Principles of X-ray perspective and X-ray photography

When an electron beam traveling at high speed in a vacuum tube hits a tungsten (or molybdenum) target, it will produce X-rays. X-ray has short wave length and strong penetrating power, and can penetrate all kinds of substances with different densities that ordinary visible light cannot penetrate, and is absorbed or attenuated to some extent in the process of penetration. The penetration of X-ray is closely related to the voltage of X-ray tube. The higher the voltage, the shorter the wavelength of X-ray and the stronger the penetrating power. On the contrary, the lower the voltage, the longer the wavelength of X-rays generated, and the weaker the penetration. On the other hand, the penetrating power of X-rays is also related to the density and thickness of objects. X-ray penetrability is the basis of X-ray imaging. Fluorescence effect: X-rays can excite fluorescent substances (such as zinc cadmium sulfide and calcium tungstate) to produce visible fluorescence. That is, X-rays act on the fluorescent substance, so that X-rays having a short wavelength are converted into fluorescence having a long wavelength. This conversion is called fluorescence effect. This feature is the basis of fluoroscopy. Photographic effect: After X-ray irradiation, the film coated with silver bromide can be exposed to light, resulting in latent image. After development and fixing, silver ions (Ag+) in the exposed silver bromide are reduced to metallic silver (Ag) and deposited in the film. This metallic silver particle is black on the film. The unexposed silver bromide is washed off from the X-ray film during fixing and developing, thus showing the transparency of the film base. According to the amount of metallic silver precipitation, a black-and-white image will be produced. Therefore, the photographic effect is the basis of X-ray imaging.