X-ray is essentially the same as light, and it is also a kind of electromagnetic wave. In the process of penetrating an object, X-ray will interact with atoms in the object (including photoelectric effect, Compton effect, electron pair effect, etc.) and attenuate. In short, the larger the atomic number (the higher the mass density) is, the greater the attenuation of the X-ray is, and the weaker the penetration ability is, and vice versa. Figure 1 shows the penetration ability of aluminum at different voltages, for example.

        The penetration ability of the X-ray will directly affect the CT imaging results, especially when there is high density metal in the sample, and a clearer image can be obtained through the X-ray with higher penetration ability（As shown in Figure 2）

           Figure 1：X-ray penetration capability               Figure 2：CT images with different penetration capabilities