In 1956, it was known that in order to balance the spin states of a beta decay process, a neutrino of spin 1/2 had to be a product of the reaction n 0 → → ν ν + p + + β β − − , where n 0 is a neutron, ν ν is the neutrino, p + is a proton, and β β − − is a beta particle. In an attempt to build on the theoretical concept of a neutrino by providing empirical evidence for its existence, physicists Clyde L. Cowan and Frederik Reines constructed an experiment outside of a nuclear reactor expected to emit neutrinos. Cowan and Reines decided to construct a four-fold coincidence experiment, for while the proximity to a nuclear reactor provided ample flux of neutrinos, it also created intense backgrounds (neutrons, gamma rays, etc.).