Novel Z(eff) imaging method for deep internal areas using back-scattered X-rays

Elemental kinds, composition ratios, effective atomic number (Z(eff)), and spatial distributions are the most basic information on materials and determine the physical and chemical properties of materials. X-ray fluorescence analysis have conventionally been used for elemental mapping, however maps on deep internal areas cannot be obtained because the escape depth of fluorescence X-rays is limited to a few mm from the surface of samples. Herein, we present a novel Z(eff) imaging method that uses back-scattered X-rays. The intensity ratio of elastic and inelastic back-scattered X-rays depends on the atomic number (Z) of a single-element sample (Z(eff) for a plural-element sample), and so Z(eff) maps in deep areas can be obtained by spectrum analysis of the scattered high-energy incident X-rays. We demonstrated the feasibility of observing a phantom covered by an aluminum plate by using synchrotron radiation X-ray. A fine Z(eff) map that can be used to identify materials was obtained from only front-side observation. The novel method opens up a new way for Z(eff) mapping of deep areas of thick samples from front-side observation.