In this thesis, we present a detailed investigation of the electronic properties of particular transition-metal dichalcogenides. Applying electron-energy loss spectroscopy, the connection between the negative plasmon dispersion of tantalum diselenide and the occurrence of a charge-density wave state (CDW) in this compound as well as related materials is observed. Our studies include doping experiments with alkali metal addition altering the charge density of the compounds. This is known to suppress the CDW. We show that it further changes the plasmon dispersion from negative to positive slope. To estimate the doping rate of the investigated tantalum diselenide samples, a density functional theory approach is introduced, giving reliable results for a quantitative analysis of our findings. We refer to a theoretical model to describe the connection of the charge ordering and the plasmon dynamics. Investigations of the non-CDW compound niobium disulfide give further insights into the proposed interaction. Experimental results are further evaluated by a Kramers-Kronig-analysis. A structural analysis, by means of elastic electron scattering, shows the CDW to be suppressed upon doping, giving space for an emerging superstructure related to the introduced K atoms. / In der vorliegenden Arbeit wird eine detaillierte Untersuchung der elektronischen Eigenschaften von ausgewählten Übergangsmetall-Dichalcogeniden präsentiert. Unter Anwendung von Elektronenenergieverlust-Spektroskopie wird die Verbindung der negativen Plasmomendispersion in Tantaldiselenid zum Auftreten eines Ladungsdichtewelle-Zustands (CDW) in diesem und in verwandten Materialien untersucht. Die Untersuchungen schließen Dotierungsexperimente mit dem Zusatz von Alkalimetallen ein, die die Ladungsdichte der Proben beeinflussen. Einerseits unterdrückt dies die CDW. Es wird außerdem gezeigt, dass sich der Anstieg der Plasmonendispersion von negativ zu positiv ändert. Ein Dichtefunktional-Theorie-Zugang zur Abschätzung der Dotierungsraten der untersuchten Tantaldiselenid-Proben wird genutzt, um verlässliche Ergebnisse für die quantitative Analyse unserer Messungen zu erhalten. Ein theoretisches Modell wird einbezogen, welches die Verbindung der Ladungsordung zur kollektiven Anregung der Ladungsdichte beschreibt, Untersuchungen der nicht-CDW Substanz Niobdisulfid geben weitere Einblicke in die Verbindung der beiden Phänomene. Die experimentellen Resultate werden weiterhin mit einer Kramers-Kronig-Analyse ausgewertet. Strukturelle Untersuchungen mit elastischer Elektronenstreuung zeigen, wie die CDW unterdrückt wird und einer auftauchenden Überstruktur, verursacht von den interkalierten K-Atomen, Raum gibt.

No description available.

In the frame of this thesis, a new experimental setup for the measurement of the energy loss of carbon ions at maximum stopping power in a hot laser-generated plasma has been developed and successfully tested. In this parameter range where the projectile velocity is of the same order of magnitude as the thermal velocity of the plasma free electrons, large uncertainties of up to 50% are present in the stopping-power description. To date, no experimental data are available to perform a theory benchmarking. Testing the different stopping theories is yet essential for inertial confinement fusion and in particular for the understanding of the alpha-particle heating of the thermonuclear fuel. Here, for the first time, precise measurements were carried out in a reproducible and entirely characterized beam-plasma configuration. It involved a nearly fully-stripped ion beam probing a homogeneous fully-ionized plasma. This plasma was generated by irradiating a thin carbon foil with two high-energy laser beams and features a maximum electron temperature of 200 eV. The plasma conditions were simulated with a two-dimensional radiative hydrodynamic code, while the ion-beam charge-state distribution was predicted by means of a Monte-Carlo code describing the charge-exchange processes of projectile ions in plasma. To probe at maximum stopping power, high-frequency pulsed ion bunches were decelerated to an energy of 0.5 MeV per nucleon. The ion energy loss was determined by a time-of-flight measurement using a specifically developed chemical-vapor-deposition diamond detector that was screened against any plasma radiation. A first experimental campaign was carried out using this newly developed platform, in which a precision better than 200 keV on the energy loss was reached. This allowed, via the knowledge of the plasma and of the beam parameters, to reliably test several stopping theories, either based on perturbation theory or on a nonlinear T-Matrix formalism. A preliminary analysis suggests that the energy deposition at maximum stopping power is significantly smaller than predicted, particularly, by perturbation approaches.

