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Natural activities of 238U , 232Th and 40K in some Indian building materials
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Radiation Measurements 36 (2003) 465 – 469 www.elsevier.com/locate/radmeas
Natural activities of 238U, 232Th and 40K in some Indian building materials Ajay Kumar, Mukesh Kumar, Baldev Singh, Surinder Singh∗ Department of Physics, Guru Nanak Dev University, Amritsar 143005, India Received 21 October 2002; accepted 29 April 2003
Abstract The activity concentrations of 226 Ra, 232 Th and 40 K have been determined by gamma-ray spectrometry. The measured activity in the selected building materials ranges from (3.2 to 151:7 Bq=kg), 14 to 63:7 Bq=kg and 24.3 to 121:5 Bq=kg for 226 Ra, 232 Th and 40 K respectively. The activity concentration of 238 U has been determined using 6ssion track technique and the value ranges from 0.11 to 3:85 ppm. The concentrations for these natural radionuclides are compared with the reported data from other countries. Radium-equivalent activities (Raeq ) are calculated for the measured samples to assess the radiation hazards arising due to the use of these materials in the construction of dwellings. All building materials have shown Raeq activities lower than the limit set in the Organization for Economic Cooperation and Development (OECD) report (370 Bq=kg), equivalent to external gamma dose of 1:5 mSv yr −1 . A good correlation has been observed between 238 U and 226 Ra in these materials. c 2003 Elsevier Ltd. All rights reserved. Keywords: Natural radioactivity; Building materials; -spectrometry; Fission track; Radium-equivalent activities
1. Introduction The most important source of external radiation exposure in buildings is caused by the gamma rays emitted from members of the uranium and thorium decay chains and 40 K occurring naturally in building materials. Human populations have always been exposed to ionizing radiation from natural sources. Knowledge of radioactivity present in building materials enables one to assess any possible radiological risks to human health. Nationwide surveys have been carried out to determine the radium equivalent activity of building materials in many countries (Amrani and Tahtat, 2001; Hewamanna et al., 2001; Hayumbu et al., 1995; Ibrahim, 1999; Kumar et al., 1999; Zaidi et al., 1999). The naturally occurring radionuclides present in building materials including soil are 226 Ra, 232 Th and 40 K (Khan et al., 1998; Nageswara Rao, 1989; Menon et al., 1982). Since these radionuclides are not uniformly distributed, the knowledge of their distribution in soils and rocks play
an important role in radiation protection and measurement (Khan et al., 1994). This knowledge is essential for the development of standards and the guidelines for the use and management of these materials. The natural radioactivity in some Indian building materials have been reported by some authors in selected areas (Kumar et al., 1999; Nageswara Rao et al., 1996). However the detailed information of each state is scanty. The data regarding the concentrations of 226 Ra, 232 Th and 40 K in building materials belonging to Punjab, Himachal Pradesh and Rajasthan states of India is not available in literature. The objective of the present study is to determine the content of these radionuclides in building materials belonging to these states to assess any radiological hazard. The results obtained in the present study are compared with the results available in some other countries of the world. 2. Experimental methods 2.1. Samples
∗
Corresponding author. Tel.: +91-183-2257007; fax: +91-183-2258820. E-mail address: [email protected] (S. Singh). c 2003 Elsevier Ltd. All rights reserved. 1350-4487/$ - see front matter doi:10.1016/S1350-4487(03)00173-2
The activity levels in building materials are determined from samples collected from construction sites as well as
466
A. Kumar et al. / Radiation Measurements 36 (2003) 465 – 469
