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Medical radiation is vital in acquiring a patient diagnosis, but some clinicians are concerned with the perceived risks associated with ionizing radiation. This risk is heightened when incorporating in utero exposures due to the risk to the developing foetus. Although other organ systems have been studied, there is a paucity of data on the effects to the respiratory system from in utero exposures. The aim of this thesis was to understand the long-term effects on the respiratory system from in utero exposures, but as a first step, it was important to determine what levels patients receive whilst admitted to hospital. Two polar populations were chosen based on their predicted exposure levels during hospitalisation; one with high levels, intensive care unit (ICU) patients, and one with low levels, pregnant patients. Most patients cumulatively received < 1mSv with median exposures of 0.99 mSv (ICU patients) and 0.02 mSv (pregnant patients). However, both cohorts had patients that surpassed 10 mSv. To assess the effects from in utero exposures on the respiratory system, two animal models were conducted both exposed during late gestation, one healthy model and one acute lung injury model. In the health animal model, cardiovascular outcomes were also measured, however, ionizing radiation (50, 300, 1000 mGy) did not appear to influence these two organ systems from the outcomes measured. In the acute lung injury model, lipopolysaccharide (3mg/Kg) stimulated an acute lung inflammatory response, however, there was also no overt effect of radiation from the outcomes measured (10, 100, 1000 mGy). In both models, ionizing radiation did cause growth restriction up to 16 weeks of age, but this was only observed from doses above 100 mGy. Overall, the levels of ionizing radiation patients receive is low and from diagnostic exposures during pregnancy, there does not appear to be any strong effects on the developing foetus. / Thesis / Doctor of Philosophy (PhD) / Radiation is necessary in medicine to observe the internal structures of the body, but it can sometimes cause unwanted biological changes within the body. This risk is heightened when considering exposure to developing baby because of the dynamic changing it is naturally going through and possible lifetime left to experience effects. This thesis aimed to understand what levels of radiation patients receive in hospital, observing one population predicted to receive high levels (Intensive care patients) and one predicted to receive low levels (pregnant patients). Overall, the majority of patients in the two cohorts received less than the recommended yearly public limit of 1 millisievert (mSv). The second aim was to observe the effects on the growth, lungs and hearts of the babies in an animal model when they are exposed during pregnancy. Radiation had no overall effect on the lungs or heart but can reduce body weight at moderate (100 milligrays (mGy) and high (1000 mGy) exposures.

M.S.

The purpose of this thesis has been the determination of the nature and cause of time-softening property of the lead-tin alloys in the solid solution range. An alloy of 19% tin, 81% lead was chosen as exhibiting the property to a degree suitable for observation of the accompanying phenomena. The investigation proceeded in three parts: (1) an observation of the time-softening property itself by means of series of hardness tests to determine the degree of change and the time required for its accomplishment; (2) a search for x-ray evidence of possible precipitation which might be apparent as a change in the lattice constant of the crystal; and (3) conductivity measurements as a further check on whether the solution concentration was changing. The results accordingly may be classified under the same three headings. The change in hardness of the lead-tin alloy under investigation is intimately related to its habit of precipitating some of the excess tin from the solid solution. Both the x-ray and the conductivity test results offer supporting evidence that precipitation does occur in conjunction with the softening effect. Apparently also the softening effect observed in the lead-tin alloy is a definite phenomenon distinct from the “over-aging” effect in which an alloy aged at high temperature increases rapidly in hardness until a certain critical hardness is reached, after which softening sets in. / M.S.

X-ray polycrystalline diffraction techniques are used to determined the defect structure in a commercial Cu-l1.55 at. %Be-O.23 at. %Co alloy during low temperature aging. The analysis of the X-ray diffraction patterns is aided by the computer modeling of the defects inside the crystals using an elastic model. The research is to provide more detailed understanding of the precipitate structures in the process of aging and the age hardening mechanism of the alloy. The diffraction profiles from samples aged for different times at 315°C are collected using a position sensitive proportional counter with eu 1(0:1 radiation. The hardness values of the samples are also measured. An elastic model for the coherent precipitates in anisotrpic matrix is developed according to Eshelby's treatment of transformed regions in an elastic continuum. The displacement fields generated by the precipitates in the surrounding matrix, obtained through the elastic model, are used to explain the (110) streaks near the Bragg reflection, and to calculate the powder diffraction patterns from the aged alloys. For the latter purpose, a general X-ray diffraction theory is developed, combining the work of Krivoglaz and Dederichs. The X-ray diffraction patterns are compared with existing TEM observations in the literature. The analysis of the diffraction patterns suggests that the precipitates in the early stage of aging (GP zones) can be the matrix constrained version of 7, the equilibrium phase, similar to an observation by Khatchaturyan and Laughlin on 7 and 7'. The quantitative calculation based on this model shows excellent agreement with experimental data for samples aged at 315°C. The averaged inter-precipitate spacing in the crystals for the optimally aged sample at 315°C is determined to be 200-300A. A simplified method of evaluating the thermal diffuse scattering and a method for calculating the diffuse scattering from polycrystalline materials with textures are also presented. / Ph. D.

