The hyperfine interaction of the nucleus with the electron shell leads to energy shifts of electronic transitions that are easily accessible to laser spectroscopy. Now that Th-229m ions in the isomeric state became available at the LMU experiment, the PTB group performed laser spectroscopy on these ions and compared the spectra with Th-229 ions in the nuclear ground state. These measurements allowed the two teams to learn a lot about the properties of the nucleus when it’s excited to the isomeric state (see the paper here). The value of the observed nuclear magnetic dipole moment, however, disagrees massively with previous calculations: this clearly calls for a clarification on the theory side.
New calculations performed by the PTB group can reproduce the experimental values to an excellent degree and thus help to better understand the Th-229m nucleus. This work has now been published here.