Radiation Protection Dosimetry (2015), Vol. 164, No. 4, pp. 510 – 518 Advance Access publication 15 May 2015
doi:10.1093/rpd/ncv327
˘ RIGO ¨ Z GRANITOID, A RADIOLOGICAL SURVEY OF THE EG WESTERN ANATOLIA/TURKEY ¨ ztu¨rk1,*, G. Yaprak2, N. F. Çam1 and O. Candan3 B. Canbaz O 1 Department of Physics, Faculty of Sciences, Ege University, Bornova, Izmir 35100, Turkey 2 Institute of Nuclear Sciences, Ege University, Bornova, Izmir 35100, Turkey 3 Department of Geology, Faculty of Engineering, Dokuz Eylu¨l University, Buca, Izmir 35160, Turkey *Corresponding author: [email protected]
INTRODUCTION A general tectonic division consisting of Pontides to the north and Anatolite –Tauride Block to the south, which are separated by I˙zmir-Ankara-Erzincan suture zone representing the Late Cretaceous to Eocene closure of northern branch of the Neotethys, is suggested for Turkey(1, 2). Widespread Cenozoic magmatism following the Eocene continental collision between the Pontides (Sakarya zone; SZ) and the Anatolide –Tauride Block (ATB) covers large areas in Western Anatolia (Turkey). This magmatic activity is represented by voluminous granitoid intrusions and associated Eocene –Oligo-miocene volcanics(3). Eocene granitoid plutons including Karabiga, Kapıdag˘, Fıstıklı, Orhaneli, Topuk, Gu¨rgenyayla and Tepeldag˘ and related andesitic volcanics form the first products of this post-collisional magmatism(4). The other granitoid plutons (i.e. Kozak, Evciler, Çataldag˘, Kestanbol, Ilica-Samli, Eybek, Eg˘rigo¨z, Koyunoba) and associated widespread volcanic rocks in Western Anatolia were generated during the second magmatic episode, which occurred in the Oligocene to Early Miocene period(3, 5). Although Western Anatolia is one of the best natural laboratories to investigate the radiologic impact of the granitoid areas, as yet, quantitative information is less commonly available on the natural radioactivity levels of the granitic plutons, and a survey of the literature indicates that only a few studies have been carried out in northwestern Anatolia(6 – 8). Considering this background, a new comprehensive radiometric survey was conducted
during 2007–14 on the Karabiga, Kapıdag˘, Orhaneli, Evciler, Çataldag˘, Kestanbol and Eg˘rigo¨z granitic plutons throughout Western Anatolia. The main objective of this study is therefore to provide a detailed characterisation of the Eg˘rigo¨z pluton in terms of naturally occurring radionuclides and to assess the risk caused by exposure of the natural background radiation to the public as a part of the radiological survey of the granitoid areas in Western Anatolia. MATERIALS AND METHODS Geological setting The Eg˘rigo¨z granitoid with a composition ranging from granite to monzogranite-granodiorite is one of the largest granite intrusions (400 km2) found in Western Anatolia, as shown in Figure 1. Along the periphery, the pluton is enclosed by a fine-grained granitic chilled zone, which, inwards, passes gradually into coarser-grained rocks of holocrystalline to porphyritic texture characterised by K-feldspar phenocrystals up to 3 cm in length(9). The representative mineral assemblage is orthoclase (25– 35 %), plagioclase (30 –35 %), quartz (20 –25 %), biotite (5–10 %) and a minor amount of sanidine (1–5 %). Zircon and tourmaline (0.5 %) form the accessory minerals. Alteration minerals consist of chlorite and sericite(5). The Eg˘rigo¨z granitoid intrudes into pre-Tertiary basement units consisting of the Menderes Massif and Afyon Zone. Around the granites, a 10– 200-mwide contact metamorphic aureole, which is defined by the development of high-temperature minerals
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A radiological survey of the granitoid areas throughout Western Anatolia was conducted during 2007– 14. As a part of this radiological survey, this article presents results obtained from Eg˘rigo¨z pluton, which lies in the northeastern region of Western Anatolia. In the investigated area, the activity measurements of the natural gamma-emitting radionuclides (226Ra, 232Th and 40K) in the granitic rock samples and soils have been carried out by means of the NaI(Tl) gamma-ray spectrometry system. The activity concentrations of the relevant natural radionuclides in the granite samples appeared in the ranges as follows: 226Ra, 28–95 Bq kg21; 232Th, 50–122 Bq kg21 and 40K, 782– 1365 Bq kg21, while the typical ranges of the 226Ra, 232Th and 40K activities in the soil samples were found to be 7 –184, 11– 174 and 149–1622 Bq kg21, respectively. Based on the available data, the radiation hazard parameters associated with the surveyed rocks/soils are calculated. The corresponding absorbed dose rates in air from all those radionuclides were always much lower than 200 nGy h21 and did not exceed the typical range of worldwide average values noted in the UNSCEAR (2000) report. Furthermore, the data are also used for the mapping of the surface soil activity of natural radionuclides and the corresponding gamma dose rates of the surveyed area.
