Structure of neutron-rich nuclei around the N = 126 closed shell; the yrast structure of 205 Au 126 up to spin-parity I^π = (19/2 + )

Heavy neutron-rich nuclei have been populated through the relativistic fragmentation of a 208_ 82 Pb beam at /A = 1 GeV on a .5 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 8 mm thick perspex stopper, positioned at the centre of the RISING -ray detector spectrometer array. A previously unreported isomer with a half-life _1/2 = 163(5) ns has been observed in the N = 126 closed-shell nucleus 205_ 79 Au . Through γ -ray singles and γ - γ 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 ^π = (19/2^+) .