Nuclear shape transition in light gold isotopes

Abstract The hyperfine structure and isotope shifts of short-lived gold isotopes with 185 ⩽ A ⩽ 190 and the 11 2 − isomer of 189 Au have been investigated by application of on-line resonance ionization mass spectroscopy. A detection efficiency of e = 10 −8 for gold atoms was observed at a background of about one event per 1000 laser shots. The deduced charge radii show a drastic change between A = 187 and A = 186 which is interpreted as an onset of strong deformation (β 2 ≈ 0.25) in 186 Au and 185 Au due to the influence of the π 1 h 9 2 intruder orbital.