Radiation Protection Dosimetry (2008), Vol. 128, No. 2, pp. 213–216
Advance Access publication 29 June 2007
doi:10.1093/rpd/ncm327
DETERMINATION OF URANIUM, THORIUM AND POTASSIUM
ACTIVITY CONCENTRATIONS IN SOIL CORES IN ARABA
VALLEY, JORDAN
M. Abusini1, * , K. Al-ayasreh1 and J. Al-Jundi2
1
Department of Physics, Al-albayt University, PO Box 928125, Al-Mafraq, Jordan
2
Department of Physics, The Hashemite University, Zarqa, Jordan
Received February 28 2007, revised May 8 2007, accepted May 19 2007
Soil samples were collected from six different locations in Araba valley, situated between Aqaba port and Dead sea. The
samples have been analysed by using gamma-ray spectrometry. From the measured gamma-ray spectra, activity concentrations
are determined for 238U, 232Th and 40K. The mean activity concentration for 238U, 232Th and 40K was found to be in the
range 19 + 1.4 to 38.7 + 3, 14.3 + 0.8 to 35 + 3.2 and 94 + 18.9 to 762 + 47.4 Bq kg21, respectively. These results indicate
that the mean concentrations of 238U, 232Th and 40K in the populated Araba valley are lower than those in other populated
areas. On the other hand, the concentrations of the major oxides (Al2O3, SiO2, K2O, CaO and Fe2O3) in the samples
were determined using wavelength dispersive X-ray fluorescence. High potassium and iron content in some samples might be
attributed to the active faults, which refer to the Dead sea transform fault.
INTRODUCTION
Radioactivity of soil environment is one of the main
sources of exposure to humans. Hence it is important to know its distribution, gamma radiation from
radionuclides which are characterised by half-lives
comparable to the age of the earth, such as 40K and
radionuclides from the 238U and 232Th series. Their
decay products represent the main external source of
radiation to the human body. More specifically,
natural radioactivity and the associated external
exposure due to gamma radiation depend primarily
on the geological and geographical conditions, and
appear at different levels in the soil of each region in
the world(1 – 4). Higher radiation levels are associated
with igneous rocks, such as granite and lower levels
with sedimentary rocks. However, some shales and
phosphate rock have relative high content of those
radionuclides(5,6). Therefore, measurements of
natural radioactivity in soil are of a great interest for
many researchers throughout the world, which led to
worldwide national surveys in the last two
decades(7 – 10). This study complements a few other
studies, which were conducted at different locations
in Jordan(11 – 13). In this paper, we measure the
specific activity of the naturally occurring radionuclides 238U, 232Th and 40K in soil cores obtained
from six locations of Araba valley, along with the
*
Corresponding author: [email protected]
concentrations of various chemical oxides in the collected samples. The results will be used to establish a
baseline map for that area. This map will be used as
a reference information to assess any change in the
radioactivity background level due to the change in
the topography of the location, other developments
and settlement around it, or any artificial influences
on the environment.
MATERIALS AND METHODS
Araba valley situated between the Aqaba port and
the Dead sea (Figure 1). Soil samples were collected
from transects perpendicular to the traffic flow along
the Araba valley– Aqaba way. The area of the Araba
valley was divided into six locations, eight samples
from each location depths (0–10 and 10–20 cm)
were collected. The sampling sites were located at
distance of 30 m from the roadside curb. Soil
samples crushed, oven dried at a temperature of
708C for 24 h and sieved through a 0.2 mm mesh.
About 10 g of the collected samples were taken for
chemical analysis, the concentration of Al2O3, SiO2,
K2O, CaO and Fe2O3 compounds in the samples
were determined using wavelength dispersive X-ray
fluorescence spectrometer. The remaining portions
of each sample were then packed in a standard
Marinelli beaker that was hermetically sealed, dryweighed and stored for about 4 weeks to allow equilibration of 226Ra with 222Rn. 238U and 232Th
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M. ABUSINI ET AL.
Figure 1. Map shows sampling points along Araba valley –Aqaba way.
were assumed to be in equilibrium with their
progeny(8,14). The background with empty beaker
was subtracted.
The gamma-ray activities were measured using a
low-level counting system of a high-purity germanium computer-controlled detector by conventional
electronic, of 20% relative efficiency. The resolution
was 2 keV for the 1333 keV 60Co. The detector was
shielded in a 10 cm thick lead internally lined with
2 mm copper foil. A reference sample from Canberra
Industries, Inc, type MGS-5, was used for efficiency
calibration in the same geometry as the measured
for 20 h. The gamma-ray lines of 212Pb(238.6 keV),
208
TI(583 keV) and 228Ac(911.2 keV) were used to
determine the activity of 232Th, whereas the ray lines
of 214Pb(295.2 keV and 351.9 keV) and 214Bi(609.3 KeV
and 1120.3 KeV) were used to determine the activity
of 238U. The activity of 40K is based on the detection
of its 1460.8 KeV gamma-ray.
