Cancer is a global problem, and many people in low-income countries do not have access to the treatment options, such as radiation therapy, that are available in wealthy countries. Where radiation therapy is available, it is often delivered using older Co-60 equipment that has not been updated to modern standards. Previous research has indicated that an updated Co-60 radiation therapy machine could deliver treatments that are equivalent to those performed with modern linear accelerators. Among the key features of these modern treatments is a tightly conformal dose distribution-- the radiation dose is shaped in three dimensions to closely match the tumour, with minimal irradiation of surrounding normal tissues. Very accurate alignment of the patient in the beam is therefore necessary to avoid missing the tumour, so all modern radiotherapy machines include imaging systems to verify the patient's position before treatment. Imaging with the treatment beam is relatively cost-effective, as it avoids the need for a second radiation source and the associated control systems. The dose rate from a Co-60 therapy source, though, is more than an order of magnitude too high to use for computed tomography (CT) imaging of a patient. Digital tomosynthesis (DT), a limited-arc imaging method that can be thought of as a hybrid of CT and conventional radiography, allows some of the three-dimensional selectivity of CT but with shorter imaging times and a five- to fifteen-fold reduction in dose. In the present work, a prototype Co-60 DT imaging system was developed and characterized. A class of clinically useful Co-60 DT protocols has been identified, based on the filtered backprojection algorithm originally designed for CT, with images acquired over a relatively small arc. Parts of the reconstruction algorithm must be modified for the DT case, and a way to reduce the beam intensity will be necessary to reduce the imaging dose to acceptable levels. Some additional study is required to determine whether improvements made to the DT imaging protocol translate to improvements in the accuracy of the image guidance process, but it is clear that Co-60 DT is feasible and will probably be practical for clinical use. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2012-01-30 12:56:56.075

Cancer is a global problem, and many people in low-income countries do not have access to the treatment options, such as radiation therapy, that are available in wealthy countries. Where radiation therapy is available, it is often delivered using older Co-60 equipment that has not been updated to modern standards. Previous research has indicated that an updated Co-60 radiation therapy machine could deliver treatments that are equivalent to those performed with modern linear accelerators. Among the key features of these modern treatments is a tightly conformal dose distribution-- the radiation dose is shaped in three dimensions to closely match the tumour, with minimal irradiation of surrounding normal tissues. Very accurate alignment of the patient in the beam is therefore necessary to avoid missing the tumour, so all modern radiotherapy machines include imaging systems to verify the patient's position before treatment. Imaging with the treatment beam is relatively cost-effective, as it avoids the need for a second radiation source and the associated control systems. The dose rate from a Co-60 therapy source, though, is more than an order of magnitude too high to use for computed tomography (CT) imaging of a patient. Digital tomosynthesis (DT), a limited-arc imaging method that can be thought of as a hybrid of CT and conventional radiography, allows some of the three-dimensional selectivity of CT but with shorter imaging times and a five- to fifteen-fold reduction in dose. In the present work, a prototype Co-60 DT imaging system was developed and characterized. A class of clinically useful Co-60 DT protocols has been identified, based on the filtered backprojection algorithm originally designed for CT, with images acquired over a relatively small arc. Parts of the reconstruction algorithm must be modified for the DT case, and a way to reduce the beam intensity will be necessary to reduce the imaging dose to acceptable levels. Some additional study is required to determine whether improvements made to the DT imaging protocol translate to improvements in the accuracy of the image guidance process, but it is clear that Co-60 DT is feasible and will probably be practical for clinical use. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2012-01-30 12:56:56.075

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This thesis contains three major areas of work. Chapter 1 describes the various film deposition techniques available for the growth of thin films. These different growth methods, substrate preparation and vacuum techniques, are discussed in the context of the effect of the growth process and deposition environment on film structure and quality. Chapter 2 describes the two film growth chambers. Chapter 3 describes the origin of giant magnetoresistance (GMR) in magnetic multilayered structures, and investigates the magnetoresistive properties of ion-beam sputtered CoCu multilayered thin films. Different film structures and deposition conditions have been investigated in order to maximise the size of negative magnetoresistance seen. Chapter 4 investigates the magnetic and giant magnetoresistive properties of sputtered CoCu and CoAg heterogenous alloys. The magnitude of the GMR effect is found to depend on the Co concentration and Co particle size. Chapter 5 describes an investigation of molecular beam epitaxy (m.b.e.) grown Dy/Y multilayer structures. The temperature dependences of helical magnetic structure in the Dy layers is investigated in two samples of different multilayer structures. Chapter 6 describes an acoustic interferometer which has been used to measure velocity and attenuation changes in an ultrasonic signal at frequencies of order IGHz. Also described is the production of the thin film piezoelectric transducers used in this technique, which are grown directly onto a single crystal of the material under investigation. The acoustic interferometer is used to investigate the dynamics of of a relaxation process between two time-reversed antiferromagnetic states in DyAlG, and a model for domain growth in this system is postulated. Chapter 7 investigates the phase diagram of DyPO₄ using the acoustic interferometry technique. The observations of hysteresis effects are used to define a mixed phase region below the tricritical point.

