Gaseous phase is a critical state of matter around us. It mediates between the solid crust on earth and inter-stellar vacuum. Apart from the atmosphere surrounding us where compounds are present, natively, in a gaseous phase, they are also trapped within soil and dissolved in oceanic water. Further, those that are less volatile do enter the gaseous phase at high temperatures. It is this gaseous phase that we inhale every second. It is thus critical that we possess the tools to analyze a mixture of gaseous compounds. One such method is to separate the components in time and then identify, primarily based on the retention times, also known as gas chromatography. This research focuses on the development of gas detectors and their integration, in different styles, primarily for gas chromatography. Utilizing fabrication techniques used in semiconductor industry and exploiting scaling laws we investigate the ability to improve on conventional gas separation and identification techniques. Specifically, we have provided a new spin to the age-old thermal conductivity detector enabling its monolithic integration with a separation column. A reference-less, two-port integration architecture and a one-of-its-kind released resistor on glass are some of its salient features. The operation of this integrated device with a preconcentrator and in a matrix array was investigated. The more unique contribution of this research lies in the innovative discharge ionization detector. An ultra-low power, sensitive, easy to fabricate detector, it requires more investigation for a thorough understanding and will likely mature to replace the thermal conductivity detector, as the detector of choice for universal detection, in time to come. / Ph. D.

<p>Currently film is being replaced by electronic detectors for portal imaging in radiation therapy. This development offers obvious advantages such as on-line quality assurance and digital images that can easily be accessed, processed and communicated. In spite of the improvements, the image quality has not been significantly enhanced, partly since the quantum efficiency compared to film is essentially the same, and the new electronic devices also suffer from sensitivity to the harsh radiation environment. In this thesis we propose a third generation electronic portal imaging device with increased quantum efficiency and potentially higher image quality.</p><p>Due to the parallel readout capability it is much faster than current devices, providing at least 200 frames per second (fps), and would even allow for a quality assurance and adaptive actions after each accelerator pulse. The new detector is also sensitive over a broader range of energies (10 keV - 50 MeV) and can be used to obtain diagnostic images immediately prior to the treatment without repositioning the patient. The imaging could be in the form of portal imaging or computed tomography. The new detector is based on a sandwich design containing several layers of Gas Electron Multipliers (GEMs) in combination with, or integrated with, perforated converter plates. The charge created by the ionizing radiation is drifted to the bottom of the assembly where a tailored readout system collects and digitizes the charge. The new readout system is further designed in such a way that no sensitive electronics is placed in the radiation beam and the detector is expected to be radiation resistant since it consists mainly of kapton, copper and gas.</p><p>A single GEM detector was responding linearly when tested with a 50 MV photon beam at a fluence rate of ~10¹⁰ photons mm^-2 s^-1 during 3-5 μs long pulses, but also with x-ray energies of 10-50 keV at a fluence rate of up to ~10⁸ photons mm^-2 s^-1. The electron transmission of a 100 μm thick Cu plate with an optical transparency of ~46% was found to be ~15.4%, i.e. the effective hole transmission for the electrons was about one third of the hole area. A low effective GEM gain is enough to compensate for the losses in converters of this dimension. A prototype for the dedicated electronic readout system was designed with 50 x 100 pixels at a pitch of 1.27 mm x 1.27 mm. X-ray images were achieved with a single GEM layer and also in a double GEM setup with a converter plate interleaved. To verify the readout speed a Newton pendulum was imaged at a frame rate of 70 fps and alpha particles were imaged in 188 fps. The experimental studies indicates that the existing prototype can be developed as a competitive alternative for imaging in radiation therapy.</p>

Currently film is being replaced by electronic detectors for portal imaging in radiation therapy. This development offers obvious advantages such as on-line quality assurance and digital images that can easily be accessed, processed and communicated. In spite of the improvements, the image quality has not been significantly enhanced, partly since the quantum efficiency compared to film is essentially the same, and the new electronic devices also suffer from sensitivity to the harsh radiation environment. In this thesis we propose a third generation electronic portal imaging device with increased quantum efficiency and potentially higher image quality. Due to the parallel readout capability it is much faster than current devices, providing at least 200 frames per second (fps), and would even allow for a quality assurance and adaptive actions after each accelerator pulse. The new detector is also sensitive over a broader range of energies (10 keV - 50 MeV) and can be used to obtain diagnostic images immediately prior to the treatment without repositioning the patient. The imaging could be in the form of portal imaging or computed tomography. The new detector is based on a sandwich design containing several layers of Gas Electron Multipliers (GEMs) in combination with, or integrated with, perforated converter plates. The charge created by the ionizing radiation is drifted to the bottom of the assembly where a tailored readout system collects and digitizes the charge. The new readout system is further designed in such a way that no sensitive electronics is placed in the radiation beam and the detector is expected to be radiation resistant since it consists mainly of kapton, copper and gas. A single GEM detector was responding linearly when tested with a 50 MV photon beam at a fluence rate of ~1010 photons mm-2 s-1 during 3-5 μs long pulses, but also with x-ray energies of 10-50 keV at a fluence rate of up to ~108 photons mm-2 s-1. The electron transmission of a 100 μm thick Cu plate with an optical transparency of ~46% was found to be ~15.4%, i.e. the effective hole transmission for the electrons was about one third of the hole area. A low effective GEM gain is enough to compensate for the losses in converters of this dimension. A prototype for the dedicated electronic readout system was designed with 50 x 100 pixels at a pitch of 1.27 mm x 1.27 mm. X-ray images were achieved with a single GEM layer and also in a double GEM setup with a converter plate interleaved. To verify the readout speed a Newton pendulum was imaged at a frame rate of 70 fps and alpha particles were imaged in 188 fps. The experimental studies indicates that the existing prototype can be developed as a competitive alternative for imaging in radiation therapy.

