Discovery of a new isomeric state in ${}^{68}$Ni: Evidence for a highly-deformed proton intruder state

Abstract

We report on the observation of a new isomeric state in ${}^{68}$Ni. We suggest that the newly observed state at 168(1) keV above the first 2${}^{+}$ state is a $\ddot{I}€(2p-2h)$ 0${}^{+}$ state across the major Z=28 shell gap. Comparison with theoretical calculations indicates a pure proton intruder configuration and the deduced low-lying structure of this key nucleus suggests a possible shape coexistence scenario involving a highly deformed state.

5 pages, 3 figures, accepted for publication in Physical Review C