The concept of laser-based conversion electron Mössbauer spectroscopy for a precise energy determination of 229mTh
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229Th is the only nucleus currently under investigation for the development of a nuclear optical clock (NOC) of ultra-high accuracy. The insufficient knowledge of the first nuclear excitation energy of 229Th has so far hindered direct nuclear laser spectroscopy of thorium ions and thus the development of a NOC. Here, a nuclear laser excitation scheme is detailed, which makes use of thorium atoms instead of ions. This concept, besides potentially leading to the first nuclear laser spectroscopy, would determine the isomeric energy to 40 μeV resolution, corresponding to 10 GHz, which is a 104 times improvement compared to the current best energy constraint. This would determine the nuclear isomeric energy to a sufficient accuracy to allow for nuclear laser spectroscopy of individual thorium ions in a Paul trap and thus the development of a single-ion nuclear optical clock.
KeywordsNuclear optical clock Nuclear laser spectroscopy Thorium-229
We would like to thank S. Stellmer and T. Schumm for discussions and lending of the VUV excimer laser. For discussions we are also grateful to G. Kazakov, A. Pálffy, J. Weitenberg and E. Peik. This work was supported by DFG (Th956/3-2) and by the European Union’s Horizon 2020 research and innovation programme under grant agreement 6674732 ”nuClock”. The efforts at UCLA have been supported in part by DARPA (QuASAR program), ARO (W911NF-11-1-0369), NSF (PHY-1205311), NIST PMG (60NANB14D302), RCSA (20112810), and DOE Office of Nuclear Physics, Isotope Programme.
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