Discovery of doubly magic Ni-48

In an experiment at the SISSI/LISE3 facility of GANIL, we used the projecti le fragmentation of a primary Ni-58(26+) beam at 74.5 MeV/nucleon with an a verage current of 3 mu A on a natural nickel target to produce very neutron -deficient isotopes. In a 10-day experiment, 287 Cr-42 isotopes, 53 Fe-45 i sotopes, 106 Ni-49 isotopes, and 4 Ni-48 isotopes were unambiguously identi fied. The doubly magic nucleus Ni-48, observed for the first time, is the m ost proton-rich isotope ever identified with an isospin projection T-z = -4 . It is probably the last doubly magic nucleus with "classical" shell closu res accessible for present-day facilities. Its observation allows us to ded uce a lower limit for the half-life of Ni-48 of 0.5 mu s.