Where are X-rays used? History of discovery and applications of X-rays

18.08.2020

X-ray radiation (synonymous with X-rays) is with a wide range of wavelengths (from 8·10 -6 to 10 -12 cm). X-ray radiation occurs when charged particles, most often electrons, decelerate in the electric field of the atoms of a substance. The resulting quanta have different energies and form a continuous spectrum. The maximum photon energy in such a spectrum is equal to the energy of incident electrons. In (see) the maximum energy of quanta x-ray radiation, expressed in kiloelectron-volts, is numerically equal to the magnitude of the voltage applied to the tube, expressed in kilovolts. When passing through a substance, X-rays interact with the electrons of its atoms. For X-ray quanta with energies up to 100 keV, the most characteristic type of interaction is the photoelectric effect. As a result of such an interaction, the quantum energy is completely spent on pulling out an electron from the atomic shell and imparting kinetic energy to it. With an increase in the energy of an X-ray quantum, the probability of the photoelectric effect decreases and the process of scattering of quanta on free electrons becomes predominant - the so-called Compton effect. As a result of such an interaction, a secondary electron is also formed and, in addition, a quantum flies out with an energy lower than the energy of the primary quantum. If the energy of an X-ray quantum exceeds one megaelectron-volt, a so-called pairing effect can occur, in which an electron and a positron are formed (see). Consequently, when passing through a substance, the energy of X-ray radiation decreases, i.e., its intensity decreases. Since low-energy quanta are more likely to be absorbed in this case, X-ray radiation is enriched with higher-energy quanta. This property of X-ray radiation is used to increase the average energy of quanta, i.e., to increase its rigidity. An increase in the hardness of X-ray radiation is achieved using special filters (see). X-ray radiation is used for X-ray diagnostics (see) and (see). See also Ionizing radiation.

X-ray radiation (synonym: x-rays, x-rays) - quantum electromagnetic radiation with a wavelength of 250 to 0.025 A (or energy quanta from 5 10 -2 to 5 10 2 keV). In 1895, it was discovered by V.K. Roentgen. The spectral region of electromagnetic radiation adjacent to x-rays, whose energy quanta exceed 500 keV, is called gamma radiation (see); radiation, whose energy quanta are below 0.05 keV, is ultraviolet radiation (see).

Thus, representing a relatively small part of the vast spectrum of electromagnetic radiation, which includes both radio waves and visible light, X-ray radiation, like any electromagnetic radiation, propagates at the speed of light (about 300 thousand km / s in a vacuum) and is characterized by a wavelength λ ( the distance over which the radiation propagates in one period of oscillation). X-ray radiation also has a number of other wave properties (refraction, interference, diffraction), but it is much more difficult to observe them than for longer-wavelength radiation: visible light, radio waves.

X-ray spectra: a1 - continuous bremsstrahlung spectrum at 310 kV; a - continuous bremsstrahlung spectrum at 250 kV, a1 - spectrum filtered by 1 mm Cu, a2 - spectrum filtered by 2 mm Cu, b - K-series of the tungsten line.

To generate x-rays, x-ray tubes are used (see), in which radiation occurs when fast electrons interact with atoms of the anode substance. There are two types of x-rays: bremsstrahlung and characteristic. Bremsstrahlung X-ray radiation, which has a continuous spectrum, similar to ordinary white light. The distribution of intensity depending on the wavelength (Fig.) is represented by a curve with a maximum; in the direction of long waves, the curve falls gently, and in the direction of short waves, it steeply and breaks off at a certain wavelength (λ0), called the short-wavelength boundary of the continuous spectrum. The value of λ0 is inversely proportional to the voltage on the tube. Bremsstrahlung arises from the interaction of fast electrons with atomic nuclei. The bremsstrahlung intensity is directly proportional to the strength of the anode current, the square of the tube voltage, and the atomic number (Z) of the anode material.

