The behaviour of an NMR signal (the 'NMR response') from a sample depends on the method used to excite the signal, and on three characteristic NMR properties of the sample; the concentration of NMR-sensitive atomic nuclei, the long itudinal relaxation time and the transverse relaxation time. In NMR imaging cross sectional maps are produced which are related to the spatial distribution of NMR properties within the sample. This thesis forms part of a continuing programme of research to investigate the application of NMR imaging to biological systems. The relationship between the intensities on an NMR image and the NMR properties of the sample is analysed. For the medically important case of biological systems imaged by the method of reconstruction from projections a new model is described which predicts the observed behaviour. Earlier models are shown to be unsatisfactory. A review is made of published measurements of the NMR properties of excised tissues. For the soft body organs the NMR response is shown to arise mainly from tissue water, with contributions up to 20% from fat. The relaxation times for excised tissues are shown to depend on the intracellular water content. A model is described which explains this dependence as the result of water molecules exchanging rapidly between two phases of the intracellular water. An extensive series of measurements of the relaxation times of live human tissues is presented. The properties of live tissues are shown to be significantly different from excised tissues. It is suggested that the difference is due to the presence of blood in live tissues. Experiments are described which will measure the properties of the tissue intracellular water and blood supply separately. The relative intensities of different tissues on an NMR image is shown to depend in a complicated way on the imaging method, with drastic changes in relative intensities for even small changes in the imaging method. The use of earlier simple models to interpret NMR images is shown to be misleading in many cases. A procedure is proposed, using, the new models described, which allows the 'optimum' NMR imaging method to be chosen for any given application.

X-ray Photoelectron Spectroscopy (XPS) has been evaluated as a technique for the investigation of the interface between synthetic biomaterials and the physiological environment, with a view to assisting the development of superior materials for implant surgery. In the adaptation of the XPS technique for the study of the acrylic copolymers used in this work a novel algorithm has been derived which models the effects of a concentration gradient in the sample surface. XPS has been compared with radiolabelling techniques for the estimation of proteins adsorbed to surfaces, and has indicated that the latter technique may cause a change in the protein adsorption behaviour. Finally, XPS has been used in conjunction with zeta potential and contact angle measurement to elucidate the ion exchange mechanisms taking place in the surfaces of the acrylic copolymers when immersed in simulated physiological saline. A mechanism has been proposed on the basis of these studies to explain some of the unusual characteristics of protein adsorption to surfaces, which is widely thought to be a determining factor in the physiological response to the surface of a biomaterial.

Nuclear Magnetic Resonance imaging in the medical and biological fields has been well established since the early 1970's, and high quality, well resolved images are now routinely obtained. Only recently has the enormous potential of Nuclear Magnetic Resonance as a means of non-invasive imaging of solid samples been recognised. The broad natural linewidths associated with solid samples has been the cause of the paucity of published solid imaging papers, and the techniques put forward in order to overcome the broad lines and resolve the spatially encoded contributions to the lineshapes range from the simple, single radiofrequency pulse methods, to the more complex multiple-pulse sequences. This thesis describes an attempt to return to the simple radiofrequency pulse methods, employing as few pulses as possible, by way of the "Solid Echo". A theory of solid echo imaging has been put forward, and a general result governing the form of the images in terms of the Fourier transformed, modulated, quadrature solid echo peak is postulated. Validation of the theory is provided by a series of one and two dimensional images of various nuclear spin configurations and spin species. Rapid gradient field switching was not a viable option during this period of research and, because of this, the gradient fields had to be left on during the radiofrequency pulses. The resulting nuclear spin motions about the two effective fields of the solid echo pulse sequence due to the combination of the gradient and radiofrequency fields has been modelled by a first order approximation. An evaluation of solid imaging using the MREV-8 multiple-pulse sequence is also given, and profiles obtained using this method are demonstrated.

