In this work we show the operation and results of an X-ray fluorescence imaging system using a cascade of three gas electron multipliers (GEM) and a pinhole assembly. The detector operates in Ar/CO 2 (90/10) at atmospheric pressure, with resistive chains applied to the strip readout, which allow to use only five electronic channels: two for each dimension and a fifth for energy and trigger. The corrections applied to the energy spectra to compensate for small changes in the signal amplitude and also differences in gain throughout the sensitive area are described and the clear improvement of the energy resolution is shown.To take advantage of the simultaneous sensitivity to the energy and to the position of interaction, a color scale matching the energy spectrum to the RGB range was applied, resulting in images where the color has a direct correspondence to the energy in each pixel and the intensity is reflected by the brightness of the image. The results obtained with four different color pigments are shown.
AgradecimentosEste trabalho recebeu apoio financeiro da Fundação de Amparo à Pesquisa do Estado de São Paulo, com a bolsa FAPESP 2017/00426-9.My sincere thanks to the whole GDD lab at CERN, in special Leszek Ropelewski, Eraldo Oliveri, Patrik Thuiner and Florian Brunbauer.Gostaria de agradecer primeiramente ao professor Alexandre Suaide, por me introduzir ao grupo e pela ajuda nos mais diversos assuntos. À professora Marcia Rizzuto e à minha amiga Hellen Santos, pelo interesse nesse trabalho e troca de informações.Aos professores Marco Bregant, Marcelo Munhoz, Nelson Carlin, Tiago Fiorini, Mauro Cosentino e Zwinglio Guimarães pelas ideias e sugestões, tornando esse trabalho muito mais completo.Ao meu orientador e amigo, Hugo Natal da Luz, pelos ensinamentos, conselhos e paciência. Aos amigos que fiz durante a graduação e o mestrado, pela diversão, aprendizado e companhia durante todos esse anos. Um agradecimento especial aos amigos do grupo, Henrique, Milton, Camila, Chiara, Thais e Lucas. À minha familia, meus pais, Marco Aurélio e Maria Cabrine, e meu irmão Ramon, por toda confiança e suporte. Vocês são os melhores exemplos para mim. À Mayumi, pelo carinho e por estar ao meu lado nos melhores e piores momentos."All we have to decide is what to do with the time that is given us." -J.R.R. Tolkien, The Lord of The Rings Abstract GEMs (Gas Electron Multiplier) and Thick-GEMs (Thick-Gas Electron Multiplier) are MPGDs (Micropattern Gas Detector) that make part of the new generation of gaseous detectors, allowing high counting rates, low cost when compared to solid state detectors, high radiation hardness and gain when using multiple structures. Besides that, the handling and maintenance of these detectors is relatively simple, being versatile to detect different types of radiation. Therefore, these detectors are an effective alternative to build imaging systems with large sensitive area. This work consists in the study and characterization of a set of gaseous detectors, more specifically the Thick-GEMs produced in the High Energy Physics and Instrumentation Center at IFUSP, which were tested showing promising results in terms of gain, energy resolution and operational stability. However, due to the low signal-to-noise ratio of the Thick-GEMs, the X-ray fluorescence imaging system was mounted using GEMs. During this work the necessary software tools for image processing and reconstruction were developed as a parallel study in computational simulations to better understand the operation of gaseous detectors.X-ray fluorescence techniques are essential in areas such as medicine and the study of historical and cultural heritage since they are non-invasive and non-destructive. Techniques to check the authenticity of masterpieces are required and museums are gradually becoming more interested in the Physics and instrumentation needed to characterize their patrimony.
In this work, we characterized an X‐ray position sensitive gaseous detector based in a triple stack of gas electron multipliers. The readout circuit is divided in 256 strips for each dimension and using a resistive chain interconnecting the strips, we are able to reconstruct the radiation interaction points by resistive charge division. The detector achieved gains above 104, energy resolution of 15.28% (full width at half maximum) for 5.9 keV X‐rays, and position resolution of 1.2 mm, while operating in Ar/CO2(90/10) at atmospheric pressure.
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