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. The result was an oxygen-20 nucleus — with one extra neutron.
This nucleus is unstable: some of its states live for less than a millionth of a second and immediately break apart, emitting a neutron. For the first time, scientists observed several of these short-lived states with energies from 7.6 to 9.8 MeV, like capturing freeze-frames of a falling cup. To spot them, they had to simultaneously detect the ejected proton and the gamma radiation from the decay.
Such neutron-rich nuclei occur in nature, for example, inside neutron stars. By understanding how they live and decay, we get a better picture of how matter behaves in the most extreme corners of the universe.
as written by the authors arXiv:2601.03053
The single-neutron transfer reaction $$^{19}$$O(d,p$$\gamma$$)$$^{20}$$O has been performed at GANIL, populating states up to and above the neutron separation energy. Bound states populated by s-wave and d-wave transfer have been observed with improved experimental angular distributions. Critically, several unbound states between 7.6 MeV and 9.8 MeV have been accessed for the first time through the 19O(d,p) channel, and isolated via particle-$$\gamma$$ spectroscopy.
The oxygen-20 nucleus lives for less than one trillionth of a second, yet it still manages to tell us about the forces that hold atoms together.
Science fiction often features unstable elements that explode at the slightest touch. Here we have a similar idea: an extra neutron makes the nucleus so fragile that it decays almost instantly.