Introduction

Human beings have been continuously and inevitably under the influence of radiation since their existence. Radiation is caused by radioactive nuclei in the structure of the world, cosmic heat in the solar system or artificial radiation produced by human beings. Natural resources are very important in the evaluation of radiation dose. The highest amount of annual dose of a human is taken from natural radioactivity. Annual average dose values from natural radiation are 9.5–10% in foods, 8.7% in drinks, 8.7–9% in gamma rays, 17.5–18% in cosmetics, 14.8–15% in cosmic rays and 48–49.4% in radon [1]. The rate of radionuclide concentration in soil, water and air is increased by nuclear tests or nuclear reactor accidents (such as Chernobyl).

There are many studies in the literature about the determination of natural radionuclide concentrations in soil [2,3,4,5,6,7,8]. The aim of these studies is to determine the level of natural radioactivity in the country or regionally and to determine how many people are taking these natural sources. Under the influence of radioactive materials in the rocks that pass through the waters of the ground or the depths of the ground. They gain some radioactivity. The most important radioactive elements encountered in groundwater are K40, Rb87, Th232, U235 and U238 [9, 10]. Studies on the determination of the natural radioactivity level in the waters were carried out only in thermal waters. Because the activity concentration of groundwater is higher than surface water. In recent years, natural radionuclide was found in drinking water, in the underground waters. Mostly uranium-series elements are radium and radon. Radioactive radon, which is the product of the disintegration of 226Ra is found in some underground waters at very high concentrations [1]. It is very difficult to detect the elements of the actinium series in groundwater. Although in some waters 232Th and 226Ra from the thorium series are found in detectable amounts, the 220Rn, which has a very short half-life, does not allow to accumulate in water and rocks [1, 11]. In the researches related to drinking water, total Alpha and Beta activities are generally examined [12,13,14,15,16]. Total alpha activity is due to uranium and radium isotopes due to low thorium solubility in natural waters [17]. In principle, although the main cause of Alpha activity is 226Ra. It is sometimes reported to contribute 232Th. 210Po or 224Ra [18]. As such, it is stated that beta activity is mainly caused by 40K and 228Ra [13, 14]. Drinking water in terms of human health, the World Health Organization (WHO) and Turkey Standards Institute (TSE) adopted by the upper limits; the total alpha is 0.1 Bq/l, the total is Beta 1 Bq/l and Tritium 100 Bq/l [11, 19]. The other study, researches determined radiological distribution of gross alpha, gross beta, 226Ra, 232Th, 40K, and 137Cs for a total of 40 natural spring water samples obtained from seven cities of the Eastern Black Sea Region was determined by artificial neural network (ANN) method [20]. Gültekin and Dilek in 2005, In their study on mineral water resources in Gümüşhane, they determined that the total alpha activity in the mineral water resources varies between 122 and 780 mBq/l [12].

In addition, the relationship between the radionuclides in the environment and the radiation dose that people receive from these sources should also be determined. However, after much research, it can be decided whether a region is suitable for natural radiation in terms of healthy legislation [21]. In this field, research studies are carried out in Turkey and abroad [1, 22,23,24,25,26]. For this purpose, research on the International Commission on Radiological Protection (ICRP), United States Radiation Protection and Measurement National Committee (UNSCEAR) and Turkey Atomic Energy Agency Çekmece Nuclear Research and Training Center (TAEK ÇNAEM) is carried out by national and international organizations. The main purpose of the environmental radiation measurements is to determine the radiation type and dose that people receive from the environmental sources and to evaluate the risk. Utilizing natural radioactivity, it is used in various fields such as the explanation of the nuclear structure of the atom, estimation of the age of the world and measurement of the sediment formation rates at the bottom of the oceans. These studies are important in terms of determining both the levels of natural radioactivity and the rate at which people are exposed to radiation from nuclear power plants in the regions where nuclear power plants are established. This study was carried out to determine the environmental radiation of Gumushane.

Materials and methods

Studied area

More than 40% of the pre-Liassic basement rocks of the Eastern Pontides are composed of granitoids. Gümüşhane Batolite is the largest of these granitoids with a surface area of ~ 400 km2.

