Characterization of materials embedded in thick objects using spectral small-angle x-ray scattering

Abstract

Small-angle x-ray scattering (SAXS) can identify a material based on its scattering features. However, SAXS techniques have been limited to the study of thin samples in the mm scale. We investigated the use of spectral SAXS (sSAXS) in the 30–45 keV energy range to identify embedded materials in up to 5 cm thick objects. A prototype sSAXS system was built by integrating a polychromatic x-ray source and a 2D spectroscopic detector in a two-pinhole collimation setup. The elastically scattered x-rays at deflection angles smaller than 10° were measured without collimating the scattered rays or filtering the energy spectrum. Using caffeine as a target material in 1 to 5 cm polymethyl methacrylate (PMMA) slabs, we demonstrate the capability of sSAXS technique to identify caffeine targets in all cases with 600 s acquisition times. The distinct Bragg peaks of caffeine at 8.44 and 18.64 nm−1 were recovered with a q-resolution of 0.6 nm−1 after attenuation and background corrections. Furthermore, we show the effect of PMMA thickness and target location to estimate the caffeine amount from the recovered signal using area-under-the-peak (AUP) analysis. We found that AUPs were slightly overestimated due to signal contamination by PMMA when the scattered photons from the caffeine target traverse through 1 to 3 cm PMMA slabs. This effect was more significant in the 5 cm thick PMMA with an average transmission factor of 24%, where the AUP was overestimated approximately by 34%.