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Tese de doutoramento em Engenharia Física, na especialidade de Instrumentação, apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra Desde cedo que a comunidade científica compreendeu que gases nobres em liquido são excelentes meios de detecção de radiação, combinando a sua elevada densidade, elevado grau de homogeneidade e de elevado rendimento de cintilação. Para além destas características inerentes, estes têm a potencialidade de fornecer ambos sinais de ionização – criando electrões livres – e cintilação em resposta à interacção com radiação ionizante e, tendo em vista a sua aplicação em experiências de eventos raros relacionados com física de neutrinos ou matéria–escura, a capacidade de autoblindagem garante a exclusão de eventos induzidos por radiação de fundo. O facto de não absorverem a sua própria luz, emergente dos eventos de cintilação, permite a expansão deste tipo de detectores até grandes volumes, sendo que as colaborações mais recentes propõem detectores com dezenas de toneladas de xénon em estado liquido. As experiências actuais que usam gases nobres em estado líquido empregam xénon ou árgon numa só fase (estado líquido) ou em dupla-fase (estado líquido + gasoso) e as suas aplicações abrangem desde as já referidas experiências de procura de eventos raros, passando por imagiologia médica tais como detectores de radiação gama para PET ou câmaras Compton “3- γ” em combinação com PET, passando também por aplicações de segurança como sistemas de inspecção para detecção de material físsil e, finalmente, em câmaras Compton para aplicações de astrofísica. Em ambas as configurações a leitura dos sinais de cintilação é geralmente feita através de um grande número de dispendiosos fotomultiplicadores de vácuo agrupados. A presente tese de doutoramento é dedicada aos fotomultiplicadores gasosos de grande área para aplicações criogénicas desenvolvidos no contexto do programa doutoral, tendo em vista a sua eventual aplicação como um dispositivo complementar aos métodos existentes de detecção de cintilação, para aplicação em futuras experiências de grande escala. Esta pesquisa foi direccionada tendo em vista o desenvolvimento de eficientes fotomultiplicadores gasosos de grande área, potencialmente mais económicos por unidade de área, baseados em “Thick Gas-Electron Multipliers” (THGEMs). Combinando fotocátodos de alta eficiência com multiplicadores gasosos de electrões capazes de atingir elevado ganho em carga obteve-se assim um dispositivo com elevada sensibilidade para a detecção de fotões únicos, com a possibilidade de discriminação em posição com resolução espacial inferior a um milímetro e com resolução temporal da ordem de poucos nano segundos. Contrariamente ao que sucede com a tecnologia de vácuo actualmente, com este dispositivo a localização em posição de fotões em grandes áreas é feita num único dispositivo integrando electrónica habitualmente utilizada em experiências de rastreamento de partículas. Neste trabalho o fotomultiplicador gasoso desenvolvido consiste numa cadeia de THGEMs combinados com um fotocátodo de iodeto de césio (CsI) sensível ao ultravioleta enquanto que os testes criogénicos foram realizados na Time Projection Chamber (TPC) de dupla fase de xénon líquido recentemente desenvolvida no Weizmann Institute of Science (WILiX). Relativamente ao GPM desenvolvido foram medidos ganhos máximos em carga de ~8×10^5 em misturas de Ne/CH4(5%) e de ~3×10^5 em misturas de Ne/CH4(20%), a uma pressão de 0.7bar à temperatura de ~180K, para fotões únicos. Foi obtida uma probabilidade de descarga com uma mistura de Ne/CH4(5%) a um ganho em carga de 1×10^5 e com sinais de cintilação secundária S2, induzidos por partículas alfa, a uma taxa de 40Hz de cerca 10^-6. Foram medidos desvios no ganho em carga de cerca de 7–15% durante um período de dois meses, operando em modo selado com 0.7bar de Ne/CH4(20%) a uma temperatura de ~190K, não se registando mudanças significativas tanto para fotões únicos induzidos por uma lâmpada UV como para sinais de cintilação primária S1 induzidos por partículas alfa, indicando a estabilidade da mistura em modo selado assim como para a estabilidade da eficiência quântica do fotocátodo de iodeto de césio. Para além disso foi obtido um valor de 1.2 – 1.3ns para a resolução temporal do GPM em resposta a sinais de cintilação, induzindo cerca de 170–200 fotoelectrões iniciais no GPM. Para a leitura em posição de eventos o GPM foi equipado com um ânodo segmentado em “pads” individuais, cujo desenho foi precedido por extensas simulações em GEANT4 que forneceram dados importantes para a optimização da geometria dos ânodos e qual a resolução espacial esperada para diferentes configurações. Das simulações pôde-se determinar que a resolução espacial esperada do GPM será ~5mm para sinais de cintilação devido a 10 electrões numa TPC de xénon liquido de dupla fase. Nos testes realizados determinou-se que para ~1.3×10^5 fotoelectrões iniciais a posição calculada apresenta um desvio menor que um milímetro da posição real. Os estudos iniciados em Coimbra combinando multiplicadores gasosos de electrões com regiões de indução micrométricas (GEM–MIGAS) fomentaram o desenvolvimento de um análogo com THGEMs e regiões de indução sub–milimétricas. Estes estudos envolveram simulações electrostáticas de forma a compreender a relação entre os campos eléctricos no interior de THGEMs e da região de indução enquanto que o trabalho experimental demonstrou que com misturas de Ne-CH4, sendo mais eficientes em absorver a radiação UV das avalanches, permitem atingir ganhos mais elevados em condições estáveis. Foram também testadas misturas à base de hélio uma vez que podem