Structure of neutron-rich nuclei around the N = 126 closed shell; the yrast structure of 205Au126 up to spin-parity $I^{\pi}$ = (19/2+)

Heavy neutron-rich nuclei have been populated through the relativistic fragmentation of a \(\ensuremath ^{208}_{\ 82}{\rm Pb}\) beam at \(\ensuremath E/A = 1\) GeV on a \(\ensuremath 2.5 {\rm g/cm^2}\) thick Be target. The synthesised nuclei were selected and identified in-flight using the fragment separator at GSI. Approximately 300 ns after production, the selected nuclei were implanted in an \(\ensuremath \sim 8\) mm thick perspex stopper, positioned at the centre of the RISING \(\ensuremath \gamma\) -ray detector spectrometer array. A previously unreported isomer with a half-life \(\ensuremath T_{1/2} = 163(5)\) ns has been observed in the N = 126 closed-shell nucleus \(\ensuremath ^{205}_{\ 79}{\rm Au}\) . Through \( \gamma\) -ray singles and \( \gamma\) -\( \gamma\) coincidence analysis a level scheme was established. The comparison with a shell model calculation tentatively identifies the spin-parity of the excited states, including the isomer itself, which is found to be \(\ensuremath I^{\pi} = (19/2^+)\) .