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The performance of the energy degrader in terms of beam properties directly impacts the design and cost of cyclotron-based proton therapy centers. The aim of this study is to evaluate the performances of different existing and novel degrader materials. The quantitative estimate is based on detailed GEANT4 simulations that analyze the beam-matter interaction and provide a determination of the beam emittance increase and transmission. Comparisons between existing (aluminum, graphite, beryllium) and novel (boron carbide and diamond) degrader materials are provided and evaluated against semi-analytical models of multiple Coulomb scattering. The results showing a potential in emittance reduction for novel materials are presented and discussed in detail., SCOPUS: cp.p, info:eu-repo/semantics/published

Purpose: In IOERT breast treatments, a shielding disk is frequently used to protect the underlying healthy structures. The disk is usually composed of two materials, a low-Z material intended to be oriented towards the beam and a high-Z material. As tissues are repositioned around the shield before treatment, the disk is no longer visible and its correct alignment with respect to the beam is guaranteed. This paper studies the dosimetric characteristics of four possible clinical positioning scenarios of the shielding disk. A new alignment method for the shielding disk in the beam is introduced. Finally, it suggests a new design for the shielding disk. Methods: As the first step, the IOERT machine “Mobetron 1000” was modeled by using Monte Carlo simulation, tuning the MC model until an excellent match with the measured PDDs and profiles was achieved. Four possible shielding disk positioning scenarios were considered, determining the dosimetric impact. Furthermore, in our center, to prevent beam misalignment, we have developed a shielding disk equipped with guiding rods. Having ascertained a correct alignment between the disk and the beam, we can propose a new internal design of the shielding disk that can improve the dose distribution with a better coverage of the treated area. Results: All MC simulations were performed with a 12 MeV beam, the maximum energy of Mobetron 1000 and a 5.5 cm diameter flat tip applicator, this applicator being the most clinically used. The simulations were compared with measurements performed in a water phantom and showed good results within 2.2% of root mean square difference (RMSD). The misplacement positions of the shielding disk have dosimetric impacts in the treatment volume and a small translation could have a significant influence on healthy tissues. The D-scenario is the worst which could happens when the shielding disk is flipped upside down, giving up to 144% dose instead of 90% at the surface of the Pb/Al shielding disk. A new s, SCOPUS: ar.j, info:eu-repo/semantics/published

The activation of concrete is a real problem from the point of view of waste management. Because of the complexity of the issue, Monte Carlo (MC) codes have become an essential tool to its study. But various codes or even nuclear models exist in MC. MCNPX and PHITS have already been validated for shielding studies but GEANT4 is also a suitable solution. In these codes, different models can be considered for a concrete activation study. The Bertini model is not the best model for spallation while BIC and INCL model agrees well with previous results in literature., SCOPUS: ar.j, info:eu-repo/semantics/published

This paper describes a multi-scale approach for the modelling of the degradation of model cement pastes using reactive transport. It specifically aims at incorporating chemistry-transport feedback results from a pore-scale approach into a continuum description. Starting from a numerical representative elementary volume of the model cement paste, which was built according to extensive experimental dedicated chacarterizations, this paper provides three separate descriptions of two different degradations: leaching and carbonation. First, 2D pore-scale simulations are performed and predict degradation depths in very good agreement with experiments. Second, 3D pore scale descriptions of how the microstructre evolves provides accurate description of the evolution of transport properties through degradation. Finally, those latter results are incorporated as a feedback law between porosity and effective diffusion coefficient into a 1D continuum approach of reactive transport. This paper provides pore-scale explanations of why reactive transport modelling has encountered mitigated success when applied to cementitious materials, especially during carbonation or degradations consisting of precipitation reactions. In addition to that, different degradation modellings are in very good agreement with experimental observations., SCOPUS: ar.j, info:eu-repo/semantics/published

Cementitious materials are widely used in the concepts of radioactive waste disposal facilities. During the lifetime of these disposals, those materials will undergo physicochemical degradations. To assess their impacts, reactive transport modelling is used. Reactive transport codes modify the transport properties based on the modelled porosity evolution by using Archie's law as a feedback between porosity and diffusive properties. These laws are not suited to cementitious materials, whose pore structure is complex and expands over a wide range of pore sizes. The ultimate goal of this research is about developing a microstructure-based feedback relation for the diffusive properties of complex porous structures such as cementitious ones. Therefore, we developed an algorithm designed to generate numerical microstructures representative of simplified cement pastes and performed an experimental campaign consisting of dedicated experiments. A random-walk algorithm is used to compute the effective diffusion coefficients of our numerical microstructures. This paper investigates the description of the initial numerical microstructure and how transport properties are sensitive to different microstructural features that can be controlled from the designed algorithm. Simulations both on the experimental microtomograph and the generated microstructures allow to show that our models are complete to describe the microstructure and diffusion transport property of simplified cementitious materials. Sensitivity analysis is also provided, whose results show that a simple feedback relation cannot properly describe these transport properties. This gives confidence in our approach and its future extension toward the description of cementitious material degradations., SCOPUS: ar.j, info:eu-repo/semantics/published

