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An analytical technique, “X-ray fluorescence spectrometry" (XRF) has been introduced in the first chapter as a precursor of its applications to soils, alloys of refractory nature, and nuclear waste. It covers the applications of the modern technique to the development of human resources. The history has been reviewed, literature surveyed, the references cited, principles described, characteristic features highlighted and the purpose of the studies defined. An XRF spectrum is a statistical phenomenon which has been reviewed theoretically in the second chapter. Primary X-rays generate the representative secondary radiation from the samples after photoelectric as well as scattering phenomena. Aggregate number of photons generated here are sensed by the detector to produce observable electrical pulses after interaction of the X-ray photons with its sensitive matter. These pulses are accumulated and processed by the processor to produce an energy spectrum in spectroscopy. The statistical functions describing the discrete as well as the continuous distributions have thus been reviewed. The shape of these distributions are affected by the transport of the photons in sample matrix. Qualitative, semi-quantitative and then quantitative elemental analyses require theoretical mechanism to convert the characteristic intensities observed from elements constituting a sample to the chemical concentrations. One amongst numerous such algorithms is called ZAF correction factor. The theoretically developed software is already available commercially. It has been used for its empirical applications during these studies. Studying a natural phenomena require representative sampling from the bulk matter and then its analysis at a laboratory scale. The available instruments have therefore been described in the third chapter. The generally available materials as well as the special ones required for use with XRF have been narrated here. The methods for applications to the liquid as well as solid samples for presentation to XRF techniques have been discussed. These contained thick samples in rugged polyethylene bottles as well as that in thin samples on a filter paper distributed homogeneously. Attenuation of the photons is reduced by presentation of the samples in sampling cups fixed with Mylar films. The thick liquid samples in polyethylene bottles were presented to the wavelength dispersive (WDXRF) spectrometer containing an X-ray tube capable of producing stable but strong primary X-ray beam. The solid samples of refractory nature, available in the form of a powder were filled in a cavity of a prepared pellet. The samples have also been mixed with in cellulose powder and subsequently pressed with a die to form a briquetted pellet. The methods have been described along with those to form a glass bead using different types of fluxes. The standard metal and alloy samples were presentable to the machine directly. They have already been shaped with lathe machines. The surfaces were washed and finished with metal free water, liquid detergents and emery papers of proper grit size. They were presented to the energy dispersive (EDXRF) system. A high voltage of 50kV and 50mA was applied to produce an intense primary X-ray beam in WDXRF tube where as in the EDXRF it was comparatively of low intensity and produced with a voltage of 20kV and minimum current 0.01 mA. The Standard (SRMs) and the certified (CRMs) reference materials used during the studies have also been described here. The experimental part of the studies has been narrated in the fourth chapter. It contains instrumental calibration method with an isotope 241Am95 used occasionally. However as a routine the calibration was monitored with FeK line from a standard pellet or a bead containing oxide of iron (Fe2O3). The standard radioisotope has been studied and compared after presentation ,as a point source as well as that on a steel planchet containing its thin film. The spectra of the isotope and that of a planchet has been compared with and without energizing the primary beam of the X-ray tube. The simultaneous nature of EDXRF system has been used for general-purpose studies of refractory materials. Efforts have been made to optimize the conditions for simultaneous studies of fissile and fission fragments of nuclear materials with WDXRF system. The basic parameters of the instrument as well as the environments of the sample have been studied. This contained studies of FeK lines using primary flux produced at different volts and current, secondary radiation from samples of different geometry in air and vacuum, pulse processor’s sensitivity ranges arid pulse processing times, apertures defining the path and the size of the beam, and finally the effect of the concentrations of an element producing the analyte line. Data of the representative spectra of the elements of the periodic table and the intensities (gross, net, background, and profile) of the analyte line as a function of time of measurement has been saved in the computer memory as a base. The analyte lines are strongly effected by other elements in a sample of complex matrix. The profile intensities can be deconvoluted from the spectrum of simple matrix. Quantitative evaluations were carried out with ZAF correction factors technique. This required simple elemental profiles to be summed up to simulate a complex spectrum. This is then compared with that of an unknown by applying least square top hat fitting technique and standardization. The manufacturer of the XRF system has developed the theoretical software for this purpose. The technique has been applied during these studies to analyze natural and complex standard refractory materials of the primary rocks and soil origin. Known and determined results of a ceramic material of kaolinite origin and NIMROC standard set containing primary rock samples such as Granite, Syenite, Norite, Lujaverite, Pyroxenite, and Dunite have been compared here. Similarly, the metal alloys have also been analyzed. The alloys were iron and nickel base such as: corrosion resistant iron and iron base alloys classified as mild, low, high manganese, tool, high speed, austenitic, maraging steels; Nickel base alloys called inconel, waspealloy, monel, nimonic, incoloy, hastealloy. The sequential nature of the WDXRF using high voltage and high current has been studied and suggested for analysis of toxic radioactive materials like a nuclear waste solution in rugged polyethylene bottles. The gross and net intensities of the analyte lines as function of concentrations have also been regressed and the empirical coefficients evaluated during analyses with WDXRF studies. Fissile materials such as uranium from the actinides are burnt-up and the fission fragments like lanthanides are generated in nuclear reactors. Rationales of an analyte line ULα.l have been studied by WDXRF spectroscopy whereas the mutual effects of uranium and cerium as a representative of lanthanides have been studied with EDXRF. Nuclear wastes are generated in nuclear fuel cycle. Toxicity of the materials therein demands strict monitoring of these before their disposal. Strontium as a burn-up monitor was suggested and studied in presence of other elements. This contained a nuclear waste simulated for a CANDU reactor fuel at a burn-up of 180 MWh/Kg after 0.5 years cooling. It was diluted fifty times as pretention for reduction of activity to a permissible level (0.5 mCi) for working in a glove box. The analyses of the experimental data led us to few observations. These have been mentioned and the results of the experiments discussed in the fifth chapter.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: x-ray fluorescence, soil alloys, nuclear wastes, edxrf system, wdxrf system, fek lines, secondary radiation, pulse processor, energy dispersive xrf, wavelength dispersive xrf
Subjects: Q Science > QD Chemistry
Depositing User: Muhammad Khan Khan
Date Deposited: 25 Oct 2016 07:38
Last Modified: 25 Oct 2016 07:38
URI: http://eprints.hec.gov.pk/id/eprint/2676

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