Effect of wavelength-dependent attenuation on strain measurement using pulsed neutron diffraction

The measurement of stresses in engineering components and structures by neutron diffraction has traditionally been limited to depths of a few centimetres. However, recent developments in instrumentation open up the possibility of deeper measurements. It has been suggested that a systematic error may occur when measuring stresses deep in materials due to wavelength-dependent attenuation of the incident and/or diffracted beam. A series of experiments to evaluate the magnitude of this effect on ENGIN, a pulsed neutron strain scanner will be presented in this paper. It was found that the pseudo-strains induced by the attenuation of the diffracted beam were negligible, whereas there was a small but still noticeable effect produced by the attenuation in the incident beam. The possible causes of this shift and the consequences for deep measurements are discussed.