Spectroscopy of neutron-unbound 27,28F

The ground state of F-28 has been observed as an unbound resonance 220 keV above the ground state of F-27. A comparison of this result with USDA/USDB shell model predictions leads to the conclusion that the F-28 ground state is primarily dominated by sd-shell configurations. Here we present a detailed report on the experiment in which the ground state resonance of F-28 was first observed. Additionally, we report the first observation of a neutron-unbound excited state in F-27 at an excitation energy of 2500(220) keV.