Abstract

Today’s most precise time and frequency measurements are performed with optical atomic clocks. However, it has been proposed that they could potentially be outperformed by a nuclear clock, which employs a nuclear transition instead of an atomic shell transition. There is only one known nuclear state that could serve as a nuclear clock using currently available technology, namely, the isomeric first excited state of 229Th (denoted 229mTh). Here we report the direct detection of this nuclear state, which is further confirmation of the existence of the isomer and lays the foundation for precise studies of its decay parameters. On the basis of this direct detection, the isomeric energy is constrained to between 6.3 and 18.3 electronvolts, and the half-life is found to be longer than 60 seconds for 229mTh2+. More precise determinations appear to be within reach, and would pave the way to the development of a nuclear frequency standard.

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Acknowledgements

We acknowledge discussions with D. Habs, T. W. Hänsch, T. Udem, T. Lamour, J. Weitenberg, A. Ozawa, E. Peters, J. Schreiber, P. Hilz, T. Schumm, S. Stellmer, F. Allegretti, P. Feulner, J. Crespo, M. Schwarz, L. Schmöger, P. Micke, C. Weber, P. Bolton and K. Parodi. We thank T. Lauer for the Ti sputtering of the Si wafers and the MPQ for the temporary loan of the MCP detector. We thank I. Cortrie, L. Black and J. Soll for graphic design support. This work was supported by DFG (Th956/3-1), by the European Union’s Horizon 2020 research and innovation programme under grant agreement 664732 “nuClock” and by the LMU department of Medical Physics via the Maier-Leibnitz Laboratory.

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Affiliations

  1. Ludwig-Maximilians-Universität München, 85748 Garching, Germany

    • Lars von der Wense
    • , Benedict Seiferle
    • , Jürgen B. Neumayr
    • , Hans-Jörg Maier
    • , Hans-Friedrich Wirth
    •  & Peter G. Thirolf
  2. GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany

    • Mustapha Laatiaoui
    • , Jörg Runke
    •  & Christoph E. Düllmann
  3. Helmholtz-Institut Mainz, 55099 Mainz, Germany

    • Mustapha Laatiaoui
    • , Christoph Mokry
    • , Klaus Eberhardt
    •  & Christoph E. Düllmann
  4. Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany

    • Christoph Mokry
    • , Jörg Runke
    • , Klaus Eberhardt
    • , Christoph E. Düllmann
    •  & Norbert G. Trautmann

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Contributions

L.v.d.W., B.S. and P.G.T. performed the experiments. M.L. and J.B.N. did preparatory experimental work. H.-J.M. and H.-F.W. produced the radioactive source 1. C.M., J.R., K.E., C.E.D., N.G.T. and L.v.d.W. produced the radioactive sources 2 and 3. L.v.d.W., P.G.T. and B.S. wrote the manuscript with input from all authors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Lars von der Wense.

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https://doi.org/10.1038/nature17669

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