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A radioterapia externa ocupa lugar de destaque nos tratamentos de câncer. As construções das salas que abrigam os aceleradores lineares são custosas e este fator é limitante para que sejam instalados mais equipamentos. Faz-se necessária a pesquisa de opções construtivas com objetivo de redução de custos, mantendo-se a estabilidade estrutural e a barreira de proteção radiológica. Para a blindagem destas instalações podem ser empregados diversos materiais para a atenuação de radiação. O concreto armado é empregado em muitas destas instalações, seja pelo seu custo ou a prática construtiva no Brasil, face ao notório conhecimento deste material e abundância de matéria prima. Foram elaborados dois projetos estruturais de bunker em concreto armado. O projeto denominado bunker enterrado foi concebido com estrutura localizada no subsolo e dimensionado levando-se em conta inclusive os esforços decorrentes do solo adjacente às paredes. Foi adotada blindagem de concreto no teto. As demais faces da construção tem atenuação de radiação por solo compactado. O projeto do bunker não enterrado considerou a geometria de um projeto padrão do Ministério da Saúde e o acesso é pelo pavimento térreo. Em função da espessura necessária de blindagem, foi projetada uma estrutura com dimensões que contemplam a barreira no teto e paredes. Os resultados obtidos neste estudo foram satisfatórios quanto aos dois modelos estruturais propostos, com vantagens e desvantagens. Foi mostrada a diferença de custos entre uma estrutura de edificação enterrada e outra não enterrada. A estrutura enterrada mostrou-se mais viável, pois aproveita o solo compactado adjacente para atenuação da radiação. / External radiotherapy occupies a prominent place in cancer treatments. The constructions of the rooms that shelter the linear accelerators are costly and this is a limiting factor to have more equipment installed. It is necessary to research construction options with the objective of reducing costs, maintaining the structural stability and the radiological protection barrier. For the shielding of these installations, various materials can be used for the attenuation of radiation. Reinforced concrete is used in many of these facilities, either for its cost or the constructive practice in Brazil, due to the know-how of this material and abundance of raw material. Two structural bunker structural projects were developed. The buried bunker project was designed with a structure located underground and dimensioned taking into account including the efforts from the soil adjacent to the walls. Concrete shield was used in the ceiling. The other faces of the construction have radiation attenuation by compacted soil. The not buried bunker project considered the geometry of a standard design of the Health Ministry and its access is by the ground floor. Due to the required thickness of shielding, a structure with dimensions that contemplate the barrier in the ceiling and walls was designed. The results obtained in this study were satisfactory, regarding the two proposed structural models, taking in consideration advantages and disadvantages. The difference in costs of a buried structure and not buried one was provided. The buried structure proved to be more viable, since it utilizes adjacent compacted soil to attenuate the radiation.

A radioterapia externa ocupa lugar de destaque nos tratamentos de câncer. As construções das salas que abrigam os aceleradores lineares são custosas e este fator é limitante para que sejam instalados mais equipamentos. Faz-se necessária a pesquisa de opções construtivas com objetivo de redução de custos, mantendo-se a estabilidade estrutural e a barreira de proteção radiológica. Para a blindagem destas instalações podem ser empregados diversos materiais para a atenuação de radiação. O concreto armado é empregado em muitas destas instalações, seja pelo seu custo ou a prática construtiva no Brasil, face ao notório conhecimento deste material e abundância de matéria prima. Foram elaborados dois projetos estruturais de bunker em concreto armado. O projeto denominado bunker enterrado foi concebido com estrutura localizada no subsolo e dimensionado levando-se em conta inclusive os esforços decorrentes do solo adjacente às paredes. Foi adotada blindagem de concreto no teto. As demais faces da construção tem atenuação de radiação por solo compactado. O projeto do bunker não enterrado considerou a geometria de um projeto padrão do Ministério da Saúde e o acesso é pelo pavimento térreo. Em função da espessura necessária de blindagem, foi projetada uma estrutura com dimensões que contemplam a barreira no teto e paredes. Os resultados obtidos neste estudo foram satisfatórios quanto aos dois modelos estruturais propostos, com vantagens e desvantagens. Foi mostrada a diferença de custos entre uma estrutura de edificação enterrada e outra não enterrada. A estrutura enterrada mostrou-se mais viável, pois aproveita o solo compactado adjacente para atenuação da radiação. / External radiotherapy occupies a prominent place in cancer treatments. The constructions of the rooms that shelter the linear accelerators are costly and this is a limiting factor to have more equipment installed. It is necessary to research construction options with the objective of reducing costs, maintaining the structural stability and the radiological protection barrier. For the shielding of these installations, various materials can be used for the attenuation of radiation. Reinforced concrete is used in many of these facilities, either for its cost or the constructive practice in Brazil, due to the know-how of this material and abundance of raw material. Two structural bunker structural projects were developed. The buried bunker project was designed with a structure located underground and dimensioned taking into account including the efforts from the soil adjacent to the walls. Concrete shield was used in the ceiling. The other faces of the construction have radiation attenuation by compacted soil. The not buried bunker project considered the geometry of a standard design of the Health Ministry and its access is by the ground floor. Due to the required thickness of shielding, a structure with dimensions that contemplate the barrier in the ceiling and walls was designed. The results obtained in this study were satisfactory, regarding the two proposed structural models, taking in consideration advantages and disadvantages. The difference in costs of a buried structure and not buried one was provided. The buried structure proved to be more viable, since it utilizes adjacent compacted soil to attenuate the radiation.