If the energy of electrons accelerated in the X-ray tube exceeds the critical value for the anode substance (this energy is determined by the tube voltage Vcr, which is critical for this substance), then characteristic radiation occurs. The characteristic spectrum is line, its spectral lines form a series, denoted by the letters K, L, M, N.

The K series is the shortest wavelength, the L series is longer wavelength, the M and N series are observed only in heavy elements (Vcr of tungsten for the K-series is 69.3 kv, for the L-series - 12.1 kv). Characteristic radiation arises as follows. Fast electrons knock atomic electrons out of the inner shells. The atom is excited and then returns to the ground state. In this case, electrons from the outer, less bound shells fill the spaces vacated in the inner shells, and photons of characteristic radiation with an energy equal to the difference between the energies of the atom in the excited and ground states are emitted. This difference (and hence the energy of the photon) has a certain value, characteristic of each element. This phenomenon underlies the X-ray spectral analysis of elements. The figure shows the line spectrum of tungsten against the background of a continuous spectrum of bremsstrahlung.

The energy of electrons accelerated in the X-ray tube is converted almost entirely into thermal energy (the anode is strongly heated in this case), only an insignificant part (about 1% at a voltage close to 100 kV) is converted into bremsstrahlung energy.

The use of x-rays in medicine is based on the laws of absorption of x-rays by matter. The absorption of x-rays is completely independent of the optical properties of the absorber material. The colorless and transparent lead glass used to protect personnel in x-ray rooms absorbs x-rays almost completely. In contrast, a sheet of paper that is not transparent to light does not attenuate X-rays.

The intensity of a homogeneous (i.e., a certain wavelength) X-ray beam, when passing through an absorber layer, decreases according to an exponential law (e-x), where e is the base of natural logarithms (2.718), and the exponent x is equal to the product of the mass attenuation coefficient (μ / p) cm 2 /g per absorber thickness in g / cm 2 (here p is the density of the substance in g / cm 3). X-rays are attenuated by both scattering and absorption. Accordingly, the mass attenuation coefficient is the sum of the mass absorption and scattering coefficients. The mass absorption coefficient increases sharply with increasing atomic number (Z) of the absorber (proportional to Z3 or Z5) and with increasing wavelength (proportional to λ3). This dependence on the wavelength is observed within the absorption bands, at the boundaries of which the coefficient exhibits jumps.

The mass scattering coefficient increases with increasing atomic number of the substance. For λ≥0,3Å the scattering coefficient does not depend on the wavelength, for λ<0,ЗÅ он уменьшается с уменьшением λ.

The decrease in the absorption and scattering coefficients with decreasing wavelength causes an increase in the penetrating power of X-rays. The mass absorption coefficient for bones [absorption is mainly due to Ca 3 (PO 4) 2 ] is almost 70 times greater than for soft tissues, where absorption is mainly due to water. This explains why the shadow of the bones stands out so sharply on the radiographs against the background of soft tissues.

The propagation of an inhomogeneous X-ray beam through any medium, along with a decrease in intensity, is accompanied by a change in the spectral composition, a change in the quality of the radiation: the long-wave part of the spectrum is absorbed to a greater extent than the short-wave part, the radiation becomes more uniform. Filtering out the long-wavelength part of the spectrum makes it possible to improve the ratio between deep and surface doses during X-ray therapy of foci located deep in the human body (see X-ray filters). To characterize the quality of an inhomogeneous X-ray beam, the concept of "half attenuation layer (L)" is used - a layer of a substance that attenuates the radiation by half. The thickness of this layer depends on the voltage on the tube, the thickness and material of the filter. Cellophane (up to an energy of 12 keV), aluminum (20–100 keV), copper (60–300 keV), lead, and copper (>300 keV) are used to measure half attenuation layers. For X-rays generated at voltages of 80-120 kV, 1 mm of copper is equivalent in filtering capacity to 26 mm of aluminum, 1 mm of lead is equivalent to 50.9 mm of aluminum.

Absorption and scattering of X-rays is due to its corpuscular properties; X-rays interact with atoms as a stream of corpuscles (particles) - photons, each of which has a certain energy (inversely proportional to the wavelength of X-rays). The energy range of X-ray photons is 0.05-500 keV.

