Overview-New Challenges Need New Tools It is now fifty years since Mayer and Jensen proposed a shell-model description of atomic nuclei [1], for which they shared the 1963 Nobel Prize for Physics. In their simple independent-particle picture, each nucleon (neutron or proton) feels an average potential due to all the others (the mean-field) and occupies and moves independently in a bound quantum mechanical orbital in this potential. These ideas have been immensely powerful in describing both

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... ematic and more detailed features of the structure of nuclei, metal clusters, and related systems. In particular, they predict that nuclei are more stable when they have the right number of neutrons (N) or protons (Z) to just fill given orbitals, because there is then a natural gap in energy to the next available level; the magic neutron and proton numbers, 2, 8, 20, 28, 50, 82, and 126 that drive many systematic properties of the stable nuclei. Today, we are able to produce very exotic nuclei, with abnormal neutron and proton combinations using dedicated accelerators. The properties of these exotic nuclei, produced in relatively small numbers in earth-based labo-