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.
On the development of compound semiconductor thallium bromide detectors for astrophysics
Abstract We discuss the detector requirements for future X-ray astrophysics missions and present preliminary results from our compound semiconductor program designed to produce X-ray detectors with high spatial and spectral resolution across the energy range of 1–200 keV. Several prototype detectors have been fabricated from monocrystalline TlBr and tested at hard X-ray wavelengths in our laboratories and at the ESRF synchrotron research facility. Energy resolutions of 1.6 keV (FWHM) at 5.9 keV and 2.6 keV (FWHM) at 26 keV have been achieved, although we find that performance is highly variable due to polarisation effects. The resolution function is dominated by high leakage current at all energies. From pulse-height measurements of 241Am as a function of detector bias, we derive the electron mobility–lifetime product at −2°C to be (2.9±0.2)×10−4 cm2 V−1. This is about an order of magnitude higher than previously reported values.
Development of compound semiconductor arrays for x- and gamma-ray spectroscopy
We present preliminary results of X-ray measurements on three small format compound semiconductor arrays. The devices, a 4x4 pixel GaAs array fabricated on 325 micrometers epitaxial material, a 4x4 pixel CdZnTe array fabricated on a 4X4X1 mm3 mono crystal and a 3x3 TlBr array fabricated on a 2.7 x 2.7 x 1.0 mm3 mono crystal. The pixel size for all arrays is 350x350micrometers 2. Results are presented of 55Fe and 241Am measurements at 5.9 keV and 59.54 keV. For detector temperatures <+5 degree(s)C typical FWHM energy resolutions of 410 eV, and 600 eV at 5.9 keV and 640 eV and 1.4 keV at 59.54 keV were recorded for the GaAs, and CdZnTe arrays, respectively. Unlike the GaAs and CdZnTe arrays, the TlBr array showed a much wider variation in pixel performance and was difficult to operate with all pixels at a common bias. For example, biasing the detector so that all pixels worked within the operating envelope of the preamplifiers resulted in average energy resolutions of 20 keV at 59.54 keV. However, optimizing the operating conditions of individual pixels resulted in a marked improvement to ~2keV.