Materiais com luminescência persistente são normalmente baseados em aluminatos e silicatos dopados com íons Eu2+, portanto buscam-se novos materiais com diferentes dopantes. Consequentemente, os materiais BaAl2O4:Eu2+,TR3+ (R: La-Lu) foram preparados pelo método de combustão com temperaturas de ignição entre 400 e 600 °C, assim como pelo método cerâmico a 1500 °C. Os sistemas mais versáteis CdSiO3:TR3+ foram preparados apenas pelo método cerâmico a 950 °C. Para estudar a estrutura e a pureza de fase dos materiais utilizou-se espectroscopia de absorção no infravermelho, difração de raios X (método do pó) e microscopia eletrônica de varredura. Os estados de oxidação e o ambiente ao redor dos íons terras raras foram investigados com a espectroscopia de absorção de raios X com radiação Síncrotron (XANES e EXAFS). As propriedades da luminescência persistente dos fósforos foram investigadas com as técnicas de termoluminescência (TL), fotoluminescência e espectroscopia com radiação Síncrotron na região do UV-UV vácuo. Baseado nas medidas de TL, a estrutura dos defeitos dos materiais BaAl2O4:Eu2+,TR3+ (TR: Nd e Dy) e CdSiO3:TR3+ (TR: Pr, Gd e Tb) mostrou-se ideal para a luminescência persistente a temperatura ambiente. Os espectros de XANES indicaram a presença dos estados divalente e trivalente do Eu dopado na matriz BaAl2O4, enquanto que apenas íons TR3+ co-dopantes foram observados (exceto CeIV). O íon Eu3+ pode estar presente devido ao processo de migração do elétron do íon Eu2+ para a banda de condução durante o processo de excitação. Em contraste, para o sistema CdSiO3:TR3+, foram observadas apenas as espécies trivalentes TR3+, excluindo, portanto, a oxidação direta TR3+→TRIV. Apenas a transição interconfiguracional 4f65d1→4f7 do íon Eu2+ foi observada na luminescência persistente dos materiais BaAl2O4:Eu2+,TR3+. Por outro lado, para a matriz CdSiO3 dopada com íons Pr3+ e Tb3+, apenas as transições 4fn-4fn foram observadas, sem a presença da banda de emissão defeitos observada tanto no espectro de emissão sob excitação no UV como no espectro de luminescência persistente do CdSiO3:Gd3+. O band gap das matrizes BaAl2O4 (6,5 eV) e CdSiO3 (5,28 eV) foi obtido com a espectroscopia de excitação no UV-UV vácuo. A posição dos níveis de energia dos íons TR2+/3+ determinada com o auxílio da banda de transferência de carga ligante metal (LMCT) O2-(2p)Eu3+ confirmou o papel dos elétrons como carregadores de carga no mecanismo da luminescência persistente dos íons Eu2+, Pr3+ e Tb3+. Por fim, os mecanismos da luminescência persistente foram desenvolvidos, e, apesar de serem diferentes, os mecanismos para os íons Eu2+, Tb3+ e Pr3+ apresentaram princípios similares. Esta semelhança confirma a solidez da interpretação dos dados experimentais dos materiais com luminescência persistentes dopados com Eu2+ e encoraja a expansão de modelos similares para outros materiais com luminescência persistente no futuro. Cálculos teóricos com, por exemplo, método DFT poderão no futuro ser utilizados para refinar o modelo, diminuir o trabalho experimental e para descobrir novos modelos para sistemas que o atual modelo não pode ser aplicado, como no caso dos materiais dopados com Eu3+. / Persistent luminescent materials are usually based on Eu2+ doped aluminates or silicates, though novel materials with different dopants are seeked for. Accordingly, BaAl2O4:Eu2+,R3+ (R: La-Lu) materials were prepared by the combustion method with ignition temperatures between 400 and 600 °C as well as with the solid state reaction at 1500 °C. The more versatile CdSiO3:R3+ systems were prepared only with the solid state reaction at 950 °C. Infrared absorption spectroscopy, X-ray powder diffraction and Scanning Electron Microscopy techniques were used to study the structure and phase purity of the materials. The oxidation states of the rare earths and their environment were investigated with synchrotron radiation X-ray absorption spectroscopy (XANES and EXAFS). The persistent luminescence properties of the phosphors were investigated with thermoluminescence (TL), photoluminescence and synchrotron radiation UV-VUV spectroscopy. Based on the TL measurements, the trap structure for BaAl2O4:Eu2+,R3+ (R: Nd and Dy) and CdSiO3:R3+ (R: Pr, Gd