Low-noise electronics for high-resolution CdZnTe X-ray detection systems

Full text: CdZnTe detector performance can be significantly improved with low-noise electronics. The main sources of noise in a room-temperature system are: leakage current, incomplete charge collection of the detector, and the feedback resistor of the preamplifier. The detector leakage current can be reduced by cooling the detector to about -30 deg. C. Normally, at these temperatures the leakage current drops to the picoampere level which enables the use of low-noise, pulsed-optical feedback preamplifiers instead of noisier resistive feedback preamplifiers. Also, because of lower leakage currents, it is possible to use higher bias voltages at lower temperatures which is important for more efficient charge collection. This 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 have tested a number of Cd0.9Zn0.1Te and Cd0.8Zn0.2Te detector crystals at temperatures between -20 deg. C and -40 deg. C, and at best obtained energy resolutions of 240 eV at the 5.9-keV line of 55Fe, 600 eV at the 59.5-keV line of 241Am, and 780 eV at the 88-keV line of 109Cd. Usually these resolutions measured at room temperature with conventional methods are about 4 to 10 times poorer. (author)