Hyperfine structure of hydrogenlike thallium isotopes -: art. no. 032506

The hyperfine splitting of the 1s ground state of hydrogenlike T1 has been measured for the two stable isotopes using emission spectroscopy in the SuperEBIT electron-beam ion trap, giving 3858.22 +/-0.30 Angstrom for Tl-203(80+) and 3821.84 +/-0.34 Angstrom for Tl-205(80+) with a wavelength difference Delta lambda =36.38 +/-0.35 Angstrom. This difference is consistent with estimates based on hyperfine anomaly data for neutral T1 only if finite size effects are included in the calculation. By using previously determined nuclear magnetic moments, and applying appropriate corrections for the nuclear charge distribution and radiative effects, the experimental splittings can be interpreted in terms of nuclear magnetization radii <r(m)(2)> (1/2)=5.83(14) fm for Tl-203 and <r(m)(2)> (1/2) = 5.89(14) fm for Tl-205. These values are 10% larger than derived from single-particle nuclear magnetization models, and are slightly larger than the corresponding charge distributions.