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/lp/ou_press/radioactivity-measurement-and-radiological-hazard-assessment-of-the-77KzxH5Pd0
- Publisher
- Oxford University Press
- Copyright
- © The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com
- ISSN
- 0144-8420
- eISSN
- 1742-3406
- DOI
- 10.1093/rpd/ncy077
- Publisher site
- See Article on Publisher Site
Abstract
Abstract Natural radioactivity of common commercial marble and granite types used in Jordanian dwellings are measured using high-resolution gamma spectrometry. The activity concentrations of 226Ra, 232Th and 40K ranged from 8.57 ± 1.55 to 152.07 ± 3.26 Bq kg−1, 6.83 ± 1.25 to 365.43 ± 4.84 Bq kg−1 and 121.25 ± 9.10 to 1604.90 ± 31.28 Bq kg−1 in granite and from 0.53 ± 0.12 to 18.61 ± 1.60 Bq kg−1, 0.51 ± 0.19 to 4.87 ± 2.13 Bq kg−1 and 3.21 ± 0.96 to 58.09 ± 6.40 Bq kg−1 in marble, respectively. Various radiological hazard indices like gamma index, internal and external hazard indices and annual effective dose equivalent were calculated and compared with the international limits. Our results show that some granite types may pose a radiation hazard. INTRODUCTION Background radiation is one of the main contributors to human radioactive exposure and is present in the environment from natural and artificial sources. The natural sources include cosmic rays and terrestrial radiation that originates from primordial radionuclides. The main primordial radionuclides include those in the natural decay series of 238U and 232Th in addition to 40K(1). These naturally occurring radioactive materials (NORM) and their radioactive daughters are gamma-ray emitters and, hence, pose an external radiation hazard while the internal hazard is due to radon gas and its progeny which are alpha-emitters(2). Primordial radionuclides are present in the soil, rocks, water and air(3, 4). The concentrations of these radionuclides vary in nature and depend on the local geological conditions(5). Moreover, different rocks mineralogical compositions imply diverse radionuclides concentrations, for example, igneous or magmatic rocks like granite are typically associated with relatively high levels of radioactivity due to the enhanced concentrations of uranium (average of 5 ppm) and thorium (average of 15 ppm)(6), whereas sedimentary rocks such as limestone usually have low radiation levels(7). On the other hand, radioactivity with intermediate levels was observed for metamorphic rocks like marble(4). Marble and granite are used as building and decorative materials in kitchens, halls, living rooms, mosques, churches, workplaces and as a cladding of houses facade due to their aesthetic features. Therefore, the measurement of primordial radionuclides in marble and granite is essential to assess the radiological hazards associated with the corresponding gamma-ray exposure of inhabitants(8). Several studies have been carried out in many countries and presented in the literature that investigate the natural radioactivity and the possible radiological risk of various building materials including marble and granite(6, 9–17). Nevertheless, to the best of our knowledge, only few research works had measured the natural radioactivity in marble and granite rocks used in Jordanian dwellings so far. Matiullah and Hussein(18) have measured the activity concentration of the primordial radionuclides and the associated hazard of different building materials including few samples of marble collected from local quarries. Moreover, as part of their work on Jordanian building materials, Sharaf and Hamideen(19) have also measured the radioactivity and the risk of some marble and granite samples. In this work, 226Ra, 232Th and 40K activity levels were measured in commercial samples of marble and granite, some of them are extracted from local quarries while the majority are imported from outside and recently spread in the market and became most commonly used in Jordanian buildings. The measured activity concentrations were