Discovery of an I π = 1 0 + Isomer in Yb 150 : Nature of the Longest 10 + Isomeric Chain

Delayed γ-ray spectroscopy was performed for evaporation residues produced in the ⁵⁸Ni+⁹⁶Ru reaction. A new isomer in ₇₀¹⁵⁰Yb (Z=70, N=80) with a half-life of 0.62(5) μs was identified at an excitation energy of 2872(2) keV. Its spin-parity is assigned as (10⁺) and a decay scheme is proposed based on a strong analogy with that of the isotonic ₆₈¹⁴⁸Er. Previously, the 10⁺ isomers were observed in the N=80 even-Z isotones from the neutron-rich ₄₆¹²⁶Pd to the neutron-deficient ₆₈¹⁴⁸Er. For the first time, by combining experimental data and comprehensive large-scale shell-model calculations, we clearly identify the configurations of these isomers and demonstrate that they all exhibit seniority structures. These findings firmly establish a configuration change in the 10⁺ isomeric chain, from a pair of maximally aligned 1h11/2 neutrons (holes) to a pair of maximally aligned 1h11/2 protons around the Z=64 subshell closure. This transition serves as a unique isomeric relay underpinning the persistence of the isomeric chain.