The release of flammable and toxic chemicals in petrochemical facilities is a major concern when designing modern process safety systems. While the proper selection of the necessary types of gas detectors needed is important, appropriate placement of these detectors is required in order to have a well-functioning gas detection system. However, the uncertainty in leak locations, gas composition, process and weather conditions, and process geometries must all be considered when attempting to determine the appropriate number and placement of the gas detectors. Because traditional approaches are typically based on heuristics, there exists the need to develop more rigorous optimization based approaches to handling this problem. This work presents several mixed-integer programming formulations to address this need. First, a general mixed-integer linear programming problem is presented. This formulation takes advantage of precomputed computational fluid dynamics (CFD) simulations to determine a gas detector placement that minimizes the expected detection time across all scenarios. An extension to this formulation is added that considers the overall coverage in a facility in order to improve the detector placement when enough scenarios may not be available. Additionally, a formulation considering the Conditional-Value-at-Risk is also presented. This formulation provides some control over the shape of the tail of the distribution, not only minimizing the expected detection time across all scenarios, but also improving the tail behavior. In addition to improved formulations, procedures are introduced to determine confidence in the placement generated and to determine if enough scenarios have been used in determining the gas detector placement. First, a procedure is introduced to analyze the performance of the proposed gas detector placement in the face of “unforeseen” scenarios, or scenarios that were not necessarily included in the original formulation. Additionally, a procedure for determine the confidence interval on the optimality gap between a placement generated with a sample of scenarios and its estimated performance on the entire uncertainty space. Finally, a method for determining if enough scenarios have been used and how much additional benefit is expected by adding more scenarios to the optimization is proposed. Results are presented for each of the formulations and methods presented using three data sets from an actual process facility. The use of an off-the-shelf toolkit for the placement of detectors in municipal water networks from the EPA, known as TEVA-SPOT, is explored. Because this toolkit was not designed for placing gas detectors, some adaptation of the files is necessary, and the procedure for doing so is presented.

<p>Position sensitive detectors represent a class of particle detectors widely used in high-energy physics, astrophysics, biophysics and medicine for imaging the spatial distribution of various radioactive sources. In recent years, a new class of gas based detectors, so-called micropattern gas detectors (MPGDs), has emerged. While modern MPGDs rival solid state detectors in terms of spatial and temporal resolution, their cost of production is significantly lower. A Thick Gaseous Electron Multiplier (THGEM) imaging detector, with a two-dimensional delay line readout, has been constructed as a concept for a large area imaging detector with reasonable spatial resolution. The delay line based THGEM imaging detector is robust, easy to manufacture and cost effective alternative to direct readout techniques which frequently employ a large number of channels. Featuring an active area of 40 x 40 mm<strong>2</strong>, the prototype has been constructed using two 0.4 mm THGEMs and successfully operated in a low pressure, propane based, gas mixture. Two sets of orthogonal electrodes, connected to individual delay lines, serve as a two-dimensional anode readout. Adjacent electrodes are separated by approximately 3.4 ns of time delay and allow the interaction position to be calculated by measuring the time difference between delay line output signals corresponding to a common axis. Using modern field programmable gate arrays (FPGAs), a time-to-digital (TDC) data acquisition (DAQ) system has been developed. The TDC DAQ performs the position reconstruction algorithm and is capable of continuous event rates up to 1.8 MHz. The imaging capabilities of the detector have been assessed using a collimated alpha source and a wide X-ray beam. Under these aforementioned conditions, the detector was able to successfully resolve 1 mm diameter holes spaced 3 mm apart. With higher operating pressures, and using Xenon based gas mixture, it is expected the imaging detector should achieve sub-mm spatial resolution. The investigations presented in this thesis serve as a framework for the development of future THGEM imaging detectors.</p> / Doctor of Philosophy (PhD)

