Measurement of a strong atomic hyperfine field allowing the determination of nuclear /g-factors in (sub)nanosecond states

An extension of the time-integrated atomic decoupling technique to measure g-factors of (sub)nanosecond isomers and/or the magnetic hyperfine field induced by highly excited atomic electrons on nuclei recoiling into vacuum is discussed. A high average field B _hf=1080 _-175⁺²⁷⁰ T and an average atomic spin J=2.7(2) is deduced using the known magnetic moment of a 4.05(7) μs isomer in ⁶⁹Ge. Such high magnetic fields allow g-factor measurements of (sub)nanosecond states. Ab initio calculations show that the combination of a high average magnetic hyperfine field and a high average atomic spin is only possible if a considerable fraction of the ions is in a metastable excited state.