Call number: LD2668 .T4 1953 W57 / Master of Science

Call number: LD2668 .T4 1956 D45 / Master of Science

This dissertation presents the characterization and evaluation of a new radiological imaging modality, Toshiba Computed Radiography (TCR) 201. The characteristics of the TCR storage phosphor imaging plates such as energy-dependent x-ray quantum efficiency, stored signal decay, low exposure rate signal build-up, and spontaneous and stimulated gain measures are presented. The TCR 201 system is characterized by the signal transfer curve, the total root-mean-squared (rms) output noise, the signal-to-noise ratio, the modulation transfer function (MTF), its noise power spectrum (NPS), and the detective quantum efficiency (DQE). The system rms noise is photon-limited for exposures less than 1.0 mR, but has contributions from phosphor structure and quantization noise for exposures higher than 1.0 mR. The phosphor's information factor is shown to explain deviations from ideal photon-limited noise for exposures of less than 1.0 mR. The MTF of the system is measured for standard imaging plates, 10% at 2.8 lp/mm, and for high resolution imaging plates, 10% at 4.4 lp/mm. An expression for the NPS is statistically derived, and experimental measurements confirm the expression and show an increase in uncorrelated noise power above 1.0 mR which is consistent with rms measurements. Expressions for the DQE are presented. A psychophysical study is performed to directly compare the TCR to film/screen combinations in imaging low-contrast objects. The results of this study show the TCR provides better images for detectability as a function of exposure. Also, the use of the TCR 201 as a two dimensional dosimeter and in single-shot dual energy subtraction is presented.

The aim of this thesis was to examine materials using high resolution X-ray diffraction techniques. Initial work involved the synthesis of various metal phosphates to investigate their suitability for charge density work. Many of these were discovered to be of insufficient quality for further study. Much of the phosphate synthesis work performed at the moment utilises an ionic liquid both as a solvent and structure directing agent which dictates the topology of the structure due to its size and charge density. As such the ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate used in the synthesis process was examined with high resolution X-ray diffraction as it was possible to produce large pure crystals which could be examined further. A high resolution data set was also collected from the metal organic framework SIMOF-1 which produced a preliminary multipole model however further data collections are required to improve the quality of the model. A multi-technique investigation involving X-ray diffraction, solid state NMR and first principles calculations was carried out on the aluminophosphate material AlPO₄-15. A synchrotron X-ray single crystal diffraction study was carried out on the same sample as that used in solid state NMR studies. The model from the single crystal study, together with a model from a literature high resolution study of the same material, were used as starting points for the first-principles calculations of the NMR parameters. This enabled the ³¹P and ²⁷Al NMR spectra to be unambiguously assigned and all the NMR parameters calculated agreed well with the experimental spectra even without relaxing the X-ray derived structural models. Highlighting that as long as a good data set has been collected in the first place the atomic positions would not change too drastically. Other aspects of this thesis involved investigations into other ionothermally prepared systems such as the use of different phosphonate sources to provide functionality to the materials. This work resulted in some interesting findings such as the ionic liquid breaking down and being incorporated into the framework via the metal. Many of the structures produced were of a layered nature however a molecular structure was also synthesised which is unlike the vast majority of hydrothermally prepared phosphonates, which are layered. The negligible vapour pressure provided by the ionic liquid has enabled synthesis reactions to be investigated with glass vessels on an energy dispersive beam line. This work highlighted how it is possible to study the synthesis process in-situ and compare microwave assisted reactions against a conventional heating method, the results indicate that two different types of reactions are occurring resulting in different intermediates which is due to the way the reagents are heated. The microwave assisted reactions also result in larger purer crystals which highlights the importance of the method in materials synthesis. The use of a specially designed environmental gas cell was used to investigate the adsorption properties of the metal organic framework CPO-27-Co in-situ. Using the cell it was possible to locate sulfur dioxide physisorbed and chemisorbed sites with in the framework which could be removed by the application of a vacuum and heat. It was also possible to locate the chemisorbed sites for nitric oxide within the metal organic framework however due to the low scattering factor and disorder from the gas it was not possible to locate the physisorbed sites.

