An experiment carried out at CERN’s ISOLDE facility has determined the western shore of a small island of atomic nuclei, where conventional nuclear rules break down.
The atomic nucleus was discovered over a century ago, yet many questions remain about the force that keeps its constituent protons and neutrons together and the way in which these particles pack themselves together within it.
In the classic nuclear shell model, protons and neutrons arrange themselves in shells of increasing energy, and completely filled outer shells of protons or neutrons result in particularly stable “magic” nuclei. But the model only works for nuclei with the right mix of protons and neutrons. Get the wrong mix and the model breaks down.