Development of a recoil ion source providing slow Th ions including 229(m)Th in a broad charge state distribution


Ions of the isomer 229mTh are a topic of high interest for the construction of a “nuclear clock” and in the field of fundamental physics for testing symmetries of nature. They can be efficiently captured in Paul traps which are ideal for performing high precision quantum logic spectroscopy. Trapping and identification of long-lived 232Th+ ions from a laser ablation source was already demonstrated by the TACTICa collaboration on Trapping And Cooling of Thorium Ions with Calcium. The 229mTh is most easily accessible as α-decay daughter of the decay of 233U. We report on the development of a source for slow Th ions, including 229mTh for the TACTICa experiment. The 229mTh source is currently under construction and comprises a 233U monolayer, from which 229mTh ions recoil. These are decelerated in an electric field. Conservation of the full initial charge state distribution of the 229mTh recoil ions is one of the unique features of this source. We present ion-flight simulations for our adopted layout and give a final source design. This source will provide Th ions in their original charge state at energies suitable for capture in a linear Paul trap for spectroscopy investigations.


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Open Access funding provided by Projekt DEAL. This work is supported by the Helmholtz Excellence Network ExNet020, Precision Physics, Fundamental Interactions and Structure of Matter (PRISMA+) from the Helmholtz Initiative and Networking Fund. Parts of this research were conducted using the supercomputer Mogon and/or advisory services offered by Johannes Gutenberg University Mainz (, which is a member of the AHRP (Alliance for High Performance Computing in Rhineland Palatinate, and the Gauss Alliance e.V.

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Correspondence to Raphael Haas.

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This article is part of the Topical Collection on Proceedings of PLATAN 2019, 1st International Conference, Merger of the Poznan Meeting on Lasers and Trapping Devices in Atomic Nuclei Research and the International Conference on Laser Probing, Mainz, Germany 19-24 May 2019

Edited by Krassimira Marinova, Michael Block, Klaus D.A. Wendt and Magdalena Kowalska

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Haas, R., Kieck, T., Budker, D. et al. Development of a recoil ion source providing slow Th ions including 229(m)Th in a broad charge state distribution. Hyperfine Interact 241, 25 (2020).

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  • Thorium ions
  • Recoil ion source
  • Highly charged ions
  • Ion-flight simulations