potencialmente apresentar uma boa alternativa para misturas à base de néon, devido ao ganho em carga elevado, aplicando tensões de operação mais reduzidas, semelhante eficiência de extracção de fotoelectrões e custos mais reduzidos. Em modo de corrente, um detector com um estágio apresentou ganhos superiores a 10^5. Liquid noble gases are known to be excellent detection media due their characteristics of high density, high homogeneity and high scintillation yield. They provide both ionization and scintillation signals when transversed by ionizing particles and efficient background suppression due to self-shielding. They are transparent to their own scintillation light and allow expansion to large detector masses. Current noble liquid detectors employ either liquid argon or liquid xenon, in single-phase (liquid only) or double-phase (liquid and gas) configurations and the present application ranges from detection of rare scattering events like Dark Matter search or neutrino physics, to medical imaging like in gamma detectors for PET and LXe Compton Telescope for “3-γ imaging” in combination with PET, gamma/neutron imaging detectors for radionuclide security inspections and Compton Cameras for applications in astrophysics. Both configurations rely on measuring the scintillation light emitted from the liquid-phase or from the liquid and gas-phases with costly large arrays of vacuum photomultipliers. This Ph.D. thesis is dedicated to the large-area cryogenic gas-avalanche photomultipliers (GPMs) prototypes developed within the Ph.D. program, envisioning their application as a complimentary scintillation detection method for current and future large scale experiments. The research and development efforts aimed for a potentially economic and efficient large-area GPM based on Thick Gas-Electron Multipliers – THGEMs – combining a high efficiency photocathode with a high-gain gas-avalanche electron multiplier, providing high single-photon sensitivity and the possibility for localization of the photons with sub-mm spatial resolution and few-ns temporal resolution. Unlike current vacuum devices, photon localization over large areas can be made in a single device, using integrated electronics developed for particle tracking. The GPM consists on a cascade of THGEMs combined with a cesium iodide UV-photocathode and the cryogenic tests were performed coupling it to a double-phase liquid xenon detector (a Time Projection Chamber; TPC), in the recently developed Weizmann Institute Liquid Xenon – WILiX – cryogenic system. Moreover, for the successful use of a cesium iodide photocathode, techniques for the production, characterization and transportation were developed and implemented which allowed systematically reproducing photocathodes whose quantum efficiency ranged from 24% to 30% for a wavelength of 175nm, corresponding to the liquid xenon scintillation light, and assembling them to the GPM successfully. Within the Ph.D. thesis it is shown that the maximum gain obtained at 0.7bar and 180K was ~8×105 for Ne/CH4(5%) and ~3×105 for Ne/CH4(20%), for single-photons. With Ne/CH4(5%) at a gain of 1×105 and alpha particle-induced S2 signals at a rate of 40Hz, the discharge probability was found to be of the order of 10-6. Over a period of two months, operating in sealed mode at 0.7bar of Ne/CH4(20%) at a temperature of ~190K, gain measurements were consistent within 7–15%, showing no significant change both for the UV–lamp induced signals and alpha-induced S1 signals, indicating that there were no significant changes in either the gas composition or the CsI quantum efficiency. In terms of the time resolution of the GPM – defined as the temporal spread, or jitter, of the GPM response pulse to a scintillation signal – it was found that for scintillation signals producing ~170 – 200 photoelectrons the resolution was on the nanosecond scale, approaching ~1.2 – 1.3ns at a gain of 3×105. For position sensitive capability the GPM was equipped with position sensitive anodes. Their design was preceded by extensive and CPU–time intensive GEANT4 simulations and analysis that provided valuable information on the expected spatial resolution for different conditions. For the selected pixel size and geometry one can expect a position resolution of ~5mm for scintillation signals due to 10electrons in a double–phase LXe TPC. The tests performed with a second GPM showed that for ~1.3×105 initial photoelectrons the calculated centers–of–gravity are in very good agreement (sub-millimeter) to the actual UV source positions. Furthermore, following the promising studies performed in Coimbra with Gas Electron Multipliers with a micro-induction gap amplifying structure – GEM–MIGAS – an analogous configuration consisting of a THGEM coupled to a submillimetric induction gap was investigated to eventually obtain a GPM configuration capable of reaching higher gains with lower biasing voltages. The investigation combined extensive simulation work showing an interdependence of hole/induction region electric fields while experimental results showed that Ne-CH4 mixtures, having a more effective UV quenching than Ne-CF4 mixtures, allowed achieving higher charge gains in stable operating conditions. Helium based mixtures were also tested in terms of charge–gain and photoelectron extraction efficiency, since they can present a good alternative to Ne-based mixtures for the potential higher gains, with lower applied voltages, similar photoelectron extraction efficiency and lower costs. A Single-THGEM detector was operated in He/CF4 and He/CH4 mixtures reaching effective charge-gains well above 105, measured in current mode, applying relatively low voltages, when compared to Ar mixtures.

