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

We investigate the ^--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 0h₉/₂0h₁₁/₂ 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.