and Tb) is ideal for room temperature persistent luminescence. The XANES spectra indicated the presence of both divalent and trivalent europium doped in the BaAl2O4 host, while only trivalent rare earth co-dopants were observed (except CeIV). Eu3+ may be present because of in situ charging of persistent luminescence. In contrast for the CdSiO3:R3+ system, only the trivalent R3+ species were observed, thus excluding the direct R3+→RIV (R: Pr and Tb) oxidation. Only the typical interconfigurational 4f65d1→4f7 transition of Eu2+ ion was observed in the persistent luminescence of BaAl2O4:Eu2+,R3+ materials. On the other hand, for the Pr3+ and Tb3+ doped CdSiO3, only 4fn-4fn transitions were observed with no traces of the defect band emission observed in either the conventional UV excited or persistent luminescence spectra of CdSiO3:Gd3+. The band gap energy for the hosts BaAl2O4 (6.5 eV) and CdSiO3 (5.28 eV) were obtained with the UV-VUV excitation spectroscopy. The R2+/3+ energy levels positions determined with the aid of the O2-(2p)→Eu3+ ligand to metal charge transfer transition (LMCT) confirmed the role of electrons as the charge carriers in the mechanism of Eu2+, Pr3+ and Tb3+ persistent luminescence. Finally, the persistent luminescence mechanisms were constructed and, despite the differences, the mechanisms for Eu2+, Tb3+ and Pr3+ proved to be rather similar. This similarity confirms the solidity of the interpretation of experimental data for the Eu2+ doped persistent luminescence materials and encourages the expansion of similar models for other persistent luminescence materials in the future. Theoretical calculations by e.g. DFT method can be used to refine the model, to decrease experimental work and to find different models for systems where the present model evidently fails, e.g. Eu3+ doped materials.

Les ceintures de radiation de la planète géante Jupiter sont constituées d’électrons, de protons et d’ions lourds de très haute énergie. Ces particules chargées représentent un risque majeur pour les satellites artificiels cherchant à explorer Jupiter. Dans le même temps, comprendre l’origine et la répartition de ces particules est une problématique fondamentale du domaine de la Physique de l’Espace.Le modèle physique Salammbô de l’ONERA répond aux deux enjeux précédents. Il a été développé pour le cas de la planète géante au cours de deux thèses successives qui se sont terminées en 2004 [Santos-Costa, 2001 ; Sicard, 2004]. Les travaux précédents ont permis de mettre en place un modèle d’électron qui s’étend de l’atmosphère de Jupiter jusqu’à l’orbite d’Europe (9 Rj) et un modèle de proton jusqu’à l’orbite de la lune volcanique Io (6 Rj). Depuis cette date, la mission américaine Galileo, qui fut en orbite autour de Jupiter jusqu’en 2003, a livré de nombreuses informations sur les ceintures de radiation et sur l’environnement qui influence celles-ci.Cette thèse revisite le modèle électron et étend le modèle proton jusqu’à l’orbite d’Europe. Cela permet, en particulier, de montrer que les ondes électromagnétiques se propageant entre les orbites des lunes Io et Europe induisent des pertes significatives de particules, celles-ci étant précipitées dans l’atmosphère de Jupiter. Les modèles proposés au cours de cette thèse sont également mieux à même de prédire l’environnement extrême et limitant des ceintures de radiation que les précédents travaux. / The radiation belts of the giant planet Jupiter are populated by very energetic electrons, protons and heavy ions. On one hand, these charged particles represent a major threat to exploration missions. On the other hand, understanding the radiation belt particles origin and distribution is a fundamental question of the broad Space Physics research domain.The physical model Salammbô of ONERA addresses the two previous challenges. It has been developed during two successive previous PhD thesis that ended in 2004 [Santos-Costa, 2001; Sicard, 2004]. Previous work has enabled to predict and study the electrons inward of Europa’s orbit (9 Rj) and the protons inward of the volcanic moon Io (6 Rj). Since 2004, the Galileo mission that was in orbit around Jupiter until 2003 has provided many inputs regarding the Jovian radiation belts and the environment that shape them.This PhD thesis revisits the electron model and expands the proton’s one up to Europa’s orbit. Our modeling effort shows that, in particular, electromagnetic waves propagating between the orbits of the moons Io and Europa create strong particle losses within the radiation belts, as the charged particles are precipitated in the Jovian atmosphere. In addition, our models are better suited than what has been proposed by previous work to predict the harsh radiative environment near Jupiter.STAR

