- Email: [email protected]
Indoor and outdoor Radon concentration measurements in Sivas, Turkey, in comparison with geological setting
Journal of Environmental Radioactivity 101 (2010) 952e957
Contents lists available at ScienceDirect
Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Indoor and outdoor Radon concentration measurements in Sivas, Turkey, in comparison with geological setting Metin Mihci a, Aydin Buyuksarac b,1, Attila Aydemir c, *, Nilgun Celebi d a
Iller Bankası, Etud Plan ve Yol Dairesi, Opera, 06053 Ankara, Turkey Canakkale Onsekiz Mart University, Department of Geophysical Engineering, 17020, Canakkale, Turkey c Turkiye Petrolleri A.O. Mustafa, Kemal Mah. 2. Cad. No: 86, 06100 Sogutozu, Ankara, Turkey d Cekmece Nuclear Research and Training Centre (CNAEM), Cekmece, Istanbul, Turkey b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 December 2009 Received in revised form 29 May 2010 Accepted 18 June 2010 Available online 27 July 2010
Indoor and soil gas Radon (222Rn) concentration measurements were accomplished in two stages in Sivas, a central eastern city in Turkey. In the first stage, CR-39 passive nuclear track detectors supplied by the Turkish Atomic Energy Authority (TAEA) were placed in the selected houses throughout Sivas centrum in two seasons; summer and winter. Before the setup of detectors, a detailed questionnaire form was distributed to the inhabitants of selected houses to investigate construction parameters and properties of the houses, and living conditions of inhabitants. Detectors were collected back two months later and analysed at TAEA laboratories to obtain indoor 222Rn gas concentration values. In the second stage, soil gas 222 Rn measurements were performed using an alphameter near the selected houses for the indoor measurements. Although 222Rn concentrations in Sivas were quite low in relation with the allowable limits, they are higher than the average of Turkey. Indoor and soil gas 222Rn concentration distribution maps were prepared seperately and these maps were applied onto the surface geological map. In this way, both surveys were correlated with the each other and they were interpreted in comparison with the answers of questionnaire and the geological setting of the Sivas centrum and the vicinity. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Radon (222Rn) Sivas CR-39 alpha-track detector Alphameter
1. Introduction Radon (222Rn) is a radioactive noble gas emitted by the decay of Ra, an element of the 238U decay series. Radon-222 decays into a series of other radioactive elements, of which 214Po and 218Po are the most significant, as they contribute the majority of radiation dose when inhaled. Following a number of decay series, 218Po transforms into 210Po and it decays into stable 206Pb. The 222Rn and its decay products are reported as major causes of lung cancer (UNSCEAR, 2000a,b; ICRP, 1987), especially when they are inhaled attached to dust particles in the air. The 222Rn exists in soil and water, and propagates into the atmosphere from these natural sources. Meteorological parameters such as temperature, pressure differences, and humidity also affect indoor 222Rn concentrations. Levels of 222Rn can also be modified by the ventilation conditions, heatingecooling systems and the life style of inhabitants. Because of these factors and impact of 222Rn on the public health, 226
geophysical studies performing 222Rn concentration measurements are very important (Shirav and Vulkan, 1997; Wysocka et al., 2005). There are many studies about the effects of geological and environmental factors on 222Rn measurements in a number of other countries (Botkin and Keller, 1988; Harley and Harley, 1990; Hubbard and Swedjemark, 1991; Robinson and Sextro, 1995; Yamasaki and Lida, 1995; Vaupotic et al, 2003; Yu et al, 1995). Programmed indoor 222Rn measurements in Turkey were started in 1984 by the Health Physics Department of the Cekmece Nuclear Research and Training Centre (CNAEM). Indoor surveys have been completed in 53 cities in the frame of this programme until 2007 (Celebi and Ulug, 2002; Gurel and Cobanoglu, 1997; Koksal et al, 1993; Ulug et al, 2004; Yarar et al, 2006), and the results are summarised in Fig. 1. 2. Materials 2.1. Environmental conditions
* Corresponding author. Tel.: þ(90) 312 207 2342; fax: þ(90) 312 286 9049. E-mail address: [email protected] (A. Aydemir). 1 Present address: Canakkale Onsekiz Mart University, Department of Geophysical Engineering, Canakkale, Turkey. 0265-931X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2010.06.013
Sivas city and the vicinity is mainly covered by Oligocene sabkha gypsum, Lower Miocene basal conglomerate, marine limestone and continental to marine clastic rocks, Middle Miocene playa gypsum levels with clastic intercalations, Pliocene fluvial clastic deposits and Quaternary unconsolidated alluvium. The climate in Sivas is continental climate. Although average temperature in winters is 0 C, it may
M. Mihci et al. / Journal of Environmental Radioactivity 101 (2010) 952e957
953
Fig. 1. Completed indoor measurements in Turkey by CNAEM (http://www.taek.gov.tr/tr/bilgi-kosesi/radyasyon-insan-ve-cevre/107-cevre-radyoaktivite-olcumleri/188-kapaliortam-radon-degisimleri.html) Location of Sivas is illustrated in gray color.
