Sandro Fabian Kraemer
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
A unique feature of thorium-229 is its isomer with an exceptionally low excitation energy, proposed as a candidate for future optical clocks [1]. The small decay width is expected to outperform the accuracy of current state-of-the-art atomic clocks by an order of magnitude [2]. The current best measurement of the excitation energy results in a value of 8.28(17)eV [3], whereby the isomer is populated in the alpha decay of uranium-233. The development of an optical clock requires however an improved precision of the excitation energy by at least an order of magnitude. Spectroscopic experiments searching for a direct signature of the radiative decay have to-date been unsuccessful, partially due to the background induced during the population of the isomer.
A new approach using the beta decay of actinium-229 is studied as a novel method to populate the isomer with high efficiency and in low background conditions [4]. Produced online at the ISOLDE facility, actinium is laser-ionized and implanted into a high-bandgap crystal in specific lattice positions, inhibiting the electron conversion decay of the isomer. A favourable feeding pattern significantly increasing the population of the isomer compared to uranium-233 and the higher degree of control over the lattice position due to the low recoil energy of the beta decay of actinium-229 are expected to increase the signal-to-noise ratio of vacuum-ultraviolet (VUV) spectroscopic measurements of the radiative decay.
A setup for VUV spectroscopy to study photons from the radiative decay of the isomer is presented. It includes implantation into thin-film CaF2 crystals and a highly efficient grating spectrometer coupled to a cooled photomultiplier detector, allowing to search for a weak signal with an energy resolution down to 6 meV. Based on a feasibility experiment performed in 2018 [4], different background contributions are studied and compared to the expected signal in order to evaluate the feasibility. The setup will be used in an experimental campaign at ISOLDE planned for the period 2021-2022 [5].
[1] E. Peik et al., Europhys. Lett. 61, 2 (2003)
[2] C. Campbell et al., PRL 108, 120802 (2012)
[3] B. Seiferle et al., Nature 573, 243-246 (2019)
[4] M. Verlinde et al., Physical Review C, 100 (2), 024315-024315
[5] S. Kraemer et al., CERN-INTC-2020-020; INTC-P-548
Sandro Fabian Kraemer
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Kjeld Beeks
(Institute of Atomic and Subatomic Physics, Vienna University of Technology, Austria)
Michael Block
(GSI Helmholtzzentrum für Schwerionenforschung, Germany)
Thomas Cocolios
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Jao Martins Correia
(ISOLDE-CERN, Switzerland)
Stefaan Cottenier
(Center for Molecular Modelling, Ghent University, Belgium)
Hilde De Witte
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Kristof Dockx
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Rafael Ferrer
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Sarina Geldhof
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Ulli Köster
(Institut Laue-Langevin Grenoble, France)
Mustapha Laatiaoui
(Helmholtz-Institut Mainz, Germany)
Razvan Lica
(ISOLDE-CERN, Switzerland)
Pin-Cheng Lin
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Vladimir Manea
(Institut de physique nucleaire d’Orsay, France)
Janni Moens
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Iain Moore
(Department of Physics, University of Jyväskylä, Finland)
Lino Pereira
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Sebastian Reader
(GSI Helmholtzzentrum f ̈ur Schwerionenforschung, Germany)
Mikael Reponen
(Department of Physics, University of Jyväskylä, Finland)
Sebastian Rothe
(ISOLDE-CERN, Switzerland)
Thorsten Schumm
(Institute of Atomic and Subatomic Physics, Vienna University of Technology, Austria)
Benedict Seiferle
(Ludwig-Maximilians-Universität München, Germany)
Simon Sels
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Peter Thirolf
(Ludwig-Maximilians-Universität München, Germany)
Paul Van den Bergh
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Piet Van Duppen
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
André Vantomme
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Matthias Verlinde
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Elise Verstraelen
(Institute for Nuclear and Radiation Physics, KU Leuven, Belgium)
Ulrich Wahl
(Centro de Ciencias e Tecnologias Nucleares, Universidade de Lisboa, Portugal)