This thesis is focused on the electronic, spin-dependent and dynamical properties of thin magnetic systems. Photoemission-related techniques are combined with synchrotron radiation to study the spin-dependent properties of these systems in the energy and time domains. In the first part of this thesis, the strength of electron correlation effects in the spin-dependent electronic structure of ferromagnetic bcc Fe(110) and hcp Co(0001) is investigated by means of spin- and angle-resolved photoemission spectroscopy. The experimental results are compared to theoretical calculations within the three-body scattering approximation and within the dynamical mean-field theory, together with one-step model calculations of the photoemission process. From this comparison it is demonstrated that the present state of the art many-body calculations, although improving the description of correlation effects in Fe and Co, give too small mass renormalizations and scattering rates thus demanding more refined many-body theories including nonlocal fluctuations. In the second part, it is shown in detail monitoring by photoelectron spectroscopy how graphene can be grown by chemical vapour deposition on the transition-metal surfaces Ni(111) and Co(0001) and intercalated by a monoatomic layer of Au. For both systems, a linear E(k) dispersion of massless Dirac fermions is observed in the graphene pi-band in the vicinity of the Fermi energy. Spin-resolved photoemission from the graphene pi-band shows that the ferromagnetic polarization of graphene/Ni(111) and graphene/Co(0001) is negligible and that graphene on Ni(111) is after intercalation of Au spin-orbit split by the Rashba effect. In the last part, a time-resolved x-ray magnetic circular dichroic-photoelectron emission microscopy study of a permalloy platelet comprising three cross-tie domain walls is presented. It is shown how a fast picosecond magnetic response in the precessional motion of the magnetization can be induced by means of a laser-excited photoswitch. From a comparision to micromagnetic calculations it is demonstrated that the relatively high precessional frequency observed in the experiments is directly linked to the nature of the vortex/antivortex dynamics and its response to the magnetic perturbation. This includes the time-dependent reversal of the vortex core polarization, a process which is beyond the limit of detection in the present experiments. / Diese Dissertation beschäftigt sich mit den elektronischen, spinabhängigen und dynamischen Eigenschaften dünner magnetischer Systeme. Auf dem Photoeffekt basierende Untersuchungsmethoden werden zusammen mit Synchrotronstrahlung eingesetzt, um die spinabhängigen Eigenschaften dieser Systeme im Energie- und Zeitbereich zu untersuchen. Im ersten Teil dieser Arbeit wird mit spin- und winkelaufgelöster Photoemission die Stärke von Elektronenkorrelationseffekten in der spinabhängigen elektonischen Struktur von ferromagnetischerm bcc Fe(110) und hcp Co(0001) untersucht. Die experimentellen Ergebnisse werden verglichen mit theoreteischen Berechnungen im Rahmen der Näherung der Drei-Körper-Streuung und der dynamischen Molekularfeldtheorie, zusammen mit Berechnungen des Photoemissionsprozesses im Rahmen des Ein-Stufen-Modells. Ausgehend von diesem Vergleich wird gezeigt, dass die gegenwärtig fortgeschrittensten Rechnung, obgleich sie die Beschreibung von Korrelationseffekten in Fe und Co verbessern, zu kleine Massenrenormalisierungen und Streuraten ergeben, was zu der Forderung nach verfeinerten Vielteilchentheorien unter Einbeziehung von nichtlokalen Fluktuationen führt. Im zweiten Teil wird unter Kontrolle durch die Photoelektronenspektroskopie im Detail gezeigt, wie Graphen durch chemische Gasphasenabscheidung auf den Übergangsmetall-Oberflächen Ni(111) und Co(0001) aufgebracht und mit einer Monolage Au interkaliert werden kann. Für beide Systeme wird eine lineare E(k)-Dispersion masseloser Dirac-Fermionen im Graphen-pi-Band in der Nähe der Fermi-Energie beobachtet. Spinaufgelöste Photoemission des Graphen-pi-Bandes zeigt, dass die ferromagnetische Polarisation von Graphen/Ni(111) und Graphen/Co(0001) vernachlässigbar ist und dass Graphen/Ni(111) nach Interkalation mit Au eine Spin-Bahn-Aufspaltung aufgrund des Rashba-Effekts zeigt. Im letzten Teil wird eine zeitaufgelöste Studie des Röntgenzirkulardichroismus mit Photoelektronenmikroskopie präsentiert, die an einer Permalloy-Probe durchgeführt wurde, die drei als Stachelwände ausgebildete Domänenwände enthält. Es wird gezeigt, wie eine schnelle magnetische Antwort auf der Pikosekundenskala in der Präzessionsbewegung der Magnetisierung durch einen laserangesteuerten Photoschalter erzeugt werden kann. Durch Vergleich mit einer mikromagnetischen Rechnung wird gezeigt, dass die relativ hohe Präzessionsfrequenz, die im Experiment beobachtet wird, in unmittelbarer Beziehung steht zu den Eigenschaften der Vortex/Antivortex-Dynamik und ihrer Antwort auf die magnetische Störung. Das schließt die zeitabhängige Umkehr der Vortexkernpolarisation ein, einem Vorgang der jenseits der Nachweisgrenze der gegenwärtigen Experimente liegt.

This thesis contains two parts. The first part concerns the research work on free molecules using synchrotron-radiation-related techniques. Auger electron spectra of two free open-shell molecules, O2 and NO, were studied experimentally and theoretically. Photoionization experimental technique with tunable synchrotron radiation source was used to induce core-level electron ionization and obtain the KVV normal Auger electron spectra. A quantitative assignment of O2 normal Auger spectrum was obtained by applying ab initio CI calculations and LVI Auger line shape simulations including the bond length dependence of Auger transition rates. The photon energy dependence of normal Auger electron spectra was focused on with photon energies in the vicinities of core-ionization threshold energies. Consequently, the MAPCI (Molecular Auger Post Collision Interaction) theory was developed. Taking the near-threshold O2 normal Auger spectrum as an example, the two extreme cases of MAPCI effect, “atomic-like PCI” and “molecular PCI”, were discovered and discussed. The effect of shape resonance on near-threshold molecular normal Auger spectrum was discussed taking NO near threshold normal Auger spectra as example. The second part deals with research work on the chemisorption of small epoxy organic molecules, ethylene oxide, methyl oxirane, on Si (100) surfaces. Synchrotron radiation related techniques, UPS, XPS and NEXAFS, were applied. Based on the valence photoemission spectra, C 1s and Si 2p XPS spectra, the epoxy ring opening reactions of these molecules in chemisorption process were proved. Further tentative search for the surface-adsorbate CDAD effect was performed, and no evident circular dichroism was confirmed.

Two innovative radiotherapy (RT) approaches are under development at the ID17 Biomedical Beamline of the European Synchrotron Radiation Facility (ESRF): microbeam radiation therapy (MRT) and minibeam radiation therapy (MBRT). The two main distinct characteristics with respect to conventional RT are the use of submillimetric field sizes and spatial fractionation of the dose. This PhD work deals with different features related to small-field dosimetry involved in these techniques. Monte Carlo (MC) calculations and several experimental methods are used with this aim in mind. The core of this PhD Thesis consisted of the development and benchmarking of an MC-based computation engine for a treatment planning system devoted to MRT within the framework of the preparation of forthcoming MRT clinical trials. Additional achievements were the definition of safe MRT irradiation protocols, the assessment of scatter factors in MRT, the further improvement of the MRT therapeutic index by injecting a contrast agent into the tumour and the definition of a dosimetry protocol for preclinical trials in MBRT.