decrease down to 36 C from time to time. The temperature is <0 for 132 days on average. In the summer, the temperature is generally above 19 C and it may reach 38 C. The difference of annual temperature between winter and summer is 74 C.
Table 1 Average indoor
18 Summer
14
W inter
12
Number of selected houses
Arithmetic avg. Geometric avg. Arithmetic Turkey’s (Bq m3) standard avg. (Bq m3) deviation (Bq m3)
Summer Winter
66 32
98 89
94 86
27.5 24
56
concentration changes, in winter and summer times. In the second stage, soil 222Rn gas measurements were accomplished using alphameters at the appropriate locations outside of the selected indoor measurements. This study was accomplished in the summer and winter of 2006. The CR-39 solid state nuclear track detectors were contained in plastic dosimeters. The container was closed with a plastic cap in order to avoid dust deposition on the detector foils.
10 8
Table 2 Maximum allowed world.
6 4
Country
222
Rn gas concentration limits (in Bq m3) in Turkey and the
Max. allowed Country Rn (Bq m3)
Max. allowed Country 222 Rn (Bq m3)
150 250 200 200 400 400
150 200 200 200 800 250
222
2
80 -8 9 10 010 9 12 012 9 14 014 9 16 016 9 18 018 9
60 -6 9
40 -4 9
20 -2 9
0
09
Number of Buildings
16
Rn concentrations in summer and winter measurements.
Season
2.2. Indoor radon measurements The 222Rn gas concentration measurements in Sivas were performed in two stages (Mihci, 2008). In the first stage, CR-39 passive nuclear track detectors were placed into the selected houses in dwellings of Sivas to monitor the seasonal gas
222
Ra don Conce ntra tion (Bq/m3) Fig. 2.
222
Rn measurements in summer and winter.
USA Germany Australia China Denmark France
India UK Ireland Sweden Canada Luxemburg
Norway Russia Turkey EU ICRP WHO
Max. allowed Rn (Bq m3)
222
200 200 400 400 400 100
Fig. 3. Locations of indoor and soil gas
Fig. 4. Surface geology and map of soil gas
222
222
Rn measurements applied onto the geological map.
Rn concentration measurements. Contour Interval: 1 kBq m3. Closed contours of high values are hatched.
M. Mihci et al. / Journal of Environmental Radioactivity 101 (2010) 952e957
Fig. 5. Surface geology and map of indoor
222
Rn concentration measurements in summer. Contour Interval: 10 Bq m3. Closed contours of high values are hatched.
