Sudden change in the nuclear charge distribution of very light gold isotopes

Abstract

On-line resonance-ionization mass spectrometry has been applied to determine the isotope shift and hyperfine structure of 185-189Au and 189mAu in the 6s 2S(1/2)→6p 2p 1/2 (λ=268 nm) transition. The Au atoms were obtained as daughters of mass-separated Hg isotopes produced at the ISOLDE facility at CERN ionized by a three-color, two-step resonant photoionization process, detected and mass-selected by time of flight. A drastic change of the nuclear charge radius was observed between 187Au and 186Au, which is interpreted as an onset of strong deformation of β≈0.25 in 186Au and 185Au.