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Radon survey and soil gamma doses in primary schools of Batman, Turkey a
a
Nevzat Damla & Kamuran Aldemir a
Department of Physics, Batman University, Batman, Turkey Published online: 20 Jan 2014.
Click for updates To cite this article: Nevzat Damla & Kamuran Aldemir (2014) Radon survey and soil gamma doses in primary schools of Batman, Turkey, Isotopes in Environmental and Health Studies, 50:2, 226-234, DOI: 10.1080/10256016.2014.870170 To link to this article: http://dx.doi.org/10.1080/10256016.2014.870170
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Isotopes in Environmental and Health Studies, 2014 Vol. 50, No. 2, 226–234, http://dx.doi.org/10.1080/10256016.2014.870170
Radon survey and soil gamma doses in primary schools of Batman, Turkey Downloaded by [Chulalongkorn University] at 06:59 01 January 2015
Nevzat Damla∗ and Kamuran Aldemir Department of Physics, Batman University, Batman, Turkey (Received 29 April 2013; accepted 21 October 2013) A survey was conducted to evaluate levels of indoor radon and gamma doses in 42 primary schools located in Batman, southeastern Anatolia, Turkey. Indoor radon measurements were carried out using CR-39 solid-state nuclear track detector-based radon dosimeters. The overall mean annual 222 Rn activity in the surveyed area was found to be 49 Bq m−3 (equivalent to an annual effective dose of 0.25 mSv). However, in one of the districts (Besiri) the maximum radon value turned out to be 307 Bq m−3 . The estimated annual effective doses are less than the recommended action level (3–10 mSv). It is found that the radon concentration decreases with increasing floor number. The concentrations of natural and artificial radioisotopes were determined using gamma-ray spectroscopy for soil samples collected in close vicinity of the studied schools. The mean gamma activity concentrations in the soil samples were 31, 25, 329 and 12 Bq kg−1 for 226 Ra, 232 Th, 40 K and 137 Cs, respectively. The radiological parameters such as the absorbed dose rate in air and the annual effective dose equivalent were calculated. These radiological parameters were evaluated and compared with the internationally recommended values. Keywords: indoor radon; natural radioactivity; primary school students; radiation exposure; Turkey
1.
Introduction
Human beings who are exposed to ionising radiation from natural sources emitting cosmic rays and naturally occurring radioactive elements are under the threat of a continuous and inevitable risk, which is a feature of life on earth. Of these radioactive elements, radon and its decay products found in the Earth crust are the most important sources of natural radiation for human exposure [1]. Radon is a colourless and odourless radioactive gas and always has been a natural component of the air we breathe. Radon is produced by the radioactive decay of radium, a naturally occurring radioactive element that is found in trace amounts in all kinds of rocks, soil, underground water and building materials. Radon gets into buildings mainly through cracks in floors or gaps around pipes or cables. Radon and its products inhaled with aerosols irradiate the respiratory tract and cause an increasing risk of getting lung cancer [2–5]. Particularly, to be exposed to ionising radiation in indoor environments has a greater impact due to the contributions of 238 U, 232 Th and 40 K and the inhalation of radon gas which comes from building materials, water, energy sources and geological structures underneath the builtup area [6]. Because many people spend much of their time indoors, e.g. in dwellings, offices, ∗ Corresponding author. Emails: [email protected], [email protected] This article was originally published with errors. This version has been corrected. Please see Corrigendum (http://dx.doi.org/10.1080/10256016.2014.890338)
© 2014 Taylor & Francis
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schools, etc. these places are likely to be the most significant sources of ionising radiation exposure. For most school students and staff, the second largest contributor to their radiation exposure is likely to be their school. Since most of the people spend a lot of time (16%) indoors, the indoor radon and soil gamma doses in primary schools are crucial in the assessment of possible radiation exposure to the students and staffs. Therefore, the purpose of this study is to determine the indoor radon concentration levels in primary schools, and natural (226 Ra, 232 Th and 40 K) and artificial (137 Cs) radioactivity concentrations in soils in the close vicinity of these schools; and to calculate the annual effective dose the population is exposed to due to the presence of terrestrial gamma radiation in primary schools of Batman Province. The data presented in this study might be useful as baseline data for future estimations of a population’s exposure.
2.
Materials and methods
2.1. Sampling area Batman Province is situated in the southeastern region of Turkey between 41◦ 10 and 41◦ 40 N latitude and between 38◦ 40 and 37◦ 50 E longitude, with a population of over 500,000. The population steadily grows as a result of the province’s natural, historical and cultural wealth and rapid industrial and economic development. The region spans an area of 4654 km2 and is divided into six districts (Figure 1). The province of Batman is important because of its oil reserves and its production, and is one of the main crude oil production centres of Turkey. 2.2. Measurements of indoor radon concentrations Indoor radon measurements were carried out in 42 primary schools in Batman Province, taking into account school population and the distribution of the schools in the study region (Table 1).
Sason Kozluk
Batman River
Center District
Besiri City Center Tigris River Hasankeyf Gercüs 0
Figure 1. The map of the sampling sites in Batman Province [10].
25km
228
N. Damla and K. Aldemir Table 1.
Distribution of indoor radon concentration measurements.