These containers were distributed to 98 randomly selected houses, 66 of the detectors were setup for the summer time measurements (from the end of May to beginning of August) and 32 of them for winter (from mid-October to midDecember). Detectors were installed in the living rooms or bedrooms for a constant exposure period and collected at the same time. The selected rooms were located on different floors, some of them were at ground level and some of them were upstairs. Before the setup of detectors, a questionnaire was distributed to the inhabitants of selected houses and all questionnaires were returned to the authors of this study. The questionnaire included questions about the buildings such as construction date, construction material, existence of a cellar, building isolation status, ventilation conditions and heating system. After 60 days exposure in each season, all detectors were collected and transferred to the Cekmece Nuclear Research and Training Centre (CNAEM). In order to develop tracks, CR-39 chips were immersed into 25% NaOH solution at 90 C and rotated slowly for 4 h. The development phase was followed by the track density counting with Radometer-2000 microscope unit connected to a computer with special analysis software and a Linux data base. The radioactivity concentration was calculated using the conversion factor of 9 nSv/(Bq/h/m3), as suggested by UNSCEAR (2000a,b) (Koksal et al, 1993). Analysis results are presented in Fig. 2, comparing summer and winter. Average (arithmetic and geometric) values and the arithmetic standard deviations for the summer and winter time are presented in Table 1.
2.3. Soil gas
222
955
Rn measurements
Soil gas 222Rn measurements were accomplished at 23 different localities outside of the buildings where the indoor measurements were performed, only in summer time of 2006 in order to avoid or at least to minimize the possible
influences of the meteorology. An alphameter 611 produced by alphaNUCLEAR (with 400-mm2 detector area and 65535-16 bit per 15 min Counting Capacity) was set into a 30-cm-deep hole with 51-mm diameter which was 5 m away from the building. The 222Rn concentration was recorded for 15 min together with the notes about characteristics of the ground such as geologic properties. This procedure was done to examine the correlation of the indoor and soil gas measurements and to investigate the relationship between the ground radon risk and the housing system (including construction material, determination of the settlement location, isolation and ventilation systems etc.).
3. Results and discussions Average 222Rn concentrations for both seasons were higher in Sivas than the national average indoor value (56 Bq m3) for Turkey (Yarar et al, 2006), although they were quite low in comparison with the maximum allowed 222Rn concentration limits, either for EU countries or for Turkey (Table 2). The 222Rn concentrations in summer were slightly higher than winter. This is related to the increase of ground permeability after melting of thick snow layer in the winter time which is common in this region. Summer time indoor measurements were consistent with the soil gas measurements. Indoor and soil gas 222Rn concentrations were mapped and the contours were applied onto the surface geological map (Buyuksarac
M. Mihci et al. / Journal of Environmental Radioactivity 101 (2010) 952e957
Fig. 6. Surface geology and map of indoor
222
Rn concentration measurements in winter. Contour Interval: 10 Bq m3. Closed contours of high values are hatched.
et al., 2007) in order to investigate possible relationships. Fig. 3 illustrates the locations of observation points distributed onto the geological map. Initially, soil gas 222Rn values were applied onto the surface geological map to observe if the 222Rn emission from the ground was directly dependent on the geological units (Fig. 4). However, there was no significant dependence on the surface geology except for an increment of contour values at the boundary between alluvium and the geological unit composed of sandstone, siltstone and marl (Fig. 4). High 222Rn concentrations were relatively intensified on the alluvium covered area to the contrary of expectations for more porous and permeable units to the north and northwest of the city. Seasonal distribution of indoor 222Rn concentrations were also mapped onto the surface geological map, seperately for summer (Fig. 5) and for winter time (Fig. 6). Closed contours are focused around the boundary between the alluvium and more porous and permeable units. There was another high concentration area on the alluvium very close to the Kizilirmak River (Fig. 5). Although it is not so clear, 222Rn concentration increased towards the north and northwest, perhaps an artifact of insufficient sampling in this area. On the contrary to the map of summer measurements, the winter concentration map indicates an increment of contour values
to the north where the more porous and permeable units are existent (Fig. 6). This could be related with the thick snow coverage in the winter creating a permeability barrier at the uppermost frozen layers of alluvium which has already a limited permeability. Although, more porous and permeable formations to the north are exposed to the same weather conditions, excess of porosity and permeability may allow extra 222Rn seepage relative to the alluvium covered area. 140 Radon Conc. (Bq/m3)
956
120 100 80 60 40 20 0
0-5
5-15
15-25
25-35
35-55
55-105
Age of Building Fig. 7. Relationship between the houses.
