Arabian Journal for Science and Engineering
Gebi Tuku Yachiso*, Prof. A.K. Chaubey2 and Birhanu Turi3
MEASUREMENTS OF NATURAL RADIOACTIVITY LEVELS IN SOIL SAMPLES AND
RADIOLOGICAL HEALTH HAZARDS IN AND AROUND LEGA DAMBI GOLD MINING
BY USING HPGe GAMMA-RAY SPECTROMETRY.
1
Addis Ababa University Department of Physics, Addis Ababa, Ethiopia.
Addis Ababa University Department of Physics, Addis Ababa, Ethiopia.
caubey@gmail.com.
2
3
e-mail address. profak-
Ethiopin Radiation Protection Authority(ERPA). e-mail address. Bire23@gmail.com
Corresponding Authors: gebituku01@gmail.com,+251911074361
Abstract
The activity concentrations of natural radionuclide in soil samples of the Lega Dembi gold mining area of
Ethiopia were investigated to assess environmental radiation levels and radiological health hazards. To measure natural radioactivity concentrations due to 226 Ra, 232 Th, and 40 K radionuclides, fifteen soil samples were
collected from three sites in and around the Lega Dembi area. This research aims to use an HPGe gamma-ray
spectrometer to measure the level of natural radioactivity. The mean activity concentration for Lga Dembi
gold mining for 238 U, 232 Th, and 40 K determined were 25.73±0.47, 60.07±1.33, and 391.43±6.41Bq/kg for
Lega Dembi gold mine soil samples (LD) and 8.89±0.18, 13.97±0.28, and 423.9±4.72Bq/kg for Lega Dembi
control area (LDC), and 22.02±0.28, 45.09±0.61, and 391.82±4.44Bq/kg for Sakaro nearby Lega Dembi gold
mining downstream (SK), respectively. With the world mean average, these results indicated higher levels
of 40 K for LD and 232 Th for SK in soil from the mining area. In our study areas, the annual effective doses
(average) for LD, LDC, and SK were 0.08, 0.034, and 0.067, respectively. The study’s mean annual effective
dose was lower than the world average. The calculated absorbed dose rate in the air, and even the results,
were 65.32, 27.64, and 54.51nGy/h. The absorbed dose rate at the LD location is higher than the world
average, which is 60nGy/h. As a result, the soil poses no radiological hazard to the community.
Keywords: Natural Radioactivity, Gamma-ray spectrometry, gold mining soil.
Introduction
Small quantities of naturally occurring radioactive elements have been found in the human environment since
the earth’s origin. The presence of these radioactivity has no negative consequences for the environment or
human health. When levels rise as a result of human activities such as mining or a natural disaster such as
earthquakes, the main concern arises [1]. Mining and processing activities have also been shown to increase
1
NORM levels in several recent studies conducted in a variety of countries [2-4]. Finally, mining generates
a large amount of waste, which may contaminate soil throughout a wide area, affecting the environment
and human health [5]. Their activity also raises NORM concentrations on the surface of the earth, offering a
health risk to humans, especially when inhaled or ingested [2]. 222 Ra and 220 Ra, which are daughter products
of 238 U and 232 Th, and potassium 40 K, respectively, are the main sources of radiation that affect human
health [3]. The activity concentration of long-lived radionuclides like 238 U, 232 Th, and 40 K is important in
determining the population’s radiological hazard.
Gold is the most well-known element in use as jewelry by a broad range of people all over the world. It is
obtained through a series of geological processes deep under the earth’s surface. The community and miners
can be exposed to radiation from “the mining and mineral processing industries in three ways: external
gamma radiation from ores, inhalation of dust containing decay progenies of 238 U, 232 Th, and 40 K, and
inhalation of radon’s short-lived decay products” [6]. Mineral mines and their processing can also harm the
environment by exposing members of the public to radiation by improper “drilling, leaching, handling, storage,
and transportation of mineral ores and” waste media [7]. There must be certain regulatory and regulatory
controls in place to limit the effects of these radionuclides, and the international body has adopted a strict
measurement to minimize the radiation health hazards connected with inhaling radionuclides like radon [8,
9].
