Abstract
This study reports an angular diffraction peak shift that scales linearly with the neutron beam path length traveled through the diffracting sample. This shift was observed in the context of mapping the residual stress state of a large U – 8 wt% Mo casting, as well as during complementary measurements on a smaller casting of the same material. If uncorrected, this peak shift implies a non-physical level of residual stress. A hypothesis for the origin of this shift is presented, based upon non-ideal focusing of the neutron monochromator in combination with changes to the wavelength distribution reaching the detector due to factors such as attenuation. The magnitude of the observed shift varies linearly with the width of the diffraction peak reaching the detector. For geometries requiring long path lengths, this effect can likely be reduced by selecting smaller voxel slit widths during strain measurements.