Doutoramento em Engenharia Física Submitted by Patrícia Correia (patriciacorreia@ua.pt) on 2016-07-15T15:48:53Z No. of bitstreams: 1 Estudo e desenvolvimento de fotodetectores UV com vista ao upgrade do COMPASS RICH-1 e a aplicações.pdf: 9163448 bytes, checksum: 19e1df4ac0db8ec809a624fbe2bbc075 (MD5) Made available in DSpace on 2016-07-15T15:48:53Z (GMT). No. of bitstreams: 1 Estudo e desenvolvimento de fotodetectores UV com vista ao upgrade do COMPASS RICH-1 e a aplicações.pdf: 9163448 bytes, checksum: 19e1df4ac0db8ec809a624fbe2bbc075 (MD5) Previous issue date: 2015

International audience; This paper reports about the first Micromegas-based telescope built for applications in muon tomo-graphy. The telescope consists of four, 50 Â 50 cm 2 resistive multiplexed Micromegas with a 2D layout and a self-triggering electronics based on the Dream chip. Thanks to the multiplexing, the four detectors were readout with a single Front-End Unit. The high voltages were provided by a dedicated card using low consumption CAEN miniaturized modules. A nano-PC (Hummingboard) ensured the HV control and monitoring coupled with a temperature feedback as well as the data acquisition and storage. The overall consumption of the instrument yielded 30 W only, i.e. the equivalent of a standard bulb. The telescope was operated outside during 3.5 months to image the water tower of the CEA-Saclay research center, including a 1.5-month campaign with solar panels. The development of autonomous, low consumption muon telescopes with unprecedented accuracy opens new applications in imaging as well as in the field of muon metrology.

Mestrado em Tecnologias da Imagem Médica Os detetores de radiação representam um dos componentes principais dos equipamentos de imagiologia, tendo como principal função o registo da intensidade do feixe de raios X após atenuação, fundamental para a posterior criação da imagem. Desde o desenvolvimento da película radiográfica, a evolução dos detetores de radiação tem sido progressiva, implementando-se diferentes materiais e técnicas na deteção de raios X com o objetivo de produção de imagens mais eficiente, com maior qualidade, reduzido tempo de exposição e menor dose de radiação no paciente. O detetor gasoso microestruturado (MicroPattern Gaseous Detector – MPGD) baseado na estrutura Thick-COBRA (THCOBRA) já mostrou, como publicado na literatura, as suas potencialidades em imagiologia por transmissão de raios X. Apesar disto, e olhando ao facto de este ser um detetor desenvolvido recentemente, não existem estudos quanto às suas características de desempenho. Daí levanta-se a seguinte questão problema que impulsionou este trabalho: “Quais são as características de desempenho de um MPGD baseado na THCOBRA?”. O objetivo do trabalho é então estudar as características de desempenho do MPGD THCOBRA a operar em Ar/CH4 (95/5) para imagiologia por transmissão de raios X, avaliando os parâmetros de resolução espacial, a Modulation Transfer Function (MTF), o Noise Power Spectrum (NPS), Detective Quantum Efficiency (DQE), ganho em carga, resolução em energia, uniformidade e relação sinal ruído (SNR). Serão ainda exploradas as potencialidades deste detetor, usando a informação em energia para obter diferentes tipos de imagem. O estudo foi realizado no laboratório do grupo de Deteção de Radiação e Imagiologia Médica (DRIM) do I3N sediado no Complexo Interdisciplinar de Ciências Físicas Aplicadas à Nanotecnologia e à Oceanografia (CICFANO) da Universidade de Aveiro, com recurso a uma ampola de raios X e um MPGD com a estrutura THCOBRA. Para estudar as características de desempenho do detetor, foram adquiridos os dados necessários em laboratório e de seguida avaliado cada um dos parâmetros de qualidade com base nos métodos existentes na literatura, adaptados para este caso concreto, visto não existirem métodos específicos para o detetor em causa. Tendo como base a literatura já publicada sobre este detetor, são limitadas as previsões acerca dos resultados esperados das características de desempenho, tendo-se conhecimento de que estes serão inferiores aos detetores de radiação usados atualmente em imagiologia. Os resultados obtidos estiveram de acordo com as previsões, mas além disso revelam que este detetor tem potencialidades para criação de imagens por transmissão cuja qualidade pode ser otimizada futuramente. Radiation detectors are one of the main components of imaging equipment, having the main function of registering the intensity of X-ray beam after attenuation, fundamental for the subsequent creation of the image. Since the development of radiographic film, the evolution of the radiation detectors has been progressive, by implementing different materials and techniques on the X-rays detection with the purpose of more efficient production of images with higher quality, reduced time of exposure and lower radiation dose in the patient. Micro Pattern Gaseous Detector (MPGD) based on Thick-COBRA structure (THCOBRA) has shown, as published in the literature, its potential for imaging by X-ray transmission. Despite this, and looking at the fact that this is a newly developed detector, there are no studies as to its performance characteristics. From there arises the question problem which boosted this work: "Which are the performance characteristics of a MPGD based on a THCOBRA?". This study aims to examine the performance characteristics of MPGD THCOBRA operating in Ar/CH4 (95/5) for imaging by X-ray transmission, evaluating the parameters of spatial resolution, Modulation Transfer Function (MTF), Noise Power Spectrum (NPS), Detective Quantum Efficiency (DQE), charge gain, energy resolution, uniformity and signal noise ratio (SNR). Also, will be explored the potential of this detector, using energy information to achieve different types of images. The study was conducted in the laboratory of Radiation Detection and Medical Imaging Group (DRIM) of I3N in the CICFANO at University of Aveiro, using an X-ray tube and a MPGD with a THCOBRA structure. To examine the detector performance characteristics the necessary data was acquired in the laboratory and then evaluated each quality parameter based on existing methods in the literature, adapted for this case, since there are no specific methods for the involved detector. Based on the published literature about this detector, the predictions are limited regarding the expected results of the performance characteristics, having knowledge that these will be lower than the radiation detectors currently used in medical imaging. The results were in line with the predictions, but additionally shown that this detector has the potential to create transmission images whose quality can be improved in the future.

