Manipulating Nonproportionality of Strontium Iodide Crystals with High-Flux Irradiation by 137Cs Gamma Rays

Abstract

Strontium iodide doped with europium (SrI2:Eu2+) is a new scintillator being developed for use in high-energy astrophysical detectors with excellent energy resolution. Nonproportionality is the primary limiting factor to improving its energy resolution, although the physics of nonproportionality is not yet fully understood. Only in the past few years have the underlying physical models of nonproportionality been reported. Materials science solutions for improving nonproportionality are also being investigated, with the main approach being the incorporation of deliberate addition of crystal defects using codoping. In this study, we look at an alternative method that is similar to codoping, using radiation damage to alter proportionality. By irradiating a SrI2:Eu2+ sample with a 2,255 Ci 137Cs source, we explore both the crystal’s potential for space-based applications in a radiation environment and this new method of altering nonproportionality. We propose a novel method of altering the nonproportionality of scintillators, using radiation-induced F-centers in place of co-dopants. We demonstrate that radiation damage is an effective approach for defect engineering that may be used to study nonproportionality in scintillators. The advantage of this proposed approach is that one can use the same crystal to vary the concentration of defects, while codoping introduces additional variables, since it requires growing a different crystal for each codoping concentration.