X-ray based evaluation of different stages of fracture healing is a well established clinical standard. However, several studies have shown plain radiography alone to be an unreliable method to assess healing. The advent of digital X-ray systems provides the potential to perform quantitative analysis on X-ray images without disrupting normal clinical practice. Two aspects were explored in this study. The first was the measurement of mechanical fracture stiffness under four point bending and axial loading. The second was the inclusion of an Aluminium step wedge to provide Aluminium-equivalent thickness calibration information. Mechanical sti ness studies involved the development of equipment to perform four point bending on intra-medullary (IM) nailed tibial fractures, equipment to perform axial loading on conservatively treated humeral fractures, and fracture models to ex- amine the developed systems. Computational procedures to automatically measure the angle and offset occurring at the fracture site by comparing loaded and unloaded X-ray images were developed utilising cross-correlation. The apparatus and procedures were tested using the fracture models both in X-ray and using the Zwick materials testing machine. The four point bending system was applied clinically to a series of IM nailed tibial fracture patients and the axial loading system to two conservatively treated humeral fracture patients. Mechanical stiffness results showed that the apparatus worked well in the clinical radiography environment and was unobtrusive to normal practice. The developed X-ray analysis procedure provided reliable measurements. However, in the case of IM nailed tibial fractures, both angular and displacement movements were too small to be accurately assessed or to provide reliable stiffness measurements. This indicated that this patient group was possibly unsuitable for mechanical stiffness measurements or that higher loads needed to be applied to the fracture site. The case studies of conservatively treated humeral fractures showed potential in detecting movement between loaded and unloaded X-rays and using this to provide sti ness information. Further investigation is required to show that this technique has the potential to aid fracture healing monitoring. Investigation into Aluminium step wedge calibration began with the design of different step wedges and X-ray phantoms. Initial image analysis involved studying the automatic processing applied by a digital Computed Radiography (CR) Fuji sys- tem and modelling of the inhomogeneities in X-ray images as well as investigation into the effect of and correction for scatter, overlying soft tissue and bone thickness. Computational procedures were developed to semi-automatically detect the steps of the step wedge, form an exponential Aluminium step thickness to grey level calibration graph, measure soft tissue and bone thickness, and correct for the heel effect and scatter contributions. Tests were carried out on pre-clinical models and results compared to ash weight and peripheral quantitative computed tomography (pQCT). A clinical study of radial fractures was used to investigate the effectiveness of the step wedge calibration system in monitoring fracture healing changes. Results using the step wedge indicated that the calibration technique was e ective in detecting and correcting for aspects in uencing Aluminium-equivalent thickness measures. With careful processing, useful information was obtained from digital X- rays that included the Aluminium step wedge and these correlated well with existing density measures. The use of the wedge in patient images showed that small increases in Aluminium-equivalent thickness of the fracture site could be detected. This was most useful for intra-patient comparisons throughout the course of healing rather than providing quantitative measurements which were comparable to other density measures. In conclusion, this thesis shows the potential for accurate analysis of digital X- rays to aid the monitoring of healing changes in fracture patients, particularly with application of axial loading and the use of step wedge calibration.

Approved for public release; distribution is unlimited / The production of nitric oxide by soft solar X-rays in the E-region of the ionosphere is investigated. An empirical expression for the variation in X-ray flux as a function of F10.7 is determined. This expression is incorporated into a one-dimensional diffusive photochemical model to compute nitric oxide densities. No results of these calculation are compared with NO observation from the Solar Mesosphere Explorer satellite. Variations of X-ray flux by a factor of 30 over the solar cycle can explain the observed variation in nitric oxide densities. / http://archive.org/details/investigationofp00duma / Lieutenant, United States Navy

