Risk Assessment Due to Naturally Occurring Radioactive Materials in Kilimambogo, Kenya

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dc.contributor.advisorNadir Hashimen_US
dc.contributor.advisorMargaret Chegeen_US
dc.contributor.advisorShinji Tokanamien_US
dc.contributor.authorNyambura, Catherine
dc.date.accessioned2024-02-05T11:44:17Z
dc.date.available2024-02-05T11:44:17Z
dc.date.issued2023-12
dc.descriptionThesis Submitted in Fulfillment of the Requirements for the Award of the Degree of Doctor of Philosophy in Physics in the School of Pure and Applied Sciences of Kenyatta Universityen_US
dc.description.abstractABSTRACT Man is continually exposed to ionizing radiation whose main origin is either natural or artificial. The primordial radionuclides found in building materials are important sources of radon and thoron in the indoor air. The main objective of this research was to assess exposure due to radioactive elements in indoor air, crops and building materials (soil and rocks), and determine the level of the risks. The concentration levels of radon, thoron, and thoron progeny were measured in mud-walled, iron sheet walled, and stone walled modern houses in Kilimambogo region, Kenya. Radon and thoron concentration levels were determined using passive radon–thoron discriminative monitors (RADUET), while thoron progeny levels were measured using thoron progeny monitors. The activity concentration of 226Ra, 232Th and 40K present in the different environmental samples like rocks, soil, and cassava crop were determined using a Thallium- activated sodium-iodide scintillation (NaI (TI)) detector Model TS-2L. Elemental concentration in water samples was determined using an atomic absorption spectrophotometer (AAS). The mean external dose received indoors by the residents due to radionuclides present in rock and soil samples was measured to be 0.91 ± 0.26 mSv y-1 and 0.86 ± 0.19 mSv y-1 respectively. This is comparable to the total exposure dose limit of 1 mSv y-1 recommended by ICRP for members of the general public. This means that, soil and rocks in the region does not pose any radiological risk to the residents of Kilimambogo region. Consequently, they can be used for agriculture and construction of dwellings. The doses received due to intake of cassava tubers and leaves was 1.82 ± 0.60 mSv y-1 and 0.81± 0.30 mSv y-1 respectively, totaling to 2.63 ± 0.70 mSv y-1. The ingestion dose contributes to 42.1% of the total dose received by the resident from measured sources. Residents should therefore reduce the intake of cassava. The annual effective dose received by the residents of Kilimambogo and Gatuanyaga regions due to inhalation of radon and thoron was determined for the three types of dwellings, from their respective progenies and found to be 1.3 ± 0.2 mSv y-1, 1.1 ± 0.1 mSv y-1 and 1.4 ± 0.2 mSv y-1 for radon progeny and 2.4 ± 0.4 mSv y-1, 0.5 ± 0.1 mSv y-1 and 1.5 ± 0.2 mSv y-1 for thoron progeny in mud-walled, iron sheet-walled and stone-walled houses respectively. It was observed that, residents living in iron sheet - walled houses with cemented floors received the lowest doses from inhalation of the radon isotopes hence such houses are safer than other types of dwellings. Residents living in mud houses and uncemented houses should consider improving the ventilation of their houses to reduce radiation exposure. The lifetime cancer risks for the residents due to intake of metal carcinogens, Cd, Ni and Pb in borehole and surface water was also estimated. The cumulative cancer risk in the borehole samples was 0.12 ± 0.06 and 0.19 ± 0.09 in the dry and wet seasons respectively. Those from surface water sources were 0.10 ± 0.07 and 0.21 ± 0.06 in the dry and wet seasons respectively. In both seasons, the cancer risks were much greater than the acceptable risks of 10-6 to 10-4 by a factor of 1000 and above. This indicates that about 10% of the residents are likely to die of cancer related ailments. RESRAD computer simulation code was used to estimate the doses received by the resident farmer and the quarry worker scenarios at time, t = 0 years. The doses received by the resident farmer and quarry worker scenarios were 0.22 mSv y-1 and 0.16 mSv y-1 respectively only for the external radiation pathway. This risk is low and does not pose any significant health risk to the residents. The data measured in this research will be used by future researchers as baseline study.en_US
dc.description.sponsorshipKenyatta Universityen_US
dc.identifier.urihttps://ir-library.ku.ac.ke/handle/123456789/27522
dc.language.isoenen_US
dc.publisherKenyatta Universityen_US
dc.subjectRisk Assessmenten_US
dc.subjectNaturally Occurring Radioactive Materialsen_US
dc.subjectRadioactive materialsen_US
dc.subjectRisken_US
dc.titleRisk Assessment Due to Naturally Occurring Radioactive Materials in Kilimambogo, Kenyaen_US
dc.typeThesisen_US
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