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Clyde Cowan and Frederick Reines detected reactor electron antineutrinos through inverse beta decay, ${\bar{\nu }}_e+p\to n+e^{+}$. The Positron supplied a prompt annihilation signal; capture of the neutron supplied a delayed signal. Requiring this pair and comparing operation at different reactor powers separated the weak interaction signature from background. Their 1956 report tested both the timing and physical origin of the signals, including changes to the neutron-capture material.^[ref]

A physicist who taught at the Catholic University of America from 1958 to 1974.^[ref]

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]