a study of environmental radioactivity measurements ...

Radiation Protection Dosimetry Advance Access published May 22, 2012 Radiation Protection Dosimetry (2012), pp. 1–7

doi:10.1093/rpd/ncs071

A STUDY OF ENVIRONMENTAL RADIOACTIVITY MEASUREMENTS IN THE SAMSUN PROVINCE, TURKEY B. Kucukomeroglu1, F. Maksutoglu1, N. Damla2,*, U. Cevik1 and N. Celebi3 1 Department of Physics, Karadeniz Technical University, 61080 Trabzon, Turkey 2 Department of Physics, Batman University, 72060 Batman, Turkey 3 Cekmece Nuclear Research and Training Center, 34149 Istanbul, Turkey

Received November 11 2011, revised April 5 2012, accepted April 19 2012 This study was concerned with the measurement of natural and artificial radionuclides in soil samples and indoor radon concentrations in the Samsun province, Turkey. In soil samples, the values of individual mean activity of 226Ra, 232Th, 40K and 137 Cs radionuclides were found to be 31, 22, 341 and 16 Bq kg21, respectively. The radiological parameters, such as the absorbed dose rate in air, the annual effective dose (AED) and excess lifetime cancer risk, were calculated. Indoor radon measurements were carried out with CR-39-based radon dosemeters at 127 dwellings in the Samsun province. The mean annual 222 Rn activity was found to be 106 Bq m23 (equivalent to an AED of 1.88 mSv). The seasonal variation of 222Rn activity shows that maximum levels are observed in the winter, while minimum levels are observed in the summer. The mean lifetime fatality risk for the studied area was estimated at 1.4531024. The results obtained did not significantly differ from those obtained in other parts of the country.

INTRODUCTION Gamma radiation from naturally occurring radionuclides and from artificial radionuclides in the environment is the main source of radiation that human beings are exposed to. Since natural environmental radiation depends mainly on the local geology of the region in question and its geographical conditions, large variations in the dose rates of both cosmic and terrestrial radiation will be found depending on where the measurements are taken. The natural radioactivity in soils primarily comes from the 238U and the 232Th series together with 40K. Moreover, there are artificial radionuclides in the world, one of the most important of which is 137Cs, which results from atmospheric nuclear weapon tests, which in the Chernobyl nuclear power plant has been emitting radiation ever since the accident and which is still radioactive in the environment predominantly in surface soil(1). Three radioactive series are the primary sources of radon in soil: 222Rn, whose half-life is 3.8 d and which is a noble radioactive gas and originates from the 238U series; 220Rn from the 232Th series and 219Rn from the 235 U series. 219Rn does not usually contribute to the signal measured with alpha particle detectors, since it decays before reaching the detecting device and the thoron is too short to allow of a significant diffusion or advection into the dwellings(2). 222Rn is the most dominant hazardous radionuclide among the radon isotopes; therefore, it is important to monitor indoor radiation to assess indoor radiation exposure. Environmental radioactivity surveys are of great importance and evoke remarkable interest in health

physics both for many practical reasons and for more fundamental scientific reasons. The objective of this study was to determine natural (226Ra, 232Th and 40K) and artificial (137Cs) radioactivity concentrations in soils and the seasonal variation of indoor radon concentration levels and to calculate the effective dose the population is exposed to because of the presence of terrestrial gamma radiation and radon in the Samsun province. The data presented in this article might be useful as baseline data for future estimations of exposure of a population. MATERIALS AND METHODS Sampling area The Samsun province is located in the Black Sea Region of Turkey (Figure 1). Samsun is the biggest city of the Black Sea Region in terms of population, industry, trade, natural and cultural wealth. It is situated in the middle part of Black Sea’s coastline between the deltas where the Yes¸ilırmak and Kızılırmak rivers flow. It has a population of 1.5 million and the region spans over an area of 9083 km2. In terms of geographical co-ordinates, the city lies between the north latitudes 408500 and 418510 and the east longitudes 378080 and 348250 . Gamma-spectrometric analysis Sampling Seventy-five soil samples were collected from the Samsun province. The sampling sites were nearly