However, a few studies in Ethiopia have studied radionuclide concentrations in mines [ 9, 10, 11, 12]. According
to most literature in the world, mining areas provide a radiological threat to the local community living near
mining areas, and there is little awareness of NORMs exposure to the local community from gold mining.
As a result, the focus of our study was to determine natural radioactivity levels in soil samples and also
radiological hazards in and around the Lega Dembi gold mining area in East Guji, Ethiopia. A gamma-ray
spectroscopy HPGe detector can be used to measure the activity concentrations of 238 U, 232 Th, and 40 K.
Experimental Methods
Study areas: Lega Dembi gold mining is located in southern Ethiopia, Oromia region, 7 km southwest
of Shakiso which is 500km from Addis Ababa and is bounded by latitude 5°42’33.475’N’ and longitude
38°54’24.914’E.
It is found within the southern slope of the Eastern Ethiopian Highlands along with the transition to the
Somalia Plateau. The area is near the eastern margin of the Main Ethiopian Rift.
2.1 Sample Collection and Preparation
Lega Dembi gold mining residual(LD) areas, Lega Dembi control(LDC) regions, and Sakaro downstream
near Lega Dembi gold mining were all included within our study (SK). The LDC is a control area about
5 kilometers from the gold mining area. This is to compare the natural radioactivity concentration in the
gold mining area to the natural radioactivity concentration in the surrounding area that people live. At a
depth of 10 - 20cm, we collect five samples from each location. To remove available moisture, the collected
samples were dried in an oven at 1050 C for 12 hours. The samples were then crushed and sieved “to remove
organic materials, stones, gravel, and lumps” to use a mesh with holes 0.426mm in diameter. Finally, a mass
of 500g was packed into a cylindrical plastic container with a height of 7 cm and a diameter of 6 cm after
the homogenized samples were weighed. “The plastic containers were hermetically sealed with adhesive tape
for 30 days to allow 238U and its short-lived progenies to attain secular radioactive equilibrium” [13].
Samples were placed over the detector for 36,000 seconds, or 10 hours, for measurements. “Background radiation was measured in an empty Marinelli beaker for the same counting time, and the effects of background
2
Figure 1: Schematic diagram of Laga Dembi gold mining from Google Map .
Figure 2: Gamma spectrometry mounted with HPGe detector and DSA circuit (ERPA Lab.)
radiation were subtracted from sample spectra”.
2.2 Measurement of Activity Concentration
“By subtracting the background radiation counts from the total photo-peak areas, the activity levels for each
radionuclide identified in the samples were determined”. The decay products 214 Pb (295.2keV) and 214 Pb
(352keV) in secular equilibrium with radium “were used to determine the activity of 238 U. (226 Ra). The
3
activity of 232 Th was determined to use its decay products 212 Pb (238.6 keV) and 208 Tl (583.2 keV), while
the activity of 40K was determined to use its gamma spectrum at 1460.8 keV” [14].
The Specific activity concentration levels, SAC (Bq/ kg) “of
(dry mass) were calculated using the following equation”:
238
U,
232
Th, and
40
K in each sample in Bq/kg
SAC= (N/T)/(m×к×η)(Bq/kg). . . . . . . . . . . . . . . .. (1)
Where N/T implies the net activity rate, N represents the net photo-peak area, m defines the sample mass,
is the absolute gamma emission probability (branching ratio), is the detector efficiency, and T is the sample
counting time. According to the IAEA, the branching ratio for each identified radionuclide was obtained
from standard radionuclide data tables (142007). The following equation was used to calculate the detector
efficiency:
Where N/T implies the net activity rate, N represents the net photo-peak area, m defines the sample mass,
is the absolute gamma emission probability (branching ratio), is the detector efficiency, and T is the sample
counting time. According to the IAEA, the branching ratio for each identified radionuclide was obtained
from standard radionuclide data tables (142007). The following equation was used to calculate the detector
efficiency:
η=
Y
AT
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..(2)
Where Y is the net photo-peak of the calibration spectrum, A is the activity of Eu-152 (radionuclide reference)
and T is the calibration spectrum counting time.
