X-rays were discovered by the German physicist W.K. Roentgen in 1895, so they are also called roentgen rays. X-rays are electromagnetic radiation with a wavelength between the ultraviolet and gamma rays, and the wavelength is very short. Therefore, it has high penetrating power and can pass through many substances that are opaque to visible light, such as ink paper and wood. This invisible radiation can make many solid materials visible fluorescence, so that the photographic film and air ionization and other effects, the shorter the wavelength of the greater the energy of X-rays, called hard X-rays, low wavelength long X-ray energy , called soft X-rays. Ultra-hard X-rays with a wavelength of less than 0.1 angstroms, hard X-rays in the range of 0.1 to 10 angstroms, and soft X-rays in the range of 10 to 100 angstroms.
The energy of the X-ray photon depends on the tube voltage when the X-ray is generated. The higher the tube voltage is, the higher the X-ray photon's ultimate energy is, and the harder the X-ray is. However, the higher the tube voltage, the higher the X-ray photon energy. Because X-rays are generated by electron bombardment of the anode target, different targets have different deceleration effects on the electrons, and the resulting X-ray energy spectrum distribution is also different. In addition, electrons do not convert all of their energy once to X-ray photon energy. Therefore, the X-ray spectrum is a continuous distribution with energy from low energy to high energy. Ultimate energy is the kinetic energy of electrons accelerated by electrons after high-voltage electric fields.
Therefore, for the same tube voltage, the greater the atomic number of the target, the better the effect of deceleration on electrons, and the higher the ratio of hard rays generated in the X-rays. For the same target, the higher the tube voltage, the higher the maximum energy of the generated rays, ie the hardest rays are harder. But no matter what target and tube voltage, the generated rays are both soft and hard rays. The X-ray obtained by our traditional method is a continuous spectrum. Energy is continuous, and it changes continuously from soft to hard.