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Test passed! - High-precision experiments allow detailed determination of the nuclear behavior in highly charged ions

G. Otto, GSI Helmholtzzentrum für Schwerionenforschung

Professor Michael Block at the SHIPTRAP experimental setup.



In high-precision measurements at the GSI Helmholtzzentrum für Schwerionenforschung and of the University Mainz an international team of scientists successfully tested the so called quantum electrodynamics of bound states (BS-QED). For the first time effects resulting from the movement of the atomic nucleus have been taken into account. The results broaden our understanding of the interactions between electrons and atomic nuclei. The results have been published in a recent article in the Nature Communications magazine.

The atomic interaction between nucleus and electrons is described by the quantum electrodynamics of bound states (BS-QED), one of the most tested theories in physics. So far no measurement showed any deviation of the theoretical predictions of BS-QED. In their recent examinations the scientists tested the magnetic momentum of bound electrons in strong electromagnetic fields as they appear at the surface of heavy atomic nuclei. This magnetic momentum is characterized by the so called g-factor. In the experiment the scientists compared the g-factors of two calcium isotopes. "Thanks to this comparison we succeeded in including all the details of the movements of the electrons and the nucleus and to precisely determine the behavior of the nuclei of the highly charged ions", explains Dr. Wolfgang Quint, physicist at GSI.

The experimental determination of the difference in the two g-factors of the lithium-like calcium-48 and calcium-40, i.e. calcium atoms that have only three electrons left in their shell, took place at two experimental setups. In an experiment at the University Mainz a single ions of each of the calcium isotopes was captured in the 3.8 tesla strong magnetic field of an apparatus consisting of three Penning traps and stored for several month. Via irradiation with microwaves the orientation of the outer bound electron was repeatedly flipped and the oscillation frequency of the electron was determined.

In a second experiment at the GSI Helmholtzzentrum the mass of the calcium isotope Ca-48 was measured with seven times the precision achieved so far. "With the ion trap SHIPTRAP at GSI we can capture the calcium isotopes and determine their mass very precisely. The calcium ions are held inside the trap by magnetic fields and circulate on a tiny spiral orbit with a certain frequency which can be directly used to calculate the mass", says GSI scientist Professor Michael Block, who is in charge of the experimental setup. The difference in the g-factors was determined from the measured data with a precision of ten parts in a billion, also the movement of the nucleus was completely taken into account for the first time. Thus the experiment lays a foundation for a new generation of tests of the BS-QED and paves the way for future basic precision measurements in atomic physics.

Participating institutes:
GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt
Max-Planck-Institut für Kernphysik, Heidelberg
Helmholtz-Institut Mainz, Mainz
Institut für Kernchemie, Johannes Gutenberg-Universität, Mainz
Department of Physics, St Petersburg State University, St Petersburg, Russia
Institut für Theoretische Physik, Technische Universität Dresden, Dresden
Institute for Theoretical and Experimental Physics, Kurchatov Institute, Moskau, Russia
Petersburg Nuclear Physics Institute, St Petersburg, Russia 
Institut für Physik, Johannes Gutenberg-Universität, Mainz

Further information

Article in Nature Communications 

Professor Michael Block at the SHIPTRAP experimental setup.
G. Otto, GSI Helmholtzzentrum für Schwerionenforschung