X-RAY RADIATION
invisible radiation capable of penetrating, albeit to varying degrees, all substances. It is electromagnetic radiation with a wavelength of about 10-8 cm. Like visible light, X-rays cause blackening of photographic film. This property is of great importance for medicine, industry and scientific research. Passing through the object under study and then falling on the film, X-ray radiation depicts its internal structure on it. Since the penetrating power of X-ray radiation is different for different materials, parts of the object that are less transparent to it give brighter areas in the photograph than those through which the radiation penetrates well. Thus, bone tissues are less transparent to x-rays than the tissues that make up the skin and internal organs. Therefore, on the radiograph, the bones will be indicated as lighter areas and the fracture site, which is more transparent for radiation, can be quite easily detected. X-ray imaging is also used in dentistry to detect caries and abscesses in the roots of teeth, as well as in industry to detect cracks in castings, plastics and rubbers. X-rays are used in chemistry to analyze compounds and in physics to study the structure of crystals. An X-ray beam passing through a chemical compound causes a characteristic secondary radiation, the spectroscopic analysis of which allows the chemist to determine the composition of the compound. When falling on a crystalline substance, an X-ray beam is scattered by the atoms of the crystal, giving a clear, regular pattern of spots and stripes on a photographic plate, which makes it possible to establish the internal structure of the crystal. The use of X-rays in cancer treatment is based on the fact that it kills cancer cells. However, it can also have an undesirable effect on normal cells. Therefore, extreme caution must be exercised in this use of X-rays. X-ray radiation was discovered by the German physicist W. Roentgen (1845-1923). His name is immortalized in some other physical terms associated with this radiation: the international unit of the dose of ionizing radiation is called the roentgen; a picture taken with an x-ray machine is called a radiograph; The field of radiological medicine that uses x-rays to diagnose and treat diseases is called radiology. Roentgen discovered radiation in 1895 while a professor of physics at the University of Würzburg. While conducting experiments with cathode rays (electron flows in discharge tubes), he noticed that a screen located near the vacuum tube, covered with crystalline barium cyanoplatinite, glows brightly, although the tube itself is covered with black cardboard. Roentgen further established that the penetrating power of the unknown rays he discovered, which he called X-rays, depended on the composition of the absorbing material. He also imaged the bones of his own hand by placing it between a cathode ray discharge tube and a screen coated with barium cyanoplatinite. Roentgen's discovery was followed by experiments by other researchers who discovered many new properties and possibilities for using this radiation. A great contribution was made by M. Laue, W. Friedrich and P. Knipping, who demonstrated in 1912 the diffraction of X-rays when it passes through a crystal; W. Coolidge, who in 1913 invented a high-vacuum X-ray tube with a heated cathode; G. Moseley, who established in 1913 the relationship between the wavelength of radiation and the atomic number of an element; G. and L. Braggi, who received the Nobel Prize in 1915 for developing the fundamentals of X-ray diffraction analysis.
OBTAINING X-RAY RADIATION
X-ray radiation occurs when electrons moving at high speeds interact with matter. When electrons collide with atoms of any substance, they quickly lose their kinetic energy. In this case, most of it is converted into heat, and a small fraction, usually less than 1%, is converted into X-ray energy. This energy is released in the form of quanta - particles called photons that have energy but have zero rest mass. X-ray photons differ in their energy, which is inversely proportional to their wavelength. In the conventional method of obtaining x-rays, a wide range of wavelengths is obtained, which is called the x-ray spectrum. The spectrum contains pronounced components, as shown in Fig. 1. A wide "continuum" is called a continuous spectrum or white radiation. The sharp peaks superimposed on it are called characteristic x-ray emission lines. Although the entire spectrum is the result of collisions of electrons with matter, the mechanisms for the appearance of its wide part and lines are different. A substance consists of a large number of atoms, each of which has a nucleus surrounded by electron shells, and each electron in the shell of an atom of a given element occupies a certain discrete energy level. Usually these shells, or energy levels, are denoted by the symbols K, L, M, etc., starting from the shell closest to the nucleus. When an incident electron of sufficiently high energy collides with one of the electrons bound to the atom, it knocks that electron out of its shell. The empty space is occupied by another electron from the shell, which corresponds to a higher energy. This latter gives off excess energy by emitting an X-ray photon. Since the shell electrons have discrete energy values, the resulting X-ray photons also have a discrete spectrum. This corresponds to sharp peaks for certain wavelengths, the specific values ​​of which depend on the target element. The characteristic lines form K-, L- and M-series, depending on which shell (K, L or M) the electron was removed from. The relationship between the wavelength of X-rays and the atomic number is called Moseley's law (Fig. 2).

If an electron collides with a relatively heavy nucleus, then it slows down, and its kinetic energy is released in the form of an X-ray photon of approximately the same energy. If he flies past the nucleus, he will lose only part of his energy, and the rest will be transferred to other atoms that fall in his way. Each act of energy loss leads to the emission of a photon with some energy. A continuous X-ray spectrum appears, the upper limit of which corresponds to the energy of the fastest electron. This is the mechanism for the formation of a continuous spectrum, and the maximum energy (or minimum wavelength) that fixes the boundary of the continuous spectrum is proportional to the accelerating voltage, which determines the speed of the incident electrons. The spectral lines characterize the material of the bombarded target, while the continuous spectrum is determined by the energy of the electron beam and practically does not depend on the target material. X-rays can be obtained not only by electron bombardment, but also by irradiating the target with X-rays from another source. In this case, however, most of the energy of the incident beam goes into the characteristic X-ray spectrum, and a very small fraction of it falls into the continuous spectrum. Obviously, the incident X-ray beam must contain photons whose energy is sufficient to excite the characteristic lines of the bombarded element. The high percentage of energy per characteristic spectrum makes this method of X-ray excitation convenient for scientific research.
X-ray tubes. In order to obtain X-ray radiation due to the interaction of electrons with matter, it is necessary to have a source of electrons, means of accelerating them to high speeds, and a target capable of withstanding electron bombardment and producing X-ray radiation of the desired intensity. The device that has all this is called an x-ray tube. Early explorers used "deep vacuum" tubes such as today's discharge tubes. The vacuum in them was not very high. Gas discharge tubes contain a large number of gas, and when a large potential difference is applied to the electrodes of the tube, the gas atoms turn into positive and negative ions. The positive ones move towards the negative electrode (cathode) and, falling on it, knock electrons out of it, and they, in turn, move towards the positive electrode (anode) and, bombarding it, create a stream of X-ray photons. In the modern X-ray tube developed by Coolidge (Fig. 3), the source of electrons is a tungsten cathode heated to a high temperature. The electrons are accelerated to high speeds by the high potential difference between the anode (or anticathode) and the cathode. Since the electrons must reach the anode without colliding with atoms, a very high vacuum is required, for which the tube must be well evacuated. This also reduces the probability of ionization of the remaining gas atoms and the associated side currents.

