Abstract
Earlier beam-foil measurements have targeted 4s-4p intercombination transitions in the Zn-, Ga- and Ge-like ions of Nb (Z=41), Mo (Z=42), Rh (Z=44), Ag (Z=47) and I (Z=53). At the time, the spectra were calibrated with literature data on prominent lines in the Cu- and Zn-like ions. Corresponding literature data on the intercombination transitions in Ga- and Ge-like ions were largely lacking, which caused some ambiguity in the line identifications. We review the (mostly computational) progress made since. We find that a consistent set of state-of-the-art computations of Ga- and Ge-like ions would be highly desirable for revisiting the beam-foil data and the former line identifications for the elements from Kr (Z=36) to Xe (Z=54). We demonstrate that the literature data for these two isoelectronic sequences are insufficient, and we contribute reference computations in the process. We discuss the option of electron beam ion trap measurements as an alternative to the earlier use of classical light sources, beam-foil interaction and laser-produced plasmas, with the example of Xe (Z=54).
Highlights
In the earlier periods (1960s to 1980s) of the quest for controlled thermonuclear fusion, the elements Fe (Z = 26) and Ni (Z = 28) as major components of the reactor vessel steel were expected to contribute contaminants to the fusion plasma
Accurate measurements at very high values of Z give a slight preference to the former computations over the latter
Liu et al [83] have produced results mostly for relatively low-Z elements. There is another set of results that has been obtained by Vilkas and Ishikawa [84] that seems to oscillate around the reference dataset, the relativistic configuration interaction (RCI) computations by Chen and Cheng [12]
Summary
We discuss a range of elements in the middle of the range of natural elements, say from Kr (Z = 36) to Xe (Z = 54) (an arbitrary choice in the present context), in order to test the accuracy of certain atomic structure calculations versus a systematic progression of complexity For this task, we concentrate on the isoelectronic sequences of Zn, Ga and. The lower transition rate usually lets the corresponding intercombination lines appear less brightly, but in principle, their wavelengths ought to be calculable with even higher accuracy, because the upper level involved is lower than that of the resonance line This problem has been studied in lighter ions before, where beam-foil spectroscopic data on Mg-, Al- and Si-like ions (all with n = 3 valence electrons outside a Ne-like electron core) have led to the identification of the intercombination lines of highly-charged Fe ions in the EUV spectrum of the solar corona [7,8]. The present study does not present a new idea, but applies the essence of the earlier findings to a specific sample of beam-foil spectroscopic and electron beam ion trap data, in order to locate the frontier of reliability of such data and the associated spectrum interpretation
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