L'autoradiographie b est une technique d'imagerie médicale qui permet de visualiser la localisation de molécules marquées avec des traceurs radioactifs émetteurs b dans des coupes histologiques. Cette technique est largement employée dans les domaines de la biologie cellulaire ou de la pharmacologie. Le développement de la technologie des détecteurs gazeux à structure PIM au laboratoire Subatech a permis d'aboutir à la conception d'un appareil d'imagerie b de très haute résolution spatiale (20 μm FWHM) réalisant des images d'une demi lame histologique sur des émetteurs de basses énergies comme du 3H ou de 14C. Le développement récent d'une nouvelle approche concernant la méthode de reconstruction du point d'émission permet d'élargir le champ d'application aux émetteurs de haute énergie tels que l'131I, le 18F ou le 46Sc. Un nouveau dispositif de grande surface (18x18 cm2), compact et conçu pour l'utilisateur final a été mis au point. Il permet désormais l'imagerie de 10 lames de microscope simultanément. Grâce à une solution de multi-modalité, il conserve les bonnes caractéristiques de résolutions spatiales acquises précédemment en l'étendant sur une grande surface d'analyse. Différentes formes d'échantillons comme des coupes sur lames de microscope ou sur rubans adhésifs peuvent ainsi être analysés. Les simulations et les expérimentations menées durant cette thèse ont permis d'aboutir à un agencement optimal des structures composant le détecteur. La caractérisation et les résultats ont montré que la structure PIM est une structure à considérer dans le cadre de l'imagerie b de haute résolution sur différents types d'émetteurs.

This work deals with the automatic testing of an ultrasonic gas leak detector, which has to be tested during normal changes in the development phase. The reader will be acquainted with the basic principles of gas detection, design of the test product, software architecture its implementation. The following is a presentation of the application and instructions for writing tests. In this work, the Beaglebone Black development board with the Debian operating system is used as the core of the entire test product.

A des fins de propreté radiologique, les exploitants nucléaires doivent évaluer l'activité surfacique résiduelle, telle que la contamination bêta. Pour cela, les contaminamètres sont essentiels. Dans ce cadre, EDF R&D a proposé un projet de recherche visant à étudier la faisabilité d’un contaminamètre innovant permettant de détecter l’activité surfacique bêta in situ, alors qu’elle est actuellement mesurée ex-situ.L'objectif principal de ce travail est de détecter une contamination bêta surfacique de 0,4 Bq/cm^2 dans un environnement gamma élevé, jusqu'à 100 µSv/h. Cela exige un détecteur ayant une performance de discrimination bêta/gamma élevée. Plusieurs technologies basées sur un scintillateur et/ou un détecteur à gaz ont été étudiées. Des simulations Geant4 ont été effectuées pour optimiser la configuration des technologies retenues (géométrie, matériaux, etc.). Suite à ces simulations, deux prototypes, de type Phoswich, optimisés ont été fabriqués et testés à l’aide de sources bêta et gamma au laboratoire ( LPC Caen). En outre, deux campagnes d’essai ont été menées dans une centrale nucléaire (CNPE de Chinon) afin d'évaluer les performances des prototypes développés dans un bruit de fond gamma réaliste. Les simulations Geant4 et les tests sont discutés dans cette thèse. / For radiological cleanliness purpose, nuclear operators have to assess surface residual activity such as beta contamination. To this aim, contamination monitors are essential. In this context, EDF R&D proposed a research project in order to study the feasibility of an innovative contamination monitor to detect beta surface activity in situ which is until now performed ex situ. The main objective is to detect a 0.4 Bq/cm^2 beta surface contamination in a high gamma background up to 100 μSv/h. This demands the detector to have a high beta/gamma discrimination performance. Several technologies based on scintillator and/or gas filled detector have been investigated. Geant4 simulations have been carried out to optimise the configuration of the chosen detector such as geometry, materials, etc. Two simulation-optimised prototypes based on Phoswich detectors have been developed and tested with beta and gamma sources in a laboratory framework (LPC Caen). Furthermore, two experimental campaigns have been conducted in a nuclear power plant (NPP of Chinon) in order to evaluate the performance of the developed prototypes in a realistic gamma background environment. The Geant4 simulations and the experimental work are discussed in this thesis.

This Master's thesis discusses about the measurement of the carbon dioxide concentration in breathing by an optical analyzer using infrared absorption spectroscopy. The method is described with the technical focus on individual components needed for subsequent implementation. A circuit diagram is created to produce Arduino platform devices that serve as hardware to connect and power individual parts and software to create a user environment, followed by a Bluetooth module to transmit measured data to mobile devices where real-time results are presented.