from various agencies supplying raw materials for building construction. The building materials investigated are cement, cement plaster, brick, sand, limestone, aqua phobic, gypsum, chips, soil, crasher and ceramics. Most of the materials are studied in their natural form as such. Some were dried and sieved, while others (bricks, crasher, ceramics, etc.) were crushed and sieved. 2.2. Estimation of natural radioactivity levels by gamma-ray spectrometry technique The gamma spectrometry system for bulk counting of environmental samples makes use of a 5 × 4 NaI (Tl) Eat detector (M/s Harshaw low background integral assembly). In the system the detector is enclosed in a massive lead shielding 10 cm thick lined with 1:5 mm thick cadmium. In order to reduce the contribution due to the X-rays Euorescence, 0:8 mm thick copper on the inner surfaces is used. The dimensions of the free surface within the shielding enclosure are 44 cm × 44 cm × 65 cm deep. About 250 g of each sample sieved through a 100 mesh sieve was dried and sealed in a plastic container, 4:5 cm in diameter and 7:0 cm in height. These were stored for 30 days before counting so as to allow 226 Ra and its short-lived decay products to reach radioactive equilibrium. The standard sources for 226 Ra and 232 Th (in secular equilibrium with 228 Th) were prepared using known activity contents and mixing with the matrix material of phthalic acid powder. In order to avoid the loss of gaseous daughter products of 226 Ra and 228 Th which may lead to disturbance in radioactive equilibrium, the prepared standard sources were kept in sealed plastic container (7:5 cm × 6:5 cm diam.). Analar grade potassium chloride (KCl) of a known amount of the same geometry was used as the standard source of 40 K. The gamma ray lines of 1.46, 1.76 and 2:62 MeV were employed for potassium, radium and thorium analysis. To compare the speci6c radioactivities of materials which contain K, Ra and Th, a common index is generally preferred to obtain the sum of the activities. This index is called the radium equivalent activity (OECD, 1979; UNSCEAR, 1982; Beretka and Mathew, 1985), which is, calculated on the assumption that 370 Bq=kg 226 Ra or 260 Bq=kg 232 Th or 4810 Bq=kg 40 K produce the same gamma dose rate. Therefore, the Raeq of the sample in (Bq/kg) can be expressed as Raeq = ARa + (ATh × 1:43) + (AK × 0:077);
(1)
where ARa ; ATh and AK are the activity concentrations of the three radionuclides 226 Ra, 232 Th and 40 K respectively, which is expressed in Bq/kg. The characteristics of the gamma ray spectrometer using are given in Table 1. 2.3. Estimation of uranium content The 6ssion track registration technique (Fleischer et al., 1975) was used for the analysis of uranium concentration in these samples. The induced 6ssion tracks were recorded in
Table 1 Characteristics of gamma spectrometer Parameter
Gamma line used (MeV) Background reduction factor Percentage eJciency MDA (Bq/kg) (for 12; 000 s counting, 7:5 cm × 6:5 cm diam. Plastic container geometry)
For radionuclides 226 Ra
232 Th
40 K
1.76 (214 Bi) 12.3
2.62 (208 Tl) 15.4
1.46 18.5
1.39 8
1.37 7
4.16 5
Equations for elemental counts: Thorium = C3 , Radium = C2 − aC3 , Potassium = C1 − bC3 − c(C2 − aC3 ), where C1 , C2 and C3 are background subtracted true counts in K, Ra and Th energy bands respectively. a = 0:58, b = 0:72, c = 1:18.
a lexan overlay detector after irradiating the pellets with a thermal neutron dose of 2 × 1015 (nvt) from CIRUS reactor at BARC, Trombay. After irradiation the detector discs were etched in 6:25 N NaOH solution at 70◦ C for 25 min to reveal the 6ssion tracks. The developed 6ssion tracks were scanned using an optical microscope at a magni6cation of 400×. The uranium concentration was calculated using the equation (Fleischer et al., 1975): Tx Is U x = Us ; (2) Ts Ix where the subscripts x and s represents the sample and standard respectively. T , the 6ssion track density and I , the isotopic abundance ratio of 235 U and 238 U. Is =Ix has been taken as unity assuming that the isotopic abundance ratio is the same for the sample and the standard. The details of the technique are the same as reported earlier (Singh et al., 2001). 3. Results and discussion The activity concentrations of 226 Ra, 232 Th and 40 K in various building materials are given in Table 2. As can be seen from Table 2, the activity concentration of 226 Ra in bricks, black cement, sand, gypsum, yellow chips and crasher is lower than that of the world average for soil (25 Bq=kg) (UNSCEAR, 1982).The results for radium-equivalent activity (Raeq ) calculated using Eq. (1) are shown in Table 2. These values range from 10:36 Bq=kg in gypsum to 234:21 Bq=kg in white cement. Somlai et al. (1998) have recommended the use of construction materials with an average Raeq value of less than 370 Bq=kg for dwellings. So these materials do not pose a signi6cant radiological hazard when used for construction of buildings. The results for uranium concentrations in building materials using track etch technique are given in Table 3.