used to calculate radium equivalent activity, gamma index, internal and external radiological hazard indices, absorbed dose and annual effective dose rate. MATERIALS AND METHODOLOGY Samples preparation A total of 11 granite samples and 8 marble samples were collected from local agencies that sell marble and granite extracted from specific locations in Jordan or imported from different countries around the world. It’s worth to say that due to the scarcity of granite rocks in Jordan, all granite used in construction activities are imported from outside. Collected samples were first crushed using a manual hammer tool then dried in an oven at a constant temperature of 104°C for 24 h for moisture removal and reaching a constant weight. The samples were further crushed using a Jaw crusher and a disk mill then pulverized using ball mill and sieved to 60 μm particle size. After that, samples were weighed and packed in plastic containers with 7.5 cm diameter and 1.5 cm height. Before gamma-ray spectrometry measurements, the containers were sealed and stored for 1 month for allowing radium and its daughters reaching secular equilibrium(20). Radioactivity measurement The activity concentrations of 226Ra, 232Th and 40K were estimated based on gamma-ray spectrometry radioanalytical technique using a co-axial type high purity germanium (HPGe) detector (ORTEC, GEM50-83 model) with energy resolution of 0.8 keV at 122 keV gamma line for 57Co and 1.9 keV at 1332.5 keV gamma line for 60Co and relative efficiency of 50%. The detector is shielded with lead for background radiation noise reduction and coupled to a multichannel analyzer with 16 k channels. The detector energy and efficiency calibrations were performed using a standard certified source. Each sample was counted for 60 000 s to reduce statistical counting error. The activity concentration of 226Ra was determined from the gamma peaks 295.2 and 351.9 keV (214Pb), 609.3 and 1764.5 keV (214Bi), while 232Th activity was calculated from the peaks 238.6 keV (212Pb), 583.1 keV (208TI), 911.1 keV (228Ac) and 1620 keV (212Bi). The activity of 40K was measured directly from its gamma-ray line at 1461 keV. The specific activity in Bq kg−1 of a radionuclide (i) in the sample using its photopeak at energy E was calculated using the following equation(21): AEi=NEiεE⋅t⋅γd⋅M (1) where NEi is the net peak area count at gamma energy line Ei after background count subtraction. εE is the counting efficiency of the detector at energy, E. t is the counting time (s). γd is the yield of gamma emission per decay of nuclide (i) at energy peak E. M is the mass of the measured sample in kg. The calculation of standard uncertainty and minimum detectable activity (MDA) is based on the work found in Ref.(22) Radiological health risk assessment Radium equivalent activity Since 226Ra, 232Th and 40K activity distributions are not uniform in rocks like marble and granite, radium equivalent activity (Req) is defined to compare the specific activity of different samples having different concentrations of these primordial radionuclides. Req is calculated using the following equation(23): Req=ARa+1.43ATh+0.077AK (2) where ARa, ATh and AK are the specific activities of 226Ra, 232Th and 40K in Bq kg−1, respectively. The equation of Req assumes that 37 Bq kg−1 of 226Ra, 25.9 Bq kg−1 of 232Th and 481 Bq kg−1 of 40K produce equal gamma dose rate. According to UNSCEAR(7) the maximum acceptable activity of Req is 370 Bq kg−1 that corresponds to an external dose of 1.5 mSv y−1. Gamma index For the purpose of identifying the safe construction materials from a radiological point of view, the European Commission proposed the gamma index (Iγ) to assess the hazard associated with gamma-ray dose originated from natural radioactivity of building rocks, Iγ is defined as follows(24, 25): Iγ=ARa150+ATh100+AK1500 (3) For superficial building materials like granite and marble Iγ < 2 corresponds to an annual effective dose excess of 0.3 mSv while 2≤Iγ≤6 will