MTL Annual Research Report 2011

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, or sensitivity, is maximized if the conductivity in the non-illuminated (dark) state is very low.  In order to achieve high sensitivity, current semiconductor technologies require device cooling to very low temperature, which adds to cost and reduces portability.  TlBr is an attractive detector material because of its low dark conductivity at room temperature as well as its high mass density, leading to higher radiation absorption.

In this project, we have characterized the dominant ionic conduction properties in TlBr 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 ionic vacancy motion.  These measurements have led us to predict a doping strategy to minimize the dark conductivity, and we are collaborating with a local company (RMD) to implement this technology as well as developing it further by studying new TlBr-based material systems.  In addition, our newfound understanding of TlBr has led us to investigate novel device designs never before used in ionic conducting systems.