Granite, granodiorite and felsic rocks (microgranite, spherulitic dacite and rhyolite) are the main rock types that form the granitoid. Granite and granodiorite are outcropped in the central and northern parts of the batholith and contain mainly hornblende, biotite, plagioclase, K-feldspar and magnetite, apatite and zircon as the secondary component. In contrast, the felsic rocks outcrop in the south and southeast parts of the batholith and consist only of quartz and feldspar. The boundary between granite/granodiorite and felsic rocks is gradual [27].

Gümüşhane province, which has an area of 6575 km2, is located between 38°45′–40°12′ east longitudes and 39°45′–40°50′ north latitudes in the Black Sea Region. Coordinates of the sample locations were recorded with Garmin Etrex 32x type handset. The coordinates of the obtained samples are introduced to the QGIS program as points and the radioactivity values corresponding to the point coordinates were introduced to the program as attribute data. In order to create radioactivity anomaly maps, anomaly and contour maps were created using the inverse distance weighted (IDW) method from the QGIS program interpolation module. The average height of the city from sea level is 1210 m. Gümüşhane study area where samples are taken were presented in Fig. 1. All samples were collected during June 2016–October 2016.

Fig. 1
figure 1

Study area map in Gumushane province

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Determination of radioactivity in water samples

Various drinking water 77 samples were collected from the vicinity of the Gümüşhane province. Of which, 27 from Gümüşhane central district, 9 from Kurtun district, 12 from Siran district, 8 from Kelkit district, 10 from Torul district and 11 from Köse district. In order to determine gross alpha and gross beta activity, a Berthold brand and LB 770 model alpha and beta counter with 10 channels low level present in ÇNAEM laboratory were used. The operation voltage of the detector is 1650 V and its diameter is 5 cm. The used in these kinds of counters contain 90% argon and 10% methane.

The main steps of the measurement procedure are detailed in Ref [29]. 500 mL of the sample to be analyzed was taken and 5 drops of diluted detergent (1 + 4) were added. The beaker placed on hot-late magnetic stirrer was mixed by adding 20 mL of 2 N H2SO4. Stir process was continued for 10 min after boiling to ensure more mixing of the solution. Then 1 mL of barium carrier was added to the solution and the stirring process was continued for 30 min. 1 mL of Bromocresol purple indicator, 1 mL of iron carrier and 5 mL of paper pulp/water mixture is added.

Then drops of ammonium hydroxide, 6 N (NH4OH, 6 N) were added until the color of the solution turns yellow to purple and the stirring process was continued for 30 min more. Then the solution was allowed to stand for precipitation. The precipitate was then filtered through a filter paper by the vacuum pump. Finally, the precipitate on the filter paper was allowed to stand for at least 3 h to remove the radon products and dried in a 105 °C oven or under a lamp. The same procedures were performed for blank. (Background activity). The above-mentioned procedures were repeated for each water sample [28,29,30,31,32,33,34].

$${\text{Gross}}\,{\text{alpha}}\,{\text{activity}}, {\text{pCi/L}} = \frac{{C_{a} - C_{b} }}{EV}$$
(1)

where E: counter efficiency, cpm/PCi, V: volume analyzed, L, Ca: sample counts per minute, cpm and Cb: reagent blank, cpm.

Determination of radioactivity in soil samples

Various 62 soil samples were collected from the vicinity of the Gümüşhane province. The distribution of the soil samples are such that 23 from the central district of Gümüşhane, 8 from the Kürtün district, 4 from the Şiran district, 9 from the Kelkit district, 8 from the Köse district and 10 from the Torul district. The samples were grounded, homogenized and sieved to about 100 mesh by a crushing machine. Then the samples were dried in an oven at a temperature of 100 °C. Samples were put into plastic cylindrical polyethylene containers. Then they were weighed, sealed and stored at least for 30 days to allow secular equilibrium between radium and thorium and their decay products. Then each sample was measured and the values are given in Bq/kg dry weight. The specific activity concentration of natural radionuclides (of 226Ra, 232Th and 40K) and artificial radionuclide (137Cs) were determined by using Gama-ray spectroscopy at Çekmece Nuclear Research and Training Center (ÇNAEM) [34].

