ABSTRACT
Atomic nuclei entered physics in a ‘shadowy’ way. In the very last years of the 19th century radioactivity constituted the first to be identified, although indirectly, nuclear property. With Rutherford’s experiments just before the First World War nuclei as such became a subject of research. Some of their basic properties were accessed in the 1930s with the identification of neutrons as constituents, together with protons, and with the pion exchange picture of nucleon-nucleon (neutron or proton) interactions. By the late 1940s both collective and single-nucleon behaviours were, to some extent, unravelled. The shell model allowed us to understand the so-called magic numbers and both fission and giant resonances had been observed, if not fully understood. The following decades saw the possibility of accelerating nuclei and smaller particles, to higher and higher energies, in larger and larger facilities, developed following the pioneering works on cyclotrons in the late 1920s. According to Heisenberg’s uncertainty principle these facilities provided access to smaller and smaller structures inside the nucleus, which gave birth to a new field of research: particle physics. In turn nucleonic physics dealing with systems of nucleons, namely nuclei in their ground state or in moderately excited states, became, and still is, a major concern of nuclear physics studies.
