The X-ray flux depends on. X-ray radiation. The negative impact of x-rays on humans

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 is on a scale electromagnetic waves lies 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 Conrad 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 much 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 chemical composition substances.

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 can 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 (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 X-ray quanta, 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, the so-called Compton effect, becomes predominant. 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, is 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 are emitted with an energy equal difference energies of an atom in the excited and ground states. 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 X-ray wavelength). 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 playing 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 that are important 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 it 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 of the 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).

In 1895, the German physicist Roentgen, while conducting experiments on the passage of current between two electrodes in a vacuum, discovered that a screen coated 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 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 some energy levels to others. 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 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 technological 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 characteristics electron shells, while the greater the atomic number of the material of the anode of the X-ray tube, the shorter the wavelength of the K-series. 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 immovable, their thermal fluctuations are not taken into account and all the 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 location without a microscope. individual atoms and changes in this location under external influences.

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 matter, in which elementary cells contain thousands of atoms.

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 alloys is determined by the arrangement of lines on X-ray patterns, the number, size and shape of crystals are determined by their width, the orientation of 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. 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 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, diffusion-free phase transition austenite - martensite, 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.

AT last years great importance acquired X-ray studies of the processing of materials with concentrated energy flows (laser beams, shock waves, neutrons, electronic pulses), 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.

The action of X-ray radiation on a substance is determined by the primary processes of interaction of an X-ray photon with electrons of atoms and molecules of a substance.

3. X-ray computed tomography.

The method of X-ray computed tomography is based on the reconstruction of an image of a certain section (section) of the patient's body by recording a large number of X-ray projections of this section, made at different angles (Fig. 5). Information from the sensors that register these projections enters the computer, which, according to a special program, calculates distribution sample density in the investigated section and displays it on the display screen. The image of the section of the patient's body obtained in this way is characterized by excellent clarity and high information content. The program allows you to increase image contrast tens or even hundreds of times. This expands the diagnostic capabilities of the method.

Rice. Fig. 5. Scheme of x-ray transillumination of a section of the organ under study (point 1 and point 2 - two consecutive positions of the x-ray source)

4. With fluorography an image from a large screen is recorded on a sensitive small-format film (Fig. 6). During analysis, the images are examined on a special magnifier.

This method is used for mass survey of the population. In this case, the radiation load on the patient is much less than in conventional fluoroscopy.

X-ray therapy- the use of X-rays to destroy malignant tumors.

The biological effect of radiation is to disrupt the vital activity of rapidly multiplying tumor cells. In this case, the energy of R - photons is 150-200 keV.

Visiographs (devices with digital X-ray image processing) in modern dentistry

In dentistry, X-ray examination is the main diagnostic method. However, a number of traditional organizational and technical features of X-ray diagnostics make it not quite comfortable for both the patient and dental clinics. This is, first of all, the need for the patient to come into contact with ionizing radiation, which often creates a significant radiation load on the body, it is also the need for a photoprocess, and, consequently, the need for photoreagents, including toxic ones. This is, finally, a bulky archive, heavy folders and envelopes with x-ray films.

In addition, the current level of development of dentistry makes the subjective assessment of radiographs by the human eye insufficient. As it turned out, of the variety of shades of gray contained in the x-ray image, the eye perceives only 64.

Obviously, to obtain a clear and detailed image of the hard tissues of the dentoalveolar system with minimal radiation exposure, other solutions are needed. Today, the search has led to the creation of so-called radiographic systems, videographers - digital radiography systems (1987, Trophy).

Without technical details, the principle of operation of such systems is as follows. X-ray radiation enters through the object not on a photosensitive film, but on a special intraoral sensor (special electronic matrix). The corresponding signal from the matrix is ​​transmitted to a digitizing device (analog-to-digital converter, ADC) that converts it into digital form and is connected to the computer. Special software builds an X-ray image on the computer screen and allows you to process it, save it on a hard or flexible storage medium (hard drive, disk), print it as a picture as a file.

In a digital system, an x-ray image is a collection of dots, which correspond to different shades of gray. The information display optimization provided by the program makes it possible to obtain an optimal frame in terms of brightness and contrast at a relatively low radiation dose.

In modern systems, created, for example, by Trophy (France) or Schick (USA), 4096 shades of gray are used when forming a frame, the exposure time depends on the object of study and, on average, is hundredths - tenths of a second, a decrease in radiation exposure in relation to to film - up to 90% for intraoral systems, up to 70% for panoramic videographers.

