Design of a charge sensitive spectroscopy amplifier for CdZnTe-based high energy x-ray detector

Wide band-gap CdZnTe material, which is widely used in the detection of the hard X-ray and the Gamma ray irradiation, has great advantages in the energy resolution and the detection efficiency. In the design of the conventional nuclear spectroscopy system using CdZnTe crystal, the requirement to eliminate the influence of the electric noise and improve the energy resolution has high priority consistently. The crucial part of the detector processing is to convert the signal which is generated by the CdZnTe detector into a Gaussian-pulse which has smaller enough pulse-width. Generally, the transient current signal which comes from the CdZnTe detector needs to be amplified by using a Charge Sensitive Amplifier (CSA) because the nA magnitude signal (Dozens of nA). The application of the CSA can also improve the system SNR and decrease the influence of the external interference in the signal transmission. Based on the theory of the nuclear electronics, researches of the CSA and the pseudo-Gaussian shaping-filter for the CdZnTe spectroscopy detector were accomplished. On the classic theory of the traditional CSA, we present a new CSA circuit structure. the time constant of attenuation can be altered without changing the value of RF and CF. In addition, there was no obvious influence on the rising time and the noise characteristics of the output-pulse of the CSA simultaneously. Moreover, we demonstrated the application of our CSA improved the sensitivity of the CdZnTe detector that we used in previous experiment. In the simulation of this paper, the optimal parameters of each component were determined according to the analysis of the functional characteristics of the CSA and the pseudo-Gaussian shaping-filters. Experiment results show that the rising time of the CSA output signal is 20ns approximately, the falling time is 150μs and the output pulse of the two stage pseudo-Gaussian shaping filter has minimum 200ns pulse width (FWHM). Based on the performance in our experiment, the designed CSA and the multi-stage pseudo-Gaussian shaping-filter can improve the energy resolution of our CdZnTe detector for the hard X-ray radiation effectively, and the energy resolution for the 137Cs(the source of Gamma) can reach up to 3.5%.