https://doi.org/10.1140/epjd/s10053-024-00833-7
Regular Article - Atomic Physics
Resonant laser ionization of neptunium: investigation on excitation schemes and the first ionization potential
1
Institute of Physics, Johannes Gutenberg University Mainz, 55099, Mainz, Germany
2
GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291, Darmstadt, Germany
3
Helmholtz Institute Mainz, 55099, Mainz, Germany
4
Department of Chemistry - Nuclear Chemistry, Johannes Gutenberg University Mainz, 55099, Mainz, Germany
5
Division Hübner Photonics, Hübner GmbH & Co. KG, 34123, Kassel, Germany
6
Department of Physics, University of Gothenburg, 41296, Gothenburg, Sweden
Received:
30
January
2024
Accepted:
20
March
2024
Published online:
4
May
2024
The atomic structure of neptunium (Np) was investigated by two-step resonance ionization spectroscopy. The study involved exploring ground-state transitions as well as following transitions to high-lying states just below the ionization potential (IP) or auto-ionizing states above the IP. That resulted in the identification of two-step ionization schemes, suitable for trace analysis and nuclear structure investigations. The lifetimes of two excited states located at 25,342.48 
and 25,277.64 were determined as 230(12) ns and 173(9) ns, respectively. Because of the absence of Rydberg series in wide-ranging spectra recorded, the first IP was determined through the field ionization of high-lying, weakly-bound states using a well-controlled static electric field. By applying the saddle-point model, an IP value of 50,535.54(15) cm
[6.265608(19) eV] was derived. This value agrees with the current literature value of 50,535(2) cm, while providing a more than ten times higher precision.
© The Author(s) 2024
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