home > Foreign > Lecture x-rays. Is X-ray radiation dangerous for the human body. The frequencies of the characteristic X-ray radiation are determined by


Lecture x-rays. Is X-ray radiation dangerous for the human body. The frequencies of the characteristic X-ray radiation are determined by




The discovery and merit in the study of the basic properties of X-rays rightfully belongs to the German scientist Wilhelm Conrad Roentgen. The amazing properties of X-rays discovered by him immediately received a huge response in the scientific world. Although then, back in 1895, the scientist could hardly imagine what benefit, and sometimes harm, X-rays can bring.

Let's find out in this article how this type of radiation affects human health.

What is x-ray radiation

The first question that interested the researcher was what is X-ray radiation? A number of experiments made it possible to verify that this is electromagnetic radiation with a wavelength of 10 -8 cm, which occupies an intermediate position between ultraviolet and gamma radiation.

Application of X-rays

All these aspects of the destructive effects of the mysterious X-rays do not at all exclude surprisingly extensive aspects of their application. Where is X-rays used?

  1. Study of the structure of molecules and crystals.
  2. X-ray flaw detection (in industry, detection of defects in products).
  3. Methods of medical research and therapy.

The most important applications of X-rays have become possible due to the very short wavelengths of the entire range of these waves and their unique properties.

Since we are interested in the impact of X-rays on people who encounter them only during a medical examination or treatment, then we will only consider this area of ​​application of X-rays.

The use of x-rays in medicine

Despite the special significance of his discovery, Roentgen did not take out a patent for its use, making it an invaluable gift for all mankind. Already in the First World War, X-ray units began to be used, which made it possible to quickly and accurately diagnose the wounded. Now we can distinguish two main areas of application of x-rays in medicine:

  • X-ray diagnostics;
  • x-ray therapy.

X-ray diagnostics

X-ray diagnostics is used in various options:

Let's take a look at the difference between these methods.

All of these diagnostic methods are based on the ability of x-rays to illuminate film and on their different permeability to tissues and the bone skeleton.

X-ray therapy

The ability of X-rays to have a biological effect on tissues is used in medicine for the treatment of tumors. The ionizing effect of this radiation is most actively manifested in the effect on rapidly dividing cells, which are the cells of malignant tumors.

However, you should also be aware of the side effects that inevitably accompany radiotherapy. The fact is that cells of the hematopoietic, endocrine, and immune systems are also rapidly dividing. A negative impact on them gives rise to signs of radiation sickness.

The effect of X-ray radiation on humans

Shortly after the remarkable discovery of X-rays, it was discovered that X-rays had an effect on humans.

These data were obtained in experiments on experimental animals, however, geneticists suggest that similar effects may apply to the human body.

The study of the effects of X-ray exposure has led to the development of international standards for acceptable radiation doses.

Doses of x-ray radiation in x-ray diagnostics

After visiting the X-ray room, many patients are worried - how will the received dose of radiation affect their health?

The dose of general irradiation of the body depends on the nature of the procedure. For convenience, we will compare the received dose with natural exposure, which accompanies a person throughout his life.

  1. X-ray: chest - the received dose of radiation is equivalent to 10 days of background exposure; upper stomach and small intestine - 3 years.
  2. Computed tomography of the abdominal cavity and pelvis, as well as the whole body - 3 years.
  3. Mammography - 3 months.
  4. Radiography of the extremities is practically harmless.
  5. With regard to dental x-rays, the radiation dose is minimal, since the patient is exposed to a narrow beam of x-rays with a short radiation duration.

These radiation doses meet acceptable standards, but if the patient feels anxious before the X-ray, he has the right to ask for a special protective apron.

Exposure of X-rays to pregnant women

Each person has to undergo X-ray examination repeatedly. But there is a rule - this diagnostic method cannot be prescribed to pregnant women. The developing embryo is extremely vulnerable. X-rays can cause chromosome abnormalities and, as a result, the birth of children with malformations. The most vulnerable in this regard is the gestational age of up to 16 weeks. Moreover, the most dangerous for the future baby is an x-ray of the spine, pelvic and abdominal regions.

Knowing about the detrimental effect of x-rays on pregnancy, doctors avoid using it in every possible way during this crucial period in a woman's life.

