Browsing by Author "Kim, Chang Hyeuk"

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    A study of an areas x-ray source for Diffraction Enhanced Imaging for Clinical and Industrial Applications
    (2004-05-21) Kim, Chang Hyeuk; Marian G. McCord, Committee Member; J. Michael Doster, Committee Member; Mohamed A. Bourham, Committee Chair; Dale E. Sayers, Committee Member
    Research in diffraction-enhanced imaging (DEI) has shown strong potential in obtaining high-resolution images as compared to conventional radiographs. A successful development of a compact size DEI system would greatly improve x-ray diagnostics in the medical field, as well as potential application in material science research and other industrial applications. DEI experimental research, using a synchrotron source, has shown success and proven to be an attractive medical diagnostics method. While the use of a synchrotron source might be applicable, however, a clinical system would rather use an x-ray source that could be integrated into a radiology system feasible for hospital and clinical practices. This research is aiming to develop an area x-ray source that replaces the need for a synchrotron source by providing a monochromatic area x-ray beam collimated over 100cm2 area. Reasonable operation time (5-10 sec) is also a desirable feature with efficient thermal management of the x-ray tube (target and housing). The x-ray flux should be comparable to synchrotron source flux (1.4 x 1012 photon/mm2/sec). The peak power must not exceed 200kW for feasible use in a major medical facility or industrial complex. A computational study of concentric filament area x-ray source has been investigated in this research. The design features are based on generating electrons from three concentric circular filaments to provide an area electron flux, with a 60kV accelerating potential. The x-ray target is a grounded stationary oxygen-free copper target with a layer of molybdenum (manufactured by BranXray Co., Inc.). Study of electron trajectories and their distribution at various tilt angles of the target was completed using the SIMION 3D code. Heat loading and thermal management is studied using an in-house developed thermal and heat transfer code. X-ray flux and energy distribution for aluminum and beryllium windows was studied using MCNP 4C2 Monte Carlo code. A prototype area x-ray source, a proof-of-principle device, is under construction in the Department of Nuclear Engineering, NCSU to investigate the feasibility of area x-ray generation and the scalability to clinical and industrial aspects. Other researchers will use the computational results of this thesis as a predicting tool to determine and optimize the prototype device operational parameters, and to benchmark the experimental results.
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    A Study of Monochromatic X-ray Area Beam for Application in Diffraction Enhanced Imaging
    (2008-08-21) Kim, Chang Hyeuk; Mohamed A. Bourham, Committee Chair; Man-Sung Yim, Committee Member; J. Michael Doster, Committee Member; David S. Lalush, Committee Member
    Synchrotron-based Diffraction Enhanced Imaging (DEI) system has shown improved contrast images on low attenuation material. In a previous DEI study great potential to detect earlier stage breast cancer was reported. However, to apply DEI technique at the clinical level, a synchrotron source is not feasible for clinically-approved systems due to the size of the accelerator, and hence a compact x-ray source that can replace synchrotron is desirable. Development of an x-ray source compatible to synchrotron radiation is an essential part for a clinical DEI system. Some important features for the design of an x-ray source, based on synchrotron radiation, are the photon flux and beam collimation. The NCSU research group suggested a wide-beam x-ray source, which consists of concentric circular filaments producing electron flux onto a cylindrically-shaped oxygen-free copper stationary target with a thin layer of Molybdenum for x-ray production. This source design emphasizes large field of view, which can eliminate the line by line scanning process experienced in a DEI experimental setup. In this study, the proof of principle model of a wide beam x-ray source was used to study for control electron trajectory of the concentric filaments design, calculations of the produced x-ray flux, simulation of the DEI imaging, and estimation of the operation time with target's active cooling system. The DEI images from the electron distribution were computationally generated by adopting a monochromator and an analyzer with a computationally generated dual cylindrical object. The image simulation showed that the wide-beam x-ray source based DEI images are highly dependent on the electron distribution at the target. Uniform electron distribution by electron trajectory optimization is carried out through independent powering of the filaments inside the focusing cup. For higher electron beam current the x-ray flux satisfies obtaining a successful DEI image scan, but such high current increases the heat loading on the target. The target cooling with a contact cold finger does not provide sufficient thermal management, and hence not enough scanning time. The impinging jet nozzle cooling option was investigated to maximize convective heat transfer, and has shown feasible thermal management and adequate operation time for DEI imaging.