Past weapons production activities have resulted in mass quantities of trans-uranic waste being buried in drums at several sites in the United States. In an effort to relocate these waste drums to more permanent storage sites, Fluor Hanford has begun characterizing their contents to ensure compliance with various shipping and storage requirements. Non-destructive analysis techniques are regularly employed, among them passive radiation detection using a Canberra Gamma-Energy-Analyzer germanium detector vault. Necessary strict legal tolerances require strong quality assurance. The detectors are frequently calibrated in the traditional method with check sources, but it would be advantageous to have an estimate of system minimum detectable activity (MDA). However, any estimate is complicated by the fact that sources are distributed stochastically in the waste drums. In this study, a method was developed to predict system detector efficiency for a variety of detector configurations and drum fill materials and calculate MDA based on these efficiencies. The various system designs were modeled in Monte Carlo N-Particle Code, version 4b, to determine photopeak detection efficiency. An external code written in C programming language was used to randomly assign between one and 20 sources to volumetric regions of the waste drum. Twenty simulations were performed for each design and drum fill material combination, each time redefining the stochastically distributed source. This provided a normally distributed spectrum of 20 efficiencies for each situation. From this, mean and lower 95% confidence limit efficiencies were used to calculate MDA. The patterns among the results were then compared with values predicted by the MDA formula. Finally, an examination was made of the impact on the MDA of the system's true design in the case of single or multiple detector failure. The results indicate that this method of estimating minimum detectable activity, although costly in computing time, provides results consistent with intuitive and calculated expectations. Future work would allow easy calibration of the model to measured efficiency results. Used in coordination with physical experiments, this method may eventually prove useful in benchmarking system performance and accurately ensuring reliable waste drum characterizations. / Graduation date: 2003

To address the commonly poor short wavelength response of the conventional solar cell structure which consists of a highly doped thin emitter layer on top of a thicker and less doped base, the novel concept of the Buried-Windowed-Emitter is introduced. This new solar cell structure makes use of a high quality semiconductor layer on top of the traditionally made highly doped emitter and greatly enhances the spectral response of the solar cell by giving the superficially generated carriers a higher chance of collection at the junction. In the proposed BWE structure the emitter is windowed in order to electrically connect the top layer to the base for current collection. The efficacy of the proposed novel device is proven by computer aided device simulations using the available device simulation tools such as MEDICI. The results of simulation show that the proposed novel Buried-Windowed-Emitter solar cell will not only improve the short wavelength spectral response of the overall cell as expected, but also will boost the spectral efficiency for all the wavelengths. Another exciting conclusion from the results of the computer simulation of the BWE solar cell is that the minority carrier lifetime in the top layer does not need to be very high for a superb performance and values as low as 1µs can still boost the short circuit current of the cell to values close to the theoretical limit of the photo-current collectable by a silicon solar cell. This is indeed a good news for manufacturability of this device as it should be practically feasible to achieve epitaxial films with minority carrier lifetime in this range. In order to increase the understanding about the rather complex structure of the proposed Buried-Windowed-Emitter solar cell, an analytical circuit level model, similar to the case of the standard solar cell, is developed for the proposed device. The developed analytical model helps to understand the importance of the main design parameters such as the dimensions of the pattern of the windowed emitter. On the path to fabricate the proposed BWE solar cell, great deal of work is done on the development of a low temperature (<300°C) epitaxial silicon technology using the benefits of Plasma Enhanced Chemical Vapor Deposition (PECVD). Highly doped epitaxial silicon layers of up to around 1µm thickness are achieved with sheet resistivity as low as 7Ω/sq which is much lower than what is reposted in the literature in similar deposition conditions. Intrinsic, phosphorous doped n-type and boron doped p-type epitaxial films have been developed on silicon substrates. Measurement of reflection spectra of the deposited epitaxial films is proposed as a fast, non destructive and process-integrate-able method to assess the crystalline quality of the epitaxial films. Effects of higher temperature post deposition annealing have been studied on the develop epitaxial films A full technology is developed for the fabrication of the proposed novel solar cells. Photo-masks are designed to create 10 different architectures for the design of the windowed emitter in the BWE cell. All the steps taken in the successful fabrication of the novel BWE cells are presented in detail and the relevant findings are discussed and proposed as future research topics. Three kinds of cells are fabricated using the developed technology to separately study the effects of partial coverage of the windowed emitter, the optical performance of the developed epitaxial silicon films and the performance and manufacturability of the novel BWE solar cell The results show that the concept of windowed-emitter by itself (even without the top layer) is capable of enhancing the performance of the solar cell when compared to a standard design. It also promises high conversion efficiency for the BWE solar cell in case a high quality top layer can be deposited on top of the windowed emitter. The results further reveal the lower than expected quality of the low temperature epitaxial films despite the indication of their full crystallinity through other analyses. Use of the epitaxial films as the emitter of the solar cell is proposed as a direct and effective method of studying the photovoltaic performance of the low temperature epitaxial films. Further development of the epitaxial technology will lead to feasibility of a BWE solar cell with very high photovoltaic performance.

