THE MOST PROTON-RICH NUCLEUS, nickel-48, has been produced for the first time at the GANIL accelerator in France, where beams of nickel-58 atoms are smashed into a target. (Nickel is conspicuous for the range of its isotope varieties: Ni-78, in contrast to Ni-48, is one of the most neutron-rich of nuclei.)

Ni-48 has been of special interest to physicists since it is a "doubly magic" nucleus. A nucleus is exalted as being "magic" if the neutrons or protons exactly fill up one of those shells (analogous to the electron shells in atom) that nature decrees as the model for stability.

It wasn't easy making the Ni-48. Producing just four Ni-48 nuclei required more than 10¹⁷ incoming Ni-58 atoms. The likelihood for creating Ni-48 in this collision process is expressed as a "cross section" of only 50 "femtobarns," the smallest cross section ever measured in nuclear physics. Nevertheless, the apparent lifetime of the Ni-48 nuclei, about half a microsecond, gives the researchers hope that they can look for signs of a never-before-seen form of radioactivity, di-proton decay. That is, with a larger sample, the GANIL scientists (Bertram Blank, blank@cenbg.in2p3.fr) believe they might observe one of the Ni-48 nuclei spitting out a two-proton parcel. (Blank et al., Physical Review Letters, 7 February /pnu/2000/; Select Article.)