Laser Excitation of the Th-229 Nucleus: Towards a Nuclear Clock
Ekkehard Peik (Physikalisch-Technische Bundesanstalt Braunschweig)

Motivated by the prospect of building a nuclear clock, we have demonstrated laser
excitation of the low-energy (8.4 eV) nuclear isomer in Th-229, using Th-doped
calciumfluoride crystals and a tabletop tunable laser system at 148 nm wavelength. A
nuclear resonance fluorescence signal has been observed in two crystals with different
Th-229 dopant concentrations, while it was absent in a control experiment using a
crystal doped with Th-232. The isomer radiative lifetime in the crystal is 630(15) s.
These results open the door towards laser Mössbauer spectroscopy and ideas from
"quantum nucleonics". An accurate nuclear clock would show high sensitivity to effects
of "new physics" for example in searches for violations of the Einstein equivalence
principle.
This is work done in a cooperation of PTB and TU Wien: J. Tiedau et al., Phys. Rev.
Lett. 132, 182501 (2024)