Speaker
Description
The hyperfine interaction between the nuclear moments and electronic charge and current distributions occurs naturally for all atoms and ions with non-zero nuclear spin, $I\neq 0$. While the hyperfine splitting of most ionic levels usually remain (very) small, this coupling of the nuclear and electronic degrees of freedom can significantly modify the lifetime of isomeric and electronic states. This applies especially, if symmetry-forbidden transitions in the pure nuclear and/or electronic system becomes allowed due to this interaction. These (so-called) hyperfine-induced transitions have been discussed, and partly obscured, by various names in the literature, including hyperfine-quenched, nuclear hyperfine mixed
or electronic-bridge processes.
Here, we shall introduce a systematic notation to classify these transitions alone in terms of their nuclear and/or electronic subsystems, while keeping their multipole character visible. It supports the evaluation of transition rates, lifetimes, and photon angular distributions and clarifies the conditions, under which the nuclear, electronic, or the mixed nuclear \&{} electronic multipole transition dominate. Well-known examples include the hyperfine-induced electronic-dipole (E1) decay of the $2s2p\;\: ^3P_{0,2}$ levels of beryllium like ions, the nuclear E1 transition in $^{235}$U ions and the nuclear-clock magnetic-dipole (M1) transition in $^{229}$Th ions as well as several other decay modes in nuclear and atomic physics [1]. Our systematic approach will support high-precision spectroscopy and the search for alternative clock transitions or for physics beyond the Standard Model.
[1] Wang W, Fritzsche S and Li Y 2025 PRA 112, 022811