The two-bias method typically used to calculate the mobility-lifetime product ( $\mu \tau $ ) in single-polarity charge sensing detectors, uses induced signals from cathode-side events to measure the $\mu \tau $ . This method assumes an ideal weighting potential (exactly zero through the bulk and a rapid rise to unity at the anode). When a non-ideal weighting potential (e.g., from a pixelated detector) is used, the $\mu \tau $ is systematically overestimated. In this work, we characterize this overestimation and present a simple correction factor $k$ that can be applied to pixelated electrode configurations. It was found that the correction factor is only dependent on the pixel-pitch to detector thickness ratio.

Thallium-bromide (TlBr) is currently under investigation as an alternative room-temperature semiconductor gamma-ray spectrometer due to its favorable material properties (large bandgap, high atomic numbers, and high density). Previous work has shown that 5 mm thick pixelated TlBr detectors can achieve sub-1% FWHM energy resolution at 662 keV for single-pixel events. These results are limited to -20 degrees C operation where detector performance is stable. During the first one to five days of applied bias at -20 degrees C, many TlBr detectors undergo a conditioning phase, where the energy resolution improves and the depth-dependent electron drift velocity stabilizes. In this work, the spectroscopic performance, drift velocity, and freed electron concentrations of multiple 5 mm thick pixelated TlBr detectors are monitored throughout the conditioning phase. Additionally, conditioning is performed twice on the same detector at different times to show that improvement mechanisms relax when the detector is stored without bias. We conclude that the improved spectroscopy results from internal electric field stabilization and uniformity caused by fewer trapped electrons.

Thallium-bromide (TlBr) is currently under investigation as an alternative room-temperature semiconductor gamma-ray spectrometer due to its favorable material properties. Previous work has shown that 5 mm thick pixelated TlBr detectors can achieve sub 1% FWHM energy resolution at 662 keV. However, these results are mostly limited to -20 °C operation. In addition to good electron mobility, some TlBr detectors show hole mobility as high as 15-20% of the electron mobility. High hole mobility can affect depth reconstruction when single-polarity charge sensing is assumed. In this work, we use digital signal processing on the planar cathode waveforms to identify and account for the motion of holes and improve depth reconstruction at all depths for high hole mobility detectors. The hole drift only affects the cathode waveforms because the generated charge induces cathode signal at all depths. Due to the small pixel effect, the anode signal induction only occurs in a region right near the anode. As a result, the motion of holes does not significantly affect the anode signal.

Due to favorable material properties such as high atomic number (Tl: 81, Br: 35), high density ( 7.56 g/cm3), and a wide band gap (2.68 eV), thallium-bromide (TlBr) is currently under investigation for use as an alternative room-temperature semiconductor gamma-ray spectrometer. TlBr detectors can achieve less than 1% FWHM energy resolution at 662 keV, but these results are limited to stable operation at - 20°C. After days to months of room-temperature operation, ionic conduction causes these devices to fail. This work correlates the varying leakage current with alpha-particle and gamma-ray spectroscopic performances at various operating temperatures. Depth-dependent photopeak centroids exhibit time-dependent transient behavior, which indicates trapping sites form near the anode surface during room-temperature operation. After refabrication, similar performance and functionality of failed detectors returned.

Having a high atomic number (TI: 81, Br: 35), high density (7.56 g/cm3), and wide band gap (2.68 eV), thalliumbromide is a favorable candidate material for room-temperature semiconductor gamma-ray detectors. Previous work has shown that TlBr detectors with thicknesses of 5 mm can achieve as good as 1 % FWHM energy resolution at 662 keV. In this work, we report on the spectroscopic performance and charge transport properties of thirteen 5-mm-thick TlBr detectors. Experimental results show that it is feasible to construct operational TlBr detectors with 5 mm thicknesses that acheive energy resolution close to 1 % FWHM at 662 keV. However, consistency in device performance remains an issue with the worst detector preforming at 4.5% FWHM at 662 keV.