However, there are side sources of X-rays:

  • electron microscopes;
  • color TV kinescopes, etc.

Expectant mothers should be aware of the danger posed by them.

For nursing mothers, radiodiagnosis is not dangerous.

What to do after an x-ray

To avoid even the minimal effects of X-ray exposure, some simple steps can be taken:

  • after an x-ray, drink a glass of milk - it removes small doses of radiation;
  • very handy taking a glass of dry wine or grape juice;
  • some time after the procedure, it is useful to increase the proportion of foods with a high content of iodine (seafood).

But, no medical procedures or special measures are required to remove radiation after an x-ray!

Despite the undoubtedly serious consequences of exposure to X-rays, one should not overestimate their danger during medical examinations - they are carried out only in certain areas of the body and very quickly. The benefits of them many times exceed the risk of this procedure for the human body.

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 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, 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 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 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 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 integument 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).

X-RAY RADIATION

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).

Rice. 1. A CONVENTIONAL X-RAY SPECTRUM consists of a continuous spectrum (continuum) and characteristic lines (sharp peaks). The K / ia and K / ib lines arise due to the interactions of accelerated electrons with the electrons of the inner K-shell.

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.

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 required 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.

Rice. 3. COOLIDGE X-RAY TUBE. 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 searchlight" of the tube. The anode subjected to electron bombardment must be made of a refractory material, since most of the kinetic energy of the bombarding electrons is converted into heat. In addition, it is desirable that the anode be made of a material with a high atomic number, since the x-ray yield increases with increasing atomic number. Tungsten, whose atomic number is 74, is most often chosen as the anode material. The design of X-ray tubes can be different depending on the application conditions and requirements. X-RAY DETECTION All methods for detecting X-rays are based on their interaction with matter. Detectors can be of two types: those that give an image, and those that do not. The former include X-ray fluorography and fluoroscopy devices, in which the X-ray beam passes through the object under study, and the transmitted radiation enters the luminescent screen or film. The image appears due to the fact that different parts of the object under study absorb radiation in different ways - depending on the thickness of the substance and its composition. In detectors with a luminescent screen, the X-ray energy is converted into a directly observable image, while in radiography it is recorded on a sensitive emulsion and can only be observed after the film has been developed. The second type of detectors includes a wide variety of devices in which the X-ray energy is converted into electrical signals that characterize the relative intensity of the radiation. These include ionization chambers, a Geiger counter, a proportional counter, a scintillation counter, and some special detectors based on cadmium sulfide and selenide. Currently, scintillation counters can be considered the most efficient detectors, which work well in a wide energy range. see also PARTICLE DETECTORS. The detector is selected taking into account the conditions of the problem. For example, if it is necessary to accurately measure the intensity of diffracted X-ray radiation, then counters are used that allow measurements to be made with an accuracy of fractions of a percent. If it is necessary to register a lot of diffracted beams, then it is advisable to use X-ray film, although in this case it is impossible to determine the intensity with the same accuracy. X-RAY AND GAMMA DEFECTOSCOPY One of the most common applications of X-rays in industry is material quality control and flaw detection. The x-ray method is non-destructive, so that the material being tested, if found to meet the required requirements, can then be used for its intended purpose. Both x-ray and gamma flaw detection are based on the penetrating power of x-rays and the characteristics of its absorption in materials. Penetrating power is determined by the energy of X-ray photons, which depends on the accelerating voltage in the X-ray tube. Therefore, thick samples and samples from heavy metals, such as gold and uranium, require an X-ray source with a higher voltage for their study, and for thin samples, a source with a lower voltage is sufficient. For gamma-ray flaw detection of very large castings and large rolled products, betatrons and linear accelerators are used, accelerating particles to energies of 25 MeV and more. The absorption of X-rays in a material depends on the thickness of the absorber d and the absorption coefficient m and is determined by the formula I = I0e-md, where I is the intensity of the radiation transmitted through the absorber, I0 is the intensity of the incident radiation, and e = 2.718 is the base of natural logarithms. For a given material, at a given wavelength (or energy) of X-rays, the absorption coefficient is a constant. But the radiation of an X-ray source is not monochromatic, but contains a wide 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).