Doutoramento em Engenharia Física COMPASS is an experiment at CERN’s SPS whose goal is to study hadron structure and spectroscopy. The experiment includes a wide acceptance RICH detector, operating since 2001 and subject to a major upgrade of the central region of its photodetectors in 2006. The remaining 75% of the photodetection area are still using MWPCs from the original design, who suffer from limitations in gain due to aging of the photocathodes from ion bombardment and due to ion-induced instabilities. Besides the mentioned limitations, the increased luminosity conditions expected for the upcoming years of the experiment make an upgrade to the remaining detectors pertinent. This upgrade should be accomplished in 2016, using hybrid detectors composed of ThGEMs and MICROMEGAS. This work presents the study, development and characterization of gaseous photon detectors envisaging the foreseen upgrade, and the progress in production and evaluation techniques necessary to reach increasingly larger area detectors with the performances required. It includes reports on the studies performed under particle beam environment of such detectors. MPGD structures can also be used in a variety of other applications, of which nuclear medical imaging is a notorious example. This work includes, additionally, the initial steps in simulating, assembling and characterizing a prototype of a gaseous detector for application as a Compton Camera. O COMPASS é uma experiência no SPS do CERN cujo objectivo é estudar a espectroscopia hadrónica e a estrutura dos nucleões. A experiência inclui um detector RICH de larga aceitação, operacional desde 2001 e sujeito a um upgrade de parte dos seus fotodetectores em 2006. Os restantes 75% da área de fotodetecção ainda utilizam as MWPCs do desenho original, que sofrem de limitações de ganho devido ao envelhecimento dos fotocátodos pelo bombardeamento com iões e a instabilidades por eles induzidas. Além destas limitações, o aumento de luminosidade expectável nos próximos anos para a experiência tornam o upgrade dos restantes fotodetectores desejável. Este upgrade deverá acontecer em 2016 e deverá fazer uso de detectores híbridos compostos por ThGEMs e MICROMEGAS. Este trabalho apresenta o estudo, desenvolvimento e caracterização de fotodetectores gasosos com vista ao upgrade referido, e o progresso na produção e nas técnicas de avaliação necessário para alcançar as maiores áreas de detecção com os desempenhos exigidos. Inclui também a descrição e tratamento de exercícios com irradiação por feixe de partículas dos detectores em causa. Os MPGDs podem também ser usados em várias outras aplicações, entre as quais se destaca a imagiologia médica nuclear. Este trabalho inclui, adicionalmente, as etapas iniciais de simulação, montagem e caracterização de um protótipo de detector gasoso para aplicação como Câmara Compton.

A multi-institutional collaboration is investigating the possibility of enhancing muon tracking and triggering capabilities in the small-angle region $1.6 < \rm{abs}(\eta) < 2.1$ of the CMS experiment at the LHC by instrumenting the end-cap muon system with large-area gas electron multiplier (GEM) detectors. A first trapezoidal prototype triple-GEM detector of size 1 m by 0.5 m was built and operated successfully in a test beam at CERN in October 2010. Front-end readout boards utilizing the ``VFAT" chip are mounted in a regular array directly on the chambers. High voltage is provided by a compact divider board implemented with surface mount components. A tracker equipped with small GEM detectors was used to precisely measure the hit position in the large-area detector. A spatial resolution of 0.29 mm was measured in a region with average strip pitch of 1.1 mm, and $\sim$98\% hit efficiency was achieved at full operating voltage. An additional prototype chamber is constructed and will undergo beam tests this summer with operation in a 3T magnetic field.

