by Wing-keung Mak. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 51-53). / by Wing-keung Mak. / Acknowledgments --- p.i / Abstract --- p.ii / Table of Content --- p.iii / Chapter Chapter One --- Introduction --- p.1 / Chapter Chapter Two --- Theory / Chapter 2.1 --- Theory of Two-wave Coupling --- p.3 / Chapter 2.2 --- Theory of Fanning --- p.8 / Chapter 2.3 --- Theory of Time Dependent Absorption Coefficients of Photorefractive Crystals --- p.10 / Chapter Chapter Three --- Photorefractive Fabry-Perot Etalon / Chapter 3.1 --- Theory and Numerical Computation --- p.12 / Chapter 3.2 --- Summary of Crystal Parameters --- p.15 / Chapter 3.3 --- Experimental Studies of Interference Patterns --- p.16 / Chapter 3.4 --- Intensity Dependence of Fabry-Perot Etalon Interference Patterns --- p.25 / Chapter 3.5 --- Fanning --- p.29 / Chapter 3.6 --- Bright Spots on Interference Patterns --- p.31 / Chapter Chapter Four --- Time Dependent Absorption Coefficients of Photorefractive Crystals / Chapter 4.1 --- Experiments Using Laser Light --- p.34 / Chapter 4.2 --- Experiments Using White Light --- p.44 / Chapter Chapter Five --- Conclusion and Future Outlook --- p.49 / References --- p.51

Thesis (M.S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2005. / Laurence J. Jacobs, Committee Chair ; Reginald DesRoches, Committee Member ; Jianmin Qu, Committee Member. Includes bibliographical references.

Photon mass attenuation coefficients are indispensable input parameters for use in several disciplines. They are of value for medical diagnostics, radiation therapy, material science, etc. Currently, photon mass attenuation coefficients derived from model calculations are widely used. This project directly measured the photon mass attenuation coefficients of water and a number of water based solutions. These measurements were made using a High Purity Germanium (HPGe) detector allowing for increased resolution beyond traditional techniques. Four sources were used (\Ba, \Eu, \Cs, \Am) producing multiple photons of interest over the range of 40 keV to 1.4 MeV, allowed for simultaneous collection of data and a refining of uncertainties beyond past techniques. Direct measurements using a new liquid technique supported the validity of Bragg's additive law, allowing for the mass attenuation coefficient of a constituent element to be calculated from a set of independent measurements. This technique allows materials not easily directly measured to be determined without an overburdening increase in uncertainty. The same direct measurements showed a deviation from the currently relied upon National Institute of Standards and Technology (NIST) database - XCOM. Investigations of the deviation and surrounding references showed XCOM being at most accurate to 5 \% relative uncertainty.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The main goal of this work is the development of an anthropomorphic head phantom for use in computed tomography dosimetry. This phantom was built with materials which are inexpensive and easy to find (alginate and acrylic resin). Additionally, its dosimetric behavior was analyzed in a CT, comparing the values of C100mm and the estimated effective dose. The phantoms were filled with water because of the fact that the mass attenuation coefficients and the mass energy-absorption coefficient indicated that this was the best material to simulate the reference brain (ICRU-44 s brain). Two phantoms were built for this work; one was created using a real skull and the other using a regular mannequin. The phantom created with the real skull showed an average percentage difference of 4% in anatomical measurements in comparison with the reference (ICRU-48). The value of the estimated effective dose in the real skull phantom was 1,29 mSv, a value 5.4 times greater than the computational phantom (MASH). Despite the discrepant value, it represents a 46% improvement in comparison with the geometric PMMA phantom. It is estimated that the cost of the phantom produced from a real skull using the techniques and materials used in this work is approximately R$ 300,00. / Este trabalho tem como objetivo principal o desenvolvimento de um phantom antropomórfico da cabeça humana para dosimetria em tomografia computadorizada. Tal objeto simulador foi construído com materiais de fácil acesso e baixo custo (alginato e resina acrílica). Além disso, o seu comportamento dosimétrico foi avaliado em um tomógrafo ao se comparar valores de C100mm e dose efetiva estimada. Os phantoms foram preenchidos com água porque os valores dos coeficientes de absorção energética e dos coeficientes atenuação mássico indicaram que este é o melhor material para simular o cérebro da referência (cérebro da ICRU-44). Dois phantoms foram construídos para este trabalho, um teve como modelo um crânio real e o outro um manequim comum. O phantom confeccionado a partir de um crânio real possui medidas anatômicas que diferem de referência (ICRU-48) em 4%. O valor da dose efetiva estimada no crânio real foi de 1,29 mSv, valor 5,4 vezes maior do que o calculado no phantom computacional (MASH). Apesar de ser um valor bastante discrepante, o mesmo representa uma melhora de 46% em relação ao objeto simulador geométrico de acrílico. O custo do phantom antropomórfico, obtido de um crânio real, utilizando as técnicas e materiais usados nesse trabalho é de, aproximadamente, R$ 300,00.