Hyperpolarisation encompasses a multitude of methods to increase the species' spin polarisation for nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) applications. Hyperpolarised 129Xe is produced via spin-exchange optical-pumping (SEOP). Firstly, electronic spins of alkali metal vapour are polarised via absorption of circularly polarised light. Alkali metal polarisation is subsequently transferred to noble gas nuclei via collisions. Within this thesis, the SEOP process is examined by probing the kinetics of the 129Xe polarisation build up. A combination of diagnostic techniques are used including low field NMR to measure 129Xe polarisation (PXe) at different spatial positions, near-IR optical absorption to give a global estimate of the alkali metal polarisation, and in situ Raman spectroscopy to spatially monitor the energy transport processes by detecting the internal gas temperatures (TN2). TN2 values were found to be dramatically elevated above oven thermocouple readings, with observations of up to 1000 K for an oven heated to only 400 K. Internal gas temperatures are presented for the first time along the length of the optical cell, showing spatial temperature and PXe variations during steady state and rubidium runaway conditions. Two contrasting methods of Raman spectroscopy are examined: a conventional orthogonal arrangement of detection and excitation optics, where intrinsic spatial filtering of the probe laser is utilised; and a newly designed inline module with all components in the same optical plane. Optical filtering is used to reduce the Rayleigh scattering and the probe laser line. This new inline device is presented herein and has a 23 fold improvement in signal to noise enabling increased accuracy and precision of `real-time' temperature monitoring. Rubidium, caesium and a rubidium/caesium hybrid are compared as the alkali metal of choice in the SEOP process. Caesium has a higher spin-exchange cross-section with 129Xe, thus a system is envisaged where current Rb D1 lasers in many polarisers can be utilised with a Rb/Cs hybrid to gain improvements in polarisation rates or levels. Xenon polarisations are shown up to 50% for a hybrid cell. Finally, preparatory experiments crucial to the imminent lung imaging study are presented, including measurements of PXe at low and high magnetic fields. In addition, polariser technology is examined including the current Nottingham device and an open-source consortium polariser.

This thesis is intended to contribute to a quantitative understanding of the blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) signal in order to increase its clinical potential. Here, the vascular, neuronal and physical processes which combine to give a resulting BOLD signal are investigated using respiratory challenges. The effect of isocapnic hyperoxia on vascular responses is investigated at 7 Tesla. No significant change was found in resting-state cerebral blood flow (CBF), resting-state cerebral blood volume (CBV) and task-evoked CBF. This challenges a previously held idea that hyperoxia is vasoconstrictive. The effect of isocapnic hyperoxia on neuronal oscillations was assessed with magnetoencephalography (MEG). Whilst a significant reduction in oscillatory power is reported in the occipital lobe, the change is significantly smaller than the global reduction previously measured with hypercapnia. These findings suggest that hyperoxia is an ideal tool for calibrated BOLD fMRI. The relationship between the change in blood oxygenation and change in transverse relaxation plays a key role in calibrated BOLD fMRI. However, previous measurements have been confounded by a change in CBV. Here, the relationship was found to be sub-linear across 1.5, 3 and 7 Tesla. Previous results which suggest a supralinear relationship at 1.5/3 Tesla and a linear relationship at 7 Tesla, are attributed to the relative contribution of intravascular/extravascular signals and their dependence on field strength, blood oxygenation and echo time. Finally, a comparison of single and multiphase ASL is made at 7 Tesla, with a modified Look-locker EPI sequence presented which allows simultaneous measurement of CBF and transit time, whilst increasing the available BOLD signal. This could have important implications for hypercapnia calibrated BOLD fMRI, where choice of ASL sequence may affect the estimated change in CMRO2. Furthermore, it provides a framework for future cerebral haemodynamic studies where simultaneous measurements are required.