Au vu de leurs différentes propriétés, les matériaux cimentaires sont largement considérés dans les différents projets de gestion de déchets radioactifs. Leurs propriétés mécaniques, leurs faibles coefficients de transport ainsi que leur capacité à fixer les principaux radionucléides sont les principaux avantages qui en font un des meilleurs choix pour la conception des barrières ouvragées.Pour les études de sûreté, leur durabilité est capitale. Au cours de la vie d’un tel dépôt,via l’infiltration d’eau ou les interfaces chimiquement agressives avec les argiles, les différents matériaux vont subir des perturbations physicochimiques qui vont altérer leurs structures et potentiellement compromettre leurs fonctions de sûreté. L’étendue de ces perturbations, fondamentale pour l’étude de sûreté, est contrôlée par les propriétés de transport de ces matériaux.Pour modéliser proprement ces phénomènes, il faut pouvoir coupler les évolutions géochimiques des matériaux tout en évaluant le transport à travers ceux-ci. C’est le but de différents codes de transport réactif, qui utilisent une loi de rétroaction pour modifier les propriétés de transport lors d’une modification de microstructure. Le problème est qu’il n’existe pas de loi de rétroaction adaptée aux matériaux cimentaires, qui possèdent une structure poreuse complexe du nanomètre jusqu’à plusieurs micromètres. En général, des lois empiriques de type Archie sont utilisées. Toutefois, même l’utilisation de lois plus sophistiquées ne permet pas de reproduire sensiblement les évolutions liées à la structure porale. Cette loi de rétroaction est probablement la principale raison pour laquelle les résultats de simulation ont du mal à reproduire lesrésultats expérimentaux. Le but de cette thèse est de proposer une meilleure loi de rétroaction et de l’intégrer dans un code de transport réactif.Pour ce faire, trois approches complémentaires ont été mises en oeuvre. La première, expérimentale,consiste en la réalisation des matéri, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

The safeguards verification of spent nuclear fuel is one of the major concern for the safeguards community, as this material represents about 80% of all material placed under safeguards.This PhD thesis described the development of two passive non-destructive assay (NDA) techniques: the Self-Indication Neutron Resonance Densitometry (SINRD) and the Partial Defect Tester (PDET).The NDA methods were investigated with Monte Carlo simulations and the benchmark experiments for SINRD were performed at the GELINA facility of JRC-IRMM in Geel, Belgium.The results for the SINRD technique showed promising results for the direct quantification of 239Pu in spent fuel, and both techniques gave encouraging results for the detection of partial defects., Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

Proton therapy uses proton beams with energies of 70 – 230 MeV to treat cancerous tumours very effectively, while preserving surrounding healthy tissues as much as possible. During nuclear interactions of these protons with matter, secondary neutrons can be produced. These neutrons can have energies ranging up to the maximum energy of the protons and can thus be particularly difficult to attenuate. In fact, the rooms of a proton therapy facility are generally surrounded by concrete walls of at least ~2 m in thickness, in order to protect the members of the staff and the public from the stray radiation. Today, the design of the shielding walls is generally based on Monte Carlo simulations. Amongst the numerous parameters on which these simulations depend, some are difficult to control and are therefore selected in a conservative manner. Despite these conservative choices, it remains important to carry out accurate neutron dose measurements inside proton therapy facilities, in order to assess the effectiveness of the shielding and the conservativeness of the simulations. There are, however, very few studies in literature which focus on the comparison of such simulations with neutron measurements performed outside the shielding in proton therapy facilities. Moreover, the published measurements were not necessarily acquired with detectors that possess a good sensitivity to neutrons with energies above 20 MeV, while these neutrons actually give an important contribution to the total dose outside the shielding. A first part of this work was dedicated to the study of the energy response function of the WENDI-2, a rem meter that possesses a good sensitivity to neutrons of more than 20 MeV. The WENDI-2 response function was simulated using the Monte Carlo code MCNPX and validation measurements were carried out with 252Cf and AmBe sources as well as high-energy quasi-monoenergetic neutron beams. Then, WENDI-2 measurements were acquired inside and outside four rooms of the pro, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

We define the interface excitation parameter (IEP) as the change in excitation probability, caused by the presence of a medium-medium interface crossed by an electron, in comparison with an electron for which only bulk excitations are considered. This definition is established by analogy with the definition of the surface excitation parameter for which one of the two media of the interface is the vacuum and which has already been extensively studied. To calculate the IEP (as well as the energy-differential IEP or DIEP), we generalize the model developed by Tung, Chen, Kwei and Chou [C. J. Tung, Y. F. Chen, C. M. Kwei and T. L. Chou, Phys. Rev. B 49 (1994) 16684] from dielectric response theory for surface excitation parameter determination. We perform these calculations for angles between 0o and 60o, for electron energies between 200 and 3000eV and for various combinations of materials, chosen for their academic (as Al/In) or practical interest (as SiO2/Si for instance). We show that for materials with “similar” dielectric properties (metal/metal), the IEP is completely negligible. On the contrary when the materials of the interface are characterized by a large energy band gap difference, as metal/insulator or semiconductor/insulator, the IEP can reach a value of about 0.26 for the smallest electron energies considered here. Moreover, we show that for the SiO2/Si interface, the energy-differential IEP obtained from our model is in good agreement with previous experimental data. Copyright © 2015 John Wiley & Sons, Ltd., SCOPUS: cp.j, info:eu-repo/semantics/published

The energy loss function (ELF) is a key parameter for the calculations of energy losses undergone by electrons in matter. It is often the only input in the calculations performed within the models based on the semi-classical dielectric response theory. Its perfect knowledge is thus of primordial importance. To evaluate the ELF, it is usual to consider as a model an expansion in Drude-Lindhard (DL) type oscillators with fixed values of the strength, width, energy and dispersion for the various oscillators. However, for materials that are characterized by a single sharp oscillator as aluminium or indium, it has been shown [Phys. Rev. B 46 (1992) 2486] that the damping parameter that corresponds in the DL model to the width of the oscillator increases for decreasing incident electron energy. To emphasize this effect, we perform in this work systematic calculation of the ELF for an indium target and for incident electron energies between 200 and 2000-eV. The ELF is determined by comparing REELS (reflection electron energy loss spectroscopy) experimental inelastic electron scattering cross sections with cross sections calculated within the semi-classical dielectric response model, which is implemented in the QUEELS-ε(k,ω)-REELS software (Quantitative analysis of Electron Energy Losses at Surfaces) [Surf. Interface Anal. 36 (2004) 824]. We also perform measurements and calculations for varying incident and exit angles of the electron, namely for angles to the surface normal between 15o and 75o, to check the validity of our results for all geometries. Our results show that the damping parameter of indium in the DL model for electron energy of 200-eV is three times larger than for energy of 2000-eV. Copyright © 2014 John Wiley & Sons, Ltd., SCOPUS: ar.j, FLWIN, info:eu-repo/semantics/published

