Hyperfine interaction with the $^{229}$Th nucleus and its low lying isomeric state

TL;DR

This study combines experimental and theoretical methods to analyze the hyperfine structure of $^{229}$Th$^{2+}$ ions, aiming to determine nuclear properties and support the development of a nuclear clock based on the low-lying isomeric state.

Contribution

It provides the first combined experimental and theoretical analysis of hyperfine structure in $^{229}$Th$^{2+}$, confirming the nuclear magnetic dipole moment of the isomeric state.

Findings

Good agreement between theory and experiment for the nuclear ground state

Confirmation of the nuclear magnetic dipole moment of the isomeric state

Supports the development of a nuclear clock using $^{229}$Th

Abstract

The thorium nucleus with mass number $A=229$ has attracted much interest because its extremely low lying first excited isomeric state at about $8$eV opens the possibility for the development of a nuclear clock. However, neither the exact energy of this nuclear isomer nor properties, such as nuclear magnetic dipole and electric quadrupole moment are known to a high precision so far. The latter can be determined by investigating the hyperfine structure of thorium atoms or ions. Due to its electronic structure and the long lifetime of the nuclear isomeric state, Th$^{2+}$ is especially suitable for such kind of studies. In this letter we present a combined experimental and theoretical investigation of the hyperfine structure of the $^{229}$Th$^{2+}$ ion in the nuclear ground and isomeric state. A very good agreement between theory and experiment is found for the nuclear ground state. Moreover, we use our calculations to confirm the recently presented experimental value for the nuclear magnetic dipole moment of the thorium nuclear isomer, which was in contradiction to previous theoretical studies.