The Micro Pixel Chamber (μ-PIC) is being developed a sacandidate for the muon system of the ATLAS detector for upgrading in LHC experiments. The μ-PIC is a micro-pattern gaseous detector that doesn’t have floating structure such as wires, mesh, or foil. This detector can be made by printed-circuit-board (PCB) technology, which is commercially available and suited for mass production. Operation tests have been performed under high flux neutrons under similar conditions to the ATLAS cavern. Spark rates are measured using several gas mixtures under 7 MeV neutron irradiation, and good properties were observed using neon, ethane, and CF4 mixture of gases.Using resistive materials as electrodes, we are also developing a new μ-PIC, which is not expected to damage the electrodes in the case of discharge sparks.

This paper presents a new multistage Micro Patterned Gaseous Detector (MPGD) made by wafer post-processing. The device consists of a double metal grid supported by SU-8 structures on top of a Timepix chip. The detector has been operated with He/iC(4)H(10) and Ar/iC(4)H(10) gas mixtures. Cosmic rays as well as Fe-55 decay events have been recorded using the Timepix chip in 2D and 3D readout modes. The detector can be operated like a Micromegas (high field close to the chip) or like a GEM (amplification stage followed by a low extraction field). This approach for manufacturing GEM-like radiation imaging detectors allows for precise dimensional control and considerable geometrical design freedom.

This thesis is dedicated to the development and characterisation of a new generation of Micromegas (MICROMEsh GAseous Structure) detectors for the COMPASS experiment at Cern, and the estimation of the diffractive processes’ contribution to the production of pions and kaons, concerning the study of the quark fragmentation functions into hadrons at COMPASS. New Micromegas detectors with a 40 x 40 cm² active area are being developed for the future physics program of the COMPASS experiment starting in 2015. These detectors will have to work in high muon and hadron flux (close to 8 MHz/cm²). In this context, a central area of about 5 cm diameter, crossed by the beam, will be composed of 1280 pixels, and discharge-reduction technologies will be used. Four prototypes with a final read-out geometry, using two different discharge-reduction technologies have been produced at Cern and studied in nominal conditions at COMPASS between 2010 and 2012. Three are hybrid detectors using a GEM (Gas Electron Multiplier) foil as a preamplification stage to reduce the discharge probability. The other is equipped with a so called “buried resistors” resistive structure allowing to strongly reduce the discharge amplitude. Their performances are presented in this thesis. The impact of these results on the production and implementation of the final series of detectors is also discussed. Quark fragmentation functions into hadrons describe the hadronisation of a quark of flavor q into a hadron h. These universal functions take part in the cross-section expression of several processes. They can be accessed at COMPASS via semi-inclusive deep inelastic scattering of muons off nucleons. The relevant observables for fragmentation function extraction are hadron multiplicities, corresponding to the mean number of hadrons produced per deep inelastic scattering event. Vector mesons produced by a diffractive process can decay into pions and kaons. As such processes do not involve quark hadronisation, they should a priori be excluded from multiplicity measurements. This work presents a Monte-Carlo study of the impact of diffractive rho and phi production on light hadrons and inclusive events yields. Multiplicity correction factors are finally established. The effect of this correction on the extraction of pion fragmentation functions is also discussed.; Le travail présenté dans cette thèse porte d’une part sur le développement et la caractérisation d’une nouvelle génération de détecteurs Micromegas (MICROMEsh GAseous Structure) pour l’expérience COMPASS au Cern, et d’autre part sur l’estimation de la contribution de canaux diffractifs à la production de pions et de kaons, dans le cadre de l’étude des fonctions de fragmentation de quarks en hadrons à COMPASS. De nouveaux détecteurs Micromegas d’une surface active de 40 x 40 cm² sont en cours de développement pour le futur de l’expérience COMPASS, à partir de 2015. Ces détecteurs devront fonctionner dans des flux de muons et hadrons approchant 8 MHz/cm². Pour cela, une zone centrale d’environ 5 cm de diamètre, traversée par le faisceau, sera constituée de 1280 pixels, et des technologies permettant de fortement réduire l’impact des décharges seront adoptées. Quatre prototypes de géométrie finale utilisant deux types de technologies de réduction des décharges différentes ont été produits au Cern et testés en conditions réelles à COMPASS entre 2010 et 2012. Trois d’entre eux sont des détecteurs hybrides utilisant une feuille GEM (Gas Electron Multiplier) en tant qu’étage de préamplification pour réduire la probabilité de décharge. Le dernier détecteur est équipé d’une structure résistive à « résistances enterrées », permettant la réduction de l’amplitude des décharges. Leurs performances sont présentées dans cette thèse. L’impact de ces résultats sur la production et la mise en œuvre de la série finale de détecteurs est également discuté. Les fonctions de fragmentation de quarks en hadrons l’hadronisation d’un quark de saveur q en un hadron h. Ces fonctions universelles interviennent dans l’expression de la section efficace de nombreux processus. Elles sont accessibles à COMPASS via la réaction de diffusion profondément inélastique semi-inclusive de muons sur des nucléons. Les observables permettant leur extraction dans ce cadre sont les multiplicités de hadrons, soit le nombre moyen de hadrons produits par événement de diffusion profondément inélastique. Les mésons vecteurs issus de processus diffractifs produisent également des pions et kaons par leur désintégration. Ces processus n’impliquant pas l’hadronisation d’un quark, il semble justifié de ne pas les comptabiliser dans la mesure des multiplicités. Ce travail propose une étude Monte-Carlo des contributions de la production diffractive de mésons vecteurs rho et phi à la production de hadrons léger et aux événements inclusifs. Des facteurs de correction des multiplicités sont finalement établis. Enfin, l’effet de cette correction sur l’extraction des fonctions de fragmentation en pions est présenté.

