Collection of holes in thick TlBr detectors at low temperature

A 3.5 3.5 4.6 mm thick TlBr detector with pixellated Au/Cr anodes made by Radiation Monitoring Devices Inc. was studied. 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 multichannel GaGe PCI digitizer board. Several experiments were carried out at 20 1C, with the detector under bias for over a month. An energy resolution of 1.7% FWHM at 662 keV was measured without any correction at 2400 V bias. Holes generated at all depths can be collected by the cathode at 2400 V bias which made depth correction using the cathode-to-anode ratio technique difficult since both charge carriers contribute to the signal. An energy resolution of 5.1% FWHM at 662 keV was obtained from the best pixel electrode without depth correction at þ1000 V bias. In this positive bias case, the pixel electrode was actually collecting holes. A hole mobility-lifetime of 0.95 10 4 cm/V has been estimated from measurement data. & 2012 Elsevier B.V. All rights reserved.