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Clyde Cowan, Frederick Reines and collaborators tested whether a particle produced by a nuclear reactor could interact again after leaving its source. At Savannah River, water targets containing cadmium chloride lay between liquid scintillators. Opposite detectors recorded prompt positron annihilation gamma rays; Neutron moderation preceded delayed neutron capture signals in cadmium. The arrangement used two target layers and three scintillator layers, with the middle scintillator shared.^[ref]

The original functional diagram separates the two signal mechanisms and their timing. It omits dimensions and phototube counts, and is not a reproduction of a historical drawing. The measured objects are detector pulses; identifying their common cause also requires calibration and background tests.

The 1956 paper describes positron-source and neutron-source calibrations, pulse-height gates and photographic pulse records. Diluting the target with heavy water halved the proton density and reactor signal while preserving neutron-detection efficiency. Changing the cadmium concentration altered capture timing; removing it removed the reactor signal. Added shielding tested competing external radiation. These interventions tested the reaction's ingredients, beyond simply observing a reactor-dependent count rate.^[ref]

For pioneering experimental contributions to lepton physics, one half went to Martin Lewis Perl for discovering the tau lepton; the other half went to Frederick Reines for detecting the neutrino.^[ref]