Berlin 2005 – wissenschaftliches Programm

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A: Atomphysik

A 8: Poster HU 1

A 8.15: Poster

Samstag, 5. März 2005, 08:30–18:30, Poster HU

Measuring the two-electron contribution to the ground-state energy of Xe using an EBIT — •C. J. Osborne, J. R. Crespo Lopéz-Urrutia, A. J. González Martínez, and J. Ullrich — Max-Planck-Institut für Kernphysik, D-69117 Heidelberg.

The two-electron contribution to the ground state binding energy of high-Z atoms provides a useful test of second-order QED calculations. This contribution manifests itself as the 1s Lamb shift, defined as the difference in measured binding energy of the 1s level and the binding energy predicted by the Dirac atomic model with a point-like nucleus. It is proposed to measure this Lamb shift in Xe ions using an Electron Beam Ion Trap (EBIT), by observing the difference in energy of radiative recombination (RR) of beam electrons into initially bare and H-like Xe ions prepared in the trap. Observing the trapped ensemble with a Ge-detector through a thorium foil and scanning the electron beam energy across the Th K-shell absorption edge will achieve very high resolution for this measurement, limited essentially only by the width of the K-shell absorption edge, rather than the resolution of the Ge-detector. This precise knowledge of the RR photon energy, combined with a high-accuracy and precise measurement of the electron beam energy through a voltage divider will yield the energy of the two states and hence, the Lamb shift.