A. Kumar et al. / Radiation Measurements 36 (2003) 465 – 469
467
Table 2 Activity concentration of materials used in building construction in India Sl. no.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Material
Ceramics Brick Brick Brick ACC cement (black) Ambuja cement (black) ACC cement (black) White cement (birla) Sand Sand Plaster of Paris Limestone Aquaphobic Gypsum Yellow chips Green chips White chips Red chips Crasher Soil Soil
a BDL—below
Location
Activity concentration (Bq/kg)
Raeq (Bq/kg)
226 Ra
232 Th
40 K
Hardware store (Punjab) Amritsar(Punjab) Batala (Punjab) Batala (Punjab) Barmana (Himachal) Ropar (Punjab)
28.2 12.6 18.1 23.4 9.4
63.7 53.9 32.1 14.0 40.9
24.3 47.2 48.5 38.7 33.1
121.16 93.31 67.74 46.40 70.43
15.5
36.5
35.8
70.45
Gaggal (Himachal) Birla company
7.1
34.1
39.6
58.91
151.7
57.7
BDL
234.21
9.4 BDLa BDL
52.6 51.5 54.2
70.5 60.5 33.6
90.05 78.30 80.09
73.9 BDL 8.3 3.2 67.9 59.3 38.6 16.0 7.5 BDL
BDL 32.4 BDL 33.2 BDL BDL BDL 36.6 31.4 46.6
64.6 24.6 26.7 31.0 76.7 32.3 121.5 49.1 44.0 109.8
78.87 48.23 10.36 53.06 73.81 61.78 47.96 72.12 55.79 75.09
Barsar (Himachal) Amritsar (Punjab) Hardware store (Punjab) Hardware store Hardware store Hardware store Kishangarh (Rajasthan) Chittorgarh (Rajasthan) Nathdiara (Rajasthan) Kishangarh (Rajasthan) Amritsar (Punjab) Una (Himachal) Amritsar (Punjab)
detection limit.
The uranium concentration in building materials varies from 0:11 ppm in soil to 3:85 ppm in white Cement. In order to observe a correlation between uranium and radium in building materials a graph (Fig. 1) was plotted and correlation coeJcient was determined. A good correlation (correlation coeJcient = 0:93) has been obtained between uranium and radium content in building materials. Table 4 compares the reported values of radium equivalent activities for selected building materials, obtained in other countries with those determined in this study. As shown in this table, the radioactivity in building materials varied from one country to another or even there are variations in the radium equivalent activities of diNerent materials and also within the same type of materials. The results may be important from the point of view of selecting suitable materials for use in building construction. Large variations in radium equivalent activities may suggest that it is advisable to monitor the radioactivity levels of materials from a new source, before adopting it for using as a building material. To limit the external gamma-radiation dose from building materials to 1:5 mSv, a model proposed by Beretka (Beretka and Mathew, 1985; Hayumbu et al., 1995) was used in
this study: ARa ATh AK + + 6 1: 370 260 4810
(3)
The criterion of this model considers that the external hazard due to gamma-rays corresponds to a maximum radium-equivalent activity of 370 Bq=kg (UNSCEAR, 1982) for the material. From Table 4, the values of radium-equivalent activities for the materials obtained in this study are as follows: (a) The value of radium-equivalent activity of gypsum is lowest as compared to other building materials and is of the same order as the Australian building materials. The values obtained for cement, cement plaster and sand are of the same order as the Algerian, Zambian and Australian samples, respectively. (b) The activity value of radium equivalent for white cement (Birla Company) is highest as compared to other building materials. (c) The results obtained for clay bricks are found to be the lowest compared to those of other countries.
468
A. Kumar et al. / Radiation Measurements 36 (2003) 465 – 469
Table 3 Uranium concentration in building materials used in building construction Sl. no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Material
Location
Uranium conc. (ppm)
Ceramics Brick Brick Brick ACC Cement (black) Ambuja Cement (black) ACC Cement (black) White Cement (birla) Sand Sand Plaster of Paris Limestone Aquaphobic Gypsum Yellow Chips Green Chips White Chips Red Chips Crasher Soil Soil
Hardware store (Punjab) Amritsar (Punjab) Batala (Punjab) Batala (Punjab) Barmana (Himachal)
1.90 0.95 1.15 1.75 0.85
Ropar (Punjab)
1.15
Gaggal (Himachal)
0.80
Birla company
3.85
Barsar (Himachal) Amritsar (Punjab) Hardware store (Punjab) Hardware store Hardware store Hardware store Kishangarh (Rajasthan) Chittorgarh (Rajasthan) Nathdiara (Rajasthan) Kishangarh (Rajasthan) Amritsar (Punjab) Una (Himachal) Amritsar (Punjab)
0.69 0.45 0.40 1.73 0.21 0.75 0.65 2.28 1.79 1.36 1.04 0.47 0.11
4.5
4
Uranium conc. (ppm)
3.5
3
2.5
2
1.5
1
0.5
0 0
20
40
60
80
100
120
Radium conc. (Bq/Kg) Fig. 1. Uranium vs. radium concentration in building materials.
