Inelasticity corrections for time-of-flight and fixed wavelength neutron diffraction experiments

Alan K Soper (1)

1 ISIS Facility

Time-of-flight neutron diffraction methods are widely used to study the structure of liquids and glasses. The scattering nuclei in these experiments suffer nuclear recoil in the course of the neutron scattering process, which gives rise to distortions to both the self and distinct structure factors extracted from the data. These distortions are in general difficult to evaluate quantitatively, especially when the mass of the nucleus is similar to that of the neutron, such as when hydrogen is present in the material being studied. Here a model for the scattering kernal is developed based on the well known harmonic oscillator model (A C Zemach and R J Glauber, Phys. Rev. \textbf{101}, 118 (1956)). This is shown to have the correct first and second moments of the scattering kernal for both the self and distinct scattering, and is used to estimate the self and distinct scattering from a diatomic ``dumbell'' molecule. The model gives a realistic account of the single atom scattering from light and heavy water over a wide range of incident neutron energies, but is not yet accurate enough to perform quantitative corrections. A new ``top hat'' convolution method is developed to perform the subtraction of residual self scattering from real data, and to allow data from multiple detector banks to be merged into a single structure factor.

Keywords: Physical Sciences

Alan K Soper. Inelasticity corrections for time-of-flight and fixed wavelength neutron diffraction experiments. Molecular Physics, 2009, 107 (16), pp.1667-1684. ⟨10.1080/00268970903025667⟩. ⟨hal-00513296⟩