Radyoaktif izleme tekniği ile rubidyumun topraktaki ilerleyişinin incelenmesi, sodyum ve potasyuma göre değerlendirilmesi

Abstract

Bu Yüksek Lisans tez çalışmasında, radyoaktif izleme tekniklerinden yararlanılarak rubidyum elementinin topraktaki ilerleyişi incelenmiş ve bu bağlamda sodyum ve potasyuma göre mukayeseli değerlendirilmesi gerçekleştirilmiştir. Radyoaktif izleme tekniği ile bir sistemin veya özel bir kısmının davranışının gözlenmesiyle sistemin bir bölümü hakkında fikir edinmek ve bilgi almak için uygulanan tekniğe izleme metodu denmektedir. Radyoaktif izleyiciler kendilerine has özelliklerinden dolayı endüstride geniş çapta uygulama alanına sahiptirler. Biyolojik, fiziksel ve kimyasal süreçlerin izlenmesinde kullanılan radyoizotopları, radyoaktif izleyici olarak tanımlamak mümkündür. Radyoaktif izleme tekniği, bugün dünyada bir çok inceleme, tespit ve araştırma programında uygulanan bir nükleer tekniktir. Bir sistemin veya sisteminin bir bölümünün bir süreç esnasında hareketlerinin izlenmesi amacı ile uygulanan bu teknikte, az miktarda radyoizotop daha büyük miktarda radyoaktif olmayan malzemeye ilave edilmektedir. Bu bağlamda, radyoaktif izleme tekniği ile deneysel olarak rubidyum, sodyum ve potasyum'un topraktaki ilerleyişine ilişkin davranış takibi ve hız tayini yapılması çalışmanın özünü oluşturmuştur. İTU Enerji Enstitüsü'nde mevcut TRIGA Mark-II Eğitim ve Araştırma reaktörü olanaklarından yararlanılarak yaptırılan (RbCl, Na2CO3 ve KNO3 bileşiklerinin) ışınlanmalar sonucu elde edilen Rb-86, Na-24 ve K-42 radyoaktif izleyicilerin kullanılmasıyla araştırmamız gerçekleştirilmiştir.Rb, Na ve K'un toprakta ilerleyişinin incelenebilmesi için deneysel çalışmalarımızda en az 30 yıl dokunulmamış olduğu düşünülen doğa toprağı kullanılmıştır. Elde edilen toprak örnekleri laboratuar koşullarında kurutma, öğütme ve eleme işlemlerinden geçirilerek polimer kolonlara titizlikle doldurulmuştur. Takiben, her biri ayrı bir çalışma ve ayrı deney uygulamasıyla gerçekleştirilen deneylerde RbCl, Na2CO3 ve KNO3 bileşikleri toprak yüzeyine olabildiğince homojen şekilde serpilmiştir. Bu işlemden sonra İstanbul ilinin gerçek yağış rejimi referans alınarak toprak yüzeyin sulaması deney süresince her gün gerçekleştirilmiştir. Radyoaktif ölçümler NaI(Tl) sintilasyon dedektörü ile polimer kolonların dış yüzeyinden farklı derinliklerde ve farklı açılarda birden fazla sayım alınarak gerçekleştirilmiştir. Alınan sayımlardan doğal sayım (background) çıkarılarak ulaşılan net sayımlar çerçevesinde değerilendirmeler yapılmıştır.Elde edilen sonuçlarla RbCl, Na2CO3 ve KNO3 bileşiklerinin toprak katmanlarındaki ilerleyişi gözlenmiştir. Takiben, rubidyum, sodyum ve potasyum deneylerinin kendi aralarındaki sonuçları mukayese edilmiş olup ilerleme hızları tayin edilmiştir.Böylelikle, gerçekleştirilen deneylerle, radyoaktif izleme tekniği kullanılarak toprak kolonlarda lizimetrik şartlara uygun olarak araştırmamız gerçekleştirilebilmiş ve anlamlı sonuçlara ulaşılabilmiştir. Fazla olarak, farklı 1A grubu elementlerden üçünün toprakta ilerleyişi, ilerleme hızları bağlamında mukayeseli ve rasyonel olarak incelenebilmiştir.

