Fast CdTe and CdZnTe Semiconductor Detector Arrays for Spectroscopic X-Ray Imaging

A growing interest has recently been observed in high flux X-ray imaging detectors with energy discrimination or spectroscopy capabilities. In this study we evaluate the performances of energy sensitive CdTe and CdZnTe detectors for X-ray imaging at fluxes of up to 2 10⁷ X/mm²/s in the 20-150 keV energy range. Linear array detectors made from 3 mm thick single CdTe or CdZnTe crystals have 16 pixels with an 800 in pitch. These detectors were coupled to an innovative custom-designed 16-channel fast spectroscopy front-end electronic circuit. For each channel, the signal is continuously digitized and a FPGA controls acquisition and reconstructs the energy spectra on 256 bins for each channel. The detector was tested under X-rays for fluxes in the 10⁵ to 2 × 10⁷ X/mm²/s range. The main problem encountered at such high fluxes is the multiplication of pile-up events that reduces count rate and degrades energy resolution. When a very short shaping time was used, dead time was lower than 50 ns, and an energy resolution of 11 keV full width at half maximum (FWHM) at 2 × 10⁶ X/mm² s and 20 keV (FWHM) at 10⁷ X/mm²/ s was achieved. We also show imaging results that illustrate the interest of the spectral information provided by each pixel.