Long Term Stability of Thallium Bromide Gamma-Ray Spectrometers

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 3×3 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.