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Inside an IBA proton therapy centre, secondary neutrons are produced due to nuclear interactions of the proton beam with matter mainly inside the cyclotron, the beam line, the treatment nozzle and the patient. Accurate measurements of the neutron ambient dose equivalent H*(10) in such a facility require the use of a detector that has a good sensitivity for neutrons ranging from thermal energies up to 230 MeV, such as for instance the WENDI-2 detector. WENDI-2 measurements have been performed at the Westdeutsches Protonentherapiezentrum Essen, at several positions around the cyclotron room and around a gantry treatment room operated in two different beam delivery modes: Pencil Beam Scanning and Double Scattering. These measurements are compared with Monte Carlo simulation results for the neutron H*(10) obtained with MCNPX 2.5.0 and GEANT4 9.6., SCOPUS: ar.j, info:eu-repo/semantics/published

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Inside an IBA proton therapy centre, secondary neutrons are produced due to nuclear interactions of the proton beam with matter mainly inside the cyclotron, the beam line, the treatment nozzle and the patient. Accurate measurements of the neutron ambient dose equivalent H*(10) in such a facility require the use of a detector that has a good sensitivity for neutrons ranging from thermal energies up to 230 MeV, such as for instance the WENDI-2 detector. WENDI-2 measurements have been performed at the Westdeutsches Protonentherapiezentrum Essen, at several positions around the cyclotron room and around a gantry treatment room operated in two different beam delivery modes: Pencil Beam Scanning and Double Scattering. These measurements are compared with Monte Carlo simulation results for the neutron H*(10) obtained with MCNPX 2.5.0 and GEANT4 9.6., SCOPUS: ar.j, info:eu-repo/semantics/published

Over the last few decades, radiotherapy using high-energy proton beams over the range from 50 MeV to 250 MeV has been increasingly used and developed. Indeed, it offers the possibility to focus the dose in a very narrow area around the tumor cells. The tumor control is improved compared to radiotherapy using photon beams and the healthy cells around the tumor are not irradiated since the range of charged particles is limited. However, due to nuclear reactions of the incident charged particles in the tissue, secondary high-energy radiations, essentially photons and neutrons, are produced and irradiate the treatment room.As a consequence, thick concrete shielding walls are placed around the treatment room to ensure that other people and workers received a dose as small as possible. The dose measurement is performed with specific dosemeters such as the WENDI-II, which gives a conservative estimation of the ambient dose equivalent up to 5 GeV. The dose in working areas may also be estimated by means of numerical calculations by using simulation codes of particle transport such as the GEANT4, MCNPX, FLUKA and PHITS Monte Carlo codes.Secondary particle yields calculated with Monte Carlo codes show discrepancies when different physical models are used but are globally in good agreement with experimental data from the literature. Neutron and photon doses decrease exponentially through concrete shielding wall but the neutron dose is definitely the main component behind a wall with sufficient thickness. Shielding parameters, e.g. attenuation coefficients, vary as functions of emission angle (regarding the incident beam direction), incident proton energy, and target material and composition.The WENDI-II response functions computed by using different hadronic models show also some discrepancies. Thermal treatment of hydrogen in the polyethylene composing the detector is also of great importance to calculate the correct response function and the detector sensitivity., Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

Structural and biochemical studies of the orf12 gene product (ORF12) from the clavulanic acid (CA) biosynthesis gene cluster are described. Sequence and crystallographic analyses reveal two domains: a C-terminal penicillin-binding protein (PBP)/beta-lactamase-type fold with highest structural similarity to the class A beta-lactamases fused to an N-terminal domain with a fold similar to steroid isomerases and polyketide cyclases. The C-terminal domain of ORF12 did not show beta-lactamase or PBP activity for the substrates tested, but did show low-level esterase activity towards 3'-O-acetyl cephalosporins and a thioester substrate. Mutagenesis studies imply that Ser173, which is present in a conserved SXXK motif, acts as a nucleophile in catalysis, consistent with studies of related esterases, beta-lactamases and d-Ala carboxypeptidases. Structures of wild-type ORF12 and of catalytic residue variants were obtained in complex with and in the absence of clavulanic acid. The role of ORF12 in clavulanic acid biosynthesis is unknown, but it may be involved in the epimerization of (3S,5S)-clavaminic acid to (3R,5R)-clavulanic acid.

Structural and biochemical studies of the orf12 gene product (ORF12) from the clavulanic acid (CA) biosynthesis gene cluster are described. Sequence and crystallographic analyses reveal two domains: a C-terminal penicillin-binding protein (PBP)/beta-lactamase-type fold with highest structural similarity to the class A beta-lactamases fused to an N-terminal domain with a fold similar to steroid isomerases and polyketide cyclases. The C-terminal domain of ORF12 did not show beta-lactamase or PBP activity for the substrates tested, but did show low-level esterase activity towards 3'-O-acetyl cephalosporins and a thioester substrate. Mutagenesis studies imply that Ser173, which is present in a conserved SXXK motif, acts as a nucleophile in catalysis, consistent with studies of related esterases, beta-lactamases and d-Ala carboxypeptidases. Structures of wild-type ORF12 and of catalytic residue variants were obtained in complex with and in the absence of clavulanic acid. The role of ORF12 in clavulanic acid biosynthesis is unknown, but it may be involved in the epimerization of (3S,5S)-clavaminic acid to (3R,5R)-clavulanic acid.

