An international team of scientists from the United States and Europe led by Yuri Shvyd’ko of Argonne National Laboratory (USA), with the participation of NSRC SOLARIS empolyee, dr. eng. Tomasz Kołodziej, excited successfully for the first time with x-rays an isomeric state in Scandium-45 – the sharpest quantum transition in hard x-ray regime. This is an achievement, which may lead to a new type of ultra-precise clocks. The results were presented in an article in the Nature journal.

Nowadays, the most precise clocks are atomic clocks. These devices use the transition of cesium (133Cs) atoms between two electronic states to control the frequency and they can measure time with an accuracy of 1 second within 300 million years. To improve this precision, scientists want to use the resonant transition between the ground and excited levels of the nucleus of long-lived isomers, e.g. scandium 45Sc (nuclear transitions are much less susceptible to external perturbations than electronic transitions).
European Free Electron Laser XFEL in the so-called self-seeding mode provided an X-ray beam with an appropriate spectral density (a sufficiently high number of photons in a narrow energy band) to excite the desired resonance. At the MID (Materials Imaging & Dynamics) beamline, 25-micrometer thick scandium foils were irradiated with an X-ray laser beam, and resonance was observed by the time-delayed emission of the characteristic Kα and Kβ radiation  by scandium atoms.

Using sophisticated noise reduction techniques and high-resolution X-ray optics, the resonant transition energy was determined with an unprecedented accuracy to 5 decimal places, 12.38959 keV. The width of the resonance is about a million times smaller than in the Mössbauer isotope of iron 57Fe (it still remains to be measured precisely in the further steps), which in turn gives a time measurement accuracy on the order of 1 s per 300 billion years, i.e. 1,000 times better than previously achieved in atomic clocks.

The resonant excitation of the scandium-45 isomer together with precise determination of the resonance energy (previously known only with an accuracy of +/-50 eV) opens up completely new possibilities for the construction of ultra-precise clocks (the so-called atomic nuclear clock), in spectroscopy and metrology with previously unattainable resolutions, and new measurements of basic physical quantities. Thanks to this project and the cooperation between Dr. Tomasz Kołodziej and the Argonne National Laboratory (USA), it will be possible to introduce X-ray laser research at the SOLARIS Centre.

Thanks to this project and the cooperation between Dr. Tomasz Kołodziej and the Argonne National Laboratory (USA), it will be possible to introduce X-ray laser research at the SOLARIS Centre.

Figure 1. Excitation and decay scheme of the 12.4-keV first excited state of 45Sc nucleus. The nonradiative internal conversion decay channel dominates, resulting in the emission of Sc characteristic X-ray fluorescent photons and Auger electrons. Kα (4.09 keV) and Kβ (4.46 keV) fluorescent photons were detected in this study. (taken from Ref. [1])

Written by: dr inż. Tomasz Kołodziej

Link to the publication: Y. Shvyd’ko, R. Röhlsberger, O. Kocharovskaya, J. Evers, G. Geloni, P. Liu, D. Shu, A. Miceli, B. Stone, W. Hippler,B. Marx-Glowna, I. Uschmann, R. Loetzsch, O. Leupold, H.C. Wille, I. Sergeev, M. Gerharz, X. Zhang, C. Grech, T. Ko-łodziej, Resonant X-ray excitation of the nuclear clock isomer Sc, Nature, 1(2023)doi: 10.1038/s41586-023-06491-w