlike radioaktiewe nukliëdes is met behulp van Volspektrumanalise bereken, waarna radioelementkaarte ontwikkel is. Kwalitatiewe-analise is met behulp van‘n hellingsraster op die kaarte, hellingsprofiele, ‘n vloei-opeenhopingsraster, winddata, Google Earth-beelde, ‘n menslike aktiwiteitskaart, grondtipekaart, Spline- teenoor Kriging-raster, Th- teenoor K- raster, U- teenoor K-raster, en ‘n U- teenoor Th-raster onderskeidelik uitgevoer. Dit is gedoen om die invloed van die geïdentifiseerde geografiese faktore op die verspreiding van die natuurlike radioaktiewe nukliëdes te bepaal. Die resultate dui daarop dat die geologie van ‘n area die verspreiding van natuurlike radioaktiewe nukliëdes beïnvloed. Die hoogste konsentrasie van natuurlike radioaktiewe nukliëdes was naby aan die graniet-dagsome van Baviaansberg gevind. Helling is gebruik om die invloed van die topografie te bepaal. Die studie het bevind dat, as gevolg van die oplosbaarheid van 40K, helling die 40K-konsentrasies tot ‘n meerdere mate as die 232Th- en 238U- konsentrasies beïnvloed. Die verskillende grondtipes binne Baviaansberg dui ook op unieke natuurlike radioaktiewe nukliëdkonsentrasies vir elke grondtipe. Volgens die resultate dui die hidrologie van Baviaansberg daarop dat die hidrolgie van ‘n area die 40K, 232Th, en 238U konsentrasies beïnvloed. Dog, as gevolg van sy oplosbaarheid, is 40K die meeste beïnvloed. Die impak van die droeë somerwind op die verspreiding van radioaktiewe nukleïdes kom aan die lig wanneer die loefkant- en lykanthellings met mekaar vergelyk word. Die lykanthelling van Baviaansberg toon hoër konsentrasies natuurlike radioaktiwiteit as die loefkanthelling as gevolg van die verwydering van klein deeltjies aan die loefkant wat aan die lykant gedeponeer word. Resultate van die invloed van menslike faktore op die verspreiding van natuurlike radioaktiewe nukliëdes was onbeduidend. Verdere navorsing word aanbeveel om ‘n bewysbare verband aan te toon. Getrou aan die die doel van hierdie navorsing, het die studie bewys dat dit moontlik is om die invloed van geografiese faktore op die verspreiding van natuurlike radioaktiewe nukliëdes te bepaal deur die natuurlike radioaktiewe konsentrasies van ‘n area te analiseer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102923
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