140
160
A. Kumar et al. / Radiation Measurements 36 (2003) 465 – 469
469
Table 4 Comparison of mean Raeq equivalent activity (Bq/kg) in building materials with some other countries of the world Material
India (present work)
Algeria (Amrani and Tahtat, 2001)
Australia (Beretka and Mathew, 1985)
Germany (Krieger, 1981)
Zambia (Hayumbu et al., 1995)
Sri Lanka (Hewamanna et al., 2001)
Brazil (Malanca et al., 1993)
Cement Cement plaster Clay bricks Sand Limestone Crasher Gypsum
108.5 80.09 69.15 84.15 78.87 72.12 10.36
112 101 130 28 37 58 —
115 15 218 70 15 115 11.1
70 41 207 59 48 322 —
79 63 — 135 24 33 —
— — 183 — — — —
— — — — 263.3 — 160.3
4. Conclusions The radium-equivalent activities obtained in the building materials are all well below the acceptable limit. Therefore, the use of these materials in construction of dwellings is considered to be safe for inhabitants. Acknowledgements The authors wish to thank Dr. S. Kumar, Joint Director and Dr. S.S. Bhatti, Defence Laboratory Jodhpur for their kind help in analysis of the samples using gamma ray spectrometry. The neutron irradiation facilities provided by BARC, Mumbai are highly acknowledged. References Amrani, D., Tahtat, M., 2001. Natural radioactivity in Algerian building materials. Int. J. Appl. Radiat. Isot. 54, 687–689. Beretka, J., Mathew, P.J., 1985. Natural radioactivity of Australian building materials, industrial wastes and by-products. Health Phys. 48, 87–95. Fleischer, R.L., Price, P.B., Walker, R.M., 1975. Nuclear Tracks in Solids, Principles and Applications. University of California Press, Berkeley, CA, pp. 489 – 495. Hayumbu, P., Zaman, M.B., Lubaba, N.C.H., Munsanje, S.S., Nuleya, D., 1995. Natural radioactivity in Zambian building materials collected from Lusaka. J. Radional. Nucl. Chem. 199, 229–238. Hewamanna, R., Sumithrarachchi, C.S., Mahawatte, P., Nanayakkara, H.L.C., Ratnayake, H.C., 2001. Natural radioactivity and gamma dose from Sri Lankan clay bricks used in building construction. Int. J. Appl. Radiat. Isot. 54, 365–369. Ibrahim, N., 1999. Natural activities of 238 U, 232 Th and 40 K in building materials. J. Environ. Radioactivity 43, 255–258. Khan, H.M., Khan, K., Atta, M.A., Jan, F., 1994. Measurement of gamma activity of soil samples of Charsadda district of Pakistan. J. Chem. Soc. Pak. 16, 183–188.
