Neutron Larmor diffraction on powder samples

• Published in: Journal of applied crystallography Vol. 53; no. 1; pp. 88 - 98
• Main Authors: Keller, Thomas, Fabrykiewicz, Piotr, Przeniosło, Radosław, Sosnowska, Izabela, Keimer, Bernhard
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01-02-2020; Blackwell Publishing Ltd
• Subjects: Blurring; Crystals; Diffraction; Diffractometers; neutron Larmor diffraction; Neutron scattering; neutron spin–echo; Neutrons; polycrystalline samples; Powder; powder diffraction; Radiation; Research Papers; Single crystals; Synchrotron radiation; polycrystalline samples; neutron Larmor diffraction; neutron spin–echo; powder diffraction
• ISSN: 1600-5767; 0021-8898; 1600-5767
• DOI: 10.1107/S160057671901611X

A hitherto unrecognized resolution effect in neutron Larmor diffraction (LD) is reported, resulting from small‐angle neutron scattering (SANS) in the sample. Small distortions of the neutron trajectories by SANS give rise to a blurring of the Bragg angles of the order of a few hundredths of a degree, leading to a degradation of the momentum resolution. This effect is negligible for single crystals but may be significant for polycrystalline or powder samples. A procedure is presented to correct the LD data for the parasitic SANS. The latter is accurately determined by the SESANS technique (spin–echo small‐angle neutron scattering), which is readily available on Larmor diffractometers. The analysis technique is demonstrated on LD and SESANS data from α‐Fe2O3 powder samples. The resulting d‐spacing range agrees with experimental data from high‐resolution synchrotron radiation powder diffraction on the same sample.
A method to analyse neutron Larmor diffraction data from polycrystalline samples is presented.