A Tomografia Computadorizada de Energia Dupla (DECT em inglês) é um dos campos das imagens tomográficas que mais evoluiu nos últimos anos. O DECT usa dois espectros para irradiar pacientes e é capaz de diferenciar tecidos com base na sua composição elementar. Apesar de serem semelhantes aos dispositivos padrão de tomografia, para essa modalidade é necessário o desenvolvimento de ferramentas específicas que permitam o estudo de suas propriedades de imagem. O objetivo deste trabalho era construir um sistema simulado de Tomografia Computadorizada (TC) com a capacidade de produzir imagens semelhantes às obtidas em dispositivos DECT reais. O TC simulado também permitiria explorar as propriedades das imagens de materiais de teste antes de sua construção física. Este trabalho presenta a simulação do processo de aquisição de imagens de um dispositivo DECT que funciona a partir da troca rápida de kV, o GE Discovery CT 750 HD. A geometria simulada foi baseada num dispositivo atualmente disponível no InRad (Instituto de Radiologia da Faculdade de Medicina da Universidade de São Paulo). As simulações foram realizadas usando o código Monte Carlo PENELOPE/penEasy para simular o transporte de radiação através dos materiais e detectores. Também é apresentada uma comparação entre as imagens obtidas no dispositivo real e nas simulações. Para isso, foi preparado um objeto simulador cilíndrico contendo concentrações de materiais equivalentes a iodo e cálcio. As imagens de tal objeto simulador foram adquiridas no equipamento GE Discovery CT 750 HD. Um objeto simulador equivalente foi modelado e as suas imagens foram simuladas com o código PENELOPE/penEasy. As imagens foram adquiridas e reconstruídas de acordo com as possibilidades do equipamento clínico de tomografia. Imagens de concentração de material e imagens monoenergéticas foram obtidas a partir do dispositivo CT clínico e das simulações. O algoritmo BMD (Basis Material Decomposition em Inglês) baseado nas projeções foi implementado usando os coeficientes de atenuação mássicos da água e do iodo. Consequentemente, imagens de concentração dos materiais água e iodo foram obtidas. A concentração medida nos cilindros de iodo foi equivalente às esperadas tanto no dispositivo real quanto nas imagens simuladas. Foram observados artefatos de endurecimento de feixe nas imagens de concentração de material. Imagens monoenergéticas foram obtidas para diferentes energias. Tais imagens foram obtidas a partir da superposição das imagens de concentração de água e iodo, que foram ponderadas pelos seus respectivos coeficientes de atenuação mássicos. Verificou-se que para as imagens monoenergéticas simuladas e reais em altas energias a imagem de concentração da água é a componente dominante, produzindo imagens que apresentaram as cavidades de iodo como menos atenuantes do que a água. Por outro lado, para energias baixas, a componente dominante nas imagens monoenergéticas foi a imagem de concentração do iodo. O CNR foi analisado nas imagens monoenergéticas como função da energia. As curvas do CNR dos dispositivos simulado e real exibiram semelhanças em sua forma, mas com escala diferente devido à diferença no ruído. Foi possível concluir que o modelo DECT simulado apresenta resultados qualitativos semelhantes aos obtidos no dispositivo real. O sistema de TC simulado permite explorar as características das imagens com diferentes materiais e composições. Ele também pode ser usado como uma ferramenta didática para melhorar a compreensão da diferenciação de materiais em tomografia espectral e DECT. / Dual Energy (DE) Computed Tomography (CT) is one of the fields of tomographic images that has evolved rapidly during the last years. DECT uses two X-ray spectra to irradiate patients It is capable to differentiate materials based on its elementary composition. Despite being similar to standard CT devices, DECT devices require the development of specific tools that allow the study of their image properties. The objective of this work was to build a modelled CT system capable of producing images similar to those obtained in real DECT devices. The modelled CT would also allow exploring the image properties of test materials before their physical construction. This work presents the simulation of the acquisition process of a DECT device that works with rapid kV switching, the GE Discovery CT 750 HD. The simulated geometry was based on a device currently available at the InRad (Institute of Radiology of the Faculty of Medicine of the University of São Paulo). The simulations were carried out using the PENELOPE/penEasy Monte Carlo code, which simulates radiation transport through the materials and detectors. A comparison between the images obtained in the real device and from simulations is also presented. To do so, a real phantom was prepared to be imaged and an equivalent system was simulated. The phantom contained inserts with concentrations of iodine and calcium. The images were acquired and reconstructed according to the possibilities of the real CT device. Standard, material concentration and virtual monoenergetic images were acquired[L1] from both, the real CT device and simulations. The Projection-Based BMD method was implemented using the mass attenuation coefficients of water and iodine. Then, material concentration images of water and iodine were obtained. The iodine concentrations estimated from the images agreed with the expected values in both real device and simulated images. Beam hardening artefacts were observed in the simulated material concentration images. Monoenergetic images were obtained for different energies. Such images were obtained as a superposition of the concentration images of water and iodine, weighed by their respective mass attenuation coefficient. It was verified that in the simulated and real device images, at high energies, the water concentration image predominated in the monoenergetic images, producing images that presented the iodine cavities as less attenuating than water. In contrast, at low energies, the predominant component of the monoenergetic images was the iodine concentration image. Contrast Noise Ratio (CNR) was analysed in the monochromatic images as a function of energy. Simulated and real device CNR curves exhibited similarities in their shape but with a different scale due to their difference in noise. It was possible to conclude that the simulated DECT model presented qualitative results similar to the obtained in the real device. The modelled CT system permits exploring the image features with different materials and compositions. It could also be used as a didactic tool to improve the understanding of material differentiation in spectral or DECT.

