In 1895, the German physicist R?ntgen (W. C. R?ntgen) in the study of cathode ray tubes in the phenomenon of gas discharges, embedded in a metal electrodes with two (one is called the anode, one is called the cathode) of the sealed glass tube, the electrodes at the ends of the high-voltage electricity plus several tens of thousands of volts, the use of pumping from the glass tube to pump out the air. In order to block the leakage of light (a kind of arc light) from the high-voltage discharge, a layer of black cardboard was placed over the glass tube. While conducting this experiment in a dark room, he happened to notice that two meters away from the glass tube, a piece of cardboard washed with a solution of barium platinum cyanide emitted bright fluorescence. Further tests with cardboard, boards, clothes and books about two thousand pages thick could not block this fluorescence. Even more surprisingly, when the fluorescent cardboard was held in the hand, the image of a hand bone was seen on the cardboard.
R?ntgen concluded that this was a kind of ray that was invisible to the human eye but could penetrate objects. Unable to explain its principle, unknown its nature, it borrowed the mathematical representation of the unknown number of "X" as a code name, known as "X" rays (or X-rays or X-ray for short). This is the discovery of X-rays and the origin of the name. This name has been used to this day. In honor of Roentgen's great discovery, it was named Roentgen rays.
The discovery of X-rays is of great significance in the history of mankind, and it opened a new path for natural science and medicine, for which R?ntgen was honored with the first Nobel Prize in physics in 1901.
Science is always in constant development, by R?ntgen and the repeated practice and research of scientists from all over the world, gradually revealing the nature of X-rays, confirming that it is a very short wavelength, a lot of energy electromagnetic waves. Its wavelength is shorter than the wavelength of visible light (about 0.001 ~ 100nm, medical applications of X-rays wavelength of about 0.001. ~ 0.1nm), and its photon energy than the photon energy of visible light several tens of thousands to hundreds of thousands of times. Therefore, X-rays in addition to the general nature of visible light, but also has its own characteristics.
Two, the nature of X-rays
(a) physical effects
1. penetration effect penetration effect refers to the X-rays through the material is not absorbed when the ability to X-rays can penetrate the general visible light can not pass through the material. Visible light because of its longer 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 with the ability to X-ray photon energy related to X-ray wavelength, X-ray wavelength is not absorbed, X-rays can penetrate 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 scattering process, the emergence of photoelectrons and recoil electrons from its atomic process called primary ionization, these photoelectrons or recoil electrons in the travel and other atomic collisions, 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 how much 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, 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 atoms 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 the role of fluorescence. 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 as a photographic enhancement of the film's sensitivity.
4. Thermal effect of X-ray energy absorbed by the material, most of which is converted into thermal energy, 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.
(ii) 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 "photographic 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 obtained on the sensitivity of different, so as to obtain the image of X-rays. This is the basis for the use of X-rays for radiographic examinations.
2. coloring effect of certain substances such as platinum barium cyanide, lead glass, crystal, etc., after long-term irradiation of X-rays, its crystals dehydrated 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 necrosis, 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 the penetrating effect of X-rays, differential absorption, sensitization 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 world's first application of non-invasive visceral examination technology.
(2) X-ray therapy
X-ray therapy, mainly based on its biological effects, 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 the purpose of the treatment of tumors.
(C) X-ray protection
In the use of X-rays at the same time, it was found to lead to patients with 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 the time of the shooting of an X-ray pelvic image, which requires up to 40 to 60min According to the data, an X-ray image of the pelvis took 40 to 60 minutes of exposure time, and the skin of the subject was burned by X-rays after the photo was taken.
(II) 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 its most important feature is that the * tungsten filament is heated to incandescence to provide the electrons required for the tube current. The most important feature is that the tungsten filament is heated to incandescent state to provide the electrons needed for the tube current, so the heating temperature of the filament can be adjusted to control the tube current, so that the tube voltage and the tube current can be adjusted independently of each other, which is exactly what is needed to improve the quality of the image.
In 1913, the invention of filter grids, partially eliminating scattered rays, improving the quality of the image. 1914 made cadmium tungstate fluorescent screen, the beginning of the application of X-ray fluoroscopy. 1923 invented the dual-focus X-ray tube, to solve the need for X-ray radiography, the power of the tube can be up to a few kilowatts, the rectangular focal length of the side of only a few millimeters, the quality of the X-ray image is greatly improved. The quality of X-ray images was greatly improved. At the same time, the gradual application of contrast agents has expanded the diagnostic scope of X-rays. It is no longer a simple tool to simply shoot bone images, but has become an important medical diagnostic facility for human tissues and organs that have poor natural contrast (small absorption of X-rays) of the gastrointestinal tract, bronchial tubes, blood vessels, ventricles, kidneys, bladders and other important medical diagnostic facilities can be examined. At the same time, X-rays are beginning to be used in therapy.