Neste trabalho, descrevemos os conceitos de alinhamento e orientação baseados no formalismo de Fano e Macek e estudamos a fotoionização do estado fundamental do átomo de Hélio. Para isso usou-se uma função de onda aproximada obtida a partir da diagonalização do operador de Gailitis- Damburg. A anisotropia do sistema formado após a colisão foi caracterizada através do cálculo da densidade eletrônica do íon e através do tensor de alinhamento e do vetor de orientação. O comportamento destes parâmetros para as transições n? -> 1s e n->n-1 em função de n (número quântico principal do íon) foi graficado para as duas simetrias relevantes, 1P° e 3P°. Observamos que o alinhamento máximo do sistema, em relação ao eixo de maior simetria definido como sendo o eixo z ocorre no limite de Wannier (n-> ?). Nesta situação o elétron iônico se encontra ao longo do eixo z para a simetria 3 P° e perpendicular ao eixo z para a simetria 1 P°. Esse fenômeno é causado pela interação elétron-elétron / In this work we describe the concepts of aligrnment and orientation based on the formalism of Fano and Macek formalism and we study the photoionization of the Helium atom ground state. We have used an approximate wave function obtained from the diagonalization of the Gailitis- Damburg operator. The anisotropy of the system formed after the colision was measured through the calculation of the ion electronic density and also by the use of the alignment tensor and orientation vector. The behaviour of these parameters for the transitions np ->1s and n ->n-1 as a function of n (the principal quantum number of the ion) was plotted for both the relevant symmetries, 1 P° and 3 P°. We have observed that the maximum alignment of the system, with respect to the dominant symmetry axis defined as the z axis, occurs in the Wannier threshold (n->?). This leads to the alignment of the ionic electron along the z axis for the 3 P°symmetry, and orthogonal to the z axis for the 1P° symmetry. This phenomenom is caused by the electron-electron Ínteraction.

Made available in DSpace on 2014-10-09T12:54:49Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:36Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O titânio é um material leve e resistente que possui aplicações em várias áreas, das quais podemos destacar a área médica, a aeronáutica e a nuclear. Porém, devido à sua alta reatividade a altas temperaturas com o oxigênio e outros elementos químicos presentes no ar, a soldagem deste material pode ser muito difícil. O uso de fontes de energia de alta intensidade como o laser, produz uma menor zona afetada pelo calor, diminuindo a área oxidada. Porém, mesmo assim há a necessidade do uso de uma atmosfera de proteção neutra, formada por hélio, argônio ou misturas destes gases. Esta atmosfera interage com o processo através de mudanças na formação de plasma, modificando as características da solda, como a largura do cordão e a penetração, podendo também provocar o aparecimento de porosidades nestes cordões. Neste trabalho foi verificada a influência do uso de argônio, hélio e misturas destes gases na soldagem com laser pulsado da liga Ti6Al4V. Também foi feito um estudo verificando a necessidade do uso de diferentes fluxos e dispositivos de proteção na soldagem. Foi verificado que as características físicas e mecânicas do cordão d solda não são modificadas significativamente pelos gases, e que apesar de haver um aumento na dureza pela falta de uma proteção de raiz, esta também não causa efeitos negativos na resistência da solda. Na soldagem do mesmo material com laser contínuo foram estudadas as influências dos parâmetros de soldagem, comparando-os com simulações matemáticas. Os resultados mostraram que a simulação pode ser utilizada para prever a largura do cordão de solda e das zonas afetadas pelo calor e oxidadas. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP / FAPESP:06/52778-1

No description available.

The purpose of this investigation was the determination of the thermal conduction properties of a single crystal of bismuth at liquid-helium temperatures in magnetic fields up to eighteen kilogauss.

The purpose of this investigation was to study head-transport phenomena in a single crystal of antimony at liquid helium temperatures. In particular, the longitudinal and transverse components of the thermal resistivity tensor were measured as a function of magnetic field up to eighteen kilogauss.

Flow visualization techniques have recently been applied for the investigation of various cryogenic flows of liquid helium. Particle image velocimetry and particle tracking velocimetry techniques, proven in the past as very fruitful in many scientific and industrial areas of research, are being used for the analysis of cryogenic flows. The Joint Low Temperature Laboratory at the Charles University in Prague is the first in Europe to employ flow visualization techniques to investigate liquid helium flows. The approach had to be optimized due to a number of technical and fundamental dificulties, i.e., the optical access to the helium bath and choice of suitable tracer particles. Water experiments at room temperature were performed to prove that the experimental apparatus is well-suited for the low-temperature experiments performed as the main part of the work. The latter focused on thermal counter flow. The results from both, room-temperature experiments and low-temperature experiments are discussed and positively compared with well-known theoretical results.

Significant sub-systems were created and others enhanced providing a platform for an order of magnitude precision increase of the small 4He interval - 23P1→23P2 laser spectroscopy measurement, as well as other helium transitions. These measurements serve as tests of helium theory and quantum electro-dynamics in general. Many improvements to the original experiment are discussed and characterized. In particular, counting speed increased 10x, the signal level was doubled, a novel Doppler shift minimization technique was implemented, a control node re-architecture was realized along with many useful features, and the development environment was updated. An initial 28% precision improvement was achieved also providing a foundation for additional gain via a created smaller and more heavily windowed vacuum cavity and picomotor controls.

