Stuttgart 2012 – wissenschaftliches Programm
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SYIB: Symposium Fast Ion Beams in Nuclear, Atomic and Molecular Physics Research
SYIB 1: Fast Ion Beams in Nuclear, Atomic and Molecular Physics Research I
SYIB 1.3: Hauptvortrag
Dienstag, 13. März 2012, 11:30–12:00, V55.22
Storage-ring measurements of hyperfine-induced one-photon transitions in highly charged ions — •Stefan Schippers — Instiut für Atom- und Molekülphysik, Justus-Liebig-Universität Gießen
Hyperfine quenching in atoms and ions is the shortening of excited-state lifetimes by the interaction of the electron shell with the magnetic moment of the atomic nucleus. A particularly drastic hyperfine quenching effect is observed in alkaline-earth-like and, in general, divalent atoms and ions (with valence shell n) where the first excited level above the ground state is the ns np 3P0 state. A total electronic angular momentum of J=0 for this level makes a single-photon decay to the (ns)2 1S0 ground state impossible. However, a nucleus with nonzero spin induces a mixing of the ns np 3P0 level with its neighboring ns np 3P1 state via the hyperfine interaction. In Be-like ions, calculated hyperfine induced (HFI) lifetimes of the 2s 2p 3P0 level decrease from about 3000 s to a few µs with increasing nuclear charge.
Accurate measurements of such long lifetimes require an experimental environment where the ions can be stored for sufficiently long times without external perturbations. The only laboratory measurements of HFI lifetimes in multiply charged ions were carried out at the heavy-ion storage ring TSR of the Max-Planck-Institute for Nuclear Physics in Heidelberg. In the talk, I will describe the experimental method which makes use of fast ion beams and state-selective, resonant electron-ion recombination. The experimental results will be compared with theoretical calculations, which — in particular for Be-like ions – are extremely sensitive to electron-correlation effects.