  In this paper we report a spectrometric approach to dual-energy digital
radiography that has been developed and applied to identify specific organic
substances and discern small differences in their effective atomic number. An
experimental setup has been designed, and a theoretical description proposed
based on the experimental results obtained. The proposed method is based on
application of special reference samples made of materials with different
effective atomic number and thickness, parameters known to affect X-ray
attenuation in the low-energy range. The results obtained can be used in the
development of a new generation of multi-energy customs or medical X-ray
scanners.
