The basic principle of X-ray imaging. The reason why X-rays can make human tissues form images on the screen or film is, on the one hand, based on the penetrability, fluorescence effect and photosensitive effect of X-rays; on the other hand, It is based on the differences in density and thickness between human tissues. When X-rays pass through different tissue structures of the human body, they are absorbed to different degrees, so the amount of X-rays reaching the screen or film is different. In this way, images with different contrasts of light and dark or black and white are formed on the screen or X-ray film.
X-rays (English: X-rays), also known as X-rays, X-rays, Roentgen rays or X-rays, are a type of A form of electromagnetic radiation in the frequency range 30?PHz to 30EHz). X-rays were originally used in medical imaging diagnostics and X-ray crystallography. X-rays are also ionizing radiation and other types of rays that are harmful to the human body. X-rays from human lungs The X-ray wavelength range overlaps at shorter wavelengths with gamma rays at longer wavelengths.
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Generation of X-rays
X-rays with a wavelength slightly larger than 0.5 nm are called soft X-rays. Those with wavelengths shorter than 0.1?nm are called hard X-rays. Hard X-rays overlap with the range of long-wavelength (low-energy) gamma rays. The difference between the two lies in the source of the radiation, not the wavelength: X-ray photons are generated by the acceleration of high-energy electrons, and gamma rays are generated by the decay of atomic nuclei.
The simplest way to generate X-rays is to hit a metal target with accelerated electrons. During the impact, the electrons suddenly decelerate, and their lost kinetic energy is released in the form of photons, forming a continuous part of the X-ray spectrum, called braking radiation. By increasing the accelerating voltage, the energy carried by the electrons increases, and it is possible to knock out the inner electrons of the metal atoms. As a result, holes are formed in the inner layer, and electrons in the outer layer jump back to the inner layer to fill the holes, and at the same time, photons with a wavelength of about 0.1 nanometers are emitted. Since the energy emitted by the outer electron transition is quantized, the wavelength of the emitted photons is also concentrated in certain parts, forming characteristic lines in the X-ray spectrum, which is called characteristic radiation.
In addition, high-intensity X-rays can also be produced by synchrotrons or free electron lasers. The synchrotron radiation light source has high intensity, continuous wavelength, beam collimation, extremely small beam cross-sectional area, and time pulse and polarization properties, making it the best X-ray light source for scientific research.
Baidu Encyclopedia-X-ray
Baidu Encyclopedia-Basic Principles of X-ray Imaging