Environmental radioactivity measurements in Kastamonu region of ...

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Applied Radiation and Isotopes 65 (2007) 440–444 www.elsevier.com/locate/apradiso

Environmental radioactivity measurements in Kastamonu region of northern Turkey Erol Kama, Ahmet Bozkurtb, a

TAEK, Cekmece Nuclear Research and Training Centre, Altınsehir Yolu 5.km, Halkali, 34303 Istanbul, Turkey b Department of Physics, Faculty of Arts and Sciences, Harran University, 63300 Sanliurfa, Turkey Received 31 May 2006; received in revised form 29 August 2006; accepted 17 November 2006

Abstract Located in the north-western part of Turkey, the province of Kastamonu has lately been receiving national attention because of its cultural and touristic attractions. This study assesses the environmental radioactivity levels of the region through measurements of indoor radon concentrations and indoor/outdoor gamma absorbed dose in air and radionuclide activities in surface soil and drinking water. The indoor 222Rn activity concentration was found to be 98:4 Bq=m3 equivalent to an annual effective dose of 2.48 mSv. The indoor and outdoor gamma absorbed doses were measured as 54.81 and 48.03 nGy/h, respectively, corresponding to a total gamma radiation level (of terrestrial and cosmic origin) of 0.33 mSv/y. The activity concentrations in the soil samples collected from the study area were determined as 32.93, 27.17, 431.43 Bq/kg for the natural radionuclides 238U, 232Th and 40K, respectively, and 8.02 Bq/kg for the fission product 137Cs. These natural radioactivity sources result in a terrestrial gamma level of 60 mSv=y. The water samples collected from the region carry an average of 0.0089 Bq/l of gross alpha and 0.271 Bq/l of gross beta activities which together cause an annual effective dose of 1:83 mSv. The measurement results obtained in this study indicate that the region has a background radiation level that is within the natural limits and shows no significant departure from the other parts of the country. r 2006 Elsevier Ltd. All rights reserved. Keywords: Gamma dose; Radioactivity; Soil; Water; Radon; Kastamonu; Turkey

1. Introduction Environmental radioactivity measurements are necessary for determining the background radiation level due to natural radioactivity sources of terrestrial and cosmic origin. The terrestrial component is due to the radioactive nuclides that are present in air, soils, rocks, water and building materials in amounts that vary significantly depending on the geological and geographical features of a region. The cosmic radiation originates from space as cosmic rays whose contribution to background changes mainly with elevation and latitude. In addition to these natural sources, the level of background radiation in a Corresponding author. Tel.: +90 414 344 0020; fax: +90 414 344 0051.

E-mail addresses: [email protected] (E. Kam), [email protected] (A. Bozkurt). 0969-8043/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2006.11.005

region is affected from man-made sources such as those from nuclear activities and accidents (UNSCEAR, 2000). Survey studies have been performed to assess the background radiation level of some regions of Turkey, especially the northern parts which were affected significantly from the Chernobyl accident (TAEK, 1988). The province of Kastamonu is situated in the western part of the Black Sea Region of Turkey (Fig. 1) with 170 km long coast line. It has a population of about 375 000, more than half of which live in rural areas. The region spans an area of 13 108 km2 and almost 34 of it is covered by forests and mountainous terrains. It has been receiving a steadily growing number of people lately because of its cultural heritage and touristic attractions. The study area lies between the longitudes of 32 430 –34 370 E and the latitudes of 40 480 –42 020 N (peak elevation: 2587 m; average elevation 780 m above sea level) with

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Fig. 1. Map of Turkey showing the study area.

a geology that shows various lithological units beginning from Paleozoic extending to Quaternary Era (Environmental Status Report, 2004). This study aims to assess the environmental radioactivity level of the Kastamonu region of Turkey based on the following types of measurements: indoor radon concentration, indoor and outdoor gamma absorbed doses in air and radionuclide activity concentrations in soil and drinking water. Comparisons of the results from this study with national and world averages are presented and the studies of this sort are expected to serve as baseline data of natural radioactivity level and will be useful in assessing public doses.

