Competition between Allowed and First-Forbidden $beta$ Decay: The Case of $^208Hgrightarrow^208Tl$
R. Carroll, Zs. Podolyák, Tom Berry, H. Grawe, T. Alexander, Andrei N. Andreyev, Shahzad Ansari, M. J. G. Borge, M. Brunet, J. R. Creswell, L. M. Fraile, Claes Fahlander, H. O. U. Fynbo, E.R. Gamba, William Gelletly, R.-B. Gerst, Magda Górska, A. Gredley, Paul T. Greenlees, L. J. Harkness-Brennan · White Rose Research Online (University of Leeds, The University of Sheffield, University of York) · 2020
The β decay of 208 Hg into the one-proton hole, one neutron-particle 208 81 Tl 127 nucleus was investigated at CERN-ISOLDE.Shell-model calculations describe well the level scheme deduced, validating the protonneutron interactions used, with implications for the whole of the N>126, Z<82 quadrant of neutron-rich nuclei.While both negative and positive parity states with spin 0 and 1 are expected within the Q β window, only three negative parity states are populated directly in the β decay.The data provide a unique test of the competition between allowed Gamow-Teller and Fermi, and first-forbidden β decays, essential for the understanding of the nucleosynthesis of heavy nuclei in the rapid neutron capture process.Furthermore, the observation of the parity changing 0 þ → 0 -β decay where the daughter state is core excited is unique, and can provide information on mesonic corrections of effective operators.