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High-Resolution Laser Spectroscopy on the Hyperfine Structure of Fm255 (Z=100)

Mitzi Urquiza-González1,2,*, Matou Stemmler3,4, Thomas E. Albrecht5, Benjamin Bally6, Michael Bender7, Sebastian Berndt3, Michael Block3,8,9, Alexandre Brizard9,10, Joseph S. Andrews8,9 et al.

Jacek Bieroń11, Premaditya Chhetri3,8,9, Holger Dorrer3, Christoph E. Düllmann3,8,9, Julie G. Ezold12, Stephane Goriely13, Manuel J. Gutiérrez8,9,14, Dag Hanstorp1, Raphael Hasse3, Reinhard Heinke15, Korbinian Hens2, Stephane Hilaire16,17, Magdalena Kaja3, Tom Kieck8,9, Nina Kneip3,4, Ulli Köster18, Andrea T. Loria Basto3,8, Christoph Mokry3,8, Danny Münzberg3,8,9, Kristian Myhre12, Thorben Niemeyer3, Sophie Péru16,17, Sebastian Raeder8,9, Dennis Renisch3,8, Jörg Runke3,9, Samantha K. Schrell12, Dominik Studer8,9, Kenneth van Beek6,9, Jessica Warbinek3,9, and Klaus Wendt3

  • *Contact author: mitzi.urquiza@gu.se
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Phys. Rev. Lett. 136, 192501 – Published 15 May, 2026

DOI: https://doi.org/10.1103/2813-b49x

Abstract

We report on high-resolution laser spectroscopy of Fm255 (T1/2=20  h), one of the heaviest nuclides available from reactor breeding. The hyperfine structures in two different atomic ground-state transitions at 398.4 nm and 398.2 nm were probed by in-source laser spectroscopy at the RISIKO mass separator in Mainz, using the perpendicularly illuminated laser ion source and trap (PI-LIST) high-resolution ion source. Experimental results were combined with hyperfine fields from various atomic ab initio calculations, in particular using multiconfiguration Dirac-Hartree-Fock theory, as implemented in grasp18. In this manner, the nuclear magnetic dipole and electric quadrupole moments were derived to be μ=−0.75(5)  μN and Qs=+5.84(13)  eb, respectively. The magnetic moment indicates occupation of the ν7/2[613] Nilsson orbital, while the large quadrupole moment confirms strong, stable prolate deformation consistent with systematics in the heavy actinides. Comparisons with available expectation values from nuclear theory show good agreement, providing a stringent benchmark for the used theoretical models. These results revise earlier data and establish Fm255 as a reference isotope for future high-resolution studies.

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Phys. Rev. Lett. 136, 192501– Published 15 May, 2026
  • Received 25 November 2025
  • Revised 10 March 2026
  • Accepted 14 April 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by Bibsam.

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