Departing together with electrons and carrying the invisible energy
The discovery of neutrons, it seemed, has clarified the structure of matter. All elementary particles needed to build atoms were known. It only remained unclear where are the electrons observed in the radioactive decay of nuclei if they are not inside nuclei. The study of beta-decay showed that the emission of electrons is caused neither by the electromagnetic nor nuclear interaction, but rather by a new type of interactions yet unknown in physics, so it has been called weak. At first, the experimental facts seem incompatible with the laws of conservation of energy, momentum and angular momentum. In order to save these laws, in 1933, Pauli suggested that in the process of beta decay, along with an electron that is easily observed, another light particle must be born with zero charge, zero rest mass and spin 1/2 — a neutrino. During the beta decay, neutrinos were emitted together with electrons and could carry the missing energy, momentum and angular momentum. In 1934, Enrico Fermi developed a theory of beta decay, which became the prototype of the modern theory of the weak interaction of elementary particles.