Locations
Number of schools
Number of detectors placed
Number of students
17 5 4 4 8 4 42
51 15 12 12 24 12 126
30,195 3298 870 1575 2735 1199 39,872
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City Center Kozluk Gercüs Sason Besiri Hasankeyf Total
Radon measurements were performed using the solid-state nuclear track detector (SSNTD) passive technique, which is the most reliable technique for the integrated and long-term monitoring of radon concentrations. The measurements were carried out for 3 months from March to May 2012. Dosimeters were installed at head height in three classrooms or the principal room of each school on different floors, if possible. Sampling was done (using school register) randomly depending on principals who permitted us to carry out the study in his or her school. CR-39 plastic track detectors purchased from the Radoys Co. Ltd., Budapest, Hungary, were used in this survey. The CR-39 detectors were designed as 20 × 20 × 1 mm3 in size and placed in a plastic container of 4 mm in height, which allows radon to diffuse. The container was closed with a plastic cap in order to avoid dust deposition on the detector foils. Evaluations of the detectors were carried out in the laboratory under defined etching conditions in a 30% NaOH at 70◦ C for 17 h. The films were then washed with distilled water and dried in a dust-free chamber. At this stage, the tracks left by alpha particles on the film exposed to radon gas were visible and counted with a microscope (× 200). Calibration measurement of SSNTD was done using a calibration chamber containing a 226 Ra source with a concentration of 3.2 kBq m−3 . The 222 Rn concentrations were determined by using a calibration factor of 7.23 kBq track−1 h−1 and subtracting the background track density from each pit track density on the films. Subsequently, the tracks on the etched film were counted manually with an optical microscope (×200). The detailed information has been described earlier [7]. 2.3. Radioactivity measurements in soil samples 2.3.1. Sampling and sample preparation The soil samples were collected in close vicinity of each school in which the radon measurements were carried out. The sampling sites were selected from nearly ground level, non-agricultural lands away from trees and buildings. After clearing the ground surface of stones, pebbles, vegetation and roots, 1.5 kg of the material from the first 10 cm of topsoil was placed in labelled polythene bags. The samples were ground, homogenised and sieved to about 100 mesh by a crushing machine. The samples were then dried at 110◦ C for 24 h to ensure that moisture was completely removed. About 160 g of each sample was sealed in gas-tight, radon impermeable, plastic cylindrical polyethylene containers. Then, the containers were completely sealed for 4 weeks to reach a secular equilibrium among the uranium and thorium and their decay products. 2.3.2. Gamma-ray measurement The gamma radiation was measured using a coaxial high purity germanium detector (Canberra, GC 1519 model). The relative efficiency of the detector is 15%, and it has a resolution of 1.9 keV at
229
the 1332.5 keV gamma ray of 60 Co. The detector was shielded in a 10 cm thick lead well internally lined with 2 mm Cu foils. The detector output was connected to a spectroscopy amplifier (Canberra, Model 2025) [8]. The spectrum analysis and nuclide identification were performed via Genie 2000 software from Canberra. A performance test using the certified reference sample (IAEA375) was carried out to check the efficiency and energy calibration of the system. The activities of the standard were in accordance with their certified values within error margins not exceeding 10 %. The quality assurance of the measurements was conducted by periodical efficiency and energy calibrations and repeating sample measurements. The counting time for each sample was selected to be 50,000 s to obtain gamma spectra with good statistics. To determine the background distribution in the environment around the detector, an empty container was counted in the same manner and in the same geometry as the samples. The background spectra were used to correct the net peak area of the gamma rays of the measured isotopes [9,10]. The gamma transition energies of 351.9 keV of 214 Pb and 609.3 keV of 214 Bi were used to determine the concentrations for the 226 Ra. The gamma transition energies of 583.1 keV of 208 Tl and 911.2 keV of 228Ac were used to determine the concentrations for the 232 Th series. The activity concentrations of 40 K and 137 Cs were determined directly using their 1460.8 and 661.7 keV gamma-ray lines, respectively. The activity of each sample was determined using the total net counts under the selected photo peak after subtracting appropriate background counts and applying appropriate factors for photo efficiency, branching intensity of radionuclides and weight of the samples.
3.
Results and discussions
The frequency distribution of radon concentrations found in this survey for all schools in Batman Province is plotted in Figure 2. The frequency distribution looks like a log-normal pattern. Radon concentrations varied from 14 to 307 Bq m−3 , with the arithmetical mean, geometric mean, median, arithmetic standard deviation and geometric standard deviation of 49, 42, 42, 41 and 1.7 Bq m−3 , respectively. The difference in the values of indoor activity can be attributed to the difference in ventilation rates, the nature and type of school building materials used in construction, the variations of the radioactivity levels in the soil underneath and particularly the geological considerations. The results of indoor radon concentration for each location are also summarised in 50
40 Frequency
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Isotopes in Environmental and Health Studies
30
20
10
40
Figure 2.
80 120 160 200 240 280 Radon concentration (Bq.m–3)
Frequency distributions of radon concentrations in the school buildings of Batman Province.
230 Table 2.
N. Damla and K. Aldemir Indoor radon concentrations in Bq m−3 for each location. City Center
Kozluk
Gercüs
Sason
Besiri
Hasankeyf
46 43 42 17 24 109
21 20 21 4 16 28
53 52 56 9 35 67
25 24 23 7 14 35
82 62 53 78 28 307
56 53 47 19 37 87
Arithmetic mean Geometric mean Median Standard deviation Minimum Maximum
Radon concentration (Bq.m–3)
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320 280 240 200 160 120 80 40 0 Ground floor Figure 3.
First floor
Second floor
Radon concentrations according to the floor number.
Table 2. Whilst the highest indoor radon concentrations were determined in the district Besiri, the district Kozluk showed the lowest indoor radon concentrations. Fifty-four percent of these values are higher than the mean values reported for the buildings worldwide of 40 Bq m−3 [1], but in almost all the buildings, except for one school, radon concentration is less than the lower limit of the range of the action level of 200–600 Bq m−3 , recommended by the International Commission on Radiological Protection [11]. The distributions of radon concentration according to the floor number are depicted in Figure 3. The radon concentration measured ranged from 14 to 307 Bq m−3 (for ground floor), from 16 to 243 Bq m−3 (for first floor), and from 18 to 51 Bq m−3 (for second floor). The radon concentrations decrease with increasing floor numbers. From these values, it can be inferred that besides soil permeability, humidity, temperature and climatic conditions, ventilation can be better for upper floors than that of ground floors since upper floors were found out to have better air circulation. Among the schools studied, the highest radon concentration was detected in the district of Besiri. In order to reduce the indoor radon concentration in this school, especially on the ground floors, some ventilation systems should be implemented. The means of 222 Rn concentrations observed in this study were lower than those for the other countries, except for Nigeria and Kuwait (Table 3). The annual effective dose from radon (222 Rn) exposure can be estimated by means of the following formula [1]: AEDRn = CRn · F · O · DCF, (1) where AEDRn is the annual effective dose (mSv), CRn is the radon activity concentration (Bq m−3 ), F is the equilibrium factor between radon and its decay products, which is assumed to be 0.4 for the buildings [1], O is the occupancy rate (1400 h y−1 ) of 16 % for students and staff, and dose
Isotopes in Environmental and Health Studies Table 3.
Comparison of indoor radon concentrations in schools from different countries.
Province
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231
Belgium Croatia (Osijek) Jordan (Amman) Italy (Friuli Venezia Giulia) Italy (Neapolitan area) Ireland Slovenia Kuwait (Kuwait city) Nigeria (Oke-Ogun) Greece Spain (Tenerife Island) Turkey
Reference
Arithmetic mean (Bq m−3 )
[12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] Present study
120 93 77 100 144 93 170 17 45 149 130 49
Table 4. The mean values of the AEDRn for each floor and district. Locations
AEDRn (mSv)
District
City Center Kozluk Gercüs Sason Besiri Hasankeyf
0.23 0.10 0.27 0.12 0.41 0.28
Floor
Ground First Second
0.28 0.23 0.17
General
Minimum Maximum Mean
0.07 1.55 0.25
Table 5. The radioactivity concentrations, ADRA and AEDE for soil samples.
Locations City Center Kozluk Gercüs Sason Besiri Hasankeyf Mean ± SD
226 Ra (Bq kg−1 )
232 Th (Bq kg−1 )
40 K (Bq kg−1 )
137 Cs (Bq kg−1 )
ADRA (nGy h−1 )
AEDE (mSv)
31 ± 7 23 ± 6 25 ± 6 24 ± 4 42 ± 13 27 ± 4 31 ± 10
23 ± 9 22 ± 6 18 ± 3 27 ± 9 37 ± 11 22 ± 3 25 ± 10
215 ± 84 366 ± 96 398 ± 67 400 ± 77 412 ± 102 361 ± 56 329 ± 126
10 ± 8 12 ± 4 16 ± 7 10 ± 2 11 ± 5 6±2 12 ± 6
37 ± 8 43 ± 7 39 ± 3 44 ± 8 59 ± 14 41 ± 6 43 ± 12
0.045 ± 0.010 0.053 ± 0.007 0.048 ± 0.012 0.054 ± 0.010 0.072 ± 0.017 0.050 ± 0.007 0.053 ± 0.014
conversion factor (DCF) is the dose conversion factor which converts radon concentration into the effective dose 9 mSv (Bq h m−3 )−1 . The calculated values of the annual effective doses due to inhalation of 222 Rn are presented in Table 4. In all areas surveyed, the estimated annual effective dose is less than the lower limit of the range of the recommended action level (3–10 mSv). The activities of the natural (226 Ra, 232 Th and 40 K) and artificial (137 Cs) radionuclides are presented in Table 5. The highest mean activity concentration of 226 Ra, 232 Th, 40 K was determined in the Besiri district. The arithmetic mean activity concentrations of the artificial radionuclide
232
N. Damla and K. Aldemir
50
226Ra
(Bq.kg–1)
40
30
20
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10
0 0
10
20
30
40 222Rn
50
60
70
80
90
(Bq.m–3)
Figure 4. Correlation between mean values of the concentrations of 226 Ra in soil samples and indoor radon for the six districts under study.
Cs is found to be minimum in the district of Hasankeyf (6 Bq kg−1 ) and is maximum in Gercüs (16 Bq kg−1 ). As radon is a daughter product of 226 Ra, one can expect high indoor radon concentrations near the schools where high 226 Ra activity concentrations were measured in the soil. Therefore, we compared arithmetic mean indoor radon concentration results with mean 226 Ra activity concentration results in soils according to district (Figure 4). There is a strong correlation between indoor radon and 226 Ra in soil (R = 0.85). The total absorbed dose rate in air (ADRA) depends on the concentrations of these radionuclides in the soil. The ADRA in nGy h−1 at 1 m above ground level was computed by means of the following equation [1]: 137
ADRA = 0.462ARa + 0.604ATh + 0.0417AK ,
(2)
where ARa , ATh and AK are the activity concentrations of 226 Ra, 232 Th and 40 K (Bq kg−1 ), respectively. The ADRA calculated from the measured activities in the samples is given in Table 5. The mean ADRA was found 43 nGy h−1 (min 37 nGy h−1 in the City Center and max 49 nGy h−1 in the Besiri district), which is lower than the world mean of 60 nGy h−1 [1]. To estimate the annual effective dose equivalent (AEDE), the conversion coefficient (0.7 Sv Gy−1 ) from the absorbed dose in air to effective dose, and the outdoor occupancy factor (0.2) proposed by United Nations Scientific Committee on the Effects of Atomic Radiation [1] were used. Therefore, the effective dose rate equivalent outdoors in units of mSv per year was computed by means of the following formula: AEDE = ADRA · T · F,
(3)
where ADRA is the calculated dose rate (in nGy h−1 ), T is the outdoor occupancy time (0.2 × 24 h × 365.25 d = 1753.2 h y−1 ), and F is the conversion factor (0.7 × 10−6 Sv Gy−1 ). The computed AEDE of the measured activities in the samples is presented in Table 5. The computed value of the AEDE in the samples varies from 0.032 to 0.112 mSv with an arithmetic mean of 0.053 mSv. This value is lower than the world mean of 0.07 mSv [1].
Isotopes in Environmental and Health Studies
4.
233
Conclusions
The present study shows that both indoor radon and external gamma rays received by students and staff are under the world mean values. Therefore, as a conclusion, it can be said that no action is necessary to be taken in the schools under consideration except for Besiri district where maximum values turned out to be 307 Bq m−3 . The results of the present study will provide useful baseline data for adopting safety measures and dealing effectively with radiation emergencies.
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Acknowledgements The authors would like to thank the National Education Deputy Manager of the city; and the cooperation of the school directors and crews is also appreciated. And also, the authors kindly thank the experienced English lecturer of Batman University, Ihsan Pilatin, for editing the paper thoroughly.
Funding This work was done with the support of the Batman University Research Fund under Project No(s). [BTUBAP-FED-5].
References [1] UNSCEAR. Sources and effects of ionizing radiation. NewYork: United Nations Scientific Committee on the Effects of Atomic Radiation; 2000. [2] Çevik U, Çelik A, Çelik N, Ozkalayci F, Akbulut S. Assessment of radiological levels at schools in Trabzon, Turkey. Indoor Built Environ. 2013;22:376–383. [3] Pershagen G, Akerblom G, Axelson O, Clavensjo B, Damber L, Desai G. Residential radon exposure and lung cancer in Sweden. New Engl J Med. 1994;330:159–164. [4] Lubin J, Boice J. Lung cancer risk from residential radon: a meta-analysis of eight epidemiological studies. J Natl Cancer Inst. 1997;89:49–57. [5] Morrison HI, Villeneuve PJ, Lubin JH. Schaubel DE Radon-progeny exposure and lung cancer risk in a cohort of Newfoundland fluorspar miners. Radiat Res. 1998;150:58–65. [6] Rahman SU, Rafique M, Matiullah, Anwar J. Radon measurement studies in workplace buildings of the Rawalpindi region and Islamabad capital area, Pakistan. Build Environ. 2010;45:421–426. [7] Can B. Kilis ilindeki evlerde radon gazı ölçümü [Radon gas measurement in dwellings in Kilis province. Master thesis]. Kilis: Kilis 7 Aralik University, Science Institute; 2011. Turkish. [8] Cevik U, Damla N, Koz B, Kaya S. Radiological characterization around Afsin Elbistan coal-fired power plant in Turkey. Energy Fuels. 2008;22:428–432. [9] Damla N, Cevik U, Kobya AI, Celik A, Van Grieken R, Kobya Y. Radiological characterization of gas concrete used in building materials in Turkey. J Hazard Mat. 2009;168:681–687. [10] Damla N, Cevik U, Kobya AI, Ataksor B, Isık U. Assessment of environmental radioactivity for Batman, Turkey. Environ Monit Assess. 2010;160:401–412. [11] ICRP. 1990 recommendations of the International Commission on Radiological Protection. Ann. ICRP 21 (1–3), ICRP publication 60. International Commission on Radiological Protection; 1991. [12] Poffin A, Uyttenhove J, Drouget B, Tounder F. The radon problem in schools and public buildings in Belgium. Radiat Prot Dosim. 1992;45:499–501. [13] Plannic J, Smit G, Faj Z, Suveliak B, Vukovic B, Radolic V. Radon in schools and dwellings of Osijek. J Radiaoanal Nucl Chem. 1995;19:45–51. [14] Kullab MK, Al-Bataina BA, Ismail AM, Abumurad KM, Ghaith AA. Study of radon-222 concentration levels inside kindergartens in Amman. Radiat Meas. 1997;28:699–702. [15] Giovani C, Cappelletto C, Garavaglia M, Villalta R. Radon concentration survey in schools of Friuli-Venezia Giulia region, north-east Italy. In: Rodi GR, editor. Proceedings 7th International Symposium Natural Radiation Environment (NRE VII); 2002 May 20–24. p. 520–527. [16] Veneso G, De Cicco F, Flores B, Gialanella L, Piugliese M, Roca V, Sabbarese C. Radon concentrations in schools of the Neapolitan area. Radiat Meas. 2009;44:127–130. [17] Synnott H, Hanley O, Fenton D, Colgan PA. Radon in Irish schools: the results of a national survey. J Radiol Prot. 2006;26:85–96. [18] Vaupotic J, Sikovec M, Kobal I. Systematic indoor radon and gamma-ray measurements in Slovenian schools. Health Phys. 2000;78:559–562. [19] Maged AF. Radon concentrations in elementary schools in Kuwait. Health Phys. 2006;90:258–262.
