First Observation of the T z = − 7 / 2 Nuclei 45 Fe and 49 Ni

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 ${T}_{z}\\phantom{\\rule{0ex}{0ex}}=\\phantom{\\rule{0ex}{0ex}}\\ensuremath{-}7/2$ 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 $({T}_{z}\\phantom{\\rule{0ex}{0ex}}=\\phantom{\\rule{0ex}{0ex}}\\ensuremath{-}3)$ 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 $({T}_{z}\\phantom{\\rule{0ex}{0ex}}=\\phantom{\\rule{0ex}{0ex}}\\ensuremath{-}3)$ in this experiment, an upper limit of 120 ns is deduced for the half-life of this isotope.