No description available.

No description available.

No description available.

No description available.

Novel photon counting Alo.8Gao.2As, GaAs and SiC X-ray photodiodes were investigated through experiments and Monte Carlo computer simulations for their suitability as spectroscopic soft (:S 25 keY) X-ray detectors in high temperature (up to 90 QC) environments. Photon counting Alo.8Gao.2As and GaAs non-avalanche p+-i-n+ mesa X-ray photodiodes were shown to operate at temperatures as high as 90 QC. The temperature dependences of their spectral resolutions (FWHM at 5.9 keY) are reported. Analyses of the noise sources contributing to the devices' measured performances are presented which suggest that efforts to improve the spectral resolutions would be well targeted at reducing the noise contributions from the packaging of the detectors. For the GaAs diodes, the X-ray characterisation of the devices was extended to higher energies (25 keY). Internal detector X-ray fluorescence was demonstrated and Monte Carlo computer simulations were compared with the experimental results. Prior to the research presented in this thesis, the only Alo.8Gao.2As photon counting X-ray avalanche photodiodes reported in the literature (Lees et al., 2008, Nucl. Instr. and Meth. A, Vol. 594, pp. 202-205) had shown anomalies in the obtained spectra. Through new experimental measurements and computer simulations, the anomaly is explained. A new method was developed which uses the phenomenon to extract measurements of the electron and hole ionisation coefficients of Alo.8Gao.2As at a typical operating field and the first report of their temperature dependence is made. Measurements characterising the X-ray spectroscopic performance of Semi-Transparent SiC Schottky Diodes over an energy range ~6 keY to 25 keY at temperatures up to 80 QC are presented and discussed, along with relative efficiency measurements and data showing the temperature dependence of the leakage current in such devices. The research presented in this thesis shows that Alo.8Gao.2As, GaAs and SiC X-ray detectors are promising devices for high temperature soft X-ray spectroscopy.

A Quadrupole Mass Filter (QMF) is a key component of a Quadrupole Mass Spectrometer (QMS) that provides the mass to charge discrimination required to separate the component species of a sample. A custom software package has been developed that accurately simulates the performance of the QMF. When used in conjunction with a public domain field solver program a powerful software tool box is created that can accurately predict the performance characteristics of a range of QMF electrode geometries. This software toolbox has been used to investigate the effects of the ratio of circular electrode radius r to electric field radius ro for zone 1 (a = 0.237, q = 0.706) and zone 3 (a= 3.16, q = 3.23) operation. The magnitude and variation of the 'tail' in the mass spectral peak shapes apparent for zone 1 is much decreased for zone 3 and does not influence QMF resolution. In collaboration with the Atomic Weapons Establishment (AWE) the requirements for a QMF and Electronic Control Unit for integration into a QMS were investigated. The QMS is be used for the qualitative and quantitative identification of Hydrogen and Helium isotopes. To successfully separate Hydrogen Tritium (HT) from diatomic Deuterium (D2) a resolution greater than 930 is required. Simulation results demonstrated that this is achievable if hyperbolic profile electrodes are used in conjunction with operation in stability zone 3. A second investigation undertaken as a collaborative project with the Massachusetts Institute of Technology (MIT) investigated the characteristics of a QMF manufactured using Micro-Electro Mechanical Systems (MEMS) technology. The process technology employed is more suited to the manufacture of square electrodes which produce electric fields that are far from optimum. Results show that this limitation in the electric field can be significantly overcome by operating the QMF in zone 3. Some of this data together with information provided by users of QMSs was used to develop a specification for an electronic control unit (BCU) for a QMS. An ECU has now been designed and manufactured. The testing and evaluation of the ECU has now commenced.

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This thesis describes developments in atomic vapour loading in hollow core photonic crystal fibre (HC-PCF) for fabrication of atomic vapour loaded photonic microcells (PMC). These developments have been targeted at addressing some of the issues associated with loading atomic vapours in confined waveguiding geometries such as increased dephasing and physio-chemical wall absorptions. Atomic vapour loaded HC-PCF and PMC’s have applications in laser metrology, coherent optics and magneto optical spectroscopy. State of the art HC-PCF have been fabricated for loading with atomic vapour including both photonic bandgap (PBG) guiding and inhibited coupling (IC) hypocycloidal core shape Kagome HC-PCF. Record loss of 70 dB/km has been achieved in IC hypocycloid core shape Kagome HC-PCF in the spectral region centred at 800 nm. This fibre retains excellent single mode propagation combined with large core and increased optical bandwidth in comparison with specialist PBG HC-PCF optimised for operation around 800 nm. Aluminosilicate sol-gel coatings have been developed and successfully applied to the inner core wall of HC-PCF’s to reduce the atomic vapour surface interaction. Confining atomic vapours in micron scaled HC-PCF results in increased dephasing rates because of the frequent atom wall collisions. Anti relaxation coating materials have been applied to the inner core wall and the longitudinal relaxation time has been measured in coated and uncoated fibres utilising a magneto optical technique. Additionally sub Doppler transparencies are investigated in anti relaxation coated and uncoated HC-PCF.

Cette thèse est consacrée à une enquête sur la structure et la dynamique, avec des modèles théoriques et essais de laboratoire, sur deux types communs de défauts arrivant dans la molécule d’ADN, après des dégâts de radiation ou le produit chimique: mésappariements des base(MB) et casseurs de brin.Tels défauts pourraient arriver naturellement, d’imperfections dans le processus cellulaire, induit par l’environnement et ou induit artificiellement, comme pour la radiothérapie de cancer. Nous avons utilisé la spectroscopie de force moléculaire exécutée par des pinces optiques accompagnées par des simulations all-atom en Dynamique Moléculaire (MD), pour caractériser des MB dans des hairpin d’ADN. Ensuite nous avons construit des modèles structurels pour les casseurs de brin d’ADN, dans les deux indexent les éléments constitutifs de la chromatine: le ADN linker et le nucléosome. Grâce à l'application de diffèrent techniques (Essential Dynamics, Steered MD, …) on a caractérisé les stades précoces de l’évolution de cette lésion d’ADN dans les deux éléments. / This thesis is dedicated to a combined theoretical and experimental investigation of the structure and dynamics of two common types of defects occurring in the DNA molecule, after chemical or radiation damage: basemismatches and strand breaks. We used single-molecule force spectroscopy performed by optical tweezers accompanied by Molecular Dynamics (MD) all-atom simulations, to characterize mismatches in short DNA hairpins. We demonstrate that it is possible to use SMFS. Subsequently, we designed structural models for the DNA strand-break defects, in the two key constitutive elements of the chromatin: the DNA linker and the nucleosome. Using different techniques (Essential Dynamics, steered MD, covariant mechanical stress, …) we characterized the early stages of the evolution of this DNA lesion in the two elements.