设计了完整的碲锌镉(CdZnTe, CZT)探测器数字核信号处理系统，包含了低功耗偏压电源、低噪声电荷灵敏放大器、数字梯形多道脉冲幅度分析器及数字上升时间甄别器。在考虑探测器与后端数字多道优化匹配前提下设计了低噪声电荷灵敏放大器；数字多道脉冲幅度分析器(Digital Multi-Channel Pulse Height Analyzer, DMCA)通过高速模数转换器将模拟核信号离散化后，在现场可编程门阵列(Field Programmable Gate Array, FPGA)中实现数字核脉冲信号处理；FPGA芯片中以快慢双通道梯形成形器为核心，针对碲锌镉探测器空穴收集不完全的问题，设计了数字上升时间甄别模块，有效消除了空穴拖尾效应，显著提升碲锌镉探测器的能量分辨率。从实验结果可知，针对西北工业大学提供的4 mm×4 mm×2 mm 的准半球结构碲锌镉探测器对241Am的分辨率最佳可达3.6%，对137Cs的分辨率可达0.96%。%Background:CdZnTe (CZT) detector has excellent detection efficiency and resolution toward gamma ray at room temperature. It is a beneficial supplement to HPGe and scintillator detectors. Digital multi-channel analyzer (DMCA) plays significant role for high resolution spectrometer of CZT.Purpose: This study aims to overcome the effect of “hole tailing” for CZT detector by implementing digital nuclear signal processing system. Methods: A low noise charge sensitive amplifier is designed by considering optimal matching of detector and digital multi-channel analyzer. High speed analog-digital converter transforms the analog signal to discrete digital sequence signal. Digitized signals are processed by Field Programmable Gate Array (FPGA) chip in the DMCA. In this FPGA chip, fast-slow dual channel trapezoidal shaper and digital rise time discriminator are designed to overcome the problem of charge trapping of CZT detector. Digital rise time discriminator could eliminate the effect of “hole tailing” and improve the energy resolution of CZT detector.Results:For the 4mm×4mm×2.5mm capture plus structure of CZT detectors offered by Northwestern Polytechnical University, the best resolution is up to 3.6% for241Am source, and up to 0.96% for137Cs source.Conclusion:The optimal matching of each unit circuit in the whole digital nuclear signal processing system could improve the energy resolution for CZT detecting system. Digital multi-channel analyzer with rising time discriminator has significant advantage for CZT detecting system.
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