Mestrado em Física Cherenkov Imaging counters require large photosensitive areas, capable of single photon detection, operating at stable high gains under radioactive backgrounds while standing high rates, providing a fast response and a good time resolution, and being insensitive to magnetic fields. The development of photon detectors based in Micro Pattern Gaseous detectors (MPGDs), represent a new generation of gaseous photon detectors. In particular, gaseous detectors based on stacked Thick-Gaseous Electron Multipliers (THGEMs), or THGEM based structures, coupled to a CsI photoconverter coating, seem to fulfil the requirements imposed by Cherenkov imaging counters. This work focus on the study of the THGEM-based detectors response as function of its geometrical parameters and applied voltages and electric fields, aiming a future upgrade of the Cherenkov Imaging counter RICH-1 of the COMPASS experiment at CERN SPS. Further studies to decrease the fraction of ions that reach the photocathode (Ion Back Flow – IBF) to minimize the ageing and maximize the photoelectron extraction are performed. Experimental studies are complemented with simulation results, also perfomed in this work. Os detetores de RICH (do inglês Ring Imaging Cherenkov) requerem grandes áreas fotossensíveis, capazes de operar em regime de fotão único, de modo estável e com ganhos elevados, em ambientes radioativos, ao mesmo tempo que são submetidos a elevadas taxas de irradiação, proporcionando uma resposta rápida e boa resolução temporal, e sendo insensíveis a campos magnéticos. O desenvolvimento de foto-detetores baseados em detetores gasosos micro-estruturados (Micro Pattern Gaseous Detectors – MPGDs) representa uma nova geração de foto-detetores gasosos. Em particular, detetores gasosos baseados em múltiplas camadas de THGEMs (THick Gaseous Electron Multipliers), ou de estruturas baseadas em THGEMs, acoplados com uma camada foto-conversora de CsI, parecem reunir os requisitos impostos para aplicação em detetores de RICH. Este trabalho incide no estudo da resposta de detetores gasosos baseados em THGEMs, em função dos seus parâmetros geométricos, e dos potenciais e campos elétricos aplicados, com vista à futura atualização do detetor RICH-1 da experiência COMPASS, no acelerador SPS no CERN. São realizados estudos adicionais para reduzir o refluxo de iões para o fotocátodo para minimizar o seu envelhecimento, e maximizar a eficiência de extração de fotoeletrões. Os estudos experimentais são complementados com resultados de simulações, realizadas também no âmbito deste trabalho.

The RICH-1 detector of the COMPASS Experiment at CERN SPS is undergoing an important upgrade: four new Photon Detectors, based on MPGD technology and covering a total active area larger than 1.4 m2 will replace the MWPC-based photon detectors in order to cope with the challenging efficiency and stability requirements of the new COMPASS measurements. The new detector architecture consists in a hybrid MPGD combination: two layers of THGEMs, the first of which also acts as a reflective photocathode as it is coted with a CsI film, are coupled to a bulk Micromegas on a pad segmented anode; the signals are read-out via capacitive coupling by analog F-E based on the APV-25 chip. These detectors are the first application in an experiment of MPGD-based single photon detectors. All aspects of the COMPASS RICH-1 Photon Detectors upgrade are presented and large emphasis is dedicated to the engineering aspects, the mass production and the quality assessment of the MPGD components. The status of the detector commissioning is also presented.

In the high-eta (1.6 - 2.4) region of the CMS endcap, Gas Electron Multipliers (GEM) present an interesting option for a future upgrade of the forward region of the CMS muon system. Large GEM detectors are challenging due to technological issues; in the view of the CMS upgrade we have designed and built the largest full-size triple GEM-based muon detector to-date. This prototype meets the stringent requirements of the hostile forward environment of CMS at high-luminosity LHC. Dedicated test beam measurements have been performed at the SPS in June 2011 to study efficiency, space resolution, and timing performance with different inter-electrode gap configurations and gas mixtures and in a strong magnetic field of 3T (as at CMS). Preliminary results of these experimental tests will be presented

A GridPix detector is a gaseous detector capable of detecting single primary electrons from ionising particles. Such a detector consists of a pixel chip as active anode covered with a thin layer of silicon rich silicon nitride (SiRN) for protection against discharges. A layer of 8 JlIl1 SiRN, and according recent tests even 4 JlIl1, is sufficient to protect against discharges. The effect of the thickness of the SiRN layer on the operation of a detector has been determined. Time walk effects due to pixel electronics response time and gas gain statistics cause errors in drift time measurements thereby worsening the resolution in the drift direction. Simulations and measurements have been performed to determine how much time walk can be compensated for. GridPix detectors are high resolution low mass detectors that measures track segments in 3D. Very recently we performed first tests in a 250 Me V proton beam, in order to investigate the application of GridPix in Proton therapy and results are promising.

