By 1930 the explanation of Beta radioactive decay produced a crisis in the domain of particle physics. Conservation of energy, momentum and quantum statistics seemed to be challenged. Pauli succeeded in solving all these anomalies by postulating the existence of neutrinos inside atomic nuclei. But he did it at the cost of assuming a model of the nucleus that was untenable after 1932, when the neutron was discovered. In 1933 Fermi put forward what we still regard as the correct explanation of Beta decay. In this article I review the explanatory virtues of the neutrino hypothesis. I contend that Pauli's invention was ad hoc in 1930 but it became a testable hypothesis in the context of Fermi's theory. I then conclude by asserting that there was not enough evidence to accept the existence of the neutrino prior to Cowan and Reines' second experiment in 1956.
Beta decay; Neutrino; Conservation laws; Quantum statistics; Scientific discovery