raise the annual effective dose with 1 mSv(25). Furthermore, a value of Iγ < 1 means a safe use as building materials without constraints. External and internal hazard indices External hazard index (Hex) is defined to estimate the radiation dose rate delivered externally from the used building materials, while the internal hazard index (Hin) is proposed to quantify the risk associated with internal exposure of respiratory system from radon and its short-lived daughters. These indices are calculated using the following relations(23): Hex=ARa370+ATh259+AK4810 (4) Hin=ARa185+ATh259+AK4810 (5) A value of less than unity for Hex and Hin assures an annual dose of 1.5 mGy that corresponds to the maximum permissible limit of Req (370 Bq/kg) and a negligible hazard of radon and its decay product on the respiratory tract(7). Annual effective dose equivalent The annual effective dose equivalent (AEDE) due to indoor gamma radiation exposure from the primordial radionuclides 226Ra, 232Th and 40K is calculated in mSv y−1 using the following formula(5): AEDE=D×8760(h/y)×0.8×0.7×10−6 (6) where 0.8 is the indoor occupancy factor and 0.7 Sv Gy−1 is the conversion coefficient from the absorbed dose rate in air (D) to the received effective dose(7). The absorbed dose rate can be estimated in the unit of nGy h−1 from the activity concentrations of 226Ra, 232Th and 40K and neglecting the contribution of other radionuclides using the following equation(4): D=0.462ARa+0.604ATh+0.042Ak (7) RESULTS AND DISCUSSION Activity concentrations of 226Ra, 232Th and 40K The specific activity levels of the primordial nuclides in the granite and marble samples are summarized in Tables 1 and 2. Table 1. The activity concentrations of 226Ra, 232Th and 40K of granite samples. Sample code Country of origin Activity of radionuclides (Bq kg−1) 226Ra 232Th 40K G1 Venezuela 152.07 ± 3.26 365.43 ± 4.84 1209.40 ± 37.51 G2 Egypt 113.97 ± 3.09 65.89 ± 3.14 1193.60 ± 28.79 G3 China 55.95 ± 1.86 79.43 ± 3.38 1272.20 ± 26.32 G4 Egypt 46.59 ± 2.03 109.54 ± 2.56 1255.70 ± 24.14 G5 India 8.57 ± 1.55 6.83 ± 1.25 121.25 ± 9.10 G6 India 18.79 ± 2.33 50.79 ± 2.82 1186.60 ± 25.82 G7 Saudi Arabia 27.91 ± 1.94 36.11 ± 2.96 1604.90 ± 31.28 G8 Saudi Arabia 31.96 ± 2.17 35.09 ± 2.62 1437.90 ± 31.52 G9 Brazil 110.63 ± 2.59 221.84 ± 3.59 1163.60 ± 32.63 G10 China 33.24 ± 2.22 62.52 ± 3.12 1316.00 ± 30.30 G11 Brazil 34.77 ± 1.70 217.14 ± 3.47 1448.90 ± 29.49 Min. 8.57 ± 1.55 6.83 ± 1.25 121.25 ± 9.10 Max. 152.07 ± 3.26 365.43 ± 4.84 1604.90 ± 31.28 Mean 57.68 ± 14.01 113.6942 ± 32.95 1200.914 ± 115.58 Worldwide average 50 50 500 Sample code Country of origin Activity of radionuclides (Bq kg−1) 226Ra 232Th 40K G1 Venezuela 152.07 ± 3.26 365.43 ± 4.84 1209.40 ± 37.51 G2 Egypt 113.97 ± 3.09 65.89 ± 3.14 1193.60 ± 28.79 G3 China 55.95 ± 1.86 79.43 ± 3.38 1272.20 ± 26.32 G4 Egypt 46.59 ± 2.03 109.54 ± 2.56 1255.70 ± 24.14 G5 India 8.57 ± 1.55 6.83 ± 1.25 121.25 ± 9.10 G6 India 18.79 ± 2.33 50.79 ± 2.82 1186.60 ± 25.82 G7 Saudi Arabia 27.91 ± 1.94 36.11 ± 2.96 1604.90 ± 31.28 G8 Saudi Arabia 31.96 ± 2.17 35.09 ± 2.62 1437.90 ± 31.52 G9 Brazil 110.63 ± 2.59 221.84 ± 3.59 1163.60 ± 32.63 G10 China 33.24 ± 2.22 62.52 ± 3.12 1316.00 ± 30.30 G11 Brazil 34.77 ± 1.70 217.14 ± 3.47 1448.90 ± 29.49 Min. 8.57 ± 1.55 6.83 ± 1.25 121.25 ± 9.10 Max. 152.07 ± 3.26 365.43 ± 4.84 1604.90 ± 31.28 Mean 57.68 ± 14.01 113.6942 ± 32.95 1200.914 ± 115.58 Worldwide average 50 50 500 Table 1. The activity concentrations of 226Ra, 232Th and 40K of granite samples. Sample code Country of origin Activity of radionuclides (Bq kg−1) 226Ra 232Th 40K G1 Venezuela 152.07 ± 3.26 365.43 ± 4.84 1209.40 ± 37.51 G2 Egypt 113.97 ± 3.09 65.89 ± 3.14 1193.60 ± 28.79 G3 China 55.95 ± 1.86 79.43 ± 3.38 1272.20 ± 26.32 G4 Egypt 46.59 ± 2.03 109.54 ± 2.56 1255.70 ± 24.14 G5 India 8.57 ± 1.55 6.83 ± 1.25 121.25 ± 9.10 G6 India 18.79 ± 2.33 50.79 ± 2.82 1186.60 ± 25.82 G7 Saudi Arabia 27.91 ± 1.94 36.11 ± 2.96 1604.90 ± 31.28 G8 Saudi Arabia 31.96 ± 2.17 