˘ RIGO ¨ Z GRANITOID A RADIOLOGICAL SURVEY OF THE EG
such as pyroxene, plagioclase and garnet, with minor amounts of sillimanite and staurolite, orthoclase, biotite, phlogopite, sphene, apatite, chlorite and quartz, is locally observed(10). Based on this mineral association and limited extension of this contact metamorphic zone, Albayrak suggests that the Eg˘rigo¨z pluton intruded into a relatively shallow crustal level(10). Sample treatments and gamma-spectrometric measurements Owing to geological consideration, 23 granitic rock samples representative of the Eg˘rigo¨z granitoid pluton were collected. In situ gamma measurements were carried out primarily for the screening of radiation levels. The measurements were also used as a guide for additional sampling in the surveyed area. Accordingly, a total of 54 rectangles of 3 km` 3 km in 500 km2 were set up in and around the surveyed
area, from each of which three sub-samples were randomly collected within a circle with a diameter of 100 m and bulked to form a single representative soil sample of 5 –6 kg. The location of each sample site was determined by a global positioning system, GPS, Garmin Model Map 60. Thus, the surface soil samples were systematically taken from 10 cm depths in all grid patterns from 54 rectangles during 2010–11 as shown in Figure 2. All samples were air dried for 2 –3 d and then oven dried at 1058C until they reach a constant weight. They were crushed to pass through a 2-mm sieve and were well homogenised and then filled in a 1-l Marinelli beaker. The containers were then sealed and stored for at least 30 d to allow for attainment of secular equilibrium between 226Ra, 222Rn and its decay products before gamma spectroscopy measurements were made. The period is also long enough to ensure equilibrium between 220Rn and its decay products (4d) in the 232Th series.
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Figure 1. Simplified geological map of Western Anatolia and location of the study area(9) (Gr: granite).
¨ ZTU ¨ RK ET AL. B. CANBAZ O
Gamma spectrometry measurements of 226Ra, Th and 40K activities in rock and soil samples were made using a Canberra 76` 76 mm, high-sensitivity NaI(Tl) detector connected to a PC-based 4 K multichannel analyser with the associated software. The detector was shielded by 100-mm-thick lead bricks internally lined with a 1.5-mm copper foil. In the present study, the activity of 226Ra was evaluated, in all cases, from the 1764.49 keV peak of 214Bi, while the 232Th activity was determined from the 2614.53 keV peak of 208Tl and the 40K activity was determined from the 40K peak at 1460.75 keV. A complete description of the method is provided by Yaprak and Aslani (11). The minimum detectable activity (MDA) for 226Ra, 232Th and 40K by this spectrometer was estimated to be 2, 2 and 5 Bq kg21, respectively, for a counting time of 10 000 s and a sample weight of 1650 g. Activity concentrations of the relevant radionuclides were systematically determined with one sigma error and expressed relatively to dry weight. Relative uncertainties of the activity concentrations at the 68 % confidence level were usually lower than 10 %. 232
RESULTS AND DISCUSSION Activity concentrations of natural radionuclides and radiation hazard parameters The soil and granitic rock samples systematically collected from the Eg˘rigo¨z granitoid were analysed for the natural radionuclides (226Ra, 232Th and 40K). Tables 1 and 2 list the calculated activity concentrations of the natural radionuclides and their absorbed dose rates (D), annual effective dose (AED), radium equivalent activity (Raeq) and the external hazard index (Hex) based on their measured activity concentrations in both of granites and soils, respectively. In the tables, the descriptive statistics are also shown to assess the variability and the distribution of each radionuclide and radiation hazard parameters. Additionally, the activity concentrations of natural radionuclides are presented in cumulative distribution plots in Figures 3 and 4 for the granites and soils, respectively. As given in Table 1, the activity of 226Ra varied in the range of 28 –95 Bq kg21 with a mean value of 55+4 Bq kg21, that of 232Th 50 –122 Bq kg21 with a
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Figure 2. Location and geological map of the study area, simplified from the MTA 1:500 000 scale geology map (http://www.mta.gov.tr/v2.0/daire-baskanliklari/jed/index.php?id=jeoloji).
