Direct detection of the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo>≈</mo><mn>8.4</mn><mspace width="0.28em"></mspace><mi>eV</mi></mrow></math> internal conversion energy of <math xmlns="http://www.w3.org/1998/Math/MathML"><mmultiscripts><mi>Th</mi><mprescripts></mprescripts><none></none><mrow><mn>229</mn><mi>m</mi></mrow></mmultiscripts></math> embedded in a superconducting nanowire

Galen O'Neil; Kjeld Beeks; Eric Hudson; Justin Jeet; David Leibrandt; Marion Mallweger; Sae Woo Nam; Sayan Patra; Gil Porat; Dileep Reddy; Thorsten Schumm; Stephen B. Schoun; Benedict Seiferle; Christian Schneider; Lars von der Wense; Peter G. Thirolf; Varun Verma; Jun Ye; Chuankun Zhang

doi:10.1103/9v5w-b8k2

Direct detection of the $\approx 8.4 eV$ internal conversion energy of ${}^{229 m}{Th}$ embedded in a superconducting nanowire

Galen O'Neil ¹, Kjeld Beeks ², Eric Hudson ³, Justin Jeet³, David Leibrandt ³, Marion Mallweger ⁴, Sae Woo Nam^1,*, Sayan Patra ^1,5,†, Gil Porat ^6,‡ et al.

Dileep Reddy ^1,5, Thorsten Schumm ⁷, Stephen B. Schoun ⁶, Benedict Seiferle⁸, Christian Schneider ³, Lars von der Wense ⁹, Peter G. Thirolf ⁸, Varun Verma ¹, Jun Ye ⁶, and Chuankun Zhang ⁶

¹National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80303, USA
²École Polytechnique Fédérale de Lausanne, Rte Cantonale, 1015 Lausanne, Switzerland
³University of California at Los Angeles, Department of Physics and Astronomy, 475 Portola Plaza Knudsen 1-129, Los Angeles, California 90095, USA
⁴Department of Physics, Stockholm University, SE-106 91 Stockholm, Sweden
⁵Department of Physics, University of Colorado, Boulder, Colorado 80303, USA
⁶JILA, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
⁷TU Wien, Institute for Atomic and Subatomic Physics, Stadionallee 2, 1020 Vienna, Austria
⁸Faculty of Physics, Ludwig-Maximilians-Universität München, Am Coulombwall 1, 85748 Garching, Germany
⁹Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7, 55128 Mainz, Germany

^*Deceased.
^†Present address: Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, California 94550, USA.
^‡Present address: Department of Electrical and Computer Engineering and Department of Physics, University of Alberta, Edmonton, Alberta T6G 1H9, Canada.

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Phys. Rev. C 112, 024322 – Published 25 August, 2025

DOI: https://doi.org/10.1103/9v5w-b8k2

Abstract

We report on a direct measurement of the $\approx 8.4 eV$ nuclear excitation energy of the isomeric first-excited state ${}^{229 m}{Th}$ via the internal conversion (IC) decay channel. Thermalized and mass-filtered recoiling ${}^{229 m}{Th}$ ions from ${}^{233}U α$ decay are delivered to the surface of a superconducting nanowire sensor and become embedded. The ion is neutralized, triggering the IC decay, and the energy released by the IC decay is detected with high quantum efficiency by the nanowire sensor. Energy resolution is enabled by the current dependence of the internal quantum efficiency of the nanowire sensor. The techniques presented here are complementary to light-based detection schemes. The IC decay channel is about eight orders of magnitude faster than the photoemission channel, thus the ability to detect IC decays with high efficiency with superconducting nanowire sensors is likely to be a valuable tool for future ${}^{229 m}{Th}$ experiments.

Physical Review C

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Direct detection of the $\approx 8.4 eV$ internal conversion energy of ${}^{229 m}{Th}$ embedded in a superconducting nanowire

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Direct detection of the ≈8.4eV internal conversion energy of Th229m embedded in a superconducting nanowire

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Direct detection of the $\approx 8.4 eV$ internal conversion energy of ${}^{229 m}{Th}$ embedded in a superconducting nanowire