Displacement fields from point-like defects are investigated by x-ray diffraction. The atomic volume changes in the interstitial compounds using crystallographic information has been found to correlate with the size of filled octahedral sites. Systematic correlations enable estimates to be made of the components of the dipole tensor for interstitials in octahedral sites for binary systems containing N, C, and 0 in V, Nb, Ta, Cr, Mo, W, and Fe lattices. X-ray diffraction analysis of the concentration and residual stress gradients in N implanted Mo crystals and Nb films show that the dominant source of internal strain arises from N located in octahedral sites. For Nb implanted at LNT, these distortion centers are aligned equally along three mutually perpendicular directions to maintain cubic symmetry. Large biaxial residual strains are developed after a 5at% implantation of N into Nb and Mo. Radiation damage is present as small vacancy and interstitial loops. A method was developed to obtain the orientation function for samples containing a fiber texture. A slit correction is included and the final results from this simplified approach are compared with the pole figure measured by direct x-scanning. Knowing the orientation function allows one to correct the integrated intensities to that for an ideal powder, thereby allowing thermal and static displacements to be obtained from textured samples. Anisotropic displacements about coherent Be rich GP zones were investigated in a Cull-at%Be alloy. The results indicate that the attenuation factor 2M which determines the relative integrated intensities of Bragg, quasiline, and static diffuse scattering can be expressed in a simplified form. Experimental data of 2M for aged Cu-Be samples show an anisotropy. The anisotropy increases with increasing aging time when the equiaxed-GP zones formed in the early stage collapse into platelike GP zones. / Ph. D.

No / The three seismic sources, S1, S2, and S3, detected from MDI Dopplergrams using the time-distance (TD) diagram technique are presented with the locations, areas, and vertical and horizontal velocities of the visible wave displacements. Within the data cube of 120 Mm, the horizontal velocities and the wave propagation times vary slightly from source to source. The momenta and start times measured from the TD diagrams in sources S1-S3 are compared with those delivered to the photosphere by different kinds of high-energy particles with the parameters deduced from hard X-ray and ¿-ray emission, as well as by the hydrodynamic shocks caused by these particles. The energetic protons (power laws combined with quasi-thermal ones, or jets) are shown to deliver momentum high enough and to form the hydrodynamic shocks deep enough in a flaring atmosphere to allow them to be delivered to the photosphere through much shorter distances and times. Then the seismic waves observed in the sources S2 and S3 can be explained by the momenta produced by hydrodynamic shocks, which are caused by mixed proton beams and jets occurring nearly simultaneously with the third burst of hard X-ray and ¿-ray emission in the loops with footpoints in the locations of these sources. The seismic wave in source S1, delayed by 4 and 2 minutes from the first and second hard X-ray bursts, respectively, is likely to be associated with a hydrodynamic shock occurring in this loop from precipitation of a very powerful and hard electron beam with higher energy cutoff mixed with quasi-thermal protons generated by either of these two bursts.

M. S.

M.S.

X-ray techniques were used extensively in this work to examine ceramic samples. The well known techniques including : (1) identification of phases and chemical species, (2) peak separation, (3) quantitative phase analysis, (4) intensity band simulation, and (5) line shape analysis, were applied to ceramic materials of silicon nitride, zirconia toughened alumina, fully and partially stabilized zirconia. A theoretical derivation of the x-ray intensity from a rough sample based on a statistical roughness model was carried out. The statistical model was then combined with the intensity band simulation technique to simulate the intensity band from a rough sample. The modified technique for intensity band simulation was used to determine the strain profile in the near surface regions of a flat and a rough fully stabilized zirconia samples. The results show that a compressive zone is present in the near surface region of each sample. A partially stabilized zirconia disk was examined using symmetrical and asymmetrical diffraction optics after a prolonged pin on disk wear test. The different diffraction optics provided different probe depths and revealed a depth gradient of the phase distribution. A general picture of the wearing process of ceramic components is described based on the examinations carried out in this work. / Ph. D.