Foetal MRI represents a non-invasive imaging technique that allows detailed visualisation of foetus in utero and the maternal structure. This thesis outlines the quantitative imaging techniques used to investigate the effect of maternal diabetes and maternal smoking on foetal development at 1.5 Tesla. The effect of maternal diabetes on placental blood flow and foetal growth was studied. The placental images were acquired using Echo Planar Imaging and blood flow was measured using Intra Voxel Incoherent Motion. The results indicate that peak blood flow in the basal plate and chorionic plate increases across gestation in both normal and diabetic pregnancies. Conversely, diffusion in the whole placenta decreases across gestation, with a more pronounced decrease in diabetic placentae. Following this, a method was developed to use a Tl weighted fat suppressed MRI scan to quantify foetal fat images in-utero. In addition, HAlf Fourier Single-shot Turbo spin Echo (HASTE) and balanced Fast Field Echo (bFFE) were used to acquire images encompassing the whole foetus in three orthogonal planes. These scans were used to measure foetal volume, foetal length and shoulder width. The data shows that foetal fat volume and intra-abdominal fat were increased in foetuses of diabetic mothers at third trimester. The HASTE and bFFE sequences were also used to study the effect of maternal smoking on foetal development. Here, foetal organ volumes, foetal and placental volume, shoulder width and foetal length were measured using a semiautomatic approach based on the concept of edge detection and a stereological method, the Cavalieri technique. The data shows that maternal smoking has significant negative effect on foetal organ growth and foetal growth, predominantly foetal kidney and foetal volume. The work described here certainly has a great potential in non-invasive assessment of abnormal placental function and can be used to study foetal development.

The Environmental Radioactivity Laboratory (ERL) at iThemba LABS undertakes experimental work using a high purity germanium (HPGe) detector for laboratory measurements. In this study the Monte Carlo transport code, MCNPX, which is a general-purpose Monte Carlo N &minus / Particle code that extends the capabilities of the MCNP code, developed at the Los Alamos National Laboratory in New Mexico, was used. The study considers how various parameters such as (1) coincidence summing, (2) volume, (3) atomic number (Z) and (4) density, affects the absolute photopeak efficiency of the ERL&rsquo / s HPGe detector in a close geometry (Marinelli beaker) for soil, sand, KCl and liquid samples. The results from these simulations are presented here, together with an intercomparison exercise of two MC codes (MCNPX and a C++ program developed for this study) that determine the energy deposition of a point source in germanium spheres of radii 1 cm and 5 cm.<br /> <br /> A sensitivity analysis on the effect of the detector dimensions (dead layer and core of detector crystal) on the photopeak detection efficiency in a liquid sample and the effect of moisture content on the photopeak detection efficiency in sand and soil samples, was also carried out. This study has shown evidence that the dead layer of the ERL HPGe detector may be larger than stated by the manufacturer, possibly due to warming up of the detector crystal. This would result in a decrease in the photopeak efficiency of up to 8 % if the dead layer of the crystal were doubled from its original size of 0.05 cm. This study shows the need for coincidence summing correction factors for the gamma lines (911.1 keV and 968.1 keV) in the 232Th series for determining accurate activity concentrations in environmental samples. For the liquid source the gamma lines, 121.8 keV, 244.7 keV, 444.1 keV and 1085.5 keV of the 152Eu series, together with the 1173.2 keV and 1332.5 keV gamma lines of the 60Co, are particularly prone to coincidence summing. In the investigation into the effects of density and volume on the photopeak efficiency for the KCl samples, it has been found that the simulated results are in good agreement with experimental data. For the range of sample densities that are dealt with by the ERL it has been found that the drop in photopeak efficiency is less than 5 %. This study shows that the uncertainty of the KCl sample activity measurement due to the effect of different filling volumes in a Marinelli beaker is estimated in the range of 0.6 % per mm and is not expected to vary appreciably with photon energy. In the case of the effect of filling height on the efficiency for the soil sample, it was found that there is a large discrepancy in the trends of the simulated and experimental curves. This discrepancy could be a result of the use of only one sand sample in this study and therefore the homogeneity of the sample has to be investigated. The effect of atomic number has been found to be negligible for the soil and sand compositions for energies above 400 keV, however if the composition of the heavy elements is not properly considered when simulating soil and sand samples, the effect of atomic number on the absolute photopeak efficiency in the low energy (&lt / 400 keV) region can make a 14 % difference.

