We have proposed a new system for X-ray computed tomography (CT) scanning. By employing the dual-energy
measurement, the obtained data can be used to deduce distribution images of the atomic number and electron density
which are useful for identifying the scanned material. In this work, two different methods were given for the derivative
process. We found method A was suitable for measuring low-Z materials while method B worked well for high-Z
materials. Therefore, the two derivative methods may work complementally for material identification.