The Daya Bay Reactor Neutrino Experiment has measured the neutrino mixing angle θ_13 to world-leading precision. The experiment uses eight antineutrino detectors filled with 20-tons of gadolinium-doped liquid scintillator to detect antineutrinos emitted from the Daya Bay nuclear power plant through the inverse beta decay reaction. The precision measurement of sin^22θ_13 relies on the relative antineutrino interaction rates between detectors at near (400 m) and far (roughly 1.8 km) distances

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... the nuclear reactors. The measured interaction rate in each detector is directly proportional to the number of protons in the liquid scintillator target. A precision detector filling system was developed to simultaneously fill the three liquid zones of the antineutrino detectors and measure the relative target mass between detectors to <0.02 operation, and performance of the system and the resulting precision measurement of the detectors' target liquid masses.