Analysis of High-Energy Tailing in TlBr Detectors

Thallium bromide (TlBr) is an attractive material for room-temperature semiconductor radiation detection due to its high atomic number and density. Performance of better than 1% full-width at half maximum at 662 keV has been measured on similar to 5 x 5 x 5 mm(3) pixelated TlBr detectors. Though most TlBr detectors show expected performance, a few detectors have high-energy tails on their photopeaks which are caused by nonflat tails on anode waveforms. The properties of these anode tails are studied and the generation of extra electrons by the movement of holes is proposed to explain the observations. The detector is operated in reverse bias (with holes drifting toward the pixelated electrode) to help confirm these observations and a mechanism for correcting preamplifier decay from long collection time digital waveforms is developed and used in the analysis.