Acta Geophysica
DOI: 10.2478/s11600-013-0109-1
Implication and Hazard of Radiation Level
in the Building Materials
Basavaraj R. KERUR1, Tanakanti RAJESHWARI1, Rajesh SIDDANNA1,
and Anil S. KUMAR2
1
Department of Physics, Gulbarga University, Gulbaga, India
e-mails: kerurbrk@yahoo.com (corresponding author),
rajeshwari.phy@gmail.com, rajeshsiddanna@gmail.com
2
Radiation Safety Systems Division, BARC, Mumbai, India
Abstract
The natural radioactivity due to radium, thorium, and potassium in
building material samples contribute to the radiation dose received by
human beings significantly. It is essential to evaluate the activity levels
of these nuclides for the assessment of natural radiation dose. Activity
concentrations of the gamma emitting primordial radionuclides 232Th,
226
Ra, and 40K were measured using high resolution gamma spectrometry
technique with high purity germanium (HPGe) detector in building materials: sand, brick, granite, cement and rock, collected from various areas
of Gulbarga and Koppal districts. The standard ASTM procedure was
followed for the sample preparation. The distribution of radionuclides
and variation in activity concentration depend upon the rock formation
and the geological properties of the region. The activity of the three radionuclides, 232Th, 226Ra, and 40K, were found to be in the range of 3.1227.1, 1.6-111, and 23.2-1505 Bq/kg, respectively. The dose related radiological parameters were also calculated for all the samples and the observations show that the activity concentrations of the radionuclides are
well within the UNSCEAR limits.
Key words: natural radioactivity, background radiation, radioactive equilibrium, gamma spectrometry, HPGe detector.
________________________________________________
© 2013 Institute of Geophysics, Polish Academy of Sciences
B.R. KERUR et al.
1.
INTRODUCTION
Human beings are continuously exposed to various terrestrial and extraterrestrial radiations. To assess the effects of radiation and radiation level, the
knowledge of radionuclide distribution in the environment is very essential.
Both terrestrial and extraterrestrial radiations constitute the natural radiation
level. The main contributors to the terrestrial radiation are the radionuclides
composing the environmental materials such as soil, rocks, building materials, water, and atmosphere. Some of the radionuclides from these sources are
transferred to man through food chain or inhalations. The extraterrestrial
radiations originate from the outer space as cosmic rays (El-Arabi 2007).
Gamma radiations emitted from the naturally occurring radionuclides,
such as 232Th, 226Ra, and their decay products and singly occurring radionuclides, such as 40K and 87Rb, contribute to the natural background radiation
level in the environment. The radionuclide content of these radionuclides in
the various environmental materials mainly depends upon the geology, rock
formation, and geochemical composition of the region (Ramola et al. 2008,
Ajayi 2009, UNSCEAR 2000).
Various types of building materials, such as sand, brick, rock, granite
and cement, have been used for construction purposes since many generations. The gamma radiations emitted from the radionuclides contained in
these materials mainly contribute to the internal radiation exposure as human
beings spend most of their time (about 80%) in dwellings and office buildings. Continuous exposure to radiation, even of low level, may bring out
effects with time. The building materials contribute to environmental radioactivity by gamma emission from 232Th, 226Ra, and 40K and their progenies,
contributing to the whole body dose and by releasing radon the decay product of 226Ra (Shousha 2006).
The earlier research has shown the results of radioactivity of different
building materials in other parts of the country and world. In this direction,
the present study measures the concentration of radionuclides 232Th, 226Ra,
and 40K in different building material samples used for construction purpose
in Gulbarga and Koppal districts using gamma spectrometry. The effective
dose equivalents, radiation hazard indices, and gamma activity index were
also estimated.
1.1 Area studied
The area under study is part of North East Karnataka. The study has been
carried out in two regions: Gulbarga and Koppal. Gulbarga basically is a district lying between 16°11′-17°45′ N latitudes and 76°03′-77°30′ E longitudes. The soil types in the district are deep black, medium black soil,
shallow soil, and lateritic soil (Radhakrishna and Vaidhyanadhan 1997). The
RADIATION HAZARD LEVEL IN THE BUILDING MATERIALS
region belongs to Deccan Traps and green schist belt. Gulbarga rocks are of
basalt type (Deccan type), which are formed by the volcanic eruption. Black
soil has been derived from basaltic rocks and varies in colour from medium
to deep black. Gulbarga is famous for stone mining and is a host of many
cement factories nearby. Various building materials sand, brick, and rock
samples have been collected from the Gulbarga region for the natural radiation level assessment. Koppal lies in the latitude 15°09′ to 16°01′ N and longitude 75°46′ to 76°48′ E. The region is part of Krishna basin recognized by
peninsular gneissic complex consisting of granites, gneisses, and Dharwar
group consisting of schist’s (younger granites). The district is moderately
plain with shallow troughs and mounds of granites hills. Soils are the weathering product of parent rock. Black cotton soil is seen in schistose terrain and
gneissic and granite terrain.
2.
MATERIALS AND METHOD
2.1 Sample collection and preparation
A total of 40 building material samples (6 of sand, 12 of brick soil, 12 of
rock, and 6 of granite) collected from the Gulbarga and Koppal districts are
studied. Four cement samples were collected from the Sedam Cement industry which is used for construction purposes in various cities of Karnataka.
The samples were collected and prepared according to ASTM procedures.
About 2-3 kg of each sample was collected in a polythene bag. The rock,
granite, brick, and sand samples were crushed to a fine powder and then
sieved using a 200-mesh sized sieve to separate the unevenly crushed particles. The sieved pulverized samples were placed in a hot air oven for drying
at 110°C for 24 h to ensure the moisture elimination. Each pulverized sieved
sample was then transferred to a 250 ml cylindrical plastic container. The
containers were filled fully, sealed with an adhesive (Araldite), named,
weighed and then stored for a period of four to five weeks to attain secular
equilibrium between radon (222Rn) and its short lived daughter products
before subjecting to the gamma spectrometric analysis.
2.2 Gamma ray spectrometry
A high resolution HPGe detector based gamma spectrometric system was
adopted for the sample counting. A co-axial p-type high purity germanium
detector (EURISYS MESURES, France) having a relative efficiency of 50%
and resolution of 2 keV for 1.332 MeV γ-ray line of 60Co was employed for
the purpose (Anil Kumar et al. 2001). The output of the detector was analyzed using a PC based 8 k multichannel analyzer system (GAMMAFAST
5016). The detector was surrounded by 3″ thick lead shield on all sides to reduce the background radiations originating from the walls and cosmic rays.
B.R. KERUR et al.
Efficiency calibration for the system was carried out using the standard uranium ore obtained from International Atomic Energy Agency (IAEA,
RGU-1) in geometry available for the sample counting by counting for sufficiently long time for better statistics. For the efficiency calibration, ten
prominent gamma energies from 226Ra, 214Pb, and 214Bi were used.
2.3 Activity measurement
Each sample was measured for a counting period of 50 000 seconds
(13.89 h) to reduce the counting errors. Assuming the daughter products of
226
Ra and 232Th were in equilibrium, the activity concentration of the radionuclides was estimated. Gamma transitions of 352 keV of 214Pb, 609 and
1764 keV of 214Bi were used for estimating 226Ra activity (where it is assumed to be in equilibrium with its daughter products). Similarly, 238.6 keV
of 212Pb, 911 keV of 228Ac, and 583.2 keV of 208Tl were used to estimate the
average 232Th concentration. The 1460 keV gamma line was counted for
estimation of 40K activity concentration. Background radiation was measured
and subtracted to get the net count rate for each sample. Activity concentrations were calculated from the intensity of several γ-rays emitted by a nuclide using the relation
Activity [Bq] =
Net area under the photopeak [cps] × 100 × 100
.
Efficiency [%] × BR [%]
(1)
2.4 Radiation dose parameters
In order to estimate the absorbed gamma dose rate and other dose related parameters the radionuclide concentrations in air were used for all the samples.
The external terrestrial gamma absorbed dose rates due to terrestrial gamma
rays at 1 m above the earth’s surface were calculated from the concentrations
of 232Th, 226Ra, and 40K and the conversion factors of 0.604, 0.462, and
0.0417, respectively, were used as given by UNSCEAR (2000) report
D = 0.604CTh + 0.462CRa + 0.0417CK [nGyh −1 ] ,
(2)
where CTh, CRa, and CK are the average activity concentrations of 232Th,
Ra, and 40K, respectively.
The annual average effective dose received by a member was calculated
using the conversion factor of 0.7 SvGy–1 used to convert absorbed dose rate
to human effective dose equivalent with an indoor occupancy of 80%, as
given by UNSCEAR 2000 report.