This thesis concerns multi-ionization coincidence measurements of atoms and small molecules using a magnetic bottle time-of-flight (TOF) spectrometer designed for multi-electron coincidence studies. Also, a time-of-flight mass spectrometer has been used together with the TOF electron  spectrometer for electron-ion coincidence measurements. The multi-ionization processes have been studied by employing a pulsed discharge lamp in the vacuum ultraviolet spectral region and synchrotron radiation in the soft X-ray region. The designs of the spectrometers are described in some detail, and several timing schemes suitable for the light sources mentioned above are presented. Studies have been performed on krypton, molecular oxygen, carbon disulfide and a series of alcohol molecules. For the latter, double ionization spectra have been recorded and new information has been obtained on the dicationic states. A recently found rule-of-thumb  and quantum chemical calculations have been used to quantify the effective distance of the two vacancies in the dications of these molecules. For Kr, O2, and CS2, single-photon core-valence spectra have been obtained at the synchrotron radiation facility BESSY II in Berlin and interpreted on the basis of quantum chemical calculations. These spectra show a remarkable similarity to conventional valence photoelectron spectra. Spectra of triply charged ions were recorded, also at BESSY II, for Kr and CS2 by measuring, in coincidence, all three electrons ejected. The complex transition channels leading to tricationic states were mapped in substantial detail for Kr. It was found that for 3d-ionized krypton, the tricationic states are dominantly populated by cascade Auger decays via distinct intermediate states whose energies have been determined. The triple ionization spectra of CS2 from the direct double Auger effect via S2p, S2s and C1s hole states contain several resolved features and show selectivity based on the initial charge localisation and on the identity of the initial state.

The structure and magnetism of selected compounds of the pnictides iron based superconductors with chemical formula LnO{1-x}FeAsFx (Ln = La,Sm and Ce), commonly known as 1111, and of rare earth iron borates RFe3(BO3)4 (R = Tb, Gd, Nd and Y), were studied by means of hard x-ray diffraction. For the 1111 pnictides compounds, Rietveld refinement of powder x-ray diffraction measurements at room temperature reveals, that the ionic substitution of O by F has no effect on the structure of the FeAs layers of tetrahedra, whereas the major changes takes place in the LnO layer. These changes are reflected as a shrinkage of the crystal lattice, specially in the c direction. Additionally, a study of the temperature dependent structure of the Sm and Ce-1111 compounds was performed and an estimation of the the structural transition temperature was obtained. The results of the structural measurements, combined with electrical resistivity and µSR, were used to construct the Sm and Ce-1111 phase diagrams. These phase diagrams are characterized by two regions, consisting of a spin density wave (SDW) state and a superconducting state, which are sharply separated upon doping. Considering the different Ln ion, upon F doping the transition temperatures are more efficiently suppressed in Ce-1111 as compared to Sm-1111. More intriguingly, for the Ce case, a coexistence region between static magnetism and superconductivity without an orthorhombic distortion has been observed. Further analysis of the width of the Bragg peaks reveals strong lattice fluctuations towards phase transitions, which are reflected in magnetic and transport properties. Moreover, a strong damping of the lattice fluctuations is observed at Tc for superconducting Sm-1111 samples, giving experimental evidence of competing orders towards phase transitions in the iron pnictides. Regarding the iron borates, non-resonant x-ray scattering studies have shown several new diffraction features, from the appearance of additional reflections that violate the reflection conditions for the low temperature crystal structure, to the emerging of commensurate superlattice peaks that appear below TN. A detailed analysis of the structure factors and q dependencies of the earlier reflections, demonstrate their magnetic nature. Additional resonant x-ray magnetic scattering experiments on NdFe3(BO3)4 were performed at the Nd L2,3 and Fe K edges. The results show that the magnetization behavior is different for the Nd and for the Fe sublattices. Moreover, we find that the magnetization of the Nd sublattice is induced by the Fe magnetization. The temperature dependent measurements also show a commensurate to incommensurate transition where the magnetic structure changes from a commensurate collinear structure, where both Nd and Fe moments align in the hexagonal basal plane, to an incommensurate spin helix structure that propagates along c. When a magnetic field is applied, the spin helix is destroyed and a collinear structure is formed where the moments align in a direction perpendicular to the applied magnetic field. Moreover, the critical field at which the spin helix is destroyed is the same field at which the magnetic induced electric polarization is maximum, thus, showing that the spin helix is not at the origin of the electric polarization.

