Single phase and boiling batch water targets are the most common designs for the cyclotron production of 18F via the 18O(p,n)18F reaction. Thermosyphon targets have design and operating characteristics which enables higher power operation than conventional boiling targets of like size. Experiments and calculations were performed in order to characterize the performance of a 1.3 cc tantalum [18F]Target. The test target led to the development of a variety of computational techniques as well as experimental methods that will be used in future target design and optimization. Computational methods include several applications of Monte Carlo Radiation Transport as well as Finite Element Analysis. In addition, experimental thermal hydraulic and radiochemical analyses were performed.

Single phase and boiling batch water targets are the most common designs for the cyclotron production of 18F via the 18O(p,n)18F reaction. Thermosyphon targets have design and operating characteristics which enable higher power operation than conventional boiling targets of like size. Experimental thermosyphon target systems demonstrated the feasibility of high intensity irradiation via bottom pressurized operation. An effective experimental characterization platform was developed and utilized in parallel with computational modeling efforts to further improve designs. A control strategy was also developed to provide a simple and robust means of remote target operation. Clinical production systems were designed and deployed at two facilities.

North Carolina State University in conjunction with Bruce Technologies Inc. is developing recirculating water targets for the cyclotron production of high yields of 18F fluoride for PET radiopharmaceuticals. Flourine-18 is commonly produced through proton irradiation of 18O enriched water by the 18O(p,n)18F reaction. Heat deposited in the target fluid by the proton beam is proportional to the 18F produced, thus production is often limited by the targets ability to reject heat. For power levels above 3 kW, boiling batch targets with local cooling can become impractical due to excessive 18O water volumes. One potential solution is a recirculating target system where the target water velocity is sufficient to prevent boiling. In this design the heated fluid travels through an external heat exchanger of sufficient capacity to remove the heat, and then through a pump which returns the cooled fluid to the target. A high-flow/low-volume pump and a high-capacity/low-volume heat exchanger are essential to the overall performance of the recirculating target. In this work, two different types of heat exchangers are considered. Laboratory testing was conducted on a small shell and tube heat exchanger that removed nearly 6 kW of heat at flows provided by a miniature regenerative turbine pump. Laboratory testing was also conducted on a small cross flow heat exchanger with measured performance of 7.4 kW and predicted peak performance approaching 10 kW.

Slant-path buildup factors for photons between 1 keV and 10 MeV for nine radiation shielding materials (air, aluminum, concrete, iron, lead, leaded glass, polyethylene, stainless steel, and water) are calculated with the most recent cross-section data available using Monte Carlo and discrete ordinates methods. Discrete ordinates calculations use a 244-group energy structure that is based on previous research at Los Alamos National Laboratory (LANL), but extended with the results of this thesis, and its focused studies on low-energy photon transport and the effects of group widths in multigroup calculations. Buildup factor calculations in discrete ordinates benefit from coupled photon/electron cross sections to account for secondary photon effects. Also, ambient dose equivalent (herein referred to as dose) buildup factors were analyzed at lower energies where corresponding response functions do not exist in literature. The results of these studies are directly applicable to radiation safety at LANL, where the dose modeling tool Pandemonium is used to estimate worker dose in plutonium handling facilities. Buildup factors determined in this thesis will be used to enhance the code?s modeling capabilities, but should be of interest to the radiation shielding community.

Strontium catalysis may be an important aspect of a novel method of power production involving hydrino reactions. These reactions allow for the release of energy from hydrogen atoms as its electron falls to an energy state below the ground state. The thermal behavior of He-H plasmas with and without Sr present was examined. The plasmas were modeled as capacitors using the Drude model for the dielectric constant. The Joule heating of the plasmas was determined and compared with differential thermal energy to see what effect the addition of strontium had on the thermal output. Most results were inconclusive, but it was clear that plasmas with 1.01% H had a marked increase in thermal output when Sr was added. This means that there may be strontium catalysis of the hydrino process in this case and further experimentation should be done to rule out other explanations for this increase.

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.