226
Annual effective dose [mSvy −1 ] = D [nGyh −1 ] × 8760 [hy −1 ] × 0.7 [SvGy −1 ] × 0.8 (3)
RADIATION HAZARD LEVEL IN THE BUILDING MATERIALS
The external (Hex) and internal (Hin) hazard indices were also estimated
by the equation derived by Beretka and Mathew (1985):
H ex =
CRa CTh
C
+
+ K ,
370 259 4810
(4)
H in =
CRa CTh
C
+
+ K .
185 259 4810
(5)
In order to examine whether a building material meets the dose criteria,
another radiation hazard index, called the gamma activity concentration index Iγ [Bq/kg], is calculated; it is given by the European Commission (1999)
as
Iγ =
3.
CRa CTh
C
+
+ K .
300 200 3000
(6)
RESULTS AND DISCUSSION
The obtained results of the mean activity concentration of the radionuclides
in the building material samples are presented in Table 1. The activity concentrations of the radionuclides 232Th, 226Ra, and 40K were found to vary
from 3.1 to 227.1 Bq/kg, 1.6 to 111 Bq/kg, and 23.2 to 1505 Bq/kg, respectively, for all the building material samples. The granite samples from the
Koppal region showed a higher mean activity of the radionuclides, as it is
known that granites are igneous type of rocks. Earlier studies have shown
that a high concentration level is observed in igneous rocks, whereas a low
level is observed in the sedimentary rocks (Tsai et al. 2008). The granite
samples exhibit an enhanced activity of radium and thorium compared to the
very low abundance of these elements observed in the mantle and crust of
the Earth. According to geologists, this behavior is due to the geochemical
and geological formation of the granites. The partial melting and fractional
crystallization of magma enabled uranium and thorium to be concentrated in
the liquid phase and become incorporated into the more silica-rich products.
For that reason, igneous rocks of granitic composition are strongly enriched
in uranium or radium and thorium compared to the other environmental materials (Alharbi et al. 2011). The samples showed higher thorium activity
than radium activity as radium is washed-out with water but thorium remains
in the earth. Also the present data showed that the 40K concentration in sand
and granite samples is higher than in the other materials, whereas the 232Th
and 226Ra concentrations are in the similar trend.
The mean activity concentration of 232Th, 226Ra, and 40K of the present
study samples were compared with those found in various building materials
of various studies of the world, as presented in Table 2. The average values
B.R. KERUR et al.
Table 1
The activity concentrations of 232Th, 226Ra, and 40K
determined in various building materials
Activity [Bq/kg]
Sample Weight
name
[g]
232
Th
226
Ra
40
K
Health hazard
Gamma
Annual
indices
Gamma
absorbed
effective
activity
dose rate
dose Exter- Interindex
D
–1
[mSvy ] nal
nal
[nGy h–1]
SEDAM CEMENT
CT01 472
CT02 414
CT03 421
CT04 437
Mean
26.3±0.5
32.4±0.5
31.1±0.8
27.1±0.9
29.4
24.0±0.5
29.9±2.2
24.0±0.9
25.3±0.4
25.8
328.5±3.2
118.9±4.7
279.7±3.8
311.4±2.7
259.6
40.64
38.34
41.56
41.08
40.40
0.20
0.19
0.20
0.20
0.20
0.23
0.23
0.24
0.24
0.23
0.30
0.31
0.31
0.31
0.31
0.32
0.30
0.33
0.32
0.32
42.77
44.69
43.88
46.93
85.48
74.09
56.31
0.21
0.22
0.21
0.23
0.42
0.36
0.27
0.10
0.24
0.24
0.25
0.19
0.18
0.2
0.14
0.26
0.28
0.29
0.22
0.21
0.23
0.34
0.36
0.35
0.37
0.69
0.59
0.45
30.90
23.51
24.72
26.37
37.13
46.92
30.71
180.4
130.4
33.95
39.33
31.58
33.49
62.65
0.15
0.11
0.12
0.13
0.18
0.23
0.15
0.88
0.64
0.17
0.19
0.16
0.16
0.31
0.19
0.14
0.14
0.16
0.21
