Investigation of the Delta n=0 selection rule in Gamow-Teller transitions: The beta-decay of Hg-207

Gamow-Teller beta decay is forbidden if the number of nodes in the radial wave functions of the initial and final states is different. This Delta n = 0 requirement plays a major role in the beta decay of heavy neutron-rich nuclei, affecting the nucleosynthesis through the increased half-lives of nuclei on the astrophysical r-process pathway below both Z = 50 (for N > 82) and Z = 82 (for N > 126). The level of forbiddenness of the Delta n = 1 nu 1g(9/2) -> pi 0g(7/2) transition has been investigated from the beta(-) decay of the ground state of Hg-207 into the single-proton-hole nucleus Tl-207 in an experiment at the ISOLDE Decay Station. From statistical observational limits on possible gamma-ray transitions depopulating the pi 0g(7/2)(-1) state in Tl-207, an upper limit of 3.9 x 10(-3)% was obtained for the probability of this decay, corresponding to log ft > 8.8 within within a 95% confidence limit. This is the most stringent test of the Delta n = 0 selection rule to date. (C) 2019 The Authors. Published by Elsevier B.V.