N.C. ASHEBIR, B.S. GOSHU#, E. MENGISTU
Department of Physics, Dire Dawa University, Ethiopia
Naturally occurring radionuclide materials have been found in the Earth’s surface. These radionuclides include uranium (238U), thorium (232Th) and potassium (40K). The natural radioactive material originated from the environment is the major source of radiation. The purpose of this work is to assess the specific activity of radionuclides in soil samples and tea leaves and to estimate the transfer factor of radionuclides from soil to tea leaves. The specific activity of natural radionuclides 238U, 232Th, and 40K in six soil samples and tea leaves from Gumero tea farm were measured by gamma spectroscopy using a High Purity Germanium (HPGe) detector, and the radiological hazard parameters due to these natural radionuclides were determined. The mean specific activity of 238U, 232Th, and 40K in soil samples were: 41.6 ± 1.4 Bq kg–1, 81.8 ± 2.4 Bq kg–1, and 184.8 ± 5.1 Bq kg–1, respectively and for tea leaves they were: 3.5 ± 1.1 Bq kg–1 for 238U, 4.9 ± 0.9 Bq kg–1 for 232Th, and 516.7 ± 32.0 Bq kg–1 for 40K. The average value of radium equivalent specific activity in soil samples was 172.0 ± 4.6 Bq kg–1 whereas, in tea leaves it was 53.3 ± 2.2 Bq kg–1. This value is lower than the world average limit which is 370 Bq kg–1. The mean absorbed dose rate (DR) was found to be 26.1 nGy h–1 and 76.3 ± 2.0 nGy h–1 in the tea leaves, and soil samples, respectively. The mean annual effective dose (AED) was 0.03 mSv y–1 and 0.09 mSv y–1 in tea leaves and soil samples, respectively. The mean external hazard index (Hex) was 0.13 in the tea leaves and 0.46 in soil samples. The internal hazard index (Hin) was 0.16 in tea leaves and 0.57 in soil samples. These values are lower than the worldwide average limit which is 1. The mean value of absorbed dose rate in the soil sample is slightly higher than the world acceptable value but, on the other hand, the radiological hazard parameters for soil samples were lower than the recommended world average values. Therefore, from the radiological point of view, this study concludes that the soil and tea leaves at Gumero tea farm cannot caused any hazardous health effects to inhabitants by the consumption of Gumero tea.
Key words: Tea leaves, specific activity, dose rate, radium equivalent, HPGe, hazard index
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