2.3 Radiological Hazard Indices Equations
In the assessment of the exposure to gamma rays that are hazardous to people exposed in radiological hazard
indices. The radium equivalent activity, external hazard index, internal risk index, and gamma indices were
therefore determined in this study.
2.3.1 Radium Equivalent Equation (Raeq)
Different indices can evaluate gamma-radiation hazards from specific radionuclides. (Raeq), a weighted sum
of three radionuclide activities is an indicator that will provide the same gamma-ray dose rate as a 370Bq/kg
of 238 U, 259Bq/kg of 232 Th, and a 4810Bq/kg dose rate of 40 K. Therefore, from this concept Raeq can be
calculated as;
Raeq =CU +1.43CTh+0.077CK
. . . . . . . . . . . . . . . . . . .(3)
CU, CTh, and CK have Bq/Kg levels of 238 U, 232 Th, and 40 K respectively [15]. It “is based on an estimate
that the same gamma-ray dose rate is attained at 1 Bq/kg of 226 Ra, 0.7 Bq/kg of 232 Th, and 13 Bq/kg of
40
K” (Siak et al., 2009).
2.3.2 Calculation of Absorbed Dose Rate in Air (DR)
The absorbed dose is measured at a height of 1 meter above the ground, ensuring that the three radionuclides
are transmitted uniformly for almost equal activities. “At this distance, the absorbed dose rate (DR) can
be calculated as”,
DR = 0.427CU +0.623CTh+0.043CK . . . . . . . . . . . . ..(4)
Where the DR lies in nGy/h, C is a 238 U, 232 Th, and 40 K activity in Bq/Kg. This dose rate indicates
outdoor radiation dose in environmental materials emitted by radionuclides. The dose limit is 59nGy/h [16].
2.3.3 Calculation of Annual Effective Dose Rate (ADR)
The health effects of the absorbed dose can be assessed by an annual effective dose rate within a year. It
can be shown as mathematically;
ADR = DR(mGy/h) ×8760h/y × 0.2× 0.7Sv/Gy×10-6 . . . . . . . . . (5)
4
“ADR is reported in mSv/y, with 0.7SvG/y used to translate the absorbed dose in the air to the effective
dose received by humans at 1m height, 0.2 representing a 20% outdoor occupancy and 80% indoors” [17,15].
Humans in the study area can change this factor based on their lifestyle patterns. The average annual
worldwide effective dose is around 2.4 mSv/y
2.3.4 External (Hex) and Internal (Hin) Hazard Indexes
The external radiation risk index Hex, which corresponds to the radionuclides in the study, is calculated
using the following equation;
Hex =
ARa
370
+
AT h
259
+
AK
4810
. . . . . . . . . . . . . . . . . . . . . ..(6)
Hazard levels emitted by “short-lived radionuclides such as 222 Rn and daughter products can be quantified
as internal hazard index Hin” [18] from inhaled alpha particles;
Hin =
ARa
185
+
AT h
259
+
AK
4810 . . . . . . . . . . . . . . . . . . . . . . . . . . . .(7)
3. Results and Discussion
In Fifteen soil samples collected in and near the Lega Dembi gold mining area, a mean concentration of 238 U,
232
Th, and 40 K was determined. Tables 3.1 - 3.3 show soil sample values Mean soil sample concentrations
from Lega Dembi gold mining residual (LD), Lega Dembi control (LDC), and Lega Dembi mining in the
area of Sakaro (SK). Their mean LD, LDC and SK activity concentration are 25,73±0.47, 60.07±1.33, and
391,43±6.41, 8,89±0.18 and 391,82±4.44, 22,02±0.28, 45,09±0.61, 8,89±0.18, 13,97±0.28 and 391,82±4.44,
22,02±0.28.
