Multianodic photomultiplier tube characterization at Angra Neutrinos Project

Full text: The Angra Neutrino Project aims to perform the antineutrino flux measurement at the Angra II nuclear reactor in Angra dos Reis, and to correlate it to the nuclear fuel fission and burn-up. A veto system is essential in the detection system, because the rate of cosmic particles reaching the detector is much higher than the antineutrinos rate (signal to background ratio 105). The planned veto system for the Angra experiment is an array of the X-Y type, consisting of orthogonal scintillator plastic plates, where particles detection is provided by the coincidence of signals from two or more scintillators. The light signals are taken to a Multianodic Photomultiplier Tube (MAPMT) with 8 x 8 pixels, through wavelength shifter optical fibers. In each MAPMT pixel, light is converted to electric charge and this analog information is brought to a data acquisition system composed of preamplifiers and data processing modules (MPDs). In the MPDs the information is digitized. A control and visualization software performs data acquisition, making use of an interface to the universal serial bus (USB). In this work we present the data acquisition chain and results for the photomultiplier characterization, which involves determining the gain of each one of the pixels by two different methods: the single photoelectron spectrum, and the statistical technique. In the latter method, by varying the number of photons hitting a given pixel one may determine the gain from a relationship between the average converted charge and its variance. We also present results of characterization for the front-end electronics and for the analog-to-digital converters in the MPDs, which were required to implement the MAPMT data acquisition system. (author)