The electrons are focused on the anode by a specially shaped electrode surrounding the cathode. This electrode is called the focusing electrode and together with the cathode forms the "electronic searchlight" of the tube. The anode subjected to electron bombardment must be made of a refractory material, since most of the kinetic energy of the bombarding electrons is converted into heat. In addition, it is desirable that the anode be made of a material with a high atomic number, since the x-ray yield increases with increasing atomic number. Tungsten, whose atomic number is 74, is most often chosen as the anode material. The design of X-ray tubes can be different depending on the application conditions and requirements.
X-RAY DETECTION
All methods for detecting X-rays are based on their interaction with matter. Detectors can be of two types: those that give an image, and those that do not. The former include X-ray fluorography and fluoroscopy devices, in which the X-ray beam passes through the object under study, and the transmitted radiation enters the luminescent screen or film. The image appears due to the fact that different parts of the object under study absorb radiation in different ways - depending on the thickness of the substance and its composition. In detectors with a luminescent screen, the X-ray energy is converted into a directly observable image, while in radiography it is recorded on a sensitive emulsion and can only be observed after the film has been developed. The second type of detectors includes a wide variety of devices in which the X-ray energy is converted into electrical signals that characterize the relative intensity of the radiation. These include ionization chambers, a Geiger counter, a proportional counter, a scintillation counter, and some special detectors based on cadmium sulfide and selenide. Currently, scintillation counters can be considered the most efficient detectors, which work well in a wide energy range.
see also PARTICLE DETECTORS . The detector is selected taking into account the conditions of the problem. For example, if it is necessary to accurately measure the intensity of diffracted X-ray radiation, then counters are used that allow measurements to be made with an accuracy of fractions of a percent. If it is necessary to register a lot of diffracted beams, then it is advisable to use X-ray film, although in this case it is impossible to determine the intensity with the same accuracy.
X-RAY AND GAMMA DEFECTOSCOPY
One of the most common applications of X-rays in industry is material quality control and flaw detection. The x-ray method is non-destructive, so that the material being tested, if found to meet the required requirements, can then be used for its intended purpose. Both x-ray and gamma flaw detection are based on the penetrating power of x-rays and the characteristics of its absorption in materials. Penetrating power is determined by the energy of X-ray photons, which depends on the accelerating voltage in the X-ray tube. Therefore, thick samples and samples from heavy metals, such as gold and uranium, require an X-ray source with a higher voltage for their study, and for thin samples, a source with a lower voltage is sufficient. For gamma-ray flaw detection of very large castings and large rolled products, betatrons and linear accelerators are used, accelerating particles to energies of 25 MeV and more. The absorption of X-rays in a material depends on the thickness of the absorber d and the absorption coefficient m and is determined by the formula I = I0e-md, where I is the intensity of the radiation transmitted through the absorber, I0 is the intensity of the incident radiation, and e = 2.718 is the base of natural logarithms. For a given material, at a given wavelength (or energy) of X-rays, the absorption coefficient is a constant. But the radiation of an X-ray source is not monochromatic, but contains a wide spectrum of wavelengths, as a result of which the absorption at the same thickness of the absorber depends on the wavelength (frequency) of the radiation. X-ray radiation is widely used in all industries associated with the processing of metals by pressure. It is also used to test artillery barrels, foodstuffs, plastics, to test complex devices and systems in electronic engineering. (Neutronography, which uses neutron beams instead of X-rays, is used for similar purposes.) X-rays are also used for other purposes, such as examining paintings to determine their authenticity or detecting additional layers of paint on top of the main layer.
X-RAY DIFFRACTION
X-ray diffraction provides important information about solids—their atomic structure and crystal form—as well as about liquids, amorphous bodies, and large molecules. The diffraction method is also used for accurate (with an error of less than 10-5) determination of interatomic distances, detection of stresses and defects, and for determining the orientation of single crystals. The diffraction pattern can identify unknown materials, as well as detect the presence of impurities in the sample and determine them. The importance of the X-ray diffraction method for the progress of modern physics can hardly be overestimated, since the modern understanding of the properties of matter is ultimately based on data on the arrangement of atoms in various chemical compounds, on the nature of the bonds between them, and on structural defects. The main tool for obtaining this information is the X-ray diffraction method. X-ray diffraction crystallography is essential for determining the structures of complex large molecules, such as those of deoxyribonucleic acid (DNA), the genetic material of living organisms. Immediately after the discovery of X-rays, scientific and medical interest was concentrated both on the ability of this radiation to penetrate through bodies, and on its nature. Experiments on the diffraction of X-rays on slits and diffraction gratings showed that it belongs to electromagnetic radiation and has a wavelength of the order of 10-8-10-9 cm. Even earlier, scientists, in particular W. Barlow, guessed that the regular and symmetrical shape of natural crystals is due to the ordered arrangement of atoms that form the crystal. In some cases, Barlow was able to correctly predict the structure of a crystal. The value of the predicted interatomic distances was 10-8 cm. The fact that the interatomic distances turned out to be of the order of the X-ray wavelength made it possible in principle to observe their diffraction. The result was the idea for one of the most important experiments in the history of physics. M. Laue organized an experimental test of this idea, which was carried out by his colleagues W. Friedrich and P. Knipping. In 1912, the three of them published their work on the results of X-ray diffraction. Principles of X-ray diffraction. To understand the phenomenon of X-ray diffraction, one must consider in order: firstly, the spectrum of X-rays, secondly, the nature of the crystal structure and, thirdly, the phenomenon of diffraction itself. As mentioned above, the characteristic X-ray radiation consists of a series of spectral lines of a high degree of monochromaticity, determined by the anode material. With the help of filters, you can select the most intense of them. Therefore, by choosing the anode material in an appropriate way, it is possible to obtain a source of almost monochromatic radiation with a very precisely defined wavelength value. The wavelengths of the characteristic radiation typically range from 2.285 for chromium to 0.558 for silver (the values ​​for the various elements are known to six significant figures). The characteristic spectrum is superimposed on a continuous "white" spectrum of much lower intensity, due to the deceleration of the incident electrons in the anode. Thus, two types of radiation can be obtained from each anode: characteristic and bremsstrahlung, each of which plays an important role in its own way. Atoms in the crystal structure are located at regular intervals, forming a sequence of identical cells - a spatial lattice. Some lattices (for example, for most ordinary metals) are quite simple, while others (for example, for protein molecules) are quite complex. The crystal structure is characterized by the following: if one shifts from some given point of one cell to the corresponding point of the neighboring cell, then exactly the same atomic environment will be found. And if some atom is located at one or another point of one cell, then the same atom will be located at the equivalent point of any neighboring cell. This principle is strictly valid for a perfect, ideally ordered crystal. However, many crystals (for example, metallic solid solutions) are disordered to some extent; crystallographically equivalent places can be occupied by different atoms. In these cases, it is not the position of each atom that is determined, but only the position of an atom "statistically averaged" over a large number of particles (or cells). The phenomenon of diffraction is discussed in the article OPTICS and the reader may refer to this article before moving on. It shows that if waves (for example, sound, light, X-rays) pass through a small slit or hole, then the latter can be considered as a secondary source of waves, and the image of the slit or hole consists of alternating light and dark stripes. Further, if there is a periodic structure of holes or slots, then as a result of the amplifying and attenuating interference of rays coming from different holes, a clear diffraction pattern arises. X-ray diffraction is a collective scattering phenomenon in which the role of holes and scattering centers is played by periodically arranged atoms of the crystal structure. Mutual amplification of their images at certain angles gives a diffraction pattern similar to that which would result from the diffraction of light on a three-dimensional diffraction grating. Scattering occurs due to the interaction of the incident X-ray radiation with electrons in the crystal. Due to the fact that the wavelength of X-ray radiation is of the same order as the dimensions of the atom, the wavelength of the scattered X-ray radiation is the same as that of the incident. This process is the result of forced oscillations of electrons under the action of incident X-rays. Consider now an atom with a cloud of bound electrons (surrounding the nucleus) on which X-rays are incident. Electrons in all directions simultaneously scatter the incident and emit their own X-ray radiation of the same wavelength, although of different intensity. The intensity of the scattered radiation is related to the atomic number of the element, since the atomic number is equal to the number of orbital electrons that can participate in scattering. (This dependence of the intensity on the atomic number of the scattering element and on the direction in which the intensity is measured is characterized by the atomic scattering factor, which plays an extremely important role in the analysis of the structure of crystals.) Let us choose in the crystal structure a linear chain of atoms located at the same distance from each other, and consider their diffraction pattern. It has already been noted that the X-ray spectrum consists of a continuous part ("continuum") and a set of more intense lines characteristic of the element that is the anode material. Let's say we filtered out the continuous spectrum and got an almost monochromatic X-ray beam directed at our linear chain of atoms. The amplification condition (amplifying interference) is satisfied if the path difference of waves scattered by neighboring atoms is a multiple of the wavelength. If the beam is incident at an angle a0 to a line of atoms separated by intervals a (period), then for the diffraction angle a the path difference corresponding to the gain will be written as a(cos a - cosa0) = hl, where l is the wavelength and h is integer (Fig. 4 and 5).

