ALPHA-DECAY RATES FOR AU-181-186 AND PT-181-185 ISOTOPES

A systematic study of the α decay of Au181-186 utilizing an on-line isotope separator has revealed several α groups and resulted in the observation of the α decay of Au186 and Pt185. By simultaneous measurement of γ-ray and x-ray spectra and use of known EC/β+ decay schemes, α-decay branching ratios and hindrance factors were deduced for each α transition. In Au185 and Au183 the ground state is known to be dominated by the 5/2-,1/2[541] configuration associated with the h9/2 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 h9/2 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 Au181 to the 5/2-,1/2[541] ground state of Ir177 suggests that the ground state of Au181 has a different configuration than those of Au183 and Au185. © 1995 The American Physical Society.