The inflationary paradigm of standard big bang cosmology provides a mechanism to generate primordial curvature perturbations and explain the large scale homogeneity and isotropy of the observable universe. This is achieved through requiring a period of accelerated expansion during the early universe and requires a deep understanding of particle physics for its correct formulation. With the emergence of string theory as a potential description of a fundamental laws of nature provides a the natural framework in which we can construct realistic models of inflation seems plausible. A common feature of string theories is the requirement of extra dimensions and, in the absence of a complete formulation of the theory, it is necessary to dimensionally reduce the theories to give a 4d effective theory. String compactifications provide a promising approach through which this can be done. However compactifications lead to the generation of a large number of massless scalar fields (moduli) which would mediate unobserved 'fifth forces'. Methods of stabilising these fields give rise to exponentially flat potentials which provide the means of obtaining inflation quite naturally. In the introductory chapters a review of Type IIb flux compactifications gives methods to stabilise the complex structure moduli and dilaton through the use of fluxes. In order to stabilise the Kähler moduli additional non perturbative corrections to the superpotential are required. We introduce the well know class of meta stable de Sitter string vacua obtained when such corrections are included. An additional class vacua at large volume are discussed, these are found when leading order perturbative corrections to the Kähler potential are also considered. The large volume vacua are then shown to give rise to a model of inflaton using a Kähler modulus as an inflaton field. We show that there exists a large class of inflationary solutions corresponding to a constant volume V of the compactification manifold. In a second chapter on this inflationary model the existence of a basin of attraction for inflation with a constant volume is described. We also find a larger class of inflationary solutions when we evolve the axionic components of the Kähler moduli and the phenomenological aspects are discussed. We finally review the standard slow roll analysis and discuss its use in multiple field inflationary models. We introduce two multiple field extensions to the standard single field slow roll approach. We proceed with an investigation into the suitability of the multiple field slow roll approaches in predicting the slow roll footprint of Supergravity models of inflation. This is achieved through comparing the results with single field results and numerical simulation data when more complex models are considered.

The inherent quantum-mechanical nature of the proton transfer process in hydrogen bonds has been investigated through its effects on the nuclear spin-lattice relaxation rate. The fast magnetic field-cycling techniques employed allowed a direct measure of the rate characterising this dynamic process, which is closely related to the potential energy environment experienced by the mobile proton. Various heteronuclear effects from magnetic and non-magnetic nuclei outside the hydrogen bond were characterised. The contribution to proton tunnelling from the displacement of heavy atoms in the molecule is an important consideration within a complete description of the process. This interdependence was accurately measured for the carboxyl-group oxygen atoms in benzoic acid dimers through the isotope effect. Careful comparison of ¹⁶O and ¹⁸O-enriched benzoic acid relaxation allowed this relationship to be measured from the difference in low-temperature tunnelling rates. Fluctuating dipolar interactions caused by proton transfer motion couples the Zeeman states of different nuclear species. The cross-relaxation occurring through this natural coupling was explored as a function of field in 2,4,6-trifluorobenzoic acid and ¹³C-enriched pure benzoic acid. Characterising the strength of this interaction endeavoured to broaden the comprehension of heteronuclear coupling and served as confirmation of the model used. Beyond the carboxylic acid dimer, this investigation also showed dynamic disorder in intermolecular short, strong hydrogen bonds of pyridine-3,5-dicarboxylic acid. This proton transfer mechanism was found to be strongly dependent on the molecular vibrational modes creating a pathway between two potential minima. A finite change in entropy between the proton sites ensured that greatest proton mobility occurred at intermediate temperature, between relatively stable configurations at the extremes of temperature. A study of different sources of molecular dynamics within one compound showed the efficiency of field-cycling NMR at separating their contributions to relaxation. Dynamic rates from the proton transfer and methyl group rotation in 4-methylbenzoic acid were reliably extracted to the extent of identifying separate contributions from a small percentage of molecules around impurity centres.

In this thesis, a study of a range of functional surfaces formed in ultra-high vacuum (UHV) conditions using primarily scanning probe microscopy is presented. The construction of a combined scanning tunnelling and atomic force microscope, and the experiments performed using this instrument, are also detailed. Boron nitride and graphene monolayers were formed on rhodium thin films in UHV and investigated with in-situ and ex-situ (ambient conditions) scanning tunnelling microscopy. Simultaneous scanning tunnelling and atomic force microscopy images were also produced for the graphene monolayers. X-ray photoelectron spectroscopy and diffraction results for graphene monolayers on Rh(111) surfaces, as well as low energy electron diffraction data, are also included. The novel formation of monolayer and few-layer graphene on nickel thin films is also described. Graphene layers were detached from these nickel thin films and isolated on other substrates. The results of characterisation experiments using scanning probe microscopy, X-ray photoelectron spectroscopy, X-ray diffraction and electron microscopy techniques are detailed. Graphene layers with approximately 75% monolayer graphene coverage and an increased electronic quality, when compared to many other methods of graphene production, were revealed. Different organic molecules were adsorbed on both the boron nitride and graphene monolayers formed on rhodium thin films in UHV conditions. Perylene tetracarboxylic diimide (PTCDI) and di(propylthio)-PTCDI molecules were investigated on these surfaces and compared with the adsorption of PTCDI on a graphite surface. Furthermore, dibutyl-coronene tetra-carboxylic diimide was deposited on the graphene (on rhodium) surface, in UHV. Although the boron nitride and graphene surfaces were similar, it was discovered that very contrasting molecular formations were formed on the dierent surfaces. The positioning of these nanostructures was determined by the Moire superstructure formed due to the mismatch between the monolayers and the Rh(111) surface. Additionally, different hydrogen-bonded molecular junctions were formed depending on the length of the side chains of the adsorbed organic molecules.