The absorption of X-ray radiation is due to the photoelectric effect: the absorption of a photon by the electron shell is accompanied by the ejection of an electron. The atom is excited and, returning to the ground state, emits characteristic radiation. The emitted photoelectron carries away all the energy of the photon (minus the binding energy of the electron in the atom).

Scattering of X-ray radiation is due to the electrons of the scattering medium. There are classical scattering (the wavelength of the radiation does not change, but the direction of propagation changes) and scattering with a change in wavelength - the Compton effect (the wavelength of the scattered radiation is greater than the incident one). In the latter case, the photon behaves like a moving ball, and the scattering of photons occurs, according to the figurative expression of Comnton, like a game of billiards with photons and electrons: colliding with an electron, the photon transfers part of its energy to it and scatters, having already less energy (respectively, the wavelength of the scattered radiation increases), the electron flies out of the atom with a recoil energy (these electrons are called Compton electrons, or recoil electrons). The absorption of X-ray energy occurs during the formation of secondary electrons (Compton and photoelectrons) and the transfer of energy to them. The energy of X-rays transferred to a unit mass of a substance determines the absorbed dose of X-rays. The unit of this dose 1 rad corresponds to 100 erg/g. Due to the absorbed energy in the substance of the absorber, a number of secondary processes occur, which have importance for X-ray dosimetry, since it is on them that X-ray measurement methods are based. (see Dosimetry).

All gases and many liquids, semiconductors and dielectrics, under the action of X-rays, increase electrical conductivity. Conductivity is found by the best insulating materials: paraffin, mica, rubber, amber. The change in conductivity is due to the ionization of the medium, i.e., the separation of neutral molecules into positive and negative ions (ionization is produced by secondary electrons). Ionization in air is used to determine the exposure dose of X-ray radiation (dose in air), which is measured in roentgens (see Ionizing Radiation Doses). At a dose of 1 r, the absorbed dose in air is 0.88 rad.

Under the action of X-rays, as a result of the excitation of the molecules of a substance (and during the recombination of ions), in many cases a visible glow of the substance is excited. At high intensities of X-ray radiation, a visible glow of air, paper, paraffin, etc. is observed (metals are an exception). The highest yield of visible light is given by such crystalline phosphors as Zn·CdS·Ag-phosphorus and others used for screens in fluoroscopy.

Under the action of X-rays, various chemical processes can also take place in a substance: the decomposition of silver halides (a photographic effect used in X-rays), the decomposition of water and aqueous solutions of hydrogen peroxide, a change in the properties of celluloid (clouding and release of camphor), paraffin (clouding and bleaching) .

As a result of complete conversion, all the X-ray energy absorbed by the chemically inert substance is converted into heat. The measurement of very small amounts of heat requires highly sensitive methods, but is the main method for absolute measurements of X-rays.

Secondary biological effects from exposure to x-rays are the basis of medical radiotherapy (see). X-rays, the quanta of which are 6-16 keV (effective wavelengths from 2 to 5 Å), are almost completely absorbed by the skin of the tissue human body; they are called boundary rays, or sometimes Bucca rays (see Bucca rays). For deep X-ray therapy, hard filtered radiation with effective energy quanta from 100 to 300 keV is used.

The biological effect of x-ray radiation should be taken into account not only in x-ray therapy, but also in x-ray diagnostics, as well as in all other cases of contact with x-rays that require the use of radiation protection (see).

X-rays are a type of high-energy electromagnetic radiation. It is actively used in various branches of medicine.

X-rays are electromagnetic waves whose photon energy on the scale of electromagnetic waves is between ultraviolet radiation and gamma radiation (from ~10 eV to ~1 MeV), which corresponds to wavelengths from ~10^3 to ~10^−2 angstroms ( from ~10^−7 to ~10^−12 m). That is, it is incomparably harder radiation than visible light, which is on this scale between ultraviolet and infrared (“thermal”) rays.

