Bursa ili orhaneli ve keleş ilçelerindeki toprakların doğal radyonüklid düzeyinin belirlenmesi = Determination of natural radionuclide levels in soil of orhaneli and keleş districts in bursa province

Abstract

Bu tez çalışmasında, Bursa'nın zengin linyit yatakları ile dikkat çeken Orhaneli ve Keleş ilçelerinden toplanan toprak örneklerindeki 226Ra, 232Th ve 40K doğal radyonüklid aktivite konsantrasyonları NaI(Tl) gama spektrometresi yöntemiyle ölçülmüş ve radyolojik risk endeksleri hesaplanmıştır. 226Ra, 232Th ve 40K doğal radyonüklidlerin ortalama aktivite konsantrasyonları Keleş ilçesi için sırasıyla 46,02 Bqkg-1, 13,72 Bqkg-1 ve 148,80 Bqkg-1 olarak bulunurken, Orhaneli ilçesi içn ise aktivite konsantrasyonları sırasıyla 37,35 Bqkg-1, 9,19 Bqkg-1 ve 119,76 Bqkg-1 olarak hesaplanmıştır. Elde edilen sonuçlar radyolojik risk açısından değerlendirildiğinde soğurulan gama doz oranı (D), yıllık etkin doz eşdeğeri (AED), radyum eşdeğer aktivitesi (Raeq) ve dış tehlike indeksi (Hex) için ortalama değerlerin Keleş ilçesi içn sırasıyla 35,75 nGyh-1, 0,04 μSvy-1, 77,11 Bqkg-1 ve 0,20 olduğu gözlenirken bu ortalama değerler Orhaneli ilçesi için sırasıyla 27,80 nGyh-1, 0,03 μSvy-1, 59,71 Bqkg-1 ve 0,16 olarak bulunmuştur. Bu çalışmada elde edilen sonuçlar ulusal ve uluslararası kuruluşlar tarafından önerilen limit değerlerle karşılaştırıldığında, çalışılan bölge topraklarının radyoaktivite açısından güvenli olduğu ve herhangi bir radyolojik tehlike oluşturmadığı görülmüştür. Orhanlei ve Keleş ilçelerinin farklı noktalarından toplanan toprak örneklerindeki doğal radyoaktivite düzeylerini belirlemek için, 226Ra, 232Th ve 40K radyonüklid aktivite konsatrasyonları gama spektrometresi yöntemi kullanılarak ölçülmüştür. Sonuçlar, çalışma alanındaki 226Ra, 232Th ve 40K radyonüklid aktivite konsantrasyonlarının farklı seviyelerde olduğunu ortaya koymaktadır. Farklı jeolojik formasyonların örnekler arasında farklılık gösteren sonuçlara neden olduğu düşünülmektedir. Ayrıca, bölgede yapılan tarımsal faaliyetlerine gübre kullanım ve bölgede meydana gelen taşkınlar gibi faktörlerin de 226Ra, 232Th ve 40K aktivite konsatrasyonlarındaki değişimlerde rol oynayabileceği düşünülmektedir. Sonuçlar ulusal ve uluslararası radyasyondan korunma kuruluşları tarafından önerilen limit değerlerinin altında elde edilmiştir.

