Isotope shift computations for medium and heavy elements: A challenge for atomic theory ?
by Stephan Fritzsche (GSI Darmstadt)
Wednesday, 25 April 2012 from to (Europe/Zurich)
at CERN ( 26-1-022 )
at CERN ( 26-1-022 )
Isotope shift measurements have been found valuable for determining changes in the nuclear distributions and charge radii. Isotopes with one or a few additional neutrons are not only heavier than others but, more often than not, also exhibit quite different charge and magnetization distributions. Using laser spectroscopy, precise isotope shift measurements have been carried during the last decade along different isotopic chains and were found a versatile alternative to x-ray measurements in muonic atoms or electron scattering.
However, in order to extract useful information about the nuclear structure and radii from shifts in the atomic transition frequencies, the `electronic response' to the nuclear changes need to be known in sufficient detail. Apart from King-plot techniques, which applies information from different stable isotopes, atomic structure theory may help understand and provide this response in terms of mass- and field-shift parameters for optical transitions of interest. Up to the present, however, little is known about these isotope parameters for most transitions in medium and heavy elements and, especially, for ions with complex shell structures. Difficulties in applying atomic theory arise, in particular, from the relativistic motion and the number of electrons in such atoms and ions as well as from (nearly) degenerate configurations. --- In this seminar, I shall outline these difficulties and discuss the recent successes (and failures) in calculating accurate isotope-shift parameters. Examples from medium-to-large scale atomic computations are presented and display how sensitive the isotope parameters behave with regard to the electronic shell structure and correlations. A few conclusions are drawn about which optical transitions might be less sensitive to correlation effects and, hence, useful for laser-spectroscopic studies.