Further investigations were conducted to verify our previous results [19] obtained from a mammography unit and a radiography unit. In this investigation, all the same measurements from the previous work were repeated with samples of 2 mm in thickness. Since a mammography unit generates characteristic X-ray energies of molybdenum (17.5 keV and 19.6 keV) or rhodium (20.2 keV and 22.7 keV), it is much easier to compare with the XAS results (see Fig. 3). In the results presented in Fig. 3, it is clearly shown that the X-ray transmission results for the mammography unit sat between the results of 15–25 keV for the XAS beam energies. In contrast, for the radiography unit, the operated X-ray tube voltages generated a broad spectrum (polychromatic X-ray beam). Thus, the equivalent energies for the X-ray tube voltages of the radiography unit were estimated from the XAS results by superimposing their data together (see Fig. 4). As can be seen in Fig. 4, the X-ray transmissions of samples for X-ray tube voltages of 40–60 kV were sitting between 25 and 40 keV while the others were sitting above 40 keV. Hence, the X-ray tube voltages of 40–60 kV operated by the radiography unit produced the equivalent X-ray energies in the range of 25–40 keV while the X-ray tube voltages of ≥ 60 kV had an equivalent energy of ≥ 40 keV.