The boundary between X-rays and gamma radiation is distinguished conditionally: their ranges intersect, gamma rays can have an energy of 1 keV. They differ in origin: gamma rays are emitted during processes occurring in atomic nuclei, while X-rays are emitted during processes involving electrons (both free and those in the electron shells of atoms). At the same time, it is impossible to determine from the photon itself during which process it arose, that is, the division into the X-ray and gamma ranges is largely arbitrary.

The X-ray range is divided into “soft X-ray” and “hard”. The boundary between them lies at the wavelength level of 2 angstroms and 6 keV of energy.

The X-ray generator is a tube in which a vacuum is created. There are electrodes - a cathode, to which a negative charge is applied, and a positively charged anode. The voltage between them is tens to hundreds of kilovolts. The generation of X-ray photons occurs when electrons “break off” from the cathode and crash into the anode surface at high speed. The resulting X-ray radiation is called “bremsstrahlung”, its photons have different wavelengths.

At the same time, photons of the characteristic spectrum are generated. Part of the electrons in the atoms of the anode substance is excited, that is, it goes to higher orbits, and then returns to its normal state, emitting photons of a certain wavelength. Both types of X-rays are produced in a standard generator.

Discovery history

On November 8, 1895, the German scientist Wilhelm Konrad Roentgen discovered that some substances, under the influence of "cathode rays", that is, the flow of electrons generated by a cathode ray tube, begin to glow. He explained this phenomenon by the influence of certain X-rays - so (“X-rays”) this radiation is now called in many languages. Later V.K. Roentgen studied the phenomenon he had discovered. On December 22, 1895, he gave a lecture on this topic at the University of Würzburg.

Later it turned out that X-ray radiation had been observed before, but then the phenomena associated with it were not given of great importance. The cathode ray tube was invented a long time ago, but before V.K. X-ray, no one paid much attention to the blackening of photographic plates near it, etc. phenomena. The danger posed by penetrating radiation was also unknown.

Types and their effect on the body

“X-ray” is the mildest type of penetrating radiation. Overexposure to soft x-rays is similar to ultraviolet exposure, but in a more severe form. A burn forms on the skin, but the lesion is deeper, and it heals much more slowly.

Hard X-ray is a full-fledged ionizing radiation that can lead to radiation sickness. X-ray quanta can break the protein molecules that make up the tissues of the human body, as well as the DNA molecules of the genome. But even if an X-ray quantum breaks a water molecule, it doesn't matter: in this case, chemically active free radicals H and OH are formed, which themselves are able to act on proteins and DNA. Radiation sickness proceeds in a more severe form, the more the hematopoietic organs are affected.

X-rays have mutagenic and carcinogenic activity. This means that the probability of spontaneous mutations in cells during irradiation increases, and sometimes healthy cells can degenerate into cancerous ones. Increasing the likelihood of malignant tumors is a standard consequence of any exposure, including x-rays. X-rays are the least dangerous type of penetrating radiation, but they can still be dangerous.

X-ray radiation: application and how it works

X-ray radiation is used in medicine, as well as in other areas of human activity.

Fluoroscopy and computed tomography

The most common application of X-rays is fluoroscopy. "Transillumination" of the human body allows you to get a detailed image of both the bones (they are most clearly visible) and images of the internal organs.

Different transparency of body tissues in x-rays is associated with their chemical composition. Features of the structure of bones is that they contain a lot of calcium and phosphorus. Other tissues are composed mainly of carbon, hydrogen, oxygen and nitrogen. The phosphorus atom exceeds the weight of the oxygen atom almost twice, and the calcium atom - 2.5 times (carbon, nitrogen and hydrogen are even lighter than oxygen). In this regard, the absorption of X-ray photons in the bones is much higher.

In addition to two-dimensional “pictures”, radiography makes it possible to create a three-dimensional image of an organ: this type of radiography is called computed tomography. For these purposes, soft x-rays are used. The amount of exposure received in a single image is small: it is approximately equal to the exposure received during a 2-hour flight in an airplane at an altitude of 10 km.