In the framework of this thesis, a simulation model, based on Monte Carlo techniques, was developed for the study of breast imaging using Synchrotron Radiation (SR). The basic core of the model was developed in previous dissertations of our Department for conventional mammography. The existing model was expanded to include SR physical and geometrical characteristics and test the potential of SR for further optimization in breast imaging. The SR model was validated against experimental data from SYRMEP beamline of the Elettra Synchrotron Light Facility. The alterations of the new model comparing to the one for conventional mammography mostly concerned the geometry used (source-to-slit distance 22m), the narrow gaussian almost monoenergetic beam, and the scanning of the region of interest by a uniform movement of the phantom and the detector. Besides the generation of an image, the model was enriched with dose parameters (incident air kerma, backscatter radiation, entrance surface air kerma-Ke), in order to evaluate SR for both image quality and dose. The validation showed excellent results for 16-28 keV, for both image quality (subject contrast-SC) and dose (incident air kerma and corresponding number of photons) indices. In the case of SC, Pearson's correlation R was calculated 0.996, while in the case of dose validation, R was equal to 1. Regarding the backscatter, the validation was based on published data and the deviation did not exceed 2% for 20 keV. The performance of SR was then evaluated with mathematical phantoms designed to simulate difficult imaging tasks; the first experiment concerned a 4cm-thick phantom made of adipose tissue with embedded spheres of PMMA, glandular tissue and water of increasing diameter; the second one concerned a step wedge of 0-75% glandularity in a 5cm-thick background of adipose tissue and small calcifications in each step. The first experiment was used to compare SR energies (16-25 keV) to conventional mammographic spectra (Mo/Mo, Mo/Rh, Rh/Rh, W/Mo, W/Rh, W/Nb and W/Pd at 28 kVp) in terms of SC and CNR (Contrast-to-Noise Ratio). The results demonstrate that there is an energy range where CNR maximized (18-21 keV). The image quality indices are highly affected by the size and composition of the lesion, with PMMA showing a slightly degraded CNR compared to the same size glandular tissue inhomogeneity. SR energies between 18-21 keV demonstrate improved imaging performance compared to conventional spectra. For the second experiment, a Figure of Merit (FOM=CNR^2/Ke), was used as an index of the overall perfomance. The energy on the detector was kept constant at 7μGy for SR energies 19-25 keV (for 20 keV, the corresponding Ke was 1.5mGy). The results showed that the best performance (highest FOM), is observed in higher energies. However, taking into consideration the contrast-detail visibility, the best performance was observed at 21-22 keV. Synchrotron Radiation seems promising for breast imaging, since it shows better performance in cases where conventional mammography faces limitations. However, further exhaustive performance studies, in terms of resolution and dose, are necessary in order to consider it as a reliable alternative for mammographic applications. / Στα πλαίσια της διατριβής αυτής, αναπτύχθηκε ένα μοντέλο προσομοίωσης με βάση τις τεχνικές Monte Carlo για την υπολογιστική μελέτη της εφαρμογής της Ακτινοβολίας Συγχρότρου (ΑΣ) στην απεικόνιση μαστού. Μια βάση για το σχεδιασμό