Rubidium is quite a rare trace mineral that is not very abundant in the human body. But despite its rarity and low presence in the body, it has some functions to perform for the health. Rubidium is considered to be the 16th most abundant element in the earth's crust. The relative abundance of rubidium has been reassessed in recent years and it is now suspected of being more plentiful than previously calculated. The metal is used in the manufacture of photocells and in the removal of residual gases from vacuum tubes. Rubidium salts are used in glasses and ceramics Potential uses are in ion engines for space vehicles, as working fluid in vapor turbines, and as getter in vacuum tubes. The wastes of the related devices can be caused the environmental pollution. Studies indicate that cesium and rubidium are only slightly toxic on an acute toxicological basis and would pose an acute health hazard only when ingested in large quantities. Therefore, it should be control with regard to both toxicity and deficiencies in humans and livestock. Rubidium has also an indicator element for alkaline because it is like potassium, sodium and cesium. Plant will adsorb rubidium quite quickly. In this way rubidium enters the food chain.In this thesis, it is aimed to observe dispersion of Rb in soil samples by using radiotracer technique as a sensitive technique for observation of nature and comparable evalution with Na and K. Soil columns were prepared in the laboratory conditions and the experiments were observed in the lyzimetric concept. For the production of the radiotracer 86Rb as rubidium chlorite compound was irradiated in ITU TRIGA Mark II Nuclear Training and Research Reactor at Energy Institute of Istanbul Technical University at ful power in central thimblel.Radioactivity measurements were carried out by using high efficiency gamma radiogauging system at the outside of the soil column for the different depth intervals. As a result, diffusion of the RbCl in soil was observed successfully. 86Rb radioactivity measurements were used to obtain the diffusion of compound of Rb in soil.Soil forms a structure that is filled with pore spaces, and can be thought of as a mixture of solids, water and air (gas). All soils contain some water-soluble salts. Plants absorb essential plant nutrients in the form of soluble salts and their excessive accumulation called soil salinity. Salinity is the major environmental factor limiting plant growth and productivity. The detrimental effects of high salinity on plants can be observed at the whole-plant level as the death of plants and/or decreases in productivity. When salts accumulate in soils, the soil becomes less permeable. Lack of good drainage is a major contributor to salinity. So is seepage from irrigation systems and drainage fields which can lead to a loss of nearly half of the water.Radiotracing technique can be used for physical, chemical, or biological properties of substance. No tracer has to be chemically identical with the radiotracer of the substance own. So, the radiotracers would be appropriate to the studying chemical reaction kinetics, solubility, vapor pressure, processes dominated by atomic and molecular diffusion and others. Radioactive isotopes of the traced elements and labeled molecules are used as intrinsic tracers. Therefore, the method provides for the identification, observation and study of the behavior of various physical, chemical or biological processes. The main particularity of radiotracers is their radiation emission. Generally, gamma emitted radioisotopes are preferred for the soil application. They offer possibility of on-line and in-situ measurements, providing information in the shortest possible time. They have high detection sensitivity for extremely small concentrations.The emission of radiation is a specific property of the radionuclide, and not affected by interference from other materials in the system. Radiotracers when chosen properly, it can possible to investigate the different properties of the substance effectively. Therefore, radiotracers can offer a complete solution to many problems, and ideal for assessing proper functioning, optimization and design of various operations in the soil.The radiotracing technique is convenient for the diffusion of salt in the soil due to taking signals from the salt molecules. Radiotracer was selected as the sodium-carbonate form that is realistic compound for the soil. It is assumed that no chemical changes occur when diffusion processes in solid during the radiotracing application.Salt is a natural element of soils and water. As the Na+ (sodium) predominates, soils can become sodic. Sodic soils present particular challenges because they tend to have very poor structure which limits or prevents water infiltration and drainage. In this thesis, Na-24 in Na2CO3 compound was used as radiotracer radioisotope.As known, plants needs a number of different chemical elements taking from the soil. Without nitrogen, phosphorus and potassium, the plant simply cannot grow adequately. If any of the macronutrients are missing or hard to obtain from the soil, this will limit the growth rate for the plant.In nature, to make plants grow faster, what you need to do is supply the elements that the plants need in readily available forms. But, in many times amounts of some essential elements are not enough in the soil. Then, fertilizing should be essential, but also excessive fertilizier applications can cause soil salinity and groundwater contamination.Potassium nitrate (KNO3) one of the mainly used fertilizers is a source of nitrogen and potassium that are two of the macro nutrients for the plants. Of course, fertilizing mechanism and behavior of the KNO3 fertilizer in soil is important. One of the ways to investigate the diffusion of isotopes in soil is usage of radioactive isotopes by using radiotracing technique.With this thesis, it is also aimed to observe diffusion of KNO3 in soil by using radiotracing technique. For this reason the potassium-42 (K-42 or 42K) radioisotope was produced and diffusion of the potassium nitrate fertilizer in the soil media was investigated experimentally by using radiotracing technique in different viewpoints.For the production of the radiotracer 42K, KNO3 compound was irradiated in pneumatic irradiation system of ITU TRIGA Mark II Training and Research Reactor at Energy Institute of Istanbul Technical University. Nitrogen has short half life (10 min) and oxygen has also short half live (26.91 sec). Therefore only K-42 was radioactive during the experiments after to 2 days waiting time after the irradiation.It is collected soil sampling that the study area is located on the eastern side of Istanbul in the Istanbul Technical University campus. The area is fairly flat, elevation is 27m and vegetation cover is grassland. Depth incremental soil samples with 6.5 cm corer height are collected from this area. Metal rings with a diameter of 8.5 cm were used for soil sample collection. Soil sampling was carried out to a depth of 32.5 cm.Firstly, soil was dried in the oven at 105 oC for 48 hours. Then it was ground and sieved under 2 mm of particle size. After that the soil was filled into a column that has 6.5 cm diameter and 32.5 cm height. Thus, the column was prepared with stowing of the soil just like realistic soil layers.Experimental setup consists of a high efficiency gamma radiogauging system including NaI(TI) scintillation detector encased in a collimated lead shield. The diameter of the collimator for the source and for the detector was 5 mm. The detector for gamma ray emission measurements from radiotracer were mounted on a vertical plate, which could be moved along the column axis in the vertical direction. This allowed the measurement of gamma radiation at any point along the column. Radioactivity measurements were carried out at the outside of the soil column for the different depth intervals for the soil column.Experiments were executed in the laboratory according to the lyzimetric concept. After the irradiation, radioactive compound was poured on to the soil surface of the prepared column and then water was sprinkled on it in the following days during the experiment period. For the observation of the diffusion of RbCl, Na2CO3 and KNO3 into the soil, watering has taken possession according to a realistic rain regime in the vicinity of Istanbul city for the year 2011.The radioactivity measurements were taken carefully. The counts repeated at least three times for each case and for each layer. Furthermore, the experiments were evaluated for the different depth conditions comparatively with the velocity of the radioisotopes. The conclusion of this thesis beyond of the soil media search experiments could be guide to investigations related with environmental effects