˘ RIGO ¨ Z GRANITOID A RADIOLOGICAL SURVEY OF THE EG Table 1. Summary statistics for granitic rock samples in Eg˘rigo¨z granitoid. Radionuclide sctivity concentration 226 Ra (Bq kg21)
232 Th (Bq kg21)
40 K (Bq kg21)
D (nGy h21)
AED (mSv y21)
Raeq (Bq kg21)
Hex
23 55+4 18 53 28 41 54 71 95 0.561 20.336 0.132 Normal
23 76+4 19 74 50 60 71 85 122 1.020 0.374 0.166 Normal
23 1111+33 159 1099 782 1007 1115 1263 1365 20.266 20.413 0.200 Normal
23 118+4 24 116 91 101 114 136 158 0.464 20.937 0.198 Normal
23 145+5 24 143 112 124 139 167 193 0.464 20.937 0.198 Normal
23 250+9 43 246 191 214 239 292 337 0.497 20.928 0.200 Normal
23 0.67+0.02 0.12 0.66 0.52 0.58 0.65 0.79 0.91 0.497 20.928 0.200 Normal
Table 2. Summary statistics for soil samples in Eg˘rigo¨z granitoid. Radionuclide activity concentration 226
No. of samples Arithmetic mean+SEM Standard deviation (SD) Geometric mean Min. 25th percentile Median 75th percentile Max. Skewness Kurtosis Kolmogorov –Smirnov Test Sig. Frequency distribution
232
40
Radiological hazard indices
Ra (Bq kg21)
Th (Bq kg21)
K (Bq kg21)
D (nGy h21)
AED (mSv y21)
Raeq (Bq kg21)
Hex
54 46+4 25 41 7 32 44 54 184 3.051 15.496 0.000 Log-normal
54 66+4 33 58 11 44 60 81 174 0.991 1.429 0.191 Normal
54 859+40 294 795 149 661 830 1061 1622 20.143 0.157 0.200 Normal
54 97+6 35 90 16 74 92 119 189 0.161 0.226 0.200 Normal
54 119+6 43 110 20 91 113 146 232 0.161 0.226 0.200 Normal
54 207+10 76 190 34 159 199 255 405 0.222 0.198 0.200 Normal
54 0.56+0.03 0.21 0.51 0.09 0.43 0.54 0.69 1.09 0.222 0.199 0.200 Normal
mean value of 76+4 Bq kg21 and of 40K 782 –1365 Bq kg21 with a mean value of 1111+33 Bq kg21 in the granitic rock samples. Table 2 exhibits the activity concentrations for soils ranging from 7 to 184 Bq kg21 with a mean value of 46+4 Bq kg21 for 226Ra, from 11 to 174 Bq kg21 with a mean value of 66+4 Bq kg21 for 232Th and from 149 to 1622 Bq kg21 with a mean value of 859+40 for 40K. The bedrock lithology is known to be a key factor in the presence of natural radionuclides in the soils. Accordingly, this relationship can be observed by comparing the radiometric results in the tables. On the other hand, the cumulative plots of the activity concentrations of the natural radionuclides for the analysed samples
shown in Figures 3 and 4 indicate that a few samples exhibit high levels of natural radionuclides, while the remaining 75 % is relatively low when compared with the maximum values of the distributions. Furthermore, there is a wide zone around the median values of the activity concentrations of 226Ra, 232Th and 40K. This zone usually includes the activity range defined by the 25th and 75th percentiles. By the way, it may be useful to remember that the estimated overall mean concentrations of 226Ra, 232Th and 40K in soil in areas of normal radioactivity given in the recent UNSCEAR report(12) are 35, 30 and 400 Bq kg21, respectively, and typical ranges are 17–60 Bq kg21 for 226 Ra, 11–64 Bq kg21 for 232Th and 140–850 Bq kg21
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No. of samples Arithmetic mean+SEM Standard deviation (SD) Geometric mean Min. 25th percentile Median 75th percentile Max. Skewness Kurtosis Kolmogorov –Smirnov Test Sig. Frequency distribution
Radiological hazard indices
¨ ZTU ¨ RK ET AL. B. CANBAZ O
Figure 4. Cumulative distribution plots of the natural radionuclide activity concentrations of the soil samples.
for 40K. In the light of the aforementioned knowledge, the values obtained fall within the typical range of worldwide average values.
In the study, all dosimetric calculations were performed based on the guidance of the UNSCEAR (2000) report (13). Many granitic and volcanic areas
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Figure 3. Cumulative distribution plots of the natural radionuclide activity concentrations of the granitic rock samples.
˘ RIGO ¨ Z GRANITOID A RADIOLOGICAL SURVEY OF THE EG
in the range of 34– 405 Bq kg21 with a mean value of 207+10 Bq kg21, while the external hazard indices (Hex) were generally in the range of 0.09 –1.09 with a mean value of 0.56. As a result, the radiological indices of Raeq activity and Hex obtained for all samples did not exceed the permissible recommended or limit values. To sum up, the parent materials of soils, i.e. bedrock geology from which it formed, largely influence the natural radiation levels of the Eg˘rigo¨z granitoid pluton. The radiological maps Since maps are more practical to interpret the results of the radiological survey, the distributions of the natural radioactivity as well as the corresponding absorbed dose rates from outdoor terrestrial gamma radiation throughout the Eg˘rigo¨z pluton are mapped in detail, as illustrated in Figures 5–8. Therefore, in most locations, 226Ra activity concentrations in soils varied in the range of 33–89 Bqkg21, as shown in Figure 5. However, the higher levels of 226Ra ranged from 89 to 126 Bq kg21 and up to 184 Bq kg21 in only one location. Figure 6 illustrates the activity concentrations of 232Th from 45 to 84 Bq kg21 and up to 174 Bq kg21. From Figures 5 and 6, it can be concluded that the distribution of 232Th activity concentrations in the surveyed area exhibits similarity to that
Figure 5. The map of 226Ra activity distribution in the soils of Eg˘rigo¨z granitoid.