0.29
0.18
1.07
0.76
0.20
0.24
0.19
0.20
0.37
0.24
0.19
0.18
0.20
0.25
0.33
0.23
1.30
0.85
0.26
0.28
0.24
0.24
0.44
0.24
0.19
0.20
0.21
0.30
0.38
0.24
1.44
1.05
0.27
0.32
0.25
0.27
0.50
3.63
10.74
13.36
12.09
13.72
63.59
10.63
0.02
0.05
0.06
0.06
0.07
0.31
0.05
0.02
0.06
0.08
0.07
0.08
0.36
0.06
0.02
0.03
0.07
0.08
0.09
0.11
0.08
0.10
0.09
0.11
0.42
0.51
0.07
0.08
to be continued
SAND
GSA01 413
GSA02 420
GSA03 395
GSA04 488
KSA01 404
KSA02 406
Mean
15.2±0.4
13.6±0.5
17.2±0.3
17.0±0.4
38.6±2.3
33.8±0.6
22.6
13.9±0.6
7.5±0.6
13.6±0.7
12.4±0.8
9.3±1.2
12.0±0.4
11.4
652.0±5.6
791.8±8.8
652.0±5.6
741.8±7.0
1388±15
1154±10
896.6
BRICK
GBS01 360
GBS02 393
GBS03 352
Mean
KBS01 356
KBS02 373
KBS03 301
KBS04 313
KBS05 377
KBS06 210
KBS07 217
KBS08 436
KBS09 369
Mean
28.0±0.6
23.0±0.5
19.6±0.5
23.5
26.8±1.4
54.9±1.7
23.9±0.9
165.8±5.9
116.7±1.9
25.2±1.3
42.3±1.6
30.0±1.3
31.6±1.0
57.5
19.5±0.8
15.9±0.7
14.7±0.7
16.7
14.2±1.3
16.3±1.3
20.1±0.5
84.0±8.2
34.5±1.7
21.3±1.2
16.0±0.9
17.3±1.1
16.0±1.1
26.7
119.1±6.2
55.8±5.3
146.1±6.3
107
345.3±0.6
144.2±11
167.5±0.7
993.8±22
1056±9.7
213.0±9.2
152.2±7.9
131.3±10
168.0±7.2
374.6
GRK01
GRK02
GRK03
GRK04
GRK05
GRK06
GRK07
3.1±0.3 1.6±0.3 23.2±4.1
7.1±0.3 3.3±0.3 116.6±4.3
8.2±0.8 5.7±0.5 138.2±4.7
5.2±0.7 3.9±0.8 171.0±5.3
8.0±0.4 5.8±0.6 149.2±5.6
45.7±0.5 21.7±0.8 622.8±7.5
6.8±0.4 5.4±0.5 97.0±4.4
ROCKS
486
502
492
451
481
405
508
RADIATION HAZARD LEVEL IN THE BUILDING MATERIALS
Tab le 1 (continuation)
Health hazard
Gamma
Activity [Bq/kg]
Annual
indices
Gamma
absorbed
Sample Weight
effective
activity
dose rate
name
[g]
dose Exter- Inter232
226
40
index
D
Th
Ra
K
–1
[mSvy ] nal
nal
[nGy h–1]
ROCKS
GRK08 432
6.9±0.3 4.8±0.5 121.4±4.4 11.46
0.06
0.06 0.08
0.09
GRK09 466
6.1±0.3 4.5±0.9 113.7±5.3 10.51
0.05
0.06 0.07
0.08
GRK10 499
5.2±0.4 3.1±0.5 107.1±4.5 9.051
0.04
0.05 0.06
0.07
GRK11 223 31.1±0.6 14.8±1.4 881.2±8.9 62.36
0.30
0.34 0.38
0.50
GRK12 398
6.3±0.3 4.3±0.5 70.3±4.9
8.71
0.04
0.05 0.06
0.70
Mean
11.7
6.6
217.6
19.15
0.09
0.11 0.12
0.20
GRANITE
KGT01 381
KGT02 350
KGT03 539
KGT04 491
KGT05 460
KGT06 476
Mean
141.7±0.5
227.1±3.1
33.6±0.7
38.4±0.5
36.1±0.5
34.8±0.9
85.6
78.2±0.4
111±2.4
27.3±0.8
21.6±0.6
29.8±0.7
28.5±0.2
49.4
1448±16
1505±12
769.3±4.6
777.7±7.6
802.6±7.5
722.6±4.7
1004.2
182.1
251.1
64.97
65.65
69.01
64.27
116.2
0.89
1.23
0.32
0.32
0.34
0.31
0.57
1.06
1.50
0.36
0.37
0.39
0.36
0.67
1.27
1.88
0.44
0.43
0.47
0.44
0.82
1.46
2.0
0.52
0.52
0.55
0.51
0.93
Table 2
Comparison of the mean concentrations of Ra, Th, and K (Bq/kg)
recorded in various building materials of several studies
226
Location
Cement
Sand
Bricks
Rock
Granite
Activity concentration [Bq/kg]
232
Th
24.98
29.40
80.21
22.60
45
40.50
19.15
11.70
14
85.60
226
Ra
72.21
25.80
94.93
11.40
132
21.70
21.79
6.60
28
49.40
232
40
40
Reference
134.49
259.60
700.79
896.60
306
240.80
399.30
217.60
267
1004.20
Shousha (2006)
Present study
Abel-Ghany et al. (2009)
Present study
Nour (2005)
Present study
Harb et al. (2012)
Present study
Issa et al. (2012)
Present study
K
of the activity concentrations of 232Th, 226Ra, and 40K for the building materials samples were found to be normal values and well comparable with the
values for other building materials from other regions of the world. Using
the activity concentrations of the radionuclides, the absorbed gamma dose
rate and other dose related parameters were estimated. Using the absorbed
dose rate, the annual average effective dose equivalents for all the samples
B.R. KERUR et al.
