Design of a prototype apparatus for on-line elemental analysis using nuclear techniques

Coal has a significant role as an energy source of the future in electricity generation worldwide. In Turkey, coal is essential as an energy source, since coal-fired power plants currently fuel about 31% of global electricity. For our country, the processes of improving the quality and preparation of the coal is important to produce the energy efficiently from the coal power plant. For that purpose, an instrument using some nuclear techniques was developed to be able to determine the content of the ash, moisture and calorific value of the coal moving on the conveyor belt as on-line. Due to the fact that being non-destructive and sensitive for some elements, neutron activation analysis (NAA) is an important technique for identifying the specific elements in materials. The technique of most devices is based on using a radioisotope such as 252Cf. The irradiation of samples depend on neutron interactions which are neutron inelastic scattering (n,n`g), and the neutron radiative capture (n,g). Because of the average neutron energy of 252Cf is about 2.5 MeV, this neutron source is convenient to analyze the samples including only the process of thermal neutron capture (n,g). The carbon content of coal which is important parameter to determine the quality of the coal, can not be detected by using 252Cf source. Therefore, a neutron generator is used to produce fast neutrons of 14 MeV releasing from deuterium – tritium (D-T) fusion reactions for the prototype device. The prototype device is composed of a neutron generator, a scintillation detector, an iron block for shadow shielding and lead shield of BGO detector. The neutron generator is a device which can be operated with pulsed mode. Therefore, the obtained gamma rays can be classified according to their interactions induced with thermal neutrons or fast neutrons. The choice of a detector is pretty significant issue for designing the prototype device. The scintillation type of detector is preferred for the reason that has high efficiency and more endurance to neutron radiation damage. As a scintillation detector, Bismuth Germinate Oxide (BGO) is chosen. The characteristic features of the BGO is studied in detailed. The energy resolution, efficiency, shape calibration are calculated by using radioactive point sources such as 60Co, 137Cs, 152Eu. Additionally, The response functions of BGO detector are experimentally found to apply on the spectrum obtained from simulation programs. A prototype apparatus can be modelled to provide nuclear techniques by using Monte Carlo simulation programs. Monte Carlo N-Particle 5 (MCNP5) and Geometry And Tracking 4 (GEANT4) simulation programs are used to design the geometry and physical interactions of the prototype apparatus. The synthetic coal samples including different element contents are simulated and analyzed.There are plenty of ways to analyze a bulk system including gamma spectrum. Some of them are peak area determination, neural network algorithm and Monte Carlo Library Least Square (MCLLS) fitting. Analyzing the obtained spectra from Pulsed Fast and Thermal Neutron Analysis (PFTNA) experiment is very difficult due to its non-linear nature. Library Least Square is a common mathematical approach for treating non-linear radiation effects in cases such as PFTNA. In this study, MCLLS technique is applied by using MCNP5 and GEANT4 simulation programs. With the aid of fixed spherical geometry, the elements inside of the coal sample are simulated individually. The obtained spectrum from MCNP5 and GEANT4 are used to build up an element library of coal sample. The method is applied on experimental spectrum which have analysis reports including element contents. So the experimental spectrum are provided to calibrate according to element library. Then, the calibrated element library is used to calculate the contents of unknown spectrum obtained experimentally. By using this mathematical approach, the element contents of experimental coal spectrum are aimed to calculate in the range of measurement precision defined commercially before.