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B. KUCUKOMEROGLU ET AL.

ground level and on non-agricultural land away from trees and buildings. After clearing the ground surface of stones, pebbles, vegetation and roots, 1 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 100 mesh by a crushing machine. The samples were then dried at 1108C for 24 h to ensure that moisture was completely removed. About 170 g of each sample was sealed in gas-tight, radon-impermeable, cylindrical polyethylene containers. Then, the containers were completely sealed for 4 weeks to bring about a

secular equilibrium between 226Ra and their short-lived decay products.

222

Rn and

Instrumental The activity concentrations of 226Ra, 232Th, 40K and Cs in the soil samples were measured using a coaxial high-purity germanium (HPGe) detector (Canberra, GC 1519 model). The relative efficiency of the detector is 15 % and it has a resolution of 1.9 keV at 1332 keV. The detector was shielded in a 10cm-thick lead well internally lined with 2-mm Cu 137

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Figure 1. The sampling sites in the Samsun province.

ENVIRONMENTAL RADIOACTIVITY IN SAMSUN

A¼

C 1PMt

(using housing register) at random depending on person who permitted the research team to carry out the study in his or her house. The total exposure period was 1 y and obtained during four 3-month surveys. Instrumental The collected detectors were sent to the Istanbul Cekmece Nuclear Research and Training Centre for analysis. The CR-39 detectors were designed to be 20201 mm3 in size and placed in a plastic container 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 708C 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 226Ra source with a concentration of 3.2 kBq m23. The 222Rn concentrations were determined by using a calibration factor of 7.23 kBq track21 h21 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). RESULTS AND DISCUSSIONS

ð1Þ

where A ðBq kg1 Þ is the activity concentration of a radionuclide, C is the total net count of a specific gamma emission, 1 is the detector efficiency of the specific gamma emission, P is the absolute transition probability of that gamma emission, M is the mass of the sample (kg) and t is the counting time. Indoor radon concentrations Sampling Radon measurements were carried out using the solid state nuclear detector (SSNTD) passive technique, which is the most reliable technique for the integrated and long-term monitoring of radon concentrations. CR-39 plastic track detectors purchased from Radoys Co. Ltd. Budapest/Hungary were used in this survey. Indoor radon measurements were carried out for a period of 1 y in four consecutive 3-month periods (seasons) in 127 dwellings in Samsun, selected as uniformly distributed on the surface area as possible. Dosemeters were installed at head height in the living room of each house. Sampling was done

The natural (226Ra, 232Th, 40K) and artificial (137Cs) radionuclides in the soil samples were determined by using a gamma-ray spectrometer with on HPGe detector; afterwards, exposure rates were calculated. The activity values of the radionuclides are presented in Table 1. The activity levels of 226Ra, 232Th, 40 K and 137Cs in the samples were expressed in becquerel per kilogram. As one can see from Table 1, the specific activities of 226Ra, 232Th and 40K were determined in the ranges 11 –76, 10 –40 and 57 –660 Bq kg21, with corresponding mean values of 31, 22 and 341 Bq kg21, respectively. The worldwide mean concentrations of these radionuclides have been reported by UNSCEAR(1) as 35, 30 and 400 Bq kg21, respectively. The mean values of 232Th and 40 K concentrations were found to be lower than those of the world values, while the concentration values of 226Ra were remarkably similar to that of UNSCEAR(1). The anthropogenic radionuclide 137 Cs was also seen in all samples. 137Cs is spread to the atmosphere through nuclear activities. Turkey, like other countries in the area, has been affected by the Chernobyl nuclear power accident since 1986 when it occurred. For the human-made radionuclide 137 Cs, the mean activity concentrations varied from

