The scientific work of Pontecorvo is full of formidable intuitions, some of which have represented milestones in modern physics. Much of this involved the neutrino, a subatomic particle first proposed theoretically by Wolfgang Pauli in 1930 in order to explain undetected energy that escaped during beta decay so that the law of conservation of energy was not violated. Fermi named it the neutrino, Italian for "little neutral one", and in 1934, proposed his theory of beta decay which explained that the electrons emitted from the nucleus were created by the decay of a neutron into a proton, an electron, and a neutrino. Initially neutrinos were thought to be undetectable, but in 1945 Pontecorvo noted that a neutrino striking a chlorine nucleus could transform it into unstable argon-37 that emits, with a 34 days half-life, after a K-capture reaction, a 2.8 keV Auger electron allowing its direct detection: