Were it not for the strong force, a nucleus would be blown apart by electrostatic repulsion. Viewed as an interaction between fundamental quarks, the strong force is well understood. The protons and neutrons that make up a nucleus, however, are composite particles. And to this day, physicists are struggling to determine the basic nuclear interactions responsible for holding the nucleus together (see the article by David Dean, Physics Today, Physics Today 0031-9228 60 11 2007 48 https://doi.org/10.1063/1.2812123 November 2007, page 48 ).
To that end, nuclear physicists often turn to barely bound nuclei, whose unusual properties and exotic decay modes can test theoretical models and thus provide valuable clues about nuclear forces. One intriguing example is proton-rich iron-45, whose lifetime is a few milliseconds. On occasion, the isotope emits two of its protons simultaneously. The signature of that decay, though not the two protons themselves, was observed in 2002,...
