(a) physical effects 1. penetration effect penetration effect refers to the X-rays through the material is not absorbed by the ability to X-rays can penetrate the general visible light can not be transmitted through the substance. Visible light because of its long wavelength, photons of its energy is very small, when shot to the object, part of the reflection, most of the material is absorbed, can not pass through the object; X-rays are not, pharyngeal its short wavelength, energy, shine in the material, only part of the material is absorbed, most of the interatomic space and through the performance of a very strong penetration ability. X-rays penetrate the material and the ability to X-ray photon energy related, X-ray wavelength, X-rays can penetrate through the material. The ability of X-rays to penetrate matter and the energy of X-ray photons, the shorter the wavelength of the X-rays, the greater the energy of the photons, the stronger the penetration of X-rays, X-rays penetration is also related to the density of the material, the density of the material, X-rays absorbed more through less; density of small, less absorbed, through more. The use of differential absorption of this nature can be different density of bone, muscle, fat and other soft tissues can be distinguished. This is the physical basis of X-ray fluoroscopy and photography. 2. Ionization of matter by X-ray irradiation, so that the nuclear electrons out of the atomic orbitals, this effect is called ionization. In the photoelectric effect and the scattering process, the emergence of photoelectrons and recoil electrons from its atomic process called primary ionization, these photoelectrons or recoil electrons in the march and other atoms collision, so that the struck atoms escape electrons called secondary ionization. In solids and liquids. Ionized positive and negative ions will be quickly compounded, not easy to collect. But in the gas in the forget ionized charge is very easy to collect, the use of ionized charge can be determined by the amount of X-ray exposure: X-ray measuring instrument is made according to this principle. As a result of ionization, gases can conduct electricity; certain substances can undergo chemical reactions; and various biological effects can be induced in organisms. Ionization is the basis of X-ray damage and treatment. 3. Fluorescence Because of the short wavelength of X-rays, so it is invisible. But it irradiated to some compounds such as phosphorus, platinum barium cyanide, zinc cadmium sulfide, calcium tungstate, etc., due to ionization or excitation of atoms in the excited state, the atom back to the base state process, due to the valence electrons of the energy level of radiation out of the visible or ultraviolet radiation, which is the fluorescence. x-rays make the material fluorescence role is called fluorescence effect. The intensity of fluorescence is proportional to the amount of X-rays. This effect is the basis for the use of X-rays in fluoroscopy. In X-ray diagnostic work using this fluorescence effect can be made into a fluorescent screen, sensing screen, image intensifier in the input screen and so on. Fluorescent screen used for fluoroscopy to observe X-rays through the human body tissue image, the screen is used to enhance the photographic film sensitivity. 4. Thermal effect of the material absorbed by the X-ray energy, most of which is converted into heat, so that the temperature of the object increases, which is the thermal effect. 5. Interference, diffraction, reflection, refraction, these effects are the same as visible light. In X-ray microscopy, wavelength determination and material structure analysis are applied. (B) chemical effects 1. photographic effect with visible light, X-rays can make the film photographic. When X-rays irradiated to the film on the silver bromide, can make silver particles. Precipitation and make the film to produce "light-sensitive effect". The strength of the film's sensitivity is directly proportional to the amount of X-rays. When X-rays through the human body, the density of the human body tissues are different, the amount of X-rays absorbed differently, resulting in the bloom of the film on the sensitivity of the different, so as to obtain the image of X-rays. This is the basis of the application of X-rays for radiographic examination. 2. coloring effect of certain substances such as barium platinum cyanide, lead glass, crystal, etc., after long-term irradiation by X-rays, its crystalline dehydration and change color, which is called coloring effect. (C) biological effects' When X-rays irradiated to the biological organism, biological cells are inhibited, destroyed or even necrotic, resulting in different degrees of physiological, pathological and biochemical changes in the organism, known as the biological effects of X-rays. Different biological cells have different sensitivity to X-rays. Maple X-rays can treat certain diseases in the human body, such as tumors. On the other hand, it also has harm to the normal organism, so to le human body protection. x-ray biological effect 'socket root is caused by the ionization of x-rays. Because X-rays have such as the above kind of hunger! Thus in industry, agriculture, scientific research and other guest _ claw field, has gained a wide range of applications, such as industrial flaw detection, crystal analysis. In medicine, X-ray technology has become the diagnosis of disease and treatment of specialized disciplines, in health care occupies an important position.
Three, X-ray applications in medicine.
(a) X-ray diagnosis X-rays are used in medical diagnosis, mainly based on X-ray penetration, differential absorption, photosensitivity and fluorescence. As X-rays through the human body, by different degrees of absorption, such as the amount of X-rays absorbed by the bone than the amount absorbed by the muscle, then the amount of X-rays through the human body is not the same, so that it carries the density distribution of the human body parts of the information in the fluorescence screen or photographic film caused by fluorescence or photographic effect of the strength of the role of a greater difference, and therefore in the fluorescent screen or photographic film (after developing, fixing ) will show a different density of shadows. According to the contrast of shadow intensity, combined with clinical manifestations, laboratory results and pathological diagnosis, it can be judged whether a certain part of the human body is normal or not. Thus, X-ray diagnostic technology has become the first non-invasive internal organ examination technology in the world. (B) X-ray therapy X-ray applied to the treatment, mainly based on its biological effect, the application of different energy X-ray on the human body foci part of the cellular tissue irradiation, can be irradiated by the cellular tissue is destroyed or inhibited, so as to achieve the treatment of certain diseases, especially tumors. (C) X-ray protection in the use of X-rays at the same time, people have found to lead to patient hair loss, skin burns, staff vision impairment, leukemia and other radiation damage, in order to prevent X-rays on the human body, must take appropriate protective measures. The above constitutes the X-ray application in the medical aspects of the three links - diagnosis, treatment and protection.
Four, a brief history of the development of medical X-ray equipment
Since 1895, X-ray diagnostic and therapeutic technology has developed rapidly, the main progress can be divided into the following phases: (a) Ion X-ray tube stage (1895 ~ 1912) This is the early stage of X-ray equipment. At that time, the structure of the X-ray machine is very simple, the use of very low-efficiency gas-containing cold cathode ion X-ray tube, the use of bulky induction coils to generate high voltage, exposed high-voltage components, not to mention the precise control device. X-ray machine device capacity is small, low-efficiency, weak penetration, image clarity is not high, the lack of protection 0 According to the data recorded at that time to shoot a picture of the pelvis X-rays, need to be as long as 40 ~ 60min According to the data, it takes 40-60min to take an X-ray image of the pelvis, and the skin of the examinee is burned by X-rays after the photo is taken. (B) the electronic X-ray tube stage (1913 ~ 1928) With the development of electromagnetism, high vacuum technology and other disciplines, in 1910 the American physicist W. D. Coolidge published a report on the success of the manufacture of tungsten filament X-ray tubes. 1913 began to be used in practice, and it is the most important feature is the * tungsten filament heated to an incandescent state in order to provide the electrons required by the tube current, so the adjustment of the The heating temperature of the filament can control the tube current, so that the tube voltage and tube current can be adjusted independently of each other, and this is exactly what is needed to improve image quality.