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THE GROSS ALPHA AND GROSS BETA ACTIVITIES OF HOLOCENE MARINE SEDIMENTS AND THE RELATIONSHIP OF THESE ACTIVITIES WITH RADIONUCLIDES IN THE WESTERN MARMARA SEA, TURKEY

. The aim of this study is to analyze the gross alpha and gross beta activities of Holocene marine sediments and to determine the relationship of these activities with radionuclides in the west of Marmara Sea (Turkey). Background and anthropogenic ionizing radiations are the main sources of environmental radioactivity human beings are exposed to. Background radiation occurs as a result of cosmogenic and terrestrial radiation, while anthropogenic refers to man-made radiation. In this context, gross alpha and beta activity of sea sediment samples collected at 29 different stations in the research region were analyzed using the low-background counter (Berthold, LB 770, 10- channel α−β low-level counter). Also, the relation between abundance of radioactive isotopes and alpha and beta activity were discussed in this paper. As a result, the average gross alpha and beta activities were determined as 223.18  14.9 Bq kg -1 and 572.00  23.9 Bq kg -1 , respectively. The results obtained can be used as a data base for Holocene marine sediments.


Introduction
Ionizing radiation pollution which is mainly caused by background and anthropogenic radiations is one of the recent environmental problems. Background radiation originates from cosmogenic and terrestrial radiations, while anthropogenic means man-made. The recent increase in the levels of environmental ionizing radiation pollution is directly related with the industrialization such as the use of fossil fuels, phosphate industry and wrong and excessive use of fertilizers (Topcuoğlu et al., 2010). The radioactive elements are found in magmatic rocks, in phosphate rocks, in sedimentary masses such as clay and shale, and in granitic rocks in high amounts. But these elements are found in small quantities in Sedimentary rocks such as sand-gravel, sandstone, and limestones with crack (Kumru et al., 2002). The source of radioactivity in the aquatic environment is water pollution which occurs with particles and minerals present in water. The geological structure of the area where the water deposit is located is also a determinant of natural radioactivity. It differs in radioactivity levels according to the quality of the rocks forming the Earth's crust (Karaman, 2003). The knowledge of environmental natural radioactivity is very important in terms of determining where the nuclear accidents and industrialization pollute the environment (Degerlier, 2007). For example, after the Chernobyl accident, anthropogenic radionuclides entered the marine environment. The atmospheric sediments spread from the nuclear weapon tests in the countries around the Black Sea reached the Marmara Sea through the Bosporus (Topcuoğlu, 2001).
The alpha particle is a helium nucleus with an electric charge (+2). Due to its large mass, it is unlikely to penetrate into matter. Alpha particles are emitted from natural radioactive isotopes such as polonium, thorium, radium, uranium, which are formed in nature and have large atomic weights. The ionization betting that the alpha rays bring into the matter is relatively high. The gross alpha radioactivity consists of U-238, Th-232, Ra-226, Rn-222 and their alpha emitter nuclei. The gross beta radioactivity is due to fission and activation products such as natural long-lived K-40, Sr-90, Cs-137, Co-60 and I-125 (Varol, 2011). Beta particles are negatively charged and have smaller mass than alpha particle. As soon as one of the neutrons in the nucleus of the isotope changes, beta degradation occurs immediately. As it carries ionizing properties, it has harmful effects on living organisms (Varol, 2011). The sediments play an important role in the aquatic environment, because of their geological and chemical structure, which provides the flow system between land, sea and atmosphere (Kurt et al., 2016). Determination of radioactivity in sediment samples provide information on the level of sea water radioactivity the sediment is receiving. One of the most commonly used methods for determining environmental radiation is gross alpha and gross beta measurements, which are the result of quick access and low cost (Bunz and Kracke, 1998). Numerous studies have been conducted in the past years on the identification of environmental radioactivity and the monitoring of pollution using heavy metals and radioactivity in marine environments (Taskin, 2006;Bozkurt et al., 2007;Varol,  In the studies given in the above paragraph, gross alpha and beta activity measurements were performed for groundwater and drinking waters and also radionuclides in sediments were examined. In this study, gross alpha and beta activity of sea sediment samples collected from 29 different stations in the Western Marmara Sea (Recent marine sediments) were analyzed and environmental radioactivity concentration values were determined. Also, the traces of nucleotides, such as Cs-137, which gave rise greatly to the pollution of marine environments, was discussed.