35.09 ± 2.62 1437.90 ± 31.52 G9 Brazil 110.63 ± 2.59 221.84 ± 3.59 1163.60 ± 32.63 G10 China 33.24 ± 2.22 62.52 ± 3.12 1316.00 ± 30.30 G11 Brazil 34.77 ± 1.70 217.14 ± 3.47 1448.90 ± 29.49 Min. 8.57 ± 1.55 6.83 ± 1.25 121.25 ± 9.10 Max. 152.07 ± 3.26 365.43 ± 4.84 1604.90 ± 31.28 Mean 57.68 ± 14.01 113.6942 ± 32.95 1200.914 ± 115.58 Worldwide average 50 50 500 Sample code Country of origin Activity of radionuclides (Bq kg−1) 226Ra 232Th 40K G1 Venezuela 152.07 ± 3.26 365.43 ± 4.84 1209.40 ± 37.51 G2 Egypt 113.97 ± 3.09 65.89 ± 3.14 1193.60 ± 28.79 G3 China 55.95 ± 1.86 79.43 ± 3.38 1272.20 ± 26.32 G4 Egypt 46.59 ± 2.03 109.54 ± 2.56 1255.70 ± 24.14 G5 India 8.57 ± 1.55 6.83 ± 1.25 121.25 ± 9.10 G6 India 18.79 ± 2.33 50.79 ± 2.82 1186.60 ± 25.82 G7 Saudi Arabia 27.91 ± 1.94 36.11 ± 2.96 1604.90 ± 31.28 G8 Saudi Arabia 31.96 ± 2.17 35.09 ± 2.62 1437.90 ± 31.52 G9 Brazil 110.63 ± 2.59 221.84 ± 3.59 1163.60 ± 32.63 G10 China 33.24 ± 2.22 62.52 ± 3.12 1316.00 ± 30.30 G11 Brazil 34.77 ± 1.70 217.14 ± 3.47 1448.90 ± 29.49 Min. 8.57 ± 1.55 6.83 ± 1.25 121.25 ± 9.10 Max. 152.07 ± 3.26 365.43 ± 4.84 1604.90 ± 31.28 Mean 57.68 ± 14.01 113.6942 ± 32.95 1200.914 ± 115.58 Worldwide average 50 50 500 Table 2. The activity concentration of 226Ra, 232Th and 40K of marble samples. Sample Code Country of origin Activity of radionuclides (Bq kg−1) 226Ra 232Th 40K M1 Egypt 11.87 ± 1.50 0.69 ± 0.23 3.21 ± 0.96 M2 Portugal 0.84 ± 0.21 1.18 ± 0.75 58.09 ± 6.40 M3 Italy 6.91 ± 2.23 0.51 ± 0.19 3.32 ± 0.92 M4 Jordan 8.02 ± 2.17 0.75 ± 0.26 3.84 ± 0.88 M5 Jordan 18.61 ± 1.60 0.83 ± 0.36 17.53 ± 5.77 M6 Jordan 18.16 ± 4.42 4.87 ± 2.13 25.91 ± 10.27 M7 Turkey 7.20 ± 1.28 0.82 ± 0.33 34.47 ± 11.04 M8 India 0.53 ± 0.12 1.01 ± 0.64 3.82 ± 0.90 Min. 0.53 ± 0.12 0.51 ± 0.19 3.21 ± 0.96 Max. 18.61 ± 1.60 4.87 ± 2.13 58.09 ± 6.40 Mean 9.02 ± 2.43 1.33 ± 0.51 18.77 ± 7.04 Worldwide average 50 50 500 Sample Code Country of origin Activity of radionuclides (Bq kg−1) 226Ra 232Th 40K M1 Egypt 11.87 ± 1.50 0.69 ± 0.23 3.21 ± 0.96 M2 Portugal 0.84 ± 0.21 1.18 ± 0.75 58.09 ± 6.40 M3 Italy 6.91 ± 2.23 0.51 ± 0.19 3.32 ± 0.92 M4 Jordan 8.02 ± 2.17 0.75 ± 0.26 3.84 ± 0.88 M5 Jordan 18.61 ± 1.60 0.83 ± 0.36 17.53 ± 5.77 M6 Jordan 18.16 ± 4.42 4.87 ± 2.13 25.91 ± 10.27 M7 Turkey 7.20 ± 1.28 0.82 ± 0.33 34.47 ± 11.04 M8 India 0.53 ± 0.12 1.01 ± 0.64 3.82 ± 0.90 Min. 0.53 ± 0.12 0.51 ± 0.19 3.21 ± 0.96 Max. 18.61 ± 1.60 4.87 ± 2.13 58.09 ± 6.40 Mean 9.02 ± 2.43 1.33 ± 0.51 18.77 ± 7.04 Worldwide average 50 50 500 Table 2. The activity concentration of 226Ra, 232Th and 40K of marble samples. Sample Code Country of origin Activity of radionuclides (Bq kg−1) 226Ra 232Th 40K M1 Egypt 11.87 ± 1.50 0.69 ± 0.23 3.21 ± 0.96 M2 Portugal 0.84 ± 0.21 1.18 ± 0.75 58.09 ± 6.40 M3 Italy 6.91 ± 2.23 0.51 ± 0.19 3.32 ± 0.92 M4 Jordan 8.02 ± 2.17 0.75 ± 0.26 3.84 ± 0.88 M5 Jordan 18.61 ± 1.60 0.83 ± 0.36 17.53 ± 5.77 M6 Jordan 18.16 ± 4.42 4.87 ± 2.13 25.91 ± 10.27 M7 Turkey 7.20 ± 1.28 0.82 ± 0.33 34.47 ± 11.04 M8 India 0.53 ± 0.12 1.01 ± 0.64 3.82 ± 0.90 Min. 0.53 ± 0.12 0.51 ± 0.19 3.21 ± 0.96 Max. 18.61 ± 1.60 4.87 ± 2.13 58.09 ± 6.40 Mean 9.02 ± 2.43 1.33 ± 0.51 18.77 ± 7.04 Worldwide average 50 50 500 Sample Code Country of origin Activity of radionuclides (Bq kg−1) 226Ra 232Th 40K M1 Egypt 11.87 ± 1.50 0.69 ± 0.23 3.21 ± 0.96 M2 Portugal 0.84 ± 0.21 1.18 ± 0.75 58.09 ± 6.40 M3 Italy 6.91 ± 2.23 0.51 ± 0.19 3.32 ± 0.92 M4 Jordan 8.02 ± 2.17 0.75 ± 0.26 3.84 ± 0.88 M5 Jordan 18.61 ± 1.60 0.83 ± 0.36 17.53 ± 5.77 M6 Jordan 18.16 ± 4.42 4.87 ± 2.13 25.91 ± 10.27 M7 Turkey 7.20 ± 1.28 0.82 ± 0.33 34.47 ± 11.04 M8 India 0.53 ± 0.12 1.01 ± 0.64 3.82 ± 0.90 Min. 0.53 ± 0.12 0.51 ± 0.19 3.21 ± 0.96 Max. 18.61 ± 1.60 4.87 ± 2.13 58.09 ± 6.40 Mean 9.02 ± 2.43 1.33 ± 0.51 18.77 ± 7.04 Worldwide average 50 50 500 The activity concentration of 226Ra in granite varied from 8.57 ± 1.55 to 152.07 ± 3.26 Bq kg−1, while in marble it varied from 0.53 ± 0.12 to 18.61 ± 1.60 Bq kg−1. On the other hand, activity