Development of Continuous Offline Sources of Francium Ions for Magneto-Optical Trapping
POSTER
Abstract
Francium-221 nuclei are highly sensitive to new symmetry-violating physics beyond the Standard Model, owing to their large mass and octupole deformation [1]. Precision measurements of both atomic parity violation [2] and CP violation via the nuclear Schiff moment [3] would benefit from continuous, offline magneto-optical traps (MOTs) of 221Fr (π‘1/2 = 4.9 min). We are developing two types of continuous offline sources of 221Fr+ ions for keV-energy beams, both fed from thorium-229 (π‘1/2 = 7880 yrs). Both sources will embed ions into a neutralizing foil which will be heated to release 221Fr for capture into a MOT.
Our first 221Fr+ source leverages two πΌ-decays in the 229Th chain to efficiently collect recoiling daughter 221Fr cations from a thin film of 229ThF2 into the catcher foil. This simple approach is expected to enable loading of reasonably bright 221Fr MOTs (βΌ105 atoms) with only βΌπCi activity of the 229Th source.
In parallel, we are developing a brighter 221Fr source fed from up to βΌ100 πCi of 229ThO2 placed in a high-temperature tantalum oven. Implanted daughter 221Fr ions from πΌ recoils will diffuse efficiently out of the tantalum [4] before surface ionizing into 221Fr+. Due to the short surface lifetimes of alkalis [5], 221Fr+ will effuse out of the oven efficiently while parent isotopes remain. We expect this to enable loading of Fr MOTs with well over 106 atoms.
These protocols combine features from several established techniques [2]. We will present our progress on both 221Fr+ sources, including in-situ alpha spectroscopy to measure 221Fr and 221Fr+ extraction. This work will enable continuous offline production of 221Fr+ ion beams for loading of Fr atom MOTs, for applications in precision measurements and perhaps beyond.
[1] Flambaum, V. V. and Mansour, A. J.. Phys. Rev. C 111, 055501 (2025).
[2] Gwinner, G. and Orozco, L. A.. QST 7(2), 024001 (2022).
[3] Marc, A., Hubert, M., and Fleig, T. Phys. Rev. A 108 062815 (2023).
[4] Legoux, Y. and Merini, J. J. Less-Common Met. 105(1) 169β183 (1985).
[5] Scheer, M. D. and Fine, J. J. Chem. Phys, 38(2) 307β309 (1963).
Our first 221Fr+ source leverages two πΌ-decays in the 229Th chain to efficiently collect recoiling daughter 221Fr cations from a thin film of 229ThF2 into the catcher foil. This simple approach is expected to enable loading of reasonably bright 221Fr MOTs (βΌ105 atoms) with only βΌπCi activity of the 229Th source.
In parallel, we are developing a brighter 221Fr source fed from up to βΌ100 πCi of 229ThO2 placed in a high-temperature tantalum oven. Implanted daughter 221Fr ions from πΌ recoils will diffuse efficiently out of the tantalum [4] before surface ionizing into 221Fr+. Due to the short surface lifetimes of alkalis [5], 221Fr+ will effuse out of the oven efficiently while parent isotopes remain. We expect this to enable loading of Fr MOTs with well over 106 atoms.
These protocols combine features from several established techniques [2]. We will present our progress on both 221Fr+ sources, including in-situ alpha spectroscopy to measure 221Fr and 221Fr+ extraction. This work will enable continuous offline production of 221Fr+ ion beams for loading of Fr atom MOTs, for applications in precision measurements and perhaps beyond.
[1] Flambaum, V. V. and Mansour, A. J.. Phys. Rev. C 111, 055501 (2025).
[2] Gwinner, G. and Orozco, L. A.. QST 7(2), 024001 (2022).
[3] Marc, A., Hubert, M., and Fleig, T. Phys. Rev. A 108 062815 (2023).
[4] Legoux, Y. and Merini, J. J. Less-Common Met. 105(1) 169β183 (1985).
[5] Scheer, M. D. and Fine, J. J. Chem. Phys, 38(2) 307β309 (1963).
*This work has been supported by the "Table-top experiments for fundamental physics" program, sponsored by the Gordon and Betty Moore Foundation, Simons Foundation, Alfred P. Sloan Foundation, and John Templeton Foundation.
Presenters
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Harish D Ramachandran
- Johns Hopkins University