To extend this approach to a three-dimensional crystal, it is only necessary to choose rows of atoms in two other directions in the crystal and solve the three equations thus obtained jointly for three crystal axes with periods a, b and c. The other two equations are

These are the three fundamental Laue equations for X-ray diffraction, with the numbers h, k and c being the Miller indices for the diffraction plane.
see also CRYSTALS AND CRYSTALLOGRAPHY. Considering any of the Laue equations, for example the first one, one can notice that since a, a0, l are constants, and h = 0, 1, 2, ..., its solution can be represented as a set of cones with a common axis a (Fig. . 5). The same is true for directions b and c. In the general case of three-dimensional scattering (diffraction), the three Laue equations must have a common solution, i.e. three diffraction cones located on each of the axes must intersect; the common line of intersection is shown in fig. 6. The joint solution of the equations leads to the Bragg-Wulf law:

l = 2(d/n)sinq, where d is the distance between the planes with indices h, k and c (period), n = 1, 2, ... are integers (diffraction order), and q is the angle formed by incident beam (as well as diffracting) with the plane of the crystal in which diffraction occurs. Analyzing the equation of the Bragg - Wolfe law for a single crystal located in the path of a monochromatic X-ray beam, we can conclude that diffraction is not easy to observe, because l and q are fixed, and sinq DIFFRACTION ANALYSIS METHODS
Laue method. The Laue method uses a continuous "white" spectrum of X-rays, which is directed to a stationary single crystal. For a specific value of the period d, the wavelength corresponding to the Bragg-Wulf condition is automatically selected from the entire spectrum. The Laue patterns obtained in this way make it possible to judge the directions of the diffracted beams and, consequently, the orientations of the crystal planes, which also makes it possible to draw important conclusions about the symmetry, orientation of the crystal, and the presence of defects in it. In this case, however, information about the spatial period d is lost. On fig. 7 shows an example of a Lauegram. The X-ray film was located on the side of the crystal opposite to that on which the X-ray beam was incident from the source.

Debye-Scherrer method (for polycrystalline samples). Unlike the previous method, monochromatic radiation (l = const) is used here, and the angle q is varied. This is achieved by using a polycrystalline sample consisting of numerous small crystallites of random orientation, among which there are those that satisfy the Bragg-Wulf condition. The diffracted beams form cones, the axis of which is directed along the X-ray beam. For imaging, a narrow strip of X-ray film is usually used in a cylindrical cassette, and X-rays are propagated along the diameter through holes in the film. The debyegram obtained in this way (Fig. 8) contains exact information about the period d, i.e. about the structure of the crystal, but does not give the information that the Lauegram contains. Therefore, both methods complement each other. Let us consider some applications of the Debye-Scherrer method.

Identification of chemical elements and compounds. From the angle q determined from the Debyegram, one can calculate the interplanar distance d characteristic of a given element or compound. At present, many tables of d values ​​have been compiled, which make it possible to identify not only one or another chemical element or compound, but also various phase states of the same substance, which does not always give a chemical analysis. It is also possible to determine the content of the second component in substitutional alloys with high accuracy from the dependence of the period d on the concentration.
Stress analysis. From the measured difference in interplanar spacings for different directions in crystals, knowing the elastic modulus of the material, it is possible to calculate small stresses in it with high accuracy.
Studies of preferential orientation in crystals. If small crystallites in a polycrystalline sample are not completely randomly oriented, then the rings on the Debyegram will have different intensities. In the presence of a pronounced preferred orientation, the intensity maxima are concentrated in individual spots in the image, which becomes similar to the image for a single crystal. For example, during deep cold rolling, a metal sheet acquires a texture - a pronounced orientation of crystallites. According to the debaygram, one can judge the nature of the cold working of the material.
Study of grain sizes. If the grain size of the polycrystal is more than 10-3 cm, then the lines on the Debyegram will consist of separate spots, since in this case the number of crystallites is not enough to cover the entire range of values ​​of the angles q. If the crystallite size is less than 10-5 cm, then the diffraction lines become wider. Their width is inversely proportional to the size of the crystallites. Broadening occurs for the same reason that a decrease in the number of slits reduces the resolution of a diffraction grating. X-ray radiation makes it possible to determine grain sizes in the range of 10-7-10-6 cm.
Methods for single crystals. In order for diffraction by a crystal to provide information not only about the spatial period, but also about the orientation of each set of diffracting planes, methods of a rotating single crystal are used. A monochromatic X-ray beam is incident on the crystal. The crystal rotates around the main axis, for which the Laue equations are satisfied. In this case, the angle q, which is included in the Bragg-Wulf formula, changes. The diffraction maxima are located at the intersection of the Laue diffraction cones with the cylindrical surface of the film (Fig. 9). The result is a diffraction pattern of the type shown in Fig. 10. However, complications are possible due to the overlap of different diffraction orders at one point. The method can be significantly improved if, simultaneously with the rotation of the crystal, the film is also moved in a certain way.