An R&D project is presented, aimed to develop a high performance gaseous detector of single photons, for the upgrade of the Ring Imaging Cherenkov Counter RICH-1 of the COMPASS Experiment at CERN SPS. The detector has to stably operate at high gain and high rate, to provide good time resolution and insensitivity to magnetic field, and to offer the possibility to cover very large areas at affordable cost. The proposed solution is based on the use of a novel and robust electron multiplier, the Thick GEM (THGEM), arranged in a multilayer architecture, where the first layer is coated with a photosensitive CsI film. A systematic study of the response of THGEMs with various geometrical and production parameters and in different conditions was performed, leading to the choice of a set of optimal parameters. Prototypes of THGEM-based photon detectors able to efficiently detect Cherenkov photons have been built, tested in laboratory and operated in test beam exercises with typical gain of 10 5 and time resolution better than 10 ns. The engineering aspects of building large area (600×600 mm 2 ) THGEM-based photon detectors are presently being investigated.

We present a new Micro Pattern Gaseous Detector (MPGD) fabricated with non polymeric materials. The device structure is similar to a Microbulk Microme gas design, consisting of a punctured metalgrid supported by a continuous perforate dinsulating structure. In this detector, the supporting structure is made out of silicon oxide. Devices were tested in He/iC4H10 (80/20) and Ar/iC4H10 (80/20)gas mixtures under 55Fe irradiation. Gas gain of 20,000 and energy resolution below 13%FWHM were achieved. The CMOS compatibility of the fabrication process has been studied in Timepix chips as well as individual 0.13-mm technology CMOS transistors. Complete detectors have been fabricated on top of Timepix chips. In an Ar/iC4H10 (80/20) gas mixture 55Fe decay events were recorded operating the Timepix chip in 2D readout mode.

RD51 collaboration was founded in April 2008 to coordinate and facilitate the development of micropattern gaseous detectors (MPGDs). 59 institutes from 20 countries bundled their effort, experience and resources to develop these emerging micropattern technologies. MPGDs are already employed in several nuclear and high-energy physics experiments, medical imaging instruments and photodetection applications; many further applications are foreseen. They outperform traditional wire chambers in terms of rate capability, time and position resolution, granularity, stability and radiation hardness. One of the most challenging goals is the possibility to realize large area MPGDs (in particular GEMs, ThickGEMs and Micromegas) for future experiments and possible LHC upgrades. In order to achieve this goal new MPGDs production techniques are being studied

11th Vienna Conference on Instrumentation (February 2007) , to appear in the Proceedings (NIM A); International audience; Micropattern Gaseous Detectors (MPGD), like Micromegas or GEM, are used or foreseen in particle physics experiments for which a very good spatial resolution is required. We have developed an experimental method to separate the contribution of the transverse diffusion and the multiplication process by varying the number of primary electrons generated by a point-like source. A pulsed nitrogen laser is focused by an optical set-up on the drift electrode which is made of a thin metal layer deposited on a quartz lamina. The number of primary electrons can be adjusted from a few to several thousands on a spot which transverse size is less than $100 \mu m$ RMS. The detector can be positioned with an accuracy of $1\mu m$ by a motorized three dimensional system. This method was applied to a small Micromegas detector with a gain set between $10^3$ and $2.10^4$ and an injection of 60 to 2000 photoelectrons. Spatial resolutions as small as $5\mu m$ were measured with 2000 primary electrons. An estimation of the upper limit of the relative gain variance can be obtained from the measurements.

Anew type high spatial resolution radiation detector based on UV scintillators + UV imaginggas photomultiplier is presented. The prototype UV detector consists of a 10cm×10cm μPIC,2GEMs,aUV transparent windowandaCsI photocathode deposited on the window or the surface of the upper GEM. The effective photo-sensitive area is o34mm andthe readouts are 400um-pitch strips.Anewlydeveloped LuLiF4(Nd) crystal which emits 183nm photonsis directly coupled to the detector as the window. The detector was tested in pulse mode operation with 5.5MeV α particles from 241 Am and 122keV γ rays from 57 Co. The window images were clearly obtained and the position resolution of o (mm) is confirmed.

In this work we have investigated the functioning of high resistivity amorphous silicon and silicon-rich nitride layers as a protection against discharges in Micro-Patterned Gaseous Detectors (MPGDs). When the anode is protected by a high resistivity layer, discharge signals are limited in charge. A signal reduction is expected when the layers are too thick; simulations presented in this paper indicate that layers up to 10 μm thick can be applied without significantly degrading the detector performance. Layers of amorphous silicon and silicon-rich nitride have been deposited on top of Timepix and Medipix2 chips in GridPix detectors; with this, chips survive naturally occurring as well as intentionally produced discharges. © 2010 Elsevier B.V. All rights reserved.