The mean activity levels for 232 Th and 40 K from LD and SK are above the mean given by (UNSCEAR,
2000). Table 3.4 calculated the average radium equivalent of the dose absorption(ADR) for LD, LDC, and
SK, and presented them as 141.78±2.01, 65.23±0.88 and 0.08, 61.48±0.57, 27.64±0.27, 0.034, 116.6±0.98,
54.51±0.44, and 0.067, respectively. The mean absorbed dose rate for LD is above the world limit of 59nGy/hr
from the above results [19]. The contribution from other natural radionuclides and cosmic rays was generally
insignificant from our study.
S.Code
LD-1
LD-2
LD-3
LD-4
LD-5
Mean
238U
232Th
40K
18.46±0.37
28.81±1.32
26.45±1.27
28.22±1.32
26.7±0.58
25.73±0.47
39.69±0.88
73.92±3.85
66.6±3.56
73.92±3.05
46.3±1.1
60.07±1.33
325±5.31
436.13±18.13
404±17.5
436±17.5
356±7.65
391.43±6.41
Table 1: Activity concentration of radionuclides of soil samples inside gold mining area.
5
Figure 3: Activity concentration of natural radionuclides in the control area.
S.Code
LDC-1
LDC-2
LDC-3
LDC-4
LDC-5
Mean
238U
232Th
40K
9.5±0.55
9.23±0.28
9.14±0.48
8.6±0.47
8.01±0.24
8.89±0.18
14.85±0.49
14.8±0.5
13.44±0.79
13.22±0.78
13.52±0.44
13.97±0.28
400.9±6.84
465±7.77
441.53±18.66
416±7.6
395±6.63
391.82±4.44
Table 3: Activity concentration of radionuclides of soil samples Lega Dembi gold mining control area.
S.Code
SK-01
SK-02
SK-03
SK-04
SK-05
Mean
238U
232Th
40K
25.6±0.57
19.17±0.52
20.82±0.95
18.8±0.44
25.7±0.54
22.02±0.28
47.7±0.5
39.17±0.4
47.4±2.51
36.55±1.07
54.61±1.23
45.09±0.61
446±8
334.8±7.9
361.3±15.2
369.8±8.84
447.2±7.5
423.9±4.72
Table 4: “Activity concentration of radionuclides of soil samples” nearby gold mining area.
The soil radionuclide activity concentration was varied due to differences in the geological structure of the
gold mining samples as shown in Fig. 3.1, 3.2, and 3.3. In location LD (60.07±1.33 Bq/kg), and SK
(45.09±0.61Bq/kg) and 40 K activity level were observed as the highest activity concentration of 232 Th in
Fig.(3.1, 3.2 and 3.3), and 40 K activity concentration, also high (423.9±4.72Bq/kg) in LDC.
The lowest activity concentration of 238 U was 18.46±0.37Bq/kg from Table 3,1, with the highest being
28.81±1.32Bq/kg, with the mean of 25.73±0.47Bq/kg
6 and minimum and maximum activity concentration
is 39.79±0.88Bq/kg and 73.92±3.85Bq/kg with an average of (60.07±1.33Bq/kg) for 232 Th and in the same
manner for 40 K was also 325±5.31Bq/kg, and 436.13±18.13Bq/kg with an average of (391.43±6.41Bq/kg). In
Table 3.2, for the 238 U,232 Th, and 40 K, lowest and highest activity LDC concentrations were 8.01±0.24Bq/kg,
9.5±0.55Bq/kg, with a mean (8.89±0.18Bq/kg), 13.22±0.78Bq/kg, 14.85±0.49Bq/kg and 395±6.63Bq/kg,
465±7.77Bq/kg an average of (423.9±4.72Bq/kg) respectively. From Tables 3.1, the lowest 238 U concentration in the LD was 18.46±0.37Bq/kg while the highest was 28.81±1.32Bq/kg with an avera-
Figure 4: “Activity concentration of radionuclides of soil samples” nearby gold mining area.
Figure 5: Activity concentration of natural radionuclides downstream of the gold mining area.
concentration of soil activity was varied from 238 U, 232 Th, and 40 K, which may be due to Lega Dembi’s Lega
gold mining geological condition. Table 4 shows that the mean annual effective dose in soil samples is lower
and hence the area for the study, as suggested in Table 4 [26], is safe for the community.
