THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Monday, November 5, 2018

1:00 PM

in MRDC 3515

will be held the

DISSERTATION PROPOSAL DEFENSE

for

Christian Struebing

“Design, Synthesis, Characterization, and Application of Rare-Earth Doped Glass and Glass-Ceramic Scintillators”

Committee Members:

Prof. Zhitao Kang, Advisor, GTRI/MSE

Prof. Emeritus Christopher Summers, Advisor, MSE

Prof. Zhiqun Lin, MSE

Prof. Jason Nadler, GTRI

Brent Wagner, Ph.D., GTRI

Abstract:

Single crystal scintillators have long been the primary candidates in gamma radiation detectors due to their high luminescent efficiency and single digit energy resolutions. However, there are several downsides to the use of single crystal scintillators. Due to the nature of single crystals the production of these scintillators is incredibly time-consuming and often requires expensive precursor materials. The end product also suffers from severe vulnerabilities to mechanical shock and high temperatures. Many of the best performing scintillators (NaI:Tl) are hygroscopic and require protective housing that further increases production expenses and the space required in the detector setup. Industries have been searching for lower cost alternatives to single crystal scintillators to reduce the overall cost of radiation detectors in order to make then more practical to implement in portable devices. 

Glass scintillators have drawn attention for their low production cost, scalability, and ease of shaping. The glass matrix self-encapsulates the material which avoids the issue of hygroscopicity even when utilizing bromides in the composition. The primary issue with glass scintillators in the past has been the low luminescent efficiency stemming from the inherent disorder in the glass structure. This downside can be mitigated through increases in density, harnessing innate energy transfer capabilities of constituent materials, as well as through production of glass ceramics from the glass composition. Glass ceramics combine the robust mechanical, thermal, and self-encapsulating capabilities of glass with the high luminescent efficiency of crystalline nanoparticles by precipitating nano-sized crystals within the glass matrix.  This study will approach the field of glass and glass ceramic based scintillator with rare-earth rich, high density compositions modeled after known crystal systems in order to produce a glass ceramic with competitive energy resolution to single crystal scintillators.

Preliminary investigation has resulted in several peer reviewed publications looking at compositions based on LaBGeO5, GdBGeO5, LiGdSiO4, and CaF2 crystal systems. From the investigation into the LaBGeO5 and GdBGeO5 compositions we have demonstrated that high rare-earth content and the energy transfer capabilities of Gd3+ ions can improve the light output of a glass threefold. The CaF2 composition has demonstrated the power of nucleating a crystalline phase within the glass leading to an increase of the light output by a factor of 46. The LiGdSiO4 investigation further demonstrated the effectiveness of high rare-earth content and the benefit of a low phonon energy environment, leading to our production of what appears to be the best performing glass scintillator composition that has been reported to date. Further improvement in the glass ceramics is projected through compositional tuning to encourage nanocrystallite production in our best performing system and increasing batch size for proof of concept of commercial production.