An experiment [CERN PS165] is described which aimed to study the interaction between a kaon and a proton by measurement of the X-ray spectrum from kaonic hydrogen in a liquid target. The spectra of exotic atoms of helium, also a liquid target, were studied first to test the apparatus. In each case the objective was to measure X-ray intensities and the strong interaction effects, namely energy shift [E] and the line broadening [T], induced by the short range nuclear force operating when a negatively charged exotic hadron reaches a low lying atomic state. The related theory and interpretation are also discussed. The results for kaonic helium, E2p = (-0.050 +/- 0.012) keV and T 2p = (0.100 +/- 0.040) keV, confirm the previous report of a disagreement with theoretical expectation. The measured 3-2 X-ray transition intensity is about 1% per atom. The results on p-helium, E 2p = (-0.012 +/- 0.014) keV and T 2p = (0.+0.040-0.) keV are in agreement with theory and contrary to the conclusions of a previous experiment (14); the absolute intensity of the 3-2 X-ray transition, measured for the first time in a liquid target, is (4.4 +/- 2.2)% per atom.

Elemental analysis of substances made of heavy elements and detection of light elements in heavy matrices are difficult by means of photon transmission techniques. Neutrons have been used in this work, taking unique advantage of their absorption and scattering properties, to detect the structure of industrial and biological objects made of strongly-neutron scattering or absorbing materials, or to study objects combining of high and low neutron cross section materials. The most convenient matrices and impurities amenable to neutron inspection were searched by obtaining expressions for minimum detectable mass and length fraction of elements in an object. Formulae to calculate the minimum required number of neutrons to detect an impurity in a matrix have also been developed. The optimum sample thickness to be investigated with a minimum number of neutrons is likewise derived. Calculations have been carried out for the minimum detectable mass fraction of hydrogen in a number of sample matrices of industrial interest and of elements in a water matrix highlighting the differences with photon attenuation measurements. Results are presented for three neutron energies cold (0.001 eV), thermal (0.025 eV), and fast (14 MeV); concentrations in the parts per million range are demonstrated. Fast neutrons were used because of their high penetration ability, in order to study bulk industrial and biological samples and for their adequacy in detection of light elements such as H, C, N and O in large objects. An attempt to simulate fast neutron transmission tomographs of biological samples was made using the MORSE-CGA Monte-Carlo code. The code was used to calculate transmission of multienergetic U-235 fast fission neutron source in a complex geometry for industrial and biological applications. A fast neutron collimator for radiography, a collimator for brain tomography and a tomography chamber were simulated to design a technique to estimate the effect of scattered neutrons in practical tomography. The macroscopic cross section and mean free path of neutrons for the media of the heterogeneous matrices were also obtained by using microscopic cross sections of elements from the DLC-100G package. Using a multienergetic source provided an opportunity to determine the optimum neutron energy for examination of objects. The analysis required establishing a technique to calculate the fraction of neutrons in each energy group for the 100 group structure of the DLC-100G package. Finally the simulated neutron tomographic images were reconstructed by using the neutron transmission data for different angles of the object, and reconstructing them by the filtered back projection technique. In non-destructive evaluation of medical organs by fast neutron simulation tomography the simulated tomography of prototype biological objects were able to distinguish brain in skull, bone-marrow in bone and bone in soft tissue with good contrast up to 0.42. These results are valuable to identify developing cystic lesions and daughter cyst within the marrow vascular spaces, solid bony tumors, aberrant masses in the facial bone, tumor in spine or other bone marrow abnormalities. In studying component characterisation of industrial objects non-destructively by fast neutron tomography a 3mm diameter duct containing engine-oil was detected at 40 cm depth inside an aluminium combustion engine with a remarkable contrast of 0.35. The minimum detectable mass of oil in aluminium for an optimum neutron energy was 0.1mg/g with a similar result for iron.

No description available.

