Long-sought isomer turns out to be the ground state of $^{76}$Cu

Author:

L. Canete, S. Giraud, A. Kankainen, B. Bastin, F. Nowacki, P. Ascher, T. Eronen, V. Girard Alcindor, A. Jokinen, A. Khanam, I. D. Moore, D. Nesterenko, F. De Oliveira, H. Penttilä, C. Petrone, I. Pohjalainen, A. De Roubin, V. Rubchenyaa, M. Vilen, J. Äystö

Keyword:

Nuclear Experiment, Nuclear Experiment (nucl-ex)

journal:

date:

2024-01-25 00:00:00

Abstract

Isomers close to the doubly magic nucleus $^{78}$Ni ($Z=28$, $N=50$) provide essential information on the shell evolution and shape coexistence far from stability. The existence of a long-lived isomeric state in $^{76}$Cu has been debated for a long time. We have performed high-precision mass measurements of $^{76}$Cu with the JYFLTRAP double Penning trap mass spectrometer at the Ion Guide Isotope Separator On-Line facility and confirm the existence of such a isomeric state with an excitation energy $E_x=64.8(25)$ keV. Based on the ratio of detected ground- and isomeric-state ions as a function of time, we show that the isomer is the shorter-living state previously considered as the ground state of $^{76}$Cu. The result can potentially change the conclusions made in previous works related to the spin-parity and charge radius of the $^{76}$Cu ground state. Additionally, the new $^{76}$Cu$(n,\gamma)$ reaction $Q$-value has an impact on the astrophysical rapid neutron-capture process.

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