Thesis--Catholic University of America. / Bibliography: p. 14-15.

The reflectivity at room temperature and the absorption coefficient at room temperature, 77°K and 12°K have been measured for CsI. These and the results of a Kramers-Kronig analysis of the reflectivity by Vergnat et al. (1969) have been compared to the calculated optical constants (complex dielectric constant and complex refractive index), reflectivity and absorption coefficient. The calculation, using the lattice dynamical data of Karo and Hardy (1963), is based on the work of Wallis and Maradudin (1962) and Cowley (1963). The cubic coupling coefficient has been evaluated for nearest neighbors with a correction due to Eldridge (1973) for long-range Coulombic forces. The predicted features in the imaginary part of the complex phase shift, gamma, are all assigned to specific two-phonon processes except for a small feature at 91 cm⁻¹. The agreement between theory and experiment is very poor at room temperature but improves significantly in all cases at low temperatures. The discrepancies between theory and experiment give evidence of the fundamental importance of third and higher-order processes in the CsI lattice and suggest that next-nearest neighbor repulsive forces need to be included in the calculation of the cubic coupling coefficient. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The thermal conductivity of three crystals of cesium iodide ranging in size from three to eight millimeters diameter was measured in the temperature range 1.15°K to 5.40°K. Thermal conductivity measurements were made using the thermal potentiometer method. Differences in the thermal conductivity of the three samples were interpreted in terms of phonon scattering from the boundaries of the crystals, and from internal structure defects. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: CT Mammography; Monte Carlo. Includes bibliographical references (p. 45-48).

In preparation for the large backgrounds expected to be present in the Belle II detector from the SuperKEKB e+e- collider, the radiation hardness of several large (5 x 5 x 30 cm3) thallium doped cesium iodide (CsI(Tl)) scintillation crystals are studied. The crystal samples studied consist of 2 spare crystals from the Belle experiment using PIN diode readout and 7 spare crystals from the BaBar experiment using photomultiplier tube readout. The radiation hardness of the scintillation properties of the CsI(Tl) crystals was studied at accumulated 1 MeV photon doses of 2, 10 and 35 Gy. At each dose, the longitudinal uniformity of the crystals light yield, scintillation decay times, time resolution and energy resolution was measured. As the Belle II collaboration is considering an upgrade to pure CsI crystals if CsI(Tl) does not satisfy radiation hardness requirements, the scintillation properties of a pure CsI scintillation crystal were also measured and compared to the CsI(Tl) crystal measurements. In addition to experimental work, Monte Carlo simulations using GEANT4 were written to compare ideal pure CsI and CsI(Tl) crystals and to study the effects of radiation damage on the performance of the Belle II electromagnetic calorimeter. / Graduate

The development of new digital mammography techniques such as dual-energy imaging, tomosynthesis and CT mammography will require investigation of optimal camera design parameters and optimal imaging acquisition parameters. One tool that is useful for this purpose is Monte Carlo simulation. This study presents a methodology for generating simulated images from a CsI-based, flat-panel imager model and for estimating the normalized glandular dose to the uncompressed breast in CT mammography. The simulation uses the GEANT 3 Monte Carlo code to model x-ray transport and absorption within the CsI scintillator, and the DETECT-II code to track optical photon spread within a columnar model of the CsI scintillator. The Monte Carlo modeling of x-ray transport and absorption within the CsI was validated by comparing to previously published values for the probability of a K-shell interaction, the fluorescent yield, the probability of a K-fluorescent emission, and the escape fraction describing the probability of a K x-ray escaping the scintillator. To validate the combined (GEANT 3 coupled with DETECT-II) Monte Carlo approach to form simulated images, comparison of modulation transfer functions (MTFs) and system sensitivity (electrons/mR/pixel) obtained from simulations were compared to empirical measurements obtained with different x-ray spectra and imagers with varying CsI thicknesses. By varying the absorption and reflective properties of the columnar CsI used in the DETECT-II code, good agreement between simulated MTFs and system sensitivity and empirically measured values were observed. The Monte Carlo software was also validated for dosimetry by comparing results of the linear attenuation coefficient values and the normalized glandular dose (DgN) values of the compressed breast, to those reposted in the literature. The normalized glandular dose was then estimated for three different sizes of the uncompressed breast with a homogeneous composition of adipose and glandular tissue. Further, fit equations of the normalized glandular dose curves were also generated using MATLAB. These equations can be used to replicate the dose for the three sizes of the breast and three compositions of the adipose and glandular tissue. In addition, images displaying energy deposition maps are presented to better understand the spatial distribution of dose in CT mammography.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 122-128). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 122-128). Also available on the Internet.