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.

Based on the current discharge rate of nuclear reactors the total inventory of SNF in the U.S. will exceed the current design capacity of the Yucca Mountain repository by 2010. This leaves no room for future SNF discharged from the current nuclear fleet or reactors that potentially will be built. Expansion of the Yucca Mountain repository would provide a large economical benefit as siting and developing a second repository would be a drawn out, divisive and expensive process. The goal of this work is to analyze the thermal loading of SNF into Yucca Mountain in order to investigate the feasibility of repository capacity increase without exceeding the thermal limitations set by the DOE. To examine the feasibility of repository capacity expansion, the concept of variable drift spacing using uniform loading and the concept of variable drift thermal loading using a non-uniform following were investigated. To support the work, a thermal analysis model, SRTA, was employed to describe the temperature changes in the rock around the waste packages against thermal design limits as a function of spent fuel characteristics and composition. Results indicated that, by implementing the scheme of variable drift spacing or variable drift thermal loading, the capacity of the repository could be increased from the legislative limit of 70,000 MTU without violating the thermal limits of the drift wall (200˚C) and the limit midway between the drifts (96˚C). By implementing different loading criteria it was found that the capacity of the repository could be increased by as much as 48% based on the mean estimate. This thesis does not include capacity increases that could result from extending the repository footprint, the number of levels in the repository or the appropriateness of the thermal design limits.

Using the MCMIS (Monte Carlo for Mammography Image Simulation) code, several possible scenarios of microcalcification images were simulated for the Fischer SenoscanTM digital mammography system, which has been approved for clinical use by the F.D.A. The cases simulated included detectors that have 100 ?Ým x 100 ?Ým, 50 ?Ým x 50 ?Ým, and 25 ?Ým x 25 ?Ým pixels in order to determine how much improvement can be obtained through decreased pixel size in the detection of microcalcification clusters in mammograms. Breast thickness was also varied for each modality from 4 to 7 cm in order to determine the effect that reduced breast compression will have on image quality under ideal conditions. The breast phantom used for each simulation included a region of microcalcification pairs of varying size and pair spacing. This microcalcification cluster phantom was designed such that simulated images would indicate the minimum required size and spacing for microcalcification clusters to become distinctly discernable in each of the modalities under scrutiny. Both qualitative and quantitative analyses were performed for each simulated image produced. A decrease in detector pixel size did not show the expected result of significant improvement in cluster detection ability, even under ideal conditions. However, for the range of breast thickness studied, results indicate that decreasing the amount of compression during a mammogram did not significantly affect the image quality in terms of image resolution or contrast for all detector modalities tested. These results suggest that new detector modalities incorporating smaller detector pixel sizes may not show significant improvement over current modalities. However, they also suggest that doctors may be able to make the mammogram process less painful for the patient while maintaining image quality.

The work presented in this thesis is a continuation of a master?s thesis research project conducted by the author to gain insight into the applicability of inverse methods to developing adaptive simulation capabilities for core physics problems. Use of adaptive simulation is intended to improve the fidelity and robustness of important core attributes predictions such as core power distribution, thermal margins and core reactivity. Adaptive simulation utilizes a selected set of past and current reactor measurements of reactor observables to adapt the simulation in a meaningful way that is reflected in higher fidelity and robustness of the adapted core simulators models. We propose an inverse theory approach in which the multitudes of input data to core simulators, i.e. reactor physics and thermal-hydraulic data, are to be adjusted to improve agreement with measured observables while keeping core simulators models unadapted. At a first glance, devising such adaption for typical core simulators models would render the approach impractical. This follows, since core simulators are based on very demanding computational models, i.e. based on complex physics models with millions of input data and output observables. This would spawn not only several prohibitive challenges but also numerous disparaging concerns. The challenges include the computational burdens of the sensitivity-type calculations required to construct Jacobian operators for the core simulators models. Also, the computational burdens of the uncertainty-type calculations required to estimate the uncertainty information of core simulators input data presents a demanding challenge. The concerns however are mainly related to the reliability of the adjusted input data. We demonstrate that the power of our proposed approach is mainly driven by taking advantage of this unfavorable situation and show that significant reductions in both computational and storage burdens can be attained for a typical BWR core simulator adaption problem without compromising the quality of the adaption.

The spread of arthropods due to trade of agricultural commodities and travel of humans is a significant problem in many countries. Limiting the movement of pest species is commonly achieved by the use of chemical pesticides at quarantine facilities. One potential alternative to chemical pesticides is direct exposure of contaminated commodities to ambient pressure electrical discharges. The arthropods are directly exposed to a 5.0 cm helium discharge with power densities on the order of 60 mW/cm3. Direct measurement of chemical species and ambient gas temperature shows the DBD treatment remains effective when the chemically reactive species are suppressed by helium, and when the ambient gas temperature of the discharge is below 40 °C. In addition to gas temperature measurements and chemical species identification, the electron temperature and electron density were measured using the neutral bremsstrahlung continuum technique. This study is the first successful implementation of the neutral bremsstrahlung continuum emission diagnostic to a barrier discharge. The primary advantages of the diagnostic for barrier discharges are the measurement is passive and the spatial resolution is only limited by the collimation of the light and the sensitivity of the detector. Although the electron temperature (1.0-1.5 eV) and electron density (~108 cm-3) are modest, non-chemical dielectric barrier discharge (DBD) treatment of arthropods has proven effective in significantly reducing the population of some arthropods including human body lice, green peach aphids, and western flower thrips. However, the treatment was not universally effective on all arthropod species. German cockroaches and citrus mealy bugs showed substantial resistance to the treatment. The study has shown the treatment does not always induce instant mortality: however, the mortality increases over a 24 hr-period after treatment. Based upon visual observation and the time after treatment to reach maximum mortality, the mode of action is either direct damage to the nervous system or changes to the hydrocarbon layer that protects the arthropods from dehydration.

