Hyperfine structure of heavy hydrogen-like ions

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Abstract

The hyperfine splittings of the 1s hydrogen-like ground level of two isotopes of thallium were measured using the SuperEBIT electron beam ion trap. The measurements allowed us to accurately infer a magnetization radius. The inferred radius exceeds the single particle estimate by about 10% and the nuclear charge radius by about 7%. Because two isotopes were measured, we were able to observe for the first time the interaction between the finite size of the nuclear magnetization distribution and the finite size of the charge distribution on the hyperfine anomaly. The measured isotope difference of 30.59 ± 0.38 meV differs from the value of 31.04 ± 0.01 meV inferred from neutral thallium using a point magnetic dipole approximation, but is in good agreement with the difference of 30.71 ± 0.16 meV calculated by using an extended magnetic dipole.

Introduction

Nuclear structure information has been sought for more than half a century by precise measurements of hyperfine splittings and isotope shifts in the spectra of neutral atoms. Neutral atoms, however, especially those of heavy elements, are many-electron systems that are difficult to calculate precisely. The situation is very different in one-electron, hydrogen-like ions, which are the simplest atomic systems. The 1s electron has a wave function that overlaps with the nucleus more than that of any other electron. The overlap means that the 1s electron represents a sensitive probe of nuclear properties such as the size and shape of the distribution of nuclear charge and nuclear magnetic moment.

In atomic hydrogen, the interaction between the magnetic moment of the nucleus and the spin of the 1s electron results in the well known 21-cm line. Because of the Z3 scaling and the large nuclear magnetic moment the 1s hyperfine splitting of heavy nuclei is as large as several eV. This means that the photons emitted by such heavy hydrogen-like ions are in the optical wavelength band where high-resolution spectroscopic techniques are available to accurately determine the photon energy and thus derive various nuclear properties.

Among these, a determination of the hyperfine anomaly requires an accurate measurement of the hyperfine transitions of two or more isotopes. By accurately measuring the 1s hyperfine transitions of 203Tl and 205Tl we have made the first measurement of the hyperfine anomaly in a high-Z hydrogen-like ion. This allowed us to assess the interaction between the magnetic dipole and the nuclear charge distribution.

Section snippets

Experiment

Two different techniques have been used to measure the hyperfine splitting of the 1s ground state of several hydrogen-like ions in recent years. The first used laser excitation on the ESR heavy-ion storage ring at Darmstadt to measure 209Bi82+ and 207Pb81+[1], [2]. The second technique employed emission spectroscopy at the SuperEBIT electron beam ion trap at Livermore to measure 165Ho66+, 185Re74+ and 187Re74+[3], [4].

Recently, we extended our use of emission spectroscopy on SuperEBIT to

Nuclear parameters

In Fig. 1, we compare two recent calculations [7], [8] to the measured values. As seen from the figure, theory differs considerably from the measurements. A difference of 0.5–1.0% corresponds to 20–50 Å, causing range-of-search problems for laser measurements. The differences are largest for those isotopes far from the doubly magic nucleus 208Pb. This suggests that inaccurate knowledge of the nuclear properties could be a cause for the discrepancies.

The large uncertainties in the calculated

Acknowledgements

The experimental work was performed under the auspices of the US Department of Energy by the University of California Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48. M.G.H.G., C.F. and A.-M.M.-P. acknowledge financial support from the Swedish Natural Science Research Council (NFR) and the Eurotraps EU-TMR Network. E.T. acknowledges support from DFG (Germany).

References (14)

  • H. Backe et al.

    Nucl. Phys. A

    (1972)
  • T. Beier

    Phys. Rep.

    (2000)
  • I. Klaft et al.

    Phys. Rev. Lett.

    (1994)
  • P. Seelig et al.

    Phys. Rev. Lett.

    (1998)
  • J.R.C. López-Urrutia et al.

    Phys. Rev. Lett.

    (1996)
  • J.R.C. López-Urrutia et al.

    Phys. Rev. A

    (1998)
  • P. Beiersdorfer et al.

    Phys. Rev. A

    (2001)
There are more references available in the full text version of this article.

Cited by (0)

1

Present address: Max-Planck-Institut für Kernphysik, Heidelberg, Germany.

2

Present address: Spectra-Physics, Mountain View, CA, USA.

3

Also at Fakultät für Physik und Astronomie, Ruhr-Universität Bochum, Germany.

4

Present address: Ericsson Microwave Systems AB, Sensors and Information Networks, Göteborg, Sweden.

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