Living organisms on Earth, including plants, animals and fungi are continuously exposed to radiation from both natural and artificial sources. Natural radioactivity is the primary source of the radiation to which all living beings are exposed. It originates from the presence of natural radioactive nuclei in the Earth's crust, including water, sand, soil, plants, rocks, and other living organisms, as well as cosmic rays. Radionuclides with very long half-lives, which have existed since the univers's formation, expose the human body to radiation both internally, through respiration and ingestion, and externally, through cosmis rays and radiation emitted by naturally occurring radionuclides in the air, Earth's crust, and construction materials. This constant exposure to radiation from various sources is a natural and unavoidable aspect of life on Earth. In the present study, the natural radionuclide activity concentrations of 226Ra, 232Th and 40K in soil samples collected from Orhaneli and Keleş districts of Bursa, know for their rich lignite deposits, were measured using the NaI (Tl) gamma spectrometry method, and radiological risk indices were calculated. For Keleş district the average activity concentration of 226Ra, 232Th and 40K natural radionuclides were found to be 46,02 Bqkg-1, 13,72 Bqkg-1 and 148,80 Bqkg-1, respectively. However, the average activity concentration for Orhaneli were found to be 37,35 Bqkg-1, 9,19 Bqkg-1 and 119,76 Bqkg-1, respectively. When the obtained results are evuluated in terms of radiological risk, it is observed that the average values for absorbed gama dose rate (D), annual effective dose equivalent (AED), radium equivalent activity (Raeq) and external hazard index (Hex) for Keleş district are 35,75 nGyh-1, 0,04 μSvy-1, 77,11 Bqkg-1 and 0,20, respectively. The corresponding average values for Orhaneli district are found to be 27,80 nGyh-1, 0,03 μSvy-1, 59,71 Bqkg-1, and 0,16, respectively. When the results obtained in this study are compared with the limit values recommended by national and international organizations, it is observed that the soils in the studied region are safe in terms of radioactivity and do not pose any radiological hazard. In order to comprehensively assess the level of natural radioactivity present in soil samples collected from various locations within the Orhaneli and Keleş districts, a thorough investigation was undertaken. The study focused on measuring the activity concentrations of three significant radionuclides, namely 226Ra, 232Th and 40K, using the advanced gamma spectrometry method. This technique enabled precise and reliable measurements of the radioactivity levels within the samples. The results obtained from the gamma spectrometry of the three radionuclides across the study area. One of the key factors contributing to the observed variations in the activity concentrations of 226Ra, 232Th and 40K radionuclides was found to be the geological formations in the respective regions. The distinct geological characteristics of the locations played role in influencing the radioactivity levels of the soil samples collected. Additionally, human activities, particularly agricultural practices such as the application of fertilizers and flooding events in the region, were identified as significant contributors to the changes observed in the radionuclide concentrations. These factors potentially influenced the natural radioactivity levels in the soil and contributed to the spatial variations seen in the study. Moreover, the research findings brought assurance regarding radioation safety. The activity concentrations of 226Ra, 232Th and 40K radionuclides detected in the soil samples were all found to be below the limit values recommended by national and international radioation protection organizations. This outcome alleviates concerns about potential hazardas to human health and the environment due to excessive levels of of natural radioactivity in the studied areas. The third part of study focused on conducting energy and efficiency calculations for the NaI(Tl) gamma detector system. To ensure accuracy, different reference sources were used for these calculations, specially RGTh, RGU and RGK sources obtained from the International Atomic Energy Agency (IAEA). Stripping ratios and sensitivity factors were carefully determined through meticulous analysis. Gamma spectroscopy is a valuable technique widely utilized for the discovery of radioactive elements and the determination of radionuclide content in geological samples containing such elements. Although trace amounts of 238U and 232Th are found in all geological structures, they lack unique, directly detectable charateristic gamma rays. To overcome this, the method relies on using charateristic high-energy gamma rays emitted from the decay products of uranium and thorium. Specifically, the 1.76 MeV gamma rays from 214Bi in the 238U series and the 2.6 MeV gamma rays from 208Tl in the 232Th series are employed for this purpose. Additionally, the concentration of 40K in the samples is directly determined using the specific 1.46 MeV gamma rays associated with this radionuclide. Geological samples usually contain varying concentrations of U, Th and K radionuclides, and the limited resolution of NaI (Tl) gamma spectrometers leads to contributions from other radionuclides within the selected energy intervals (channels) for the chosen gamma energies in the measured spectrum. The primary objective of this section was to establish a reliable method for accurately determining the activities of standard sources using two distinct measurement methods. The researchers sought to develop a robust framework that would enable precise and consistent assenssmnet of the radioactivity levels in the soil samples collected from the Keleş and Orhaneli districts of Bursa, Turkey. Building upon the outcomes of the energy and efficiency calculations, the fourth part of the study applied the most accurate method of assess the levels of natural radioactivity in a total of 78 soil samples gathered from the Keleş and Orhaneli districts of Bursa, Turkey. With the established methodology, the research team was able to confidently determine the activity concentrations of 226Ra, 232Th and 40K radionuclides in the soil samples. The findings from this comprehensive investigation shed light on the distribution and magnitude of natural radioactivity in the study area. The results provide valuable insight into the potential impact of geological formation and human activities on radioactivity levels in the region.