A sampling board optimized for pulse shape discrimination in liquid scintillator applications

Pulse shape discrimination is one of the more distinctive features of liquid scintillators. However, the optimum discrimination method to distinguish different types of particles, described in the seminal paper of Gatti and De Martini of more than 40 years ago, was not suitable for routine application until the recent development of adequately fast sampling techniques. In this work we present the features of a board explicitly designed and realized to exploit the performance of a fast, high resolution, 10-bit flash analog-to-digital converter (ADC) in order to sample with sufficient accuracy the integrated scintillation waveforms obtained under alpha or beta irradiation of a scintillator specimen. Data samples could then be processed according to the Gatti and De Martini method (modified following the prescription of Jordanov and Knoll in the case of integrated pulses) to quantify the optimum separation achievable. The board, besides providing the integration of the pulse within its analog portion and the digitization of the signal in the digital section, is also equipped with useful auxiliary functions that increase its versatility and practical operability. Using the same scintillator-phototube assembly, experimental pulse shape discrimination measurements were obtained with the new board and with the conventional charge technique and those results are illustrated here. Output from a Monte Carlo model allowed us to perform a numerical comparison of the performance of the optimum method versus the conventional one.