Papers by Keyword: Radiotracer

Abstract: In this study, diffusion of rubidium and potassium in soil was observed representing two alkaline elements. Generally, these elements are found as salt compounds in the earth. Soil columns were prepared in the laboratory conditions. Rubidium chlorite and potassium nitrate compounds were irradiated at ITU TRIGA Mark II nuclear research reactor at the Energy Institute of ITU to produce the radiotracer ⁸⁶Rb and ⁴²K. The irradiated compounds were sprinkled to the surface of different soil columns and were watered with realistic amounts. Radioactivity measurements were carried out by using a scintillation detector at the outside of the column for different soil depths in different diffusion times. As the results of the study, the behavior of two alkaline elements was observed appropriately similar in the soil.

Abstract: In this study, it is aimed to observe diffusion of sodium in soil samples by using radiotracing technique. To produce the radiotracer ²⁴Na, sodium-carbonate compound was irradiated at ITU TRIGA Mark II Research reactor at Energy Institute of Istanbul Technical University. The irradiated sodium-carbonate samples were sprinkled to the surface of soil columns. Then soil was watered with representative amounts of water according to selected rain regimes in Istanbul. Radioactivity measurements were carried out by using high efficiency gamma-ray measurement system at the outside of the column for different soil depths in different times.

Abstract: This paper describes the development of colloidal Au-SiO₂ with core-shell structure nanoparticle radioactive tracers by neutron activation in nuclear reactor that produce Au-198 (T1/2=2.7 d) emitting gamma ray of 412 keV. Using conventional citrate-reduction method, gold nanoparticles were prepared from its corresponding metal salts in aqueous solution then coated with uniform shells of amorphous silica via a sol-gel reaction. The citrate-reduction-based method provides gold nanoparticles with higher concentration and narrow size distribution. By using transmission electron microscopy (TEM), the resultant of particle size and silica coatings could be varied from tens to several hundred of nanometers by controlling the catalyzer and precipitation time. Au-SiO2 core-shell nanostructure is good to prevent the particles from getting agglomerated resulting in a big mass. In addition, silica surface offer very good chances that make the hydrophobic and hydrophilic behavior on the gold nanoparticles. EDXRF spectrum has proven that Au-SiO2 core-shell nanoparticles sample consists purely of a gold and silica particles. This target material of radiotracer application used to investigate multiphase system in process industries without disturbing the system operation.

Abstract: Silicon carbide (SiC) was investigated for deep band gap states of europium by means of deep level transient spectroscopy (DLTS). The knowledge of the properties of optoelectrically active impurities or defects is essential for a detailed understanding of the energy-transfer process resulting in the observable excitations [1]. SiC-samples of the polytypes 4H as well as 6H are ion-implanted by different europium- isotopes in order to obtain a chemical identification of the characterized energy levels. Here the concentration sensitivity of the DLTS is applied to observe the elemental transmutation of the incorporated radioactive tracer atoms 146Eu (t1/2=4.51 d) and 147Eu (t1/2=24.6 d). DLTS on samples implanted with stable Eu-ions (153Eu) was carried out for comparison and manifestation of the results. From these studies 5 Eu-related deep band gap levels are established: in 4H-SiC two levels at EV+0.86(2) eV and EC−0.47(2) eV, and in 6H-SiC three levels at EV+0.88(2) eV, EC−0.29(2) eV and EC−0.67(2) eV.

Abstract: Grain-boundary heterodiffusion of iron in pure copper and self diffusion of iron in copper–0.091at% iron were measured by the serial sectioning technique in the Harrison B-regime. The penetration profiles corresponding to iron heterodiffusion in pure copper show a strong positive curvature far beyond the (Dvt)1/2 depth . This peculiar shape, which does not exist for self diffusion in the solid solution, proves the presence of a strong non linear grain-boundary segregation of iron in copper in spite of the respective surface energies of these metals. This segregation is linked to the size effect which is, as predicted by numerical simulation, the main driving force for grainboundary segregation.

Abstract: Self-diffusion of nickel and manganese has been investigated by the radiotracer technique in Ni50Mn50 alloys over a wide temperature range. Experiments were performed on disordered fcc, B2 and L10 structure phases present in the equiatomic alloy at high, intermediate, and low temperatures, respectively. The diffusivity of manganese was found to be significantly faster (factor 3 to 5) than that of nickel in the fcc and B2 phases. More than one order of magnitude diffusivity increase was observed upon the transition from the higher temperature fcc to the intermediate temperature B2 phase. The activation enthalpy from nickel self-diffusion in the disordered fcc phase is significantly higher than the corresponding value for manganese. In the B2 phase there is only a slight difference between the activation enthalpies of the components, which indicates a coupled diffusion mechanism of the two components. A comparison of the present tracer self-diffusion data with literature data on interdiffusion in the Ni-Mn system permits to estimate thermodynamic factors by using the Darken-Manning equation. The thermodynamic factor varies from 3 to 5 depending on the structure.

Abstract: This work deals with the study of zinc self-diffusion in ZnO polycrystal of high density and of high purity. The diffusion experiments were performed using the 65Zn radioactive isotope as zinc tracer. A thin film of the tracer was deposited on the polished surface of the samples, and then the diffusion annealings were performed from 1006 to 1377oC, in oxygen atmosphere. After the diffusion treatment, the 65Zn diffusion profiles were established by means of the Residual Activity Method. From the zinc diffusion profiles were deduced the volume diffusion coefficient and the product dDgb for the grain-boundary diffusion, where d is the grain-boundary width and Dgb is the grain-boundary diffusion coefficient. The results obtained for the volume diffusion coefficient show good agreement with the most recent results obtained in ZnO single crystals using stable tracer and depth profiling by secondary ion mass spectrometry, while for the grain-boundary diffusion there is no data published by other authors for comparison with our results. The zinc grain-boundary diffusion coefficients are ca. 4 orders of magnitude greater than the volume diffusion coefficients, in the same experimental conditions, which means that grain-boundary is a fast path for zinc diffusion in polycrystalline ZnO.

Abstract: The paper presents the application of multitracer method of diffusion measurement in Cr-Mn steels. Two austenitic steels were investigated: Cr13Mn18SiCa and Cr17Mn17 as well as austenitic-ferritic one: Cr15Mn19. The serial sectioning technique was used for simultaneous evaluation of diffusion coefficients of radioisotopes of chromium 51Cr, manganese 54Mn and iron 59Fe at 1073K and 1173 K. Diffusion coefficients of radiotracers at 1173 K were calculated on the basis of both: activity of removed layer (differential method) and residual activity of the sample (integral method). The evaluated diffusion coefficients of metals in austenitic steels are higher than those in austenitic-ferritic one; their values are about 10-12 ÷ 10-11 cm2s-1. Moreover it was found that at 1173 K the diffusion rate of manganese is higher than that for iron and chromium while at 1073 K diffusion rates of chromium and manganese are comparable and higher than that for iron. Furthermore the experimental results point out that at 1173 K the volume diffusion is the dominant mechanism of metals’ transport while at 1073 K the high diffusivity paths diffusion prevails.