2. Materials and methods 2.1. Indoor

222

Rn activity concentrations

CR-39 nuclear track detectors, consisting of a 2 2 cm2 film placed in a plastic cup closed with a semipermeable membrane, were used for passively determining the 222Rn levels of the dwellings. A total of 30 detectors were placed in basements of the selected apartment buildings and houses and kept in place for three months. The detectors were collected after that period and a chemical process of etching was applied to the films in 30% NaOH solution 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 films exposed to radon gas were visible and counted with a microscope ð500 magnificationÞ and the corresponding indoor 222Rn activity concentrations were estimated in units of Bq/m3.

2.2. Gamma absorbed dose in air A total of 74 measurements (60 outdoor and 14 indoor) of gamma radiation level were carried out using a dose rate meter (Eberline smart portable device, ESP-2, connected with a SPA-6 model plastic scintillation detector). At each spot, a reading was taken in air for 1 h at 1 m above ground level and the result, which includes both terrestrial and cosmic ray components of gamma radiation level, was recorded in units of mR=h. 2.3. Radioactivity in surface soil Soil samples were collected from 10 uncultivated locations of the study area. After clearing the ground of stones, pebbles, vegetation and roots, 1–2 kg of material from the first 10 cm of topsoil was placed in labeled polythene bags and then transferred to the laboratory where the samples were first dried in air and then ground to fine powder (100 mesh). In order to maintain radioactive equilibrium between 226Ra and its daughters, the homogenized samples were transferred to 1000 ml Marinelli beakers and kept for a period of one month. Each sample was then counted for 50 000 s using a gamma spectroscopy device (Canberra, model 85) connected to a coaxial high purity germanium detector. The system was calibrated using standard mixtures of gamma emitting isotopes in 1000 ml Marinelli beakers. The activity of the samples was determined using the total net counts under the selected photopeaks (238U series: 186 keV for 226Ra, 352 keV for 214 Pb and 609 keV for 214Bi; 232Th series: 583 keV for 208Tl and 911 keV for 228Ac; 1461 keV for 40K; 662 keV for 137Cs), the measured photopeak efficiency, gamma

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intensity and weight of the sample. After correcting for background and compton contribution, the activity concentrations per unit mass of the above radionuclides were obtained for each soil sample in units of Bq/kg. 2.4. Radioactivity in drinking water A total of 10 drinking water samples were collected from selected locations of the study area and were transported to the laboratory in 500 cm3 plastic bottles. The water samples were prepared for radionuclide analyses according to a routine procedure outlined by Karahan et al. (2000). The samples were then counted for gross alpha and gross beta radioactivity in a low-background counter (Berthold, LB770-PC 10) to obtain the results in units of Bq/l. 3. Results and discussion The summary statistics for the measurement results of indoor 222Rn activity concentrations are presented in Table 1. Although the average concentration obtained in this study (98.4 Bq/m3) is comparable to those from some cities in Turkey (Erees and Yener, 1999; Erees et al., 2006; Ko¨ksal et al., 1993; Yarar et al., 2005), it is greater than the world average of 40.3 Bq/m3 (UNSCEAR, 2000). The annual average effective dose corresponding to the measured average 222Rn activity concentration was calculated using the conversion factor of 9 nSv=Bq h m3 , as suggested by UNSCEAR (2000), together with equilibrium factor of 0.4 and occupancy factor of 0.8 for indoor