222
Rn concentration and building age of selected
Indoor Radon Conc. (Bqm-3)
M. Mihci et al. / Journal of Environmental Radioactivity 101 (2010) 952e957
957
Acknowledgement
160 140 120 100 80 60 40 20 0 0
5
10
15
20
-3
Soil Radon Concentration (kBqm ) Fig. 8. Comparison of indoor and soil gas
222
Rn concentrations.
The construction materials of the houses were generally concrete and brick. Inhabitants in both seasons prefer natural ventilation in spite of usage of air conditioning (almost 100%), 94% of the houses observed in winter were regularly ventilated while only 86% of houses selected for summer were ventilated. There was no significant relationship between the 222Rn concentration and building age of the selected houses: 222Rn concentration decreased considerably only for the buildings older than 55 years (Fig. 7). Sivas can generally be classified in the low risk category because of the low soil gas 222Rn concentration and there was no direct relationship between the indoor and soil gas measurement results (Fig. 8). Geological units have limited influence on the indoor concentrations. This study was focussed around the downtown of Sivas and where there were relatively high 222Rn concentrations on the alluvium covered area. However, more porous and permeable units (sandstone, siltstone, conglomerate, etc.) are located to the north and northwest of the city. Although there is no fault system reported in the study area, the boundary between alluvium and the geological units given above could be a fault related boundary, because it is apparently linear and regularly extended. Local soils may play a significant contributory role to soil gas and indoor 222Rn concentrations. Therefore, additional soil gas and indoor 222Rn measurements should be performed with dense sampling intervals in these parts of the city centre. In general, the sampling density used in Sivas was not sufficient for most 222Rn assessment tasks, all these observations should be improved by expansion of the study area performing new measurements, especially through the northeastern part of the city. In addition, only short term intra-soil radon measurements were accomplished in this study. We suggest short term and long term outdoor measurements (paralel to the intra-soil measurements) with the track detectors to determine the local atmospheric levels (radon concentration in the air).
This study is supported by the Cumhuriyet University, Scentific Research Projects-Support Program, Project No: M-312. Authors would like to thank the Cekmece Nuclear Research and Training Centre (CNAEM), Istanbul, Turkey for analyses of track detectors at its laboratories and their support to perform the Project. We would like to extend our sincere thanks to Res. Assist. Dr. Ozcan Bektas to classify the observed data and under graduate students; Mr. Sinan Kosaroglu, Mr. Cem Yucekas and Mr. M. Turgut Ezgo for setup of detectors into the selected houses and to collect them back. Authors are also grateful to Mr. S.C. Sheppard, Editor-in-Chief of the Journal of Environmental Radioactivitiy and two anonymous reviewers for their constructive suggestions and critiques. References Botkin, D., Keller, E., 1988. Environmental Science. John Wiley & Sons, NY. Buyuksarac, A., Yilmaz, H., Bektas, O., Arisoy, M.O., 2007. Sivas Ili Deprem Duyarlik ve Mikrobolgelendirme Projesi. DPT Bilimsel Aras¸tirma Projesi. Sonuç Raporu (Project No: 2005. K.120220). Celebi, N., Ulug, A., 2002. Alpha track technique for the determination of Rn and decay products in air. In: Proceedings of 7th International Conference on Nuclear Analytical Methods in the Life Sciences (NAMLS’7), Antalya, Turkey, pp. 108e109. Gurel, C., Cobanoglu, Z., 1997. Radon Kirliligi. Cevre Sagligi Temel Kaynak Dizisi. Saglik Bakanligi, Ankara. Harley, N.H., Harley, J.H., 1990. Potential lung cancer risk from indoor radon exposure. CA Cancer J. Clin. 40, 265e275. Hubbard, L., Swedjemark, G.A., 1991. Radon dynamics in Swedish dwellings: a status report. In: Proceedings of International Symposium on Radon and Radon Reduction Technology, Philadelphia, vol. 3. US Environmental Protection Agency, Research Triangle Park, NC Paper V-4. International Commission on Radiation Protection (ICRP), 1987. Lung Cancer Risk from Indoor Exposure to Radon Daugthers Oxford. ICRP Publication. 