Rostock 2019 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 18: Precision Spectroscopy of atoms and ions V (Th 229)

A 18.3: Vortrag

Mittwoch, 13. März 2019, 14:30–14:45, S HS 2 Physik

Electronic level structure investigations in Th⁺ for the excitation of the nuclear isomer — •David-Marcel Meier, Johannes Thielking, Gregor Zitzer, Maksim Okhapkin, Robert Müller, Andrey Surzhykov, and Ekkehard Peik — Physikalisch-Technische Bundesanstalt, Braunschweig, Germany

Among all known isotopes ²²⁹Th possesses a uniquely low-lying nuclear excitation state at 7.8(5) eV with a lifetime of about ≈1000 s. Since this energy corresponds to a wavelength in the VUV region of about ≈160 nm, it makes direct laser excitation of the isomer challenging.

For the search of the transition’s frequency we attempt to excite the nucleus via the NEET [1] or electronic bridge [2] mechanisms by two-photon laser excitation which rely on the hyperfine coupling between electron shell and nucleus. Since the Th⁺ ion is a three valence electron system, it possesses a dense electronic level structure which leads to an enhanced hyperfine coupling and therefore to a higher excitation probability and strong decrease of the lifetime of the isomeric state.

For this reason, an extensive knowledge about the electronic level structure of Th⁺ in the range of the isomer energy is required. In our experiment we investigate two-photon laser excitation of high-lying levels in ²³²Th⁺ ions and we will present the latest results of the level search in the energy range from 7.8 to 9.8 eV. We found 177 previously unknown energy levels and we will furthermore report on ab-initio calculations of electronic levels in the same energy range.

[1] F.F. Karpeshin, et al., Nucl. Phys. A, 654, 579 (1999).

[2] S. G. Porsev et al., Phys. Rev. Lett. 105, 185501 (2010).