Khan, K., Khan, H.M., Tufail, M., Ahmad, N., 1998. Radiometric analysis of Hazara phosphate rock and fertilizers. J. Environ. Radioactivity 38, 77–83. Krieger, R., 1981. Radioactivity of construction materials. Betonwerk Fertigteil Techn. 47, 468–473. Kumar, V., Ramachandran, T.V., Prasad, R., 1999. Natural radioactivity of Indian building materials and by products. Int. J. Appl. Radiat. Isot. 51, 93–96. Malanca, A., Pessina, V., Dallara, G., 1993. Radionuclide content of building materials and gamma ray dose rates in dwellings of Rio-Grande Do-Norte Brazil. Rad. Prot. Dosim. 24, 27–31. Menon, M.R., Mishra, U.C., Lalit, B.Y., Shukla, V.K., Ramachandran, T.V., 1982. Uranium, thorium and potassium in Indian rocks and ores. Proc. Indian Acad. Sci. (Earth, Planet Sci.) 91, 127–136. Nageswara Rao, M.V., 1989. Natural radioactivity levels in some environmental materials from Rajasthan. Bull. Radiat. Prot. 12, 36–41. Nageswara Rao, M.V., Bhati, S.S., Seshu, P., Reddy, A.R., 1996. Natural radioactivity in soil and radiation levels of Rajasthan. Radiat. Prot. Dosim. 63, 207–216. OECD, 1979. Exposure to radiation from the natural radioactivity in building materials. Report by a group of experts of the OECD, Nuclear Energy Agency, Paris, France. Singh, S., Malhotra, R., Kumar, J., Singh, L., 2001. Uranium analysis of geological samples, water and plants from Kulu area, Himachal Pradesh, India. Radiat. Meas. 34, 427–431. Somlai, J., Horvath, M., Kanyar, B., Lendvai, Z., Nemeth, C.S., 1998. Radiation hazard of coal slags as building material in Tatabanya Town (Hungary). Health Phys. 75 (6), 648–651. UNSCEAR, 1982. Ionising radiation sources and biological eNects. United Nations Scienti6c Committee on the eNects of Atomic Radiation, A/37/45, New York. Zaidi, J.H., Arif, M., Ahmad, S., Fatima, I., Qureshi, I.H., 1999. Determination of natural radioactivity in building materials used in the Rawalpindi Islamabad area by -ray spectrometry and instrumental neutron activation analysis. Int. J. Appl. Radiat. Isot. 51, 559–564.
Radiation Measurements 36 (2003) 465 – 469 www.elsevier.com/locate/radmeas
Natural activities of 238U, 232Th and 40K in some Indian building materials Ajay Kumar, Mukesh Kumar, Baldev Singh, Surinder Singh∗ Department of Physics, Guru Nanak Dev University, Amritsar 143005, India Received 21 October 2002; accepted 29 April 2003
Abstract The activity concentrations of 226 Ra, 232 Th and 40 K have been determined by gamma-ray spectrometry. The measured activity in the selected building materials ranges from (3.2 to 151:7 Bq=kg), 14 to 63:7 Bq=kg and 24.3 to 121:5 Bq=kg for 226 Ra, 232 Th and 40 K respectively. The activity concentration of 238 U has been determined using 6ssion track technique and the value ranges from 0.11 to 3:85 ppm. The concentrations for these natural radionuclides are compared with the reported data from other countries. Radium-equivalent activities (Raeq ) are calculated for the measured samples to assess the radiation hazards arising due to the use of these materials in the construction of dwellings. All building materials have shown Raeq activities lower than the limit set in the Organization for Economic Cooperation and Development (OECD) report (370 Bq=kg), equivalent to external gamma dose of 1:5 mSv yr −1 . A good correlation has been observed between 238 U and 226 Ra in these materials. c 2003 Elsevier Ltd. All rights reserved. Keywords: Natural radioactivity; Building materials; -spectrometry; Fission track; Radium-equivalent activities
1. Introduction The most important source of external radiation exposure in buildings is caused by the gamma rays emitted from members of the uranium and thorium decay chains and 40 K occurring naturally in building materials. Human populations have always been exposed to ionizing radiation from natural sources. Knowledge of radioactivity present in building materials enables one to assess any possible radiological risks to human health. Nationwide surveys have been carried out to determine the radium equivalent activity of building materials in many countries (Amrani and Tahtat, 2001; Hewamanna et al., 2001; Hayumbu et al., 1995; Ibrahim, 1999; Kumar et al., 1999; Zaidi et al., 1999). The naturally occurring radionuclides present in building materials including soil are 226 Ra, 232 Th and 40 K (Khan et al., 1998; Nageswara Rao, 1989; Menon et al., 1982). Since these radionuclides are not uniformly distributed, the knowledge of their distribution in soils and rocks play