M.Sc. / Aspects of electron-electron correlations have for the past few decades been at the forefront of research in Solid State Physics. More traditional concepts under this topic have been phenomena such as superconductivity, and magnetic ordering in its many forms including long-range ordering and spin-glass freezing. The class of so-called strongly correlated electron systems has been a particularly active field of study, as witnessed by for instance the series of annual international conferences held under this topic since 1992. Compounds and alloys of strong electronic correlations have proved a very rich field of new and anomalous physical behaviours in metallic and semiconducting compounds and alloys of especially 4f- and 5f-electron systems, together with ceramics characterized as the so-called ¡§high-TC¡¨ superconductors. The f-electron systems have revealed a variety of behaviours such as ~ 1000-fold enhanced effective electron masses at low temperature, coexistence of superconductivity and magnetic ordering in systems where the magnetic interactions are far too strong to allow for Cooper-pair formation within the well-established BCS-interpretation, and electron transport and thermodynamic behaviour at low temperatures that completely defy our conventional Fermi-liquid paradigm of understanding the ground states of metals. The series of pseudo-ternary compounds Ce1-xLaxRu4Sn6 that were synthesized and characterized in this work for the first time are formed by substituting La for Ce in CeRu4Sn6, the parent compound. CeRu4Sn6 exhibits a number of properties which have been associated with a special class, the Kondo semiconductors of strongly correlated electron systems. CeRu4Sn6 has very recently been shown [A. M. Strydom et al. (2004)] to comprise an intriguing combination of characteristics that are thus far unique among the Kondo semiconductors: At low temperature (T 10 K) the specific heat proves the development of very strong electronic correlation out of an already low density of charge carriers (as shown by Hall-effect, resistivity, and the Sommerfeld coefficient of the specific heat). Furthermore, the specific heat follows a logarithmic increase as temperature is decreased below ~ 2 K, in a range where thermal transport shows the presence of an energy gap in the electronic density of states. The aim of this work was to investigate the intermediate and higher temperature (4.01 K „T T „T 300 K) behaviour of the electrical resistivity of the Ce1-xLaxRu4Sn6 series of compounds in which the concentration of the 4f-electron magnetic ion Ce is progressively being reduced. A steady but slow decrease of the energy gap with increasing La concentration was found in this work in contrast with what is usually the case in Kondo semiconductors. Both the presence of an energy gap and the low density of charge carriers are found to be connected to the presence of Ce in the unit cell, and are therefore not an artefact of the peculiar filledƒ{cageƒ{like tetragonal crystal structure of these compounds. An interesting strong anisotropy was found in the way in which the tetragonal unit cell expands preferentially within the aƒ{b plane, compared to the elongation along the cƒ{axis, upon moving from CeRu4Sn6 to LaRu4Sn6. / Prof. A.M. Strydom

SPIDERS (The SPectroscopic IDentification of eROSITA Sources) is a programme dedicated to the homogeneous and complete spectroscopic follow-up of X-ray active galactic nuclei and galaxy clusters over a large area (similar to 7500 deg(2)) of the extragalactic sky. SPIDERS is part of the Sloan Digital Sky Survey (SDSS)-IV project, together with the Extended Baryon Oscillation Spectroscopic Survey and the Time-Domain Spectroscopic Survey. This paper describes the largest project within SPIDERS before the launch of eROSITA: an optical spectroscopic survey of X-ray-selected, massive (similar to 10(14)-10(15) M-circle dot) galaxy clusters discovered in ROSAT and XMM-Newton imaging. The immediate aim is to determine precise (Delta(z) similar to 0.001) redshifts for 4000-5000 of these systems out to z similar to 0.6. The scientific goal of the program is precision cosmology, using clusters as probes of large-scale structure in the expanding Universe. We present the cluster samples, target selection algorithms and observation strategies. We demonstrate the efficiency of selecting targets using a combination of SDSS imaging data, a robust red-sequence finder and a dedicated prioritization scheme. We describe a set of algorithms and work-flow developed to collate spectra and assign cluster membership, and to deliver catalogues of spectroscopically confirmed clusters. We discuss the relevance of line-of-sight velocity dispersion estimators for the richer systems. We illustrate our techniques by constructing a catalogue of 230 spectroscopically validated clusters (0.031 < z < 0.658), found in pilot observations. We discuss two potential science applications of the SPIDERS sample: the study of the X-ray luminosity-velocity dispersion (L-X-sigma) relation and the building of stacked phase-space diagrams.

This problem consists primarily in determining the numerical value of the leukocytes after different amounts of roentgen rays had been applied to the subjects. The Atomic Energy Commission set up a problem concerning the effects of roentgen rays on the fertility in chickens, and grants were given to two institutions to study this. The blood work in this paper was an off-shoot from one of these five fertility grants.

We present a comprehensive study of interstellar X-ray extinction using the extensive Chandra supernova remnant (SNR) archive and use our results to refine the empirical relation between the hydrogen column density and optical extinction. In our analysis, we make use of the large, uniform data sample to assess various systematic uncertainties in the measurement of the interstellar X-ray absorption. Specifically, we address systematic uncertainties that originate from (i) the emission models used to fit SNR spectra; (ii) the spatial variations within individual remnants; (iii) the physical conditions of the remnant such as composition, temperature, and non-equilibrium regions; and (iv) the model used for the absorption of X-rays in the interstellar medium. Using a Bayesian framework to quantify these systematic uncertainties, and combining the resulting hydrogen column density measurements with the measurements of optical extinction toward the same remnants, we find the empirical relation N-H = (2.87 +/- 0.12) x 10(21) A(V) cm(-2), which is significantly higher than the previous measurements.