Neutrons cross the line

摘要

For most atomic nuclei, the maximum number of neutrons that can be bound is unknown. The discovery of two neutron-rich nuclei — and the confirmed absence of others — might help solve this conundrum. Stars are element factories. Every atom in the Universe is a product of stellar nuclear reactions, but many of the stable isotopes that predominate today have formed from nuclei that existed only fleetingly. To understand the isotopic make-up of the Universe, we must first discover which of these ephemeral nuclei can form. In other words, what are the limits of nuclear composition? Reporting in this issue, Baumann et al. describe their discovery of two new nuclei, one of which was thought to be impossible to make (see page 1022). This paves the way for a reassessment of nuclear models.