Improving CdZnTe X-ray detector performance by cooling and rise time discrimination

We have studied several methods for improving CdZnTe detector performance, especially energy resolution and charge collection properties. Energy resolution can be greatly improved by cooling the detector to about −30°C [1–3] which reduces the detector leakage current enabling the use of low-noise, pulsed-optical feedback preamplifiers and higher bias voltages. High bias voltages are necessary for more efficient charge collection which reduces spectrum background and peak tailing. Applying rise time discrimination circuitry to the linear amplifier reduces the tailing effect even further, especially at higher energies. Combining all these methods we tested a 16-mm2, 3-mm thick Cd0.9Zn0.1 Te detector crystal at −30°C, and obtained energy resolutions of 292 eV at the 5.9-keV line of 55 Fe, 600 eV at the 59.5-keV line of 241Am, and 780 eV at the 88-keV line of 109Cd. Another 9-mm2, 3-mm thick Cd0.9Zn0.1 Te detector crystal showed a charge collection problem at −30°C which caused all spectrum peaks to be doublets. However, the rise time discriminator removed the ghost peaks form the spectrum almost completely, and improved the energy resolution and background.