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associated with uranium- and thorium-bearing materials are known to have frequently higher radiation dose rates than the average global background level of 59 nGy h21 as given in the recent UNSCEAR reports(12, 13). However, the range of the national average for the dose rate in outdoor air in normal circumstances is up to 200 nGy h21. Correspondingly, applying a coefficient of 0.7 Sv Gy21 to convert the absorbed dose rate in air into the effective dose and assuming an outdoor occupancy factor of 0.2, the maximal annual effective dose is found to be about 245 mSv y21. As presented in Tables 1 and 2, the external gamma dose rate in air from natural radionuclides was always much lower than 200 nGy h21 in the granitoid area. Accordingly, the results show that the annual effective dose of all of the analysed samples is lower than this maximal dose as mentioned earlier. The gamma-ray radiation hazards due to the specified radionuclides were assessed by the radium equivalent activity and external radiation hazard indices(14, 15). In the granitic rock samples, the radium equivalent activity (Raeq) varied in the range of 191–337 Bq kg21 with a mean value of 250+9 Bq kg21, while the external hazard indices (Hex) were generally in the range of 0.52 –0.91 with a mean value of 0.67. In the case of soil samples, the radium equivalent activity appeared
¨ ZTU ¨ RK ET AL. B. CANBAZ O
Figure 7. The map of 40K activity distribution in the soils of Eg˘rigo¨z granitoid.
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Figure 6. The map of 232Th activity distribution in the soils of Eg˘rigo¨z granitoid.
˘ RIGO ¨ Z GRANITOID A RADIOLOGICAL SURVEY OF THE EG
of 226Ra, which evidently highlights the strong links between these radionuclide levels and their geological origin. The distribution of 40K in Figure 7 exhibited its highest concentrations up to 1622 Bq kg21 but generally ranged from 776 to 1144 Bq kg21 in the surveyed area. On the basis of the results, a radiological map given in Figure 8 was also set up to illustrate the distribution of the absorbed dose rates from outdoor terrestrial gamma radiation in the soils throughout the plutons. The mapped absorbed dose rates in air ranged from 16 to 119 nGy h21 and up to 189 nGy h21. Radiological mapping data for the region (maps) indicate that the distributions of natural radionuclides and gamma dose rates as well were relatively homogeneous and did not also indicate any particular special distribution tendency with respect to the underlying geology.
radiation to the public as a part of the radiological survey of the granitoid areas throughout Western Anatolia. Although the natural radionuclide contents and associated dose rates of the granitic rocks and soils are generally high, just like those of all granitic areas found in the majority of the literature, the radiological results obtained from the study fall within the typical range of worldwide average values noted in the UNSCEAR report (12). Since the natural background source forms the baseline upon which all other exposures are added, and it is a common level against which other exposures may be compared(12, 13), the baseline data are of great importance as reference information to assess any changes in the background radiation levels due to the various geochemical processes or any artificial influences.
CONCLUSION
ACKNOWLEDGEMENTS
The study deals with the natural radiation levels in soil and rock samples from the Eg˘rigo¨z granitoid pluton in Western Anatolia in order to assess the risk caused by exposure of the natural background
The authors would like to thank Dr. Fadıl I˙nceog˘lu and S¸enay S¸ahin for their cooperation during the fieldwork and their colleagues for precious help with the processes involved.
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Figure 8. The distribution of the absorbed dose rates from outdoor terrestrial gamma radiation in the soils of Eg˘rigo¨z granitoid.
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1. Okay, A. I., Satir, M., Maluski, H., Siyako, M., Monie, P., Metzger, R. and Akyu¨z, S. Paleo- and Neo-Tethyan events in northwest Turkey: geological and geochronological constraints. In: Tectonics of Asia. Yin, A. and Harrison, M. T. Eds. Cambridge University Press, pp. 420– 441 (1996). 2. Candan, O., Cetinkaplan, M., Oberhansli, R., Rimmele, G. and Akal, C. Alpine high-P/low-T metamorphism of the Afyon Zone and implications for the metamorphic evolution of Western Anatolia, Turkey. Lithos. 84(1–2), 102–124 (2005). 3. Altunkaynak, S¸., Dilek, Y., Genc¸, S¸. C., Sunal, G., Gertisser, R., Furnes, H., Foland, K. A. and Yang, Y. Spatial, temporal and geochemical evolution of Oligo – Miocene granitoid magmatism in western Anatolia, Turkey. Gondwana Res. 21, 961– 986 (2012). 4. Ko¨pru¨bas¸ı, N. and Aldanmaz, E. Geochemical constraints on the petrogenesis of Cenozoic I-type granitoids in Northwest Anatolia, Turkey: evidence for magma generation by lithospheric delamination in a post-collisional setting. Int. Geol. Rev. 46, 705–729 (2004), and references therein. 5. Akay, E. Geology and petrology of the Simav magmatic complex (NWAnatolia) and its comparison with the OligoMiocene granitoids in NWAnatolia: implications on tertiary tectonic evolution of the region. Int. J. Earth Sci. (Geol. Rundsch) 98, 1655–1675 (2009), and references therein. 6. Canbaz, B., Çam, N. F., Yaprak, G. and Candan, O. Natural radioactivity (226Ra, 232Th and 40K) and assessment of radiological hazards in the Kestanbol Granitoid, Turkey. Radiat. Prot. Dosim. 141(2), 192 – 198 (2010). ¨ ., Çıyrak, N., Yaprak, G. and Akal, C. 7. Karadeniz, O Terrestrial gamma exposure in the granodiorite area of