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[20] Obed RI, Ademola AK, Vascotto M, Giannini G. Radon measurements by nuclear track detectors in secondary schools in Oke-Ogun region, Nigeria. J Environ Radioactiv. 2011;102:1012–1017. [21] Clouvas A, Xanthos S, Takoudis G. Indoor radon levels in Greek schools. J Environ Radioactiv. 2011;102:881–885. [22] Hernandez F, Gonzalez-Manrique S, Karlsson L, Hernandez-Armas J, Aparicio A. Counting radon tracks in makrofol detectors with the ‘image reduction and analysis facility’ (IRAF) software package. Radiat Meas. 2007;42:496–504.
Isotopes in Environmental and Health Studies Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gieh20
Radon survey and soil gamma doses in primary schools of Batman, Turkey a
a
Nevzat Damla & Kamuran Aldemir a
Department of Physics, Batman University, Batman, Turkey Published online: 20 Jan 2014.
Click for updates To cite this article: Nevzat Damla & Kamuran Aldemir (2014) Radon survey and soil gamma doses in primary schools of Batman, Turkey, Isotopes in Environmental and Health Studies, 50:2, 226-234, DOI: 10.1080/10256016.2014.870170 To link to this article: http://dx.doi.org/10.1080/10256016.2014.870170
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
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Isotopes in Environmental and Health Studies, 2014 Vol. 50, No. 2, 226–234, http://dx.doi.org/10.1080/10256016.2014.870170
Radon survey and soil gamma doses in primary schools of Batman, Turkey Downloaded by [Chulalongkorn University] at 06:59 01 January 2015
Nevzat Damla∗ and Kamuran Aldemir Department of Physics, Batman University, Batman, Turkey (Received 29 April 2013; accepted 21 October 2013) A survey was conducted to evaluate levels of indoor radon and gamma doses in 42 primary schools located in Batman, southeastern Anatolia, Turkey. Indoor radon measurements were carried out using CR-39 solid-state nuclear track detector-based radon dosimeters. The overall mean annual 222 Rn activity in the surveyed area was found to be 49 Bq m−3 (equivalent to an annual effective dose of 0.25 mSv). However, in one of the districts (Besiri) the maximum radon value turned out to be 307 Bq m−3 . The estimated annual effective doses are less than the recommended action level (3–10 mSv). It is found that the radon concentration decreases with increasing floor number. The concentrations of natural and artificial radioisotopes were determined using gamma-ray spectroscopy for soil samples collected in close vicinity of the studied schools. The mean gamma activity concentrations in the soil samples were 31, 25, 329 and 12 Bq kg−1 for 226 Ra, 232 Th, 40 K and 137 Cs, respectively. The radiological parameters such as the absorbed dose rate in air and the annual effective dose equivalent were calculated. These radiological parameters were evaluated and compared with the internationally recommended values. Keywords: indoor radon; natural radioactivity; primary school students; radiation exposure; Turkey
1.
