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Thallium bromide (TlBr) has been under development for room temperature gamma ray spectroscopy. As a result of improvements in material processing and detector fabrication over the last several years, the electron and hole mobility-lifetime products of TlBr are close to those of CdTe. This has allowed us to fabricate 10 mm thick arrays. Without any correction, 4.1% FWHM energy resolution was measured from one pixel of 3x3 array at 662 keV at room temperature. To minimize the polarization effect, lowering the operation temperature was applied to 13 mm thick array and the stable operation beyond 8 months could be seen without any significant degradation of detector performance. Much improved energy resolution of 2.2% or less at 662 keV has been also obtained from one pixel with depth correction. In this paper improved charge collection with Cr contacts and our recent progress made in long term stability of TlBr detectors at room temperature by applying post annealing are presented. [ABSTRACT FROM PUBLISHER]

Nonuniformity in charge transport properties is a limiting factor in energy resolution of radiation detectors. In this paper, we investigate variations in the low temperature ambipolar diffusion length and the mobility-lifetime (\mu \tau) product in bulk doped TlBr using cathodoluminescence (CL) and transport imaging. One TlBr crystal was doped with sodium (Na), aluminum (Al), and silver (Ag). A second TlBr crystal was doped with copper (Cu), iron (Fe), and zinc (Zn). We report the first low temperature high resolution CL spectroscopy and mapping in bulk doped TlBr, showing spatial variation in recombination luminescence on a scale of \sim 10~\mum. Transport imaging is applied to quantify these variations in TlBr at 5 K. Ambipolar diffusion lengths and \mu \tau products, dominated by the transport of holes, are mapped across a 40~\mum segment of TlBr at a resolution of 2~\mum. Ambipolar diffusion lengths are found to vary between 4.6~\mum and 11.2~\mum, on a spatial scale comparable to the variation observed in the CL map. [ABSTRACT FROM PUBLISHER]

Abstract: TlBr and TlBr x I1− x are wide bandgap semiconductor materials being investigated for applications in γ-ray spectroscopy. They have a good combination of density and atomic numbers, promising to make them very efficient detectors. Their low melting points and simple cubic and orthorhombic crystal structures are favorable for bulk crystal growth. However, these semiconductors need to be extremely pure to become useful as radiation detectors. Impurities can lead to charge trapping and scattering, reducing the charge transit lengths and limiting the detector thickness to <1mm. Additional purification steps were implemented to improve the purity and mobility–lifetime product (μτ) of electrons. Detector-grade TlBr with the electron μτ product of up to 6×10−3 cm2/V has been produced, which allowed operation of detectors up to 15mm thickness. The ternary TlBr x I1− x was investigated at different compositions to vary the bandgap and explore the effect of added TlI on the long term stability of detectors. The material analysis and detector characterization results are included. [Copyright &y& Elsevier]

Abstract: Single crystals of small and large diameter Cs2LiYCl6:Ce and 6Li-enriched Cs2 6LiYCl6:Ce have been grown by the vertical Bridgman technique. These scintillator crystals are used in the fabrication of high resolution, gamma ray and neutron spectrometers. The Cs2LiYCl6:Ce and 6Li-enriched Cs2 6LiYCl6:Ce crystals we have grown have high light outputs of up to ∼22,000 photons/MeV. The emission wavelength for the Cs2LiYCl6:Ce and 6Li-enriched Cs2 6LiYCl6:Ce is λ=373nm. This material has an excellent energy resolution at room temperature of ∼4% FWHM for 662keV photons (using a super bialkali photomultiplier). Cs2LiYCl6:Ce exhibits different temporal responses to gamma and neutron radiation. This difference results in effective pulse shape discrimination. In this paper, we will report on our results to date for vertical Bridgman crystal growth and characterization of Ce-doped Cs2LiYCl6:Ce and 6Li-enriched Cs2 6LiYCl6:Ce crystals. [Copyright &y& Elsevier]