Figure 1
adapted from M. Ito/RIKEN

The Structure Within. Depending on the energy with which two helium nuclei collide, extra neutrons (dark green) within them can act like electrons in a molecule to bind the alpha-particle cores (red) in an “ionic” (top), “covalent” (center), or “atomic” configuration. A new theory predicts details of these states, which have never been seen in a single nucleus before.