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. 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