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Etude d'un système d'identification de matériaux par diffraction de rayons X à partir d'acquisitions spectrométriques multi pixels

Abstract : X-ray diffraction is becoming a prevailing technique for non invasive inspection of luggage. Compared to traditional techniques of transmission imaging, the diffraction technique can extract more characteristic information of materials, such as the Bragg peaks for crystalline materials or the molecular interference function for amorphous materials. The method of energy dispersive X Ray diffraction (EDXRD), which works at a fixed low scatter angle but with a polychromatic X-ray beam and a energy resolved detector, is particularly suited to the problem of luggage control as it allows parallelized architectures to inspect an entire object in a reasonable time. The work proposed in this thesis is to study an EDXRD system using a multi-pixelated CdZnTe detector to identify illicit materials in baggage. A first step has been to take control of this technique both experimentally with a diffraction bench and theoretically through the development of an elaborate simulation tool. The comparison between experiment and simulation has allowed to understand the physics of such a system and to better analyze its weaknesses to correct them. Relying on these two tools, we studied and implemented new concepts to improve performances of EDXRD systems, in terms of resolution, intensity and stability of the diffraction peaks. Thus, an innovative architecture, based on a dedicated treatment of transient signals delivered by the CdZnTe detectors, is proposed to significantly improve the compromise between the resolution of the diffraction peaks and their intensity. This architecture is based on an over-pixelation (1D) of the detector by an electronic positioning method and on a geometric adaptation of the system collimator/detector. The problem of instability of the diffraction peaks due to the effect of grain orientation in crystals is also handled.
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  • HAL Id : tel-00863855, version 1

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Bahaa Ghammraoui. Etude d'un système d'identification de matériaux par diffraction de rayons X à partir d'acquisitions spectrométriques multi pixels. Autre. INSA de Lyon, 2012. Français. ⟨NNT : 2012ISAL0081⟩. ⟨tel-00863855⟩

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