Fabrication of Specialized Scintillators for Nuclear Security Applications

Radiation detectors are important for a variety of fields including medical imaging, oil drilling, and nuclear security. Within nuclear security, they can serve a multitude of purposes whether that be imaging, localization, isotopic identification, or even just activity measurement. Even without directly seeing a nuclear material it is often able to notice their existence without a detector. Scintillators make up an important part of these detectors due to their large intrinsic efficiency, low cost, large volume, and relatively low upkeep. Due to the importance of the large number of purposes these scintillators may be used for, it can often be difficult to find a suitable material for use in new detector design among those that are already produced. This can lead to the need for investigation into new materials and designs to accommodate the needs. In this dissertation two such scintillators as well as the process of fabricating and characterizing them are discussed.

The first scintillator investigated is cesium hafnium chloride, which has recently show promise as a high performance scintillator. We investigate the properties of this scintillator to better understand how growth parameters effect the performance of the final product for use in isotope identification through gamma ray spectroscopy. Findings are presented on the effects of inclusions found within the crystal as well as methods which may be able to reduce the effects of the reduction in light collection caused by the inclusions. Through novel material synthesis methods and high thermal gradient we are able to show improvement iThe second portion of this dissertation discusses the design of thin activated layer scintillators for use as alpha detectors in associated particle imaging. We investigate a first generation design of these detectors using three different production methods, each with a different material. In order to investigate the performance of these scintillators a characterization system v was designed which allowed for the measurement of alpha timing resolution similar to that the would be used in a D-T generation used for associated particle imaging. We report on the results of the threemethods used including timing resolution for each of the methods.n the energy resolution of large diameter crystals.