Introduction
Human beings who are exposed to ionising radiation from natural sources emitting cosmic rays and naturally occurring radioactive elements are under the threat of a continuous and inevitable risk, which is a feature of life on earth. Of these radioactive elements, radon and its decay products found in the Earth crust are the most important sources of natural radiation for human exposure [1]. Radon is a colourless and odourless radioactive gas and always has been a natural component of the air we breathe. Radon is produced by the radioactive decay of radium, a naturally occurring radioactive element that is found in trace amounts in all kinds of rocks, soil, underground water and building materials. Radon gets into buildings mainly through cracks in floors or gaps around pipes or cables. Radon and its products inhaled with aerosols irradiate the respiratory tract and cause an increasing risk of getting lung cancer [2–5]. Particularly, to be exposed to ionising radiation in indoor environments has a greater impact due to the contributions of 238 U, 232 Th and 40 K and the inhalation of radon gas which comes from building materials, water, energy sources and geological structures underneath the builtup area [6]. Because many people spend much of their time indoors, e.g. in dwellings, offices, ∗ Corresponding author. Emails: [email protected], [email protected] This article was originally published with errors. This version has been corrected. Please see Corrigendum (http://dx.doi.org/10.1080/10256016.2014.890338)
© 2014 Taylor & Francis
Isotopes in Environmental and Health Studies
227
Downloaded by [Chulalongkorn University] at 06:59 01 January 2015
schools, etc. these places are likely to be the most significant sources of ionising radiation exposure. For most school students and staff, the second largest contributor to their radiation exposure is likely to be their school. Since most of the people spend a lot of time (16%) indoors, the indoor radon and soil gamma doses in primary schools are crucial in the assessment of possible radiation exposure to the students and staffs. Therefore, the purpose of this study is to determine the indoor radon concentration levels in primary schools, and natural (226 Ra, 232 Th and 40 K) and artificial (137 Cs) radioactivity concentrations in soils in the close vicinity of these schools; and to calculate the annual effective dose the population is exposed to due to the presence of terrestrial gamma radiation in primary schools of Batman Province. The data presented in this study might be useful as baseline data for future estimations of a population’s exposure.
2.
Materials and methods
2.1. Sampling area Batman Province is situated in the southeastern region of Turkey between 41◦ 10 and 41◦ 40 N latitude and between 38◦ 40 and 37◦ 50 E longitude, with a population of over 500,000. The population steadily grows as a result of the province’s natural, historical and cultural wealth and rapid industrial and economic development. The region spans an area of 4654 km2 and is divided into six districts (Figure 1). The province of Batman is important because of its oil reserves and its production, and is one of the main crude oil production centres of Turkey. 2.2. Measurements of indoor radon concentrations Indoor radon measurements were carried out in 42 primary schools in Batman Province, taking into account school population and the distribution of the schools in the study region (Table 1).
Sason Kozluk
Batman River
Center District
Besiri City Center Tigris River Hasankeyf Gercüs 0
Figure 1. The map of the sampling sites in Batman Province [10].
25km
228
N. Damla and K. Aldemir Table 1.
Distribution of indoor radon concentration measurements.
Locations
Number of schools
Number of detectors placed
Number of students
17 5 4 4 8 4 42
51 15 12 12 24 12 126
30,195 3298 870 1575 2735 1199 39,872
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City Center Kozluk Gercüs Sason Besiri Hasankeyf Total
Radon measurements were performed using the solid-state nuclear track detector (SSNTD) passive technique, which is the most reliable technique for the integrated and long-term monitoring of radon concentrations. The measurements were carried out for 3 months from March to May 2012. Dosimeters were installed at head height in three classrooms or the principal room of each school on different floors, if possible. Sampling was done (using school register) randomly depending on principals who permitted us to carry out the study in his or her school. CR-39 plastic track detectors purchased from the Radoys Co. Ltd., Budapest, Hungary, were used in this survey. The CR-39 detectors were designed as 20 × 20 × 1 mm3 in size and placed in a plastic container of 4 mm in height, which allows radon to diffuse. The container was closed with a plastic cap in order to avoid dust deposition on the detector foils. Evaluations of the detectors were carried out in the laboratory under defined etching conditions in a 30% NaOH at 70◦ C for 17 h. The films were then washed with distilled water and dried in a dust-free chamber. At this stage, the tracks left by alpha particles on the film exposed to radon gas were visible and counted with a microscope (× 200). Calibration measurement of SSNTD was done using a calibration chamber containing a 226 Ra source with a concentration of 3.2 kBq m−3 . The 222 Rn concentrations were determined by using a calibration factor of 7.23 kBq track−1 h−1 and subtracting the background track density from each pit track density on the films. Subsequently, the tracks on the etched film were counted manually with an optical microscope (×200). The detailed information has been described earlier [7]. 2.3. Radioactivity measurements in soil samples 2.3.1. Sampling and sample preparation The soil samples were collected in close vicinity of each school in which the radon measurements were carried out. The sampling sites were selected from nearly ground level, non-agricultural lands away from trees and buildings. After clearing the ground surface of stones, pebbles, vegetation and roots, 1.5 kg of the material from the first 10 cm of topsoil was placed in labelled polythene bags. The samples were ground, homogenised and sieved to about 100 mesh by a crushing machine. The samples were then dried at 110◦ C for 24 h to ensure that moisture was completely removed. About 160 g of each sample was sealed in gas-tight, radon impermeable, plastic cylindrical polyethylene containers. Then, the containers were completely sealed for 4 weeks to reach a secular equilibrium among the uranium and thorium and their decay products. 2.3.2. Gamma-ray measurement The gamma radiation was measured using a coaxial high purity germanium detector (Canberra, GC 1519 model). The relative efficiency of the detector is 15%, and it has a resolution of 1.9 keV at
229
the 1332.5 keV gamma ray of 60 Co. The detector was shielded in a 10 cm thick lead well internally lined with 2 mm Cu foils. The detector output was connected to a spectroscopy amplifier (Canberra, Model 2025) [8]. The spectrum analysis and nuclide identification were performed via Genie 2000 software from Canberra. A performance test using the certified reference sample (IAEA375) was carried out to check the efficiency and energy calibration of the system. The activities of the standard were in accordance with their certified values within error margins not exceeding 10 %. The quality assurance of the measurements was conducted by periodical efficiency and energy calibrations and repeating sample measurements. The counting time for each sample was selected to be 50,000 s to obtain gamma spectra with good statistics. To determine the background distribution in the environment around the detector, an empty container was counted in the same manner and in the same geometry as the samples. The background spectra were used to correct the net peak area of the gamma rays of the measured isotopes [9,10]. The gamma transition energies of 351.9 keV of 214 Pb and 609.3 keV of 214 Bi were used to determine the concentrations for the 226 Ra. The gamma transition energies of 583.1 keV of 208 Tl and 911.2 keV of 228Ac were used to determine the concentrations for the 232 Th series. The activity concentrations of 40 K and 137 Cs were determined directly using their 1460.8 and 661.7 keV gamma-ray lines, respectively. The activity of each sample was determined using the total net counts under the selected photo peak after subtracting appropriate background counts and applying appropriate factors for photo efficiency, branching intensity of radionuclides and weight of the samples.
