Irene Zanon

When an extra neutron is added to an atomic nucleus, it starts behaving like an overfilled cup: one more drop and it spills over. Physicists at the French facility GANIL orchestrated such a 'pass' of a neutron from a deuteron (the nucleus of heavy hydrogen) to an oxygen-19 nucleus.

An atomic nucleus is not just a ball of protons and neutrons. It has a shape, and that shape can change. The tin-116 nucleus was long considered almost perfectly spherical: it has 50 protons — a 'magic' number that usually gives a nucleus spherical symmetry. But a new ultra-precise measurement showed otherwise.