Cold neutron scattering in imperfect deuterium crystals

TL;DR

This paper calculates cold neutron scattering cross sections in mosaic deuterium crystals, compares them with experimental data, and highlights the importance of crystal mosaic spread in interpreting Bragg peaks and ultracold neutron upscattering.

Contribution

It provides a theoretical model for neutron scattering in imperfect deuterium crystals, explaining experimental Bragg peak structures and emphasizing the role of mosaic spread.

Findings

Bragg peak structures explained by 3° mosaic spread

Theoretical results agree with experimental data for 1-9 Å wavelengths

Implications for ultracold neutron upscattering in solid deuterium

Abstract

The differential cross sections for cold neutron scattering in mosaic deuterium crystals have been calculated for various target temperatures. The theoretical results are compared with the recent experimental data for the neutron wavelengths $\lambda\approx$~1--9~\AA. It is shown that the structures of observed Bragg peaks can be explained by the mosaic spread of about $3^{\circ}$ and contributions from a~limited number of crystal orientations. Such a~crystal structure should be also taken into account in ultracold neutron upscattering due to the coherent phonon annihilation in solid deuterium.