No description available.

Ein Ziel der modernen Physik ist die experimentelle Beobachtung des neutrinolosen Doppelbetazerfalls (0nbb). Unter den wenigen in der Natur vorkommenden Nukliden ist 76-Ge ein möglicher Kandidat an denen dieser Prozess unter anderem mit dem Experiment GERDA nachgewiesen werden soll. Die extrem geringe Wahrscheinlichkeit für das Auftreten einer 0nbb-Umwandlung ist mindestens zehn Größenordnungen kleiner ist als die des Beta-Zerfalls von 115-In mit einer Halbwertszeit von 4,41x10^14 Jahren, einem der seltensten in der Natur beobachteten Kernumwandlungen. Die dafür erforderliche hohe Detektions Sensitivität wird unter anderem vom Messuntergrund bestimmt, dessen genaue Kenntnis für die Auswertung der Messdaten erforderlich ist. In dieser Arbeit wurden neutronenphysikalische Studien an Germanium durchgeführt, die essentielle Lücken in diesem Kenntnisstand schließen. Neutronen können durch direkte Wechselwirkung mit Germanium sowie der umgebenden Materie des Detektors oder indirekt durch Aktivierung Zählereignisse hervorrufen. Für das Verständnis des damit verursachten Untergrundes wurde der Neutronenwechselwirkungsquerschnitt 70-Ge(n,3n)68-Ge, das Anregungsschema von 76-Ge und der energieabhängige Anregungsquerschnitt für einige dieser Zustände untersucht. Der mangelhafte Messdatenbestand für natürlich vorkommende Germaniumisotope wird dabei entscheidend verbessert. Um die Untersuchung des 76-Ge Anregungsschemas und den Zugang zu einer Palette weiterer Experimente zu ermöglichen, wurde im Rahmen dieser Arbeit ein leistungsfähiges, sehr speziellen Anforderungen entsprechendes Rohrpostsystem entwickelt und im Neutronenlabor der TU Dresden installiert. Ein weiteres neutronenphysikalisches Experiment untersucht den bisher unbeobachteten Elektroneneinfang von 76-As. Dadurch wird eine Möglichkeit gezeigt die oftmals nur mit theoretischen Modellen zugänglichen und mit großen Unsicherheiten behafteten Übergansmatrixelemente experimentell zu bestimmen. Diese spielen bei der Auswertung von Experimenten zum Doppelbetazerfall, insbesondere des Experimentes GERDA, eine entscheidende Rolle. / One goal of modern physics is the experimental observation of the neutrinoless double beta decay (0nbb). Among the few naturally occurring nuclides 76-Ge is one candidate to which this process is to verify, amongest others with the GERDA experiment. The extremely low probability of occurrence for a 0nbb-decay is of at least ten orders of magnitude smaller than that of the Beta-decay of 115-In, one of the rarest beta transitions observed in nature with a half-life of 4.41x10^14 years. Thefore a high detection sensitivity is required, wich depends among other things on the measuring background. Its exact knowledge is necessary for the evaluation of the measuring data. In this work neutron-physical studies were performed on germanium aiming to close the essential gaps in this state of knowledge. Neutrons can cause counting events by direct interaction with germanium and the surrounding matter of the detector or indirectly by activation of any of these materials. For understanding of those background signals, the neutron interaction cross section 70-Ge(n,3n)68-Ge, the levelsceme and the energy-dependent excitation cross section of 76-Ge has been investigated. The lack of data inventory for natural germanium has been improved significantly. To enable the investigation of the 76-Ge level sceme and the access to a range of other experiments, a powerful, very special requirements corresponding pneumatic tube system was developed and installed in scope of this work at the neutron laboratory of the TU Dresden. Another neutron physics experiment examined the so far unobserved electroncapture of 76-As. This shows one way to determine transition matrix elements experimentally, which is often only accessible through theoretical models and prone to large uncertainties. These Matrix elements play a crucial role in the analysis of experiments on double beta decay, in particular the GERDA experiment.

