Assessment and Investigation of Natural Radioactivity Levels in Leaves of Khat and Agricultural Soil Samples Collected from Haramaya East Hararghe, Ethiopia Using Gamma Spectrometry
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Date
2021-10-20
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Addis Ababa University
Abstract
The radiation released from natural radioactive materials (commonly, 40K,238 U, and
232Th series) performing natural radioactivity, which is out of control, absorbed by
the human’s body, arising from a natural source such as cosmic ray, terrestrial, and
exposure from inhalation or intake radiation sources. Those natural radionuclides
are typically present in rock and soil in different amounts and levels of activity, with
subsequent distribution to the environment and transfer to humans through inhalation
and food ingestion (soil-plant-humans) causes health risks.
This study aims to assess and investigate radioactivity levels, radiological hazard
indices in six samples of leaves of Khat plants, and six of its soil (0-30 cm deep)
samples collected from Haramaya University area. The measurement had been carried
out using a high-efficiency gamma-ray spectrometer with Digital Signal Analyser,
(DSA) coupled with a High Purify Germanium (HPGe), p-type detector. The gammaray
spectrometers are controlled by GENIE(2K)-high channel number performance,
computer software, and output result are displayed on personal computer. The investigations
identify naturally occurring radionuclide’s from 238U, and 232Th series, and
40K, in addition to those, 137Cs in agricultural soil and 54Mn in leaves of Khat samples.
The activity concentrations of 238U, 232Th, and 40K in Khat farm soils samples range
from 21.43 } 0.98 to 30.77 } 0.62,Bqkg−1, with a mean value of 23.72 } 0.85Bqkg−1,
69.27 }3.17 to 168.78 }7.55,Bqkg−1, with an average value of 111.50 }4.21Bqkg−1, and
542.15 }22.73 to 1045.96 }43.4, 4Bqkg−1, with an average value of 794 }26.44Bqkg−1,
respectively. The activity concentrations of 40K and 232Th obtained in all samples of
the soils are higher than the recommended reference levels. The radium equivalent activity
range from 221.61 }9.83 to 331.57 }13.81,BqKg−1, with an average value 244.31
BqKg−1, which is relatively higher. Gamma-ray radiation hazards caused by primordial
radionuclides of 40K, 238U and 232Th, evaluated were, the absorbed dose rate range
from 76.52 }3.40 to 152.57 }6.7, nGyh−1, with a mean value of 113.74 }4.12nGyh−1,
which is higher than the global mean value, annual effective dose range from 0.09 }0.00
to 0.19 }0.01,mSvy−1, with an average value of 0.14 }0.01mSvy−1, which is above the
world average. The calculated values of the external and internal index for agricultural
soil samples range from 0.44 to 0.72, with a mean value of 0.63, and 0.51 to 0.96, with
a mean value of 0.72, respectively, which are relatively high but less than the world
permissible value. Also the result of radioactivity level index (Iγ) in soils sample is
ranging from 0.61 } 0.03 to 1.21 } 0.05, with an average values of 0.90 } 0.03 , where
estimated values of Iγ in some soil samples are higher than one and an average relative
iv
higher.
The average concentrations of 238U, 232Th, and 40K in leaves of Khat samples were
1.32 } 0.24, 10.36 } 0.96, and 273.39 } 7.39,Bqkg−1, respectively. The radium equivalent
activity, and internal hazard indices calculated to this plant were varied from
25.20 } 2.471 to 39.50 } 2.137, BqKg−1 with average 34.44 } 2.186 BqKg−1 and from
0.05 to 0.11, with average 0.09, respectively. The average ingestion effective dose due
to intake this plant samples 238U, 232Th, and 40K calculated for adult is, 0.2 }0.04,
1.31 }0.12, and 0.81 }0.03, mSv/y,respectively, with the total summation an average,
2.32 }0.18 mSvy−1. These values are higher than the permissible limits of the world’s
total average ingestion effective dose. The obtained results were compared with the
international recommended values.
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Keywords
Natural Radioactivity, Khat Plants, Soil, Gamma Ray Spectrometry, Hpge Detector, Activity Concentration, and Radiological Hazard