[alpha]-decay rates for [sup 181-186]Au and [sup 181-185]Pt isotopes

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