Large-scale shell model study of β− -decay properties of N=126 , 125 nuclei: Role of Gamow-Teller and first-forbidden transitions in the half-lives

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We investigate the β^--decay properties of $N=125$ and $N=126$ isotones with $Z=52--79$ through large-scale shell model calculations, considering both Gamow-Teller and first-forbidden transitions. We observed that the distributions of GT strength exhibit a prominent peak at lower excitation energies, making a substantial contribution to the resulting half-lives. This peak, dominated by the ν0h9/2→π0h11/2 transition, is enhanced on the proton-deficient side because the Pauli-blocking effect caused by the occupying the valence proton 0h11/2 orbit is weakened. It is also observed that the contributions of first-forbidden transitions are diminished with a decrease in proton number from $Z=82$.