Structural and biochemical studies of the orf12 gene product (ORF12) from the clavulanic acid (CA) biosynthesis gene cluster are described. Sequence and crystallographic analyses reveal two domains: a C-terminal penicillin-binding protein (PBP)/beta-lactamase-type fold with highest structural similarity to the class A beta-lactamases fused to an N-terminal domain with a fold similar to steroid isomerases and polyketide cyclases. The C-terminal domain of ORF12 did not show beta-lactamase or PBP activity for the substrates tested, but did show low-level esterase activity towards 3'-O-acetyl cephalosporins and a thioester substrate. Mutagenesis studies imply that Ser173, which is present in a conserved SXXK motif, acts as a nucleophile in catalysis, consistent with studies of related esterases, beta-lactamases and d-Ala carboxypeptidases. Structures of wild-type ORF12 and of catalytic residue variants were obtained in complex with and in the absence of clavulanic acid. The role of ORF12 in clavulanic acid biosynthesis is unknown, but it may be involved in the epimerization of (3S,5S)-clavaminic acid to (3R,5R)-clavulanic acid.

The WENDI-II rem meter is one of the most popular neutron dosemeters used to assess a useful quantity of radiation protection, namely the ambient dose equivalent. This is due to its high sensitivity and its energy response that approximately follows the conversion function between neutron fluence and ambient dose equivalent in the range of thermal to 5 GeV. The simulation of the WENDI-II response function with the Geant4 toolkit is then perfectly suited to compare low- and high-energy hadronic models provided by this Monte Carlo code. The results showed that the thermal treatment of hydrogen in polyethylene for neutron <4 eV has a great influence over the whole detector range. Above 19 MeV, both Bertini Cascade and Binary Cascade models show a good correlation with the results found in the literature, while low-energy parameterised models are not suitable for this application., Journal Article, SCOPUS: ar.j, info:eu-repo/semantics/published

The WENDI-II rem meter is one of the most popular neutron dosemeters used to assess a useful quantity of radiation protection, namely the ambient dose equivalent. This is due to its high sensitivity and its energy response that approximately follows the conversion function between neutron fluence and ambient dose equivalent in the range of thermal to 5 GeV. The simulation of the WENDI-II response function with the Geant4 toolkit is then perfectly suited to compare low- and high-energy hadronic models provided by this Monte Carlo code. The results showed that the thermal treatment of hydrogen in polyethylene for neutron <4 eV has a great influence over the whole detector range. Above 19 MeV, both Bertini Cascade and Binary Cascade models show a good correlation with the results found in the literature, while low-energy parameterised models are not suitable for this application., Journal Article, SCOPUS: ar.j, info:eu-repo/semantics/published

L'expérience nommée femto-FT-CEAS a été mise en place durant ce travail. Ellecombine une source d'absorption laser femto-opo, une cavité optique haute finesseet un interféromètre à transformée de Fourier. Ce montage instrumental a permisd'enregistrer des spectres sur un domaine de 100 cm−1 avec un coefficient d'absorptionminimal détectable de 5 10−10cm−1 pour des paramètres de résolution spectrale de2 10−2cm−1 et un temps d'enregistrement d'une heure. Le coefficient d'absorptionequivalent par moyenne quadratique par élément spectral correspondant est de 1.210−12cm−1 Hz−1/2. Un chemin optique équivalent de 13 km a été obtenu dans unecellule de 77 cm de long. La gamme spectrale accessible est de 6000 − 6700 cm−1 et7800 − 8300 cm−1.Les spectres enregistrés à l'aide du montage femto-FT-CEAS ont permis d'attribuerplus de 1000 transitions rovibrationelles d'échantillons de CO2 enrichis en 17O,d'OCS, CS2, H12C13CD, et CH3CCH. Les bandes suivantes ont été enrégistrées :pour 12C17O2, les bandes 30013e, 30012e, 30011e, 31113e, 31113f, 31112e, 31112f,et 31111e; pour 17O12C18O, les bandes 30013e, 30012e, et 30011e; pour 16O12C32S,les bandes 540, 0, 501, 0, 511, 1e, 511, 1f, 601, 0, 460, 0, 421, 0, 431, 1e, 431, 1f,521, 0, 341, 0, 351, 1e, 351, 1f, 302, 0, 312, 1e, 312, 1f, 402, 0, 322, 2e, et 322, 2f;pour 16O12C34S, les bandes 501, 0 et 302, 0; pour 16O13C32S, la bande 302, 0 ;pour16O12C33S, la bande 302, 0; pour 12C32S2, les bandes 0403, 0114, 3003 et 2203; pour32S12C34S, la bande 3003. Les conventions de notation vibrationelles utilisées ici sontpour CO2, ν1 ν2 l ν3 n où les bandes vibrationelles perturbées par la résonance deFermi ν1 2ν2 sont ordonnées selon n par ordre décroissant d'énergie. Pour l'OCS,les conventions de notation sont ν1 ν2 ν3, l et pour le CS2, ν1 νl2 ν3. Leur analysespectrale a été réalisée, aboutissant à de nouvelles constantes rovibrationelles ou desconstantes améliorées par rapport, Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