Studies of liquids and gases. It is known that liquids, gases and amorphous bodies do not have the correct crystal structure. But here, too, there is a chemical bond between the atoms in the molecules, due to which the distance between them remains almost constant, although the molecules themselves are randomly oriented in space. Such materials also give a diffraction pattern with a relatively small number of smeared maxima. The processing of such a picture by modern methods makes it possible to obtain information about the structure of even such non-crystalline materials.
SPECTROCHEMICAL X-RAY ANALYSIS
A few years after the discovery of X-rays, Ch. Barkla (1877-1944) discovered that when a high-energy X-ray flux acts on a substance, secondary fluorescent X-ray radiation is generated, which is characteristic of the element under study. Shortly thereafter, G. Moseley, in a series of his experiments, measured the wavelengths of the primary characteristic X-ray radiation obtained by electron bombardment of various elements, and deduced the relationship between the wavelength and the atomic number. These experiments, and Bragg's invention of the X-ray spectrometer, laid the foundation for spectrochemical X-ray analysis. The possibilities of X-rays for chemical analysis were immediately recognized. Spectrographs were created with registration on a photographic plate, in which the sample under study served as the anode of an X-ray tube. Unfortunately, this technique turned out to be very laborious, and therefore was used only when the usual methods of chemical analysis were inapplicable. An outstanding example of innovative research in the field of analytical X-ray spectroscopy was the discovery in 1923 by G. Hevesy and D. Coster of a new element, hafnium. The development of high-power X-ray tubes for radiography and sensitive detectors for radiochemical measurements during World War II largely contributed to the rapid growth of X-ray spectrography in the following years. This method has become widespread due to the speed, convenience, non-destructive nature of the analysis and the possibility of full or partial automation. It is applicable in the problems of quantitative and qualitative analysis of all elements with an atomic number greater than 11 (sodium). And although X-ray spectrochemical analysis is usually used to determine the critical components in a sample (from 0.1-100%), in some cases it is suitable for concentrations of 0.005% and even lower.
X-ray spectrometer. A modern X-ray spectrometer consists of three main systems (Fig. 11): excitation systems, i.e. x-ray tube with an anode made of tungsten or other refractory material and a power supply; analysis systems, i.e. an analyzer crystal with two multi-slit collimators, as well as a spectrogoniometer for fine adjustment; and registration systems with a Geiger or proportional or scintillation counter, as well as a rectifier, amplifier, counters and a chart recorder or other recording device.

X-ray fluorescent analysis. The analyzed sample is located in the path of the exciting x-rays. The region of the sample to be examined is usually isolated by a mask with a hole of the desired diameter, and the radiation passes through a collimator that forms a parallel beam. Behind the analyzer crystal, a slit collimator emits diffracted radiation for the detector. Usually, the maximum angle q is limited to 80–85°, so that only X-rays whose wavelength l is related to the interplanar distance d by the inequality l can diffract on the analyzer crystal. X-ray microanalysis. The flat analyzer crystal spectrometer described above can be adapted for microanalysis. This is achieved by constricting either the primary x-ray beam or the secondary beam emitted by the sample. However, a decrease in the effective size of the sample or the radiation aperture leads to a decrease in the intensity of the recorded diffracted radiation. An improvement to this method can be achieved by using a curved crystal spectrometer, which makes it possible to register a cone of divergent radiation, and not only radiation parallel to the axis of the collimator. With such a spectrometer, particles smaller than 25 µm can be identified. An even greater reduction in the size of the analyzed sample is achieved in the X-ray electron probe microanalyzer invented by R. Kasten. Here, the characteristic X-ray emission of the sample is excited by a highly focused electron beam, which is then analyzed by a bent-crystal spectrometer. Using such a device, it is possible to detect amounts of a substance of the order of 10–14 g in a sample with a diameter of 1 μm. Installations with electron beam scanning of the sample have also been developed, with the help of which it is possible to obtain a two-dimensional pattern of the distribution over the sample of the element whose characteristic radiation is tuned to the spectrometer.
MEDICAL X-RAY DIAGNOSIS
The development of x-ray technology has significantly reduced the exposure time and improved the quality of images, allowing even soft tissues to be studied.
Fluorography. This diagnostic method consists in photographing a shadow image from a translucent screen. The patient is placed between an X-ray source and a flat screen of phosphor (usually cesium iodide), which glows when exposed to X-rays. Biological tissues of varying degrees of density create shadows of X-ray radiation with varying degrees of intensity. A radiologist examines a shadow image on a fluorescent screen and makes a diagnosis. In the past, a radiologist relied on vision to analyze an image. Now there are various systems that amplify the image, display it on a television screen or record data in the computer's memory.
Radiography. The recording of an x-ray image directly on photographic film is called radiography. In this case, the organ under study is located between the X-ray source and the film, which captures information about the state of the organ at a given time. Repeated radiography makes it possible to judge its further evolution. Radiography allows you to very accurately examine the integrity of bone tissue, which consists mainly of calcium and is opaque to x-rays, as well as muscle tissue ruptures. With its help, better than a stethoscope or listening, the condition of the lungs is analyzed in case of inflammation, tuberculosis, or the presence of fluid. With the help of radiography, the size and shape of the heart, as well as the dynamics of its changes in patients suffering from heart disease, are determined.
contrast agents. Parts of the body and cavities of individual organs that are transparent to X-ray radiation become visible if they are filled with a contrast agent that is harmless to the body, but allows one to visualize the shape of internal organs and check their functioning. The patient either takes contrast agents orally (such as barium salts in the study of the gastrointestinal tract), or they are administered intravenously (such as iodine-containing solutions in the study of the kidneys and urinary tract). In recent years, however, these methods have been supplanted by diagnostic methods based on the use of radioactive atoms and ultrasound.
CT scan. In the 1970s, a new method of X-ray diagnostics was developed, based on a complete photograph of the body or its parts. Images of thin layers ("slices") are processed by a computer, and the final image is displayed on the monitor screen. This method is called computed x-ray tomography. It is widely used in modern medicine for diagnosing infiltrates, tumors and other brain disorders, as well as for diagnosing diseases of soft tissues inside the body. This technique does not require the introduction of foreign contrast agents and is therefore faster and more effective than traditional techniques.
BIOLOGICAL ACTION OF X-RAY RADIATION
The harmful biological effect of X-ray radiation was discovered shortly after its discovery by Roentgen. It turned out that the new radiation can cause something like a severe sunburn (erythema), accompanied, however, by deeper and more permanent damage to the skin. Appearing ulcers often turned into cancer. In many cases, fingers or hands had to be amputated. There were also deaths. It has been found that skin damage can be avoided by reducing exposure time and dose, using shielding (eg lead) and remote controls. But gradually other, more long-term effects of X-ray exposure were revealed, which were then confirmed and studied in experimental animals. The effects due to the action of X-rays, as well as other ionizing radiations (such as gamma radiation emitted by radioactive materials) include: 1) temporary changes in the composition of the blood after a relatively small excess exposure; 2) irreversible changes in the composition of the blood (hemolytic anemia) after prolonged excessive exposure; 3) an increase in the incidence of cancer (including leukemia); 4) faster aging and early death; 5) the occurrence of cataracts. In addition, biological experiments on mice, rabbits and flies (Drosophila) have shown that even small doses of systematic irradiation of large populations, due to an increase in the rate of mutation, lead to harmful genetic effects. Most geneticists recognize the applicability of these data to the human body. As for the biological effect of X-ray radiation on the human body, it is determined by the level of the radiation dose, as well as by which particular organ of the body was exposed to radiation. For example, blood diseases are caused by irradiation of the hematopoietic organs, mainly the bone marrow, and genetic consequences - by irradiation of the genital organs, which can also lead to sterility. The accumulation of knowledge about the effects of X-ray radiation on the human body has led to the development of national and international standards for permissible radiation doses, published in various reference publications. In addition to X-rays, which are purposefully used by humans, there is also the so-called scattered, side radiation that occurs for various reasons, for example, due to scattering due to the imperfection of the lead protective screen, which does not completely absorb this radiation. In addition, many electrical devices that are not designed to produce X-rays nevertheless generate X-rays as a by-product. Such devices include electron microscopes, high-voltage rectifier lamps (kenotrons), as well as kinescopes of outdated color televisions. The production of modern color kinescopes in many countries is now under government control.
HAZARDOUS FACTORS OF X-RAY RADIATION
The types and degree of danger of X-ray exposure for people depend on the contingent of people exposed to radiation.
Professionals working with x-ray equipment. This category includes radiologists, dentists, as well as scientific and technical workers and personnel maintaining and using x-ray equipment. Effective measures are being taken to reduce the levels of radiation they have to deal with.
Patients. There are no strict criteria here, and the safe level of radiation that patients receive during treatment is determined by the attending physicians. Physicians are advised not to unnecessarily expose patients to x-rays. Particular caution should be exercised when examining pregnant women and children. In this case, special measures are taken.
Control methods. There are three aspects to this:
1) availability of adequate equipment, 2) enforcement of safety regulations, 3) proper use of equipment. In an x-ray examination, only the desired area should be exposed to radiation, be it dental examinations or lung examinations. Note that immediately after turning off the X-ray apparatus, both primary and secondary radiation disappear; there is also no residual radiation, which is not always known even to those who are directly connected with it in their work.
see also
ATOM STRUCTURE;

