Observation of the radiative decay of the 229Th nuclear clock isomer

Sandro Kraemer (), Janni Moens, Michail Athanasakis-Kaklamanakis, Silvia Bara, Kjeld Beeks, Premaditya Chhetri, Katerina Chrysalidis, Arno Claessens, Thomas E. Cocolios, João G. M. Correia, Hilde De Witte, Rafael Ferrer, Sarina Geldhof, Reinhard Heinke, Niyusha Hosseini, Mark Huyse, Ulli Köster, Yuri Kudryavtsev, Mustapha Laatiaoui, Razvan Lica, Goele Magchiels, Vladimir Manea, Clement Merckling, Lino M. C. Pereira, Sebastian Raeder, Thorsten Schumm, Simon Sels, Peter G. Thirolf, Shandirai Malven Tunhuma, Paul Van Den Bergh, Piet Van Duppen, André Vantomme, Matthias Verlinde, Renan Villarreal and Ulrich Wahl
Additional contact information
Sandro Kraemer: KU Leuven, Instituut voor Kern- en Stralingsfysica
Janni Moens: KU Leuven, Quantum Solid State Physics
Michail Athanasakis-Kaklamanakis: KU Leuven, Instituut voor Kern- en Stralingsfysica
Silvia Bara: KU Leuven, Instituut voor Kern- en Stralingsfysica
Kjeld Beeks: TU Wien
Premaditya Chhetri: KU Leuven, Instituut voor Kern- en Stralingsfysica
Katerina Chrysalidis: CERN
Arno Claessens: KU Leuven, Instituut voor Kern- en Stralingsfysica
Thomas E. Cocolios: KU Leuven, Instituut voor Kern- en Stralingsfysica
João G. M. Correia: Universidade de Lisboa
Hilde De Witte: KU Leuven, Instituut voor Kern- en Stralingsfysica
Rafael Ferrer: KU Leuven, Instituut voor Kern- en Stralingsfysica
Sarina Geldhof: KU Leuven, Instituut voor Kern- en Stralingsfysica
Reinhard Heinke: CERN
Niyusha Hosseini: TU Wien
Mark Huyse: KU Leuven, Instituut voor Kern- en Stralingsfysica
Ulli Köster: Institut Laue-Langevin
Yuri Kudryavtsev: KU Leuven, Instituut voor Kern- en Stralingsfysica
Mustapha Laatiaoui: Johannes-Gutenberg-Universität
Razvan Lica: CERN
Goele Magchiels: KU Leuven, Quantum Solid State Physics
Vladimir Manea: KU Leuven, Instituut voor Kern- en Stralingsfysica
Clement Merckling: imec
Lino M. C. Pereira: KU Leuven, Quantum Solid State Physics
Sebastian Raeder: Helmholtz-Institut Mainz
Thorsten Schumm: TU Wien
Simon Sels: KU Leuven, Instituut voor Kern- en Stralingsfysica
Peter G. Thirolf: Ludwig-Maximilians-Universität München
Shandirai Malven Tunhuma: KU Leuven, Quantum Solid State Physics
Paul Van Den Bergh: KU Leuven, Instituut voor Kern- en Stralingsfysica
Piet Van Duppen: KU Leuven, Instituut voor Kern- en Stralingsfysica
André Vantomme: KU Leuven, Quantum Solid State Physics
Matthias Verlinde: KU Leuven, Instituut voor Kern- en Stralingsfysica
Renan Villarreal: KU Leuven, Quantum Solid State Physics
Ulrich Wahl: Universidade de Lisboa

Nature, 2023, vol. 617, issue 7962, 706-710

Abstract: Abstract The radionuclide thorium-229 features an isomer with an exceptionally low excitation energy that enables direct laser manipulation of nuclear states. It constitutes one of the leading candidates for use in next-generation optical clocks1–3. This nuclear clock will be a unique tool for precise tests of fundamental physics4–9. Whereas indirect experimental evidence for the existence of such an extraordinary nuclear state is substantially older10, the proof of existence has been delivered only recently by observing the isomer’s electron conversion decay11. The isomer’s excitation energy, nuclear spin and electromagnetic moments, the electron conversion lifetime and a refined energy of the isomer have been measured12–16. In spite of recent progress, the isomer’s radiative decay, a key ingredient for the development of a nuclear clock, remained unobserved. Here, we report the detection of the radiative decay of this low-energy isomer in thorium-229 (229mTh). By performing vacuum-ultraviolet spectroscopy of 229mTh incorporated into large-bandgap CaF2 and MgF2 crystals at the ISOLDE facility at CERN, photons of 8.338(24) eV are measured, in agreement with recent measurements14–16 and the uncertainty is decreased by a factor of seven. The half-life of 229mTh embedded in MgF2 is determined to be 670(102) s. The observation of the radiative decay in a large-bandgap crystal has important consequences for the design of a future nuclear clock and the improved uncertainty of the energy eases the search for direct laser excitation of the atomic nucleus.

Date: 2023
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DOI: 10.1038/s41586-023-05894-z

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