In an experiment at the SISSI/LISE3 facility of GANIL, we used the projectile fragmentation of a primary ${}^{58}{\mathrm{Ni}}^{26+}$ beam at 74.5 MeV/nucleon with an average current of $3\mu \mathrm{A}$ on a natural nickel target to produce very neutron-deficient isotopes. In a 10-day experiment, 287 ${}^{42}\mathrm{Cr}$ isotopes, 53 ${}^{45}\mathrm{Fe}$ isotopes, 106 ${}^{49}\mathrm{Ni}$ isotopes, and 4 ${}^{48}\mathrm{Ni}$ isotopes were unambiguously identified. The doubly magic nucleus ${}^{48}\mathrm{Ni}$, observed for the first time, is the most proton-rich isotope ever identified with an isospin projection $T_z=-4\mathrm{}$. It is probably the last doubly magic nucleus with “classical” shell closures accessible for present-day facilities. Its observation allows us to deduce a lower limit for the half-life of ${}^{48}\mathrm{Ni}$ of $0.5\mu \mathrm{s}$.

• Received 20 October 1999

DOI:https://doi.org/10.1103/PhysRevLett.84.1116