Pixellated thallium bromide X- and gamma-ray detectors

Thallium bromide is a very promising compound semiconductor for fabrication of X- and gamma-ray detectors due to its wide bandgap (2.68 eV) and higher photon stopping power than other semiconductor materials used for radiation detector fabrication such as CdTe and HgI₂. Our studies made an effort to fabricate pixellated TlBr detectors with sufficient detection efficiency and good charge collection efficiency. In this study, pixellated X- and gamma-ray detectors were fabricated from TlBr crystals. The TlBr crystal was purified by the multipass zone-refining method and grown by the traveling molten zone method. The pixellated TlBr detector has a continuous cathode over one crystal surface and 3 × 3 pixellated anodes (0.57 × 0.57 mm² each) surrounded by a guard ring on the opposite side. The electrodes were prepared by vacuum evaporation of palladium through a shadow mask. Typical thickness of the detectors was around 2 mm. Spectrometric performance of the pixellated TlBr detectors was tested by irradiating them with ²⁴¹Am (59.5 keV), ⁵⁷Co (122 keV) and ¹³⁷Cs (662 keV) gamma-ray sources. Each of the anode pixels of the detector was connected to each charge sensitive preamplifier and the guard ring was grounded. Typical energy resolutions (FWHM) obtained for a pixel of the TlBr detector at -20°C were 4 keV, 7 keV and 10 keV for 59.5 keV, 122 keV and 662 keV gamma-rays, respectively.