High Resolution Neutron Imaging with Li-glass Multicore Scintillating Fiber and Diffusion Studies to Enable Improved Neutron Imaging
Date of Award
Doctor of Philosophy
Steven Zinkle, Charles Melcher, Howard Hall, Lawrence Heilbronn
High resolution neutron imaging is an essential tool used for fundamental characterization of novel x-ray opaque microstructures. Currently, advanced neutron scattering facilities enable users to image materials with state-of-the-art neutron radiography spatial resolutions of approximately 10-15 microns. Continued progress towards micron resolution is limited by the intensity and the linearity of available thermal neutron fluxes. This places an emphasis on increasing neutron conversion/detection efficiency while maintaining the spatial accuracy of the projected radiograph.This dissertation reports the results of experimental fabrication and characterization of a microstructured multicore 6-lithium-glass scintillating fiber as a proof-of-concept high resolution neutron imager. The approach towards micron–level thermal neutron imaging and fundamental scintillator materials research for relevant imaging technologies are presented. Fabrication trials and neutron/gamma discrimination observations for an initial square-packed multicore design are described first. Then the fabrication process used for a proof-of-concept hexagonal-packed multicore design,and an evaluation of its radioluminescence and chemical stability is presented. Scintillation characteristics of a neutron imaging face plate were estimated, and its spatial resolution was experimentally measured. The ultimate resolving power of the proof-of-concept multicore was comparable to the state-of-the-art. The impact of even higher resolution designs, with potential to track neutron conversion particles using smaller core pitch or different cladding material, is discussed. Neutron imaging often requires nonlinear detection systems that can accurately represent the spatial features of an irradiated object. While thin film and microchannel plate detectors have been heavily researched for this application, little effort has been made to create selective scintillating regions within structured silicate glass detectors. This dissertation presents the continued research of diffusing trivalent cerium in lithium loaded glass. The creation of near surface regions of scintillation with thermal diffusion of the Ce3+ activator into 6Li glass is presented, and its use for neutron imaging with a bent optical fiber taper is discussed. The activation energy of Ce within the silicate is calculated and its valance state is observed as a function of diffusion depth. The diffusion process is then adopted for use with YAP (YAlO3:Ce) for associated particle imaging applications.
Moore, Michael, "High Resolution Neutron Imaging with Li-glass Multicore Scintillating Fiber and Diffusion Studies to Enable Improved Neutron Imaging. " PhD diss., University of Tennessee, 2019.