Approved for public release; distribution is unlimited. / Thermophotovoltaic cells are a good candidate for use in high efficiency radioisotope thermoelectric generator (RTG) power devices for deep space missions. This thesis examines the use of Silvaco Virtual Wafer Fabrication Software as a tool for designing and optimizing TPV cells for different possible spectra. It gives results for GaSb and InGaAs cells optimized to the AM0 spectrum which closely match published data as well as hypothetical cells optimized to the spectrum of a 1300K blackbody. / Ensign, United States Navy

"Ionizing radiation is produced as the result of the decay of an unstable nucleus. The standard measure of radioactivity is quantified according to the rate of disintegration of the unstable nucleus. This method of quantification does not incorporate the total amount of ionizing radiation that is associated with each disintegration of the radionuclide. The ionizing radiation that is produced as a result of decay is specific to a given radionuclide. A radionuclide can be conceptualized as a source of ionizing radiation. Disintegration of the unstable nucleus will therefore result in the continual release of ionizing radiation throughout the fixed existence of the radionuclide. This thesis will present a reasonable and practical adjustment to the current mechanism regarding the quantification of radionuclides. This adjustment will provide a basis to which the specific decay attributes of radionuclides can be normalized. Such a normalization will allow for direct comparisons among important inventories of radionuclides. This adjustment will be used to formulate a characterization of common radionuclides that exist in the environment. Such a characterization can provide a control inventory of ionizing radiation to which more specific systems of radionuclides can be compared."

The U.S Environmental Protection Agency (USEPA) Airborne Spectral Photometric Environmental Collection Technology (ASPECT) program is designed in part to provide first responders with radiological mapping of potentially hazardous locations. This program utilizes an aircraft fitted with a gamma-ray spectrometer capable of remote detection of radioisotopes. The challenges present in detecting a radioisotope signal remotely are strongly tied to the signal-to-noise ratio of the collected gamma-ray spectra and the specific signal processing and pattern recognition methods used in the data analysis. Depending on the distance from the detector to the radioisotope source, Compton scattering can significantly reduce the analyte signal, and weakened signals pose a significant challenge when attempting to design an effective classifier for detecting radioisotopes of interest. In this research, a basic methodology has been developed for the detection of cesium-137 (¹³⁷Cs) and cobalt-60(⁶⁰Co) utilizing only laboratory collected spectra and backgrounds from the field collected only once. The presented classifier methodology has been proven to provide a fundamental structure for which more advanced algorithms can be developed. Furthermore, this methodology has demonstrated the ability to strongly associate a level of confidence in a detection which allows for intelligent decision making. From this basic methodology, more sensitive and selective algorithms can be designed. The Compton effect has previously been problematic in the development of gamma-ray pattern recognition systems. In this research, a background suppression methodology utilizing linear regression has been implemented to enhance the basic pattern recognition methodology. This background correction strategy has led to significant improvements in the remote detection of radioisotopes and enables the classification of more complex radioisotopes such as europium-152 (¹⁵²Eu). This research demonstrates not only the capabilities of the pattern recognition methodology, but also the flexibility of the procedure. In the remote detection of radioisotopes, false detections and low sensitivity are the key challenges when developing a classifier. While the background corrected methodology was shown to greatly enhance the classifier performance, further advances can be made into the methodology through the use of committee classifiers. Since every classifier utilizes a different dataspace, a standardization procedure has been developed from which the classifier result can be averaged and generate a committee classifier result. This classifier methodology has been demonstrated to further improve the radioisotope classifier performance without sacrificing either sensitivity or selectivity. While the development of targeted radioisotope classifiers is invaluable to the first responder, developing a general gamma-ray anomaly classifier can handle those radioisotopes that have no dedicated classifier. From this objective, a unique anomaly classifier based on the Compton region of the gamma-ray spectrum has been developed and demonstrated to operate in the field. Utilizing all of the strategies and techniques developed for single radioisotope classifiers, the anomaly classifier has been proven to detect background and natural radioactive sources as well as controlled and man-made radioisotope targets. From the developed remote detection classifiers via pattern recognition techniques, robust radiation detection classifiers have been developed. This pattern recognition methodology eschews the need for extensive field data collection for training the algorithms, while also removing the need for on-site calibrations. When used in conjunction with one another, the dedicated radioisotope and anomaly classifiers provide a thorough and rugged remote detection capability to the first responder. The presented methodology also demonstrates that any radioisotope classifier can be generated, implying that this method can be used for the detection of any radioisotope in the field.

No description available.

Carbon-14, a radioactive nuclide, is used in many industrial applications. Due to its wide range of uses in industry, many workers are at risk of accidental internal exposure to 14C. Being a low energy beta emitter, 14C is not a significant external radiation hazard, but the internal consequences posed by 14C are important, especially because of its long half life of 5730 years. The current biokinetic model recommended by the International Commission on Radiological Protection (ICRP) is a conservative estimate of how radiocarbon is treated by the human body. The ICRP generic radiocarbon model consists of a single compartment representing the entire human body. This compartment has a biological half life of 40 days yielding an effective dose coefficient of 5.8×10-10 Sv Bq-1. This overestimates the dose of all radiocarbon compounds that have been studied. An improved model has been developed that includes and alimentary tract, a urinary bladder, CO2 model, and an "Other" compartment used to model systemic tissues. The model can be adapted to replicate any excretion curve and excretion pattern. In addition, the effective dose coefficient produced by the updated model is near the mean effective dose coefficient of carbon compounds that have been considered in this research. The major areas of improvement are: more anatomically significant, a less conservative dose coefficient, and the ability to manipulate the model for known excretion data. Due to the wide variety of carbon compounds, it is suggested that specific biokinetic models be implemented for known radiocarbon substances. If the source of radiocarbon is dietary, then the physiologically based model proposed by Whillans that splits all ingested radiocarbon compounds into carbohydrates, fats, and proteins should be used.

published_or_final_version / Radioisotope / Master / Master of Philosophy

No description available.

Radon transport mechanisms in soils were studied to determine the dominant transport mechanism for Delaware county soils. In modeling the soil, it was assumed that is was homogenous and moisture-free. Two transport mechanisms were investigated, the transport of radon in the soil by molecular diffusion (assumed to be governed by Fick's law) and transport by pressure-induced flow or convection (assumed to be governed by Darcy's law). Following the previous work of W. E. Clements, a general transport equation was described which incorporated both diffusion and convection. In steady-state conditions, a closed-form solution was obtained for the concentration of radon in the soil interstices as a function of depth. Similarly, solutions were examined for transport by diffusion alone. Representative soil parameters were assigned and the diffusion fraction (the ratio of concentration due to diffusion to the concentration due to both diffusion and convection) was calculated. Referring to the work of A. B. Tanner, a radon availability number (RAN) was determined for the soils; the RAN value was a measure of the activity of radon per unit area. Analyses were also performed to determine the significance of pressure variations on calculated diffusion fractions and RAN values. For 99% of the acreage in Delaware county, the diffusion fraction was 0.95 or greater. Therefore, it was concluded that molecular diffusion is the dominant transport mechanism for the soils of Delaware county. / Department of Physics and Astronomy

Some mounted ill. / Bibliography: leaves 203-263 / vii, 263, [52], [29] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Medicine, 1984

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1982. / Includes bibliographical references (leaves 58-61).