Resonant X-ray excitation of the nuclear clock isomer 45Sc

Abstract

Resonant oscillators with stable frequencies and large quality factors help us to keep track of time with high precision. Examples range from quartz crystal oscillators in wristwatches to atomic oscillators in atomic clocks, which are, at present, our most precise time measurement devices1. The search for more stable and convenient reference oscillators is continuing2–6. Nuclear oscillators are better than atomic oscillators because of their naturally higher quality factors and higher resilience against external perturbations7–9. One of the most promising cases is an ultra-narrow nuclear resonance transition in 45Sc between the ground state and the 12.4-keV isomeric state with a long lifetime of 0.47 s (ref. 10). The scientific potential of 45Sc was realized long ago, but applications require 45Sc resonant excitation, which in turn requires accelerator-driven, high-brightness X-ray sources11 that have become available only recently. Here we report on resonant X-ray excitation of the 45Sc isomeric state by irradiation of Sc-metal foil with 12.4-keV photon pulses from a state-of-the-art X-ray free-electron laser and subsequent detection of nuclear decay products. Simultaneously, the transition energy was determined as $${\mathrm{12,389.59}}_{+0.12\left({\rm{syst}}\right)}^{\pm 0.15\left({\rm{stat}}\right)}\,{\rm{eV}}$$ 12,389.59 + 0.12 syst ± 0.15 stat eV with an uncertainty that is two orders of magnitude smaller than the previously known values. These advancements enable the application of this isomer in extreme metrology, nuclear clock technology, ultra-high-precision spectroscopy and similar applications.

Nuclear quantum memory for hard x-ray photon wave packets

“…The NFC is not restricted to the 57 Fe resonance but can be applied to all Mössbauer nuclear resonances, including the long-lived isomer transitions in 45 Sc at 12.4 keV or in 229m Th at 8.3 eV, which are both promising candidates for nuclear clocks ( 48 – 50 ). With the effective broadening of the absorption spectrum and its distinct echo structure, the NFC can be a tool for enhancing the excitation and detection efficiency of the extremally narrow resonances of 0.1 Hz ( 45 Sc) and 0.1 mHz ( 229m Th) while still using the existing orders of magnitude broader radiation sources.…”