Hard X- and γ-ray measurements with a 3×3×2 mm3 CdZnTe detector

We report the results of a series of X- and γ-ray measurements on a 3×3mm2, 2 mm thick CdZnTe detector carried out at the HASYLAB and ESRF synchrotron radiation facilities. The detector energy response function was found to be linear over the energy range 10–100 keV with an average rms non-linearity of 0.6%, consistent with statistics. Under full area illumination, the FWHM energy resolution was 270 eV at 5.9 keV and rises to 930 eV at 59.54 keV. Under pencil beam illumination, the measured energy resolution at 10 keV was 310 eV FWHM and rises to ∼1000 eV at 100 keV. At 60 keV the resolution was found to be ∼30% lower than that measured under uniform illumination, indicating a degree of non-uniform crystallinity and stoichiometry in the bulk. For energies <50 keV, the measured energy-loss spectra show symmetric photopeaks, becoming increasing tailed at higher energies due to hole trapping. Using risetime discrimination (RTD) to filter out events due to holes, it was found that the shape of the photopeaks could be substantially improved at high energies, albeit at the expense of photopeak efficiency. In fact, the relative number of counts in photopeak, dropped from ∼90% at 10 keV to ∼15% at 100 keV. The results show that a combination of low-noise front-end architecture and RTD leads to very good performances below, say, 100 keV, but above this energy, other techniques (e.g., bi-parametric corrections or single carrier sensing techniques) need to be employed if spectrometric performance is to be maintained.