Advancements in TlBr for Gamma-Ray Detection and Imagin

Thallium bromide is an attractive material for room-temperature gamma-ray spectroscopy and imaging because of its high atomic number (Tl: 81, Br: 35), high density (7.56 g/cm3), and a wide bandgap (2.68 eV). TlBr detectors can achieve better than 1% FWHM at 662 keV for single-pixel events, but these results are limited to stable operation at --20 °C. After days to weeks of room-temperature operation, ionic conduction leads to device failure, or polarization. In this work, methods for extending the room-temperature lifetime of these detectors was investigated, and stable operation for greater than 3 months was achieved using special surface processing techniques. Additionally, the effects of intermediate temperature operation (between --20 °C and room temperature) were investigated and noticeably longer lifetimes were observed with cooling to only 2 °C. This can help reduce the cooling power requirements in field deployable systems if longer term stability at room temperature cannot be achieved.;Important material characterization is also presented including the use of detailed waveform analysis showing that some TlBr detectors have charge multiplication by drifting holes and the measurement of the ionization energy of TlBr. Which when corrected for trapping was shown to be below 5.5 eV. This means the limiting theoretical performance is close to CZT even with TlBr's wider bandgap.;The performance of large volume (12 x 12 x 5 mm 3) TlBr detectors is presented; measured using newly developed digital ASIC based systems. These systems include both benchtop systems which have cooling for the detectors and a prototype hand-held system designed for room-temperature operation. 2.2 % FWHM at 662 keV for all single-pixel events was achieved by the best large volume detector. Better performance should be achievable with these systems with improvements in material as more focus is placed on growing and fabricating large volume detectors.