an important role in radiation protection and measurement (Khan et al., 1994). This knowledge is essential for the development of standards and the guidelines for the use and management of these materials. The natural radioactivity in some Indian building materials have been reported by some authors in selected areas (Kumar et al., 1999; Nageswara Rao et al., 1996). However the detailed information of each state is scanty. The data regarding the concentrations of 226 Ra, 232 Th and 40 K in building materials belonging to Punjab, Himachal Pradesh and Rajasthan states of India is not available in literature. The objective of the present study is to determine the content of these radionuclides in building materials belonging to these states to assess any radiological hazard. The results obtained in the present study are compared with the results available in some other countries of the world. 2. Experimental methods 2.1. Samples
∗
Corresponding author. Tel.: +91-183-2257007; fax: +91-183-2258820. E-mail address: [email protected] (S. Singh). c 2003 Elsevier Ltd. All rights reserved. 1350-4487/$ - see front matter doi:10.1016/S1350-4487(03)00173-2
The activity levels in building materials are determined from samples collected from construction sites as well as
466
A. Kumar et al. / Radiation Measurements 36 (2003) 465 – 469
from various agencies supplying raw materials for building construction. The building materials investigated are cement, cement plaster, brick, sand, limestone, aqua phobic, gypsum, chips, soil, crasher and ceramics. Most of the materials are studied in their natural form as such. Some were dried and sieved, while others (bricks, crasher, ceramics, etc.) were crushed and sieved. 2.2. Estimation of natural radioactivity levels by gamma-ray spectrometry technique The gamma spectrometry system for bulk counting of environmental samples makes use of a 5 × 4 NaI (Tl) Eat detector (M/s Harshaw low background integral assembly). In the system the detector is enclosed in a massive lead shielding 10 cm thick lined with 1:5 mm thick cadmium. In order to reduce the contribution due to the X-rays Euorescence, 0:8 mm thick copper on the inner surfaces is used. The dimensions of the free surface within the shielding enclosure are 44 cm × 44 cm × 65 cm deep. About 250 g of each sample sieved through a 100 mesh sieve was dried and sealed in a plastic container, 4:5 cm in diameter and 7:0 cm in height. These were stored for 30 days before counting so as to allow 226 Ra and its short-lived decay products to reach radioactive equilibrium. The standard sources for 226 Ra and 232 Th (in secular equilibrium with 228 Th) were prepared using known activity contents and mixing with the matrix material of phthalic acid powder. In order to avoid the loss of gaseous daughter products of 226 Ra and 228 Th which may lead to disturbance in radioactive equilibrium, the prepared standard sources were kept in sealed plastic container (7:5 cm × 6:5 cm diam.). Analar grade potassium chloride (KCl) of a known amount of the same geometry was used as the standard source of 40 K. The gamma ray lines of 1.46, 1.76 and 2:62 MeV were employed for potassium, radium and thorium analysis. To compare the speci6c radioactivities of materials which contain K, Ra and Th, a common index is generally preferred to obtain the sum of the activities. This index is called the radium equivalent activity (OECD, 1979; UNSCEAR, 1982; Beretka and Mathew, 1985), which is, calculated on the assumption that 370 Bq=kg 226 Ra or 260 Bq=kg 232 Th or 4810 Bq=kg 40 K produce the same gamma dose rate. Therefore, the Raeq of the sample in (Bq/kg) can be expressed as Raeq = ARa + (ATh × 1:43) + (AK × 0:077);
(1)
where ARa ; ATh and AK are the activity concentrations of the three radionuclides 226 Ra, 232 Th and 40 K respectively, which is expressed in Bq/kg. The characteristics of the gamma ray spectrometer using are given in Table 1. 2.3. Estimation of uranium content The 6ssion track registration technique (Fleischer et al., 1975) was used for the analysis of uranium concentration in these samples. The induced 6ssion tracks were recorded in
Table 1 Characteristics of gamma spectrometer Parameter
Gamma line used (MeV) Background reduction factor Percentage eJciency MDA (Bq/kg) (for 12; 000 s counting, 7:5 cm × 6:5 cm diam. Plastic container geometry)
For radionuclides 226 Ra
232 Th
40 K
1.76 (214 Bi) 12.3
2.62 (208 Tl) 15.4
1.46 18.5
1.39 8
1.37 7
4.16 5
Equations for elemental counts: Thorium = C3 , Radium = C2 − aC3 , Potassium = C1 − bC3 − c(C2 − aC3 ), where C1 , C2 and C3 are background subtracted true counts in K, Ra and Th energy bands respectively. a = 0:58, b = 0:72, c = 1:18.