Upgraded high-resolution X-ray diagnostics on JET is expected to monitor the plasma radiation emitted by W46+ and Ni26+ ions at 2.4 keV and 7.8 keV photon energies, respectively. Both X-ray lines will be monitored by new generation energy-resolved micropattern gas detectors with 1-D position reconstruction capability. The detection structure is based on triple GEM (T-GEM) amplification structure followed by the strip readout electrode. This article presents a design of new detectors and prototype detector tests. (C) 2012 Elsevier B.V. All rights reserved.

Mestrado em Física Submitted by Patrícia Correia (patriciacorreia@ua.pt) on 2015-03-19T14:43:41Z No. of bitstreams: 1 Microestruturas para MPGDs.pdf: 8490193 bytes, checksum: e4a056dd71d16d6971d9c8f137cc20fa (MD5) Made available in DSpace on 2015-03-19T14:43:41Z (GMT). No. of bitstreams: 1 Microestruturas para MPGDs.pdf: 8490193 bytes, checksum: e4a056dd71d16d6971d9c8f137cc20fa (MD5) Previous issue date: 2014

This thesis describes the first attempts to perform both absorption and scattering muon tomography using high granularity Micromegas detectors. This imaging technique using the free, available and harmless cosmic ray muons radiation shows great possibilities to study various sized objects. In order to make compact and precise portable devices, using one channel of electronics per readout pattern is not possible. To avoid this problem multiplexed detectors have been designed, extensively tested and used in numerous conditions. Latest developments in Micromegas design have been used such as the genetic multiplexing and the 2D strip readout using a resistive layer. The prototypes made were able to achieve a 300µm resolution at the scale of 50cm while using only 61 channels of electronics. Using these detectors, muography data taking campaigns have been performed both in the semi-controlled environment of the Saclay site of CEA and in the wild of the Giza plateau in Egypt. These two campaigns succeeded in imaging the CEA Saclay water tower and the Khufu's pyramid despite the extreme conditions endured by the Micromegas muon telescopes. Large temperature variations of a few tens of Kelvin have been recorded together with a stable operation i.e. an even gain ensuring a steady self triggering system. This stability was achieved using high voltage variations with respect to the environmental conditions. Together with this very first worldwide operation of a Micromegas-based tracker outside a laboratory, scattering muographies have also been done. A small setup imaging handheld objects performed well in separating various materials in time scales of the order of the day while a bigger 1m² setup allowing the scan of a full container was successfully operated. The inversion of the ill-posed problem of the muon scattering was performed using the crude PoCA method and the maximum likelihood one described by Schultz et al.; Cette thèse décrit les premiers essais de tomographie muonique par absorption et par déviation en utilisant des détecteurs Micromegas à haute granularité. Cette technique d'imagerie utilisant les rayons cosmiques gratuits, sans dangers et disponibles partout a démontré sa capacité à imager des objets de tailles variées. Afin de construire des outils compacts, précis, et portables, utiliser une voie d'électronique pour lire chaque motif de lecture est impossible. Pour éviter ce problème, des détecteurs multiplexés ont été conçus, testés et mis en situation dans différentes conditions. Il a été tiré parti des dernières améliorations concernant le détecteur Micromegas telles que le multiplexage génétique ou la lecture 2D par pistes sous une couche résistive. Les prototypes qui ont été fabriqués ont atteint une résolution de 300µm sur une surface d'un quart de mètre carré en ne nécessitant que 61 voies d'électronique. Grâce à ces détecteurs, des campagnes de prise de données ont été faites, à la fois dans l'environnement semi-contrôlé du centre CEA de Saclay et sur le plateau de Gizeh en Egypte. Ces deux campagnes ont permis d'imager avec succès le château d'eau du CEA Saclay ainsi que la pyramide de Khéops et ce malgré les conditions extrêmes que les télescopes à muon ont endurées. Des variations de température de plusieurs dizaines de Kelvin ont été enregistrées alors que l'acquisition de données se déroulait de manière stable, c'est-à-dire que les variations du gain n'impactaient pas le système d'auto déclenchement. Cette stabilité a été rendue possible grâce à un ajustement des hautes tensions vis à vis des conditions environnementales. Cela constitue la première mondiale concernant le fonctionnement d'un dispositif de reconstruction de trace à base de Micromégas en extérieur. En parallèle des expériences de muographie par déviation ont été menées. Un dispositif imageant des objets de petite taille est capable de distinguer divers matériaux sur une échelle de temps de l'ordre d'une journée. Une plus grande installation a permis d'imager un conteneur entier. La résolution du problème inverse a été faite en utilisant à la fois l'algorithme simple dit du PoCA ainsi que celui de maximisation de vraisemblance proposé par Schultz et son équipe.