What exactly is an X-ray?

x-rays are also called roentgen rays. It is a kind of electromagnetic radiation with short wavelength, and its wavelength is about (2 ~ .6) × 1-8 cm. Roentgen rays have a high penetration ability, and can penetrate many substances that are opaque to visible light, such as ink paper and wood. This kind of invisible ray can make visible fluorescence of many solid materials, make photographic negatives sensitive and ionize air. The shorter the wavelength, the greater the energy of X-rays, which is called hard X-rays, and the longer the wavelength, the lower the energy, which is called soft X-rays. When high-speed electrons bombard a metal target in vacuum, the target emits X-rays, which is the structural principle of an X-ray tube. The emitted X-rays are divided into two categories: (1) If the energy of electrons blocked by the target does not exceed a certain limit, only continuous spectrum radiation is emitted. This kind of radiation is called bremsstrahlung; (2) a kind of discontinuous, it only has a few special linear spectrum, this kind of emission linear spectrum radiation is called characteristic radiation. The properties of continuous spectrum have nothing to do with the target material, but the characteristic spectrum is related to the target material. Different materials have different characteristic spectra, which is why it is called "characteristic". X-rays are characterized by very short wavelength and high frequency. Therefore, X-rays must be produced by the transition of atoms between two energy levels with very different energy levels. Therefore, the X-ray spectrum is emitted when the electrons in the innermost layer of the atom transition, while the optical spectrum is emitted when the electrons in the outer layer transition. X-rays do not deflect in electric and magnetic fields. This shows that X-rays are uncharged particle streams. In 196, the experiment proved that X-ray is an electromagnetic wave with short wavelength, so it can produce interference and diffraction. X-rays are used to help people make medical diagnosis and treatment; Used for the inspection of non-destructive materials in industry; In the fields of basic science and applied science, it is widely used in crystal structure analysis, chemical analysis and atomic structure research through X-ray spectrum and X-ray absorption.

In order to make a definite diagnosis, clinicians often need patients to go to the radiology department for various examinations, such as fluoroscopy, radiography, barium meal in digestive tract and special radiography. Therefore, patients often ask radiologists questions of one kind or another, among which the most common question is: Do these tests have a great impact on my health? To answer this question is not a simple sentence. To treat < P > concretely, we should start with the basic principle of X-ray. X-ray was discovered by German physicist Roentgen William Conrad on November 8, 1895. At that time, because people didn't understand this kind of ray, they gave it an unknown name "X", and later people called it "X-ray". X-rays are indeed harmful to human health. The greater the X-ray exposure, the greater the damage to human health. X-ray exposure can accumulate in the body, and its main harm is that it has certain lethality to white blood cells in human blood components, which reduces the number of white blood cells in human blood, and then leads to the decline of immune function of the body, making it easy for germs to invade the body and cause diseases. According to the principle of X-ray theory, the patient's safe exposure should be within 1 roentgen during X-ray examination, and the allowable exposure times and time should be determined according to this exposure. For example, the total accumulation of chest fluoroscopy should not exceed 12 minutes within a few days, and gastrointestinal examination should not exceed 1 minutes. As for the photo examination, the exposure amount is different because of different parts, so the corresponding allowable exposure times are also different. The impact of patients doing 2 ~ 3 examinations in a year on their health is negligible. Moreover, with the continuous development of medical imaging, at present, both films and cassette clips adopt "green screen" and "green film", so that the X-ray irradiation dose is reduced by 1/2 compared with the original dose, thus protecting the health of patients more, and the diagnostic effect is not reduced at all. In addition, in recent years, all major hospitals have adopted the method of taking photos as the main method, supplemented by fluoroscopy. On the one hand, it is to reduce patients' excessive intake of X-rays (fluoroscopy is more than X-rays taken), and on the other hand, it can provide evidence for the diagnosis of diseases, so as to facilitate treatment and reexamination. < P > Although X-ray examination is safe for most people, it should still be emphasized that pregnant women, infants and children should try to avoid X-ray examination because they are very sensitive to X-rays. If inspection is necessary, especially for pelvic measurement or fetal examination, the exposure times shall not exceed 2 ~ 3 times. X-ray examination of infants and young children is best to expose only the examined parts and cover the rest. Under normal circumstances, it should be relatively safe if the allowable irradiation time and times are not exceeded. However, the sensitivity to X-rays is different for everyone, and it is also related to the general health status of the human body. More importantly, the so-called safe exposure dose does not guarantee that it is also safe for genetic factors, because at present, it is not very clear how much exposure dose is enough to affect heredity. However, from the perspective of prevention, the fewer X-ray examinations, the better.