Bergama (Pergamon)– Kozak, Turkey. J. Radioanal. Nucl. Chem. 288, 919– 926 (2011). ¨ ztu¨rk, B., Çam, N. F. and Yaprak, G. Canbaz O Reference levels of natural radioactivity and 137Cs in and around the surface soils of Kestanbol pluton in Ezine region of Çanakkale province, Turkey. J. Environ. Sci. Health A Tox. Hazard. Subst. Environ. Eng. 48, 1522–1532 (2013). Haso¨zbek, A., Akay, E., Erdog˘an, B., Satır, M. and Siebel, W. Early Miocene granite formation by detachment tectonics or not? A case study from the northern Menderes Massif (Western Turkey). J. Geodynamics 50, 67– 80 (2010). Albayrak, O. Genetic investigation of polymetalic mineralizations along the northern and western border of the Eg˘rigo¨z Massif (Tavs¸anlı, Ku¨tahya). Definition of the geodynamic conditions of Eg˘rigo¨z Massif. MSc Thesis. Dokuz Eylul University, 90 pp. (in Turkish with English abstract) (2003). Yaprak, G. and Aslani, M. A. A. External dose-rates for natural gamma emitters in soils from an agricultural land in West Anatolia. J. Radioanal. Nucl. Chem. 283, 279– 287 (2010). United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and Effects of Ionizing Radiation. 2000 Report. United Nations (2000). United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and Effects of Ionizing Radiation. 1993 Report to the General Assembly, with Scientific Annexes. United Nations (1993). United Nations Scientific Committee on the Effects of Atomic Radiation. Sources, Effects and Risks of Ionizing Radiation. United Nations (1988). United Nations Scientific Committee on the Effects of Atomic Radiation. Ionizing Radiation: Sources and Biological Effects. United Nations (1982).
doi:10.1093/rpd/ncv327
˘ RIGO ¨ Z GRANITOID, A RADIOLOGICAL SURVEY OF THE EG WESTERN ANATOLIA/TURKEY ¨ ztu¨rk1,*, G. Yaprak2, N. F. Çam1 and O. Candan3 B. Canbaz O 1 Department of Physics, Faculty of Sciences, Ege University, Bornova, Izmir 35100, Turkey 2 Institute of Nuclear Sciences, Ege University, Bornova, Izmir 35100, Turkey 3 Department of Geology, Faculty of Engineering, Dokuz Eylu¨l University, Buca, Izmir 35160, Turkey *Corresponding author: [email protected]
INTRODUCTION A general tectonic division consisting of Pontides to the north and Anatolite –Tauride Block to the south, which are separated by I˙zmir-Ankara-Erzincan suture zone representing the Late Cretaceous to Eocene closure of northern branch of the Neotethys, is suggested for Turkey(1, 2). Widespread Cenozoic magmatism following the Eocene continental collision between the Pontides (Sakarya zone; SZ) and the Anatolide –Tauride Block (ATB) covers large areas in Western Anatolia (Turkey). This magmatic activity is represented by voluminous granitoid intrusions and associated Eocene –Oligo-miocene volcanics(3). Eocene granitoid plutons including Karabiga, Kapıdag˘, Fıstıklı, Orhaneli, Topuk, Gu¨rgenyayla and Tepeldag˘ and related andesitic volcanics form the first products of this post-collisional magmatism(4). The other granitoid plutons (i.e. Kozak, Evciler, Çataldag˘, Kestanbol, Ilica-Samli, Eybek, Eg˘rigo¨z, Koyunoba) and associated widespread volcanic rocks in Western Anatolia were generated during the second magmatic episode, which occurred in the Oligocene to Early Miocene period(3, 5). Although Western Anatolia is one of the best natural laboratories to investigate the radiologic impact of the granitoid areas, as yet, quantitative information is less commonly available on the natural radioactivity levels of the granitic plutons, and a survey of the literature indicates that only a few studies have been carried out in northwestern Anatolia(6 – 8). Considering this background, a new comprehensive radiometric survey was conducted
during 2007–14 on the Karabiga, Kapıdag˘, Orhaneli, Evciler, Çataldag˘, Kestanbol and Eg˘rigo¨z granitic plutons throughout Western Anatolia. The main objective of this study is therefore to provide a detailed characterisation of the Eg˘rigo¨z pluton in terms of naturally occurring radionuclides and to assess the risk caused by exposure of the natural background radiation to the public as a part of the radiological survey of the granitoid areas in Western Anatolia. MATERIALS AND METHODS Geological setting The Eg˘rigo¨z granitoid with a composition ranging from granite to monzogranite-granodiorite is one of the largest granite intrusions (400 km2) found in Western Anatolia, as shown in Figure 1. Along the periphery, the pluton is enclosed by a fine-grained granitic chilled zone, which, inwards, passes gradually into coarser-grained rocks of holocrystalline to porphyritic texture characterised by K-feldspar phenocrystals up to 3 cm in length(9). The representative mineral assemblage is orthoclase (25– 35 %), plagioclase (30 –35 %), quartz (20 –25 %), biotite (5–10 %) and a minor amount of sanidine (1–5 %). Zircon and tourmaline (0.5 %) form the accessory minerals. Alteration minerals consist of chlorite and sericite(5). The Eg˘rigo¨z granitoid intrudes into pre-Tertiary basement units consisting of the Menderes Massif and Afyon Zone. Around the granites, a 10– 200-mwide contact metamorphic aureole, which is defined by the development of high-temperature minerals
