Hyperfine-structure measurements in the ground state of radioactive Eu+150 ions

The hyperfine constants A and B for magnetic dipole and electric quadrupole interaction in the 9S4 ground state of unstable Eu+150 ions have been determined with high precision in an optical microwave double-resonance experiment. The ions were produced by nuclear reactions at the ISOLDE facility at CERN, collected on a foil, reevaporated, and stored in a Paul ion trap. Three of eight possible hyperfine transitions between different F sublevels have been observed with well resolved Zeeman substructure in a residual magnetic field. Analysis of the transition frequencies and extensive second-order hyperfine correction yield values of A=559 010 325(40) Hz, B=-926.2(3.0) kHz. A preliminary value for the nuclear quadrupole moment Q (150Eu+)=1.264(23) b has also been obtained.