Tales of clustering in the microphysics world

The works presented in this thesis unfold between the deeply intertwined realms of nu- clear physics and chemistry: despite the ordinary perception which may lead to consider these two sciences as separated, the picture appears completely different when diving deep in the study of some peculiar characteristics and phenomena. Symmetries, inter- actions, reactions, excitation modes and the concept of molecular assemblies itself are, in fact, not exclusive of neither of the two frameworks. These analogies are firstly presented through a detailed and organized parade following the historical steps in the development of several models for the description of the simplest atoms and/or nuclei, and of the interactions between their constituents. The cases in which a chemical approach has proved itself useful for the description of a nuclear phenomenon, and vice versa, are not rare, and will be broken down along the Sections in the first Chapter. These include the development of models for nuclear and chemical potentials, for intermolecular and inter-cluster interactions and for the study of clustering in light nuclei and chemical solutions. On the basis of these models and analogies, different investigation techniques are thus presented in Chapter two before entering the experimental heart of the matter. Three Chapters are indeed dedicated to the experimental investigations conducted for three of the most important self-conjugate nuclei: 12C, 16O and 20Ne. The understand- ing of the spectroscopy and of the occurrence of cluster configurations in their ground and excited states, is extremely important to unveil some sketchy features and to solve long-standing questions about crucial aspects of astrophysical and nuclear physics phe- nomena. The development of cluster structures in their ground states (for 12C and 16O) was studied through the applications of a so-called crystallographic model, while the features of some important excited states (such as the Hoyle state in 12C) have been investigated through low-energy nuclear reactions, designed and performed with fine state-of-the-art set-ups and techniques. All comes to an ending with a radiochemistry experiment representing the closure of a cycle, where nuclear physics phenomena (such as neutron radiative capture and nuclear recoil) are finally exploited to investigate the bizarre behaviors of radioactive atoms inside a solution, not describable through the exclusive application of ordinary chemistry approaches.