50 17(1). Koksal, M., Celebi, N., Ozcinar, B., 1993. Indoor radon concentrations in Istanbul houses. Health Phys. 65, 87e88. Mihci, M., 2008. Sivas merkez yerlesiminde radon gazi dagiliminin belirlenmesi ve Turkiye’de yapilasma oncesi radon gazi olcumune yonelik yonetmelik taslagi hazirlanmasi. M.Sc. Thesis, Cumhuriyet University, Turkey (unpublished), (in Turkish with English abstract). Robinson, A.L., Sextro, R.G., 1995. The influence of a subslab gravel layer and open area on soil-gas and radon entry into two experimental basements. Health Phys. 69, 367e377. Shirav, M., Vulkan, U., 1997. Mapping radon-prone areas: a geophysical approach. Environ. Geol. 31 (3/4). Ulug, A., Karabulut, M.T., Celebi, N., 2004. Radon measurements with CR-39 track detectors at specific locations in Turkey. Nucl. Technol. Radiat. Prot. 19, 46e49. UNSCEAR, 2000a. Sources and Effects of Ionizing Radiation. Report to the General Assembly. UNSCEAR, 2000b. Scientific Annexes, vol. I New York, United Nations. Vaupotic, J., Andjelov, M., Kobal, I., 2003. Relationship between radon concentrations in indoor air and in soil gas. Environ. Geol. 42, 583e587. Wysocka, M., Kotyrba, A., Chalupnik, S., Skowronek, J., 2005. Geophysical methods in radon risk studies. J. Environ. Radioact. 82, 351e362. Yamasaki, T., Lida, T., 1995. Measurements of thoron progeny concentration using a potential alpha-energy monitor in Japan. Health Phys. 68, 840e844. Yarar, Y., Gunaydin, T., Celebi, N., 2006. Determination of radon concentrations of the Dikili geothermal area in Western Turkey. Radiat. Prot. Dosimetry 118, 78e81. Yu, K.N., Chan, T.F., Young, E.C., 1995. The variation of radon exhalation rates from building surfaces of different ages. Health Phys. 68, 716e718.
Contents lists available at ScienceDirect
Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Indoor and outdoor Radon concentration measurements in Sivas, Turkey, in comparison with geological setting Metin Mihci a, Aydin Buyuksarac b,1, Attila Aydemir c, *, Nilgun Celebi d a
Iller Bankası, Etud Plan ve Yol Dairesi, Opera, 06053 Ankara, Turkey Canakkale Onsekiz Mart University, Department of Geophysical Engineering, 17020, Canakkale, Turkey c Turkiye Petrolleri A.O. Mustafa, Kemal Mah. 2. Cad. No: 86, 06100 Sogutozu, Ankara, Turkey d Cekmece Nuclear Research and Training Centre (CNAEM), Cekmece, Istanbul, Turkey b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 December 2009 Received in revised form 29 May 2010 Accepted 18 June 2010 Available online 27 July 2010
Indoor and soil gas Radon (222Rn) concentration measurements were accomplished in two stages in Sivas, a central eastern city in Turkey. In the first stage, CR-39 passive nuclear track detectors supplied by the Turkish Atomic Energy Authority (TAEA) were placed in the selected houses throughout Sivas centrum in two seasons; summer and winter. Before the setup of detectors, a detailed questionnaire form was distributed to the inhabitants of selected houses to investigate construction parameters and properties of the houses, and living conditions of inhabitants. Detectors were collected back two months later and analysed at TAEA laboratories to obtain indoor 222Rn gas concentration values. In the second stage, soil gas 222 Rn measurements were performed using an alphameter near the selected houses for the indoor measurements. Although 222Rn concentrations in Sivas were quite low in relation with the allowable limits, they are higher than the average of Turkey. Indoor and soil gas 222Rn concentration distribution maps were prepared seperately and these maps were applied onto the surface geological map. In this way, both surveys were correlated with the each other and they were interpreted in comparison with the answers of questionnaire and the geological setting of the Sivas centrum and the vicinity. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Radon (222Rn) Sivas CR-39 alpha-track detector Alphameter
1. Introduction Radon (222Rn) is a radioactive noble gas emitted by the decay of Ra, an element of the 238U decay series. Radon-222 decays into a series of other radioactive elements, of which 214Po and 218Po are the most significant, as they contribute the majority of radiation dose when inhaled. Following a number of decay series, 218Po transforms into 210Po and it decays into stable 206Pb. The 222Rn and its decay products are reported as major causes of lung cancer (UNSCEAR, 2000a,b; ICRP, 1987), especially when they are inhaled attached to dust particles in the air. The 222Rn exists in soil and water, and propagates into the atmosphere from these natural sources. Meteorological parameters such as temperature, pressure differences, and humidity also affect indoor 222Rn concentrations. Levels of 222Rn can also be modified by the ventilation conditions, heatingecooling systems and the life style of inhabitants. Because of these factors and impact of 222Rn on the public health, 226
geophysical studies performing 222Rn concentration measurements are very important (Shirav and Vulkan, 1997; Wysocka et al., 2005). There are many studies about the effects of geological and environmental factors on 222Rn measurements in a number of other countries (Botkin and Keller, 1988; Harley and Harley, 1990; Hubbard and Swedjemark, 1991; Robinson and Sextro, 1995; Yamasaki and Lida, 1995; Vaupotic et al, 2003; Yu et al, 1995). Programmed indoor 222Rn measurements in Turkey were started in 1984 by the Health Physics Department of the Cekmece Nuclear Research and Training Centre (CNAEM). Indoor surveys have been completed in 53 cities in the frame of this programme until 2007 (Celebi and Ulug, 2002; Gurel and Cobanoglu, 1997; Koksal et al, 1993; Ulug et al, 2004; Yarar et al, 2006), and the results are summarised in Fig. 1. 2. Materials 2.1. Environmental conditions
* Corresponding author. Tel.: þ(90) 312 207 2342; fax: þ(90) 312 286 9049. E-mail address: [email protected] (A. Aydemir). 1 Present address: Canakkale Onsekiz Mart University, Department of Geophysical Engineering, Canakkale, Turkey. 0265-931X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2010.06.013
Sivas city and the vicinity is mainly covered by Oligocene sabkha gypsum, Lower Miocene basal conglomerate, marine limestone and continental to marine clastic rocks, Middle Miocene playa gypsum levels with clastic intercalations, Pliocene fluvial clastic deposits and Quaternary unconsolidated alluvium. The climate in Sivas is continental climate. Although average temperature in winters is 0 C, it may
M. Mihci et al. / Journal of Environmental Radioactivity 101 (2010) 952e957
953
Fig. 1. Completed indoor measurements in Turkey by CNAEM (http://www.taek.gov.tr/tr/bilgi-kosesi/radyasyon-insan-ve-cevre/107-cevre-radyoaktivite-olcumleri/188-kapaliortam-radon-degisimleri.html) Location of Sivas is illustrated in gray color.
decrease down to 36 C from time to time. The temperature is <0 for 132 days on average. In the summer, the temperature is generally above 19 C and it may reach 38 C. The difference of annual temperature between winter and summer is 74 C.
Table 1 Average indoor
18 Summer
14
W inter
12
Number of selected houses
Arithmetic avg. Geometric avg. Arithmetic Turkey’s (Bq m3) standard avg. (Bq m3) deviation (Bq m3)
Summer Winter
66 32
98 89
94 86
27.5 24
56
concentration changes, in winter and summer times. In the second stage, soil 222Rn gas measurements were accomplished using alphameters at the appropriate locations outside of the selected indoor measurements. This study was accomplished in the summer and winter of 2006. The CR-39 solid state nuclear track detectors were contained in plastic dosimeters. The container was closed with a plastic cap in order to avoid dust deposition on the detector foils.
10 8
Table 2 Maximum allowed world.