were estimated. The values are within the permissible dose equivalent limit
of 1 mSv y–1 for the general public (ICRP 1990) for all the samples. The
granite samples showed a high dose compared to other samples.
The most important sources of external radiation exposure are radium
and thorium, their decay products and 40K. The internal exposure is due to
radon (222Rn) an inert gas enters through inhalation and affects the respiratory system of man. If the annual effective dose rate for building materials is
less than 1.5 mSv and Raeq is less than 370 Bq/kg, then the external hazard
index (Hex) is always less than one. For insignificant radiation hazard, the indices should be less than unity or 1. Its effect can be estimated from internal
hazard index (Hin) and for safe use of materials; this index must also be less
than unity. The data acquired in the present study is well in accordance with
the recommended safety limit of 1 mSv for the public and do not pose any
health hazard for the dwellers residing in the buildings. The granites showed
a higher internal hazard index, as shown in Fig. 1, which in future can introduce possible radiation hazards due to the accumulative dose, if proper ventilation is not accounted for while constructing the building.
According to EU regulations No. 112 (1999) building materials should
be exempted from all restrictions concerning radioactivity. Effective doses
exceeding the dose criterion of 1 mSv y–1 should be taken into account in
terms of radiation protection. It is recommended by the EU and ICRP that
the gamma dose from the building materials should be in the range 0.31 mSv y–1. To examine whether or not our building materials meet the above
dose criteria, gamma activity index is also estimated.
External H azard Index
Internal H azard Index
G am m a activity index
1.2
1.1
1.0
Hazard indices
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
G Rock
G Brick
Cem ent
G Sand
K Brick
K Sand K G ranite
S am p le
Fig. 1. The health hazard indices and gamma activity index for the building
materials.
RADIATION HAZARD LEVEL IN THE BUILDING MATERIALS
The index Iγ is correlated with the annual dose rate due to the excess external gamma radiation caused by superficial material. If the values of gamma index Iγ ≤ 2, the dose rate corresponds to 0.3 mSv y–1, whereas 2 ≤ Iγ ≤ 6
corresponds to a criterion of 0.3-1 mSv y–1 (Abel-Ghany 2011). Thus, the activity concentration index is used only as a screening tool to identify materials for the safe applicability of the construction materials. The materials with
Iγ > 6 should be avoided for construction purposes as it corresponds to
a dose rate higher than 1 mSv y–1. The index Iγ ranges from 0.07 for rock to
2.0 for granite which lies in the limits. The obtained results of mean hazard
indices are shown in Fig. 1. The values obtained indicate that the building
materials studied in the present work are safe for construction purpose.
Hence it is desirable to select the materials of low radioactivity for use in
building construction.
4.
CONCLUSIONS
The gamma activity of natural radionuclides 232Th, 226Ra, and 40K was estimated using high resolution gamma spectrometry system with a high purity
germanium detector. The average values of the activity concentrations of
226
Ra, 232Th, and 40K for the building materials samples were found to be
normal values and well comparable with the values for other building materials from other regions of the world. The higher activity of granite samples
may be attributed to the geological formation of the region and geochemical
formation of the granites. The gamma activity index was also found to be
within the corresponding dose criterion of ICRP limits of 1 mSv y–1 for the
public. The present study reveals that the activity values obtained are the
natural background radiations and well comparable with the national and international values. The data produced in the present work can be used as
baseline radiological data for future investigations and programs.
A c k n o w l e d g e m e n t . The authors are grateful to Board of Research in
Nuclear Science for providing the financial support to carry out this work.
The Author (RT) acknowledges Council of Scientific and Industrial Research (CSIR), New Delhi, for awarding her Senior Research Fellowship.
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Received 29 July 2012
Received in revised form 26 November 2012
Accepted 13 December 2012