X-ray flaw detection allows you to detect small internal defects in products. Hard x-rays are used for it, since many materials (metal, for example) are poorly “translucent” due to the high atomic mass of their constituent substance.

X-ray diffraction and X-ray fluorescence analysis

X-rays have properties that allow them to examine individual atoms in detail. X-ray diffraction analysis is actively used in chemistry (including biochemistry) and crystallography. The principle of its operation is the diffraction scattering of X-rays by atoms of crystals or complex molecules. Using X-ray diffraction analysis, the structure of the DNA molecule was determined.

X-ray fluorescence analysis allows you to quickly determine the chemical composition of a substance.

There are many forms of radiotherapy, but they all involve the use of ionizing radiation. Radiotherapy is divided into 2 types: corpuscular and wave. Corpuscular uses flows of alpha particles (nuclei of helium atoms), beta particles (electrons), neutrons, protons, heavy ions. Wave uses rays of the electromagnetic spectrum - x-rays and gamma.

Radiotherapy methods are used primarily for the treatment of oncological diseases. The fact is that radiation primarily affects actively dividing cells, which is why the hematopoietic organs suffer this way (their cells are constantly dividing, producing more and more new red blood cells). Cancer cells are also constantly dividing and are more vulnerable to radiation than healthy tissue.

A level of radiation is used that suppresses the activity of cancer cells, while moderately affecting healthy ones. Under the influence of radiation, it is not the destruction of cells as such, but the damage to their genome - DNA molecules. A cell with a destroyed genome may exist for some time, but can no longer divide, that is, tumor growth stops.

Radiation therapy is the mildest form of radiotherapy. Wave radiation is softer than corpuscular radiation, and X-rays are softer than gamma radiation.

During pregnancy

It is dangerous to use ionizing radiation during pregnancy. X-rays are mutagenic and can cause abnormalities in the fetus. X-ray therapy is incompatible with pregnancy: it can only be used if it has already been decided to have an abortion. Restrictions on fluoroscopy are softer, but in the first months it is also strictly prohibited.

In case of emergency, X-ray examination is replaced by magnetic resonance imaging. But in the first trimester they try to avoid it too (this method has appeared recently, and with absolute certainty to speak about the absence of harmful consequences).

An unequivocal danger arises when exposed to a total dose of at least 1 mSv (in old units - 100 mR). With a simple x-ray (for example, when undergoing fluorography), the patient receives about 50 times less. In order to receive such a dose at a time, you need to undergo a detailed computed tomography.

That is, the mere fact of a 1-2-fold “X-ray” at an early stage of pregnancy does not threaten with serious consequences (but it’s better not to risk it).

Treatment with it

X-rays are used primarily in the fight against malignant tumors. This method is good because it is highly effective: it kills the tumor. It is bad because healthy tissues are not much better, there are numerous side effects. The organs of hematopoiesis are at particular risk.

In practice, various methods are used to reduce the effect of x-rays on healthy tissues. The beams are directed at an angle in such a way that a tumor appears in the zone of their intersection (due to this, the main absorption of energy occurs just there). Sometimes the procedure is performed in motion: the patient's body rotates relative to the radiation source around an axis passing through the tumor. At the same time, healthy tissues are in the irradiation zone only sometimes, and the sick - all the time.

X-rays are used in the treatment of certain arthrosis and similar diseases, as well as skin diseases. In this case, the pain syndrome is reduced by 50-90%. Since the radiation is used in this case is softer, side effects similar to those that occur in the treatment of tumors are not observed.

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. With 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. one.

Rice. one. A CONVENTIONAL X-RAY SPECTRUM consists of a continuous spectrum (continuum) and characteristic lines (sharp peaks). The Kia and Kib lines arise due to the interactions of accelerated electrons with the electrons of the inner K-shell.

The wide "continuum" is called the 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).