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foils. The detector output was connected to a spectroscopy amplifier (Canberra, Model 2025)(3). A spectrum analysis was carried out using the Genie 2000 software from Canberra. A performance test using the certified reference sample (IAEA-375) 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 carried out by periodical efficiency and energy calibrations and repeating sample measurements. The sample counting time was 50 000 s to obtain gamma-spectra with good statistics. To determine the detector background, 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(4, 5). The gamma transition energies of 351.9 keV of 214 Pb and 609.3 keV of 214Bi were used to determine the concentrations of 226Ra. The gamma transition energies of 583.1 keV of 208Tl and 911 keV of 228Ac were used to determine the concentrations of the 232 Th series. 40K activity was determined from the 1460.8 keV emission gamma-lines and 137Cs activity was determined from the 661.6 keV emission gamma-lines. The activity concentrations of the radionuclides in the measured samples were computed using the following equation:

0.021 0.014 0.018 0.017 0.014 0.019 0.019 0.018 0.06 0.04 0.05 0.05 0.04 0.05 0.05 0.05 629 450 433 370 507 527 660 22 34 23 20 32 23 40 40 16 10 13 20 11 14 12 73 33 56 48 35 36 37

37 31 33 18 40 29 35 41 22 36 31

27 25 24 21 35 39 25 38 19 31 22

431 299 289 298 522 580 274 443 358 341 341

8 9 8 7 9 5 12 25 54 14 16

Present study.

8 to 70 Bq kg21 with a mean value of 16 Bq kg21. A comparison of the measured activity concentrations of the soil samples with those reported for other parts of Turkey is given in Table 2. The contribution of natural radionuclides (226Ra, 232 Th and 40K) to the absorbed dose rate in air (ADRA) depends on the concentrations of these radionuclides in the soil. Gamma-ADRA in nGy h21 at 1 m above ground level was computed by means of the following equation(1): ð2Þ

where AK, ARa and ATh are the activity concentrations of Ra, Th and K (Bq kg21), respectively. The absorbed dose rates in air calculated from the measured activities in the samples are given in Table 1. The mean ADRA was found to be 42 nGy h21 (min. 33 nGy h21 in Tekkekoÿ and max. 49 nGy h21 in Ladik), which is lower than the world mean of 60 nGy h21. To predict the annual effective dose (AED), the conversion coefficient (0.7 Sv Gy21) from the absorbed dose in air to effective dose received by adults, and the outdoor occupancy factor (0.2) proposed by UNSCEAR(1) were used. Therefore, the effective outdoor dose rate (AED) in units of mSv per year was computed by means of the following formula: AEDE ¼ ADRA T F

8 6 5 8 6 5 9

21 12 12 14 11 21 17

31

41+17 20+9 37+20 29+12 20+9 31+6 31+7

34 29 28 11 11 13 31+16 26+15 41+20 76 49 60 12 12 17

226 232 40 137 Ra Th K Cs (Bq kg21) (Bq kg21) (Bq kg21) (Bq kg21)

ADRA ¼ 0:462ARa þ 0:604ATh þ 0:0417AK

Centrum Bafra Ondokuz Mayıs Ladik Tekkekoÿ Terme Kavak Çars¸amba Vezirko¨pru¨ Havza Mean

20 4 4

Kastamonu(8) Sanliurfa(9) Gaziantep(10) Adana(11) Bayburt(12) Tekirdag(13) Batman(5) Trabzon(14) Artvin(15) Ardahan(15) Samsuna a

340+200 360+72 365+60 272+97 324+159 372+105 345+236 341 86 262 270 89 57 298 50 19+6 14+5 16+3 25+4 18+6 23+10 26+10

16

23+19 11+2 17+9 17+4 15+6 14+4 19+6 70 14 33 26 25 19 32 12 8 10 13 10 9 11

49 33 42 40 34 44 44 42

14+3 12+1 16+5 21 13 23 8 11 10 358+125 325+74 333+218 71 232 115 22+7 22+7 19+7

570 409 625

Mean value+SD

Min. Max.

Mean value+SD

43 39 44

0.05 0.05 0.05

Province

Min. Max. Mean value+SD Min. Max. Mean value+SD Min. Max.

