Identification of the Lowest $T=2$, $J^{\pi=}0^+$ Isobaric Analog State in $^{52}$Co and Its Impact on the Understanding of $\beta$-Decay Properties of $^{52}$Ni

TL;DR

This study precisely measured the masses of $^{52g,52m}$Co, identified the lowest $T=2$, $J^{ ext{pi}}=0^+$ isobaric analog state in $^{52}$Co, and revealed its dominant gamma decay mode, refining understanding of $eta$-decay properties in $^{52}$Ni.

Contribution

First precise mass measurements of $^{52g,52m}$Co and the identification of the lowest $T=2$, $J^{ ext{pi}}=0^+$ IAS in $^{52}$Co, challenging previous assignments and enhancing nuclear structure models.

Findings

Masses of $^{52g,52m}$Co measured with ~10 keV accuracy.

The $^{52}$Co IAS decays mainly via gamma transitions, with negligible proton emission.

The $T=2$ multiplet masses fit well into the Isobaric Multiplet Mass Equation.

Abstract

Masses of $^{52g,52m}$Co were measured for the first time with an accuracy of $\sim 10$ keV, an unprecedented precision reached for short-lived nuclei in the isochronous mass spectrometry. Combining our results with the previous $\beta$-$\gamma$ measurements of $^{52}$Ni, the $T=2$, $J^{\pi}=0^+$ isobaric analog state (IAS) in $^{52}$Co was newly assigned, questioning the conventional identification of IASs from the $\beta$-delayed proton emissions. Using our energy of the IAS in $^{52}$Co, the masses of the $T=2$ multiplet fit well into the Isobaric Multiplet Mass Equation. We find that the IAS in $^{52}$Co decays predominantly via $\gamma$ transitions while the proton emission is negligibly small. According to our large-scale shell model calculations, this phenomenon has been interpreted to be due to very low isospin mixing in the IAS.