του μοντέλου είχε διαμορφωθεί στο Εργαστήριο Ιατρικής Φυσικής για κλασική μαστογραφία. Το νέο μοντέλο σχεδιάστηκε και πιστοποιήθηκε ως προς την ακρίβεια των αποτελεσμάτων του, με βάση πειραματικές μετρήσεις που πραγματοποιήθηκαν με τη δέσμη SYRMEP του Elettra Synchrotron Light Facility στην Τεργέστη. Οι διαφορές του μοντέλου για ΑΣ σε σχέση με το προηγούμενο που είχε αναπτυχθεί για κλασική μαστογραφία παρατηρήθηκαν κυρίως στη διάταξη (απόσταση πηγής-σχισμής 22m), στη στενή gaussian μορφή της σχεδόν μονοενεργειακής δέσμης, αλλά και στην σάρωση της περιοχής ενδιαφέροντος από τη δέσμη, που πραγματοποιείται στην πράξη με την ομοιόμορφη κίνηση του συστήματος ομοίωμα-ανιχνευτής. Εκτός από τη δημιουργία εικόνας, στο μοντέλο προστέθηκαν και παράμετροι για τον υπολογισμό δοσιμετρικών στοιχείων (προσπίπτον kerma στην επιφάνεια του ομοιώματος, οπισθοσκεδαζόμενη ακτινοβολία, kerma εισόδου στην επιφάνεια του μαστού-Ke), για τη συνολική εκτίμηση της απόδοσης της ΑΣ στην απεικόνιση μαστού. Η πιστοποίηση του μοντέλου ως προς την ακρίβεια των παραγόμενων αποτελεσμάτων είχε εξαιρετικά αποτελέσματα, τόσο για την ποιότητα εικόνας (αντίθεση υποκειμένου-subject contrast), όσο και για τη δόση (προσπίπτον kerma και αντίστοιχος αριθμός φωτονίων). Ο συντελεστής συσχέτισης του Pearson, R, μεταξύ των δεικτών ποιότητας πειραματικής και προσομοιωμένης εικόνας, βρέθηκε 0.996, ενώ στην περίπτωση της επαλήθευσης της δόσης, ο συντελεστής R άγγιξε το 1. Για την οπισθοσκεδαζόμενη ακτινοβολία, η επαλήθευση πραγματοποιήθηκε με βάση βιβλιογραφικά στοιχεία και τα αποτελέσματα έδωσαν απόκλιση μικρότερη του 2% για 20 keV. Στη συνέχεια, πραγματοποιήθηκαν πειράματα προσομοίωσης για την αξιολόγηση της ΑΣ με χρήση μαθηματικών ομοιωμάτων; στο πρώτο πείραμα σχεδιάστηκε ομοίωμα πάχους 4cm από λιπώδη ιστό με σφαιρικές ανομοιογένειες τριών διαφορετικών διαμέτρων και τριών διαφορετικών πυκνοτήτων (PMMA, αδενώδης ιστός και νερό); το δεύτερο πείραμα αφορά σε ομοίωμα αδενώδους ιστού αυξανόμενου πάχους (step wedge) 0-75% glandularity μέσα σε λιπώδη ιστό πάχους 5cm και με ενσωματωμένες αποτιτάνωσεις σε κάθε βήμα. Στο πρώτο πείραμα, συγκρίθηκαν ενέργειες ΑΣ (16-25 keV) με τα συνήθη μαστογραφικά φάσματα (Mo/Mo, Mo/Rh, Rh/Rh, W/Mo, W/Rh, W/Nb and W/Pd) στα 28 kVp ως προς το Subject Contrast (SC) και το Contrast-to-Noise Ratio (CNR). Τα αποτελέσματα έδειξαν ότι υπάρχει ένα εύρος ενεργειών (18-21 keV) όπου το CNR γίνεται βέλτιστο. Οι δείκτες ποιότητας εικόνας εξαρτώνται σημαντικά από το μέγεθος και τη σύνθεση της ανομοιογένειας με το PMMA να εμφανίζει ελαφρώς υποβαθμισμένο CNR σε σχέση με το αντίστοιχο μέγεθος ανομοιογένειας από αδενώδη ιστό. Οι ενέργειες ΑΣ στο εύρος 18-21 keV παρουσίασαν καλύτερη απόδοση από τα συμβατικά φάσματα. Για το δεύτερο πείραμα, χρησιμοποιήθηκε ένας δείκτης συνολικής απόδοσης (Figure of Merit - FOM=CNR^2/Ke). Για εύρος ενεργειών 19-25 keV, διατηρήθηκε σταθερή η ενέργεια στον ανιχνευτή (7 μGy), που αντιστοιχεί σε Ke=1.5mGy για 20 keV. Τα αποτελέσματα έδειξαν ότι την καλύτερη απόδοση (υψηλότερο FOM) παρουσίασαν οι υψηλότερες ενέργειες ΑΣ. Λαμβάνοντας όμως υπόψη και την ανιχνευσιμότητα των αποτιτανώσεων, η καλύτερη απόδοση παρατηρήθηκε στα 21-22 keV. Η Ακτινοβολία Συγχρότρου φαίνεται εξαιρετικά υποσχόμενη στην απεικόνιση μαστού, καθώς έχει καλύτερη απόδοση σε περιπτώσεις όπου η συμβατική μαστογραφία παρουσιάζει περιορισμούς. Εντούτοις, πρέπει να υποβληθεί σε περισσότερες μελέτες απόδοσης, ώστε να θεωρηθεί ως αξιόπιστη εναλλακτική για τις μαστογραφικές εφαρμογές.