This doctoral thesis reports analytical and numerical results for the electrostatic response of a dusty plasma to a moving test charge. Two important physical aspects of dusty plasmas, namely grain size distribution and grain charging dynamics were taken into account. In the first case, a dusty plasma in thermal equilibrium and with a distribution of grain sizes is considered. A size distribution is assumed which decreases exponentially with the grain mass for large sizes and gives a simple smooth reduction for small sizes. The electrostatic response to a slowly moving test charge, using a second order approximation is found and the effects of collisions are also investigated. It turns out that for this particular size distribution, there is a remarkably simple result that the resulting effective distribution for the electrostatic response is a kappa (generalized Lorentzian) distribution. In the second case, we present an analytical model for the shielding of a slowly moving test charge in a dusty plasma with dynamical grain charging for cases both with and without the collision effects. The response potential is treated as a power series in test charge velocity. Analytical expressions for the response potential are found up to second order in test charge velocity. The first-order dynamical charging term is shown to be the consequence of the delay in the shielding due to the dynamics of the charging process. It is concluded that the dynamical charging of the grains in a dusty plasma enhances the shielding of a test charge. To clarify the physics, a separate study is made where the charging is approximated by using a time delay. The resulting potential shows the delayed shielding effect explicitly. The terms in the potential that depend on the charging dynamics involve a spatial shift given by the test charge velocity and the charging time. The wake potential of a fast moving test charge in the case of grain charging dynamics was also found. It was observed that the grain charging dynamics leads to a spatial damping and a phase shift in the potential response. Finally, combining these two physical aspects, generalized results for the electrostatic potential were found incorporating the terms from both grain size distribution and grain charging dynamics. The generalized results contain the previous work where these two effects were studied separately and which can now be found as special limiting cases. This kind of work has relevance both in space and astrophysical plasmas. / QC 20100920

This thesis explores theoretical aspects of scanning transmission electron microscopy (STEM) and the comparison of simulation with experiment. / The long standing contrast mismatch problem between theory and experiment in conventional high resolution transmission electron microscopy (HRTEM) is examined using the principle of reciprocity and bright field scanning transmission electron microscopy (BFSTEM). It is found that quantitative agreement between theoretical and experimental images is possible provided that theory suitably accounts for the spatial incoherence of the source, and that experimental images are placed on an absolute scale with respect to the incident beam current. Agreement between theory and experimental image contrast is found to be independent of specimen thickness and probe defocus. / Core-loss electron energy-loss spectroscopy (EELS) is a powerful experimental tool with the potential to provide atomic-resolution information about the electronic structure at defects and interfaces in materials and nanostructures. Interpretation, however, is nonintuitive due to the nonlocal ionization potential. Novel improvements in microscope design and operating environment have enabled two dimensional chemical maps. This has permitted a more thorough theoretical analysis. This thesis compares experimental STEM EELS images of LaMnO3, BiSrMnO3 and Si samples to the relevant theoretical simulations. Image features which at first appear counter intuitive are discussed and explained with the accompanying theoretical simulations. It is demonstrated, using a sample of SrTiO3, that more direct interpretation of atomic resolution chemical maps is possible when using energy dispersive x-ray spectroscopy (EDS) in STEM. / This thesis considers extending chemical mapping in STEM EELS to three dimensions using depth sectioning. It explores, theoretically, the feasibility to depth section zone-axis aligned crystals that contain embedded impurities. In STEM EELS this is found to be possible for point defects but not for larger extended objects such as nanoparticles. / The theory describing the mechanism by which contrast is obtained in elastic scanning confocal electron microscopy (SCEM) is developed. It is shown that there is no first order phase contrast in SCEM and thus low image contrast. Finally, energy filtered scanning transmission electron microscopy (EFSCEM) is developed theoretically. The fundamental equation describing image formation is derived and an efficient computation method is developed to allow the rapid calculation of EFSCEM images.

Un point crucial pour l'avenir de la Physique de Particules est représenté par la mesure de la masse et des paramètres qui gouvernent l'oscillation du neutrino, qui représentent la preuve de Physique au-delà du Model Standard. Depuis 2011, la valeur élevée de l'angle de mélange θ13 a ouvert la voie à l'étude sur la violation de symétrie CP dans le secteur de neutrinos. La nouvelle d'expérience DUNE (Deep Underground Neutrino Experiment) a un potentiel sans précédent pour effectuer une mesure très précise des paramètres d'oscillation de neutrinos. Les grands détecteurs souterrains nécessaires pour ces mesures sont également un milieu idéal pour la recherche sur la désintégration du proton et sur la détection de neutrinos provenant des supernovæ.Les détecteurs utilisés pour ces expériences sont des Chambres à Projection Temporelle (TPC) dont la cible, très massive, est constituée d'Argon liquide. Ce type de détecteur fournit une très bonne résolution de l'image reconstruite, une excellente résolution en énergie et la possibilité d'identifier les particules. Les interactions de neutrino produisent des particules secondaires qui ionisent l'Argon liquide. Les électrons produits par ionisation dérivent sur de longues distances, sous l'effet d'un champ électrique uniforme, jusqu'à rejoindre l‘anode, équipé pour la détection de la charge. Un signal électrique est alors produit et est utilisé pour la reconstruction 3D de l'interaction primaire. La TPC en double phase liquide-gaz permet l'amplification du signal d'ionisation par des avalanches qui se produisent dans la phase gazeuse, au-dessus du niveau de l'Argon liquide. Cette technique améliore les performances de TPC en augmentant son rapport signal-bruit.Le sujet de cette thèse est la reconstruction et l'analyse de la charge de ionisation dans une TPC à Argon liquide : la mesure de la charge déposée par ionisation fournit des informations sur l'énergie cinétique des particules chargées secondaires produites lors de l'interaction de neutrino. De cette manière, il est possible de reconstruire l'énergie du neutrino entrant, de reconnaître et d'exclure les gerbes électromagnétiques produites par la désintégration du π0, puis d'effectuer l'indentification des particules à partir de la mesure des pertes d'énergie par ionisation.La mesure de l'ionisation implique une connaissance approfondie de la réponse du détecteur et de l'algorithme de reconstruction. Afin d'atteindre cette connaissance nous avons effectué une analyse détaillée des pertes d'énergie simulée en étudiant les divergences entre les connaissances théoriques et la simulation. Ensuite, la simulation de la réponse du détecteur a été étudiée, en examinant les effets qui se produisent au cours de la dérive des charges et les effets liés à la réponse de l'instrumentation électronique. Ces effets systématiques qui affectent l'exactitude de l'algorithme de reconstruction sont alors caractérisés par rapport à la génération de Monte-Carlo.Par la suite, nous montrons comment il est possible d'effectuer la rejection du π0 en étudiant les pertes d'énergie. En mesurant les pertes par ionisation au début d'une gerbe électromagnétique, il est possible de comprendre si elle a été produite par un électron ou par un photon. Cela permet d'exclure le bruit dans la détection des produits d'interaction du neutrino électronique fondamental pour la recherche de la violation de CP.Par l'échantillonnage de la trajectoire d'une particule chargée et en mesurant ses pertes d'énergie, il est possible d'identifier sa nature. Une TPC à Argon liquide est également un milieu idéal pour la recherche de la désintégration du proton, en particulier en regardant certaines chaînes de désintégration exclusives, comme p  K + ν. Dans cette thèse, nous montrons ainsi comment il est possible d'identifier des particules à partir de la mesure des pertes d'énergie, et plus abordons plus précisément l'identification des kaons chargés / This is an important period for High Energy Physics: many recent results, including the Higgs discovery and its characterization, confirm the Standard Model. A crucial point for the future of Particle Physics is the study of neutrino masses and mixing representing the first established evidence of physics beyond the SM. Since 2011, the large value of the ?13 mixing angle opened the way to the investigation of CP violation in the neutrino sector. A next generation long baseline neutrino experiment (DUNE) has unprecedented potential to precisely measure the neutrino oscillation parameters, determine the neutrino mass hierarchy and has a very good chance to discover evidence for CP violation in the leptonic sector. The large underground neutrino detectors needed for this task will also address the search for proton decay and the observation of supernovae neutrinos. Giant Liquid Argon Time Projection Chambers (LAr TPCs) will be employed as neutrino targets and detectors. They provide bubble-chamber quality imaging coupled to excellent energy resolution and particles identification capabilities. Neutrino interactions produce secondary particles, which ionize the liquid argon. The ionization electrons drift for long distances along a uniform electric field until they reach finely segmented and instrumented anodes, producing electrical signals that are used for 3D imaging and analysis of the primary interactions. The dual-phase readout technique foresees the amplification of the ionization signal in avalanches occurring in the gas phase above the liquid argon level. This technique further enhances the performance of the LAr TPC by increasing its signal to noise ratio. The subject of thesis is the ionization charge reconstruction and analysis in the dual-phase LAr TPC: the ionization charges measurement provides information about the kinetic energy of secondary charged particles produced in neutrino interactions. In this way, it is possible to reconstruct the incoming neutrino energy, identify and reject electromagnetic shower generated by photons from pi0 decay and perform particles identification from the measurement of the specific ionization losses.The measurement of the ionization implies a detailed knowledge of the detector response and of the reconstruction algorithm. In order to achieve this knowledge a detailed analysis of the simulated energy losses has been performed by studying the differences between the theoretical knowledge and the simulation

No description available.

[pt] A estimação dos fluxos de potência e perdas técnicas nos sistemas de subtransmissão é um grande desafio para as distribuidoras pela importância no planejamento e operação do sistema. Por isso, surge a necessidade de contar com modelos que permitam simular estas grandezas, para o adequado planejamento do sistema. Neste trabalho é proposto e implementado um modelo de estimação de fluxos de potência e perdas técnicas em um sistema de subtransmissão baseado na desagregação de potência da demanda importada da rede de transmissão. A metodologia envolve a determinação de fatores de desagregação por barra associados à importação total de potência, estimação dos fluxos de potência DC usando a matriz de sensibilidade ramo-barra caraterística da rede elétrica e, finalmente, a estimação das perdas elétricas. O sistema IEEE 24 barras foi utilizado para o caso de estudo. Neste caso, a rede elétrica de 230 kV foi tratada como a rede de transmissão e a rede de 138 kV como a rede de subtransmissão. Dados de geração e carga realistas, com base horária e ao longo de um ano, foram utilizados para estimar os parâmetros dos modelos. Para avaliar os resultados, foram utilizadas métricas estatísticas e os resultados foram comparados com um modelo puramente estatístico, que correlaciona a importação total com as potências injetadas em cada barra, os fluxos nas linhas e as perdas totais. Os resultados obtidos indicaram que o modelo proposto ganha importância quando é possível controlar algumas injeções da rede elétrica, tornando-o mais dependente da rede elétrica. / [en] The estimation of the power flows and technical losses in the subtransmission systems is a great challenge for electricity distribution companies because of their importance in the planning and operation of the system. Therefore, there is the increasing need to have models that allow to simulate these variables for the proper planning of the system. In this work, a model of estimation of power flows and technical losses in a subtransmission system is proposed and implemented; this model is based on the power disaggregation of the imported demand from the transmission network. The methodology involves the determination of buses disaggregation factors associated with total power import, estimation of DC power flows using the bus-branch sensitivity matrix of the network and finally the estimation of the electrical losses. The IEEE 24 bus system was used for this study case. In this case, the 230 kV power grid was treated as the transmission network and the 138 kV network as the subtransmission network. Realistic generation and loading data, based on hourly time and over the span of a year, were used to estimate the parameters of the models. In order to evaluate the results, statistical metrics were used and the results were compared with a purely statistical model, which correlates the total imports with the injected power in each bus, line flows and total losses. The obtained results indicate that the proposed model gains importance when it is possible to control some of the injections into the power grid, turning it more dependent of the power grid.