The German scientist Wilhelm Conrad Roentgen can rightly be considered the founder of radiography and the discoverer of the key features of X-rays.

Then back in 1895, he did not even suspect the breadth of application and popularity of X-radiation discovered by him, although even then they raised a wide resonance in the world of science.

It is unlikely that the inventor could have guessed what benefit or harm the fruit of his activity would bring. But today we will try to find out what effect this kind of radiation has on the human body.

• X-radiation is endowed with a huge penetrating power, but it depends on the wavelength and density of the material that is irradiated;
• under the influence of radiation, some objects begin to glow;
• the x-ray affects living beings;
• thanks to X-rays, some biochemical reactions begin to occur;
• An x-ray beam can take electrons from some atoms and thereby ionize them.

Even the inventor himself was primarily concerned with the question of what exactly the rays he discovered were.

After a whole series of experimental studies, the scientist found out that X-rays are intermediate waves between ultraviolet and gamma radiation, the length of which is 10 -8 cm.

The properties of the X-ray beam, which are listed above, have destructive properties, but this does not prevent them from being used for useful purposes.

So where in the modern world can X-rays be used?

1. They can be used to study the properties of many molecules and crystalline formations.
2. For flaw detection, that is, to check industrial parts and devices for defects.
3. In the medical industry and therapeutic research.

Due to the short lengths of the entire range of these waves and their unique properties, the most important application of the radiation discovered by Wilhelm Roentgen became possible.

Since the topic of our article is limited to the impact of X-rays on the human body, which encounters them only when going to the hospital, then we will consider only this branch of application.

The scientist who invented X-rays made them an invaluable gift for the entire population of the Earth, because he did not patent his offspring for further use.

Since World War I, portable X-ray machines have saved hundreds of wounded lives. Today, X-rays have two main applications:

1. Diagnosis with it.

X-ray diagnostics is used in various options:

• X-ray or transillumination;
• x-ray or photograph;
• fluorographic study;
• tomography using x-rays.

Now we need to understand how these methods differ from each other:

1. The first method assumes that the subject is located between a special screen with a fluorescent property and an X-ray tube. The doctor, based on individual characteristics, selects the required strength of the rays and receives an image of the bones and internal organs on the screen.
2. In the second method, the patient is placed on a special x-ray film in a cassette. In this case, the equipment is placed above the person. This technique allows you to get an image in the negative, but with finer details than with fluoroscopy.
3. Mass examinations of the population for lung disease allows for fluorography. At the time of the procedure, the image is transferred from a large monitor to a special film.
4. Tomography allows you to get images of internal organs in several sections. A whole series of images are taken, which are hereinafter referred to as a tomogram.
5. If you connect the help of a computer to the previous method, then specialized programs will create a complete image made using an x-ray scanner.

All these methods of diagnosing health problems are based on the unique property of X-rays to light up photographic film. At the same time, the penetrating ability of inert and other tissues of our body is different, which is displayed in the picture.

After another property of X-rays to influence tissues from a biological point of view was discovered, this feature began to be actively used in tumor therapy.

Cells, especially malignant ones, divide very quickly, and the ionizing property of radiation has a positive effect on therapeutic therapy and slows down tumor growth.

But the other side of the coin is the negative effect of x-rays on the cells of the hematopoietic, endocrine and immune systems, which also divide rapidly. As a result of the negative influence of the X-ray, radiation sickness manifests itself.

The effect of x-rays on the human body

Literally immediately after such a loud discovery in the scientific world, it became known that X-rays can affect the human body:

1. In the course of research on the properties of X-rays, it turned out that they are capable of causing burns on the skin. Very similar to thermal. However, the depth of the lesion was much greater than domestic injuries, and they healed worse. Many scientists dealing with these insidious radiations have lost their fingers.
2. By trial and error, it was found that if you reduce the time and vine of endowment, then burns can be avoided. Later, lead screens and the remote method of irradiating patients began to be used.
3. The long-term perspective of the harmfulness of rays shows that changes in the composition of the blood after irradiation leads to leukemia and early aging.
4. The degree of severity of the impact of X-rays on the human body directly depends on the irradiated organ. So, with X-rays of the small pelvis, infertility can occur, and with the diagnosis of hematopoietic organs - blood diseases.
5. Even the most insignificant exposures, but over a long period of time, can lead to changes at the genetic level.

Of course, all studies were conducted on animals, but scientists have proven that pathological changes will also apply to humans.

IMPORTANT! Based on the obtained data, X-ray exposure standards were developed, which are uniform throughout the world.

Doses of x-rays for diagnosis

Probably, everyone who leaves the doctor's office after an x-ray is wondering how this procedure will affect their future health?

Radiation exposure in nature also exists and we encounter it daily. To make it easier to understand how x-rays affect our body, we compare this procedure with the natural radiation received:

• on a chest x-ray, a person receives a dose of radiation equivalent to 10 days of background exposure, and the stomach or intestines - 3 years;
• tomogram on the computer of the abdominal cavity or the whole body - the equivalent of 3 years of radiation;
• examination on chest x-ray - 3 months;
• limbs are irradiated, practically without harming health;
• dental x-ray due to the precise direction of the beam beam and the minimum exposure time is also not dangerous.

IMPORTANT! Despite the fact that the given data, no matter how frightening they may sound, meet international requirements. However, the patient has every right to ask for additional means of protection in case of strong fear for his well-being.

All of us are faced with x-ray examination, and more than once. However, one category of people outside of the prescribed procedures are pregnant women.

The fact is that X-rays extremely affect the health of the unborn child. These waves can cause intrauterine malformations as a result of the effect on the chromosomes.

IMPORTANT! The most dangerous period for x-rays is pregnancy before 16 weeks. During this period, the most vulnerable are the pelvic, abdominal and vertebral regions of the baby.

Knowing about this negative property of x-rays, doctors all over the world are trying to avoid prescribing it for pregnant women.

