Kraemer, Sandro Chhetri, Premaditya Bara, Silvia Claessens, Arno De Witte, Hilde Elskens, Yens Ferrer, Rafael Kudryavtsev, Yuri Sels, Simon Van Den Bergh, Paul Van Duppen, Piet A setup for vacuum-ultraviolet spectroscopy of the $^{229}$Th low-energy isomer Nucl. Instrum. Methods Phys. Res., B 1-3 542 The ground-state transition of the low-energy isomer in $^{229}$Th 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 sevenfold 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. eng 2023

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