When processing images, videographers allow:

1. Get positive and negative images, false color images, relief images.

2. Increase the contrast and enlarge the area of ​​interest in the image.

3. Evaluate the change in the density of dental tissues and bone structures, control the uniformity of filling the canals.

4. In endodontics, determine the length of the canal of any curvature, and in surgery, select the size of the implant with an accuracy of 0.1 mm.

The unique Caries detector system with elements of artificial intelligence during the analysis of the image allows you to detect caries in the stain stage, root caries and hidden caries.

Solve problems:

1. How many times is the maximum energy of an X-ray bremsstrahlung quantum that occurs at a tube voltage of 80 kV greater than the energy of a photon corresponding to green light with a wavelength of 500 nm?

2. Determine the minimum wavelength in the spectrum of radiation resulting from deceleration on the target of electrons accelerated in the betatron to an energy of 60 MeV.

3. The layer of half attenuation of monochromatic X-ray radiation in some substance is 10 mm. Find the attenuation of this radiation in the given substance.

[*] Φ l - the ratio of energy emitted in a narrow range of wavelengths for 1s. to the width of this interval

* "F" in formula (4) refers to the entire range of radiated wavelengths and is often referred to as "Integral Energy Flux".

1. Bremsstrahlung and characteristic x-rays,

basic properties and characteristics.

In 1895, the German scientist Roentgen first discovered the glow of a fluorescent screen, which was caused by radiation invisible to the eye coming from a portion of the gas discharge tube glass located opposite the cathode. This type of radiation had the ability to pass through substances impenetrable to visible light. Roentgen called them X-rays and established the basic properties that make it possible to use them in various branches of science and technology, including medicine.

X-ray is called radiation with a wavelength of 80-10 -5 nm. Long-wave X-ray radiation overlaps short-wave UV radiation, short-wave overlaps with long-wave g-radiation. In medicine, X-ray radiation with a wavelength of 10 to 0.005 nm is used, which corresponds to a photon energy of 10 2 EV to 0.5 MeV. X-ray radiation is invisible to the eye, therefore, all observations with it are made using fluorescent screens or photographic films, since it causes x-ray luminescence and has a photochemical effect. It is characteristic that the majority of bodies that are impenetrable to optical radiation are largely transparent to X-ray radiation, which has properties common to electromagnetic waves. However, due to the smallness of the wavelength, some properties are difficult to detect. Therefore, the wave nature of radiation was established much later than their discovery.

According to the method of excitation, X-ray radiation is divided into bremsstrahlung and characteristic radiation.

Bremsstrahlung X-rays are due to the deceleration of fast moving electrons by the electric field of the atom (nucleus and electrons) of the substance through which they fly. The mechanism of this radiation can be explained by the fact that any moving charge is a current around which a magnetic field is created, the induction (B) of which depends on the speed of the electron. When braking, the magnetic induction decreases and, in accordance with Maxwell's theory, an electromagnetic wave appears.

When electrons decelerate, only part of the energy goes to create an X-ray photon, the other part is spent on heating the anode. The frequency (wavelength) of a photon depends on the initial kinetic energy of the electron and the intensity of its deceleration. Moreover, even if the initial kinetic energy is the same, then the deceleration conditions in the substance will be different, therefore, the emitted photons will also have the most diverse energy, and, consequently, the wavelength, i.e. the X-ray spectrum will be continuous. Figure 1 shows the bremsstrahlung spectrum at various voltages U 1

.

If U is expressed in kilovolts and the ratio between other quantities is taken into account, then the formula looks like: l k \u003d 1.24 / U (nm) or l k \u003d 1.24 / U (Å) (1Å \u003d 10 -10 m).

From the graphs above, it can be established that the wavelength l m, which accounts for the maximum radiation energy, is in a constant ratio with the limiting wavelength l k:

.

The wavelength characterizes the energy of a photon, on which the penetrating power of radiation depends when it interacts with matter.

Short-wave X-rays usually have a high penetrating power and are called hard, while long-wave X-rays are called soft. As can be seen from the above formula, the wavelength at which the maximum radiation energy falls is inversely proportional to the voltage between the anode and cathode of the tube. Increasing the voltage at the anode of the x-ray tube, change the spectral composition of the radiation and increase its hardness.

When the filament voltage changes (the filament temperature of the cathode changes), the number of electrons emitted by the cathode per unit time changes, or, accordingly, the current strength in the tube anode circuit. In this case, the radiation power changes in proportion to the first power of the current. The spectral composition of the radiation will not change.

