Durán M Teresa, Nedjadi Youcef, Juget Frédéric, Bochud François, Bailat Claude
Institute of Radiation Physics (IRA), Lausanne, Switzerland.
Institute of Radiation Physics (IRA), Lausanne, Switzerland.
Appl Radiat Isot. 2020 May;159:109100. doi: 10.1016/j.apradiso.2020.109100. Epub 2020 Feb 27.
Signal processing is a core part of any electronic chain for radioactivity measurement systems and can influence measurement results drastically. A thorough study of the different alternatives for this treatment is especially worthwhile when developing a new digital system. This article describes an evaluation performed to optimize the digital pulse processing stage of the β-γ coincidence counting system at the Institute of Radiation Physics (IRA) designated laboratory for the activity unit. This study is a part of IRA's digitalization project to modernize the aging analog electronic hardware of its primary measurement systems. The β-γ coincidence counting system consists of a plastic scintillation detector in the beta channel and a well-type NaI detector in the gamma channel. Six pulse shaping digital filters along with amplitude calculation algorithms were implemented to obtain beta and gamma pulse amplitude values. In addition, four timing digital filters and time pick-off methods were set up to calculate arrival times (timestamps) for the pulses generated by both detectors. Filter parameters and algorithm settings were adjusted to obtain the best performance. Combination of filters into traditional two channel (fast for timing and slow for shaping) or one channel configuration using dCFD (digital constant fraction discrimination) and LE (leading edge) time pick-off methods were also tested and compared to study the whole digital pulse processing system, using both real measurement signals (Am, Cs, Co and Ho) and simulated reference pulses. The results of these tests were quantified by evaluating the following metrics: processing speed, signal-to-noise ratio (SNR) at different energies, gamma energy resolution, time measurement accuracy, time resolution and detection efficiency. The results of this evaluation provide a rational ground to assess the system and help decide which digital pulse processing (DPP) method should be the most appropriate.
信号处理是放射性测量系统任何电子链的核心部分，会对测量结果产生极大影响。在开发新的数字系统时，深入研究这种处理的不同替代方案尤其值得。本文描述了在辐射物理研究所（IRA）指定的活度单位实验室对β-γ符合计数系统的数字脉冲处理阶段进行优化的评估。这项研究是IRA数字化项目的一部分，该项目旨在使其主要测量系统老化的模拟电子硬件实现现代化。β-γ符合计数系统由β通道中的塑料闪烁探测器和γ通道中的井型碘化钠探测器组成。实现了六个脉冲整形数字滤波器以及幅度计算算法，以获得β和γ脉冲幅度值。此外，设置了四个定时数字滤波器和时间提取方法，以计算两个探测器产生的脉冲的到达时间（时间戳）。调整滤波器参数和算法设置以获得最佳性能。还测试并比较了将滤波器组合成传统的两通道（定时用快速，整形用慢速）或使用数字恒比甄别（dCFD）和前沿（LE）时间提取方法的单通道配置，以研究整个数字脉冲处理系统，使用实际测量信号（镅、铯、钴和钬）和模拟参考脉冲。通过评估以下指标对这些测试结果进行量化：处理速度、不同能量下的信噪比（SNR）、γ能量分辨率、时间测量精度、时间分辨率和探测效率。该评估结果为评估系统提供了合理依据，并有助于确定哪种数字脉冲处理（DPP）方法最合适。