RESULTS AND CONCLUSION
Table 1 represents the activity concentrations
obtained by direct gamma-ray spectrometry
measurements of the soil samples. Activity of 238U,
232
Th and 40K is reported throughout this paper in
Bq kg21 dry weight. The mean activity
concentration of 238U was found to be in the range
19 + 1.4 to 38.7 + 3 Bq kg21, while for 232Th it is in
the range 14.3 + 0.8 to 35 + 3.2 Bq kg21.On the
other hand, the activity of 40K was found to be in
the range 94 + 18.9 to 762 + 47.4 Bq kg21. The
results show a high activity of 40K in Locations 1
and 2. The obtained results are comparable to the
worldwide average concentration of these radionuclide in soil reports by the UNSCEAR(1), which
are 40 Bq kg21 for 238U and 232Th and 370 Bq kg21
for 40K. The small variation between the mean
activity concentration obtained for 238U and 232Th
in all locations may be ascribed to the fine particle
nature of soil, since the distributions of elements
were found to be very particle size-dependent (15). It
is also noticed that the mean activity concentrations
of 238U, 232Th and 40K are slightly decreased with
depth. This may be explained by the variation of the
spatial movement of the fine particles, which is
expected to be faster than leaching downward and
also to the differences of the sample’s grain size.
The gamma dose rate (D) in nGy h21 in the
outdoor air at 1 m above the ground is calculated
using the following equation by the UNSCEAR(1):
214
DðnGy h1 Þ ¼ 0:0417CK þ 0:462CU þ 0:604CTh
URANIUM, THORIUM AND POTASSIUM ACTIVITY CONCENTRATIONS
Table 1. Natural radionuclide contents in soil samples from different locations along Araba valley, Jordan.
Location
Activity concentration (Bq kg21)
Depth
(cm)
238
232
U
Mean
L1
L2
L3
L4
L5
L6
0 –10
10–20
0 –10
10–20
0 –10
10–20
0 –10
10–20
0 –10
10–20
0 –10
10–20
Range
28.0
26.3
21.0
22.1
23.3
19.7
38.7
26.9
21.8
24.9
24.6
19.0
Mean
25.5 –31.9
20.2 –29.4
19.0 –23.2
19.6 –24.9
19.7 –25.6
15.7 –22.6
36.0 –41.7
21.5 –30.4
20.5 –33.2
24.4 –25.4
16.7 –38.2
16.5 –23.2
The average absorbed dose rate in (nGy h21)
40
L1
L2
L3
L4
L5
L6
31.8
27.6
4
11
11.5
7.9
K
238
232
12.9
9.7
10.8
17.9
10.1
11.4
21.1
16.9
10.4
14.9
15.8
9.1
U
Th
Range
35.0
30.3
28.0
26.6
17.2
14.3
24.6
21.3
26.1
21.6
15.1
15.6
Table 2. The average absorbed dose rate in (nGy h21)
caused by 40K, 238U, 232Th and the total absorbed dose
obtained from 40K, 238U and 232Th.
Locations
40
Th
Total
65.8
54.2
25.2
43.8
37.4
28.4
where CK, CU and CTh are the average activity concentrations of 40K, 238U and 232Th in Bq kg21,
respectively.
The air-absorbed dose rate due to the gamma-ray
emission from the samples ranges between 25.2 and
65.8 nGy h21.The average absorbed dose rate values
calculated for each site is shown in Table 2.
28.8– 43.8
20.3– 36.1
25.4– 30.5
21.3– 30.1
14.0– 20.3
12.5– 16.0
20.2– 28.5
17.3– 24.8
25.2– 26.8
20.3– 24.4
12.9– 17.8
12.0– 17.6
K
Mean
762
741
663
651
96.0
94.0
263
210
276
250
189
176
Range
660– 860
716– 929
531– 752
619– 672
87.0– 104
57.0– 146
195– 317
142– 257
255– 305
243– 259
162– 244
139– 237
The mean concentrations of 238U, 232Th and 40K
in the populated Araba valley and other studies conducted nationally and internationally are shown in
Table 3, obviously demonstrate that the average
activity concentrations obtained in this study are
lower than presented in other studies. It may be
noted that the higher activity concentration of 40K
obtained in the surface soil samples of Araba valley
is 762 Bq kg21, yet it is still in the range of
UNSCEAR report (16), which is 140–850 Bq kg21.
The concentration of the major metal oxides in
the samples is given in Table 4; no enriched area was
observed. Samples of high potassium and iron
content are further characterised by decreased silicate content, which might be attributed to the active
faults which refer to the Dead sea transform
faults(17).
SUMMARY
The obtained results confirm some facts in agreement with many reported previously. They are
Table 3. Reported values of gamma activity in soil (Bq kg21), from work conducted worldwide and results obtained in
this study.
Region
Amman, Jordan
Karak, Jordan
Agaba-Amman highway
Rajasthan, India
Istanbul, Turkey
Taiwan
Taiwan
Araba valley: surface
samples
238
U
56.4
229
44.4
30.0–78.0
21.0
54.0
30.0
21.0–38.7
232
Th
28.8
27.2
36.3
43– 106
37.0
32.4
44.0
15.1 –35.0
215
40
K
501
410
208
50.0– 137
342
794
431
96.0– 762
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