Absorption correction of peak positions for neutron strain measurements


In angle-dispersive neutron strain scanning the information about residual strain comes from the whole gauge volume that is defined by slits in the incoming and diffracted beams. Since the intensity of the neutron beam decreases with the amount of material it has travelled, neutrons diffracted from different locations within the gauge volume contribute with different intensities to the recorded diffraction peak. This can lead to peak shifts, and thus apparent strains. The magnitude of this peak shift depends mostly on the beam attenuation and the size of the gauge volume, but also on the sample geometry and position of the gauge volume within the sample. The peak shift plays a significant role when the size of the gauge volume becomes large because of peak broadening by the sample. An analytic expression for the peak shift was derived for a simple geometry to evaluate a numerical simulation. The numerical simulation was developed to quantify necessary corrections in detail. The attenuation-induced peak shift was demonstrated by measurements on a strain-free powder sample and the results were compared with the numerical predictions.
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