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Nanocomposite glass-ceramic scintillators for radiation spectroscopy

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In recent years, the United States Departments of Homeland Security DHS and Customs and Border Protection CBP have been charged with the task of scanning every cargo container crossing domestic borders for illicit radioactive material. This is accomplished by using gamma-ray detection systems capable of discriminating between non-threatening radioisotopes, such as Cs-137, which is often used in nuclear medicine, and fissile material, such as U-238, that can be used to make nuclear weapons or -dirty- bombs. Scintillation detector systems, specifically thallium-doped sodium iodide NaITl single crystals, are by far the most popular choice for this purpose because they are inexpensive relative to other types of detectors, but are still able to identify isotopes with reasonable accuracy. However, increased demand for these systems has served as a catalyst for the research and development of new scintillator materials with potential to surpass NaITl. The focus of a majority of recent scintillator materials research has centered on sintered transparent ceramics, phosphor-doped organic matrices, and the development of novel single crystal compositions. Some of the most promising new materials are glass-ceramic nanocomposites. By precipitating a dense array of nano-scale scintillating crystals rather than growing a single monolith, novel compositions such as LaBr₃Ce may be fabricated to useful sizes, and their potential to supersede the energy resolution of NaITl can be fully explored. Also, because glass-ceramic synthesis begins by casting a homogeneous glass melt, a broad range of geometries beyond the ubiquitous cylinder can be fabricated and characterized. Finally, the glass matrix ensures environmental isolation of the hygroscopic scintillating crystals, and so glass-ceramic scintillators show potential to serve as viable detectors in alpha- and neutron-spectroscopy in addition to gamma-rays. However, for the improvements promised by glass-ceramics to become reality, several material properties must be considered. These include the degree of control over precipitated crystallite size, the solubility limit of the glass matrix with respect to the scintillating compounds, the variation in maximum achievable light yield with composition, and the peak wavelength of emitted photons. Studies will focus on three base glass systems, sodium-aluminosilicate NAS, sodium-borosilicate NBS, and alumino-borosilicate ABS, into which a cerium-doped gadolinium bromide GdBr₃Ce scintillating phase will be incorporated. Scintillator volumes of 50 cubic centimeters or greater will be fabricated to facilitate comparison with NaITl crystals currently available.

Georgia Tech Theses and Dissertations - School of Materials Science and Engineering Theses and Dissertations -

Autor: Barta, Meredith Brooke - -


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