Room temperature X- and gamma-ray detectors using thallium bromide crystals

Thallium bromide (TlBr) is a compound semiconductor with wide band gap (2.6 8 eV) and high X- and gamma-ray stopping power. The TlBr crystals were grow n by the horizontal travelling molten zone (TMZ) method using purified mate rial. Two types of room temperature X- and gamma-ray detectors were fabrica ted from the TlBr crystals: TlBr detectors with high detection efficiency f or positron annihilation gamma-ray (511 keV) detection and TlBr detectors w ith high-energy resolution for low-energy X-ray detection. The detector of the former type demonstrated energy resolution of 56 keV FWHM (11%) for 511 keV gamma-rays. Energy resolution of 1.81 keV FWHM for 5.9 keV was obtaine d from the detector of the latter type. In order to analyze noise character istics of the detector-preamplifier assembly, the equivalent noise charge ( ENC) was measured as a function of the amplifier shaping time for the high- resolution detector. This analysis shows that parallel white noise and 1/f noise were dominant noise sources in the detector system. Current-voltage c haracteristics of the TlBr detector with a small Peltier cooler were also m easured. Significant reduction of the detector leakage current was observed for the cooled detectors. (C) 1999 Elsevier Science B.V. All rights reserv ed.