This thesis primarily deals with accuracy obtainable when using IBA (Ion Beam Analysis) techniques to characterize materials. RBS (Rutherford Backscattering Spectrometry) is the main technique used, together with EBS (Elastic Backscattering Spectrometry), ERDA (Elastic Recoil Detection Analysis) and NRA (Nuclear Reaction Analysis). An exhaustive literature review on these analytical methods is made in connection with accuracy issues such as stopping powers and multiple scattering. The experimental set-ups and procedures are described, with emphasis laid on critical aspects of work where the highest accuracy is required. The instrumentation for dosimetry on ion implanters is first estabhshed at the 1% level for high-dose heavy implants in silicon. A new parameterisation of He stopping power in Si is used, and this latter material, via the surface yield, is used as a calibration standard. A precision (standard uncertainty) in the determination of implantation doses by RBS is conclusively demonstrated at 1.5%. The IBA DataFurnace code is validated for such accurate analysis, which can now be made routinely and rapidly. The certified Sb sample IRMM-302/BAM-L001, which has a certification of 0.6% traceable to the international standard of weight in Paris, is measured, and more importantly this measurement demonstrates the reliability of the stopping power parameterisation at 1.4%. Using conventional ERDA, the H dose of an amorphised Si wafer, implanted with 6-keV H+ ions, is found to be 57.8(1.0)x1015 at/cm2, which is a 1.8% standard uncertainty. The estimated combined uncertainty of this measurement is ~6%, and this mainly comes from the determination of the ERDA solid angle by using standard Kapton. The Kapton composition is carefully determined using RBS. The RBS solid angle is obtained using the amorphised silicon surface yield as a calibration standard as in the dosimetry analysis mentioned above. The ERDA H absolute dose obtained is compared with the results from other participants from all over the world in a Round Robin exercise, which includes measurements by using both He-ERDA and HI-ERDA (Heavy Ion-ERDA) together using various detectors. The results from each participant are given and compared. The overall absolute dose obtained of the implant is 57.0(1.2)x1015 H/cm2, and this represents an inter-lab reproducibility of 2.2% (standard uncertainty). Unstable surface hydrogen contamination was observed, and this surface peak was resolved by some of the methods. This implant can now be used as a standard for quantitative analysis of hydrogen. Low-fluorine content SiO2:F films are analysed by RBS for absolute fluorine concentration determination. Prior to the RBS analysis, the uniformity of the films and stability of F under beam irradiation is investigated. Because the RBS is not very sensitive to F and the F signal has a large matrix background, an internally consistent method of data handling, which enables the relative collected charge to be determined very precisely for the spectra from different samples, is developed. This method has as a parameter the F content, which is then extracted iteratively. A F concentration of 10 at% is determined with an estimated uncertainty of 10% (one percentage point, i.e. 10 +/- 1%). The O stopping powers are found to be the main factor governing the accuracy of the absolute determination of the F content. All the other uncertainties add up to only ~1%. The elemental composition of residual deposits from an ion implanter is thoroughly investigated using several complementary analytical methods, namely, RBS, BBS and NRA. Preliminary SEM/EDAX results are used as a guide. Depth profiles of such non-homogeneous, non-fiat and brittle samples are obtained, which give an indication of the concentration of each element present. From this complete IBA elemental study, some unprecedented light is brought on both the history of the implanter and the way in which these deposits are formed. Such an investigation is essential for a better understanding and the development/miniaturisation of semiconductors as it impressively pushes the boundaries of accuracy obtainable in IBA material characterisation.