exposure. The mean value was obtained as 2.48 mSv/y which is larger than the world average of 1.094 mSv/y (Thorne, 2003). Table 2 gives the absorbed dose results in air for gamma rays of terrestrial and cosmic origin recorded in this study. The readings, converted to nGy/h using the conversion factor of 8:7 nGy=mR (from the definition of Roentgen), show a lower gamma background in Kastamonu area compared to some Turkish cities (Erees et al., 2006; Karahan and Bayulken, 2000) except Tekirdag (Yarar and Kam, 2005). The gamma absorbed doses in nGy/h can further be converted to annual effective dose in mSv/y using the conversion factor of 0.7 Sv/Gy and occupancy factors of 0.8 for indoor and 0.2 for outdoor (UNSCEAR, 1993). The calculated values of annual effective dose due to gamma radiation range from 0.26 to 0.44 mSv with a mean value of 0.33 mSv, which is lower than the world average of 0.48 mSv (UNSCEAR, 2000). The results of activity concentrations in the soil samples collected from the studied site are given in Table 3 for the radionuclides 226Ra, 214Pb, 214Bi, 208Tl, 228Ac, 40K and 137 Cs. The average concentrations found in this study are 32.93 Bq/kg for 238U, 27.17 Bq/kg for 232Th and 431.43 Bq/kg for 40K and are comparable to those of I˙stanbul (21, 37, and 342 Bq/kg for 238U, 232Th and 40K, respectively; Karahan and Bayulken, 2000) and Manisa (28.5, 27, and 340 Bq/kg for 238U, 232Th and 40K, respectively; Erees et al., 2006). The world averages are 35, 30, and 400 Bq/kg, for these natural radionuclides 238U, 232Th and 40 K, respectively (UNSCEAR, 2000). For the man-made

Table 1 Indoor 222Rn activity concentrations (30 samples) and comparison with literature 222

Rn activity concentrations (Bq/m3)

Effective dose (mSv/y)

Mean Standard deviation Median

98.4 (29–177) 42.9 99.5

2.48 (0.73–4.46) 1.08 2.51

I˙stanbul—Turkey (Ko¨ksal et al., 1993) I˙zmir—Turkey (Erees and Yener, 1999) Manisa—Turkey (Erees et al., 2006) Tekirdag—Turkey (Yarar et al., 2005)

10–260 53–86 97 (47–146) 87

0.5–13 2.65–4.3 4.86 (2.35–7.3) 2.01

The ranges corresponding to data are given in parantheses.

Table 2 Indoor and outdoor gamma absorbed dose in air (60 outdoor and 14 indoor locations) and comparison with literature Indoor gama level (nGy/h)

Outdoor gama level (nGy/h)

Effective dose (mSv/y)


54.81 (44.9–68.5) 6.39 55.45

48.03 (36.1–84.6) 8.52 45.5

0.33 (0.26–0.44) 0.04 0.33

I˙stanbul—Turkey (Karahan and Bayulken, 2000) Manisa—Turkey (Erees et al., 2006) Tekirdag—Turkey (Yarar and Kam, 2005)

113.1–243.6 50 (30.5–68.8)

65 (32 – 94) 78.3–135.72 43 (30.4–54.3)

0.29


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Table 3 Soil radioactivity concentrations (in units of Bq/kg; 10 samples) 238

232

U series 214

214

208

228

37.4 8.63 36.06 26.80–49.79

26.34 7.36 24.38 19.48–40.05

35.04 15.96 32.04 14.65–65.69

23.56 6.38 21.76 17.06–35.62

30.79 15.25 28.72 9.34–61.01

Pb

Bi

Tl

40

137

431.43 214.03 458.25 155.7–868.77

8.02 5.63 8.43 0.75–16.94

K

226

Ra

Mean Standard deviation Median Range

Th series

Cs

Ac

Table 4 Gross alpha and gross beta radioactivity levels in drinking water (10 samples) and comparison with literature Gross alpha activity (Bq/l)

Gross beta activity (Bq/l)


0.0089 (0.0014–0.026) 0.0078 0.0063

0.271 (0.0162–2.241) 0.6929 0.051

Giresun (Damla et al., 2006) I˙stanbul (Karahan et al., 2000) Rize (Damla et al., 2006) Trabzon (Damla et al., 2006)

