Engineering Commons^™

A High Rate Pixelated Neutron Detector For Neutron Reflectometry At The Spallation Neutron Source, Su-Ann Chong

Doctoral Dissertations

This work presents the development of a high-rate 6Li-based pixelated neutron detector for neutron reflectometry instruments at the Spallation Neutron Source (SNS), Oak Ridge National Laboratory. The current detector technology falls short on the instrument requirements, particularly on the counting rate capability. This detector was designed specifically to overcome the limitation in counting rate by having a fully pixelated design from neutron conversion layer to photodetector and readout system. For the neutron converting layer, a 6Li-based neutron scintillator was used. Each scintillator element was coupled to a photodetector, in this case, a silicon photomultiplier (SiPM). The output of each SiPM …

Fabrication Of Specialized Scintillators For Nuclear Security Applications, Cordell James Delzer

Doctoral Dissertations

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 …

Synthesis And Characterization Of Novel Li-Containing Garnet Ceramic Scintillators For Nuclear Security Applications, Joshua Paul Smith

Doctoral Dissertations

In the field of nuclear security, the ability to detect neutrons is a critical part of the prevention of the smuggling of illicit nuclear materials. The use of dual-mode detector would drastically reduce the number of passive detector systems necessary to meet the detection needs of the nuclear security industry. Li-containing scintillators have been researched for over 70 years; however, relatively few efficient dual-mode detector materials have been discovered. The currently available Li-containing scintillators are relatively low density, very difficult to grow, and highly hygroscopic. These limitations make the wide-spread use of Li-containing scintillators as dual-mode detectors inefficient and expensive. …

Development And Improvement Of Cerium Activated Gadolinium Gallium Aluminum Garnets Scintillators For Radiation Detectors By Codoping, Fang Meng

Doctoral Dissertations

Ce doped Gd3Ga3Al2O12 [gadolinium gallium aluminium oxides] is considered as a promising candidate for the next generation Positron Emission Tomography material due to its high light yield in theory. This dissertation is focused on studying the Gd3Ga3Al2O12:Ce crystals by codoping, aiming to improve the light yield and decay time experimentally and understand the underlying mechanism.

The work starts from prescreening appropriate codopants for Gd3Ga3Al2O12:Ce crystals. A cost-effective method is developed to predict the performance of the single crystals by characterizing the radioluminescence intensity and photoluminescence decay of the small polycrystalline pellets. This method is demonstrated by showing that the results …

Discovery And Improvement Of Novel Metal Halide Scintillators For Radiation Detection Applications, Hua Wei

Doctoral Dissertations

Scintillation materials are in great demand for radiation detection applications. In this dissertation work, a series of new metal halide scintillation materials are presented. A comprehensive procedure of candidate scintillator screening, single crystal growth, scintillation properties characterizations, and scintillation mechanism investigations are established. The potential candidate materials are firstly synthesized by melt-freeze method to form polycrystalline. The scintillation properties of the polycrystalline specimen are characterized to select the most promising scintillators. The selected scintillators are grown into single crystals. Protocols including raw materials purification, materials pre-mixing, ampoule design, and furnace manipulation are developed to improve the scintillators’ performance.

Cerium-doped ternary …

A Study Of Energy Resolution And Non-Proportionality Of Yalo3:Ce And Gd3ga3al2o12:Ce, Samuel Bradley Donnald

Doctoral Dissertations

For many radiation detection applications, energy resolution is one of the most important detector characteristics. In well designed scintillation detectors, the energy resolution is primarily driven by two main factors - the light output and light yield non-proportionality. A great deal of research has already focused on understanding and improving the light yield of scintillation detectors; however, light yield non-proportionality is less well understood. Until recently, light yield non-proportionality was thought to be an intrinsic scintillator property with very little sample-to-sample variation. In this work, two materials have been investigated that demonstrate a variable light yield non-proportionality. The first material …

Discovery And Development Of Rare Earth Activated Binary Metal Halide Scintillators For Next Generation Radiation Detectors, Kan Yang

Doctoral Dissertations

This work focuses on discovery and development of novel binary halide scintillation materials for radiation detection applications. A complete laboratory for raw materials handling, ampoule preparation, material rapid synthesis screening, single crystal growth, sample cutting, polishing and packaging of hygroscopic halide scintillation materials has been established. Ce³⁺ and Eu²⁺ activated scintillators in three binary systems: Alkali Halide – Rare Earth Halide (AX–REX₃), Alkali Halide – Alkaline Earth Halide (AX–AEX₂) and Alkalin Earth Halide – Rare Earth Halide (AEX₂–REX₃) were systematically studied. Candidates for new scintillation materials in the three systems …

Thin Film Combinatorial Synthesis Of Advanced Scintillation Materials, Jonathan Daniel Peak

Doctoral Dissertations

The development and application of a combinatorial sputtering thin film technique to screen potential scintillation material systems was investigated. The technique was first benchmarked by exploring the binary lutetium oxide-silicon oxide material system, which successfully identified the luminescence phases of the system, Lu2SiO5 (LSO) and Lu2Si2O7 (LPS). The second application was to optimize the activator concentration in cerium doped LSO. The successfully optimized cerium concentration in the thin film LSO of 0.34 atomic percent was much greater than the standard cerium concentration in single crystal LSO. This lead to an intensive study based on temperature dependent steady-state and lifetime photoluminescence …