The 76Cu conundrum remains unsolved

Near the doubly-magic nucleus 78Ni (Z=28, N=50), there has been a decades-long debate on the existence of a long-lived isomer in 76Cu. A recent mass measurement claimed to have settled the debate, by measuring the energy of the isomer and shedding light on the structure of the nucleus. In this work, we present new, more accurate, and precise values of the half-lives of the isomeric and ground states in 76Cu. Our findings suggest that both states have very similar half-lives, in the 600–700 ms range, in disagreement with the literature values, implying that they cannot be differentiated by their decay curves. These results raise more questions than they answer, reopening the debate and showing that the structures in 76Cu are still not fully understood.