The phenomenon of energy loss that occurs when an ion interacts with matter, also called stopping power, has been investigated for more than a century, and has provided findings of interest. However, reliable procedures for obtaining accurate experimental measurements and a fully theoretical comprehension of the process are tasks still in high demand by the scientific community. Moreover, stopping power data are prerequisites in several applications in modern science, such as engineering, ion implantation and modification of materials, damage to electronics devices (e.g. space radiation), medical physics (e.g. proton therapy), among others. In this thesis we i) develop a rigorous experimental protocol to measure stopping power with high precision, and ii) investigate the collapse of the free electron gas (FEG) model in energy loss of light ions (protons) at a low energy range in transition and rare-earth metals. In the first part, we present an approach to obtain, with high accuracy, the stopping cross sections in the pure materials Al and Mo for protons in the energy range of [0.9 - 3.6] MeV by means of the transmission method. The traceability of the sources of uncertainties are fully evaluated and the final accuracy of the results is 0.63% (0.32% rand. and 0.54% syst.) for Al, and 1.5 % (0.44 % rand. and 1.4% syst.) for Mo, with both results primarily limited by the quality and homogeneity of the stopping foils. For Al, this high accuracy represents an improvement compared to the results obtained in previous studies and serves as a benchmark for our procedure. The most important sources of uncertainties were random - the uncertainty in the peak positions and in the Gaussian fits; and systematic - the non-uniformity thickness of the foils (a special procedure was developed to correct this). Even though the final uncertainty for Mo is higher than for Al, our results improve on the amount of data currently available for the energy range considered. Both data sets are compared with the most commonly employed theoretical models and Monte Carlo codes in the literature. In the second part, electronic stopping cross sections of nontrivial solids, that is, transition and rare earth metals (Ta and Gd) for slow protons are experimentally investigated, and the data were compared with the results for Pt and Au, to understand how energy losses in these metals are correlated with electronic band structures, and to understand the failure of the FEG model predictions. The higher stopping powers found for Ta and Gd cannot be explained by means of the FEG model; however, these effects are successfully correlated with the high density of states (DOS) of both the occupied and unoccupied electronic levels in these metals. For the case of Gd, the experimental data are extended in the energy range until the Bragg\'s peak is reached. The two parts of this thesis were published in Physical Review A 93 022704 (2016), and in Physical Review Letters 18 103401 (2017), respectively. / O fenômeno de perda de energia quando um íon interage com a matéria, também conhecido como poder de freamento, vem sendo investigado por mais de um século, gerando grandes descobertas. Entretanto, conseguir obter medidas experimentais com alta precisão, ou elaborar um completo entendimento teórico dos processos de perda de energia são tarefas extremamente difíceis e ainda muito requeridas pela comunidade científica. Além disso, dados de perda de energia são pré-requisitos em várias aplicações e ramos da ciência moderna, tais como: engenharia, implantação e modificação de materiais, danos em dispositivos eletrônicos (radiação espacial), física médica (próton terapia), etc. Esta tese tem dois focos: i) desenvolver um rigoroso protocolo experimental para medir stopping power com alta precisão e ii) investigar a quebra de validade do modelo de Gás de Elétrons Livres (FEG) para a perda de energia de prótons lentos em metais de transição e terra raras. Na primeira parte apresentamos uma abordagem experimental para obter com alta precisão o poder de freamento em materiais puros (Al e Mo) para prótons no intervalo de energia de [0,9 - 3,6] MeV pelo método de transmissão. A rastreabilidade das fontes de incerteza foi determinada e as incertezas finais encontradas foram: 0,63 % (0,32 % aleat. e 0,54 % sist.) para Al e 1,5 % (0,44 % aleat. e 1,4 % sist.) para Mo, ambas devido a qualidade e homogeneidade das folhas freadoras. Para Al, esta acurácia representa um avanço comparado com publicações anteriores e, assim, serviu como uma referência de nosso procedimento. As mais importantes fontes de incerteza foram: aleatória incerteza das posições dos picos e dos ajustes Gaussianos e sistemática não-uniformidade das folhas-alvo (um procedimento foi desenvolvido para corrigir isso). Embora a incerteza final do Mo é um pouco maior do que do Al, nossos resultados ajudaram a complementar a baixa quantidade de dados disponíveis para o intervalo de energia considerado. Ambos conjuntos de dados foram comparados com os mais comuns modelos teóricos e códigos de Monte Carlo na literatura. Para a segunda parte, poder de freamento em metais não tão comuns tais como transição (Ta) e terras-raras (Gd) para prótons com baixas velocidades foram experimentalmente investigados, e os dados comparados com resultados de Pt e Au, a fim de entender como o stopping power destes metais está correlacionado com as estruturas de bandas eletrônicas, e assim tentar explicar a falha do modelo de FEG. Os altos valores das perdas de energias encontradas para Ta e Gd não puderam ser explicadas pelo modelo de FEG, e portanto foram correlacionados com a densidade de estados (DOS) em ambos os níveis ocupados e não ocupados destes metais. Para o caso do Gd, os dados experimentais foram estendidos em um intervalo de energia até alcançarem o pico de Bragg. A primeira parte desta tese foi publicada na Physical Review A 93 022704 (2016), e a segunda parte na Physical Review Letters 18 103401 (2017).

Submitted by Geandra Rodrigues (geandrar@gmail.com) on 2018-01-19T16:53:31Z No. of bitstreams: 1 humbertovargasduque.pdf: 4514345 bytes, checksum: 706c4aafb25bb9c14ffc14039c8c53d0 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2018-01-24T11:47:55Z (GMT) No. of bitstreams: 1 humbertovargasduque.pdf: 4514345 bytes, checksum: 706c4aafb25bb9c14ffc14039c8c53d0 (MD5) / Made available in DSpace on 2018-01-24T11:47:55Z (GMT). No. of bitstreams: 1 humbertovargasduque.pdf: 4514345 bytes, checksum: 706c4aafb25bb9c14ffc14039c8c53d0 (MD5) Previous issue date: 2016-07-29 / O avanço dos estudos teóricos e experimentais dos processos de interação de radiações ionizantes com o DNA [1]–[7] demonstrou que estas radiações, ao interagirem com sistemas biológicos, podem levar à produção de um número significativo de elétrons secundários. Tais elétrons, por sua vez, ao realizarem colisões inelásticas com biomoléculas, as levam a estados excitados (estados vibracionais e eletrônicos) e à produção de estados ressonantes. Estudos recentes [1], [3], [6] reportam que estes processos têm a real capacidade de causar mutação celular ou necrose, devido à simples e dupla quebra da cadeia de DNA, possuindo, portanto, grande potencialidade danosa a qualquer tecido vivo. Com o intuito de entender melhor estas interações de elétrons de baixa energia com as espécies encontradas em sistemas biológicos, no presente trabalho utilizou-se a Espectroscopia de Perda de Energia de Elétrons para estudar as seções de choque diferenciais (SCD) e integrais (SCI). A região de energias de impacto utilizada foi capaz de promover excitação de níveis vibracionais do tetrahidrofurano (THF) e do álcool α-tetrahidrofurfuril (THFA - α-tetrahydrofurfuryl álcool) e bandas de Rydberg de estados eletrônicos do THFA. Estas espécies moleculares foram escolhidas por serem quimicamente análogas aos anéis de açúcar presentes na estrutura do fosfato-desoxirribose, constituintes do DNA, sendo THFA identificado recentemente, como uma melhor opção análoga à estrutura desoxirribose, quando comparado a sua espécie química semelhante, a molécula de THF. As energias de impacto de elétrons utilizadas para o THFA, foram de 20, 30, 40 e 50eV, enquanto o intervalo angular dos elétrons espalhados foi de 10°- 90°. Já para a molécula de THF, tais energias foram de 15, 20, 30 e 50eV, enquanto que os processos de espalhamento foram estudados na faixa angular de 15º - 90º. Nesse sentido, as SCD’s e SCI’s de THFA, apresentaram sutil diferença das obtidas por Khakoo et al. [8] para THF, em razão de suas propriedades físico-químicas diversas. A importância do momento de dipolo e polarizabilidade das moléculas nos espalhamentos de elétrons foi verificada, principalmente seus reflexos