a lexan overlay detector after irradiating the pellets with a thermal neutron dose of 2 × 1015 (nvt) from CIRUS reactor at BARC, Trombay. After irradiation the detector discs were etched in 6:25 N NaOH solution at 70◦ C for 25 min to reveal the 6ssion tracks. The developed 6ssion tracks were scanned using an optical microscope at a magni6cation of 400×. The uranium concentration was calculated using the equation (Fleischer et al., 1975): Tx Is U x = Us ; (2) Ts Ix where the subscripts x and s represents the sample and standard respectively. T , the 6ssion track density and I , the isotopic abundance ratio of 235 U and 238 U. Is =Ix has been taken as unity assuming that the isotopic abundance ratio is the same for the sample and the standard. The details of the technique are the same as reported earlier (Singh et al., 2001). 3. Results and discussion The activity concentrations of 226 Ra, 232 Th and 40 K in various building materials are given in Table 2. As can be seen from Table 2, the activity concentration of 226 Ra in bricks, black cement, sand, gypsum, yellow chips and crasher is lower than that of the world average for soil (25 Bq=kg) (UNSCEAR, 1982).The results for radium-equivalent activity (Raeq ) calculated using Eq. (1) are shown in Table 2. These values range from 10:36 Bq=kg in gypsum to 234:21 Bq=kg in white cement. Somlai et al. (1998) have recommended the use of construction materials with an average Raeq value of less than 370 Bq=kg for dwellings. So these materials do not pose a signi6cant radiological hazard when used for construction of buildings. The results for uranium concentrations in building materials using track etch technique are given in Table 3.
A. Kumar et al. / Radiation Measurements 36 (2003) 465 – 469
467
Table 2 Activity concentration of materials used in building construction in India Sl. no.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Material
Ceramics Brick Brick Brick ACC cement (black) Ambuja cement (black) ACC cement (black) White cement (birla) Sand Sand Plaster of Paris Limestone Aquaphobic Gypsum Yellow chips Green chips White chips Red chips Crasher Soil Soil
a BDL—below
Location
Activity concentration (Bq/kg)
Raeq (Bq/kg)
226 Ra
232 Th
40 K
Hardware store (Punjab) Amritsar(Punjab) Batala (Punjab) Batala (Punjab) Barmana (Himachal) Ropar (Punjab)
28.2 12.6 18.1 23.4 9.4
63.7 53.9 32.1 14.0 40.9
24.3 47.2 48.5 38.7 33.1
121.16 93.31 67.74 46.40 70.43
15.5
36.5
35.8
70.45
Gaggal (Himachal) Birla company
7.1
34.1
39.6
58.91
151.7
57.7
BDL
234.21
9.4 BDLa BDL
52.6 51.5 54.2
70.5 60.5 33.6
90.05 78.30 80.09
73.9 BDL 8.3 3.2 67.9 59.3 38.6 16.0 7.5 BDL
BDL 32.4 BDL 33.2 BDL BDL BDL 36.6 31.4 46.6
64.6 24.6 26.7 31.0 76.7 32.3 121.5 49.1 44.0 109.8
78.87 48.23 10.36 53.06 73.81 61.78 47.96 72.12 55.79 75.09
Barsar (Himachal) Amritsar (Punjab) Hardware store (Punjab) Hardware store Hardware store Hardware store Kishangarh (Rajasthan) Chittorgarh (Rajasthan) Nathdiara (Rajasthan) Kishangarh (Rajasthan) Amritsar (Punjab) Una (Himachal) Amritsar (Punjab)
detection limit.
The uranium concentration in building materials varies from 0:11 ppm in soil to 3:85 ppm in white Cement. In order to observe a correlation between uranium and radium in building materials a graph (Fig. 1) was plotted and correlation coeJcient was determined. A good correlation (correlation coeJcient = 0:93) has been obtained between uranium and radium content in building materials. Table 4 compares the reported values of radium equivalent activities for selected building materials, obtained in other countries with those determined in this study. As shown in this table, the radioactivity in building materials varied from one country to another or even there are variations in the radium equivalent activities of diNerent materials and also within the same type of materials. The results may be important from the point of view of selecting suitable materials for use in building construction. Large variations in radium equivalent activities may suggest that it is advisable to monitor the radioactivity levels of materials from a new source, before adopting it for using as a building material. To limit the external gamma-radiation dose from building materials to 1:5 mSv, a model proposed by Beretka (Beretka and Mathew, 1985; Hayumbu et al., 1995) was used in
this study: ARa ATh AK + + 6 1: 370 260 4810
(3)
The criterion of this model considers that the external hazard due to gamma-rays corresponds to a maximum radium-equivalent activity of 370 Bq=kg (UNSCEAR, 1982) for the material. From Table 4, the values of radium-equivalent activities for the materials obtained in this study are as follows: (a) The value of radium-equivalent activity of gypsum is lowest as compared to other building materials and is of the same order as the Australian building materials. The values obtained for cement, cement plaster and sand are of the same order as the Algerian, Zambian and Australian samples, respectively. (b) The activity value of radium equivalent for white cement (Birla Company) is highest as compared to other building materials. (c) The results obtained for clay bricks are found to be the lowest compared to those of other countries.
