Date of Award
Doctor of Philosophy
Jason P. Hayward
Charles L. Melcher, Lawrence H. Heilbronn, Xiaodong Zhang
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 investigated was Gd3Ga3Al2O12:Ce. For this material, it was determined that co-doping led to an observable change in light yield non-proportionality and light output, which in turn led to an improvement from 9.0% to 7.8% as a result of boron co-doping and a degradation to 10.1% as a result of calcium co-doping. The second scintillator investigated was YAlO3:Ce (YAP:Ce). This material was investigated because it is one of the few materials which exhibits a large sample-to-sample variation of light yield non-proportionality without intentional co-doping. Some of the best samples display a nearly ideal light yield non-proportionality and have an energy resolution as good as 4.3%, while some of the less optimal samples have an energy resolution as poor as 9% as a result of reduced light output, worsened proportionality, and a detrimental optical absorption band. Based on experimental evidence, it was determined that growth in a reducing atmosphere can suppress the detrimental optical absorption band and improve the light output. In addition, it was found that the Ce 3+ concentration was a key parameter in influencing the variable non-proportional behavior. Samples with a higher Ce 3+ concentration exhibited favorable proportionality, and it seems likely that the behavior can be explained by activator saturation.
Donnald, Samuel Bradley, "A Study of Energy Resolution and Non-proportionality of YAlO3:Ce and Gd3Ga3Al2O12:Ce. " PhD diss., University of Tennessee, 2014.