Calibrating SANS data for instrument geometry and pixel sensitivity effects: access to an extended Q range

The multi-slit very small angle neutron scattering instrument at the China Spallation Neutron Source

A multi-slit very small angle neutron scattering (MS-VSANS) instrument has been finally accepted at the China Spallation Neutron Source (CSNS). It is the first spallation neutron source based VSANS instrument. MS-VSANS has a good signal-to-noise ratio and can cover a wide scattering vector magnitude range from 0.00028 to 1.4 Å-1. In its primary flight path, a combined curved multichannel beam bender and sections of rotary exchange drums are installed to minimize the background downstream of the instrument. An exchangeable multi-slit beam focusing system is integrated into the primary flight path, enabling access to a minimum scattering vector magnitude of 0.00028 Å-1. MS-VSANS has three modes, namely conventional SANS, polarizing SANS and VSANS modes. In the SANS mode, three motorized high-efficiency 3He tube detectors inside the detector tank cover scattering angles from 0.12 to 35° simultaneously. In the polarizing SANS mode, a double-V cavity provides highly polarized neutrons and a high-efficiency 3He polarization analyser allows full polarization analysis. In the VSANS mode, an innovative high-resolution gas electron multiplier detector covers scattering angles from 0.016 to 0.447°. The absolute scattering intensities of a selection of standard samples are obtained using the direct-beam technique; the effectiveness of this method is verified by testing the standard samples and comparing the results with those from a benchmark instrument. The MS-VSANS instrument is designed to be flexible and versatile and all the design goals have been achieved.

Mutually Beneficial Combination of Molecular Dynamics Computer Simulations and Scattering Experiments

We showcase the combination of experimental neutron scattering data and molecular dynamics (MD) simulations for exemplary phospholipid membrane systems. Neutron and X-ray reflectometry and small-angle scattering measurements are determined by the scattering length density profile in real space, but it is not usually possible to retrieve this profile unambiguously from the data alone. MD simulations predict these density profiles, but they require experimental control. Both issues can be addressed simultaneously by cross-validating scattering data and MD results. The strengths and weaknesses of each technique are discussed in detail with the aim of optimizing the opportunities provided by this combination.

Characterization of anisotropic pores and spatially oriented precipitates in sintered Mo-base alloys using small-angle neutron scattering

Small-angle neutron scattering (SANS) is a powerful method for the characterization of materials in the mesoscopic size range. For example, the method can be used to investigate the precipitation mechanisms in powder metallurgically processed materials. As a result of the processing route, the alloy matrix is usually heavily textured. If precipitates have an orientation relationship to the alloy matrix, they can produce an anisotropic scattering pattern showing streaks. The scattering is superimposed by a background with ellipsoidal shape, originating from deformed large-scale structures. The evaluation of such data quickly becomes elaborate and a quantitative analysis of precipitation is difficult. The present work reports a method for treating the anisotropic scattering from such samples. A systematic study of the ellipsoidal background reveals that it originates from uniaxially deformed sinter pores. Irrespective of the degree of deformation during the processing route, SANS shows that sinter pores remain present in the matrix, and their morphology and relative volume fractions are determined. Consequently, their scattering signal can be subtracted to reveal the scattering from aligned precipitates. The method is demonstrated on powder metallurgically produced pure Mo and an Mo–Hf–C alloy.

Calibration of the Suanni small-angle neutron scattering instrument at the China Mianyang Research Reactor

A series of calibration measurements have been performed on Suanni – the first small-angle neutron scattering spectrometer entering into routine user operation in China – aiming to characterize instrument performance and to provide a reference for user experiments. Various calibration standards were used to verify the precise association of the scattering intensity I with the scattering vector magnitude q at short and medium sample–detector distances. The measurements recorded for silver behenate powder revealed a slight shift of the neutron wavelength (λ) at the sample position as compared to the nominal λ calculated by the selector constant. The deviation was more significant with λ > 0.8 nm owing to the shape of the incoming neutron spectrum incident on the selector. The measured dead time for the entire detection system is 2.7 µs, as determined by measurements with varying fluxes. A protonated/deuterated polystyrene blend was employed as the primary standard to calibrate the secondary standard H2O. The instrument covers an effective q range between 0.013 and 5 nm−1, as demonstrated by scattering curves obtained from a monodisperse poly(methyl methacrylate) nanoparticle suspension and a glassy carbon plate.