This study suggests an improved X-ray inspection method to determine the effective atomic number to identify explosives during luggage inspection with high resolution of the effective atomic number (Zeff). To obtain high resolution in Zeff, the suggested inspection method uses the ratio of the total and Compton scattering attenuation coefficients between two different energies for decomposing the attenuation coefficients of the Rayleigh scattering and photoelectric absorption that are highly dependent on the atomic number. To acquire the total and Compton scattering coefficient ratio of two different energies, dual-energy X-ray beams and four detectors for the photons transmitted and scattered in three different angles were introduced. MCNP6 simulations were carried out for several materials with X-ray source spectra from a tungsten anode generator to show the effectiveness of the method. The estimated Zeff values with the line beam assumption showed good agreement with the reference values for explosive substances within a relative error of 3% while the additional simulation considering beam width showed increased errors that are acceptable for beam widths less than 1.5 mm. •An improved method for determining effective atomic numbers of explosives is suggested.•The separation of the photoelectric and Rayleigh components led to improved accuracy.•High accuracy of new method for explosives was shown from Monte Carlo simulations.