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Thesis--University of California, 1959. / Xerographic reproduction. Includes bibliographical references (p. 165-174).

This thesis consists of two completely separate parts. In Part I, we look at disorder in fastionic conductors, and in Part II we examine the pseudoquadrupole effect in ordered magnets. Part I looks at two aspects of the disordered state in fastionics, where the disorder is due to ions moving off their regular sites to positions close to other regular sites, a feature especially characteristic of the fluorites. The first aspect is how Coulomb interactions could be responsible for the co-operative behaviour of defects which causes the transition to fastionic behaviour. We look at this with a model of charged defects on a lattice, applying techniques involving classical diagrammatic perturbation theory to find the free energy of our model system. Using elementary thermodynamics, we show how this model can predict co-operative behaviour. The second aspect is the nature of the disorder above the fastionic transition. We look at disorder in lead fluoride using a molecular dynamics simulation with an interionic potential that we obtained. We use the simulation to examine the distribution of anions in both real space and k space. Simulations have been made on the other fluorites CaF₂ and SrCl₂ and it is possible that the high dielectric constant of lead fluoride might lead to qualitatively different behaviour. Our results show that this is not the case and we find defect concentrations similar to those obtained from CaF₂ and SrCl₂. Our Is space analysis however gives defect concentrations an order of magnitude larger, in approximate agreement with experiment. In Part II we set up a theory for the pseudoquadrupole effect in cubic ferromagnets and show that it is related to the difference in longitudinal and transverse magnetic susceptibilities. Model calculations are performed for a Heisenberg ferromagnet using molecular field theory near the critical temperature t_c, and spin wave theory at low temperatures; and the itinerant model at absolute zero and t_c. We find that the pseudoquadrupole effect in iron and nickel and at impurities in these metals appears to be very much less than measured quadrupole effects. We also look at the effect in GdAl₂ and show that it can not explain a temperature dependent quadrupole interaction seen experimentally We therefore conclude that the observed quadrupole effects are due to real electric field gradients.

Quadrupolar relaxation-based methods in Fast Field-Cycling MRI Nicholas R. Payne Aberdeen Biomedical Imaging Centre, University of Aberdeen, AB25 2ZD, Scotland, UK Fast Field-Cycling MRI (FFC-MRI) can access contrast based on the dependence of a sample's relaxation rate to the applied magnetic field strength. This technique can provide signal based on interactions with local quadrupolar nuclei through cross-relaxation, however, there are other so-called Nuclear Quadrupole Double Resonance (NQDR) techniques described in the literature. This work has been centred on efforts to apply these techniques to FFC-MRI and otherwise explore how interactions between protons and quadrupolar nuclei can be further exploited. Through this work two irradiation systems were designed and built for manual tuning, in the first instance, and automatic tuning. The latter was able to quickly retune to coil, however, it was limited in RF power handling capability. A second strand of work was concerned with the reduction in receiver deadtime required to detect signal from solid-state samples such as those previously used in NQDR experiments in the literature. However, circuitry designed to dampen coil ringing by temporarily reducing the resonator's Q-factor following a pulse, along with a novel method utilising field-cycling were not able to reduce the deadtime enough to detect signal from relevant samples. This, coupled with a lack of evidence of NQDR effects in gel-like samples, proved the ultimate stumbling block for NQDR in FFC-MRI. Success was seen in a third strand of work in which simulations were used to design custom experiments which could be used to provide large increases to the signal-to-noise ratio in some experiments. The simulated environment also allowed for fast testing and development of new post-process algorithms which could more accurately calculate relaxation rates. The work concluded that NQDR is unlikely to be useful in FFC-MRI due to the constraints on both the sample and the technique. However the information from quadrupolar nuclei can be improved with better post-processing and tailored pulse sequence parameters.

Thesis (M.S.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 2005. / Includes bibliographical references (p. 91-93).

In this study frequency modulation was used with a regenerative spectrometer and a super-regenerative spectrometer to detect the nuclear quadrupole resonance frequencies of chlorine in two commercially available compounds, 1, 3, 6, 8 - tetrachlorophyrene and 3, 4, 5, 6 - tetrachlorophthalimide.

M.S.

M.S.

This thesis includes introductions into the theory of nuclear quadrupole resonance (NQR) detection, a brief history of early developments in NQR, and the basic theory of Zeeman modulation and its effects upon NQR line shapes. A brief description of the individual pieces of apparatus and their contribution to the detection and recording of resonance signals is also included. The primary purpose of this research was to determine those parameters for operation of the apparatus which optimize recorded NQR signals from linear chlorinated compounds. Finally, the determination of the apparatus parameters for the four different compounds are summarized within this thesis.Ball State UniversityMuncie, IN 47306