concentration of 232Th in granite ranged from 6.83 ± 1.25 to 365.43 ± 4.84 Bq kg−1, whereas in marble it ranged from 0.51 ± 0.19 to 4.87 ± 2.13 Bq kg−1. Furthermore, the activity concentration of 40K in granite varied from 121.25 ± 9.10 to 1604.90 ± 31.28 Bq kg−1, while it varied from 3.21 ± 0.96 to 58.09 ± 6.40 Bq kg−1 in marble. In all granite samples, 40K activity concentration is the highest among the three measured radionuclides due to the high contents of K-feldspar minerals in these plutonic or igneous rocks(26). The Saudi granite sample, G7, exhibits the highest 40K activity concentration reaching 1604.9 Bq kg−1, while the Venezuelans granite sample, G1, have the highest 226Ra activity concentration of 152.07 Bq kg−1. For the granite samples, G1 exhibits also the highest 232Th activity concentration reaching 365.43 Bq kg−1, which is more than seven times compared to the corresponding worldwide average of 50 Bq kg−1. The Brazilian granite samples G9 and G11 appear to present the second and third highest activity concentrations of 232Th reaching 221.84 and 217.14 Bq kg−1, respectively. These concentrations are almost four times more than the worldwide average activity concentration of 232Th. Also, these values are consistent with 232Th activity concentrations in Brazilian granite samples investigated in Ref. (13) that were found to be in the range of 17–906 Bq kg−1. Such high activity concentrations will have significant contribution in increasing the AEDE. On the other hand, the Indian granite sample G5 shows the lowest specific activity among all investigated granite samples with levels as of 8.57 Bq kg−1 for 226Ra, 6.83 Bq kg−1 for 232Th and 121.25 Bq kg−1 for 40K. The variation of the activity concentration of the three radionuclides in the granite and marble samples is due to the rock formation process and the geological and geochemical characteristics that vary according to the source origin. The activity of 226Ra, 232Th and 40K in all marble samples are significantly lower than the corresponding worldwide averages. On the other hand, as illustrated in Table 1, the concentration levels of these radionuclides in some of the granite types are higher than corresponding worldwide average values 50, 50 and 500 Bq kg−1, respectively(27). Therefore, the radiological hazard associated with using granite as a building material must be investigated. Moreover, the activity concentration of 226Ra, 232Th and 40K measured in this work for granite and marble used in Jordanian dwellings are comparable with those used in other countries as illustrated in Table 3. Table 3. Comparison of the activity concentration of 226Ra, 232Th and 40K in granite and marble used in Jordan with those used in other countries. Type Country 226Ra 232Th 40K References Granite Pakistan (Bunair) 42 58 1130 (12) Pakistan (Mansehra) 27 50 953 (11) Cyprus 74 140 1076 (13) Turkey 88 95 1055 (14) China 90 116 969 (15) Saudi Arabia (Riyadh) 55 43 678 (10) Egypt 137 82 1082 (6) European Union 78 89 1094 (28) Sudan (NUBA) 21 31 295 (16) Jordan 58 114 1201 Present study Marble Pakistan 8 3 26 (17) Turkey 23 15 149 (8) China 8–157 6–166 44–1353 (9) Saudi Arabia (Riyadh) 6 2 34 (10) Egypt 88 115 671 (3) Nigeria 2 1 7 (29) Jordan 9 1 19 Present study Type Country 226Ra 232Th 40K References Granite Pakistan (Bunair) 42 58 1130 (12) Pakistan (Mansehra) 27 50 953 (11) Cyprus 74 140 1076 (13) Turkey 88 95 1055 (14) China 90 116 969 (15) Saudi Arabia (Riyadh) 55 43 678 (10) Egypt 137 82 1082 (6) European Union 78 89 1094 (28) Sudan (NUBA) 21 31 295 (16) Jordan 58 114 1201 Present study Marble Pakistan 8 3 26 (17) Turkey 23 15 149 (8) China 8–157 6–166 44–1353 (9) Saudi Arabia (Riyadh) 6 2 34 (10) Egypt 88 115 671 (3) Nigeria 2 1 7 (29) Jordan 9 1 19 Present study Table 3. Comparison of the activity concentration of 226Ra, 232Th and 40K in granite and marble used in Jordan with those used in other countries. Type Country 226Ra 232Th 40K References Granite Pakistan (Bunair) 42 58 1130 (12) Pakistan (Mansehra) 27 50 953 (11) Cyprus 74 140 1076 (13) Turkey 88 95 1055 (14) China 90 116 969 (15) Saudi Arabia (Riyadh) 55 43 678 (10) Egypt 137 82 1082 (6) European Union 78 89 1094 (28) Sudan (NUBA) 21 31 295 (16) Jordan 58 114 1201 Present study Marble Pakistan 8 3 26 (17) Turkey 23 15 149 (8) China 8–157 6–166 44–1353 (9) Saudi Arabia (Riyadh) 6 2 34 (10) Egypt 88 115 671 (3) Nigeria 2 1 7 (29) Jordan 9 1 19 Present study Type Country 226Ra 232Th 40K References Granite Pakistan (Bunair) 42 58 1130 (12) Pakistan (Mansehra) 27 50 953 (11) Cyprus 74 140 1076 (13) Turkey 88 95 1055 (14) China 90 116 969 (15) Saudi Arabia (Riyadh) 55 43 678 (10) Egypt 137 82 1082 (6) European Union 78 89 1094 (28) Sudan (NUBA) 21 31 295 (16) Jordan 58 114 1201 Present study Marble Pakistan 8 3 26 (17) Turkey 23 15 149 (8) China 8–157 6–166 44–1353 (9) Saudi Arabia (Riyadh) 6 2 34 (10) Egypt 88 115 671 (3) Nigeria 2 1 7 (29) Jordan 9 1 19 Present study The correlations between the specific activities of the three radionuclides were investigated. However, strong evident correlations are not expected due to the varying sources of the samples studied in this work. Figure 1 shows a moderate and weak positive correlation between 226Ra and 232Th in granite and marble, respectively. Correlations between the radionuclides combinations 226Ra–40K and 232Th–40K are absent (and therefore are not shown here). The significant positive relation between 226Ra and 232Th in granite igneous rocks is due to the increase of both isotopes’ concentration in the liquid phase of magma during partial melting and fractional crystallization(30). Figure 1. View largeDownload slide Correlation between 226Ra and 232Th concentrations in granite (left) and marble (right). Figure 1. View largeDownload slide Correlation between 226Ra and 232Th concentrations in granite (left) and marble (right). Radiological hazard assessment The assessment of the radiological hazards associated with gamma emission in the investigated granite and marble samples was made by calculating radium equivalent activity (Reeq), gamma index (Iγ), external (Hex) and internal (Hint) hazard indices, absorbed dose rate (D) and AEDE. The levels of these indices are summarized in Table 4 for granite and Table 5 for marble. Table 4. Calculated radiological hazard parameters for granite. Sample code Reeq (Bq kg−1) Iγ Hex Hin D (nGy h−1) AEDE (mSv y−1) G1 767.76 5.47 2.07 2.48 341.77 1.68 G2 300.11 2.21 0.81 1.12 142.59 0.70 G3 267.50 2.02 0.72 0.87 127.26 0.62 G4 299.93 2.24 0.81 0.94 140.43 0.69 G5 27.67 0.21 0.07 0.09 13.18 0.06 G6 182.79 1.42 0.49 0.54 89.19 0.44 G7 203.13 1.62 0.55 0.62 102.11 0.50 G8 192.86 1.52 0.52 0.61 96.35 0.47 G9 517.46 3.73 1.39 1.70 233.97 1.15 G10 223.98 1.72 0.60 0.69 108.39 0.53 G11 456.85 3.37 1.23 1.33 208.07 1.02 Min. 27.67 0.21 0.07 0.09 13.18 0.06 Max. 767.76 5.47 2.07 2.48 341.77 1.68 Mean 312.73 2.32 0.84 1.00 145.76 0.72 Permissible limit or worldwide average 370.00 – <1 <1 55 1 Sample code Reeq (Bq kg−1) Iγ Hex Hin D (nGy h−1) AEDE (mSv y−1) G1 767.76 5.47 2.07 2.48 341.77 1.68 G2 300.11 2.21 0.81 1.12 142.59 0.70 G3 267.50 2.02 0.72 0.87 127.26 0.62 G4 299.93 2.24 0.81 0.94 140.43 0.69 G5 27.67 0.21 0.07 0.09 13.18 0.06 G6 182.79 1.42 0.49 0.54 89.19 0.44 G7 203.13 1.62 0.55 0.62 102.11 0.50 G8 192.86 1.52 0.52 0.61 96.35 0.47 G9 517.46 3.73 1.39 1.70 233.97 1.15 G10 223.98 1.72 0.60 0.69 108.39 0.53 G11 456.85 3.37 1.23 1.33 208.07 1.02 Min. 27.67 0.21 0.07 0.09 13.18 0.06 Max. 767.76 5.47 2.07 2.48 341.77 1.68 Mean 312.73 2.32 0.84 1.00 145.76 0.72 Permissible limit or worldwide average 370.00 – <1 <1 55 1 Table 4. Calculated radiological hazard parameters for granite. Sample code Reeq (Bq kg−1) Iγ Hex Hin D (nGy h−1) AEDE (mSv y−1) G1 767.76 5.47 2.07 2.48 341.77 1.68 G2 300.11 2.21 0.81 1.12 142.59 0.70 G3 267.50 2.02 0.72 0.87 127.26 0.62 G4 299.93 2.24 0.81 0.94 140.43 0.69 G5 27.67 0.21 0.07 0.09 13.18 0.06 G6 182.79 1.42 0.49 0.54 89.19 0.44 G7 203.13 1.62 0.55 0.62 