137

K (Bq kg21) 40

Th (Bq kg21) 232

Ra (Bq kg21)

226

Number of dwellings Sample location

Table 1. Radionuclide activities and radiological parameters.

Table 2. Radioactivity concentrations in the soil samples in different parts of Turkey.

ð3Þ

where ADRA is the calculated dose rate (in nGy h21), T is the outdoor occupancy time (0.224 h365.25 d ¼ 1753.2 h y21) and F is the conversion factor (0.71026 Sv Gy21). In Table 4, the results obtained for the AED in the samples are presented. The mean computed value of the AED in the

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Cs (Bq kg21)

ADRA (nGy h21)

AED (mSv y21)

0.018 0.017 0.019

ELCR (%)


3.5 4.0 4.4 4.4 4.3 4.3 2.9 4.1 1.86 1.93 2.01 1.59 1.79 2.20 2.19 1.88 1.44 1.49 1.56 1.22 1.39 1.70 1.69 1.45 109 113 118 93 105 129 128 106

96 70 52

96 59 71 63 52 98 115

10 20 33

28 37 35 29 40 31 28

48

54+23 52+8 50+14 39+14 45+6 55+21 78+23

40+14 44+13 44+8

95 104 104

1.25 1.37 1.37

1.62 1.78 1.78

Province Istanbul(16) Ankara(17) Erzurum(18) Sanliurfa(18) Antalya(18) Tekirdag(19) Manisa(20) Kastamonu(8) Edirne(21) Kars(22) Giresun(23) Çanakkale(24) Bayburt (12) Batman(5) Ardahan(15) Artvin(15) Trabzon(14) Samsuna

225 75 90 80 66 125 146 27 15 44 37 51 39 32 193 125+34 163 141+22 197 139+39 175 112+38 144 124+18 272 152+58 319 137+50 124 121 155 152 126 173 134 156 11 7 6 5 3 11 12

240 190+34 256 208+41 308 218+61 273 171+59 225 194+28 425 237+90 498 226+61 194

78 122 97 80 111 86 78

122 89 66 13 25 42 43 87 143 50 17 5

416 303 225

175+59 191+58 192+33

28 55 91

266 194 144

112+38 126+33 123+21

58

67+54 50+26 64+18 50+17 57+8 70+26 71+27

51+17 56+17 56+10

a

Centrum Bafra Ondokuz Mayıs Ladik Tekkekoÿ Terme Kavak Çars¸amba Vezirko¨pru¨ Havza Mean

Mean Min. Max. Mean Min. Max. Mean Min. Max. Mean value+SD value+SD value+SD value+SD Min. Max.

Rn (Bq m23) in summer

222

Rn (Bq m23) in autumn 222

Rn (Bq m23) in spring 222

Rn (Bq m23) in winter

222

Number of dwellings Sample location

Table 3. Seasonal indoor radon levels recorded in different areas of the Samsun province.

Table 4. Indoor radon concentrations from different parts of Turkey. Mean (Bq m23) 50 55 85 68 29 87 97 98 49 114 125 68 56 84 173 132 97 106

Present study.

samples is 0.05 mSv y21. This value is lower than the world mean of 0.07 mSv(1). Excess lifetime cancer risk (ELCR) was calculated by using the following equation: ELCR ¼ AEDE DL RF

ð4Þ

where DL is the duration of life (70 y) and RF is the risk factor (Sv21), fatal cancer risk per Sievert. For stochastic effects, ICRP uses a value of 0.05 for the public(6). The calculated lifetime cancer risks are presented in Table 1. As shown in Table 1, the mean ELCR was found to be 0.018 %. Indoor radon (222Rn) concentration levels were measured in 10 residential areas (127 dwellings) in the Samsun province, Turkey, in every season of the year. The seasonal variation, AED, mean lifetime fatality risk and winter-to-summer ratio for each area were also calculated. The results obtained are summarised in Table 3. The lowest radon concentration was found in the summer (in the Centrum: 10 Bq m23), while the highest concentration was found in the winter (in Havza: 498 Bq m23). The mean annual indoor value varied from the lowest radon concentration of 93 Bqm23 in Kavak, and the highest value of 129 Bqm23 was found in the Vezirko¨pru¨. These values are higher than the mean value of 40 Bq m23(1), reported for the dwellings worldwide, but less than the lower limit of the range of the action level of (200–600) Bq m23, recommended by the ICRP(6). Some indoor radon concentrations presented in the other parts of Turkey are given in Table 4 for

