Measurements of Natural Radioactivity Levels in the Soil, Coffee and Zuwaye Lake Water Samples Collected from the Selected Area, in Ethiopia, by Using Gamma Ray Spectroscopy.
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Date
2020-06-06
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Addis Ababa University
Abstract
People are exposed to radioactivity in soil, plant and even in other environment that is raised from
uranium, thorium and potassium-40 radionuclides. Environmental radioactivity and the associated
external exposure due to gamma radiations depend primarily on the geological, geographical and
human activities. In this study the activity concentration of 238U, 232Th and 40K radionuclides were
determined in 12 soil samples, Four coffee samples and Four Zuwaye lake water samples
collected from some parts West-Arsi Zone, Shashemane and Zuwaye, Ethiopia using High Pure
Germanium Detector (HPGe). The average activity concentration of 238U, 232Th and40K in the soil
samples was 45.83, 100.525, 845.65Bq/Kg, respectively. These values were higher than the
average world recommended values for 238U , 232Th , 40K , respectively which are 35, 30 and 400
Bq/Kg for 238U , 232Th , 40K respectively [UNSCEAR, 2000].
During our experimental activities our detector could identify only potassium-40 in the coffee
samples. All coffee samples had 591.185 Bq/Kg average values of 40K concentrations that were
higher than the acceptable value (412 Bq/kg) [UNSCEAR, 2010].
Activity concentration of 238U in Lake Zuwaye Water was vary from 2.94±0.25 Bq/L to
3.02±0.27 Bq/L with an average value of 2.99±0.267 Bq/L, 232Th was vary from 6.9±0.73 Bq/L to
8.39±0.82 Bq/L also with an average value of 7.5 ±0.76 Bq/L and the activity concentration of
40K varies from 98.12 4.16154 to 101.99 4.91556 with an average value 99.77±4.80Bq/L.
The activity concentration from the studied areas were found to be below WHO guidelines of 10
Bq/L for 238U and higher than 1 Bq/L for 232Th. The World Health Organization recommended
level of 40K in water meant for drinking is unavailable.
The values of radium equivalent for different soil samples in area under investigated were ranged
from 124.96 to 330.7 Bq/kg with average value 248.75Bq/kg which is lower than the
recommended maximum value 370 Bq/kg [Gilmore, G.R.,2008].
The calculated values of Dr were found to vary from 96.64 to 191.02nGy h-1, with an average
value of 149.5117nGy h-1. The measured average absorbed dose rate in the air and the measured
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average value of the representative level index are higher than the recommended international
levels of 55 nGy h-1. Such locations are not safe for human residency and agriculture.
The calculated values for Dout, Din, and Dtot respectively 0.185, 1.035, and 1.22 mSv/year to
global measured values, these values were all higher than the assigned worldwide values of 0.08,
0.42, and 0.5 year-1, respectively [UNSCEAR,2000]. The locations from which the soil samples
collected were all not safe according to the Radiation Protection, and such locations cannot be
classified as hazard free.
The external hazard index (Hex) and internal hazard index (Hin) due to the emitted -rays of
the soil samples were calculated according to the following criterion: The value of Hex must be
lower than unity in order to keep the radiation hazard insignificant. The calculated external
hazard index values were found to vary between 0.43 and 0.78 with average value of 0.668 these
values are less than unity, which is 33.2 % less than world recommended value. The calculated
internal hazard index values were found to vary between 0.5 and 0.93 with average value of 0.79,
which is 11.0% less than world recommended value [Dabayneh K et al,.2008].
Radioactivity level index vary from 1.19 to 2.395 Bq/Kg with average values is 1.917 Bq/Kg.
The average value of Radioactivity level index is higher than the recommended safe limit ≤ 1
[Thabayneh K, Jazzar M.2012]. Therefore, the soils have radiation hazard and are harmful to
society living there.
The values of radium equivalent for different coffee samples in study area were vary from 42.5
to 54.92 Bq/Kg with average value 47.44Bq/Kg which is lower than the world recommended
maximum value 370 Bq/Kg [Gilmore, 2008].
The determined values of absorbed dose rate (Dr) were found to vary from 23.73 to 30.67nGy h-
1, with an average value of 26.49nGy h-1. The measured average absorbed dose rate in the air was
lower than the recommended international levels of 55 nGy h-1[Turner J et al., 2007] and the
coffee was safe for use.
The determined average values for Dout, Din, and Dtot respectively 0.0325, 0.181, and 0.107
mSv /year to global measured values, these values were all lower than the worldwide values of
0.08, 0.42, and 0.50 mSvyear-1, respectively [UNSCEAR, 2000].
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The external (Hex) and internal (Hin) hazard index due to the emitted -rays of the coffee
samples were calculated and examined according to the following criterion: The value of Hex
must be lower than unity in order to keep the radiation hazard insignificant. This is the radiation
exposure due to the radioactivity from a construction material, limited to 1.5 mGy•y−1. The
maximum values of Hex equal to unity correspond to the upper limit of Raeq (370 Bq/Kg) [48].
The calculated external hazard index values were found to vary between 0.115 and 0.148 with
average value of 0.128 these values are less than unity, which is 87.2 % less than world
recommended value. The calculated internal hazard index values were found to vary between
0.115 and 0.148 with average value of 0.128, which is 87.2% less than world recommended
value [Knoll G.F, 2000].
Radioactivity level index to vary between 0.36 to 0.475 Bq/Kg with average value is 0.4 Bq/Kg.
The average value of Radioactivity level index is lower than one the recommended safe limit ≤ 1
[Van Rooyen T.J., 2002]. Therefore, the coffee had no health radiation hazard.
Hence it can be concluded that the radionuclide concentration of measured coffee samples poses
no radiological health hazard to the community.
The annual effective dose calculated for the Zuwaye lake Water was varied from 0.081 to 0.09
mSv/y with an average of 0.086 mSv/y. This value, when compared with the ICPR standard
value of 1mSvyr-1 is very low, hence, it can be concluded that the radionuclide concentration of
Zuwaye Lake water is negligible and poses no radiological health hazard to the community.
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Keywords
Measurements, Natural Radioactivity Levels, Soil, Coffee and Zuwaye Lake, Water Samples Collected, Selected Area, Ethiopia, Using Gamma Ray Spectroscopy