102.11 0.50 G8 192.86 1.52 0.52 0.61 96.35 0.47 G9 517.46 3.73 1.39 1.70 233.97 1.15 G10 223.98 1.72 0.60 0.69 108.39 0.53 G11 456.85 3.37 1.23 1.33 208.07 1.02 Min. 27.67 0.21 0.07 0.09 13.18 0.06 Max. 767.76 5.47 2.07 2.48 341.77 1.68 Mean 312.73 2.32 0.84 1.00 145.76 0.72 Permissible limit or worldwide average 370.00 – <1 <1 55 1 Sample code Reeq (Bq kg−1) Iγ Hex Hin D (nGy h−1) AEDE (mSv y−1) G1 767.76 5.47 2.07 2.48 341.77 1.68 G2 300.11 2.21 0.81 1.12 142.59 0.70 G3 267.50 2.02 0.72 0.87 127.26 0.62 G4 299.93 2.24 0.81 0.94 140.43 0.69 G5 27.67 0.21 0.07 0.09 13.18 0.06 G6 182.79 1.42 0.49 0.54 89.19 0.44 G7 203.13 1.62 0.55 0.62 102.11 0.50 G8 192.86 1.52 0.52 0.61 96.35 0.47 G9 517.46 3.73 1.39 1.70 233.97 1.15 G10 223.98 1.72 0.60 0.69 108.39 0.53 G11 456.85 3.37 1.23 1.33 208.07 1.02 Min. 27.67 0.21 0.07 0.09 13.18 0.06 Max. 767.76 5.47 2.07 2.48 341.77 1.68 Mean 312.73 2.32 0.84 1.00 145.76 0.72 Permissible limit or worldwide average 370.00 – <1 <1 55 1 Table 5. Calculated radiological hazard parameters for marble. Sample code Reeq (Bq kg−1) Iγ Hex Hin D (nGy h−1) AEDE (mSv y−1) M1 13.10 0.09 0.04 0.07 6.03 0.03 M2 6.99 0.06 0.02 0.02 3.54 0.02 M3 7.89 0.05 0.02 0.04 3.64 0.02 M4 9.38 0.06 0.03 0.05 4.32 0.02 M5 21.15 0.14 0.06 0.11 9.83 0.05 M6 27.13 0.19 0.07 0.12 12.42 0.06 M7 11.03 0.08 0.03 0.05 5.27 0.03 M8 2.27 0.02 0.01 0.01 1.02 0.01 Min. 6.99 0.02 0.01 0.01 1.02 0.01 Max. 27.13 0.19 0.07 0.12 12.42 0.06 Mean 12.37 0.09 0.03 0.06 5.76 0.03 Permissible limit or worldwide average 370.00 – <1 <1 55 1 Sample code Reeq (Bq kg−1) Iγ Hex Hin D (nGy h−1) AEDE (mSv y−1) M1 13.10 0.09 0.04 0.07 6.03 0.03 M2 6.99 0.06 0.02 0.02 3.54 0.02 M3 7.89 0.05 0.02 0.04 3.64 0.02 M4 9.38 0.06 0.03 0.05 4.32 0.02 M5 21.15 0.14 0.06 0.11 9.83 0.05 M6 27.13 0.19 0.07 0.12 12.42 0.06 M7 11.03 0.08 0.03 0.05 5.27 0.03 M8 2.27 0.02 0.01 0.01 1.02 0.01 Min. 6.99 0.02 0.01 0.01 1.02 0.01 Max. 27.13 0.19 0.07 0.12 12.42 0.06 Mean 12.37 0.09 0.03 0.06 5.76 0.03 Permissible limit or worldwide average 370.00 – <1 <1 55 1 Table 5. Calculated radiological hazard parameters for marble. Sample code Reeq (Bq kg−1) Iγ Hex Hin D (nGy h−1) AEDE (mSv y−1) M1 13.10 0.09 0.04 0.07 6.03 0.03 M2 6.99 0.06 0.02 0.02 3.54 0.02 M3 7.89 0.05 0.02 0.04 3.64 0.02 M4 9.38 0.06 0.03 0.05 4.32 0.02 M5 21.15 0.14 0.06 0.11 9.83 0.05 M6 27.13 0.19 0.07 0.12 12.42 0.06 M7 11.03 0.08 0.03 0.05 5.27 0.03 M8 2.27 0.02 0.01 0.01 1.02 0.01 Min. 6.99 0.02 0.01 0.01 1.02 0.01 Max. 27.13 0.19 0.07 0.12 12.42 0.06 Mean 12.37 0.09 0.03 0.06 5.76 0.03 Permissible limit or worldwide average 370.00 – <1 <1 55 1 Sample code Reeq (Bq kg−1) Iγ Hex Hin D (nGy h−1) AEDE (mSv y−1) M1 13.10 0.09 0.04 0.07 6.03 0.03 M2 6.99 0.06 0.02 0.02 3.54 0.02 M3 7.89 0.05 0.02 0.04 3.64 0.02 M4 9.38 0.06 0.03 0.05 4.32 0.02 M5 21.15 0.14 0.06 0.11 9.83 0.05 M6 27.13 0.19 0.07 0.12 12.42 0.06 M7 11.03 0.08 0.03 0.05 5.27 0.03 M8 2.27 0.02 0.01 0.01 1.02 0.01 Min. 6.99 0.02 0.01 0.01 1.02 0.01 Max. 27.13 0.19 0.07 0.12 12.42 0.06 Mean 12.37 0.09 0.03 0.06 5.76 0.03 Permissible limit or worldwide average 370.00 – <1 <1 55 1 The calculated Raeq values in granite ranged between 27.67 Bq kg−1 for the Indian granite and 767.76 Bq kg−1 for the Venezuelan granite. It is observed that Req for the Venezuelan, and Brazilian granite is significantly higher than the maximum permitted level of 370 Bq kg−1, while for the other granite samples and all marble samples Req is lower than the recommended value. The correlations between the measured specific activity of 226Ra, 232Th and 40K in granite samples and Req were plotted to examine the contribution of each radionuclide on Req value as shown in Figure 2. The main contributor to Raeq is 232Th due to the significant correlation coefficient of 0.96. On the other hand, a moderate correlation with a coefficient of 0.69 between 226Ra and Req, and a least significant correlation with a coefficient of 0.11 between 40K and Reeq were found. Figure 2. View largeDownload slide Correlation