Thallium halide radiation detectors

During a series of experiments on crystal conduction counters performed at Stanford University on thallium halide crystals, we have observed motion of both hole and electron carriers in a TlBr crystal. At a temperature near -90°C the hole motion produces larger pulses than electron motion. We have studied the behavior of TlBr, TlCl, and KRS-5 (40 mol% TlBr + 60 mol% TlI) crystals and examined them as possible crystal conduction detectors of $\alpha$ particles and $\gamma$ rays. TlBr appears to be a promising candidate for applications to nuclear physics and high-energy $\gamma$-ray physics. Modules of TlBr in "crystal-ball" geometry may lead to new detection possibilities. At -20°C space-charge accumulation in TlBr decreases to such an extent that operation at this temperature seems possible with moderate electrical gradients. In the long-neglected field of crystal conduction counters, we have potentially removed the space-charge limitation in TlBr and, allowing for both hole and electron motion, raised the possibility for spectroscopic performance of this material for $\gamma$-ray studies.