Neutron scattering by ultrasound in mosaic single crystals

TL;DR

This study investigates how ultrasound affects neutron scattering in mosaic single crystals, revealing effects beyond thermal phonons and proposing a new model based on mosaic block disorientation to explain the observations.

Contribution

A new modified model for neutron scattering in mosaic crystals under ultrasound is proposed, considering non-smooth angular distributions of mosaic block orientations.

Findings

Ultrasound intensifies quasi-elastic neutron scattering.

Standard theories cannot explain the ultrasound effect observed.

The proposed model aligns well with experimental data.

Abstract

The Time-of-Flight and Neutron-Spin-Echo techniques have been applied for the research of ultrasonic effect at the cold neutron diffraction in mosaic single crystals (KBr and mica). It was found that h.f. ultrasound intensifies quasi-elastic neutron scattering and this effect cannot be explained as a result of neutron scattering by thermal phonons in a sample heated by ultrasound; neither can it be interpreted in the context of standard secondary extinction theory. A new modified model is proposed based on the assumption that the angular distribution function describing mosaic block disorientation is not smooth but contains deep narrow troughs. This model is qualitatively equivalent to the preposition about existence large block structure of sample. The corresponding kinetic equations are formulated and exactly solved. The results obtained correlate well with experimental data. Our results evidence that such an approach is applicable for studying the ultrasonic effect at neutron diffraction in different technologies dealing with mosaic single crystals. PACS: 61.05F-,62.65, 63.20.dd Keywords: neutron, ultrasound, mosaic, time-of-flight, spin-echo