Half-life measurements in doubly-odd sup(186,188,190)Au nuclei and the 188Hg -> Au decay

A level scheme has been established for 188Hg -> Au decay which was studied with the online isotope separator ISOCELE. Precise conversion-electron measurements were performed with a semicircular magnetic spectrograph. The half-lives of the 16.0, 82.7 and 114.8 keV levels in 188Au were measured with a lens electron spectrometer and reduced transition rates were deduced. Similarly the half-lives of the 36.1, 113.9, 227.7, 251.5, 288.0 and 363.6 keV levels in 186Au and of the 28.9 and 171.5 keV levels in 190Au were measured. Comparison of the reduced e.m. transition rates shows that a 1+ and a 2- state have respectively the same structure in sup(186,) sup(188,) sup(190,) 192Au, the same conclusion holding for the 1-sub(g.s.) of sup(188,) sup(190,) 192Au. Additional measurements in 189, 191Hg and 185, 187Au together with data from the literature enable us to interpret them as a coupling of certain quasiparticle states of neighbouring odd-A nuclei corresponding to oblate shapes. Indications are given that some other negative- and positive-parity states in 188Au also belong to an oblate system. The nucleus 188Au appears as the last of a series of doubly-odd gold nuclei where no shape coexistence has, as yet, been observed. (orig.)