Sn Mossbauer spectroscopy has been used to study the nuclear environment of three organotin stabilisers present in PVC, after exposure of the polymer to gamma-irradiation up to a maximum dose of 200 kGy, in order to identify the tin-containing degradation products which could migrate into foodstuffs in contact with the polymer. Chapter One of this thesis covers the aspects of the degradation and stabilisation of organotin-stabilised PVC which may influence the chemical nature of the tin-containing degradation products resulting from gamma-irradiation of the polymer. Chapter Two contains a description of the theory of the Mossbauer effect and the instrumentation and computational methods for recording and processing Mossbauer data. Chapter Three is concerned with the effect of gamma-irradiation, at doses in excess of food irradiation applications, in order to identify the terminal tin-containing degradation products of the stabilisers. In Chapter Four, evidence for the progressive degradation of organotin stabilisers upon increasing irradiation exposure is presented and intermediate degradation products are proposed. A mechanism for the degradation of stabilisers is suggested. In Chapter Five, evidence for dealkylated tin-containing degradation products in irradiated organotin-stabilised PVC is presented. Chapter Six involves the application of the Debye model of solids to variable temperature Mossbauer data for two organotin stabiliser degradation products, dibutyltin dichloride and stannic chloride, in PVC. A significant change in recoilless fraction is shown to occur when these compounds are dispersed in PVC compared with those of the pure compounds. This is attributed to changes in coordination number of the tin atom upon dispersion in PVC, and has a significant effect upon the relative sensitivity of the technique to the degradation products. Chapter Seven contains a comparison of the degradation processes occurring in thermal and gamma-irradiation degradation of organotin-stabilised PVC.It is shown that degradation.of the stabiliser during gamma-irradation is much more severe. In Chapter Eight, an appraisal of the key experimental results and their implications for the gamma-irradiation sterilisation of polymer-packaged foodstuffs is presented.

This text investigates THz-TDS signals in the time-frequency domain. Addi- tionally this text discusses the prospects of using time-frequency analysis to alleviate distortion in THz spectrographic characterizations induced by back- reflections in the free space electro optic sampling used in the THz time-domain spectroscopy detection scheme. THz time domain spectroscopy is a technique for characterization of materials in the terahertz regime. The THz regime offers interesting properties of materials such as strong phonon-photon interaction and resonances for vibration states of molecules. Three time-frequency representations are compared for the analysis of the time-domain signal, the short-time Fourier transform, the Wigner-Ville transform and the continuous wavelet transform. It is concluded that the Wigner-Ville transform is most suited for analysis of the spectral properties of a single pulse due to the Wigner-Ville transforms inherit high spectral resolution. The continuous wavelet transform is most suited for analysis of the time-domain signal since it has no cross-term interference as compared to the Wigner-Ville transform. By masking the continuous wavelet transform with a Lorentzian time-frequency mask the back-reflections are dampened and the resolution of the characterization is improved.

Diffusing Wave Spectroscopy (DWS) was studied as a method of laboratory analysis of submicron particles, and developed as a prospective in-line, industrial, process control sensor, capable of near real-time feedback. No sample pre-treatment was required and measurement was via a noninvasive, flexible, dip in probe. DWS relies on the concept of the diffusive migration of light, as opposed to the ballistic scatter model used in conventional dynamic light scattering. The specific requirements of the optoelectronic hardware, data analysis methods and light scattering model were studied experimentally and, where practical, theoretically resulting in a novel technique of analysis of particle suspensions and emulsions of volume fractions between 0.01 and 0.4. Operation at high concentrations made the technique oblivious to dust and contamination. A pure homodyne (autodyne) experimental arrangement described was resilient to environmental disturbances, unlike many other systems which utilise optical fibres or heterodyne operation. Pilot and subsequent prototype development led to a highly accurate method of size ranking, suitable for analysis of a wide range of suspensions and emulsions. The technique was shown to operate on real industrial samples with statistical variance as low as 0.3% with minimal software processing. Whilst the application studied was the analysis of Ti02 suspensions, a diverse range of materials including polystyrene beads, cell pastes and industrial cutting fluid emulsions were tested. Results suggest that, whilst all sizing should be comparative to suitable standards, concentration effects may be minimised and even completely modelled-out in many applications. Adhesion to the optical probe was initially a significant problem but was minimised after the evaluation and use of suitable non stick coating materials. Unexpected behaviour in the correlation in the region of short decay times led to consideration of the effects of rotational diffusion coefficient. The inherent instability of high density suspensions instigated high speed analysis techniques capable of monitoring suspensions that were undergoing rapid change as well as suggesting novel methods for the evaluation of the state of sample dispersion.