In this thesis work, the K-shell photoionization of multi-charged ions has been studied as well as the valence photoionization of atomic and small molecular ions. The K-shell photoionization cross sections were measured for nitrogen iso-nuclear series, from N+ to N4+ ions using the ion-photon merged beam technique and the valence photoionization cross sections for Xe+ and Kr+ ions and the small molecular ions CO_2^+ and N_2^+ using both the merged beam and ion trap techniques at the SOLEIL synchrotron radiation facility in Saint-Aubin, France. Combination of the two techniques allows for the measurement of the pure ground state ionization cross section on an absolute scale.The experimental K-shell photoionization cross sections are compared with theoretical results obtained from the multi-configuration Dirac-Fock (MCDF), R-matrix and the Screening Constant by Unit Nuclear Charge (SCUNC) methods. The interplay between experiment and theory enables the identification and characterization of the strong 1s→2p and 1s→3p resonances observed in the spectra. The experimental valence photoionization cross sections for Xe+ and Kr+ ions are compared with MCDF calculations results obtained for the direct photoionization process. The quality of the absolute cross section measurements using the merged beam techniques is strongly dependent on the performance of Electron Cyclotron Resonance Ion Source (ECRIS). In order to improve the current of ions in the interaction region, the ions extraction system and transport was simulated by using IGUN program and ECRopt.

Multiferroic materials with a coupled ordering of electric and magnetic moments could be used to build energy-efficient, magnetic computer memory that is written with an electrical field. To understand the interaction between the magnetic and electric ordering in such materials, two examples, namely yttrium manganate YMn2O5 and neodymium iron borate NdFe3(BO3)4, are studied by means of resonant x-ray diffraction. The important role of a pure electronic contribution to the ferroelectric polarization is shown in YMn2O5. Furthermore, substitution of Fe can change the magnetic order of YMn2O5 from antiferromagnetic into ferrimagnetic, allowing the storage of easily readable magnetic information. Therefore the change of the magnetic structure upon small Fe substitution is studied. Although most of the magnetic structure of the parent compound is kept, the Fe moments have larger components along the c-direction. In NdFe3(BO3)4 the microscopic origin of the magnetoelectric coupling is addressed as the consequence of the frustration of the Fe and Nd magnetic sublattices. The application of an electrical field shifts the balance from the helical to the collinear magnetic domains, revealing again the strong magnetoelectric coupling. / Multiferroische Materialien mit einer starken magnetoelektrischen Kopplung können als energieeffizienter, magnetischer Speicher benutzt werden, welcher mit einem elektrischen Feld geschrieben wird. Um die Wechselwirkung der elektrischen mit der magnetischen Ordnung in solchen Materialien zu verstehen, werden hier zwei Beispiele, nämlich Yttriummanganat YMn2O5 und Neodymeisenborat NdFe3(BO3)4, mit resonanter Röntgenbeugung untersucht. In YMn2O5 wird die wichtige Rolle eines rein elektronischen Beitrags zur ferroelektrischen Polarisation gezeigt. Um die magnetische Struktur von YMn2O5 von antiferromagnetisch zu ferrimagnetisch zu verändern, kann Fe substituiert werden. Dies ermöglicht es, leicht zu lesende, magnetische Informationen zu speichern. Daher wurde die Änderung der magnetischen Struktur bei leichter Fe Substituierung untersucht. Auch wenn die magnetische Struktur von Fe im wesentlichen der magnetischen Struktur von Mn folgt, haben die Fe Momente größere Komponenten entlang der c-Richtung. In NdFe3(BO3)4 wird der Ursprung der starken magnetischen Kopplung als Folge der Frustration des Nd und Fe Untergitters erklärt. Das Anlegen eines elektrischen Feldes führt zur Verschiebung des Gleichgewichts von den helikalen zu den kollinearen magnetischen Domänen, welches wieder die starke magnetoelektrische Kopplung veranschaulicht.