It is important to know the heat generated due to nuclear decay in the final repository for spent nuclear fuel. In Sweden, the heating powers generated in spent nuclear fuels are currently measured in the calorimeter System 251 at the Clab facility, Oskarshamn. In order to better measure, and increase understanding, of the temperature measurements in the calorimeter, a simple thermodynamic model of its temperature evolution was developed. The model was described as a system of ordinary differential equations, which were solved, and the solution was applied to calibration measurements of the calorimeter. How precise the model is, how its parameters affect the model, et cetera, are addressed. How the temperature evolution of the system changes as the values of parameters in the model are changed is addressed. The mass correction of the calorimeter could be estimated from this model, which validated the established mass correction of the calorimeter. How the measurement results from the calorimeter would be affected if the volume of the calorimeter was changed was also considered. Additionally, gamma radiation escape from the calorimeter without being detected as heat in the calorimeter. The gamma escape energy fraction was estimated by SERPENT simulations of the calorimeter, as a function of the initial photon energy. The gamma escape was also estimated for different values of the radius of System 251.

Ein Ziel der modernen Physik ist die experimentelle Beobachtung des neutrinolosen Doppelbetazerfalls (0nbb). Unter den wenigen in der Natur vorkommenden Nukliden ist 76-Ge ein möglicher Kandidat an denen dieser Prozess unter anderem mit dem Experiment GERDA nachgewiesen werden soll. Die extrem geringe Wahrscheinlichkeit für das Auftreten einer 0nbb-Umwandlung ist mindestens zehn Größenordnungen kleiner ist als die des Beta-Zerfalls von 115-In mit einer Halbwertszeit von 4,41x10^14 Jahren, einem der seltensten in der Natur beobachteten Kernumwandlungen. Die dafür erforderliche hohe Detektions Sensitivität wird unter anderem vom Messuntergrund bestimmt, dessen genaue Kenntnis für die Auswertung der Messdaten erforderlich ist. In dieser Arbeit wurden neutronenphysikalische Studien an Germanium durchgeführt, die essentielle Lücken in diesem Kenntnisstand schließen. Neutronen können durch direkte Wechselwirkung mit Germanium sowie der umgebenden Materie des Detektors oder indirekt durch Aktivierung Zählereignisse hervorrufen. Für das Verständnis des damit verursachten Untergrundes wurde der Neutronenwechselwirkungsquerschnitt 70-Ge(n,3n)68-Ge, das Anregungsschema von 76-Ge und der energieabhängige Anregungsquerschnitt für einige dieser Zustände untersucht. Der mangelhafte Messdatenbestand für natürlich vorkommende Germaniumisotope wird dabei entscheidend verbessert. Um die Untersuchung des 76-Ge Anregungsschemas und den Zugang zu einer Palette weiterer Experimente zu ermöglichen, wurde im Rahmen dieser Arbeit ein leistungsfähiges, sehr speziellen Anforderungen entsprechendes Rohrpostsystem entwickelt und im Neutronenlabor der TU Dresden installiert. Ein weiteres neutronenphysikalisches Experiment untersucht den bisher unbeobachteten Elektroneneinfang von 76-As. Dadurch wird eine Möglichkeit gezeigt die oftmals nur mit theoretischen Modellen zugänglichen und mit großen Unsicherheiten behafteten Übergansmatrixelemente experimentell zu bestimmen. Diese spielen bei der Auswertung von Experimenten zum Doppelbetazerfall, insbesondere des Experimentes GERDA, eine entscheidende Rolle. / One goal of modern physics is the experimental observation of the neutrinoless double beta decay (0nbb). Among the few naturally occurring nuclides 76-Ge is one candidate to which this process is to verify, amongest others with the GERDA experiment. The extremely low probability of occurrence for a 0nbb-decay is of at least ten orders of magnitude smaller than that of the Beta-decay of 115-In, one of the rarest beta transitions observed in nature with a half-life of 4.41x10^14 years. Thefore a high detection sensitivity is required, wich depends among other things on the measuring background. Its exact knowledge is necessary for the evaluation of the measuring data. In this work neutron-physical studies were performed on germanium aiming to close the essential gaps in this state of knowledge. Neutrons can cause counting events by direct interaction with germanium and the surrounding matter of the detector or indirectly by activation of any of these materials. For understanding of those background signals, the neutron interaction cross section 70-Ge(n,3n)68-Ge, the levelsceme and the energy-dependent excitation cross section of 76-Ge has been investigated. The lack of data inventory for natural germanium has been improved significantly. To enable the investigation of the 76-Ge level sceme and the access to a range of other experiments, a powerful, very special requirements corresponding pneumatic tube system was developed and installed in scope of this work at the neutron laboratory of the TU Dresden. Another neutron physics experiment examined the so far unobserved electroncapture of 76-As. This shows one way to determine transition matrix elements experimentally, which is often only accessible through theoretical models and prone to large uncertainties. These Matrix elements play a crucial role in the analysis of experiments on double beta decay, in particular the GERDA experiment.