3.
Results and discussions
The frequency distribution of radon concentrations found in this survey for all schools in Batman Province is plotted in Figure 2. The frequency distribution looks like a log-normal pattern. Radon concentrations varied from 14 to 307 Bq m−3 , with the arithmetical mean, geometric mean, median, arithmetic standard deviation and geometric standard deviation of 49, 42, 42, 41 and 1.7 Bq m−3 , respectively. The difference in the values of indoor activity can be attributed to the difference in ventilation rates, the nature and type of school building materials used in construction, the variations of the radioactivity levels in the soil underneath and particularly the geological considerations. The results of indoor radon concentration for each location are also summarised in 50
40 Frequency
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Isotopes in Environmental and Health Studies
30
20
10
40
Figure 2.
80 120 160 200 240 280 Radon concentration (Bq.m–3)
Frequency distributions of radon concentrations in the school buildings of Batman Province.
230 Table 2.
N. Damla and K. Aldemir Indoor radon concentrations in Bq m−3 for each location. City Center
Kozluk
Gercüs
Sason
Besiri
Hasankeyf
46 43 42 17 24 109
21 20 21 4 16 28
53 52 56 9 35 67
25 24 23 7 14 35
82 62 53 78 28 307
56 53 47 19 37 87
Arithmetic mean Geometric mean Median Standard deviation Minimum Maximum
Radon concentration (Bq.m–3)
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320 280 240 200 160 120 80 40 0 Ground floor Figure 3.
First floor
Second floor
Radon concentrations according to the floor number.
Table 2. Whilst the highest indoor radon concentrations were determined in the district Besiri, the district Kozluk showed the lowest indoor radon concentrations. Fifty-four percent of these values are higher than the mean values reported for the buildings worldwide of 40 Bq m−3 [1], but in almost all the buildings, except for one school, radon concentration is less than the lower limit of the range of the action level of 200–600 Bq m−3 , recommended by the International Commission on Radiological Protection [11]. The distributions of radon concentration according to the floor number are depicted in Figure 3. The radon concentration measured ranged from 14 to 307 Bq m−3 (for ground floor), from 16 to 243 Bq m−3 (for first floor), and from 18 to 51 Bq m−3 (for second floor). The radon concentrations decrease with increasing floor numbers. From these values, it can be inferred that besides soil permeability, humidity, temperature and climatic conditions, ventilation can be better for upper floors than that of ground floors since upper floors were found out to have better air circulation. Among the schools studied, the highest radon concentration was detected in the district of Besiri. In order to reduce the indoor radon concentration in this school, especially on the ground floors, some ventilation systems should be implemented. The means of 222 Rn concentrations observed in this study were lower than those for the other countries, except for Nigeria and Kuwait (Table 3). The annual effective dose from radon (222 Rn) exposure can be estimated by means of the following formula [1]: AEDRn = CRn · F · O · DCF, (1) where AEDRn is the annual effective dose (mSv), CRn is the radon activity concentration (Bq m−3 ), F is the equilibrium factor between radon and its decay products, which is assumed to be 0.4 for the buildings [1], O is the occupancy rate (1400 h y−1 ) of 16 % for students and staff, and dose
Isotopes in Environmental and Health Studies Table 3.
Comparison of indoor radon concentrations in schools from different countries.
Province
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Belgium Croatia (Osijek) Jordan (Amman) Italy (Friuli Venezia Giulia) Italy (Neapolitan area) Ireland Slovenia Kuwait (Kuwait city) Nigeria (Oke-Ogun) Greece Spain (Tenerife Island) Turkey
Reference
Arithmetic mean (Bq m−3 )
[12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] Present study
120 93 77 100 144 93 170 17 45 149 130 49
Table 4. The mean values of the AEDRn for each floor and district. Locations
AEDRn (mSv)
District
City Center Kozluk Gercüs Sason Besiri Hasankeyf
0.23 0.10 0.27 0.12 0.41 0.28
Floor
Ground First Second
0.28 0.23 0.17
General
Minimum Maximum Mean
0.07 1.55 0.25
Table 5. The radioactivity concentrations, ADRA and AEDE for soil samples.
