The stability of TlBr detectors at low temperature

Thallium bromide (TlBr) is a promising 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 pixellated anodes made by Radiation Monitoring Devices Inc. was used in the experiments. The detector has a planar cathode and nine anode pixels surrounded by a guard ring. The pixel pitch is 1.0-mm. Digital pulse waveforms of preamplifier outputs were recorded using a multi-channel GaGe PCI digitizer board for pulse shaping. Several experiments were carried out at −20 °C while the detector was under bias for over a month. No polarization effect was observed and the detector's spectroscopic performance improved over time. Energy resolution of 1.5% FWHM at 662 keV has been measured without depth correction at −2000 V cathode bias. Average electron mobility-lifetime of (5.7±0.8) ×10−3 cm2/V has been measured from four anode pixels.