​​In the years immediately following Antoine Henry Bequerel’s discovery of radioactivity, Ernest Rutherford observed that the radiation emitted by the atom was of at least two distinct types. The first, which he called alpha radiation, was quickly absorbed by matter; the second, beta radiation, was much more penetrating. A third type of radiation, even more penetrating,  was called gamma radiation.

The discovery of the nuclear processes giving rise to these emissions or decay has required considerable research. While scientists found a brilliant theoretical explanation for alpha decay, beta decay was more complicated.

According to Heisenberg’s uncertainty principle, a light particle like an electron confined in a minimal space like a nucleus should acquire a very high energy. Furthermore, it was difficult to imagine any force that could produce this confinement.
The second problem concerned the principle of conservation of energy.
To explain this phenomenon, Niels Bohr even proposed that the law of energy conservation, a fundamental pillar of Physics, was valid on average but not in a single event.
To construct my theory of beta decay, I decided to go beyond the framework of ordinary quantum mechanics. I adopted a point of view of quantum field theory, in which particles can be created and destroyed. I also took up a hypothesis by Wolfgang Pauli from 1930, according to which, in the decay process, a new hypothetical very light particle with zero charge is created: the neutrino. This particle takes up the missing energy.
I therefore imagined that the electron and the neutrino do not already exist in the nucleus but are created and emitted at the moment of decay.
I had discovered a new elemental force: the weak nuclear force. It is not weak per se but less intense than the strong nuclear force and the electromagnetic force.

In December 1933, I wrote the article “Attempt at a theory of the emission of beta rays”, published by the Italian magazine il Nuovo Cimento. In this article, I calculated the value of the constant g, which characterizes the intensity of the weak interaction and regulates beta decay. It iis now known as the Fermi constant.
Within the current standard model of elementary particles, weak and electromagnetic interactions are unified into a single electroweak interaction. The neutrino was discovered and detected through a fission reactor only 22 years later, in 1956.

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