Hard X-ray photoelectron spectroscopy (HXPS) using X-rays in the 1.5-15 keV energy range generated by synchrotron sources becomes an increasingly important analysis technique due to its potential for bulk sensitive measurements. However, besides their high energy, another characteristic of photons generated by synchrotron sources is their linear polarization while X-rays from Al Kα or Mg Kα for instance are unpolarized. This difference implies a possible variation in total path travelled by the photoelectrons generated by the X-rays inside the medium and consequently a modification of the resulting spectrum shape. We show the influence of the polarization on the partial intensity distributions, namely the number of electrons escaping after n inelastic scattering events, for photoelectron with energies of 0.5, 1, 2, 3, 4 and 5 keV and originating from Si 1s 1/2, Cu 1s 1/2, Cu 2p 3/2, Au 4d 3/2 and Au 4f 7/2 subshells. Moreover, we point out the influence of the dipole approximation leading to an underestimation of the partial intensity distributions due to the neglect of the forward-backward asymmetry of the angular photoelectron distribution. © 2011 Elsevier B.V. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Treatments delivered by proton therapy are affected by uncertainties on the range of the beam within the patient, requiring medical physicists to add safety margins on the penetration depth of the beam. To reduce these margins and deliver safer treatments, different projects are currently investigating real-time range control by imaging prompt gammas emitted along the proton tracks in the patient. This study reports on the feasibility, development and test of a new concept of prompt gamma camera using a slit collimator to obtain a one-dimensional projection of the beam path on a scintillation detector. This concept was optimized, using the Monte Carlo code MCNPX version 2.5.0, to select high energy photons correlated with the beam range and detect them with both high statistics and sufficient spatial resolution. To validate the Monte Carlo model, spectrometry measurements of secondary particles emitted by a PMMA target during proton irradiation at 160MeV were realized. An excellent agreement with the simulations was observed when using subtraction methods to isolate the gammas in direct incidence. A first prototype slit camera using the HiCam gamma detector was consequently prepared and tested successfully at 100 and 160MeV beam energies. Results confirmed the potential of this concept for real-time range monitoring with millimetre accuracy in pencil beam scanning mode for typical clinical conditions. If we neglect electronic dead times and rejection of detected events, the current solution with its collimator at 15 cm from the beam axis can achieve a 12mm standard deviation on range estimation in a homogeneous PMMA target for numbers of protons that correspond to doses in water at the Bragg peak as low as 15 cGy at 100MeV and 25 cGy at 160MeV assuming pencil beams with a Gaussian profile of 5mm sigma at target entrance. © 2012 Institute of Physics and Engineering in Medicine., SCOPUS: ar.j, info:eu-repo/semantics/published

Treatments delivered by proton therapy are affected by uncertainties on the range of the beam within the patient, requiring medical physicists to add safety margins on the penetration depth of the beam. To reduce these margins and deliver safer treatments, different projects are currently investigating real-time range control by imaging prompt gammas emitted along the proton tracks in the patient. This study reports on the feasibility, development and test of a new concept of prompt gamma camera using a slit collimator to obtain a one-dimensional projection of the beam path on a scintillation detector. This concept was optimized, using the Monte Carlo code MCNPX version 2.5.0, to select high energy photons correlated with the beam range and detect them with both high statistics and sufficient spatial resolution. To validate the Monte Carlo model, spectrometry measurements of secondary particles emitted by a PMMA target during proton irradiation at 160MeV were realized. An excellent agreement with the simulations was observed when using subtraction methods to isolate the gammas in direct incidence. A first prototype slit camera using the HiCam gamma detector was consequently prepared and tested successfully at 100 and 160MeV beam energies. Results confirmed the potential of this concept for real-time range monitoring with millimetre accuracy in pencil beam scanning mode for typical clinical conditions. If we neglect electronic dead times and rejection of detected events, the current solution with its collimator at 15 cm from the beam axis can achieve a 12mm standard deviation on range estimation in a homogeneous PMMA target for numbers of protons that correspond to doses in water at the Bragg peak as low as 15 cGy at 100MeV and 25 cGy at 160MeV assuming pencil beams with a Gaussian profile of 5mm sigma at target entrance. © 2012 Institute of Physics and Engineering in Medicine., SCOPUS: ar.j, info:eu-repo/semantics/published

Méthodes numériques pour le calcul des valeurs propres les plus à droite des matrices creuses et non-hermitiennes de très grande taille, Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

In a growing number of cutting edge centres around the world, radiotherapy treatments delivered by beams of protons and carbon ions offer the opportunity to target tumours with unprecedented conformality. But a sharper dose distribution increases the need for efficient quality control. Treatments are still affected by uncertainties on the penetration depth of the beam within the patient, requiring medical physicists to add safety margins. To reduce these margins and deliver safer treatments, different projects investigate real time range control by imaging prompt gammas emitted along the proton or carbon ion tracks in the patient.This thesis reports on the feasibility, development and test of a new type of prompt gamma camera for proton therapy. This concept uses a knife-edge slit collimator to obtain a 1-dimensional projection of the beam path on a gamma camera. It was optimized, using the Monte Carlo code MCNPX version 2.5.0, to select high energy photons correlated with the beam range and detect them with both high counting statistics and sufficient spatial resolution for use in clinical routine. To validate the Monte Carlo model, spectrometry measurements of secondary particles emitted by a PMMA target during proton irradiation at 160 MeV were realised. An excellent agreement with the simulations was observed when using subtraction methods to isolate the gammas in direct incidence. A first prototype slit camera using the HiCam gamma detector was consequently prepared and tested successfully at 100 and 160 MeV beam energies. If we neglect electronic dead times and rejection of detected events, the current solution with its collimator at 15 cm from beam axis can achieve a 1-2 mm standard deviation on range estimation in a homogeneous PMMA target for numbers of protons that correspond to doses in water at Bragg peak as low as 15 cGy at 100 MeV and 25 cGy at 160 MeV assuming pencil beams with a Gaussian profile of 5 mm sigma at target entrance.This thesi, Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

Surface excitations significantly influence the measured peak intensities in elastic peak electron spectroscopy. They are characterised by the surface excitation parameter (SEP) defined as the change in excitation probability of an electron caused by the presence of the surface in comparison with an electron moving in an infinite medium. It is thus important to have a large database of SEP values or to have the possibility to determine it with a user-friendly software. Recently, Novák developed the programme Software for Electron Solid Inelastic Interaction Parameter Calculations (SESINIPAC) within the model of Tung, Chen, Kwei and Chou, which allows to determine inelastic mean free path, differential inelastic mean free path, SEP and differential SEP for various energy loss function models and dispersion relations with as only input the energy loss function of the material. Using SESINIPAC, we calculate SEP for 27 different types of materials (metals, semiconductors and insulators) and for various angles and energies. We compare these results with those obtained previously with the software Quantitative Analysis of Electron Energy Losses at Surfaces (QUEELS), which uses the Yubero-Tougaard model. We show that the dependence on angle of emission and energy is quite similar for the two models. However, the absolute values calculated with SESINIPAC are generally larger than those calculated with QUEELS, and the mean relative difference is 20% for metals and semiconductors but exceeds 50% for insulators. Copyright © 2012 John Wiley & Sons, Ltd. Copyright © 2012 John Wiley & Sons, Ltd., SCOPUS: cp.j, FLWIN, info:eu-repo/semantics/published

info:eu-repo/semantics/published

Cette thèse étudie deux aspects d'interaction entre deux joueurs dans le modèle du calcul et de la communication quantique.Premièrement, elle étudie deux primitives cryptographiques quantiques, des briques de base pour construire des protocoles cryptographiques complexes entre deux joueurs, comme par exemple un protocole d'identification.La première primitive est la "mise en gage quantique". Cette primitive ne peut pas être réalisée de manière inconditionnellement sûre, mais il est possible d'avoir une sécurité lorsque les deux parties sont soumises à certaines contraintes additionnelles. Nous étudions cette primitive dans le cas où les deux joueurs sont limités à l'utilisation d'états et d'opérations gaussiennes, un sous-ensemble de la physique quantique central en optique, donc parfaitement adapté pour la communication via fibres optiques. Nous montrons que cette restriction ne permet malheureusement pas la réalisation de la mise en gage sûre. Pour parvenir à ce résultat, nous introduisons la notion de purification intrinsèque, qui permet de contourner l'utilisation du théorème de Uhlman, en particulier dans le cas gaussien.Nous examinons ensuite une primitive cryptographique plus faible, le "tirage faible à pile ou face", dans le modèle standard du calcul quantique. Carlos Mochon a donné une preuve d'existence d'un tel protocole avec un biais arbitrairement petit. Nous donnons une interprétation claire de sa preuve, ce qui nous permet de la simplifier et de la raccourcir grandement.La seconde partie de cette thèse concerne l'étude de méthodes pour prouver des bornes inférieures dans le modèle de la complexité en requête. Il s'agit d'un modèle de complexité central en calcul quantique dans lequel de nombreux résultats majeurs ont été obtenus. Dans ce modèle, un algorithme ne peut accéder à l'entrée uniquement qu'en effectuant des requêtes sur chacune des variables de l'entrée. Nous considérons une extension de ce modèle dans lequel un algor, Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/nonPublished

Cette thèse étudie deux aspects d'interaction entre deux joueurs dans le modèle du calcul et de la communication quantique.Premièrement, elle étudie deux primitives cryptographiques quantiques, des briques de base pour construire des protocoles cryptographiques complexes entre deux joueurs, comme par exemple un protocole d'identification.La première primitive est la "mise en gage quantique". Cette primitive ne peut pas être réalisée de manière inconditionnellement sûre, mais il est possible d'avoir une sécurité lorsque les deux parties sont soumises à certaines contraintes additionnelles. Nous étudions cette primitive dans le cas où les deux joueurs sont limités à l'utilisation d'états et d'opérations gaussiennes, un sous-ensemble de la physique quantique central en optique, donc parfaitement adapté pour la communication via fibres optiques. Nous montrons que cette restriction ne permet malheureusement pas la réalisation de la mise en gage sûre. Pour parvenir à ce résultat, nous introduisons la notion de purification intrinsèque, qui permet de contourner l'utilisation du théorème de Uhlman, en particulier dans le cas gaussien.Nous examinons ensuite une primitive cryptographique plus faible, le "tirage faible à pile ou face", dans le modèle standard du calcul quantique. Carlos Mochon a donné une preuve d'existence d'un tel protocole avec un biais arbitrairement petit. Nous donnons une interprétation claire de sa preuve, ce qui nous permet de la simplifier et de la raccourcir grandement.La seconde partie de cette thèse concerne l'étude de méthodes pour prouver des bornes inférieures dans le modèle de la complexité en requête. Il s'agit d'un modèle de complexité central en calcul quantique dans lequel de nombreux résultats majeurs ont été obtenus. Dans ce modèle, un algorithme ne peut accéder à l'entrée uniquement qu'en effectuant des requêtes sur chacune des variables de l'entrée. Nous considérons une extension de ce modèle dans lequel un algor, Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/nonPublished

Relations between propagators and Greenfunctions of Hamiltonians which are SUSY partners have been obtained. New exact propagators for the family of multi-well, time-dependent and non-hermitian potentials have been calculated.Non-conservative SUSY transformation has been studied inthe case of multichannel Schrodinger equation with different thresholds. Spectrum (bound/virtual states and resonances) of thenon-conservative SUSY partner of zero potential has been founded. Exactly solvable model of the magnetic induced Feshbach resonancehas been constructed. This model was tested in the case of Rb$^{85}$.Conservative SUSY transformations of the first and the second order have been studied in the case of multichannel Schrodinger equation with equal thresholds. Transformations which introduce non-trivial coupling between scattering channels have been founded. The first order SUSY transformation which preserves $S$-matrix eigen-phase shifts andmodifies mixing parameter has been founded in the case of two channel scattering with partial waves of different parities. In the case of coinciding parities we have found the second order SUSY transformation which preserves $S$-matrix eigen-phase shifts and modifies mixing parameter. Phenomenological two channel $^3S_1-^3D_1$neutron-proton potential has been obtained by using single channel, phase equivalent and coupling SUSY transformations applied to zero potential., Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