# The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at University of Otago on November 13, 2015
A radiological survey of the granitoid areas throughout Western Anatolia was conducted during 2007– 14. As a part of this radiological survey, this article presents results obtained from Eg˘rigo¨z pluton, which lies in the northeastern region of Western Anatolia. In the investigated area, the activity measurements of the natural gamma-emitting radionuclides (226Ra, 232Th and 40K) in the granitic rock samples and soils have been carried out by means of the NaI(Tl) gamma-ray spectrometry system. The activity concentrations of the relevant natural radionuclides in the granite samples appeared in the ranges as follows: 226Ra, 28–95 Bq kg21; 232Th, 50–122 Bq kg21 and 40K, 782– 1365 Bq kg21, while the typical ranges of the 226Ra, 232Th and 40K activities in the soil samples were found to be 7 –184, 11– 174 and 149–1622 Bq kg21, respectively. Based on the available data, the radiation hazard parameters associated with the surveyed rocks/soils are calculated. The corresponding absorbed dose rates in air from all those radionuclides were always much lower than 200 nGy h21 and did not exceed the typical range of worldwide average values noted in the UNSCEAR (2000) report. Furthermore, the data are also used for the mapping of the surface soil activity of natural radionuclides and the corresponding gamma dose rates of the surveyed area.
˘ RIGO ¨ Z GRANITOID A RADIOLOGICAL SURVEY OF THE EG
such as pyroxene, plagioclase and garnet, with minor amounts of sillimanite and staurolite, orthoclase, biotite, phlogopite, sphene, apatite, chlorite and quartz, is locally observed(10). Based on this mineral association and limited extension of this contact metamorphic zone, Albayrak suggests that the Eg˘rigo¨z pluton intruded into a relatively shallow crustal level(10). Sample treatments and gamma-spectrometric measurements Owing to geological consideration, 23 granitic rock samples representative of the Eg˘rigo¨z granitoid pluton were collected. In situ gamma measurements were carried out primarily for the screening of radiation levels. The measurements were also used as a guide for additional sampling in the surveyed area. Accordingly, a total of 54 rectangles of 3 km` 3 km in 500 km2 were set up in and around the surveyed
area, from each of which three sub-samples were randomly collected within a circle with a diameter of 100 m and bulked to form a single representative soil sample of 5 –6 kg. The location of each sample site was determined by a global positioning system, GPS, Garmin Model Map 60. Thus, the surface soil samples were systematically taken from 10 cm depths in all grid patterns from 54 rectangles during 2010–11 as shown in Figure 2. All samples were air dried for 2 –3 d and then oven dried at 1058C until they reach a constant weight. They were crushed to pass through a 2-mm sieve and were well homogenised and then filled in a 1-l Marinelli beaker. The containers were then sealed and stored for at least 30 d to allow for attainment of secular equilibrium between 226Ra, 222Rn and its decay products before gamma spectroscopy measurements were made. The period is also long enough to ensure equilibrium between 220Rn and its decay products (4d) in the 232Th series.
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Figure 1. Simplified geological map of Western Anatolia and location of the study area(9) (Gr: granite).
¨ ZTU ¨ RK ET AL. B. CANBAZ O
Gamma spectrometry measurements of 226Ra, Th and 40K activities in rock and soil samples were made using a Canberra 76` 76 mm, high-sensitivity NaI(Tl) detector connected to a PC-based 4 K multichannel analyser with the associated software. The detector was shielded by 100-mm-thick lead bricks internally lined with a 1.5-mm copper foil. In the present study, the activity of 226Ra was evaluated, in all cases, from the 1764.49 keV peak of 214Bi, while the 232Th activity was determined from the 2614.53 keV peak of 208Tl and the 40K activity was determined from the 40K peak at 1460.75 keV. A complete description of the method is provided by Yaprak and Aslani (11). The minimum detectable activity (MDA) for 226Ra, 232Th and 40K by this spectrometer was estimated to be 2, 2 and 5 Bq kg21, respectively, for a counting time of 10 000 s and a sample weight of 1650 g. Activity concentrations of the relevant radionuclides were systematically determined with one sigma error and expressed relatively to dry weight. Relative uncertainties of the activity concentrations at the 68 % confidence level were usually lower than 10 %. 232
RESULTS AND DISCUSSION Activity concentrations of natural radionuclides and radiation hazard parameters The soil and granitic rock samples systematically collected from the Eg˘rigo¨z granitoid were analysed for the natural radionuclides (226Ra, 232Th and 40K). Tables 1 and 2 list the calculated activity concentrations of the natural radionuclides and their absorbed dose rates (D), annual effective dose (AED), radium equivalent activity (Raeq) and the external hazard index (Hex) based on their measured activity concentrations in both of granites and soils, respectively. In the tables, the descriptive statistics are also shown to assess the variability and the distribution of each radionuclide and radiation hazard parameters. Additionally, the activity concentrations of natural radionuclides are presented in cumulative distribution plots in Figures 3 and 4 for the granites and soils, respectively. As given in Table 1, the activity of 226Ra varied in the range of 28 –95 Bq kg21 with a mean value of 55+4 Bq kg21, that of 232Th 50 –122 Bq kg21 with a
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Figure 2. Location and geological map of the study area, simplified from the MTA 1:500 000 scale geology map (http://www.mta.gov.tr/v2.0/daire-baskanliklari/jed/index.php?id=jeoloji).