The objective of this research is to comprehensively compare bulk accumulation and inversion MOSFETs, and find application areas where each is superior.Short channel effect (SCE) models for accumulation and inversion MOSFETs are derived that accurately predict threshold voltage, subthreshold swing, and subthreshold current. A source/drain junction depth dependent characteristic length is derived that can be used to rapidly assess the impact of junction depth scaling on minimum channel length. A fast circuit simulation methodology is developed that uses physically based I-V models to simulate inversion and accumulation MOSFET inverter chains, and is found to be accurate over a wide range of supply voltages. The simulation methodology can be used for rapid technology optimization, and performance prediction. Design guidelines are proposed for accumulation MOSFET design; the guidelines result in a low process sensitivity, low SCE, and a subthreshold current less than the allowable limit. The relative performance advantage of accumulation/inversion MOSFETs is gate-technology dependent. In critical comparisons, on-current is evaluated by means of a full band Monte Carlo device simulation. Gate-leakage, and band-to-band tunneling leakage at the drain-substrate region are included in the performance analysis. For mid-bandgap metal gate, accumulation MOSFETs perform better than inversion MOSFETs for hi-performance (HiP) and low-operating power (LOP) applications. For tunable metal gate technology, inversion MOSFETs always perform better than accumulation MOSFETs. For dual poly technology, accumulation MOSFETs perform better than inversion MOSFETs for low standby power (LSTP) applications. A comprehensive scaling analysis has been performed on accumulation and inversion MOSFETs using both SCE models and 2-D simulations. Results show that accumulation MOSFETs can scale better than inversion MOSFETs for mid-bandgap metal gate HiP, and LOP applications; and poly gate LSTP applications.

A Simple way to improve solar cell efficiency is to enhance the absorption of light and reduce the shading losses. One of the main objectives for the photovoltaic roadmap is the reduction of metalized area on the front side of solar cell by fin lines. Industrial solar cell production uses screen-printing of metal pastes with a limit in line width of 70-80 μm. This paper will show a combination of the technique of laser grooved buried contact (LGBC) and Screen-printing is able to improve in fine lines and higher aspect ratio. Laser grooving is a technique to bury the contact into the surface of silicon wafer. Metallization is normally done with electroless or electrolytic plating method, which a high cost. To decrease the relative cost, more complex manufacturing process was needed, therefore in this project the standard process of buried contact solar cells has been optimized in order to gain a laser grooved buried contact solar cell concept with less processing steps. The laser scribing process is set at the first step on raw mono-crystalline silicon wafer. And then the texturing etch; phosphorus diffusion and SiNx passivation process was needed once. While simultaneously optimizing the laser scribing process did to get better results on screen-printing process with fewer difficulties to fill the laser groove. This project has been done to make the whole production of buried contact solar cell with fewer steps and could present a cost effective opportunity to solar cell industries. / <p>In collaboration with Institute for Photovoltaics <strong><em>IPV</em></strong>, University of Stuttgart.</p>