468
A. Kumar et al. / Radiation Measurements 36 (2003) 465 – 469
Table 3 Uranium concentration in building materials used in building construction Sl. no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Material
Location
Uranium conc. (ppm)
Ceramics Brick Brick Brick ACC Cement (black) Ambuja Cement (black) ACC Cement (black) White Cement (birla) Sand Sand Plaster of Paris Limestone Aquaphobic Gypsum Yellow Chips Green Chips White Chips Red Chips Crasher Soil Soil
Hardware store (Punjab) Amritsar (Punjab) Batala (Punjab) Batala (Punjab) Barmana (Himachal)
1.90 0.95 1.15 1.75 0.85
Ropar (Punjab)
1.15
Gaggal (Himachal)
0.80
Birla company
3.85
Barsar (Himachal) Amritsar (Punjab) Hardware store (Punjab) Hardware store Hardware store Hardware store Kishangarh (Rajasthan) Chittorgarh (Rajasthan) Nathdiara (Rajasthan) Kishangarh (Rajasthan) Amritsar (Punjab) Una (Himachal) Amritsar (Punjab)
0.69 0.45 0.40 1.73 0.21 0.75 0.65 2.28 1.79 1.36 1.04 0.47 0.11
4.5
4
Uranium conc. (ppm)
3.5
3
2.5
2
1.5
1
0.5
0 0
20
40
60
80
100
120
Radium conc. (Bq/Kg) Fig. 1. Uranium vs. radium concentration in building materials.
140
160
A. Kumar et al. / Radiation Measurements 36 (2003) 465 – 469
469
Table 4 Comparison of mean Raeq equivalent activity (Bq/kg) in building materials with some other countries of the world Material
India (present work)
Algeria (Amrani and Tahtat, 2001)
Australia (Beretka and Mathew, 1985)
Germany (Krieger, 1981)
Zambia (Hayumbu et al., 1995)
Sri Lanka (Hewamanna et al., 2001)
Brazil (Malanca et al., 1993)
Cement Cement plaster Clay bricks Sand Limestone Crasher Gypsum
108.5 80.09 69.15 84.15 78.87 72.12 10.36
112 101 130 28 37 58 —
115 15 218 70 15 115 11.1
70 41 207 59 48 322 —
79 63 — 135 24 33 —
— — 183 — — — —
— — — — 263.3 — 160.3
4. Conclusions The radium-equivalent activities obtained in the building materials are all well below the acceptable limit. Therefore, the use of these materials in construction of dwellings is considered to be safe for inhabitants. Acknowledgements The authors wish to thank Dr. S. Kumar, Joint Director and Dr. S.S. Bhatti, Defence Laboratory Jodhpur for their kind help in analysis of the samples using gamma ray spectrometry. The neutron irradiation facilities provided by BARC, Mumbai are highly acknowledged. References Amrani, D., Tahtat, M., 2001. Natural radioactivity in Algerian building materials. Int. J. Appl. Radiat. Isot. 54, 687–689. Beretka, J., Mathew, P.J., 1985. Natural radioactivity of Australian building materials, industrial wastes and by-products. Health Phys. 48, 87–95. Fleischer, R.L., Price, P.B., Walker, R.M., 1975. Nuclear Tracks in Solids, Principles and Applications. University of California Press, Berkeley, CA, pp. 489 – 495. Hayumbu, P., Zaman, M.B., Lubaba, N.C.H., Munsanje, S.S., Nuleya, D., 1995. Natural radioactivity in Zambian building materials collected from Lusaka. J. Radional. Nucl. Chem. 199, 229–238. Hewamanna, R., Sumithrarachchi, C.S., Mahawatte, P., Nanayakkara, H.L.C., Ratnayake, H.C., 2001. Natural radioactivity and gamma dose from Sri Lankan clay bricks used in building construction. Int. J. Appl. Radiat. Isot. 54, 365–369. Ibrahim, N., 1999. Natural activities of 238 U, 232 Th and 40 K in building materials. J. Environ. Radioactivity 43, 255–258. Khan, H.M., Khan, K., Atta, M.A., Jan, F., 1994. Measurement of gamma activity of soil samples of Charsadda district of Pakistan. J. Chem. Soc. Pak. 16, 183–188.
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