Large volume thallium bromide detectors for gamma-ray spectroscopy

Thallium bromide (TlBr) is a wide bandgap compound semiconductor characterized with high photon stopping power. In this study large volume γ-ray detectors (approximately 3.8·3.8·3.8 mm ³) have been fabricated from the TlBr crystals grown by the horizontal travelling molten zone (TRIZ) method using zone-purified material. In order to extract the energy information of the incident radiation from the thick detectors the short charge collection time technique has been applied to the detectors. By this technique, the induced charge on the electrode is measured for the period of time short compared to the carrier transit time in order to minimize the deviation of the measured induced charge. The large volume TlBr detectors irradiated with ²²Na and ¹³⁷Cs isotopic sources at room temperature have exhibited good energy resolutions of 18.7% and 17.4% (FWHM) for the 511 and 662 keV peaks, respectively. To our knowledge, it is the first achievement that full-energy peaks with good energy resolutions have been obtained from TlBr detectors several mm thick. Time stability of the detector operation has been studied as well. Detailed discussions of the device operation are given