6 4
Country
222
Rn gas concentration limits (in Bq m3) in Turkey and the
Max. allowed Country Rn (Bq m3)
Max. allowed Country 222 Rn (Bq m3)
150 250 200 200 400 400
150 200 200 200 800 250
222
2
80 -8 9 10 010 9 12 012 9 14 014 9 16 016 9 18 018 9
60 -6 9
40 -4 9
20 -2 9
0
09
Number of Buildings
16
Rn concentrations in summer and winter measurements.
Season
2.2. Indoor radon measurements The 222Rn gas concentration measurements in Sivas were performed in two stages (Mihci, 2008). In the first stage, CR-39 passive nuclear track detectors were placed into the selected houses in dwellings of Sivas to monitor the seasonal gas
222
Ra don Conce ntra tion (Bq/m3) Fig. 2.
222
Rn measurements in summer and winter.
USA Germany Australia China Denmark France
India UK Ireland Sweden Canada Luxemburg
Norway Russia Turkey EU ICRP WHO
Max. allowed Rn (Bq m3)
222
200 200 400 400 400 100
Fig. 3. Locations of indoor and soil gas
Fig. 4. Surface geology and map of soil gas
222
222
Rn measurements applied onto the geological map.
Rn concentration measurements. Contour Interval: 1 kBq m3. Closed contours of high values are hatched.
M. Mihci et al. / Journal of Environmental Radioactivity 101 (2010) 952e957
Fig. 5. Surface geology and map of indoor
222
Rn concentration measurements in summer. Contour Interval: 10 Bq m3. Closed contours of high values are hatched.
These containers were distributed to 98 randomly selected houses, 66 of the detectors were setup for the summer time measurements (from the end of May to beginning of August) and 32 of them for winter (from mid-October to midDecember). Detectors were installed in the living rooms or bedrooms for a constant exposure period and collected at the same time. The selected rooms were located on different floors, some of them were at ground level and some of them were upstairs. Before the setup of detectors, a questionnaire was distributed to the inhabitants of selected houses and all questionnaires were returned to the authors of this study. The questionnaire included questions about the buildings such as construction date, construction material, existence of a cellar, building isolation status, ventilation conditions and heating system. After 60 days exposure in each season, all detectors were collected and transferred to the Cekmece Nuclear Research and Training Centre (CNAEM). In order to develop tracks, CR-39 chips were immersed into 25% NaOH solution at 90 C and rotated slowly for 4 h. The development phase was followed by the track density counting with Radometer-2000 microscope unit connected to a computer with special analysis software and a Linux data base. The radioactivity concentration was calculated using the conversion factor of 9 nSv/(Bq/h/m3), as suggested by UNSCEAR (2000a,b) (Koksal et al, 1993). Analysis results are presented in Fig. 2, comparing summer and winter. Average (arithmetic and geometric) values and the arithmetic standard deviations for the summer and winter time are presented in Table 1.
2.3. Soil gas
222
955
Rn measurements
Soil gas 222Rn measurements were accomplished at 23 different localities outside of the buildings where the indoor measurements were performed, only in summer time of 2006 in order to avoid or at least to minimize the possible
influences of the meteorology. An alphameter 611 produced by alphaNUCLEAR (with 400-mm2 detector area and 65535-16 bit per 15 min Counting Capacity) was set into a 30-cm-deep hole with 51-mm diameter which was 5 m away from the building. The 222Rn concentration was recorded for 15 min together with the notes about characteristics of the ground such as geologic properties. This procedure was done to examine the correlation of the indoor and soil gas measurements and to investigate the relationship between the ground radon risk and the housing system (including construction material, determination of the settlement location, isolation and ventilation systems etc.).
