First Observation of theTz=−7/2Nuclei45Fe and49Ni

A primary beam of ${}^{58}$Ni at 600 MeV/nucleon from the SIS synchrotron at GSI was used to produce proton-rich isotopes in the titanium-to-nickel region by projectile fragmention on a beryllium target. The fragments were separated by a projectile-fragement separator and unambiguously identified. We report here the first observation of the $T_z=-7/2\mathrm{}$ nuclei ${}^{45}$Fe and ${}^{49}$Ni, the most proton-rich nuclei ever synthesized with an excess of seven protons. In addition, the new isotope ${}^{42}$Cr $(T_z=-3\mathrm{})$ was identified. According to commonly used mass predictions, these isotopes are all unbound with respect to two-proton emission from their ground states. From the nonobservation of ${}^{38}$Ti $(T_z=-3\mathrm{})$ in this experiment, an upper limit of 120 ns is deduced for the half-life of this isotope.