A systematic study of the α decay of ${}_{}{}^{181\mathrm{-}186}{}_{}{}^{}\mathrm{Au}$ utilizing an on-line isotope separator has revealed several α groups and resulted in the observation of the α decay of ${}_{}{}^{186}{}_{}{}^{}\mathrm{Au}$ and ${}_{}{}^{185}{}_{}{}^{}\mathrm{Pt}$. By simultaneous measurement of γ-ray and x-ray spectra and use of known EC/${\mathrm{\beta }}^{+}$ decay schemes, α-decay branching ratios and hindrance factors were deduced for each α transition. In ${}_{}{}^{185}{}_{}{}^{}\mathrm{Au}$ and ${}_{}{}^{183}{}_{}{}^{}\mathrm{Au}$ the ground state is known to be dominated by the 5/$2^{\mathrm{-}}$,1/2[541] configuration associated with the ${\mathit{h}}_{9/2}$ intruder from above the Z=82 closed shell. Thus, the unhindered α decay of these parents identify levels in the Ir daughters which also are dominated by the ${\mathit{h}}_{9/2}$ orbital. Several previously unknown low-lying γ-ray transitions were observed in the Ir daughters by means of α-γ coincidence measurements. The hindrance factor for the α decay of ${}_{}{}^{181}{}_{}{}^{}\mathrm{Au}$ to the 5/$2^{\mathrm{-}}$,1/2[541] ground state of ${}_{}{}^{177}{}_{}{}^{}\mathrm{Ir}$ suggests that the ground state of ${}_{}{}^{181}{}_{}{}^{}\mathrm{Au}$ has a different configuration than those of ${}_{}{}^{183}{}_{}{}^{}\mathrm{Au}$ and ${}_{}{}^{185}{}_{}{}^{}\mathrm{Au}$.

• Received 5 August 1994

DOI:https://doi.org/10.1103/PhysRevC.51.125