Gamma Ray Spectrometry of Phonolite–Kenyte Sequence of Volcanic Sediments from the Selected Areas in Nyeri County, Kenya
Ndichu, Tirus Njuguna
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NORM is the major contributor of human exposure to radiations. Health hazard risks emanating from this exposure are lives threatening and they include ailments such as cancer, eye lens opacity, tumors and fibroids. A good proportion of these materials were buried deep inside the earth crust during the earth formation about 4.543 billion years ago. Some of these NORM have found their way to the surface of the earth either through natural processes such as volcanicity, faulting and erosion or through anthropogenic activities such as mining and construction of dams and roads. In Nyeri County on the slopes of Mount Kenya, scanty information is available on health risk levels from Mountains volcanic sediments. In this work, radiological survey and assessment was done on 22 samples of phonolites- kenytes sequence of volcanic sediments from five locations mostly in Nyeri County. These samples were sun and oven dried, pulverized and analyzed using a high energy resolution gamma- ray spectrometry. Standard certified samples from IAEA were used for energy calibrations and calculation of efficiency of the spectrum. The investigations carried out revealed that the samples collected had in average safe levels of radioactivity. The range for activity concentration for the samples collected was found to be (465±36 1385±92) BqKg 1for 40K, (77± 180±4.) BqKg 1 for 232Th and (60±2 199±5) BqKg 1 for 238U. From these results it is evident that potassium recorded the highest activity concentration compared to other radionuclides. The internal hazard and external hazard indices of the samples analysed were found to be within the internationally accepted upper limit of a unity. The annual environmental effective dose rate ranged from (0.38±0.02 0.77±0.03) mSvy 1 with a mean of 0.60±0.03mSvy 1. The obtained average value of radium equivalent activities for the samples collected was 367±9 Bqkg 1. The average value of Raeq is slightly below the acceptable maximum safe value of 370Bq/kg. The conclusion of this study showed that the volcanic sediments pose no significant radiation hazards to the people living in Nyeri County on the slopes of Mount Kenya.