˘ RIGO ¨ Z GRANITOID A RADIOLOGICAL SURVEY OF THE EG Table 1. Summary statistics for granitic rock samples in Eg˘rigo¨z granitoid. Radionuclide sctivity concentration 226 Ra (Bq kg21)
232 Th (Bq kg21)
40 K (Bq kg21)
D (nGy h21)
AED (mSv y21)
Raeq (Bq kg21)
Hex
23 55+4 18 53 28 41 54 71 95 0.561 20.336 0.132 Normal
23 76+4 19 74 50 60 71 85 122 1.020 0.374 0.166 Normal
23 1111+33 159 1099 782 1007 1115 1263 1365 20.266 20.413 0.200 Normal
23 118+4 24 116 91 101 114 136 158 0.464 20.937 0.198 Normal
23 145+5 24 143 112 124 139 167 193 0.464 20.937 0.198 Normal
23 250+9 43 246 191 214 239 292 337 0.497 20.928 0.200 Normal
23 0.67+0.02 0.12 0.66 0.52 0.58 0.65 0.79 0.91 0.497 20.928 0.200 Normal
Table 2. Summary statistics for soil samples in Eg˘rigo¨z granitoid. Radionuclide activity concentration 226
No. of samples Arithmetic mean+SEM Standard deviation (SD) Geometric mean Min. 25th percentile Median 75th percentile Max. Skewness Kurtosis Kolmogorov –Smirnov Test Sig. Frequency distribution
232
40
Radiological hazard indices
Ra (Bq kg21)
Th (Bq kg21)
K (Bq kg21)
D (nGy h21)
AED (mSv y21)
Raeq (Bq kg21)
Hex
54 46+4 25 41 7 32 44 54 184 3.051 15.496 0.000 Log-normal
54 66+4 33 58 11 44 60 81 174 0.991 1.429 0.191 Normal
54 859+40 294 795 149 661 830 1061 1622 20.143 0.157 0.200 Normal
54 97+6 35 90 16 74 92 119 189 0.161 0.226 0.200 Normal
54 119+6 43 110 20 91 113 146 232 0.161 0.226 0.200 Normal
54 207+10 76 190 34 159 199 255 405 0.222 0.198 0.200 Normal
54 0.56+0.03 0.21 0.51 0.09 0.43 0.54 0.69 1.09 0.222 0.199 0.200 Normal
mean value of 76+4 Bq kg21 and of 40K 782 –1365 Bq kg21 with a mean value of 1111+33 Bq kg21 in the granitic rock samples. Table 2 exhibits the activity concentrations for soils ranging from 7 to 184 Bq kg21 with a mean value of 46+4 Bq kg21 for 226Ra, from 11 to 174 Bq kg21 with a mean value of 66+4 Bq kg21 for 232Th and from 149 to 1622 Bq kg21 with a mean value of 859+40 for 40K. The bedrock lithology is known to be a key factor in the presence of natural radionuclides in the soils. Accordingly, this relationship can be observed by comparing the radiometric results in the tables. On the other hand, the cumulative plots of the activity concentrations of the natural radionuclides for the analysed samples
shown in Figures 3 and 4 indicate that a few samples exhibit high levels of natural radionuclides, while the remaining 75 % is relatively low when compared with the maximum values of the distributions. Furthermore, there is a wide zone around the median values of the activity concentrations of 226Ra, 232Th and 40K. This zone usually includes the activity range defined by the 25th and 75th percentiles. By the way, it may be useful to remember that the estimated overall mean concentrations of 226Ra, 232Th and 40K in soil in areas of normal radioactivity given in the recent UNSCEAR report(12) are 35, 30 and 400 Bq kg21, respectively, and typical ranges are 17–60 Bq kg21 for 226 Ra, 11–64 Bq kg21 for 232Th and 140–850 Bq kg21
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No. of samples Arithmetic mean+SEM Standard deviation (SD) Geometric mean Min. 25th percentile Median 75th percentile Max. Skewness Kurtosis Kolmogorov –Smirnov Test Sig. Frequency distribution
Radiological hazard indices
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Figure 4. Cumulative distribution plots of the natural radionuclide activity concentrations of the soil samples.
for 40K. In the light of the aforementioned knowledge, the values obtained fall within the typical range of worldwide average values.