To address the commonly poor short wavelength response of the conventional solar cell structure which consists of a highly doped thin emitter layer on top of a thicker and less doped base, the novel concept of the Buried-Windowed-Emitter is introduced. This new solar cell structure makes use of a high quality semiconductor layer on top of the traditionally made highly doped emitter and greatly enhances the spectral response of the solar cell by giving the superficially generated carriers a higher chance of collection at the junction. In the proposed BWE structure the emitter is windowed in order to electrically connect the top layer to the base for current collection. The efficacy of the proposed novel device is proven by computer aided device simulations using the available device simulation tools such as MEDICI. The results of simulation show that the proposed novel Buried-Windowed-Emitter solar cell will not only improve the short wavelength spectral response of the overall cell as expected, but also will boost the spectral efficiency for all the wavelengths. Another exciting conclusion from the results of the computer simulation of the BWE solar cell is that the minority carrier lifetime in the top layer does not need to be very high for a superb performance and values as low as 1µs can still boost the short circuit current of the cell to values close to the theoretical limit of the photo-current collectable by a silicon solar cell. This is indeed a good news for manufacturability of this device as it should be practically feasible to achieve epitaxial films with minority carrier lifetime in this range. In order to increase the understanding about the rather complex structure of the proposed Buried-Windowed-Emitter solar cell, an analytical circuit level model, similar to the case of the standard solar cell, is developed for the proposed device. The developed analytical model helps to understand the importance of the main design parameters such as the dimensions of the pattern of the windowed emitter. On the path to fabricate the proposed BWE solar cell, great deal of work is done on the development of a low temperature (<300°C) epitaxial silicon technology using the benefits of Plasma Enhanced Chemical Vapor Deposition (PECVD). Highly doped epitaxial silicon layers of up to around 1µm thickness are achieved with sheet resistivity as low as 7Ω/sq which is much lower than what is reposted in the literature in similar deposition conditions. Intrinsic, phosphorous doped n-type and boron doped p-type epitaxial films have been developed on silicon substrates. Measurement of reflection spectra of the deposited epitaxial films is proposed as a fast, non destructive and process-integrate-able method to assess the crystalline quality of the epitaxial films. Effects of higher temperature post deposition annealing have been studied on the develop epitaxial films A full technology is developed for the fabrication of the proposed novel solar cells. Photo-masks are designed to create 10 different architectures for the design of the windowed emitter in the BWE cell. All the steps taken in the successful fabrication of the novel BWE cells are presented in detail and the relevant findings are discussed and proposed as future research topics. Three kinds of cells are fabricated using the developed technology to separately study the effects of partial coverage of the windowed emitter, the optical performance of the developed epitaxial silicon films and the performance and manufacturability of the novel BWE solar cell The results show that the concept of windowed-emitter by itself (even without the top layer) is capable of enhancing the performance of the solar cell when compared to a standard design. It also promises high conversion efficiency for the BWE solar cell in case a high quality top layer can be deposited on top of the windowed emitter. The results further reveal the lower than expected quality of the low temperature epitaxial films despite the indication of their full crystallinity through other analyses. Use of the epitaxial films as the emitter of the solar cell is proposed as a direct and effective method of studying the photovoltaic performance of the low temperature epitaxial films. Further development of the epitaxial technology will lead to feasibility of a BWE solar cell with very high photovoltaic performance.

Detonation of an explosive charge, such as a mine or an improvised explosive device (IED) at the ground surface or buried at shallow depth in soil, can produce high airblast pressures and significant dynamic soil debris loads on an overlying or nearby structure, such as a vehicle passing over the explosive. The blast loading environment is a function of many factors including the explosive type, configuration, mass, and depth of burial, soil characteristics, and the distance between the ground surface and the structure or object. During the past several years, the US Army has focused considerable attention on developing improved methods for predicting this environment, particularly for use by vehicle/armor analysts, thereby, improving the survivability of these platforms. Research is needed to better understand the aboveground environment created by the detonation of a shallow-buried explosive in order to design adequate protective measures for an aboveground structure. Unfortunately, there is no accurate methodology for predicting these airblast and soil debris loads to support the designs. Development of the required prediction tools is hampered by lack of well controlled and documented experimental results for these complex loads. Without detailed experimental data, the numerical simulations of these loads cannot be adequately validated for the large deformation, stress, and motion gradients and the resulting interactions with structures. The focus of this research is to quantify the influence of soil properties on the aboveground environment from the detonation of a bare explosive charge resting on the soil surface or shallow-buried. In order to fully quantify the influence of soil parameters, well-controlled experiments were designed to directly measure soil debris and airblast loadings on an aboveground reaction structure due to the detonation of explosives at the surface of and shallow buried in three very different soils. The experiments were performed using specifications and strict quality controls that limited the influence of outside variables and ensured the experiments were repeatable. The experiments provided blast pressure, soil stress, and impulse data for each soil type. These data were analyzed to investigate the influence of the properties of the different soil types on the aboveground environment.

No description available.