İstanbul Boğazı, Türk Boğazlar Sistemini oluşturan Marmara Denizi ve Çanakkale Boğazı’ndan daha özel bir önem taşımaktadır. Karadeniz’den gelen nispeten az tuzlu su üst akış olarak ve Marmara Denizi’nden gelen daha tuzlu su alt akış olarak İstanbul Boğazı boyunca iki katmanlı akışı oluşturmaktadır. Yoğunluk farkından dolayı iki katmanlı akış halinde boğaz boyunca akan tuzlu suda farklı akış rejimlerinden dolayı karışımlar meydana gelmektedir. Önemli bir dar su yolu olan İstanbul Boğazı’nın yüzey tuzluluk değerleri farklı lokasyon ve mevsimlerde nötron aktivasyon analiziyle tayin edilmiştir. Günümüzde çok çeşitli tuzluluk tayin yöntemleri kullanılmakla beraber literatürde, nötron aktivasyon analiziyle tuzluluk tayinine ilişkin bir yayına rastlanmamıştır. Nötron aktivasyon analizi element analizinde sıkça kullanılan bir nükleer teknik durumundadır. Tuzluluk tayini için kullanılan nötron akivasyon analizi yönteminde sodyum konsantrasyonu elde edilerek tuzluluk değerlerine gidilmiştir. Nötron aktivasyon analizi tuzluluk sonuçlarını kıyaslamak için konvansiyonel bir tuzluluk tayin tekniği olan uçurma yöntemi seçilmiştir. Nötron aktivasyon analizi tuzluluk sonuçlarının uçurma sonuçlarına yakınsadığı gösterilmiştir. Nötron aktivasyon analizi tuzluluk değerleri kullanılarak yere ve zamana bağlı matematik bir model geliştirilmiştir. Bu yeni model İstanbul Boğazı’na özgü parametreleri barındırmaktadır. Deneysel ve matematik model sonuçları FEMLAB 3.1 programında tek boyutlu difüzyon denkleminin çözülmesiyle oluşan simülasyon sonuçlarıyla kıyaslanmıştır. Deneysel ve teorik sonuçların iyi bir uyum içinde olduğu ortaya çıkmıştır. Böylelikle nötron aktivasyon analizi ile deniz suyu tuzluluk tayininin yapılabileceği ve önerilen analitik modelin güvenilirlikle kullanılabileceği gösterilmiştir.Anahtar Kelimeler: İstanbul Boğazı, tuzluluk, Na-24, uçurma yöntem, nötron aktivasyon analizi. Turkish Strait System consists of the Bosphorous, Marmara Sea and Dardanelles. The Bosphorous is the most interesting one because of its strategic role. The Bosphorous is a very important channel in which there are two flows with different salinities. The seawater of Black Sea passes by as the top layer flow and the seawater of Marmara Sea as the bottom layer because of the density difference. For years, the oceanographers work on the Bosphorous two- layer flow. This two-layer flow mixes along the Bosphorous causing salinity dispersion. To have an idea about the surface salinity dispersion, the salinity levels should be determined along the channel. The main aim of the experimental work is to measure the surface salinity level with neutron activation analysis. There are many studies to determine the salinity with different methods which are primarily based on physical and chemical principles. Physical salinity determination methods depend on refractive index, density and electrical conductivity measurements. On the other hand chemical methods are based on chlorinity determination. Beyond the physical and chemical methods there are alternative salinity measuring systems as well. These can be called as "alternative methods". In this study for the salinity determination, neutron activation analysis has been chosen as the experimental method but in the literature there is no study that deals with salinity determination by neutron activation analysis. Neutron activation analysis is a nuclear technique that has widely been used for the element analysis. In neutron activation analysis the sample is irradiated and the isotopes of the mother elemental is formed. The activated samples are usually gamma-active and detecting the gamma rays, the concentration and the element identification can be performed Neutron activation analysis can be named as the "new alternative method for salinity measurement". Initially, surface salinity of the Bosphorous was determined by the neutron activation analysis. On the other hand. evaporation technique which is a routine salinity determination method has been chosen. From the specified sample locations along the Bosphorous, the seawater samples have been collected and stored in polymer bottles. In order to determine the salinity of the samples, small amounts of samples were prepared. First of all, the water of the small samples about 100 cc. were evaporated and from the salt remaining after the water evaporation, again small samples have been prepared for the irradiation. The Bosphorous samples were irradiated with a reference salt sample. The salinity of the Bosphorous samples were determined with an equation which allows a comparison of the reference results with those of the irradiated samples. The results of neutron activation analysis have been compared with those of evaporation and literature. Neutron activation analysis results were in good accuracy with those of evaporation and the literature. With the neutron activation analysis results, a model which depends on position and time has been offered. The offered model was a product of two independent functions. The function depending on the position is an exponential and the time dependent one is a sinusoid. The parameters of the independent functions have been determined by neutron activation salinity results. They have been compared with those of evaporation. The model results were in good agreement with the evaporation ones. A theoretical comparison has also been chosen to be done with the results of neutron activation analysis which have been compared in many ways. For this comparison, a widely used computer programme. FEMLAB 3.1 (Finite Element Method Laboratory). has been selected. This programme has widely been used in many different studies where finite element method is valid. The suitable geometry for the Bosphorous has been formed and one dimensional diffusion equation has also been solved with the parameters of the Bosphorous. The values obtained from one dimensional diffusion equation that has been solved for the Bosphorous have been used in comparison with those of neutron activation analysis, evaporation and the mathematical model and it has been concluded that neutron activation results have been in good accuracy with those of the programme. It is also concluded that neutron activation analysis can be used to determine the salinity and mathematical model as well in relevance. A different study has been done in terms of the experimental work and the analytical model. Keywords: Bosphorous, salinity, Na-24, evaporation method, neutron activation analysis
