The Bohr-Weisskopf effect: from hydrogenlike-ion experiments to heavy-atom calculations of the hyperfine structure

TL;DR

This paper investigates how electron screening influences the Bohr-Weisskopf effect in many-electron atoms, enabling more accurate atomic hyperfine structure calculations by relating hydrogenlike ion data to neutral atoms.

Contribution

It introduces a method to connect BW effects in hydrogenlike ions with those in neutral atoms using screening factors, improving accuracy in heavy-atom hyperfine structure calculations.

Findings

Electron screening effects are small for s states.

The method relates BW effects in H-like ions to neutral atoms.

Application to Tl isotopes demonstrates improved accuracy.

Abstract

In this paper we study the influence of electron screening on the Bohr-Weisskopf (BW) effect in many-electron atoms. The BW effect gives the finite-nucleus magnetization contribution to the hyperfine structure. Relativistic atomic many-body calculations are performed for s and p_1/2 states of several systems of interest for studies of atomic parity violation and time-reversal-violating electric dipole moments -- Rb, Cs, Fr, Ba+, Ra+, and Tl. For s states, electron screening effects are small, and the relative BW correction for hydrogenlike ions and neutral atoms is approximately the same. We relate the ground-state BW effect in H-like ions, which may be cleanly extracted from experiments, to the BW effect in s and p_1/2 states of neutral and near neutral atoms through an electronic screening factor. This allows the BW effect extracted from measurements with H-like ions to be used, with screening factors, in atomic calculations without recourse to modelled nuclear structure input. It opens the way for unprecedented accuracy in accounting for the BW effect in heavy atoms. The efficacy of this approach is demonstrated using available experimental data for H-like and neutral Tl-203 and Tl-205.