复合晶体探测器中数字化波形甄别器的设计

Design of digital pulse shape discriminator for phoswich detector

为满足X射线辐射探测脉冲波形甄别器(PSD)实时性要求,提出了一种新型的数字PSD设计。应用快速模数转换(Flash-ADC)技术,在电路前端对电压脉冲采样将模拟信号数字化;用数字信号处理技术计算采到的波形与理想NaI和CsI波形模板相关系数的差,并以此特征量作为判别采到的信号是否为NaI信号的依据,经计算处理可实时给出甄别结果。用Geant4和Matlab模拟了光子从入射探测器到最后生成相关系数差的分布的整个过程。结果表明:新型数字PSD误判率小于0.5%,满足实时处理事例50ms-1计数率的要求。

A digital pulse shape discriminator (PSD) was developed for real-time processing of X-ray radiation. The X-ray photons react in the phoswich detector to generate a voltage pulse through the electronics. Signals from the front-end circuit are digitized by a flash analog to digital converter. A DSP chip calculates the cross- correlation between the sampled signal and the ideal signal template for NaI and CsI. The difference between the two cross-correlations is used to judge whether the sampled signal was from NaI crystal. The whole system was simulated with Geant4 and Matlab programs. The simulation results show that the PSD has excellent particle discrimination capability with an error of less than 0.5% and fast real-time performance of 50 particles per millisecond.