Rice. 2. The wavelength of the CHARACTERISTIC X-RAY RADIATION emitted by chemical elements depends on the atomic number of the element. The curve corresponds to Moseley's law: the larger the atomic number of the element, the shorter the wavelength of the characteristic line.

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.

Discharge tubes contain a small amount 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 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.

Rice. 3. X-RAY TUBE COOLIDGE. When bombarded with electrons, the tungsten anticathode emits characteristic x-rays. The cross section of the X-ray beam is less than the actual irradiated area. 1 - electron beam; 2 - cathode with a focusing electrode; 3 - glass shell (tube); 4 - tungsten target (anticathode); 5 - cathode filament; 6 - actually irradiated area; 7 - effective focal spot; 8 - copper anode; 9 - window; 10 - scattered x-rays.

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 spotlight" 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. The most commonly chosen anode material is tungsten, whose atomic number is 74.

The design of X-ray tubes may vary depending on the application and requirements.

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. With 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. Discharge tubes contain a small amount 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 more high voltage, 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 range 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 is also used for similar purposes, which uses neutron beams instead of X-rays.) X-rays are also used for other purposes, such as examining paintings to determine their authenticity or to detect additional layers of paint over 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-ray radiation, 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-ray radiation 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 difference between the paths 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 individual 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
Already 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-rays appear, which are 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. X-ray capabilities 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 most important 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 spacing d by the inequality l 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, a highly focused electron beam excites the characteristic X-ray emission of the sample, 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 for whose characteristic radiation the spectrometer is tuned.
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 examined.
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-rays become visible if they are filled with a contrast agent that is harmless to the body, but allows one to visualize the shape of the 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 blood-forming organs, mainly 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 books. 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;

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X-ray radiation plays a huge role in modern medicine; the history of the discovery of X-rays dates back to the 19th century.

X-rays are electromagnetic waves that are produced with the participation of electrons. With strong acceleration of charged particles, artificial x-rays are created. It passes through special equipment:

particle accelerators.

Discovery history

These rays were invented in 1895 by the German scientist Roentgen: while working with a cathode ray tube, he discovered the fluorescence effect of barium platinum cyanide. Then there was a description of such rays and their amazing ability to penetrate the tissues of the body. The rays began to be called x-rays (x-rays). Later in Russia they began to be called X-ray.

X-rays are able to penetrate even through walls. So Roentgen realized that he had made the greatest discovery in the field of medicine. It was from that time that separate sections in science began to form, such as radiology and radiology.

The rays are able to penetrate soft tissues, but are delayed, their length is determined by the obstacle of a hard surface. The soft tissues in the human body are the skin, and the hard tissues are the bones. In 1901, the scientist was awarded the Nobel Prize.

However, even before the discovery of Wilhelm Conrad Roentgen, other scientists were also interested in a similar topic. In 1853, the French physicist Antoine-Philiber Mason studied a high-voltage discharge between electrodes in a glass tube. The gas contained in it at low pressure began to emit a reddish glow. Pumping out excess gas from the tube led to the decay of the glow into a complex sequence of individual luminous layers, the hue of which depended on the amount of gas.

In 1878, William Crookes (English physicist) suggested that fluorescence occurs due to the impact of rays on the glass surface of the tube. But all these studies were not published anywhere, so Roentgen did not know about such discoveries. After the publication of his discoveries in 1895 in a scientific journal, where the scientist wrote that all bodies are transparent to these rays, albeit to a very different degree, other scientists became interested in similar experiments. They confirmed the invention of Roentgen, and further development and improvement of x-rays began.

Wilhelm Roentgen himself published two more scientific papers on the subject of x-rays in 1896 and 1897, after which he took up other activities. Thus, several scientists invented, but it was Roentgen who published scientific papers on this subject.

