Investigation of polarization effect with TlBr detectors at different operating temperatures

In this work, we report on the polarization effect in thallium bromide (TlBr) detectors at different operating temperatures. TlBr is a promising room-temperature semiconductor detector material due to its high atomic number (Tl: 81, Br: 35), high density (7.56 g/cm3) and wide band gap (2.68 eV). Current TlBr detectors suffer from polarization, which causes performance degradation over time when high voltage is applied. A 4.6 mm thick TlBr detector with a pixellated Au/Cr anode fabricated by Radiation Monitoring Devices, Inc. is used in the experiments. The detector has a planar cathode and nine anode pixels with 1.0 mm pitch surrounded by a guard ring. The same detector successfully operated under bias at -20°C for over a month [1]. Several experiments at -15, -10, -5, 0, 5, 10, and 15°C were carried out where the detector was under bias for four weeks at -1000 V. Measured energy resolution from a typical pixel at -5°C is 1.6% at 662 keV without any depth correction. Other spectroscopic properties such as photopeak amplitude and efficiency were studied over time.