Rice. 4. AMPLIFICATION OF THE X-RAY BEAM occurs when the difference in the path of the waves scattered by neighboring atoms is equal to an integer multiple of the wavelength. Here a0 is the angle of incidence, a is the diffraction angle, and a is the distance between atoms.

Rice. 5. The solution of the LAUE EQUATIONS for each value of h can be represented as a family of cones, the common axis of which is directed along the crystallographic axis (for the other two axes, similar patterns can be drawn). An effective method for studying crystal structures is based on the Laue equations.

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

<="" div="" style="border-style: none;">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. . five). 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:

Rice. 6. GENERAL SOLUTION OF LAUE EQUATIONS corresponds to the intersection of three cones with axes a, b, c, having a common straight line R.

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< 1. При таких условиях, чтобы имела место дифракция для рентгеновского излучения с длиной волны l, плоскость кристалла с периодом d должна быть повернута на правильный угол q. Для того чтобы реализовать это маловероятное событие, применяются различные методики. 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.

Rice. 7. LAUEGRAM. X-ray radiation of a wide spectral range is passed through a fixed crystal. Diffraction beams correspond to spots on the Lauegram.

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.

Ministry of Education and Science of the Russian Federation

Federal Agency for Education

GOU VPO SUSU

Department of Physical Chemistry

at the KSE course: “X-ray radiation”

Completed:

Naumova Daria Gennadievna

Checked:

Associate Professor, K.T.N.

Tanklevskaya N.M.

Chelyabinsk 2010

Introduction

Chapter I. Discovery of X-rays

Receipt

Interaction with matter

Biological impact

Registration

Application

How an x-ray is taken

natural x-rays

Chapter II. Radiography

Application

Image Acquisition Method

Benefits of radiography

Disadvantages of radiography

Fluoroscopy

Receipt principle

Benefits of Fluoroscopy

Disadvantages of Fluoroscopy

Digital technologies in fluoroscopy

Multiline scanning method

Conclusion

List of used literature

Introduction

X-ray radiation - electromagnetic waves, the photon energy of which is determined by the energy range from ultraviolet to gamma radiation, which corresponds to the wavelength range from 10−4 to 10² Å (from 10−14 to 10−8 m).

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.

Chapter I. Discovery of X-rays

The discovery of X-rays is attributed to Wilhelm Conrad Roentgen. He was the first to publish an article on X-rays, which he called x-rays (x-ray). An article by Roentgen titled "On a new type of rays" was published on December 28, 1895 in the journal of the Würzburg Physico-Medical Society. It is considered, however, proven that X-rays have already been obtained before. The cathode ray tube that Roentgen used in his experiments was developed by J. Hittorf and W. Kruks. This tube produces X-rays. This was shown in the experiments of Crookes and from 1892 in the experiments of Heinrich Hertz and his student Philipp Lenard through the blackening of photographic plates. However, none of them realized the significance of their discovery and did not publish their results. Also, Nikola Tesla, starting in 1897, experimented with cathode ray tubes, received x-rays, but did not publish his results.

For this reason, Roentgen did not know about the discoveries made before him and discovered the rays, later named after him, independently - while observing the fluorescence that occurs during the operation of a cathode ray tube. Roentgen studied X-rays for a little over a year (from November 8, 1895 to March 1897) and published only three relatively small articles about them, but they provided such an exhaustive description of the new rays that hundreds of papers by his followers, then published over the course of 12 years, could neither add nor change anything essential. Roentgen, who had lost interest in X-rays, told his colleagues: "I already wrote everything, don't waste your time." Also contributing to Roentgen's fame was the famous photograph of his wife's hand, which he published in his article (see image on the right). Such fame brought Roentgen in 1901 the first Nobel Prize in Physics, and the Nobel Committee emphasized the practical importance of his discovery. In 1896, the name "X-rays" was first used. In some countries, the old name remains - X-rays. In Russia, the rays began to be called "X-ray" at the suggestion of a student V.K. Roentgen - Abram Fedorovich Ioffe.