Material and Methods
The sampling stations were between Silivri (Istanbul) -Bandırma (Balıkesir) in Western Marmara Sea which is at the west part of Turkey (Fig. 1). The bathymetry of the study area varies between 20.00 m and 35.00 m in core samples. Core samples from 29 locations were used in the study. The samples were taken between 15-20.10.2015 and the coordinates and depth information of the samples are given in Table 1. Because the samples are obtained from about 30 m, the samples are in the form of fine-grained, sandy-silty clay (Yümün, 2017). Sediment samples were immediately taken in a nylon bag and protected from atmospheric moisture. Later, the samples were taken to the laboratory, where they were removed from the nylon bags and dried in room temperature.

Figure 1. Location map of investigation area and sample's locations
The dried sediment samples were ground in granite bowls and sieved with a stainless-steel sieve to remove the portion that came to the size of the powder. Approximately 100 mg of each sample was weighed on a precision scale and placed in an empty aluminum bowl. Distilled pure water has been used to homogeneously distribute the samples in the bowl. The specimens were dried for 2 hours at 105 °C, then left in the desiccator to cool to room temperature without drawing any moisture. Then, the prepared samples were homogenized with distilled water and placed in the oven. This process is important to determine the amount of residue. If the amount of the residue is more than 400 mg, the self-absorption effect of the alpha particles increases. In this way, fewer particles will reach the detector, causing the results to be erroneous (Taskin, 2006). Finally, the gross alpha and gross beta activity rates of all samples were measured using two low-level LLB 770-PC 10-channel alpha-beta counting systems in two cycles of 500 minutes each. LLB 770-PC 10-channel alpha-beta counting systems have been produced by Contact Berthold Technologies GmbH & Co. in Germany. Each analysis was repeated twice and the arithmetic mean of these measurements was used. The samples were taken from the sea using a boat and the gravity core method. The diameter of the samples (54 mm) and the sampling depths are given in Table 1. Gross Alpha and Beta concentration obtained from analysis results have been analyzed by Kriging method (Figures 2 and 3). The Kriging method is an interpolation method that estimates the optimal values of the data at one point using the data from the other known points (Inal et al., 2002). Kriging method is a technique in which the estimation of spatial changes in not sampled points is made optimally using semi variogram structural properties (Trangmar et al., 1985). The activities were obtained using the following formulas:  Low level counting system is commonly used for measuring environmental samples with low natural radiation. Its calibration has been carried out with standard solutions, which contained known activities of 241 Am for alphas and 90 Sr for betas which are similar to the sample geometry (Currie, 1968). Gross alpha radioactivity is composed of radionuclides (U-238, Th-232, Ra-226, Rn-222) and their alpha emitting nuclei, Gross beta radioactivity is of natural long-lived radionuclides (K-40, Sr-90, Cs-137, Co-60 and I-125) are known to originate from fission and activation products (

