CowanReines

CowanReines refers to the Cowan–Reines neutrino experiment, the first direct observation of the neutrino. In 1956, physicists Clyde L. Cowan Jr. and Frederick Reines conducted the experiment at the Los Alamos National Laboratory near a nuclear reactor in Los Alamos, New Mexico. The goal was to detect neutrinos emitted by fission processes in the reactor, providing direct confirmation of the neutrino’s existence, long predicted by Pauli and incorporated into Fermi’s theory of beta decay.

The experiment relied on the inverse beta decay reaction: anti-neutrino + proton → positron + neutron. The detector searched for a prompt signal from the positron annihilation, followed by a delayed signal from the neutron’s capture on a nucleus such as cadmium, producing gamma rays. The two signals needed to occur in close succession (delayed coincidence) to suppress background events. A liquid scintillator detector, surrounded by shielding and neutron detectors, registered the events.

Results from the measurements were in agreement with expectations for reactor anti-neutrinos, providing the first solid evidence for neutrinos and confirming a key aspect of weak-interaction theory. The work is regarded as a landmark in particle physics and led to broader neutrino research and detector techniques that remain in use. Frederick Reines later received the Nobel Prize in Physics in 1995 for the detection of the neutrino; Cowan did not receive the prize, having died in 1974.