Neutron Larmor diffraction on powder samples

Abstract

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 -Fe 2 O 3 powder samples. The resulting d-spacing range agrees with experimental data from high-resolution synchrotron radiation powder diffraction on the same sample. research papers J. Appl. Cryst. (2020). 53, 88-98 Thomas Keller et al. Neutron Larmor diffraction on powder samples 89

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“…For powder samples, the resolution might be degraded by parasitic small‐angle scattering of the neutrons inside the sample, but this effect is minimized by proper design of the shape of the sample containers. [ 71 ] As LD is difficult to integrate into conventional powder diffractometers with multiangle detectors, Rekveldt suggested the configuration in Figure 3b using only one PD upstream of the sample, at the cost of a reduced resolution. [ 72,73 ] Such an instrument could enhance the resolution of powder diffraction by one order of magnitude toward , that is about one order of magnitude less than for the standard LD configuration with two PDs.…”

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