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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
121

COMAS development for concentration probing of gas phase discharge systems

Hatcher, M. G. January 1999 (has links)
The work presented in this thesis describes the further development of the pump-probe laser spectroscopic technique known as Concentration-Modulated Absorption Spectroscopy (COMAS), concentrating on its use as an analytical tool for the investigation of various atomic systems. The systems analysed here include a direct current glow discharge with a lithium cathode, and a neon hollow cathode discharge lamp. The COMAS method necessitates the use of a Lock-In Amplifier (LIA) for signal derivation and output measurement. A substantial feature of the work presented here is concerned with the way in which COMAS signals are affected by phasing effects, and Chapter 2 concentrates on the relationship between COMAS signal generation and LIA measurement of that signal. Meaningful, quantitative analysis using COMAS generally requires the use of an accompanying absorbance measurement of the sample in question, and the development of COMAS has in fact been limited by the quality of such absorbance measurements. This problem is addressed in Chapter 3, which describes the investigation of two novel absorption techniques with a view to future use in conjunction with COMAS. With the theoretical and experimental basis to COMAS fully described in Chapter 4, the technique is subsequently used to probe the distribution of sputtered Li atoms in d.c. glow discharge for a variety of conditions. The results allow determination of the first experimentally derived values of thermalisation cross-sections in the gas phase, and provide valuable data for glow discharge modelling. In the final three chapters, the COMAS technique is significantly extended to incorporate analysis of dynamic 3-level systems. This development is approached theoretically in Chapter 6, and shows that certain extra parameters which affect COMAS signals require determination. The 3-level theoretical treatment is tested experimentally in Chapters 7 and 8 by investigation of a neon hollow cathode discharge, with the atomic neon electronic scheme providing an analogous 3-level system. The phase behaviour of the cw COMAS neon signals is briefly investigated in Chapter 8a.
122

Ionization processes and breakdown in krypton and rare gas mixtures

Mat Yunus, W. M. January 1985 (has links)
No description available.
123

Multi element in vivo analysis by neutron activation

Ryde, S. J. S. January 1988 (has links)
The design, construction and commissioning of a unique, versatile clinical instrument for multi-element in vivo analysis by neutron activation is described. In this instrument a 4 GBq Cf-252 neutron source is stored below ground level and can be pneumatically propelled to one of two irradiation ports. From these ports collimated beams of fast neutrons, of different intensities and dose-rates, are delivered either to a localised volume such as the liver or kidneys, or across the width of a patient for head-to-toe scanning. The instrument is intended primarily for measurement of total-body calcium and nitrogen, and partial-body cadmium via the prompt-gamma-ray technique in which the characteristic gamma-ray emission is measured during neutron activation. Repeated bilateral irradiations of a tissue equivalent phantom have shown that using high-resolution germanium spectroscopy the elements calcium, chlorine, nitrogen, carbon and hydrogen can be simultaneously measured with precisions (the coefficient of variation) of 2.6% , 1.5% , 3.1% , 4.3% and 0.4% respectively for a radiation dose equivalent to the skin of 6.4 mSv (QF= 10). When nitrogen is the element of prime interest it is advantageous to use NaI(Tl) rather than germanium detectors and the elements nitrogen, chlorine and carbon can then be simultaneously measured with precisions of 1.6% , 5.1% and 7.9% respectively for a radiation dose equivalent to the skin of 0.45 mSv. The detection limits (2 standard deviations of the net peak counts) obtained for cadmium are 2.8 mg and 3.5 ppm for the kidney and liver respectively, for an incident dose equivalent to the skin of 4.4 mSv. The instrument has so far been calibrated for quantitative in vivo measurement of nitrogen and cadmium, and for measurements of calcium counts in sequential studies of the same individual.
124

