Identification of the Lowest T=2, Jπ=0+ Isobaric Analog State in Co 52 and Its Impact on the Understanding of β -Decay Properties of Ni 52

Masses of Co52g,52m were measured for the first time with an accuracy of ∼10 keV, an unprecedented precision reached for short-lived nuclei in the isochronous mass spectrometry. Combining our results with the previous β-γ measurements of Ni52, the T=2, Jπ=0+ isobaric analog state (IAS) in Co52 was newly assigned, questioning the conventional identification of IASs from the β-delayed proton emissions. Using our energy of the IAS in Co52, the masses of the T=2 multiplet fit well into the isobaric multiplet mass equation. We find that the IAS in Co52 decays predominantly via γ 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.