between 226Ra, 232Th and 40K and Raeq activity concentrations in granite. Figure 2. View largeDownload slide Correlation between 226Ra, 232Th and 40K and Raeq activity concentrations in granite. The calculated values of Iγ in granite ranged from 0.21 to 5.47, where the Indian (G5 and G6), Saudi (G7 and G8) and Chinese (G10) samples’ values were less than the value of 2 that corresponds to the 0.3 mSv y−1; the exemption dose limit. On the other hand, the Venezuelan, Egyptian (G2 and G4), Chinese (G3) and Brazilian(G9 and G11) samples exhibit values between 2 and 6 that meets the upper dose control criteria of 1 mSv y−1 of superficial materials recommended by the European Commission of radiation protection, but the AEDE must not exceed 1 mSv y−1. Regarding marble, Iγ values varied from 0.02 to 0.19, which are all lower than the recommended Iγ value of 1 for unrestricted use for building purposes. The values of Hin and Hex for granite samples varied from 0.09 and 0.07 to 2.48 and 2.07, respectively. Once again, the Venezuelan and Brazilian samples exceeded the limit of unity with values of 2.07, 1.39 and 1.23 for Hex and 2.48, 1.70 and 1.33 for Hin, respectively. For all marble samples, Hex and Hin values are well below the limit of unity. The absorbed dose rate (D) from the investigated samples varied from 13.18 to 341.77 nGy h−1 for granite and from 1.02 to 12.42 nGy h−1 for marble. It is clear that the absorbed dose values for all marble samples and the Indian granite sample are below the worldwide average absorbed dose of 55 nGy h−1(6), while the dose from all other granite samples is above the world average. The contribution of 226Ra, 232Th and 40K to the absorbed dose was found consistent with that of Raeq as shown in Figure 2. For the AEDE, the minimum and maximum values in granite samples were 0.06 and 1.68 mSv y−1, respectively. The AEDE is expected to exceed the safe limit of 1 mSv y−1 when the Venezuelan or Brazilian granite is used. On the other hand, the AEDE levels for all marble samples varied from 0.01 to 0.06 mSv y−1 that are definitely within the safety limit of 1 mSv y−1. Therefore, the use of Venezuelan or Brazilian granite available in the Jordanian market could be accompanied with relatively high radiation hazard. CONCLUSION The activity concentrations of the primordial radionuclides; 226Ra, 232Th and 40K, were measured using HPGe gamma-ray detector in 11 granite and 8 marble samples, which are considered as the most commonly used decorative material in Jordanian buildings and widely utilized as the main constructing material for kitchens. Measurements showed that the highest concentrations of 226Ra and 232Th came from the Venezuelan granite, while the highest 40K concentration came from the Saudi granite. The lowest concentrations of the three radionuclides in granite samples were observed in the Indian granite sample. On the other hand, the radionuclides specific activities in all marble samples were insignificant. The estimated values of the investigated radiological hazard indices for all marble and most of granite samples fall within the international accepted limits that makes them safe with no significant radiation hazard except the Venezuelan G1 and Brazilian G9 and G11 granite samples that delivers an annual effective dose equivalent of 1.68, 1.15 and 1.02 mSv y−1, respectively, therefore, arising of radiation health hazard is expected when using these three granite samples. ACKNOWLEDGEMENTS The authors would like to thank Jordan Atomic Energy Commission (JAEC) for granting permission to use JAEC laboratory facilities. REFERENCES 1 Pehlivanovic , B. , Avdic , S. , Gazdic , I. and Osmanovic , A. Measurement of natural environmental radioactivity and estimation of population exposure in Bihac, Bosnia and Herzegovina . J. Radioanal. Nucl. Chem. 311 ( 3 ), 1909 – 1915 ( 2017 ). 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Radiation Protection Dosimetry – Oxford University Press
Published: Dec 1, 2018