A sampling board optimised 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 particle of different origin described in a seminal paper of Gatti and De Martini of more than 40 years ago, was not suited to 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 performances of a fast, high resolution, 10 bit flash ADC in order to sample with enough accuracy the integrated scintillation waveforms obtained under alpha or beta irradiation of a scintillator specimen. The data samples are then 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 digitisation of the signal in the digital section, is also equipped with useful auxiliary functions that increase its versatility and practical operability. Our work is completed with the illustration of the experimental results obtained using with the same scintillator-phototube assembly either the new board or a classical measurement set up which implements the charge technique, and with the output of a Monte Carlo modelling through which we performed a numerical comparison of the performances of the optimum method with respect to the conventional charge technique.