MTL Annual Research Report 2013

Ionic Conduction Studies in TlBr Radiation Detector Materials

Detection of high-energy radiation (e.g., γ-rays) is key in nuclear non-proliferation strategies.  When a wide-band gap semiconductor detector intercepts a γ-ray, electron-hole pairs are formed, resulting in an increase in electrical conductivity. This change in conductivity is maximized if the conductivity in the non-illuminated (dark) state is very low. Current semiconductor technologies require cooling to very low temperatures, adding to cost and reducing portability.  TlBr is an attractive detector material given its low room temperature dark conductivity, as well as its high mass density, leading to higher radiation absorption.

In this project, we characterize the dominant ionic conduction properties in TlBr, dopant association, and exsolution using impedance spectroscopy.  Through doping techniques, we have determined that TlBr is primarily a Schottky- type ionic conductor, meaning that Tl and Br move through the material by vacancy motion.  These measurements have led us to predict a doping strategy to minimize the dark conductivity. We are collaborating with a local company (Radiation Monitoring Devices, Inc.) to implement this technology as well as developing it further by studying new TlBr-based material systems.  The focus has now shifted to understanding long-term aging affects tied to electrode processes.