Results and Discussion
The gross alpha and gross beta concentration of the obtained sediments are given in Table 1 and the position of the sample stations are given in Fig. 1. According to the analysis results, gross beta values were found higher than gross alpha values at all locations except M5. The lowest and highest gross alpha and gross beta values are 32, 23-608, 41 Bq/kg (average value: 223, 18 Bq/kg) and 38, 38-1320, 14 Bq/kg (average value: 572, 00 Bq/kg), respectively. The lowest concentration of gross alpha is in M11, M26, while Beta is in M5. However, M16 is the region with the highest gross alpha and beta intensities.
Since there is no regulatory standard for radiological pollutants in sediments, the results obtained in this study are compared with those in different countries in Table 3 and gross alpha and gross beta activity concentration of sediment samples are shown in Figure 4. According to Table 3, the gross alpha concentration of the study is higher than that in Los Alamos and Sir Dam Pond. The gross beta concentration of the western Marmara sea samples is considerably lower than the values for the Bendimahi River, but higher than the data for other locations referenced in the manuscript. Although the gross alpha and gross beta concentrations in studies conducted in other countries are close to the average value, the concentrations obtained in this study have very large ranges. This is due to the high concentration of environmental pollutants in some locations in this region. According to the locations where the samples are taken, there are differences in the analysis results. Core samples have a fine-grained, sandy-silty clayey composition, because they have been taken from areas, where higher than 30 m depth. Concentrations of radionuclides vary depending on sediment particle size, mineral composition, local pollution and organic matter content (Papaefthymiou et al., 2007).  In the graph given in Figure 4, it is seen that gross alpha and gross beta concentrations decreased and increased similarly in each location. In Table 2, gross alpha and gross beta activities were also compared with radionuclides (40K, 137Cs, 226Ra, 232Th, 95+Zr, 54Mn) of the same samples. It is seen that gross alpha and gross beta values increase in locations where radionuclide concentrations increase, and decrease in locations where radionuclide concentrations decrease. It is thought that domestic and industrial wastes, agricultural activities and ship wastes are among the reasons for the very high concentrations of gross alpha and gross beta, especially in settlements, agricultural areas, piers and ports. Another important reason why the gross alpha and beta concentrations are generally high is that the fertilizers used in agriculture contain uranium, thorium and their decomposition products and natural potassium-40 (NCRP, 1987).
This study shows that fertilizer and agricultural pesticide residues from the soil carried by Kocasu, Gönen and Biga streams in the areas where agricultural activities are concentrated cause radioactive pollution . Another contribution to gross beta results is the Chernobyl nuclear reactor accident and nuclear weapon trials. Radioactive nuclei of Cs-137, Sr-90, I-131, Te-132 and Pu-239 are spread from the nuclear reactor accident and nuclear weapon tests. The points where Gros alpha and Gros Beta activity values are high are the locations close to Çanakkale. The locations with low activity values were obtained in the samples taken near the Kapıdağ Peninsula. The high activity values may be related to the geological structure and pollution. In part, it could be the effects of the Chernobyl accident. Especially high Cs values may be due to weapon trials. After the Chernobyl accident, the vertical velocity of 134Cs and 137Cs in the soil was found to be 0.2-0.3 cm/hour (Bunz and Kracke, 1988).
Especially Cs-137 (half-life 30 years) and Sr-90 (half-life 29, 12 years) radionuclides have quite long half-lives. For this, background levels should be determined for the individual radionuclides that may create the potential pollution cause of the regions. The radionuclide potential of marine sediments from the same locations where this study was conducted was determined (Yümün and Kam, 2020  . The radionuclide potential obtained from the study is given in Table 2. In Table 2, gross alpha and gross beta values are presented together with radionuclides and correlations are made. When the values given in Table 2 are examined, it is seen that the gross alpha radioactivity consists of radionuclides (U-238, Th-232, Ra-226, Rn-222) and their alpha emitter cores. Again in Table 2 it was seen that gross beta radioactivity resulted from fission and activation products such as natural long-lived radionuclides (K-40, Sr-90, Cs-137, Co-60 and I-125). However, in most of the sediment samples taken in this study, it is seen that the radionuclides are above the world average values. The high radionuclide concentrations seen here are responsible for the high gross alpha and gross beta activities. These analyses can be applied to water and sediment samples, as well as to foodstuffs (Pintilie et al., 2017) such as bread (Pintilie et al., 2018).

Conclusion
The main purpose of this study was to determine the natural radioactivity of the region by examining the gross alpha and gross beta concentrations of sediment samples from the Western Marmara Sea. In addition, studies have been carried out to define the relationship of gross alpha and gross beta activities with radionuclides. As a result, beta activity has been found to be significantly higher than alpha activity at all locations. Natural radioactivity depends directly on the regional geology, weather conditions and physicochemical variability of the water. The fact that the agricultural activities of the study area is high and is in the leading region of the country in terms of population and industry, strongly influences radioactive pollution.
Gross alpha radioactivity consists of U-238, Th-232, Ra-226, Rn-222 and their alpha emitting nuclei. The gross beta radioactivity is due to fission and activation products of natural long-lived radionuclides (K-40, Sr-90, Cs-137, Co-60 and I-125) (Varol, 2011). According to the values given in Table 2, Gross alpha and gross beta concentrations are also high in locations where K40 and other radionuclides are high. In addition, the presence of Cs-137, which cannot occur in the natural environment, in many locations in this study area, is thought to be a result of the Chernobyl Nuclear accident. In addition, there may have been nuclear weapon tests carried out by some countries recently. This is an important issue and needs to be taken seriously.
The data published in this paper can be the base data which also will be used to evaluate future changes. In future studies to determine the radioactive pollution of the Marmara Sea, sea water and sea sediment samples should be sampled at more frequent intervals.