First observation of 60Ge and 64Se

Two new neutron-deficient isotopes, 60Ge and 64Se, were observed for the first time. They were produced by projectile fragmentation of a 140-MeV/nucleon 78Kr primary beam on a beryllium target. The secondary fragments were unambiguously identified after separation in the A1900 fragment separator. The nucleus 60Ge corresponds to the heaviest isotone of the N=28 neutron shell and it is most likely the last isotone to be observed. Lower limits of 110 and 180 ns were extracted for the half-life of 60Ge and 64Se, respectively. No events of 59Ga or 63As have been observed, providing very strong evidence that these nuclei are unbound with respect to proton emission. This non-observation implies an upper limit for the half-life of 43 ns for 59Ga and 63As.