01-The discovery of X-rays
The night of November 8, 1895, the German physicist Wilhelm Conrad Röntgen found a strange phenomenon in the laboratory, cathode ray tube wrapped in black paper leaving only a narrow slit, in the connection with the high-voltage current for the experiment, he found that 2 meters away from a fluorescent screen coated with barium cyano platinum acid emitted a weak light green flash, once cut off the power supply flashes will immediately disappear. More than a month later, the obsessive physicist in order to capture the source of this mysterious phenomenon, and finally persuaded his wife to act as an experimental subject, will be placed in front of the fluorescent screen, the amazing scene was recorded in the history books, the fluorescent screen clearly shows the hands of the bones and that the ring on the ring finger, which is the history of the first X-ray film. 1901, Röntgen is also with the discovery of X-rays called the first Nobel Prize for Physics In 1901, Röntgen was awarded the first Nobel Prize in Physics for his discovery of X-rays.
02-Principle of X-ray production
X-rays are produced in an X-ray tube (a vacuum tube with a cathode and an anode made of a tungsten filament and a target made of metal). Between the cathode and anode with a very high DC voltage (tube voltage), when the cathode is heated to incandescent state released a large number of electrons, these electrons are accelerated in the high-voltage electric field, from the cathode to the anode (tube current), and ultimately with a great speed to impact on the metal target, the loss of kinetic energy, the vast majority of these kinetic energy is converted into heat, only a very small portion of the conversion for the X-rays radiated in all directions.
X-rays emitted by the X-ray tube can be divided into two types: one with a continuous wavelength of X-rays, constituting a continuous X-ray spectrum, which is similar to the visible white light, also known as multicolor X-rays, white X-rays, commonly used in flaw detection; the other is a number of wavelengths superimposed on the basis of the continuous spectrum of the spectral line with a certain wavelength, constituting the logo (characteristic) X-ray spectrum, which is similar to the visible species of monochromatic light, it is also known as the monochromatic X-rays, commonly used in crystallography. It is similar to monochromatic visible light, so it is also called monochromatic X-ray, and is commonly used for crystal diffraction.
03-Film Inspection
The discovery of X-rays was rapidly applied to the field of medicine, creating the first medical imaging technology. x-rays have a strong penetrating ability, when passing through the material is absorbed by the nuclear scattering so that the intensity of its attenuation, and the degree of attenuation depends on the attenuation coefficient of the material and the thickness of the ray penetration. In general, the higher the density of the material, the greater the attenuation of the radiation, so that when the radiation passes through the human body, the denser bones have a greater attenuation than the organic soft tissues, thus presenting the internal bone structure on the negative.
In the field of industrial production, X-ray technology is widely used in metal, non-metallic material parts defect detection, especially castings, welds and other internal quality inspection. In the figure below, after the X-rays pass through the stepped test block, the attenuation of the thicker parts is large and the film exposure is low, thus the blackness on the negative is low. The presence of a hole defect in the test block results in a localized reduction in thickness there, with higher attenuation and higher blackness, and a projection of the defect is shown on the negative (but no information on the location of the thickness where it is located can be provided). In addition to porosity, cracks, inclusions different from the density of the substrate, unwelded, unfused and other defects can be recognized by ray detection.
X-rays of good brother, γ-rays, is also a kind of naked eye invisible electromagnetic waves, it is by radioactive isotopes after decay, in the excited state to the stable state of the transition process from the atomic nucleus. γ-rays than the X-rays of a higher frequency, shorter wavelengths, penetration ability is much stronger, suitable for the detection of greater thickness of the parts. 420kV of X-rays can penetrate the thickness of the steel of about 80mm, 60 Co- Gamma rays penetrate the steel thickness of about 150mm, greater thickness of the specimen requires the use of special equipment - gas pedal, generating high-energy X-rays, the maximum penetration thickness of up to 400mm or more.
04-Digital Ray Inspection
Along with the daily life of the traditional film photographic technology gradually transition to digital photographic technology, applied to the medical and industrial fields of radiographic inspection technology also in the 1990s began to develop digital imaging technology. Digital radiography (DR) is a radiographic inspection technique that allows digital inspection images to be obtained, and consists of two commonly used methods: digital panel radiography (Director digital panel radiography) and computerized radiography (computed radiography, CR). radiography (CR). The former, also often referred to as DR technology, belongs to the direct digital radiography technology, mainly using rigid flat panel detectors, data acquisition takes only a few seconds to achieve near real-time imaging, and has been widely used in the medical industry (e.g., chest X-ray) and industrialized mass production inspection (Figure below); the latter CR technology mainly uses a cut and bendable imaging plate (Ima).