Hyperfine structure of heavy hydrogen-like ions

The hyperfine splittings of the Is 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. (C) 2003 Elsevier Science B.V. All rights reserved.