The total flux (power) of radiation, the distribution of energy over wavelengths, and also the boundary of the spectrum on the side of short wavelengths depend on the following three factors: the voltage U that accelerates the electrons and is applied between the anode and cathode of the tube; the number of electrons involved in the formation of radiation, i.e. tube filament current; atomic number Z of the anode material, in which the electron deceleration occurs.

The bremsstrahlung flux is calculated by the formula: , where ,

Z-serial number of an atom of a substance (atomic number).

By increasing the voltage on the x-ray tube, one can notice the appearance of separate lines (line spectrum) against the background of continuous bremsstrahlung radiation, which corresponds to the characteristic x-ray radiation. It arises during the transition of electrons between the inner shells of atoms in a substance (shells K, L, M). The line character of the characteristic radiation spectrum arises due to the fact that accelerated electrons penetrate deep into the atoms and knock out electrons from their inner layers outside the atom. Electrons (Fig. 2) from the upper layers pass to free places, as a result of which X-ray photons are emitted with a frequency corresponding to the difference in the transition energy levels. The lines in the spectrum of characteristic radiation are combined into series corresponding to transitions of electrons with a higher level at the level of K, L, M.

The external action, as a result of which the electron is knocked out of the inner layers, must be strong enough. In contrast to optical spectra, the characteristic x-ray spectra of different atoms are of the same type. The uniformity of these spectra is due to the fact that the inner layers of different atoms are the same and differ only energetically, because the force effect from the side of the nucleus increases as the ordinal number of the element increases. This leads to the fact that the characteristic spectra shift towards higher frequencies with increasing nuclear charge. This relationship is known as Moseley's law: , where A and B are constants; Z-order number of the element.

There is another difference between X-ray and optical spectra. The characteristic spectrum of an atom does not depend on the chemical compound in which the atom is included. So, for example, the X-ray spectrum of the oxygen atom is the same for O, O 2 , H 2 O, while the optical spectra of these compounds are significantly different. This feature of the x-ray spectra of atoms served as the basis for the name "characteristic".

Characteristic radiation occurs whenever there are free places in the inner layers of an atom, regardless of the reasons that caused it. For example, it accompanies one of the types of radioactive decay, which consists in the capture of an electron from the inner layer by the nucleus.

2. The device of x-ray tubes and protozoa

x-ray machine.

The most common source of X-ray radiation is an X-ray tube - a two-electrode vacuum device (Fig. 3). It is a glass container (p = 10 -6 - 10 -7 mm Hg) with two electrodes - anode A and cathode K, between which a high voltage is created. The heated cathode (K) emits electrons. Anode A is often referred to as the anticathode. It has an inclined surface in order to direct the resulting X-ray radiation at an angle to the axis of the tube. The anode is made of a metal with good thermal conductivity (copper) to remove the heat generated by the impact of electrons. At the beveled end of the anode there is a plate Z made of refractory metal (tungsten) with a high atomic number, called the anode mirror. In some cases, the anode is specially cooled with water or oil. For diagnostic tubes, the pinpointness of the X-ray source is important, which can be achieved by focusing the electrons in one place of the anode. Therefore, constructively, two opposite tasks have to be taken into account: on the one hand, electrons must fall on one place of the anode, on the other hand, in order to prevent overheating, it is desirable to distribute electrons over different parts of the anode. For this reason, some X-ray tubes are manufactured with a rotating anode.

In a tube of any design, electrons accelerated by the voltage between the anode and the cathode fall on the anode mirror and penetrate deep into the substance, interact with atoms and are decelerated by the field of atoms. This produces bremsstrahlung X-rays. Simultaneously with the bremsstrahlung, a small amount (several percent) of characteristic radiation is formed. Only 1-2% of the electrons that hit the anode cause bremsstrahlung, and the rest cause a thermal effect. For the concentration of electrons, the cathode has a guide cap. The part of the tungsten mirror on which the main electron flow falls is called the focus of the tube. The width of the radiation beam depends on its area (focus sharpness).

To power the tube, two sources are required: a high voltage source for the anode circuit and a low voltage source (6-8 V) to power the filament circuit. Both sources must be independently regulated. By changing the anode voltage, the hardness of the X-ray radiation is regulated, and by changing the incandescence, the current of the output circuit and, accordingly, the radiation power.

