Precision Spectroscopy on Trapped Radioactive Ions: Ground-State Hyperfine Splittings of 133 Ba + and 131 Ba +

The ground-state hyperfine splitting of radioactive Ba+ isotopes of mass 133 and 131, confined in a r.f. quadrupole trap, has been measured by laser-microwave double resonances. The results are Δν(133) = 9 925 453 554.59(10) Hz and Δν(131) = 9 107 913 698.97 (50) Hz. The experiment, including measurements of systematic shifts, was performed on quantities of about 1012 isotopes, produced by nuclear reactions and collected at the ISOLDE facility at CERN. The precision is comparable to equivalent measurements on stable isotopes and demonstrates the high-sensitivity of the stored-ion technique. The experiment can be regarded as a first step to a systematic precision study of hyperfine anomalies…