But there are other sources of radiation that a pregnant woman may encounter:

• microscopes powered by electricity;
• color TV monitors.

Those who are preparing to become a mother must be aware of the danger that awaits them. During lactation, X-rays do not pose a threat to the body of the nursing and the baby.

What about after the x-ray?

Even the most minor effects of X-ray exposure can be minimized by following a few simple recommendations:

• drink milk immediately after the procedure. As you know, it is able to remove radiation;
• dry white wine or grape juice has the same properties;
• it is desirable at first to eat more foods containing iodine.

IMPORTANT! You should not resort to any medical procedures or use medical methods after visiting the x-ray room.

No matter how negative the properties of the once discovered X-rays, the benefits of their use far outweigh the harm. In medical institutions, the transillumination procedure is carried out quickly and with minimal doses.

In 1895, the German physicist W. Roentgen discovered a new, previously unknown type of electromagnetic radiation, which was named X-ray in honor of its discoverer. W. Roentgen became the author of his discovery at the age of 50, holding the post of rector of the University of Würzburg and having a reputation as one of the best experimenters of his time. One of the first to find a technical application for Roentgen's discovery was the American Edison. He created a handy demonstration apparatus and already in May 1896 organized an X-ray exhibition in New York, where visitors could look at their own hand on a luminous screen. After Edison's assistant died from the severe burns he received from constant demonstrations, the inventor stopped further experiments with X-rays.

X-ray radiation began to be used in medicine due to its high penetrating power. Initially, X-rays were used to examine bone fractures and locate foreign bodies in the human body. Currently, there are several methods based on X-rays. But these methods have their drawbacks: radiation can cause deep damage to the skin. Appearing ulcers often turned into cancer. In many cases, fingers or hands had to be amputated. Fluoroscopy(synonymous with translucence) is one of the main methods of X-ray examination, which consists in obtaining a planar positive image of the object under study on a translucent (fluorescent) screen. During fluoroscopy, the subject is between a translucent screen and an x-ray tube. On modern X-ray translucent screens, the image appears at the moment the X-ray tube is turned on and disappears immediately after it is turned off. Fluoroscopy makes it possible to study the function of the organ - heart pulsation, respiratory movements of the ribs, lungs, diaphragm, peristalsis of the digestive tract, etc. Fluoroscopy is used in the treatment of diseases of the stomach, gastrointestinal tract, duodenum, diseases of the liver, gallbladder and biliary tract. At the same time, the medical probe and manipulators are inserted without tissue damage, and the actions during the operation are controlled by fluoroscopy and are visible on the monitor.
Radiography - method of X-ray diagnostics with the registration of a fixed image on a photosensitive material - special. photographic film (X-ray film) or photographic paper with subsequent photo processing; With digital radiography, the image is fixed in the computer's memory. It is performed on X-ray diagnostic devices - stationary, installed in specially equipped X-ray rooms, or mobile and portable - at the patient's bedside or in the operating room. On radiographs, the elements of the structures of various organs are displayed much more clearly than on a fluorescent screen. Radiography is performed in order to detect and prevent various diseases, its main goal is to help doctors of various specialties correctly and quickly make a diagnosis. An x-ray image captures the state of an organ or tissue only at the time of exposure. However, a single radiograph captures only anatomical changes at a certain moment, it gives the statics of the process; through a series of radiographs taken at certain intervals, it is possible to study the dynamics of the process, that is, functional changes. Tomography. The word tomography can be translated from Greek as slice image. This means that the purpose of tomography is to obtain a layered image of the internal structure of the object of study. Computed tomography is characterized by high resolution, which makes it possible to distinguish subtle changes in soft tissues. CT allows to detect such pathological processes that cannot be detected by other methods. In addition, the use of CT makes it possible to reduce the dose of X-ray radiation received by patients during the diagnostic process.
Fluorography- a diagnostic method that allows you to get an image of organs and tissues, was developed at the end of the 20th century, a year after X-rays were discovered. In the pictures you can see sclerosis, fibrosis, foreign objects, neoplasms, inflammations that have a developed degree, the presence of gases and infiltrate in the cavities, abscesses, cysts, and so on. Most often, a chest x-ray is performed, which allows to detect tuberculosis, a malignant tumor in the lungs or chest, and other pathologies.
X-ray therapy- This is a modern method with which the treatment of certain pathologies of the joints is performed. The main directions of treatment of orthopedic diseases by this method are: Chronic. Inflammatory processes of the joints (arthritis, polyarthritis); Degenerative (osteoarthritis, osteochondrosis, deforming spondylosis). The purpose of radiotherapy is the inhibition of the vital activity of cells of pathologically altered tissues or their complete destruction. In non-tumor diseases, X-ray therapy is aimed at suppressing the inflammatory reaction, inhibiting proliferative processes, reducing pain sensitivity and secretory activity of the glands. It should be borne in mind that the sex glands, hematopoietic organs, leukocytes, and malignant tumor cells are most sensitive to X-rays. The radiation dose in each case is determined individually.

For the discovery of X-rays, Roentgen was awarded the first Nobel Prize in Physics in 1901, and the Nobel Committee emphasized the practical importance of his discovery.
Thus, X-rays are invisible electromagnetic radiation with a wavelength of 105 - 102 nm. X-rays can penetrate some materials that are opaque to visible light. They are emitted during the deceleration of fast electrons in matter (continuous spectrum) and during transitions of electrons from the outer electron shells of the atom to the inner ones (linear spectrum). Sources of X-ray radiation are: X-ray tube, some radioactive isotopes, accelerators and accumulators of electrons (synchrotron radiation). Receivers - film, luminescent screens, nuclear radiation detectors. X-rays are used in X-ray diffraction analysis, medicine, flaw detection, X-ray spectral analysis, etc.

Modern medicine uses many physicians for diagnosis and therapy. Some of them have been used relatively recently, while others have been practiced for more than a dozen or even hundreds of years. Also, a hundred and ten years ago, William Conrad Roentgen discovered the amazing X-rays, which caused a significant resonance in the scientific and medical world. And now doctors all over the planet use them in their practice. The topic of our today's conversation will be X-rays in medicine, we will discuss their application in a little more detail.

X-rays are one of the varieties of electromagnetic radiation. They are characterized by significant penetrating qualities, which depend on the wavelength of radiation, as well as on the density and thickness of the irradiated materials. In addition, X-rays can cause the glow of a number of substances, affect living organisms, ionize atoms, and also catalyze some photochemical reactions.

The use of X-rays in medicine

To date, the properties of x-rays allow them to be widely used in x-ray diagnostics and x-ray therapy.

X-ray diagnostics

X-ray diagnostics is used when carrying out:

X-ray (transmission);
- radiography (picture);
- fluorography;
- X-ray and computed tomography.

Fluoroscopy

To conduct such a study, the patient needs to position himself between the X-ray tube and a special fluorescent screen. A specialist radiologist selects the required hardness of the X-rays, receiving on the screen a picture of the internal organs, as well as the ribs.

Radiography

For this study, the patient is placed on a cassette containing a special film. The X-ray machine is placed directly above the object. As a result, a negative image of the internal organs appears on the film, which contains a number of fine details, more detailed than during a fluoroscopic examination.

