Half-life measurements in doubly-odd ^{186, 188, 190}Au nuclei and the ¹⁸⁸Hg → Au decay

Abstract

A level scheme has been established for ¹⁸⁸Hg → Au decay which was studied with the on-line 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 ^{186, 188, 190, 192}Au, the same conclusion holding for the 1⁻_g.s of ^{188, 190, 192}Au. Additional measurements in 189, 191Hg and ^{185, 187}Au 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.