Gamma spectrometry measurements were conducted with a coaxial high purity Ge detector of 15% relative efficiency and resolution 1.2 keV at the 1332 keV gamma of 60Co. The energy calibration and absolute efficiency calibration of the spectrometer were carried out using calibration sources. The gamma ray transitions of energies 351.9 keV (214Pb) and 609.3 keV (214Bi) were used to determine the activity concentration of the 226Ra series [31]. The gamma-ray lines at 911.1 keV (228Ac) and 583.1 keV (208Tl) were used to determine the activity concentration of the 232Th series [31]. The activity concentrations of 40K were measured directly through the gamma line emission at 1460 keV. The 661.6 keV gamma transitions was used to determine the 137Cs concentrations. The activity concentrations for the natural radionuclides in the measured samples were computed using the following relation; [31].

$$C_{s} = \frac{{N_{a} }}{\varepsilon Ptw}({\text{B}}\,{\text{q}} \cdot {\text{kg}}^{ - 1} )$$
(2)

where Na is the net counting rate of gamma ray, ε is the counting efficiency of the used detector, P the absolute transition of gamma decay, t the counting time in seconds and w the weight of dried sample in kg.

The radium equivalent activity is calculated from the following equation: [31, 35].

$$Ra_{\text{eq}} = C_{\text{Ra}} + 1.43C_{\text{Th}} + 0.077C_{\text{K}}$$
(3)

The gamma absorbed dose rates in air were calculated using the following formula [31, 35]:

$$D\left( {{\text{nGy}}\,{\text{h}}^{ - 1} } \right) = 0.462C_{\text{Ra}} + 0.604C_{\text{Th}} + 0.0417C_{\text{K}}$$
(4)

The external hazard index (Hex) due to the emitted gamma rays for each sample was calculated according to the following formula [31, 35]:

$$H_{\text{ex}} = \frac{{C_{\text{Ra}} }}{370} + \frac{{C_{\text{Th}} }}{259} + \frac{{C_{\text{K}} }}{4810} \le 1$$
(5)

The annual effective dose rate (AEDR) was calculated using the following equation [31, 35]:

$${\text{AEDR }}\left( {\upmu{\text{Sv}}\,{\text{y}}^{ - 1} } \right) = D\left( {{\text{nGy}}\,{\text{h}}^{ - 1} } \right) \times 8760\left( {{\text{h}}\,{\text{y}}^{ - 1} } \right) \times 0.2 \times 0.7\,{\text{SvG}}\,{\text{y}}^{ - 1} \times 10^{ - 3} .$$
(6)

Carrying out air measurements

In this study, 338 measurements were taken from Gümüşhane Province and its districts in order to determine environmental gamma dose rates. In this study, the portable aluminum scintillation detector, which brands the LUDLUM brand 2241-2 Survey Meter, was used to determine the external gamma radiation level. With the environmental radiation monitor, measurements were taken from the height of 1 m above the ground during the gamma radiation measurements, after waiting 2–3 min for the device to reach a certain equilibrium. Radiation levels were read from the digital display and recorded in μSv/h.

Results

In this study, radioactivity levels were determined in water, soil samples and air. Kelkit, Şiran, Torul, Kürtün and Köse districts and villages are the districts of the studied area. Water samples were counted in the alpha–beta counting system and soil samples were counted in the gamma spectrometer system. The air measurement was carried out with the 2241-2 Survey Meter scintillation gamma detector.

Water samples

The results are presented in Table 1. It can be seen from the table that the minimum and the maximum gross alpha and gross beta activity results 3 mBq/L, 110 mBq/L, 4 mBq/L and 190 mBq/L, respectively. The mean value for gross alpha is 13.97 mBq/L, whereas the mean values for gross beta is 46.77 mBq/L. Gross alpha and gross beta activity results with the sampling points were presented in Figs. 2 and 3, respectively.

