Influence of crystalline surface quality on TlBr radiation detector performance
In this study, TlBr detectors were fabricated from crystals purified by the multipass zone refining and grown by the Bridgman method. Detectors were prepared using TlBr 0.3-mm-thick wafers, with surface submitted to different mechanical and chemical treatments. Optical microscopy and scanning electron microscopy evaluated the TlBr wafers surface quality. To analyze the surface quality influence in the detector response, systematic measurements of the pulse height spectra and energy resolution were carried out for each prepared radiation detector. The radiation response for these detectors was performed under /sup 241/Am gamma radiation excitation at room temperature. The influence of the surface quality of the TlBr wafer on its performance as a radiation detector was observed.
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.
Hard X-ray spectroscopy using small format GaAs arrays
We present preliminary results of X-ray measurements on a prototype 5 � 5 GaAs array. The device was fabricated from 40mm thick epitaxial material and has a pixel size of 200mm � 200mm and pitch 250mm. Measurements from 5.9 to 100 keV were carried out both in our laboratory and at the HASYLAB synchrotron research facility in Hamburg, Germany. The average non-linearity in the spectral response is 51% across the energy range 5.9–98 keV. Using a 12 keV, 20mm � 20mm pencil beam, the uniformity in a pixels spatial response was found to be better than 98%. The energy resolution at –408C is 400 eV, FWHM at 5.9 keV rising to 700 eV at 98 keV. By best-fitting the expected resolution function to the entire data set, we derive a Fano factor of 0.1440 � 0.005, assuming trapping noise is insignificant. Further improvement in the energy resolution has been achieved by replacing the conventional resistive feedback preamplifiers with a new resistor-less design. In this case, an energy resolution of 266 eV FWHM at 5.9 keV has been achieved at room temperature (238C) and 219 eV FWHM with only modest cooling (–318C). # 2001 Elsevier Science B.V. All rights reserved. PACS: 07.85.F; 29.4.W