Translational spectroscopy of ions

Jonathan, P. January 1987 (has links)
Translational spectroscopy is used to examine the keV collision reactions of small ions with thermal neutral species. State selective single electron capture data for Ar<SUP>2+</SUP> on rare gas and small molecular targets is interpreted in terms of calculated reaction windows and charge exchange channels. Evidence for double ionisation of hydrocarbon targets is presented. Dissociation of H<SUB>2<SUP>+</SUB></SUP> occurs predominantly via direct electronic excitation. A second two collision process involving H<SUB>2</SUB> intermediates accounting for 5% of H^+ fragment yield is examined; H^- fragments arise from dissociative capture of H_2 intermediates. Approximate relative cross sections, and translational energy release distributions, for H^+ and H^- from the dissociation of H_2^+ in H_2, rare gases and hydrocarbons are measured. An investigation of E/2 mass spectra, involving consecutive charge stripping and electron capture reactions of organic ions, elucidates the parameters governing the reproducibility of spectra. A short study involving benzene, 1,5-hexadiyne, methylbenzene and nitrobenzene demonstrates the effects found. Cations consisting of a rare gas atom associated to a small molecule or radical, are investigated by means of the thermal ion molecule reactions by which they are formed in the ion source of the spectrometer, and their subsequent keV collision reactions. For diatomic dications of this form, charge stripping and charge separation data, discussed in terms of semi empirical potential energy curves, yields valuable information as to ion structure and stability. The design of a novel translational energy spectrometer, capable of an ultimate resolving power of 3 meV on product ion spectra at 500 eV ion translational energy, is described. Matrix calculations for projectile trajectories are performed. A simple theoretical model for inelastic scattering permits the evaluation of the effect of collisional broadening on the resolving power of the instrument.
125

Determination of ferromagnetic dust levels in the lungs by magnetic measurements using a SQUID system

Al-Sewaidan, H. A. I. January 1991 (has links)
This thesis is an account of research carried out in the Department of Physics, University College of Swansea, on the development of a magnetopneumography system and the assessment of its performance. Magnetopneumography (MPG) is one area within the rapidly growing field of biomagnetism and the development of this field, with detailed references to MPG, is presented in Chapter 1. Physical, chemical and biological aspects of the major iron and nickel-bearing dusts (detection of which is the main aim of MPG) are discussed in Chapter 2. Exposure, toxicity and other biological effects (e.g. carcinogenecity) of these dusts are also reviewed in an industrial context. Details of construction and principles of operation of a SQUID magnetometer are considered in Chapter 3, with particular reference to the Swansea biomagnetometry system. The performance of this system is then investigated by means of remanent magnetisation studies on small polyurethane samples containing known quantities of magnetite and nickel powders. These measurements are presented and discussed in Chapter 4 where the detection limits of the SQUID system are established for this type of study. These results are also used in a study of <i>post mortem</i> lung samples from asbestos miners which forms the subject of Chapter 5. The relevance and benefits of the magnetic technique to occupational health and industrial hygiene are also discussed. In Chapter 6, as a logical continuation of the <i>in vitro</i> work, remanent magnetisation studies (similar to those of Chapter 4) are reported for anatomically accurate whole-lung phantoms. These measurements are compared with a simplified lung model for which an analytical solution is derived. Finally, to demonstrate the suitability of both the technique and the apparatus, <i>in vivo</i> studies on a random selection of healthy volunteers were conducted, the results and implications of which are examined in Chapter 7.
126

Trace-element analysis of metallic and organic matrix materials exploiting RIMS

Abraham, C. J. January 1998 (has links)
Sputter initiated Resonance Ionisation Spectroscopy (SIRIS) was used to perform trace analysis for a number of elements in various matrices. The system consisted of a reflection time of flight (ToF) mass spectrometer combined with a duoplasmatron primary ion source which was coupled to a Nd:YAG pumped dye laser. External electronics were constructed to synchronise precisely the timing of the laser pulse, primary ion source and dual channel plate detector. The present set-up allowed the utilisation of the simplest of all ionisation routes, namely the one-colour, two-photon RIS schemes. The elements titanium, chromium, nickel, molybdenum, iron and tin were photo-ionised in the 290-300 nm and 280-290 nm range. Various resonances for these elements were obtained providing valuable information on efficient RIS routes, which could be used in trace analysis. The sensitivity of the RIMS technique was demonstrated by the detection of 15 ppm of iron in a nickel host, with an ultimate detection limit of less than 5ppb. Trace detection of potentially toxic elements such as iron and aluminium in brain homogenate tissue was demonstrated for samples, with concentrations of 100 ppm of aluminium and 400 ppm of iron: detection was possible without isobaric interferences. These elements have been linked to the neurological disorders of Alzheimer's disease and Parkinsonian dementia. In a separate application, the detection of 480 ppm of tin in an insulator of silicone gum is shown, demonstrating the diverse range of samples which can be analysed using RIMS. A brief review of the theoretical modelling for ion sputtering and the process of resonance ionisation is given, including the benefits and limitations of the various methods.
127

