figure caption: A new form of the helium nucleus, He-2, consists of only two protons. This unstable di-proton nuclear fragment was observed in scattering events in which a neon-18 nucleus decayed into an oxygen-16 nucleus plus the He-2. This scenario (top figure) is to be differentiated from the case in which the Ne-18 decays directly into two protons and an O-16 (lower figure)