Relations between propagators and Greenfunctions of Hamiltonians which are SUSY partners have been obtained. New exact propagators for the family of multi-well, time-dependent and non-hermitian potentials have been calculated.Non-conservative SUSY transformation has been studied inthe case of multichannel Schrodinger equation with different thresholds. Spectrum (bound/virtual states and resonances) of thenon-conservative SUSY partner of zero potential has been founded. Exactly solvable model of the magnetic induced Feshbach resonancehas been constructed. This model was tested in the case of Rb$^{85}$.Conservative SUSY transformations of the first and the second order have been studied in the case of multichannel Schrodinger equation with equal thresholds. Transformations which introduce non-trivial coupling between scattering channels have been founded. The first order SUSY transformation which preserves $S$-matrix eigen-phase shifts andmodifies mixing parameter has been founded in the case of two channel scattering with partial waves of different parities. In the case of coinciding parities we have found the second order SUSY transformation which preserves $S$-matrix eigen-phase shifts and modifies mixing parameter. Phenomenological two channel $^3S_1-^3D_1$neutron-proton potential has been obtained by using single channel, phase equivalent and coupling SUSY transformations applied to zero potential., Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

De nombreux noyaux atomiques et hypernoyaux se modélisent comme des structures à trois corps. C'est le cas, par exemple, de noyaux à halo, comme 6He, ou de noyaux stables, comme 12C et 9Be. En effet, 6He se caractérise comme un système à trois corps, formé d'un coeur (une particule alpha) et de deux neutrons de valence faiblement liés. Le noyau de 12C peut s'étudier comme un système lié formé de trois particules alphas, tandis que 9Be peut être décrit comme la liaison de deux particules alphas et d'un neutron.Dans les exemples précédents, les particules alphas sont des amas de nucléons. Elles possèdent donc une structure interne dont il faut tenir compte en raison du principe de Pauli.Les modèles les plus réalistes pour décrire les structures à trois corps sont les modèles "microscopiques". Ces modèles prennent en compte explicitement tous les nucléons et respectent exactement le principe d'antisymétrisation de Pauli. Cependant, l'application de ces modèles est fortement limitée en pratique, car ils exigent de trop nombreux et trop longs calculs.Par conséquent, pour simplifier considérablement les calculs et permettre l'étude des structures à trois corps, des modèles moins détaillés, de type "semi-microscopiques", sont également développés. Dans ces modèles, on représente les amas de nucléons comme de simples particules ponctuelles. Dans ce cas, la modélisation consiste à construire les potentiels effectifs entre les amas, puis à les employer dans les modèles à trois corps.Dans ce travail, nous avons développé les modèles "semi-microscopiques à trois corps". Les potentiels effectifs entre amas sont directement déduits des forces entre nucléons (selon la RGM à 2 corps). Ces potentiels sont "non-locaux", et dépendent des énergies des amas qui interagissent. Ils permettent de simuler le principe de Pauli et les échanges de nucléons entre les amas. La dépendance en l'énergie se révèle être un inconvénient dans les modèles à trois corps. Les poten, Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/nonPublished

De nombreux noyaux atomiques et hypernoyaux se modélisent comme des structures à trois corps. C'est le cas, par exemple, de noyaux à halo, comme 6He, ou de noyaux stables, comme 12C et 9Be. En effet, 6He se caractérise comme un système à trois corps, formé d'un coeur (une particule alpha) et de deux neutrons de valence faiblement liés. Le noyau de 12C peut s'étudier comme un système lié formé de trois particules alphas, tandis que 9Be peut être décrit comme la liaison de deux particules alphas et d'un neutron.Dans les exemples précédents, les particules alphas sont des amas de nucléons. Elles possèdent donc une structure interne dont il faut tenir compte en raison du principe de Pauli.Les modèles les plus réalistes pour décrire les structures à trois corps sont les modèles "microscopiques". Ces modèles prennent en compte explicitement tous les nucléons et respectent exactement le principe d'antisymétrisation de Pauli. Cependant, l'application de ces modèles est fortement limitée en pratique, car ils exigent de trop nombreux et trop longs calculs.Par conséquent, pour simplifier considérablement les calculs et permettre l'étude des structures à trois corps, des modèles moins détaillés, de type "semi-microscopiques", sont également développés. Dans ces modèles, on représente les amas de nucléons comme de simples particules ponctuelles. Dans ce cas, la modélisation consiste à construire les potentiels effectifs entre les amas, puis à les employer dans les modèles à trois corps.Dans ce travail, nous avons développé les modèles "semi-microscopiques à trois corps". Les potentiels effectifs entre amas sont directement déduits des forces entre nucléons (selon la RGM à 2 corps). Ces potentiels sont "non-locaux", et dépendent des énergies des amas qui interagissent. Ils permettent de simuler le principe de Pauli et les échanges de nucléons entre les amas. La dépendance en l'énergie se révèle être un inconvénient dans les modèles à trois corps. Les poten, Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/nonPublished

Nuclear fuel performance is highly affected by the behaviour of fission gases, particularlyat elevated burnups, where large amounts of gas are produced and canpotentially be released. The importance of fission gas release was the motivationfor large efforts, both experimentally and theoretically, in order to increase ourunderstanding of the different steps of the process, and to continuously improveour models.Extensions to higher burnups, together with the growing interest in novel typesof fuels such as inert matrix fuels envisaged for the transmutation of minor actinides,make that one is still looking for a permanently better modelling, basedon a physical understanding and description of all stages of the release mechanism.Computer simulations are nowadays envisaged in order to provide a betterdescription and understanding of atomic-scale processes such as diffusion, but evenin order to gain insight on specific processes that are inaccessible by experimentalmeans, such as the fuel behaviour during thermal spikes.In the present work simulation techniques based on empirical potentials havebeen used, focusing in a first stage on pure uranium dioxide. The behaviour ofpoint defects was at the core of this part, but also the estimation of elastic andmelting properties.Then, in a second stage, the study has been extended to the behaviour of heliumand xenon. For helium, the diffusion in different domains of stoichiometrywas considered. The simulations enabled to determine the diffusion coefficient andthe migration mechanism, using both molecular dynamics and static calculationtechniques. Xenon behaviour has been investigated with the additional intentionto model the behaviour of small intragranular bubbles, particularly their interactionwith thermal spikes accompanying the recoil of fission fragments. For thatpurpose, a simplified description of these events has been proposed, which opensperspect, Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

