Twenty (20) different local and imported tiles were sampled from major hardware's in Bungoma. The samples collected were separately ground, sieved, through a 0.5mm mesh, dried at 110° C, weight and packed in a 200ml stoppered plastic bottles. The samples were stamped with identification numbers and kept for 30 days for secular equilibrium to be reached between the activity of 238 U, 232 Th , 40 K radium and their progeny. The average activity concentration of 238 U, 232 Th and 40 K was found to be 109±5.48Bqkg -1 , 11±0.55 Bqkg -1 and 1574±78.7 Bqkg -1 respectively. The average absorbed dose rate was found to be 140±7.03 nGyh -1 which is higher than the worlds average value of 60 nGyh -1 . The average radium equivalent was found to be 288±14.44 Bqkg -1 which is lower than the world limit value of 370Bqkg -1 . External and internal hazard indices were found to be 0.70±0.03 msvy -1 and 0.80±0.04 msvy -1 respectively. Therefore, the sampled tiles used in Bungoma county for construction has minimal radiological threat to population.
Samples of sand were collected along the course of ten selected rivers two from each river through random sampling. Activity concentration of 238 U, 232 Th and 40 K were measured using high resolution NaI(Ti) gamma ray spectrometer. Activity concentration of the three primordial radionuclides obtained were used to calculate, absorbed dose rate, annual effective dose rate, interna and external hazard indices and radium equivalent. The average activity concentration for the three primordial radioactive nuclides were; 2±0.1Bq/kg with a range of 0± 0.03Bq/kg to 4±0.24Bq/kg for 238 U, 55±2.78Bq/kg with a minimum value of 32±1.6Bq/kg and a maximum value of 87±4.38Bq/kg for 232 Th and 51±2,56Bq/kg with a minimum value of 27±1.37Bq/kg and a maximum value of 76±3.8Bq/kg for 40 K. The mean activity concentrations for 238 U and 40 K were below the world averages of 33Bq/kg and 420Bq/kg respectively. The indoor and outdoor annual effective dose rate varied from 0±0mSv/y to 0.2±0.01mSv/y with an average of 0.1±0 mSv/y and 0±0.003mSv/y to 0.1±0.009mSv/y with a mean of 0.1±0.006 mSv/y respectively. The annual effective dose rates were below the safe limits of 1mSv/y. Therefore, use of sand from the selected rivers in Bungoma County, Kenya for construction has minimal health risks to the inhabitants.
A radiological risk assessment of 238 U, 232 Th and 40 K in the top soils of Ahero paddy fields of Kisumu County has been measured using NaI(TI) gamma ray spectroscopy. A total of 17 samples were collected at a depth of 15 -20 cm and measured for activity concentrations of three radionuclides which were used to calculate the absorbed dose rates and Annual effective dose rates of the samples. Samples were collected from fields at various stages of farming process i.e., four (4) weeks after transplanting (field 1), during transplanting (field 2), after harvesting and land ploughed (field 3) and a control field (field 4) where rice farming had not been done for 2 years. The average activity concentrations for the three radionuclides for field 1 were 32.63 ± 1.63 Bq/kg for 238 U, 104.69 ± 5.20 Bq/kg for 232 Th and 75.00 ± 3.2 6 Bq/kg for 40 K. The average activity concentrations of the radionuclides from field 2 were 16.97 ± 0.84 Bq/kg, 68.03 ± 3.40 Bq/kg and 70.31 ± 3.51 Bq/kg for 238 U, 232 Th and 40 K respectively. The average activity concentrations of the radionuclides from field 3 (post harvesting) were 28.92 ± 1.44 Bq/kg, 91.73 ± 4.58 Bq/kg and 122.60 ± 6.13 Bq/kg for 238 U, 232 Th and 40 K respectively. The average activity concentrations of the radionuclides were 29.74 ± 1.48 Bq/kg, 121.11 ± 6.05 Bq/kg and 87.51 ± 4.37 Bq/kg for 238 U, 232 Th and 40 K respectively. The average Absorbed Dose Rates were 81.50 ± 4.07 nGy/h for field 1, 52.59 ± 2.62 nGy/h for field 2; 74.68 ± 3.73 nGy/h for field 3 and 91.79 ± 4.59 nGy/h for field 4. The values were below the permissible limit of 1500 nGy/h, thus the radiological risk associated with the top soils of the Ahero Paddy fields of Kisumu County, Kenya is insignificant.
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