Monte Carlo simulations of neutron porosity logs were performed to examine the possibility of replacing the standard Americium-Beryllium neutron source. The candidate replacement sources were the Californium-252 radioisotope and the Deuterium-Tritium fusion reaction based particle accelerator neutron source. It was found that the differences in the energy spectra of neutrons emitted by the sources made an impact on the observed response. Both candidates were found to have potential as sources for the log.

The purpose of this research has been to characterize the parameters of an Atmospheric Plasma Device used for surface modifications and functionalization of textile materials. Device parameters are determined in absence and presence of a substrate to quantify the optimal operational conditions. Neutral gas temperature profiles were determined for a variety of gas mixtures including 100% helium and helium with 1 or 2% reactive gases, such as oxygen and carbontetrafluoride. A plasma model was developed to solve for other plasma parameters including the electron-neutral collision frequency and the electron number density. Wool substrates were treated with various gas mixtures for a range of exposure durations and the effects of plasma treatment on weight, surface-functionality, and strength were assessed. Assessment methods include percent weight change calculations, energy dispersive X-ray spectroscopy (EDS), and tensile testing. In addition, cellulosic paper was exposed to 1% oxygen plasma to determine the feasibility of permanently grafting the anti-microbial agent HTCC (quaternized ammonium chitosan). The success of the bond was tested using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), colorimetry, and percent weight change, and the permanency of the bond was tested though soxhlet extraction.

F-18 is a short-lived radioisotope commonly used in Positron Emission Tomography (PET). This radionuclide is typically produced through the O-18(p,n)F-18 reaction by proton bombardment of O-18-enriched water. Thermosyphon batch targets have been proposed as a means to increase F-18 production due to their enhanced heat rejection capabilities. These boiling targets have been operated with up to 3.2 kW of beam power with manageable O-18 enriched water volumes. The purpose of this research project has been to develop computational methods which can be used to design new targets with enhanced production capabilities. The computational methods developed in this work were used to design a low power thermosyphon production target for the Duke Medical Center cyclotron. This design was modeled to be range thick, and operate within the desired margins for beam powers in excess of 1 kW, the operating limit of the Duke cyclotron. A sensitivity analysis of the computational methods was performed which indicated the model is most sensitive to the boiling and condensing heat transfer coefficients. Even with a high uncertainty in these coefficients, the target should still operate well within the desired margins.

A system based on the concept of three detectors radio active particle tracking, to track a particle non-invasively in the three dimensions is presented. It consists of a set of three well collimated detectors mounted on a platform that can be moved to track the radioactive particle vertically through one collimated detector with a horizontal slot opening. The other two collimated detectors with vertical slot opening can be rotated angularly to track the radioactive particle in the planar domain, and deduce the polar coordinates. A complete description of the actual system developed is outlined including the hardware, the automation and control software, and the data acquisition aspects. A critique of the conventional tomographic radioactive particle tracking was established in comparison to the new three detectors system we developed. A number of obvious and valuable advantages of the new method were pointed out. The result presented here are illustrative through a series of benchmark experiments to test and verify the performance of the system. Results of real trajectories of a single radioactive particle moving in air, and in a bed filled with a mass of granular spherical attenuating medium is also presented. Through testing benchmark experiments that include a variety of real time trajectories the success of the tracking system is demonstrated.

Characteristics of non-thermal atmospheric-pressure plasma generated in a coaxial cylindrical Dielectric-Barrier Discharge (DBD) were investigated for application in treatment of polymer and 100% un-mercerized cotton yarns. The discharge characteristics were investigated by measuring the electrical parameters and utilization of developed plasma circuit models to obtain plasma electron temperature, number density and the electron-neutral collision frequency. The experiments were conducted in helium and oxygenated helium plasma in absence and presence of yarns. The discharge is capacitively-coupled and is induced by an audio-frequency, 4.5 kHz, oscillating voltage. The electrical voltage-current (V-I) characteristics optimized for plasma processing, by the oxygen and helium flow rate ratio, was found to be about 40sccm for oxygen flow. Optical emission spectroscopy (OES) was used to determine the plasma composition and to evaluate plasma temperature and number density. The plasma electron number density decreased from 2.2 x 10^16 to 1.4 x 10^16 per cubic meter when oxygen flow rate was increased to 100sccm in a 10,000sccm helium flow, while the electron temperature increased from 0.15 to 0.4 eV for the same increase in oxygen flow rate. It was also found that the plasma experiences some streamers and that the streamer?s electron temperature has a wide range between 0.5 to 2 eV. The optimized oxygen flow rate for polymer yarn processing was found to be 40sccm in a 10,000sccm helium flow.