Schematic diagram of the simplest X-ray machine is shown in Fig.4. The circuit has two high voltage transformers Tr.1 and Tr.2 for powering the filament. The high voltage on the tube is regulated by an autotransformer Tr.3 connected to the primary winding of the transformer Tr.1. Switch K regulates the number of turns of the autotransformer winding. In this regard, the voltage of the secondary winding of the transformer, supplied to the anode of the tube, also changes, i.e. hardness is adjustable.

The filament current of the tube is regulated by a rheostat R, included in the primary circuit of the transformer Tr.2. The anode circuit current is measured with a milliammeter. The voltage applied to the electrodes of the tube is measured with a kV kilovoltmeter, or the voltage in the anode circuit can be judged by the position of the switch K. The filament current, regulated by the rheostat, is measured with an ammeter A. In the scheme under consideration, the x-ray tube simultaneously rectifies a high alternating voltage.

It is easy to see that such a tube radiates only in one half-cycle of alternating current. Therefore, its power will be small. In order to increase the radiated power, many devices use high-voltage full-wave X-ray rectifiers. For this purpose, 4 special kenotrons are used, which are connected in a bridge circuit. An x-ray tube is included in one diagonal of the bridge.

3. Interaction of X-ray radiation with matter

(coherent scattering, incoherent scattering, photoelectric effect).

When X-rays fall on a body, it is reflected from it in a small amount, but mostly passes deep into. In the mass of the body, radiation is partially absorbed, partially scattered, and partially passes through. Passing through the body, X-ray photons interact mainly with the electrons of the atoms and molecules of the substance. Registration and use of X-ray radiation, as well as its impact on biological objects, is determined by the primary processes of interaction of an X-ray photon with electrons. Three main processes take place depending on the ratio of photon energy E and ionization energy AI.

a) coherent scattering.

Scattering of long-wavelength X-rays occurs mainly without changing the wavelength, and it is called coherent. The interaction of a photon with the electrons of the inner shells, tightly bound to the nucleus, only changes its direction, without changing its energy, and hence the wavelength (Fig. 5).

Coherent scattering occurs if the photon energy is less than the ionization energy: E = hn<А И. Так как энергия фотона и энергия атома не изменяется, то когерентное рассеяние не вызывает биологического действия. Однако при создании защиты от рентгеновского излучения следует учитывать возможность изменения направления первичного пучка.

b) Incoherent scattering (Compton effect).

In 1922, A. Compton, observing the scattering of hard X-rays, discovered a decrease in the penetrating power of the scattered beam compared to the incident beam. The scattering of X-rays with changing wavelength is called the Compton effect. It occurs when a photon of any energy interacts with the electrons of the outer shells of atoms weakly bound to the nucleus (Fig. 6). An electron is detached from an atom (such electrons are called recoil electrons). The energy of the photon decreases (the wavelength increases accordingly), and the direction of its movement also changes. The Compton effect occurs if the X-ray photon energy is greater than the ionization energy: , . In this case, recoil electrons with kinetic energy E K appear. Atoms and molecules become ions. If E K is significant, then electrons can ionize neighboring atoms by collision, forming new (secondary) electrons.

in) Photoelectric effect.

If the energy of a photon hn is sufficient to detach an electron, then when interacting with an atom, the photon is absorbed, and the electron is detached from it. This phenomenon is called the photoelectric effect. The atom is ionized (photoinization). In this case, the electron acquires kinetic energy and, if the latter is significant, then it can ionize neighboring atoms by collision, forming new (secondary) electrons. If the photon energy is insufficient for ionization, then the photoelectric effect can manifest itself in the excitation of an atom or molecule. In some substances, this leads to the subsequent emission of photons in the visible radiation region (X-ray luminescence), and in tissues, to the activation of molecules and photochemical reactions.

The photoelectric effect is typical for photons with an energy of the order of 0.5-1 MeV.

The three main interaction processes discussed above are primary, they lead to subsequent secondary, tertiary, etc. phenomena. When X-ray radiation enters a substance, a number of processes can occur before the energy of an X-ray photon is converted into the energy of thermal motion.

As a result of the above processes, the primary X-ray flux is weakened. This process obeys Bouguer's law. We write it in the form: Ф =Ф 0 e - mx, where m is a linear attenuation coefficient that depends on the nature of the substance (mainly on density and atomic number) and on the radiation wavelength (photon energy). It can be represented as consisting of three terms corresponding to coherent scattering, incoherent scattering, and the photoelectric effect: .