This thesis reports a study of polydentate amino acid complexes of cobalt(III). The complexes prepared during this project have been characterized by a range of techniques, including ¹³C{¹H} and ¹H NMR spectroscopy, UV-visible spectroscopy, infra-red spectroscopy, elemental analysis and single crystal X-ray structure determination. A total of seven single crystal X-ray structure determinations have been performed during these studies. The imino acid polydentate complex, [Co(Aim₂trien)]₂[ZnCl₄], was reduced to the corresponding amino acid complex, [Co(A₂trien)]Cl, where as many as ten diastereoisomers could be formed due to the formation of new stereogenic centres. The crude product of these reactions was a mixture of isomers, according to ¹³C{¹H} NMR data. These isomers were separated using ion-exchange chromatography. The major isomer (I1), a minor isomer (I2a) and a half reduced complex (I4a) from the [Co(A₂trien)]Cl reduction and separation experiment were characterised. The predominant isomers produced were found to have had the proton on the α-carbon atoms positioned on the amine face of each amino acid ligand fragment. To investigate the ratio of the isomers formed by the initial borohydride reduction, an isomerisation study of the major isomer of the [Co(A₂trien)]⁺ complex (I1) was performed. This study hoped to establish the degree to which the distribution of isomers was a result of dynamic equilibrium. Experiments on a small scale showed the initial isomer distribution to be similar to that obtained from the borohydride reduction reaction. However, prolonged exposure to the carbonate buffer (≈ two weeks) resulted in isomers not previously seen. Experiments on a large scale were performed to establish whether the results were consistent. The materials from both the two hour and two week experiments were mixtures of isomers by ¹³C{¹H} NMR spectroscopy and were separated using ion-exchange chromatography. ¹H NMR data of the two hour experiment showed only epimerisation of the amine proton adjacent to the α-carbon atom. Therefore the isomers produced from the isomerisation of I1 have the same configuration of the proton on the α-carbon atoms, which is on the amine face of each amino acid chelate ring. ¹H NMR data from the two week experiment resulted in new isomers not previously seen as both the amine proton and the proton on the α-carbon atom have been epimerised. The polyamine wrapping around the central metal ion may also have changed in some cases. It would appear, from the ¹H NMR data that the methyl group signals of these isomers fall in two distinct clusters; a cluster at δ 1.50-1.65 ppm and a cluster at δ 1.40-1.49 ppm. From these results, and the results of Chapter Two, it has been calculated that there is at least 92% facial selectivity for the amine face of the molecule during the initial borohydride reduction reactions. This may be due to a di-hydrogen bonding interaction between an adjacent amine proton and a hydride of the borohydride, which directs the attack. Following on from this study, a new range of imino and amino acid complexes were synthesised using different tetraamine and pentaamine cobalt(III) complexes. X-ray quality crystals of [Co(Aim₂2,2,3-tet)][ClO₄] and [Co(Aim₂2,3,2-tet)][ClO₄] were obtained and solved with assistance from Dr. Chris Fitchett and Dr. Jennifer Burgess. Borohydride reductions were performed on the [Co(Aim₂2,2,3-tet)]⁺ and [Co(Aim₂2,3,2-tet)]⁺ systems. The products were a mixture of isomers according to 1H and ¹³C{¹H} NMR spectroscopy. The results from the ¹H NMR experiments showed similarity between the [Co(A₂2,3,2-tet)]⁺ and [Co(A₂trien)]⁺ systems, where three major stereoisomers were present in solution. Analogous results for the asymmetric [Co(A₂2,2,3-tet)]⁺ system were also observed. Preliminary attempts have been made to separate these isomers using ion-exchange chromatography.

No description available.

A series of SNS ligands have been successfully synthesised and characterised by IR, NMR and MS. The ligands are divided into two groups and represented by the general formulae: 2,6- bis(RSCH2)pyridine [R= methyl, ethyl, butyl, cyclohexyl, phenyl] and bis(RSCH2CH2)amine [R= ethyl, butyl, decyl]. Cobalt complexes of the respective ligands with the general formulae Co[2,6-bis(RSCH2)pyridine]Cl2 and Co[bis(RSCH2CH2)amine]Cl2 were synthesised and characterised by IR, elemental analysis and X-ray crystallography (for selected complexes). Thus, to investigate the electronic and steric effects of the ligand structure on the chemistry and reactivity of the complexes, the substituents bonded to the two sulfur donor atoms were sequentially varied and two different nitrogen sources were chosen. Crystal structures of Co[2,6- bis(CH2SCH2)pyridine]Cl2 (Ia), Co[2,6-bis(CH2CH2SCH2) pyridine]Cl2 (IIa) and Co[2,6- bis(CH2CH2CH2CH2SCH2)pyridine]Cl2 (IIIa) were obtained. It was found that complex Ia exists as a molecular dimer linked through two chloride bridges resulting in an octahedral geometry around each metal centre, while complexes IIa and IIIa are monomers exhibiting a trigonal bypyrimidal geometry. The complexes were tested as catalysts for the activation of paraffinic C−H bonds towards the formation of oxygenated products: octanol, octanone, octanal and octanoic acid from the substrate n-octane. Gas chromatography was utilised to quantify the products formed and also to calculate the conversion and selectivity of each catalyst system. The catalytic testing revealed that the ketone products were the most dominant with selectivities of ca. 90%. The catalyst that was the most active was Co[bis(CH2CH2SCH2CH2)amine]Cl2 (Ib) with a total n-octane conversion of 23%. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2012.

Typescript. / Thesis (Ph. D.)--University of Hawaii, 1966. / Bibliography: leaves [122]-127. / ix, 127 l illus., tables (1 fold)