0.0071 0.0228 (0.007–0.045) 0.0083 0.0065

0.0971 0.0664 (0.02–0.13) 0.0828 0.1008


radionuclide 137Cs, this study found an activity concentration of 8.02 Bq/kg. To estimate the terrestrial component of gamma level from the measured 238U, 232Th and 40K concentrations, the procedure outlined by Karahan and Bayulken (2000) was followed. This method, first suggested by Beck (1972), utilizes the conversion factors of 0.427, 0.662 and 0.043 (nGy/h)/(Bq/kg) for 238U, 232Th and 40K, respectively, to estimate the absorbed doses in air due to natural radionuclides in soil samples. Based on the average radionuclide concentrations measured in this study, the mean absorbed gamma dose in air was calculated as 52.76 nGy/h (Min: 28.74; Max: 96.15) and found to be comparable to the world average of 60 nGy/h (UNSCEAR, 2000). The average contributions of terrestrial radionuclides 238U, 232Th and 40K to absorbed dose in air were 12.43, 21.79 and 18.55 nGy/h, respectively, 232Th series being the dominant contributor. From the calculated average absorbed dose of 52.76 nGy/h, the average annual effective dose due to terrestrial gamma radiation in Kastamonu was calculated and found to be 60 mSv,which falls below the world average of 70 mSv (UNSCEAR, 2000). Table 4 presents the results of gross alpha and gross beta activity measurements for the water samples collected in this study. For every sample, the beta activity is always higher than the alpha activity. Gross alpha activity of 0.0089 Bq/l found in this study is typical to other Black Sea cities (Damla et al., 2006) and is lower than that of Istanbul (Karahan et al., 2000). However, the measured gross beta activity is higher because of an outlier present in the data (Seyh Saban Veli, 2.2410 Bq/l) belonging to a location near a spring water. The averages measured for the study region

are lower than those recommended by World Health Organization (WHO, 2004) for drinking water, which are 0.5 and 1 Bq/l for alpha and beta activities, respectively. In order to estimate the total annual effective dose from the average gross alpha activity, dose conversion coefficient of 2:8 104 ðSv=BqÞ for 226Ra (an alpha emitter) was used assuming that an adult, on the average, consumes 2 l of water per day (WHO, 2004). This resulted an annual effective dose of 1:83 mSv for this study. The uncertainties are approximately 30% for gross alpha, 5% for gross beta and 2% for gamma spectrometric measurements probable causes being the sample preparation and geometry as well as the counting time. For external gamma dose measurements, the uncertainties of readings were constrained to the smallest scale on the instrument used, which was 1%. 4. Conclusion This study intends to layout the bacground radiation level of the Kastamonu region located in northwestern Black Sea region of Turkey through various radioactivity measurements. The results obtained indicate that the study area has a background radiation level that is within the natural limits and shows no significant departure from the other parts of the country. References Beck, H.L., 1972. The physics of environmental radiation fields. Natural radiation environment II, CONF-720805 P2. In: Proceedings of the

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Second International Symposium on the Natural Radiation Environment. Damla, N., Cevik, U., Karahan, G., Kobya, A.I., 2006. Gross alpha and beta activities in tap waters in Eastern Black Sea region of Turkey. Chemosphere 62, 957–960. Environmental Status Report, 2004. Provincial Directorate of Environment and Forestry, Kastamonu, Turkey. Erees, F.S., Yener, G., 1999. Radon levels in new and old buildings. In: Baumstarks-Khan, C., et al. (Eds.), Fundamentals for the Assessment of Risks from Environmental Radiation. Kluwer Academic Publishers, The Netherland, pp. 65–68. Erees, F.S., Akozcan, S., Parlak, Y., Cam, S., 2006. Assessment of dose rates around Manisa (Turkey). Radiat. Meas. 41, 598–601. Karahan, G., Bayulken, A., 2000. Assessment of gamma dose rates around Istanbul (Turkey). J. Environ. Radioact. 47, 213–221. Karahan, G., Ozturk, N., Bayulken, A., 2000. Natural radioactivity in various surface waters in Istanbul, Turkey. Water Res. 34 (18), 4367–4370. Ko¨ksal, E.M., C - elebi, N., O¨zc- ınar, B., 1993. Indoor 222Rn concentrations in Istanbul houses. Health Phys. 65 (1), 87–88.

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