7
S. code
LD-1
LD-2
LD-3
LD-4
LD-5
Mean
LDC-01
LDC-02
LDC-03
LDC-04
LDC-05
Mean
SK-1
SK-2
SK-3
SK-4
SK-5
Mean
Raeq
DR
ADR
Hex
Hin
100.25±1.37
168.09±5.8
152.79±5.4
167.49±5.8
120.3±1.7
141.78±2.01
61.61±1.04
66.19±0.97
62.35±1.87
59.0±1.35
57.74±0.85
61.48±0.57
127.81±1.1
100.96±0.98
116.48±3.9
99.54±1.73
138.22±1.93
116.6±0.98
46.51±0.62
77.1±2.58
70.15±2.27
76.85±2.56
55.54±0.79
65.23±0.88
30.55±0.48
33.04±0.46
31.26±0.96
14.51±0.53
28.86±0.4
27.64±0.27
60.01±0.5
47.12±0.49
54.15±1.75
46.85±0.79
64.44±0.86
54.51±0.44
0.06
0.09
0.09
0.1
0.07
0.08
0.04
0.04
0.04
0.02
0.04
0.03
0.07
0.07
0.07
0.05
0.08
0.07
0.26
0.44
0.41
0.45
0.32
0.38
0.17
0.18
0.16
0.15
0.15
0.16
0.34
0.26
0.3
0.27
0.37
0.31
0.31
0.53
0.48
0.52
0.39
0.45
0.19
0.2
0.19
0.17
0.17
0.18
0.4
0.3
0.36
0.32
0.44
0.36
Table 5: The value of “radium equivalent(Raeq), absorbed doses(DR), Annual effective dose(ADR) the
external(Hex), and the internal(Hin) hazard index of soil samples of” LD, LDC, and SK.
Reference
Present Study
Kumar et al.
291.06 ± 0.57
Akpanowoetal.
151.15±21.09
Gyuketal.
459.56
A.K. Ademola
26.4
W. O. Aguko
640
Country
238U
232Th
40K
Ethiopia
2017
18.88±0.19
India
39.71±0.4
30.24 ± 0.53
402.38±3.04
29.89 ± 0.61
2019
380.34±116.41
2017
Nigeria
2014
505.1
2013
Nigeria
Nigeria
Kenya
41.6±11.06
62.28
155.36
55.3
44
40
Table 7: Comparision of the study with literature.
4. Conclusions
The activity concentrations of natural radionuclides and their radiological health hazards were measured with
gamma-ray spectroscopy coupled with an HPGe detector in soil samples taken from and near Lega Dembi
gold mining in Ethiopia. The average active concentrations in the Lega Dembi gold mining and nearby soil
samples of natural radionuclides such as 238 U, 232 Th, and 40 K have been investigated. The mean activity
concentration of 238 U, 232 Th, and 40 K was estimated at 25.73±0.47, 60.07±1.33 and 391.43±6.41Bq/kg,
8.79±0.18, 13.97+±0.28, and 423.9±4.72Bq/kg in Lega Dembi gold mining(LD), Lega Dembi control(LDC),
and in Sakaro near gold mining (SK), respectively. In the Lega Dembi control area, mean activity concentrations of 238 U, 232 Th, and 40 K were estimated at 22.02±1.42Bq/kg in gold mining samples (LD). The results
in the SK and LDC, 40 K in LD are about the world average at mean active concentrations of 232 Th. In
comparison with the world average effective dose less than the international standard and the areas of study
are safe (UNSCEAR, 2000). Results in this area of studies show that the main average for the mining areas
8
is low levels of natural radionuclides. According to our studies, the mining activities at Lega Dembi Gold
Mining pose no significant radiological risk to the host community.
Acknowledgments: The authors are thankful to Prof. A.K. Chaubey for his valuable comments and Addis
Ababa University department Physics.
Conflicts of Interest: The authors declare no conflict of interest.
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