3. Results and discussions Average 222Rn concentrations for both seasons were higher in Sivas than the national average indoor value (56 Bq m3) for Turkey (Yarar et al, 2006), although they were quite low in comparison with the maximum allowed 222Rn concentration limits, either for EU countries or for Turkey (Table 2). The 222Rn concentrations in summer were slightly higher than winter. This is related to the increase of ground permeability after melting of thick snow layer in the winter time which is common in this region. Summer time indoor measurements were consistent with the soil gas measurements. Indoor and soil gas 222Rn concentrations were mapped and the contours were applied onto the surface geological map (Buyuksarac
M. Mihci et al. / Journal of Environmental Radioactivity 101 (2010) 952e957
Fig. 6. Surface geology and map of indoor
222
Rn concentration measurements in winter. Contour Interval: 10 Bq m3. Closed contours of high values are hatched.
et al., 2007) in order to investigate possible relationships. Fig. 3 illustrates the locations of observation points distributed onto the geological map. Initially, soil gas 222Rn values were applied onto the surface geological map to observe if the 222Rn emission from the ground was directly dependent on the geological units (Fig. 4). However, there was no significant dependence on the surface geology except for an increment of contour values at the boundary between alluvium and the geological unit composed of sandstone, siltstone and marl (Fig. 4). High 222Rn concentrations were relatively intensified on the alluvium covered area to the contrary of expectations for more porous and permeable units to the north and northwest of the city. Seasonal distribution of indoor 222Rn concentrations were also mapped onto the surface geological map, seperately for summer (Fig. 5) and for winter time (Fig. 6). Closed contours are focused around the boundary between the alluvium and more porous and permeable units. There was another high concentration area on the alluvium very close to the Kizilirmak River (Fig. 5). Although it is not so clear, 222Rn concentration increased towards the north and northwest, perhaps an artifact of insufficient sampling in this area. On the contrary to the map of summer measurements, the winter concentration map indicates an increment of contour values
to the north where the more porous and permeable units are existent (Fig. 6). This could be related with the thick snow coverage in the winter creating a permeability barrier at the uppermost frozen layers of alluvium which has already a limited permeability. Although, more porous and permeable formations to the north are exposed to the same weather conditions, excess of porosity and permeability may allow extra 222Rn seepage relative to the alluvium covered area. 140 Radon Conc. (Bq/m3)
956
120 100 80 60 40 20 0
0-5
5-15
15-25
25-35
35-55
55-105
Age of Building Fig. 7. Relationship between the houses.
222
Rn concentration and building age of selected
Indoor Radon Conc. (Bqm-3)
M. Mihci et al. / Journal of Environmental Radioactivity 101 (2010) 952e957
957
Acknowledgement
160 140 120 100 80 60 40 20 0 0
5
10
15
20
-3
Soil Radon Concentration (kBqm ) Fig. 8. Comparison of indoor and soil gas
222
Rn concentrations.
The construction materials of the houses were generally concrete and brick. Inhabitants in both seasons prefer natural ventilation in spite of usage of air conditioning (almost 100%), 94% of the houses observed in winter were regularly ventilated while only 86% of houses selected for summer were ventilated. There was no significant relationship between the 222Rn concentration and building age of the selected houses: 222Rn concentration decreased considerably only for the buildings older than 55 years (Fig. 7). Sivas can generally be classified in the low risk category because of the low soil gas 222Rn concentration and there was no direct relationship between the indoor and soil gas measurement results (Fig. 8). Geological units have limited influence on the indoor concentrations. This study was focussed around the downtown of Sivas and where there were relatively high 222Rn concentrations on the alluvium covered area. However, more porous and permeable units (sandstone, siltstone, conglomerate, etc.) are located to the north and northwest of the city. Although there is no fault system reported in the study area, the boundary between alluvium and the geological units given above could be a fault related boundary, because it is apparently linear and regularly extended. Local soils may play a significant contributory role to soil gas and indoor 222Rn concentrations. Therefore, additional soil gas and indoor 222Rn measurements should be performed with dense sampling intervals in these parts of the city centre. In general, the sampling density used in Sivas was not sufficient for most 222Rn assessment tasks, all these observations should be improved by expansion of the study area performing new measurements, especially through the northeastern part of the city. In addition, only short term intra-soil radon measurements were accomplished in this study. We suggest short term and long term outdoor measurements (paralel to the intra-soil measurements) with the track detectors to determine the local atmospheric levels (radon concentration in the air).
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