nas SCD’s para os baixos ângulos de espalhamento (≤30°). Foram utilizados, ainda, cálculos teóricos, realizados pela parte teórica deste grupo de pesquisa, para a comparação com os dados experimentais aqui apresentados, obtendo-se excelente concordância, o que levou a comprovação dos modelos utilizados. Ademais, realizou-se a revisão do trabalho de Garland et al. [9], o que demonstrou que a faixa de energia e os poucos modos vibracionais considerados em seu trabalho, derivados de Allan [10], deixam a desejar no que tange a completude dos estudos das propriedades de transporte. A apresentação do trabalho inclui primeiramente os embasamentos teóricos importantes para a análise dos dados obtidos e dos cálculos teóricos realizados. Posteriormente, é apresentado uma descrição do Espectrômetro de Perda de Energia de Elétrons utilizado e a estrutura de análise de dados. Por fim, são apresentados os dados experimentais e teóricos obtidos no trabalho e as discussões. Adicionalmente, é feita uma revisão do conjunto de dados de excitações de estados vibracionais do THF utilizados em outros estudos publicados na literatura, para a obtenção de propriedades de transporte de elétrons neste gás. / The progress of theoretical and experimental studies of ionizing radiation interaction processes with DNA [1]–[7] demonstrated that such radiation when interacting with biological systems can lead to the production of a significant number of secondary electrons. These electrons, in turn, carry the inelastic collisions with biomolecules, leading to the excited states (vibrational and electronic states) and the production of resonant states. Recent studies [1], [3], [6] report that those processes have the actual ability to cause cell mutation or necrosis, due to single and double break of the DNA chain, having therefore, great potential harmful to any living tissue. In order to better understand these interactions of low-energy electrons with the species found in biological systems, we used in this thesis the Electron Energy Loss Spectroscopy to study the differential (DCS) and integral cross sections (ICS). The region of impact energies used was able to promote excitation of vibrational levels of the tetrahydrofuran (THF) and α-tetrahydrofurfuryl alcohol (THFA), and bands of electronic Rydberg states of TFA. These molecular species were chosen because they are chemically similar to sugar rings present in phosphate-deoxyribose structure, DNA constituents, and the THFA recently identified as a best analogous option for deoxyribose structure, when compared to their similar chemical species, the THF molecule. The electron impact energies used for THFA, were 20, 30, 40 and 50eV, while the angular interval of the scattered electrons was 10 ° - 90 °. The THF molecule was studied for energies of 15, 20, 30 and 50eV, while scattering processes were studied in the angular range of 15º - 90º. In this sense, the DCS's and ICS's of THFA showed subtle difference from those obtained by Khakoo et al. [8] for THF, because of their different physical and chemical properties. The role of the dipole moment and polarizability of the molecules in the electron scattering process was observed, especially its effects on DCS's for low scattering angles (≤30 °). Theoretical calculations, carried out by the theoretical part of this research group, were used also in order to compare with the experimental data presented here, resulting in an excellent agreement, which led to confirmation of the models used. In addition, there was a review of work of Garland et al. [9], which has shown that the energy range and the few vibrational modes considered in their work, derived from Allan [10], were underestimating the role of vibrational excitation with respect to completion of studies of the transport properties. The presentation of this work firstly includes the important theoretical background for data analysis and theoretical calculations performed. Posteriorly, is presented a description of the Electron Energy Loss Spectrometer used and the data analysis framework applied. Finally, the experimental and theoretical data at work and discussions are presented. Additionally, is made a review of the set of vibrational states excitations data of THF used in other studies published in the literature for obtaining electron transport properties of this gas.