Inelastic neutron scattering on the high-frequency ultrasound in single crystals

Neutron scattering from ultrasonic waves in silicon and KBr single crystals was studied. By the use of neutron spin echo spectroscopy we have observed ultrasonic phonons for the first time by inelastic neutron scattering. One, double and zero phonon scattering were observed in Si. The intensity of the last scattering was almost independent from the acoustic wave amplitude. These results are in a good agreement with dynamic theory calculations. The results obtained in KBr are consistent with a model that each mosaic bloc oscillates as a whole. Our approach lends itself for the investigation of ultrasonic waves in wide varieties of substances.