Design of digital nuclear signal processing system for CdZnTe detector

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 4 mm×4 mm×2.5 mm capture plus structure of CZT detectors offered by Northwestern Polytechnical University, the best resolution is up to 3.6% for ²⁴¹Am source, and up to 0.96% for ¹³⁷Cs 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.