In the study, all dosimetric calculations were performed based on the guidance of the UNSCEAR (2000) report (13). Many granitic and volcanic areas
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Figure 3. Cumulative distribution plots of the natural radionuclide activity concentrations of the granitic rock samples.
˘ RIGO ¨ Z GRANITOID A RADIOLOGICAL SURVEY OF THE EG
in the range of 34– 405 Bq kg21 with a mean value of 207+10 Bq kg21, while the external hazard indices (Hex) were generally in the range of 0.09 –1.09 with a mean value of 0.56. As a result, the radiological indices of Raeq activity and Hex obtained for all samples did not exceed the permissible recommended or limit values. To sum up, the parent materials of soils, i.e. bedrock geology from which it formed, largely influence the natural radiation levels of the Eg˘rigo¨z granitoid pluton. The radiological maps Since maps are more practical to interpret the results of the radiological survey, the distributions of the natural radioactivity as well as the corresponding absorbed dose rates from outdoor terrestrial gamma radiation throughout the Eg˘rigo¨z pluton are mapped in detail, as illustrated in Figures 5–8. Therefore, in most locations, 226Ra activity concentrations in soils varied in the range of 33–89 Bqkg21, as shown in Figure 5. However, the higher levels of 226Ra ranged from 89 to 126 Bq kg21 and up to 184 Bq kg21 in only one location. Figure 6 illustrates the activity concentrations of 232Th from 45 to 84 Bq kg21 and up to 174 Bq kg21. From Figures 5 and 6, it can be concluded that the distribution of 232Th activity concentrations in the surveyed area exhibits similarity to that
Figure 5. The map of 226Ra activity distribution in the soils of Eg˘rigo¨z granitoid.
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associated with uranium- and thorium-bearing materials are known to have frequently higher radiation dose rates than the average global background level of 59 nGy h21 as given in the recent UNSCEAR reports(12, 13). However, the range of the national average for the dose rate in outdoor air in normal circumstances is up to 200 nGy h21. Correspondingly, applying a coefficient of 0.7 Sv Gy21 to convert the absorbed dose rate in air into the effective dose and assuming an outdoor occupancy factor of 0.2, the maximal annual effective dose is found to be about 245 mSv y21. As presented in Tables 1 and 2, the external gamma dose rate in air from natural radionuclides was always much lower than 200 nGy h21 in the granitoid area. Accordingly, the results show that the annual effective dose of all of the analysed samples is lower than this maximal dose as mentioned earlier. The gamma-ray radiation hazards due to the specified radionuclides were assessed by the radium equivalent activity and external radiation hazard indices(14, 15). In the granitic rock samples, the radium equivalent activity (Raeq) varied in the range of 191–337 Bq kg21 with a mean value of 250+9 Bq kg21, while the external hazard indices (Hex) were generally in the range of 0.52 –0.91 with a mean value of 0.67. In the case of soil samples, the radium equivalent activity appeared
¨ ZTU ¨ RK ET AL. B. CANBAZ O
Figure 7. The map of 40K activity distribution in the soils of Eg˘rigo¨z granitoid.
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Figure 6. The map of 232Th activity distribution in the soils of Eg˘rigo¨z granitoid.
˘ RIGO ¨ Z GRANITOID A RADIOLOGICAL SURVEY OF THE EG
of 226Ra, which evidently highlights the strong links between these radionuclide levels and their geological origin. The distribution of 40K in Figure 7 exhibited its highest concentrations up to 1622 Bq kg21 but generally ranged from 776 to 1144 Bq kg21 in the surveyed area. On the basis of the results, a radiological map given in Figure 8 was also set up to illustrate the distribution of the absorbed dose rates from outdoor terrestrial gamma radiation in the soils throughout the plutons. The mapped absorbed dose rates in air ranged from 16 to 119 nGy h21 and up to 189 nGy h21. Radiological mapping data for the region (maps) indicate that the distributions of natural radionuclides and gamma dose rates as well were relatively homogeneous and did not also indicate any particular special distribution tendency with respect to the underlying geology.
radiation to the public as a part of the radiological survey of the granitoid areas throughout Western Anatolia. Although the natural radionuclide contents and associated dose rates of the granitic rocks and soils are generally high, just like those of all granitic areas found in the majority of the literature, the radiological results obtained from the study fall within the typical range of worldwide average values noted in the UNSCEAR report (12). Since the natural background source forms the baseline upon which all other exposures are added, and it is a common level against which other exposures may be compared(12, 13), the baseline data are of great importance as reference information to assess any changes in the background radiation levels due to the various geochemical processes or any artificial influences.
CONCLUSION
ACKNOWLEDGEMENTS
The study deals with the natural radiation levels in soil and rock samples from the Eg˘rigo¨z granitoid pluton in Western Anatolia in order to assess the risk caused by exposure of the natural background
The authors would like to thank Dr. Fadıl I˙nceog˘lu and S¸enay S¸ahin for their cooperation during the fieldwork and their colleagues for precious help with the processes involved.
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Figure 8. The distribution of the absorbed dose rates from outdoor terrestrial gamma radiation in the soils of Eg˘rigo¨z granitoid.
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