Sudbury neutrino observatory neutral current detectors signal readout system

Two precise measurements of the ⁸B solar neutrino flux have been made at the Sudbury Neutrino Observatory (SNO) and a third measurement will be made with an array of neutral current detectors (NCD). The NCDs are ³He proportional counters which detect thermalized neutrons liberated by the neutral current reaction ν_x+d→ν_x+n+p in SNO´s D₂O. Due to the very low rate of neutrino interactions relative to the rates of other ionizing particles, one major criteria of the array readout system is to facilitate particle identification for the measurement of the solar neutrino flux. Data acquisition at a rate expected to be produced by the neutrino flux from supernovae within our galaxy (10 kpc) is another major requirement. To accomplish these two tasks, a readout system was constructed based upon two distinct pieces of hardware. Digital oscilloscopes are used to maximize particle identification, but are only capable of handling the expected data rate produced by solar neutrinos. Custom-designed VME-based shaping-discriminating-ADC boards measure the total charge of events and are capable of being read out at 20 kHz.