Locations City Center Kozluk Gercüs Sason Besiri Hasankeyf Mean ± SD
226 Ra (Bq kg−1 )
232 Th (Bq kg−1 )
40 K (Bq kg−1 )
137 Cs (Bq kg−1 )
ADRA (nGy h−1 )
AEDE (mSv)
31 ± 7 23 ± 6 25 ± 6 24 ± 4 42 ± 13 27 ± 4 31 ± 10
23 ± 9 22 ± 6 18 ± 3 27 ± 9 37 ± 11 22 ± 3 25 ± 10
215 ± 84 366 ± 96 398 ± 67 400 ± 77 412 ± 102 361 ± 56 329 ± 126
10 ± 8 12 ± 4 16 ± 7 10 ± 2 11 ± 5 6±2 12 ± 6
37 ± 8 43 ± 7 39 ± 3 44 ± 8 59 ± 14 41 ± 6 43 ± 12
0.045 ± 0.010 0.053 ± 0.007 0.048 ± 0.012 0.054 ± 0.010 0.072 ± 0.017 0.050 ± 0.007 0.053 ± 0.014
conversion factor (DCF) is the dose conversion factor which converts radon concentration into the effective dose 9 mSv (Bq h m−3 )−1 . The calculated values of the annual effective doses due to inhalation of 222 Rn are presented in Table 4. In all areas surveyed, the estimated annual effective dose is less than the lower limit of the range of the recommended action level (3–10 mSv). The activities of the natural (226 Ra, 232 Th and 40 K) and artificial (137 Cs) radionuclides are presented in Table 5. The highest mean activity concentration of 226 Ra, 232 Th, 40 K was determined in the Besiri district. The arithmetic mean activity concentrations of the artificial radionuclide
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N. Damla and K. Aldemir
50
226Ra
(Bq.kg–1)
40
30
20
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10
0 0
10
20
30
40 222Rn
50
60
70
80
90
(Bq.m–3)
Figure 4. Correlation between mean values of the concentrations of 226 Ra in soil samples and indoor radon for the six districts under study.
Cs is found to be minimum in the district of Hasankeyf (6 Bq kg−1 ) and is maximum in Gercüs (16 Bq kg−1 ). As radon is a daughter product of 226 Ra, one can expect high indoor radon concentrations near the schools where high 226 Ra activity concentrations were measured in the soil. Therefore, we compared arithmetic mean indoor radon concentration results with mean 226 Ra activity concentration results in soils according to district (Figure 4). There is a strong correlation between indoor radon and 226 Ra in soil (R = 0.85). The total absorbed dose rate in air (ADRA) depends on the concentrations of these radionuclides in the soil. The ADRA in nGy h−1 at 1 m above ground level was computed by means of the following equation [1]: 137
ADRA = 0.462ARa + 0.604ATh + 0.0417AK ,
(2)
where ARa , ATh and AK are the activity concentrations of 226 Ra, 232 Th and 40 K (Bq kg−1 ), respectively. The ADRA calculated from the measured activities in the samples is given in Table 5. The mean ADRA was found 43 nGy h−1 (min 37 nGy h−1 in the City Center and max 49 nGy h−1 in the Besiri district), which is lower than the world mean of 60 nGy h−1 [1]. To estimate the annual effective dose equivalent (AEDE), the conversion coefficient (0.7 Sv Gy−1 ) from the absorbed dose in air to effective dose, and the outdoor occupancy factor (0.2) proposed by United Nations Scientific Committee on the Effects of Atomic Radiation [1] were used. Therefore, the effective dose rate equivalent outdoors in units of mSv per year was computed by means of the following formula: AEDE = ADRA · T · F,
(3)
where ADRA is the calculated dose rate (in nGy h−1 ), T is the outdoor occupancy time (0.2 × 24 h × 365.25 d = 1753.2 h y−1 ), and F is the conversion factor (0.7 × 10−6 Sv Gy−1 ). The computed AEDE of the measured activities in the samples is presented in Table 5. The computed value of the AEDE in the samples varies from 0.032 to 0.112 mSv with an arithmetic mean of 0.053 mSv. This value is lower than the world mean of 0.07 mSv [1].
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Conclusions
The present study shows that both indoor radon and external gamma rays received by students and staff are under the world mean values. Therefore, as a conclusion, it can be said that no action is necessary to be taken in the schools under consideration except for Besiri district where maximum values turned out to be 307 Bq m−3 . The results of the present study will provide useful baseline data for adopting safety measures and dealing effectively with radiation emergencies.
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Acknowledgements The authors would like to thank the National Education Deputy Manager of the city; and the cooperation of the school directors and crews is also appreciated. And also, the authors kindly thank the experienced English lecturer of Batman University, Ihsan Pilatin, for editing the paper thoroughly.
Funding This work was done with the support of the Batman University Research Fund under Project No(s). [BTUBAP-FED-5].
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