Table 1 Total alpha and total beta values obtained from water sources in Gumushane province
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Fig. 2
figure 2

Total alpha radioactivity distribution map in Gumushane province waters (mBq/l)

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Fig. 3
figure 3

Total beta radioactivity distribution map in Gumushane province waters (mBq/l)

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Soil samples

The specific activity concentration of natural radionuclides (of 226Ra, 232Th and 40K) and artificial radionuclide (137Cs) were determined by using Gama-ray spectroscopy present in Çekmece Nuclear Research and Training Center (ÇNAEM). Activity concentrations and mean radium equivalent activity (Raeq) of 226Ra, 232Th, 40K, and 137Cs are presented in Table 2. It was found that activity concentrations ranged from 1.23 to 120.34 Bq/kg for 226Ra, from 1.86 to 159.5 Bq/kg for 232Th and from 50.89 to 1223 Bq/kg for 40K. 37Cs activity concentration was found to range from 0.1 to 21.47 Bq/kg. Obtained values show that the mean radium equivalent activity (Raeq) were from 7.45 to 434 Bq/kg. The gamma absorbed dose rates in air were in the range of 3.7–202.9 nGy h−1, with an arithmetic mean of 61 nGy h−1, while the annual effective dose rates (AEDR) were determined to be in the range of 4.67–248.8 μSv y−1. External hazard index (Hex) for the soil samples were in the range of 0.02–1.19. The results of activity concentrations are presented in Figs. 4, 5, 6 and 7.

Table 2 Activity concentrations in soil samples in Gumushane province (Bq/kg)
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Fig. 4
figure 4

The 226Ra iso-activity map of the soil of Gumushane province (Bq/kg)

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Fig. 5
figure 5

The 232Th iso-activity map of the soil of Gumushane province (Bq/kg)

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Fig. 6
figure 6

The 40K iso-activity map of the soil of Gumushane province (Bq/kg)

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Fig. 7
figure 7

The 137Cs iso-activity map of the soil of Gumushane province (Bq/kg)

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Air measurements

The coordinates and measurement values of natural radioactivity measurements made in the air from Gümüşhane, Kelkit, Şiran, Torul, Kürtün and Köse districts are given in Table 3. In addition, the data points of the air data and the map are given in Fig. 8.

Table 3 Coordinates and measurement values of points in air measurements in Gümüşhane province
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Fig. 8
figure 8

Iso-dose map of natural gamma radiation in Gümüşhane province air (μSv/h)

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The average radiation value in Gümüşhane province is 0.1058 μSv/h. The highest and lowest radiation value in the air environment in the province of Gümüşhane is in the village of Yaydemir 0.405 μSv/h and in the village of Harmancık 0.023 μSv/h, respectively.

Discussion

In this study, the lowest and the highest gross alpha activities in water samples were found in the range of 3–110 mBq/L and gross beta activity was in the range of 4–190 mBq/L. The mean values for gross alpha and gross beta activities were 15.06 mBq/L and 48.05 mBq/L, respectively. In 2016, Kaya and his colleagues conducted a study in tap and natural water samples collected only from the Gumushane city center and Bahcecik village and they found that the gross alpha and gross beta activities were in the range 10–15 mB/L and 12–128 mB/L, respectively [16]. This may be because the region we are investigating is more extensive and we have taken water samples from regions where concentrations of 226Ra, 232Th, 210Po or 224Ra are relatively higher, which affect gross alpha and gross beta activity concentrations [18]. In 2005, Gültekin and Dilek determined the gross alpha and gross beta activity concentrations in mineral water samples in the Gümüşhane center ranged from 122 to 780 mBq/L and from 67 to 401 mBq/l, respectively [12]. As can be seen, gross alpha and gross beta activity concentrations in mineral waters are considerably higher than those in natural spring drinking waters. It is also seen that gross alpha and gross beta activity concentrations are relatively high in the water that comes into contact with environments containing elevated concentrations of thorium and uranium elements. It is seen that the results of the current study are below the upper limit values of World Health Organization (WHO), which are 0.1 Bq/L for gross alpha and 1 Bq/L for gross beta.

