The 76Cu conundrum remains unsolved

TL;DR

This paper presents new measurements of the half-lives of isomeric and ground states in uc{Cu}{76}, challenging previous assumptions and highlighting unresolved questions about its nuclear structure.

Contribution

It provides more accurate half-life measurements for uc{Cu}{76} states, revealing both have similar durations and reopening the debate on its nuclear structure.

Findings

Half-lives of uc{Cu}{76} states are 600-700 ms.

Both states have similar decay characteristics.

Results contradict previous literature values.

Abstract

Near the doubly-magic nucleus \nuc{Ni}{78} ($Z=28$, $N=50$), there has been a decades-long debate on the existence of a long-lived isomer in \nuc{Cu}{76}. 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 \nuc{Cu}{76}. 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 \nuc{Cu}{76} are still not fully understood.