This thesis treats several topics in the study of extra-dimensional models of the world, concerning Heterotic M-Theory and the dynamics of branes. We describe a reduction to five dimensions, over a Calabi-Yau manifold, of an improved version of Heterotic M-Theory, which is valid to all orders in the gravitational coupling. This provides a starting point for considering the consequences of the improved theory for the very fruitful phenomenology of the original. We investigate the singularities formed by the collision of gravitating branes in scalar field theory. By considering the asymptotic structure of the spacetime, the properties of the horizons formed and the growth of the curvature we argue that the singularity is not a black brane, as one might have expected, but rather a big crunch. Finally, we construct a restricted class of multi-galileon theories as braneworld models with codimension greater than one, developing in the process some of the formalism needed for the general construction.

The work described in this thesis involves an investigation of the implementation and application of simultaneous EEG and fMRI. The two techniques arc complementary, with EEG providing excellent temporal resolution and fMRI having good spatial resolution. Combined EEG/fMRI thus forms a powerful tool for neuroscience studies. In initial work, methods for improving the removal of the gradient and pulse artefacts, which are induced in EEG traces recorded during concurrent MRI, have been developed. Subsequently, the effects of the EEG hardware on MR images were investigated. This involved acquiring a series of scans to identify the sources of B0- and B1 inhomogeneities and the extent to which these affect EPI data. The adverse effects on data quality of combining EEG and fMRI increase with field strength. Consequently, EEG-fMRI at 7T is particularly challenging, although a number of advantages make its implementation desirable. Safety tests were performed which showed the presence of the EEG system caused a negligible increase in RF heating effects during scanning at 7T. After elimination of a number of noise sources, the first simultaneous EEG-fMRI experiments at 7T using commercially available equipment were performed. Concurrent EEG/fMRI at 3T was then used to investigate the correlation between the BOLD (blood oxygenation level dependent) response measured during visual stimulation and both the preceding alpha power and the strength of the driven, electrical response. In considering the correlation of the range of variation of the alpha power and BOLD response, a trend emerged which allowed tentative conclusions to be drawn. Variation of the BOLD and driven response with the frequency of visual stimulation relative to a subject's individual alpha frequency (IAF) was also investigated. A significant increase in the driven response, accompanied by a decrease in the BOLD response was observed in visual cortex when it was driven at the IAF.

In recent years the number of applications using NMR spectroscopy of hyperpolarised noble gases has expanded rapidly. The signal enhancement hyperpolarisation provides has led to its implementation in studies as diverse as materials science and biological imaging. 129Xe in particular, with its easily deformed electron cloud, is proving to be a uniquely sensitive probe for nanoporous structures. At present hyperpolarises gas production is limited to optical pumping (SEOP). In this study we investigate another approach, the brute force technique. At very low temperatures and high magnetic fields the Boltzmann distribution of spins for magnetic nuclei is heavily biased in a single direction. At temperatures below 10 mK and in magnetic fields of 15 T, 129Xe polarisations exceeding 40% are attainable. The utilisation of the brute force technique is hindered by the extraordinarily long relaxation time need for this polarisation to occur. In this study, we give details of our investigations of two relaxation catalysts, oxygen and helium-3. It is shown that paramagnetic molecular oxygen causes rapid relaxation of solid xenon at temperatures as low as 500 mK. We report on the enhanced relaxation, by liquid 3He of xenon films adsorbed on to silica gel and exfoliated graphite substrates. The investigation of this mechanism is extended to other magnetic nuclei and improved rates of relaxation are observed in 13C and 1 H. Details are also given, of how this mechanism of relaxation can be halted by the addition of superfluid 4He. Unique observations in the 129Xe NMR spectra are reported, providing a unique opportunity to study the coupling between individual layers of 129Xe atoms. Finally, a novel mechanism of cooling, by the filtering of energetic atoms through a porous ceramic membrane, is investigated.