Imaging Principles

The features of this radiation are determined by the very nature of their appearance. Radiation occurs due to an electromagnetic wave. Its main properties include:

Reflection. If the wave hits the surface perpendicularly, it will not be reflected. In some situations, a diamond has the property of reflection.
The ability to penetrate tissue. In addition, the rays can pass through opaque surfaces of materials such as wood, paper, and the like.
absorbency. Absorption depends on the density of the material: the denser it is, the more X-rays absorb it.
Some substances fluoresce, that is, they glow. As soon as the radiation stops, the glow also disappears. If it continues after the cessation of the action of the rays, then this effect is called phosphorescence.
X-rays can illuminate photographic film, just like visible light.
If the beam passed through the air, then ionization occurs in the atmosphere. This state is called electrically conductive, and it is determined using a dosimeter, which sets the rate of radiation dosage.

Radiation - harm and benefit

When the discovery was made, the physicist Roentgen could not even imagine how dangerous his invention was. In the old days, all devices that produced radiation were far from perfect, and as a result, large doses of emitted rays were obtained. People did not understand the dangers of such radiation. Although some scientists even then put forward versions about the dangers of x-rays.

X-rays, penetrating into tissues, have a biological effect on them. The unit of measurement of radiation dose is roentgen per hour. The main influence is on the ionizing atoms that are inside the tissues. These rays act directly on the DNA structure of a living cell. The consequences of uncontrolled radiation include:

cell mutation;
the appearance of tumors;
radiation burns;
radiation sickness.

Contraindications for X-ray examinations:

The patients are in critical condition.
Pregnancy period due to negative effects on the fetus.
Patients with bleeding or open pneumothorax.

How x-rays work and where it is used

In medicine. X-ray diagnostics is used to translucent living tissues in order to identify certain disorders within the body. X-ray therapy is performed to eliminate tumor formations.
In science. The structure of substances and the nature of X-rays are revealed. These issues are dealt with by such sciences as chemistry, biochemistry, crystallography.
In industry. To detect violations in metal products.
For the safety of the population. X-ray beams are installed at airports and other public places to scan luggage.

Medical use of X-ray radiation. X-rays are widely used in medicine and dentistry for the following purposes:

For diagnosing diseases.
For monitoring metabolic processes.
For the treatment of many diseases.

The use of X-rays for medical purposes

In addition to detecting bone fractures, x-rays are widely used for medical purposes. The specialized application of x-rays is to achieve the following goals:

To destroy cancer cells.
To reduce the size of the tumor.
To reduce pain.

For example, radioactive iodine, used in endocrinological diseases, is actively used in thyroid cancer, thereby helping many people get rid of this terrible disease. Currently, to diagnose complex diseases, X-rays are connected to computers, as a result, the latest research methods appear, such as computed axial tomography.

Such a scan provides doctors with color images that show the internal organs of a person. To detect the work of internal organs, a small dose of radiation is sufficient. X-rays are also widely used in physiotherapy.

Basic properties of X-rays

penetrating ability. All bodies are transparent to the x-ray, and the degree of transparency depends on the thickness of the body. It is due to this property that the beam began to be used in medicine to detect the functioning of organs, the presence of fractures and foreign bodies in the body.
They are able to cause the glow of some objects. For example, if barium and platinum are applied to cardboard, then, after passing through the beam scanning, it will glow greenish-yellow. If you place your hand between the X-ray tube and the screen, then the light will penetrate more into the bone than into the tissue, so the bone tissue will shine brightest on the screen, and the muscle tissue will be less bright.
Action on film. X-rays can, like light, darken film, which makes it possible to photograph the shadow side that is obtained when objects are examined by x-rays.
X-rays can ionize gases. This makes it possible not only to find rays, but also to reveal their intensity by measuring the ionization current in the gas.
They have a biochemical effect on the body of living beings. Thanks to this property, X-rays have found their wide application in medicine: they can treat both skin diseases and diseases of internal organs. In this case, choose the right dosage radiation and the duration of the rays. Prolonged and excessive use of such treatment is very harmful and detrimental to the body.

The consequence of the use of X-rays was the saving of many human lives. X-ray helps not only to diagnose the disease in a timely manner, treatment methods using radiation therapy relieve patients of various pathologies, from hyperfunction of the thyroid gland to malignant tumors of bone tissues.