No description available.

Inconel X-750 is a Ni-rich super-alloy with high strength and creep resistance. In CANDU reactors, it is used as tight fitting fuel channel annulus spacers (in the form of a spring). Unlike other reactor designs, the CANDU reactor has a high thermal neutron flux spectra, which, combined with the higher thermal neutron cross section of 58Ni results in an enhancement of the radiation damage and the internal production of helium and hydrogen. In recent years, it has been observed these spacers are losing ductility and strength following irradiation. The mechanical property evolution of these components is dependent on the irradiation temperature and dose. The primary degradation mechanism remains unclear, and thus provides the focus of this investigation. Inconel X-750 irradiated to these extreme conditions have never been examined prior to this research. The microstructural characterization included in this dissertation include: fractography, microstructural evolution and mechanical property evolution. The discussion of the microstructural evolution is focused on the characterization of helium bubbles. The bubbles form homogeneously in the matrix and aligned along sinks such as dislocations, grain boundaries and precipitates. Electron energy loss spectroscopy (EELS) has been used to probe individual nano-sized bubbles to provide insights into the helium density, helium-to-vacancy ratio, and pressures through the use of a hard sphere equation of state (HSEOS). In addition to understanding the influence of irradiation on helium bubbles, the evolution of secondary strengthening precipitates, gamma prime, are of interest as these precipitates play an important role on the strength and creep resistance of the unirradiated material. The stability of these precipitates with irradiation is thus an important factor to consider with respect to the microstructural degradation. The microstructure is linked to the mechanical properties via microhardness testing on adjacent material. A major contribution to this field is an approach to utilize a focused ion beam (FIB) and transmission electron microscopy (TEM) to perform high ii resolution failure analysis of an intergranular fracture surface. Although this technique is not altogether revolutionary, the application of this approach towards post irradiation examination of heavily irradiated Inconel X-750 is unique. This approach provides direct evidence of likely degradation mechanisms, and provides insights for future post irradiation failure analysis for other applicable nuclear components. Working with ex-service material creates some complications with respect to known and unknown variables making it difficult to assess all factors responsible for material degradation. To compliment the program, a controlled proton irradiation program has been performed to gain additional insights into in the effects of irradiation on the microstructure and mechanical property evolution of Inconel X-750, due to the inability to perform controlled experiments with in-service reactor components. In addition to providing a detailed analysis of a CANDU component’s degradation, this study provides comprehensive information on irradiation damage processes applicable to other reactor core components. / Thesis / Doctor of Philosophy (PhD)

<p> The isotopic composition and concentration of dissolved helium have been measured in over 250 samples of Atlantic and Pacific seawater. The helium isotope ratios were measured using a double collection "static" mass spectrometer specifically designed and constructed for this purpose. The helium and neon contents of 118 of these samples were determined using the isotope dilution technique, and the helium contents of the remaining samples were determined by peak-height comparison with standard air aliquots. Krypton and xenon concentrations were measured by isotope dilution for the Pacific samples. </p> <p> Two sources of excess nonatmospheric ³He are discerned in the Atlantic Ocean: a primordial component and a component produced by in situ decay of bomb-produced tritium. The former component occurs in three distinct features; two emanating from the south at 1000 m and greater than 4000 m depths, and one emanating from the north at about 3000 m depth. The spatial properties of these features are studied in the framework of simple models. The latter, or "tritiugenic" component is coupled with tritium concentrations measured by others to obtain Tritium-helium Ages, the characteristics of which are compared with hydrographic features. For example, the spreading velocity of the Mediterranean Water is determined to be ⪝ 1.5cm sec⁻¹ in the North-Western Atlantic. </p> <p> The helium and neon concentrations measured in Atlantic Waters indicate that significant variations occur for helium contents, both as a function of depth and latitude. The Antarctic Bottom Water appears to be a source of excess helium. </p> <p> In the Pacific, the distribution of excess ³He is shown to be consistent with injection of primordial ³He into the Deep and Bottom Waters from the East Pacific Rise. The characteristic mid-depth maximum seen in the helium isotope ratio anomaly profiles is shown to be a circulational feature. Upper and lower limits on the amount of excess nonatmospheric ⁴He are set at 5.5 and 2.6% respectively. Application of the simple one-dimensional diffusive-advective model indicate an upward flux of 6±2 and 1.1 ± 0.5 × 10⁶ atoms/cm²/sec for ³He and ⁴He respectively. </p> Pacific seawater is, on the average, 16 and 31% supersaturated in krypton and xenon respectively. Although there is no known process that is capable of such enrichments, the spatial distribution of the krypton and xenon concentrations indicate that a significant amount of the enrichment occurs in situ in Pacific Deep Waters. </p> / Thesis / Doctor of Philosophy (PhD)