In the current study, we found that the absorbed gamma dose rate in air was 0.106 μSv/h. The measured highest absorbed gamma dose rate (0.405 μSv/h) was recorded in the air of the Yaylademir village, which is located between 40.4323 N and 39.38044 E. The lowest absorbed gamma dose rate of 0.023 μSv/h was recorded in the air of Harmancık village located in 40.43896 N and 39.63322 E. Considering the mean absorbed gamma dose rate for Turkey (90 nSv/h) it can be seen that the result of the current study is close that value. In 2011 some searchers determined the absorbed gamma dose rate for the Gumushane province to be as average 0.150 μSv/h [36]. As seen, this value is relatively higher than our finding. This might be explained by the fact that Maden and his colleagues carried out their study in a limited region and fewer sampling points were considered [36].

In this study, activity concentrations in surface soil samples were found to range from 1.8 ± 0.3 Bq/kg–159.5 ± 13.1 Bq/kg for 232Th, 1.2 ± 0.2 Bq/kg–120.3 ± 9.9 Bq/kg for 226Ra, 50.8 ± 2.9 Bq/kg–1223 ± 120 Bq/kg for 40K and 0.3 Bq/kg–21 ± 2 Bq/kg for 137Cs. The mean values for the radionuclide concentrations were found to be 38.4 Bq/kg for 232Th, 24.5 Bq/kg for 226Ra, 621.4 Bq/kg for 40K and 3.7 Bq/kg for 137Cs, respectively.

In the UNSCEAR (2000) report, the weighted world average values for 232Th, 226Ra and 40K activity concentrations in the Earth’s crust are given as 45, 32 and 420 Bq/kg, respectively [37,38,39]. In this study, it is seen that the average value of 40K activity is above the world average. Radioactivity concentration of natural radionuclides are strongly correlated with the geology of the region. It has been studied that the Gümüşhane province contains eocene volcanic rocks. Volcanic rocks are basaltic andesite, basaltic trachy andesite, trachy andesite, andesite, dacite and rhyolite in composition, and consists of mainly plagioclase, alkali feldspar, quartz, hornblende, augite and biotite minerals. These rock type shows calc-alkaline affinities and have high K contents [40]. The reason that the 40K activity concentration is higher than the world average could be related to the potassium concentration in the rocks that the province is build upon.

40K, 137Cs, 226Ra and 232Th, gross alpha and gross beta in water readings and air effective dose values obtained from the measurements in the study area are the coordinates of the point and the value in this coordinate is measured in UTM ED50 projection system transferred to the numerical environment. The minimum curvature superficial grid maps were generated for each reading value of these numerically expressed readings and some anomaly regions were determined. These anomaly areas are overlapped with the geology map of the drawing editor taken over the MTA (http://yerbilimleri.mta.gov.tr/anayfa.aspx) and overlapped and compared on a similar scale as 40K, 137Cs, 226Ra and 232Th values for grid anomalies, especially for 40K anomaly.[41,42,43,44]

Conclusion

This research aimed to assess radioactivity levels of gross alpha and beta activity in the drinking waters, natural (226Ra, 232Th and 40K) and artificial (137Cs) radionuclides in soil samples and the coordinates and measurement values of natural radioactivity measurements made in the air, Gumushane province, Turkey. The aggregate Alpha–Beta analysis of collected samples from local water sources have been done at The Küçükçekmece Atom Energy Institute of Turkey in İstanbul. It has been found that radioactivity levels in Gümüşhane drinking water, are below the limits of constituting a health hazard for the public.

The activity concentrations of natural (226Ra, 232Th and 40K) and artificial (137Cs) radionuclides in 62 soil samples were determined by using Gama-ray spectroscopy present in Çekmece Nuclear Research and Training Center (ÇNAEM). The measured activity concentrations were further evaluated for mean radium equivalent activity (Raeq), gamma absorbed dose rates in air (D), annual effective dose rates (AEDR) and external hazard index(Hex). Obtained values show that the mean radium equivalent activity (Raeq) were from 7.4 to 434 Bq/kg. The gamma absorbed dose rates in air were in the range of 3.7–202.9 nGy h−1, with an arithmetic mean of 60.4 nGy h−1, while the annual effective dose rates were determined to be in the range of 4.7–248.8 μSv y−1. The calculated values of external hazard index (Hex) for the soil samples in the study area were in the range of 0.02–1.19. The activity concentrations of radionuclides in soil samples were compared with the international data reported by UNSCEAR, 2000. It was observed that the obtained activity concentration results in soil samples were below the mean values for Turkey.