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

TL;DR

This paper reports the discovery of a new isomeric state in $^{68}$Ni, indicating a highly deformed proton intruder state and suggesting shape coexistence in this nucleus.

Contribution

It provides the first evidence of a proton intruder isomeric state in $^{68}$Ni, combining experimental observation with theoretical analysis.

Findings

Identification of a 168 keV isomeric state in $^{68}$Ni.

Evidence for a proton intruder configuration across the Z=28 shell gap.

Indications of shape coexistence involving a highly deformed 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 $\pi(2p-2h)$ 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.