Hard X- and γ-ray measurements with a large volume coplanar grid CdZnTe detector

The recent introduction of coplanar grid techniques has led to resurgence in interest in developing large volume compound semiconductor detectors that have a reasonable γ-ray response but also good spectroscopic resolution. We report the results of a series of hard X- and γ-ray measurements on a large 15×15mm2, 10mm thick CdZnTe coplanar grid detector. The measurements were carried out at the HASYLAB and ESRF synchrotron radiation facilities using highly monochromatic pencil beams across the energy range 20–800keV. Additional full-area measurements were carried out using radioactive sources. All measurements were carried out at room temperature. The measured energy resolution under full-area illumination was 8 and 12keV FWHM at 59.95 and 662keV, respectively. Under pencil beam illumination, the measured resolutions were essentially the same. The detector energy response function was found to be linear over the energy range 20–1400keV with an average rms nonlinearity of 1.4%, consistent with statistics. The spatial uniformity of the detector was evaluated at 30, 60 and 180keV by raster scanning a 20×20μm2 monoenergetic X-ray beam across the active area. Apart from a few localized areas, the detector response was found to uniform at the few percent level, consistent with statistics. At 180keV, the nonuniformity in the energy response due to the grids was estimated to be at the 0.7% level.