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Mean annual 222 Rn (Bq 23 m )

Lifetime fatality risk 1024

Mean annual dose (mSv)

4.4 4.3 4.4

Winter/ summer ratio



Figure 3. Comparison of the annual mean effective dose in different seasons.

comparison. Also, the relation between 226Ra in soil and indoor radon is demonstrated in Figure 2, where the correlation is found to be 0.67. It is evident from results that the maximum value of radon concentration is observed during the winter and minimum during the summer as expected. This is because the doors and windows of the dwellings remain closed most of the time in winter compared with the summer, and therefore ventilation is poor in the winter. The ratio of radon concentration from the winter to the summer was computed for all the 127 dwellings. This ratio of indoor radon ranges from 2.9 to 4.4 with a mean of 4.1. The AED from radon (222Rn) and the mean lifetime fatality risk were estimated according to ICRP(7). ICRP assumes 80 % indoor occupancy (70 000 h y21) and an F (equilibrium factor) value of 0.4 for dwellings. One working level month (WLM) corresponds to the exposure of an individual to radon progeny of 1 WL concentration (2.081022 mJ m23) for a duration of 170 h, which results in 1 WLM equivalent to 3.54 mJ h m23. The lifetime fatality risk and the AED received by the bronchial and pulmonary regions of the human lung have been calculated by using the conversion factors of 31024 WLM21 and 3.88 mSv WLM21, respectively. In Table 3, the lifetime fatality risk and the calculated AED are presented. The lifetime fatality risk varies from 1.221024 to 1.701024 with a mean value of 1.451024. The estimated AED received by the residents of the studied areas varies from 1.59 mSv (Kavak) to 2.20 mSv (Vezirko¨pru¨) with a mean of 1.88 mSv. From the measured indoor levels, the AED for each season was also calculated and is shown in Figure 3. The estimated AED in different seasons is found to be higher in the winter and lower in the summer as expected. In all the areas surveyed, the estimated AED is less than even the lower limit of the recommended action level (3–10 mSv).

CONCLUSIONS This study tried to attract attention to the natural and artificial radionuclides in the soil samples and indoor radon concentrations in the Samsun province, Turkey. The activities of the natural (226Ra, 232Th and 40K) and artificial (137Cs) radionuclides in the soil samples were determined by gamma ray spectroscopy. The mean activity concentrations of 226Ra, 232 Th, 40K and 137Cs in the samples were 31, 22, 341 and 16 Bq kg21, respectively. The values obtained show that the mean ADRA, the AED and ELCR for all the samples are 42 nGy h21, 0.05 mSv y21 and 0.018 %, respectively. In this study, indoor radon measurements in 127 dwellings belonging to 10 regions of the Samsun province were carried out using CR-39-based radon dosemeters. The annual indoor radon value in the study area varies from 93 to 129 Bq m23 which is higher than the world mean of 40 Bq m23; however, these values are below the recommended action level (200– 300 Bq m23). The results indicate that the indoor radon concentration is higher in the winter than in the summer as expected. The present values for mean AED ranged from 1.59 to 2.20 mSv with a mean value of 1.88 mSv, which is lower than the recommended action level (3 –10 mSv). Therefore, this study shows that the measured samples were within the recommended safety limits and did not pose any significant source of radiation hazard. The results of this study will provide useful baseline data for adopting safety measures and dealing effectively with radiation emergencies. ACKNOWLEDGEMENT The authors would like to thank the Cekmece Nuclear Research and Training Centre of Turkish Atomic Energy Department for their support and cooperation to perform this work.

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Figure 2. Correlation between 226Ra in soil samples and indoor radon concentrations.


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