The emission of particles from a laser produced plasma

Davies, R. A. January 1985 (has links)
No description available.
128

Compositional, spatial and temporal analysis of laser produced plasmas

Williams, C. L. January 1993 (has links)
This thesis describes the application of the methods of Laser Induced Breakdown Spectroscopy (LIBS) and Laser Induced Fluorescence (LIF) for the analysis of laser-produced plasmas. Spatial and temporal evolution as well as the compositional structure of expanding plumes were investigated. One of the main aims was to use the aforementioned spectroscopic techniques to improve on the detection limits for elements present in a laser-produced plasma evolving in air at atmospheric pressure. In the first set of experiments the technique of LIBs is explored for the analysis of solid samples. Radiation from a high power pulsed Nd:YAG laser is focused onto the sample to produce a luminous plasma. The fluorescence emitted from the plasma as it cools is analysed using spectroscopic equipment. Two different methods of detection and data acquisition were used, namely a photomultiplier based system and a gated diode array detector arrangement. Several solid standard steel targets were studied. The environments in which the plasma were allowed to form were varied, including vacuum, buffer gases, atmospheric air and flowing buffer gases &43 atmospheric air. As well as obtaining information regarding the population levels and temperatures of the species in the plasmas, the technique was used as an analytical tool for compositional analysis. Calibration curves were constructed for two elements [Cu and Cr] under different ambient conditions and comparisons made between the results. The second set of experiments is devoted to the technique of LIF and its application as an analytical tool in the detection of chromium in steel samples. LIF is an extension of the LIBS method because initially a laser-produced plasma is generated in the same manner as with the LIBS studies; the plasma plume is allowed to expand into an environment of air at atmospheric pressure.
129

Neutron beam for partial- and whole-body in vivo activation analysis

Mohd Zin, S. January 1985 (has links)
No description available.
130

An examination of bubble dynamics and double metastability within an improved glass Berthelot tube

Rogers, D. January 2005 (has links)
This thesis presents the developmental, practical and theoretical aspects of an improved Berthelot tube apparatus used to investigate cavitation phenomena in deionised water. Values of the breaking tension of deionised water in the range of 2.5 bar to 30 bar are herein reported for experiments in the improved apparatus and the obtained breaking tensions are certainly comparable to those previously reported for experiments carried out using both the Berthelot tube technique and other methods. Herein dynamic pressure records and high-speed photographic images of cavitation occurring in deionised water are reported, for what is believed to be the first time. The initial formation, growth and collapse of cavitation bubbles are compared to the dynamic pressures existing in the tube using analytical methods to process the high-speed images and dynamic pressure traces. The growth/collapse cycles of bubbles associated with cavitation in the improved apparatus are shown to be an order of magnitude higher than those occurring in bullet-piston experiments (a typical cycle taking about 240 μs in the improved Berthelot tube), and the corresponding velocity of the initial growth of the cavity is reported to be in the order of 21 m/s. In Chapter 6 high-speed images of the formation of ice in deionised water under double metastable conditions are reported for the first time. In these experiments it was shown that it was possible for deionised water in a double metastable phase to be cooled to -18°C before ice suddenly started to form, at a specific point, and rapidly propagated throughout the water at a much greater rate (upwards of 25 cm/s) than would otherwise be predicted for the formation of ice under ‘free’ conditions, suggesting that some additional factor was involved in the ice formation. Several proposals have been put forward in an attempt to explain the mechanism behind the ice formation.

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