Fluorography

This study is carried out during mass medical examinations of the population, including for the detection of tuberculosis. At the same time, a picture from a large screen is projected onto a special film.

Tomography

When conducting tomography, computer beams help to obtain images of organs in several places at once: in specially selected transverse sections of tissue. This series of x-rays is called a tomogram.

Computed tomogram

Such a study allows you to register sections of the human body by using an X-ray scanner. After the data is entered into the computer, getting one picture in cross section.

Each of the listed diagnostic methods is based on the properties of the X-ray beam to illuminate the film, as well as on the fact that human tissues and bone skeleton differ in different permeability to their effects.

X-ray therapy

The ability of X-rays to influence tissues in a special way is used to treat tumor formations. At the same time, the ionizing qualities of this radiation are especially actively noticeable when exposed to cells that are capable of rapid division. It is these qualities that distinguish the cells of malignant oncological formations.

However, it is worth noting that X-ray therapy can cause a lot of serious side effects. Such an impact aggressively affects the state of the hematopoietic, endocrine and immune systems, the cells of which also divide very quickly. Aggressive influence on them can cause signs of radiation sickness.

The effect of X-ray radiation on humans

During the study of x-rays, doctors found that they can lead to changes in the skin that resemble a sunburn, but are accompanied by deeper damage to the skin. Such ulcers heal for a very long time. Scientists have found that such lesions can be avoided by reducing the time and dose of radiation, as well as using special shielding and remote control methods.

The aggressive influence of X-rays can also manifest itself in the long term: temporary or permanent changes in the composition of the blood, susceptibility to leukemia and early aging.

The effect of x-rays on a person depends on many factors: on which organ is irradiated, and for how long. Irradiation of the hematopoietic organs can lead to blood ailments, and exposure to the genital organs can lead to infertility.

Carrying out systematic irradiation is fraught with the development of genetic changes in the body.

The real harm of x-rays in x-ray diagnostics

During the examination, doctors use the minimum possible amount of x-rays. All radiation doses meet certain acceptable standards and cannot harm a person. X-ray diagnostics poses a significant danger only for the doctors who carry it out. And then modern methods of protection help to reduce the aggression of the rays to a minimum.

The safest methods of radiodiagnosis include radiography of the extremities, as well as dental x-rays. In the next place of this rating is mammography, followed by computed tomography, and after it is radiography.

In order for the use of X-rays in medicine to bring only benefit to a person, it is necessary to conduct research with their help only according to indications.

In 1895, the German physicist Roentgen, while conducting experiments on the passage of current between two electrodes in a vacuum, discovered that a screen covered with a luminescent substance (barium salt) glows, although the discharge tube is closed with a black cardboard screen - this is how radiation was discovered that penetrates through opaque barriers, called X-ray X-rays. It was found that X-rays, invisible to humans, are absorbed in opaque objects the stronger, the greater the atomic number (density) of the barrier, so X-rays easily pass through the soft tissues of the human body, but are retained by the bones of the skeleton. Sources of powerful X-rays were designed, which made it possible to shine through metal parts and find internal defects in them.

The German physicist Laue suggested that X-rays are the same electromagnetic radiation as visible light rays, but with a shorter wavelength and all the laws of optics are applicable to them, including diffraction is possible. In visible light optics, diffraction at the elementary level can be represented as the reflection of light from a system of grooves - a diffraction grating, occurring only at certain angles, while the angle of reflection of the rays is related to the angle of incidence, the distance between the grooves of the diffraction grating and the wavelength of the incident radiation. For diffraction, it is necessary that the distance between the strokes be approximately equal to the wavelength of the incident light.

Laue suggested that X-rays have a wavelength close to the distance between individual atoms in crystals, i.e. atoms in a crystal create a diffraction grating for x-rays. X-rays directed at the surface of the crystal were reflected on the photographic plate, as predicted by theory.

Any changes in the position of atoms affect the diffraction pattern, and by studying the diffraction of x-rays, one can find out the arrangement of atoms in a crystal and the change in this arrangement under any physical, chemical and mechanical influences on the crystal.

Now X-ray analysis is used in many areas of science and technology, with its help they learned the arrangement of atoms in existing materials and created new materials with a given structure and properties. Recent advances in this field (nanomaterials, amorphous metals, composite materials) create a field of activity for the next scientific generations.

The occurrence and properties of X-rays

The source of x-rays is an x-ray tube, which has two electrodes - a cathode and an anode. When the cathode is heated, electron emission occurs, the electrons emitted from the cathode are accelerated by the electric field and hit the anode surface. An X-ray tube is distinguished from a conventional radio lamp (diode) mainly by a higher accelerating voltage (more than 1 kV).

When an electron flies out of the cathode, the electric field makes it fly towards the anode, while its speed continuously increases, the electron carries a magnetic field, the strength of which increases with the electron's speed. Reaching the anode surface, the electron is sharply decelerated, and an electromagnetic pulse arises with wavelengths in a certain range (bremsstrahlung). The distribution of radiation intensity over wavelengths depends on the material of the anode of the X-ray tube and the applied voltage, while on the side of short waves this curve begins with a certain threshold minimum wavelength, which depends on the applied voltage. The set of rays with all possible wavelengths forms a continuous spectrum, and the wavelength corresponding to the maximum intensity is 1.5 times the minimum wavelength.

With increasing voltage, the X-ray spectrum changes dramatically due to the interaction of atoms with high-energy electrons and quanta of primary X-rays. An atom contains internal electron shells (energy levels), the number of which depends on the atomic number (denoted by the letters K, L, M, etc.). Electrons and primary X-rays knock out electrons from one energy level to another. A metastable state arises, and a jump of electrons in the opposite direction is necessary for the transition to a stable state. This jump is accompanied by the release of an energy quantum and the appearance of X-rays. Unlike continuous spectrum X-rays, this radiation has a very narrow wavelength range and high intensity (characteristic radiation) ( cm. rice.). The number of atoms that determine the intensity of the characteristic radiation is very large, for example, for an X-ray tube with a copper anode at a voltage of 1 kV, a current of 15 mA, 10 14–10 15 atoms give characteristic radiation for 1 s. This value is calculated as the ratio of the total X-ray power to the energy of the X-ray quantum from the K-shell (K-series of X-ray characteristic radiation). The total power of X-ray radiation in this case is only 0.1% of the power consumed, the rest is lost, mainly due to the transition to heat.

Due to its high intensity and narrow wavelength range, characteristic X-ray radiation is the main type of radiation used in scientific research and process control. Simultaneously with the K-series beams, L and M-series beams are generated, which have much longer wavelengths, but their application is limited. The K-series has two components with close wavelengths a and b, while the intensity of the b-component is 5 times less than a. In turn, the a-component is characterized by two very close wavelengths, the intensity of one of which is 2 times greater than the other. To obtain radiation with a single wavelength (monochromatic radiation), special methods have been developed that use the dependence of the absorption and diffraction of X-rays on the wavelength. An increase in the atomic number of an element is associated with a change in the characteristics of the electron shells, and the larger the atomic number of the X-ray tube anode material, the shorter the K-series wavelength. The most widely used tubes with anodes from elements with atomic numbers from 24 to 42 (Cr, Fe, Co, Cu, Mo) and wavelengths from 2.29 to 0.712 A (0.229 - 0.712 nm).

