Observation of the 22.5-keV Resonance in ¹⁴⁹Sm by the Nuclear Lighthouse Effect

We have observed coherent nuclear resonant scattering of synchrotron radiation at the 22.5-keV resonance of ¹⁴⁹Sm. High-speed rotational sample motion led to an angular deflection of the resonantly scattered radiation off the nonresonant primary beam. This allowed us to determine the resonance energy of the first excited nuclear level of ¹⁴⁹Sm to be 22496(4) eV. Because of the angular deflection of the resonant photons, time spectra of coherent nuclear resonant scattering can be recorded as a function of a spatial coordinate. Time resolutions of a few 10 ps can be expected, which are beyond the limits of existing x-ray detection schemes.