= Cowan-Reines reactor antineutrino experiment
{c}
{title2=1956}
<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.<The Neutrino: From Poltergeist to Particle by Frederick Reines>[Printed pp. 210–212, Figs. 4–5; individual Washington reproduction]{ref}
\Image[/reactor-antineutrino-prompt-delayed-readout.png]
{title=Separate prompt and delayed readouts of an antineutrino interaction}
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.<Detection of the Free Neutrino: a Confirmation by Clyde Cowan and others>[pp. 103–104, detector analysis and Experimental Results, tests 2–5]{ref}
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