Ce travail s’inscrit dans le cadre d’étude de la sûreté de fonctionnement.La sûreté de fonctionnement est progressivement devenue partie intégrante de l’évaluation des performances des systèmes industriels. En effet, les pannes d’équipements, les pertes de production consécutives, et la maintenance des installations ont un impact économique majeur dans les entreprises. Il est donc essentiel pour un manager de pouvoir estimer de manière cohérente et réaliste les coûts de fonctionnement de l’entreprise, en tenant notamment compte des caractéristiques fiabilistes des équipements utilisés, ainsi que des coûts induits entre autres par le non-fonctionnement du système et la restauration des performances de ses composants après défaillance.Le travail que nous avons réalisé dans le cadre de ce doctorat se concentre sur un aspect particulier de la sûreté de fonctionnement, à savoir les politiques de remplacement d’équipements basées sur la fiabilité des systèmes qu’ils constituent. La recherche menée part de l’observation suivante :si la littérature consacrée aux politiques de remplacement est abondante, elle repose généralement sur l’hypothèse implicite que les nouveaux équipements envisagés présentent les mêmes caractéristiques et performances que celles que possédaient initialement les composants objets du remplacement.La réalité technologique est souvent bien différente de cette approche, quelle que soit la discipline industrielle envisagée. En effet, de nouveaux équipements sont régulièrement disponibles sur le marché ;ils assurent les mêmes fonctions que des composants plus anciens utilisés par une entreprise, mais présentent de meilleures performances, par exemple en termes de taux de défaillance, consommation d’énergie, " intelligence " (aptitude à transmettre des informations sur leur état de détérioration).De plus, il peut devenir de plus en plus difficile de se procurer des composants de l’ancienne génération pour remplacer ceux qui ont été déclassé, Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/nonPublished

REELS = reflection electron energy loss spectroscopy, info:eu-repo/semantics/nonPublished

11 pages, REELS = reflection electron energy loss spectroscopy, info:eu-repo/semantics/published

info:eu-repo/semantics/nonPublished

Ce travail s’inscrit dans le cadre d’étude de la sûreté de fonctionnement.La sûreté de fonctionnement est progressivement devenue partie intégrante de l’évaluation des performances des systèmes industriels. En effet, les pannes d’équipements, les pertes de production consécutives, et la maintenance des installations ont un impact économique majeur dans les entreprises. Il est donc essentiel pour un manager de pouvoir estimer de manière cohérente et réaliste les coûts de fonctionnement de l’entreprise, en tenant notamment compte des caractéristiques fiabilistes des équipements utilisés, ainsi que des coûts induits entre autres par le non-fonctionnement du système et la restauration des performances de ses composants après défaillance.Le travail que nous avons réalisé dans le cadre de ce doctorat se concentre sur un aspect particulier de la sûreté de fonctionnement, à savoir les politiques de remplacement d’équipements basées sur la fiabilité des systèmes qu’ils constituent. La recherche menée part de l’observation suivante :si la littérature consacrée aux politiques de remplacement est abondante, elle repose généralement sur l’hypothèse implicite que les nouveaux équipements envisagés présentent les mêmes caractéristiques et performances que celles que possédaient initialement les composants objets du remplacement.La réalité technologique est souvent bien différente de cette approche, quelle que soit la discipline industrielle envisagée. En effet, de nouveaux équipements sont régulièrement disponibles sur le marché ;ils assurent les mêmes fonctions que des composants plus anciens utilisés par une entreprise, mais présentent de meilleures performances, par exemple en termes de taux de défaillance, consommation d’énergie, " intelligence " (aptitude à transmettre des informations sur leur état de détérioration).De plus, il peut devenir de plus en plus difficile de se procurer des composants de l’ancienne génération pour remplacer ceux qui ont été déclassé, Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

Nuclear fuel performance is highly affected by the behaviour of fission gases, particularlyat elevated burnups, where large amounts of gas are produced and canpotentially be released. The importance of fission gas release was the motivationfor large efforts, both experimentally and theoretically, in order to increase ourunderstanding of the different steps of the process, and to continuously improveour models.Extensions to higher burnups, together with the growing interest in novel typesof fuels such as inert matrix fuels envisaged for the transmutation of minor actinides,make that one is still looking for a permanently better modelling, basedon a physical understanding and description of all stages of the release mechanism.Computer simulations are nowadays envisaged in order to provide a betterdescription and understanding of atomic-scale processes such as diffusion, but evenin order to gain insight on specific processes that are inaccessible by experimentalmeans, such as the fuel behaviour during thermal spikes.In the present work simulation techniques based on empirical potentials havebeen used, focusing in a first stage on pure uranium dioxide. The behaviour ofpoint defects was at the core of this part, but also the estimation of elastic andmelting properties.Then, in a second stage, the study has been extended to the behaviour of heliumand xenon. For helium, the diffusion in different domains of stoichiometrywas considered. The simulations enabled to determine the diffusion coefficient andthe migration mechanism, using both molecular dynamics and static calculationtechniques. Xenon behaviour has been investigated with the additional intentionto model the behaviour of small intragranular bubbles, particularly their interactionwith thermal spikes accompanying the recoil of fission fragments. For thatpurpose, a simplified description of these events has been proposed, which opensperspect, Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

REELS = reflection electron energy loss spectroscopy, info:eu-repo/semantics/nonPublished

info:eu-repo/semantics/nonPublished

11 pages, REELS = reflection electron energy loss spectroscopy, info:eu-repo/semantics/published

info:eu-repo/semantics/nonPublished