In addition to the x-ray tube, radioactive isotopes can be sources of x-rays, some can directly emit x-rays, others emit electrons and a-particles that generate x-rays when bombarding metal targets. The X-ray intensity of radioactive sources is usually much less than that of an X-ray tube (with the exception of radioactive cobalt, which is used in flaw detection and gives radiation of a very small wavelength - g-radiation), they are small in size and do not require electricity. Synchrotron X-rays are obtained in electron accelerators, the wavelength of this radiation is much higher than that obtained in X-ray tubes (soft X-rays), its intensity is several orders of magnitude higher than the intensity of X-ray tubes. There are also natural sources of X-rays. Radioactive impurities have been found in many minerals, and X-rays from space objects, including stars, have been recorded.

Interaction of X-rays with crystals

In the X-ray study of materials with a crystalline structure, the interference patterns resulting from the scattering of X-rays by electrons belonging to the atoms of the crystal lattice are analyzed. Atoms are considered immobile, their thermal vibrations are not taken into account, and all electrons of the same atom are considered to be concentrated at one point - a node of the crystal lattice.

To derive the basic equations of X-ray diffraction in a crystal, the interference of rays scattered by atoms located along a straight line in the crystal lattice is considered. A plane wave of monochromatic X-ray radiation falls on these atoms at an angle whose cosine is equal to a 0 . The laws of interference of rays scattered by atoms are similar to those existing for a diffraction grating that scatters light radiation in the visible wavelength range. In order for the amplitudes of all vibrations to add up at a great distance from the atomic series, it is necessary and sufficient that the difference in the path of the rays coming from each pair of neighboring atoms contains an integer number of wavelengths. When the distance between atoms a this condition looks like:

a(a – a0) = h l ,

where a is the cosine of the angle between the atomic series and the deflected beam, h- integer. In all directions that do not satisfy this equation, the rays do not propagate. Thus, the scattered beams form a system of coaxial cones, the common axis of which is the atomic row. Traces of cones on a plane parallel to the atomic row are hyperbolas, and on a plane perpendicular to the row, circles.

When rays fall at a constant angle, polychromatic (white) radiation decomposes into a spectrum of rays deflected at fixed angles. Thus, the atomic series is a spectrograph for X-rays.

Generalization to a two-dimensional (flat) atomic lattice, and then to a three-dimensional volumetric (spatial) crystal lattice gives two more similar equations, which include the angles of incidence and reflection of X-rays and the distances between atoms in three directions. These equations are called the Laue equations and underlie X-ray diffraction analysis.

The amplitudes of rays reflected from parallel atomic planes add up, and since the number of atoms is very large, the reflected radiation can be fixed experimentally. The reflection condition is described by the Wulff-Bragg equation2d sinq = nl, where d is the distance between adjacent atomic planes, q is the glancing angle between the direction of the incident beam and these planes in the crystal, l is the X-ray wavelength, and n is an integer called the order of reflection. The angle q is the angle of incidence with respect to the atomic planes, which do not necessarily coincide in direction with the surface of the sample under study.

Several methods of X-ray diffraction analysis have been developed, using both continuous spectrum radiation and monochromatic radiation. In this case, the object under study can be stationary or rotating, can consist of one crystal (single crystal) or many (polycrystal), diffracted radiation can be recorded using a flat or cylindrical X-ray film or an X-ray detector moving around the circumference, however, in all cases, during the experiment and interpretation of the results, the Wulf-Bragg equation is used.

X-ray analysis in science and technology

With the discovery of X-ray diffraction, researchers have at their disposal a method that allows them to study the arrangement of individual atoms and changes in this arrangement under external influences without a microscope.

The main application of X-rays in fundamental science is structural analysis, i.e. establishing the spatial arrangement of individual atoms in a crystal. To do this, single crystals are grown and X-ray analysis is carried out, studying both the location and intensity of the reflections. Now the structures of not only metals, but also complex organic substances, in which elementary cells contain thousands of atoms, have been determined.

In mineralogy, the structures of thousands of minerals have been determined by x-ray analysis and express methods for the analysis of mineral raw materials have been created.

Metals have a relatively simple crystal structure and the X-ray method makes it possible to study its changes during various technological treatments and create the physical foundations of new technologies.

The phase composition of the alloys is determined by the arrangement of lines on the X-ray patterns, the number, size and shape of crystals are determined by their width, the orientation of the crystals (texture) is determined by the intensity distribution in the diffraction cone.

These techniques are used to study the processes during plastic deformation, including the crushing of crystals, the occurrence of internal stresses and imperfections in the crystal structure (dislocations). When deformed materials are heated, stress relief and crystal growth (recrystallization) are studied.

When X-ray analysis of alloys determine the composition and concentration of solid solutions. When a solid solution appears, the interatomic distances and, consequently, the distances between atomic planes change. These changes are small, therefore, special precision methods have been developed for measuring the periods of the crystal lattice with an accuracy of two orders of magnitude higher than the measurement accuracy with conventional x-ray methods of research. The combination of precision measurements of the periods of the crystal lattice and phase analysis makes it possible to plot the boundaries of the phase regions on the state diagram. The X-ray method can also detect intermediate states between solid solutions and chemical compounds - ordered solid solutions in which impurity atoms are not arranged randomly, as in solid solutions, and at the same time not with a three-dimensional order, as in chemical compounds. There are additional lines on the x-ray patterns of ordered solid solutions; the interpretation of the x-ray patterns shows that impurity atoms occupy certain places in the crystal lattice, for example, at the vertices of a cube.

During quenching of an alloy that does not undergo phase transformations, a supersaturated solid solution can occur, and upon further heating or even holding at room temperature, the solid solution decomposes with the release of particles of a chemical compound. This is the effect of aging and it appears on radiographs as a change in the position and width of the lines. The study of aging is especially important for non-ferrous alloys, for example, aging transforms a soft, hardened aluminum alloy into a durable structural material, duralumin.

X-ray studies of steel heat treatment are of the greatest technological importance. During hardening (rapid cooling) of steel, a diffusionless austenite-martensite phase transition occurs, which leads to a change in the structure from cubic to tetragonal, i.e. the unit cell takes the form of a rectangular prism. On radiographs, this appears as an expansion of the lines and the separation of some lines into two. The reasons for this effect are not only a change in the crystal structure, but also the occurrence of large internal stresses due to the thermodynamic nonequilibrium of the martensitic structure and rapid cooling. During tempering (heating of hardened steel), the lines on the X-ray patterns narrow, this is due to the return to the equilibrium structure.

In recent years, X-ray studies of the processing of materials with concentrated energy flows (laser beams, shock waves, neutrons, electron pulses) have acquired great importance, they required new techniques and gave new X-ray effects. For example, under the action of laser beams on metals, heating and cooling occur so quickly that in the metal, when cooled, the crystals have time to grow only to a size of several unit cells (nanocrystals) or do not have time to form at all. Such a metal after cooling looks like an ordinary one, but does not give clear lines on the X-ray pattern, and the reflected X-rays are distributed over the entire range of glancing angles.

After neutron irradiation, additional spots (diffuse maxima) appear on the X-ray patterns. Radioactive decay also causes specific x-ray effects associated with a change in structure, as well as the fact that the sample under study itself becomes a source of x-rays.