From parity violation to two neutrinos, 1956–1962.
In 1930, Wolfgang Pauli postulated the existence of the neutrino, a light, feebly interacting particle. Pauli did this to account for the electron spectrum seen in beta decay. If the electron were the only particle emitted in beta decay, it would always have an energy equal to the difference between the initial and final nuclear state energies. Measurements showed, however, that the electron’s energy was variable and calorimetric measurements confirmed that some of the energy was being lost. So disturbing was this problem that Bohr even suggested that energy might only be conserved on average!
Beta decay could not be understood without a successful model of the nucleus and ...