An investigation of the Radioecology of the Carbonatite deposits in the Homa Mountain region in South Nyanza, Kenya


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The level of radiation due to the naturally occurring radioactive materials was investigated and the radiological hazard was calculated for Homa Mountain located at the intersection of longitude 330 26' E and 340 34; E latitude 00 30' N and 00 20'N in southwestern Kenya. The absorbed dose rate in air at 1 meter above the ground was measured using calibrated hand held survey meters that could be coupled to sodium iodide (NaI) radiation detector. The measured mean dose rate of 474.1 nSv h-I translated to annual dose due to external radioactivity of 4.15 mSv y-I. The radioactivity concentrations of 40K, 226Ra and 232Th in rock and soil samples were measured using gamma ray spectroscopy from two different institutions for comparison purposes of accuracy and precision. The cumulative mean activity concentrations obtained were 915.6, 195.3 and 409.5 Bq kg-I of 40K, 226Ra and 232Th, respectively. The calculated mean absorbed dose rate was 383.33 nGy h-I; the radium equivalent activity mean was 838.6 Bq kg+; the representative level index mean value was 5.93; the gamma activity index mean value was 2.96; the external hazard index mean was 2.26 and the internal hazard index mean was 2.77. It was observed that the pattern of high values of the radiological indices follows that of the corresponding activity concentrations. These indices are important parameters for the radiological protection of the population since soils are used for making earthen huts and pottery while bricks and rocks for building human habitations. The resultant total effective dose (TED) equivalent was 5.03 mSv Y' 1. Using RESRAD software program, the impact of these naturally occurring radioactive materials on the environment was evaluated for different age sets of the population and the results showed that infants and teenagers receive more effective doses than other segments of the populations. The RESRAD code enabled modeling of 40K, 232Th and 238U environmental pathways. This led to exposure pathways of external radiation, inhalation and ingestion resulting in total effective dose equivalent to exposed individuals estimated as 4.93 mSv y-I. The excellent correlation of similar TED derived from the different measurements and modeling methodologies increased the certainty of the conclusions arrived at for the work done. The Homa Mountain study has established data on radiation dose to the population and qualifies the region as a high background radiation area due to dominance of carbonatite rocks. Investigations of the health hazards of radiation and the impacts of high levels of background radiation on the local inhabitants can be done in future epidemiological studies. The exploration of the possible economic benefits that can be derived from the minerals associated with carbonatite deposits, Rare Earth Elements and Thorium is open for consideration.

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