A setup for vacuum-ultraviolet spectroscopy of the 229Th low-energy isomer

The ground-state transition of the low-energy isomer in 229Th has been proposed as the basis for the development of a novel optical clock as a tool for fundamental-physics studies. Vacuum-ultraviolet studies of the β-decay of 229Ac recently enabled to measure the de-excitation energy of the isomer with a seven-fold improvement in precision compared to previous results by directly observing photons from the isomer’s radiative decay. In this contribution, the setup used for this study and the systematic uncertainty on the measured photon wavelength is discussed.