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RECENT IMPROVEMENTS FOR SCATTER SIMULATION IN SINDBAD, A COUPLED PHOTON MONTE CARLO AND CAD SOFTWARE

RECENT IMPROVEMENTS FOR SCATTER SIMULATION IN SINDBAD, A COUPLED PHOTON MONTE CARLO AND CAD SOFTWARE,J. Tabary,P. Hugonnard,F. Mathy,R. Guillemaud

RECENT IMPROVEMENTS FOR SCATTER SIMULATION IN SINDBAD, A COUPLED PHOTON MONTE CARLO AND CAD SOFTWARE   (Citations: 3)
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In an X-ray radiography, scattering of photons from the inspected object, as well as backscattering or scattering from the environment, may have significant deleterious effects on image quality, reducing the relative contrast of the flaw indication. Therefore, development of computational models simulating scattering in radiographic studies is of primary interest, to correctly evaluate flaw detectability. The X-ray radiographic simulation software, Sindbad, developed for Non-Destructive Evaluation applications, models the whole radiographic set-up, with the X-ray source, the beam interaction inside the object represented by its CAD model and the imaging process in the detector. An analytical computation is used for the uncollided image whereas the scatter flux is computed with a Monte Carlo approach. Two major evolutions in Sindbad have been recently developed to provide realistic scatter images in reasonable computing time. Up to now, because of a geometrical restriction of the coupling of EGS4 Nova and BRL-CAD, we couldn't simulate detectors inside the object. An algorithm has been recently modified to consider the whole radiographic set-up, including the environment and all the parts of the object and detector which are behind the sensitive detector layer. Therefore, both backscattering and scattering from the environment are computed. Examples of simulations on industrial parts under experimental conditions show that the contribution of backscattering can exceed half of the overall scattering flux. Moreover, as scattering is not sensitive to sharp structures of the inspected items, an object simplification algorithm has been developed to speed up the Monte Carlo computation without modifying the scatter image. This simplification is automatic and takes into account the spectrum energy, the materials and the set-up geometry. On complex industrial objects, the computations can be twenty times faster. Introduction: An X-ray radiographic image is generated by both uncollided and scattered photons. Only the uncollided photons contribute to the exploitable part of radiographs, with the sharp structures of the examined parts. On the other hand, scattered radiation generated inside an object may have significant deleterious effects on image quality (1, 2, 3). First, the scattered radiation adds an important continuous component to the whole beam detected in the detector, with a contribution which may exceed the uncollided flux. Consequently and especially for film detectors, scattered radiation can induce problems of saturation and contrast. Moreover, depending on the equipment set-up and the examined part, the scattered radiation component can present low frequencies which disturb the radiograph. Finally, the scattered radiation can also add significant noise to the signal, thus reducing the relative contrast of the flaw indication. Many parameters of the radiographic scene may influence the shape and the contribution of the scattered radiation. Of course, the energy of the source as well as the materials of the object to be examined have an influence on the scattering phenomena (Compton, Rayleigh, Photoelectric) and on the deviation of particles. The scattered image is also largely dependant on the position, specifically on the distance between the object and the detector. Indeed, when the object is closer to the detector, more scattered radiation is detected and the associated image is a closer representation of the object. Finally, backscatter radiation coming from the environment (detector, wall, equipment set-up) can also present a considerable contribution to the overall radiation detected in the detector. In the context of a scattering study, X-ray simulation tools are of primary interest during the design stage of radiographic facilities, when they can help to choose the device parameters (X-ray tube settings such as voltage and filtration, detector type and thickness, geometry of the bench,
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