Requirements and quantitative comparison of fast waveform digitizers for data-acquisition systems designed for nuclear nonproliferation applications

Accurate pulse shape discrimination (PSD) is essential for organic scintillators such as EJ-301s (or EJ-309s with higher flash point) because they are sensitive to both neutrons and gamma rays. Because of the background gamma-ray presence the accurate neutron detection requires accurate discrimination of neutrons from gamma rays. This is especially important for applications where fast and robust systems are paramount, such as nuclear nonproliferation and safeguards. For nuclear nonproliferation and safeguards applications, accurate discrimination of neutrons from gamma rays significantly influences the outcome of material identification/characterization. Specifically, particle misclassification can lead to longer measurement times or even to false identification/misclassification of measured material. In this paper, various fast waveform digitizers are compared from the PSD-performance point of view. Specifically, a 12-bit, 250-MHz digitizer is compared to a 12-bit, 500-MHz digitizer and a 10-bit 1-GHz/2-GHz digitizer. The results presented in this paper indicate that the 12-bit-500-MHz resolution combination leads to the best PSD results. The results also show that a 10-bit digitizer can perform better than a 12-bit digitizer, if the 10-bit digitizer has a significantly better time resolution.