The X-ray response of TlBr

We present the results of a series of X-ray measurements on several prototype TlBr detectors. The devices were fabricated from mono-crystalline material and were typically of size 2.7×2.7×0.8 mm3. The material is extremely pure, having impurity concentrations <100 ppm. The measured electron and hole mobility–lifetime products were found to be 3×10−4 and 1×10−5 cm2 V−1, respectively, which are about an order of magnitude higher than previously reported values. Three detectors were fabricated and extensively tested over the energy range 2.3–100 keV at three synchrotron radiation facilities: the Physikalisch-Technische Bundesanstalt (PTB) laboratory at the Berliner Elektronenspeicherring für Synchrotronstrahlung (BESSY II), the European Synchrotron Radiation Research Facility (ESRF) and the Hamburger Synchrotron-strahlungslabor (HASYLAB) radiation facility. Room temperature energy resolutions under full-area illumination of 1.8 and 3.3 keV FWHM have been achieved at 5.9 and 59.95 keV, respectively. At reduced detector temperatures of −30°C, these fall to 800 eV and 2.6 keV FWHM, respectively. Under monochromatic pencil beam illumination, the measured energy resolutions at 6 and 60 keV were 664 eV and ∼3 keV FWHM at the same temperature. For energies <20 keV, the measured spectra display symmetric photopeaks. However, the peaks become increasingly tailed at higher energies. At the highest energies, the energy-losses due to the electrons and holes are clearly separated. Whilst the detectors gave reproducible results over 12 months of operation, it was observed that for synchrotron beam measurements above ∼45 keV, they were unstable, showing rate dependent gain shifts and polarization effects. These were not observed at lower energies. atial uniformity of the detectors was measured using a 50×50 μm2, 12 keV mono-energetic X-ray beam, raster scanned over the forward active area. Whilst two detectors were spatially uniform to a level commensurate with statistics, the third was not. In all cases, evidence was found for charge collection problems caused by field fringing.