Structure and Lamb shift of 2s1/2-2p3/2 levels in lithiumlike Th87+ through neonlike Th80+

P. Beiersdorfer, A. Osterheld, S. R. Elliott, M. H. Chen, D. Knapp, and K. Reed
Phys. Rev. A 52, 2693 – Published 1 October 1995
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Abstract

We report the measurement of thirteen 2s1/2-2p3/2 dipole-allowed transitions in the highly ionized thorium ions Th80+ through Th87+. The transitions have been measured with a high-resolution crystal spectrometer on the Livermore electron beam ion trap in which highly charged thorium ions were produced and excited in the interaction with a 100-keV electron beam. The observed 2s1/2-2p3/2 transitions are readily identified from a qualitative analysis of the dipole-allowed radiative decay channels. The identifications are confirmed by detailed modeling calculations of the line excitation processes, which account for all radiative processes, including radiative cascades among levels in the n=2 and n=3 shells, and all electron-impact excitation processes. The transition energies have been determined with an overall accuracy of 35 ppm. A detailed discussion of the measurement uncertainties is given, including the effects of beam-induced polarization on the hydrogenic reference transitions used for calibration. Measurements of the 1s2-1snp (n≤10) transitions in heliumlike Ar16+, which fall into the same wavelength region as the 2s1/2-2p3/2 transitions in thorium, are presented that validate the estimate of our experimental uncertainties. These measurements achieved twice the accuracy of previous measurements of the Ar16+ lines. A value of 4025.23±0.14 eV is found for the 2s1/2-2p3/2 transition in lithiumlike Th87+.

The value is sensitive to the effect of nuclear polarization and tests predictions of the 36-eV contribution from quantum electrodynamics to within 0.39%. A similar test of quantum electrodynamics calculations is given by the twelve 2s1/2-2p3/2 transitions measured in the neighboring charge states. A comparison of the measured energies of the 2s1/2-2p3/2 transitions in berylliumlike Th86+ through neonlike Th80+ with theoretical predictions from multiconfiguration Dirac-Fock calculations demonstrates the need for a better treatment of the electron-correlation terms in these highly charged multielectron ions. The measurements thus provide benchmarks for the development of theoretical approaches, such as relativistic many-body perturbation theory and large-scale configuration-interaction calculations, that attempt to account for electron correlations in very highly charged ions.

  • Received 21 April 1995

DOI:https://doi.org/10.1103/PhysRevA.52.2693

©1995 American Physical Society

Authors & Affiliations

P. Beiersdorfer, A. Osterheld, S. R. Elliott, M. H. Chen, D. Knapp, and K. Reed

  • Lawrence Livermore National Laboratory, University of California, Livermore, California, 94551

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Vol. 52, Iss. 4 — October 1995

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