Since the linear absorption coefficient depends on the density of the substance, it is preferable to use the mass attenuation coefficient, which is equal to the ratio of the linear attenuation coefficient to the density of the absorber and does not depend on the density of the substance. The dependence of the X-ray flux (intensity) on the thickness of the absorbing filter is shown in Fig. 7 for H 2 O, Al, and Cu. Calculations show that a layer of water 36 mm thick, aluminum 15 mm and copper 1.6 mm reduce the X-ray intensity by 2 times. This thickness is called the half layer thickness d. If a substance attenuates X-ray radiation by half, then , then , or , ; ; . Knowing the thickness of the half layer, you can always determine m. Dimension .

4. The use of x-rays in medicine

(fluoroscopy, radiography, X-ray tomography, fluorography, radiotherapy).

One of the most common applications of X-rays in medicine is the transillumination of internal organs for diagnostic purposes - X-ray diagnostics.

For diagnostics, photons with an energy of 60-120 keV are used. In this case, the mass absorption coefficient is determined mainly by the photoelectric effect. Its value is proportional to l 3 (in which the large penetrating power of hard radiation is manifested) and proportional to the third power of the number of atoms of the substance - absorber: , where K is the coefficient of proportionality.

The human body consists of tissues and organs that have different absorbing capacity in relation to X-rays. Therefore, when it is illuminated with X-rays, a non-uniform shadow image is obtained on the screen, which gives a picture of the location of internal organs and tissues. The densest radiation-absorbing tissues (heart, large vessels, bones) are seen as dark, while the less absorbing tissues (lungs) are seen as light.

In many cases, it is possible to judge their normal or pathological state. X-ray diagnostics uses two main methods: fluoroscopy (transmission) and radiography (image). If the organ under study and the tissues surrounding it approximately equally absorb the X-ray flux, then special contrast agents are used. So, for example, on the eve of an X-ray examination of the stomach or intestines, a mushy mass of barium sulfate is given, in which case one can see their shadow image. In fluoroscopy and radiography, an x-ray image is a summary image of the entire thickness of the object through which the x-rays pass. The most clearly defined are those details that are closer to the screen or film, and the distant ones become fuzzy and blurry. If in some organ there is a pathologically altered area, for example, the destruction of lung tissue inside an extensive focus of inflammation, then in some cases this area on the x-ray in the amount of shadows can be “lost”. To make it visible, a special method is used - tomography (layered recording), which allows you to take pictures of individual layers of the area under study. This kind of layer-by-layer tomograms is obtained using a special apparatus called a tomograph, in which the x-ray tube (RT) and film (Fp) are periodically, jointly, in antiphase moved relative to the study area. In this case, X-rays at any position of the RT will pass through the same point of the object (changed area), which is the center relative to which the RT and FP periodically move. The shadow image of the area will be captured on film. By changing the position of the “swing center”, it is possible to obtain layered images of the object. Using a thin beam of X-rays, a special screen (instead of Fp) consisting of semiconductor detectors of ionizing radiation, it is possible to process the image during tomography using a computer. This modern variant of tomography is called computed tomography. Tomography is widely used in the study of the lungs, kidneys, gallbladder, stomach, bones, etc.

The brightness of the image on the screen and the exposure time on the film depends on the intensity of the X-ray radiation. When using it for diagnostics, the intensity cannot be high, so as not to cause an undesirable biological effect. Therefore, there are a number of technical devices that improve the brightness of the image at low X-ray intensities. One of these devices is an image intensifier tube.

Another example is fluorography, in which an image is obtained on a sensitive small-format film from a large X-ray luminescent screen. When shooting, a lens of large aperture is used, the finished pictures are examined on a special magnifier.

Fluorography combines a great ability to detect latent diseases (diseases of the chest, gastrointestinal tract, paranasal sinuses, etc.) with a significant throughput, and therefore is a very effective method of mass (in-line) research.

Since photographing an x-ray image during fluorography is performed using photographic optics, the image on the fluorogram is reduced in comparison with the x-ray. In this regard, the resolution of the fluorogram (i.e., the visibility of small details) is less than that of a conventional radiograph, however, it is greater than with fluoroscopy.

A device was designed - a tomofluorograph, which makes it possible to obtain fluorograms of body parts and individual organs at a given depth - the so-called layered images (sections) - tomofluorograms.

X-ray radiation is also used for therapeutic purposes (X-ray therapy). The biological effect of radiation is to disrupt the vital activity of cells, especially rapidly developing ones. In this regard, X-ray therapy is used to influence malignant tumors. It is possible to choose a dose of radiation sufficient for the complete destruction of the tumor with relatively minor damage to the surrounding healthy tissues, which are restored due to subsequent regeneration.