Position on the scale of electromagnetic waves

The energy ranges of X-rays and gamma-rays overlap in a wide energy range. Both types of radiation are electromagnetic radiation and are equivalent for the same photon energy. The terminological difference lies in the mode of occurrence - X-rays are emitted with the participation of electrons (either in atoms or free ones), while gamma radiation is emitted in the processes of de-excitation of atomic nuclei. X-ray photons have energies from 100 eV to 250 keV, which corresponds to radiation with a frequency of 3 1016 Hz to 6 1019 Hz and a wavelength of 0.005 - 10 nm (there is no generally accepted definition of the lower limit of the X-ray range in the wavelength scale). Soft X-rays are characterized by the lowest photon energy and radiation frequency (and the longest wavelength), while hard X-rays have the highest photon energy and radiation frequency (and the shortest wavelength).

(X-ray photograph (roentgenogram) of his wife's hand, taken by V.K. Roentgen)

)

Receipt

X-rays are produced by strong acceleration of charged particles (mainly electrons) or by high-energy transitions in the electron shells of atoms or molecules. Both effects are used in X-ray tubes, in which electrons emitted by a hot cathode are accelerated (no X-rays are emitted, because the acceleration is too low) and hit the anode, where they are sharply decelerated (in this case, X-rays are emitted: the so-called . bremsstrahlung) and at the same time knock out electrons from the inner electron shells of the atoms of the metal from which the anode is made. Empty spaces in the shells are occupied by other electrons of the atom. In this case, X-ray radiation is emitted with a certain energy characteristic of the anode material (characteristic radiation, frequencies are determined by the Moseley law:

,

where Z is the atomic number of the anode element, A and B are constants for a certain value of the principal quantum number n of the electron shell). At present, anodes are made mainly of ceramics, and the part where the electrons hit is made of molybdenum. In the process of acceleration-deceleration, only 1% of the kinetic energy of the electron goes to X-rays, 99% of the energy is converted into heat.

X-rays can also be obtained in particle accelerators. so-called. Synchrotron radiation occurs when a beam of particles is deflected in a magnetic field, as a result of which they experience acceleration in a direction perpendicular to their motion. Synchrotron radiation has a continuous spectrum with an upper limit. With appropriately chosen parameters (the magnitude of the magnetic field and the energy of the particles), X-rays can also be obtained in the spectrum of synchrotron radiation.

Schematic representation of an x-ray tube. X - X-rays, K - cathode, A - anode (sometimes called anticathode), C - heat sink, Uh - cathode filament voltage, Ua - accelerating voltage, Win - water cooling inlet, Wout - water cooling outlet (see x-ray tube) .

Interaction with matter

The refractive index of almost any substance for x-rays differs little from unity. A consequence of this is the fact that there is no material from which an X-ray lens can be made. In addition, when X-rays are incident perpendicular to the surface, they are almost not reflected. Despite this, in X-ray optics, methods have been found for constructing optical elements for X-rays.

X-rays can penetrate matter, and different substances absorb them differently. The absorption of x-rays is their most important property in x-ray photography. The intensity of X-rays decreases exponentially depending on the path traveled in the absorbing layer (I = I0e-kd, where d is the layer thickness, the coefficient k is proportional to Z3λ3, Z is the atomic number of the element, λ is the wavelength).

Absorption occurs as a result of photoabsorption and Compton scattering:

Photoabsorption is understood as the process of knocking out an electron from the shell of an atom by a photon, which requires that the photon energy be greater than a certain minimum value. If we consider the probability of the act of absorption depending on the energy of the photon, then when a certain energy is reached, it (probability) increases sharply to its maximum value. For higher energies, the probability continuously decreases. Because of this dependence, it is said that there is an absorption limit. The place of the electron knocked out during the act of absorption is occupied by another electron, while radiation with a lower photon energy is emitted, the so-called. fluorescence process.

Modern medical diagnostics and treatment of certain diseases cannot be imagined without devices that use the properties of X-rays. The discovery of X-rays occurred more than 100 years ago, but even now work continues on the creation of new methods and apparatus to minimize the negative effect of radiation on the human body.

Who and how discovered X-rays

Under natural conditions, the flux of X-rays is rare and is emitted only by certain radioactive isotopes. X-rays or X-rays were only discovered in 1895 by the German scientist Wilhelm Röntgen. This discovery happened by chance, during an experiment to study the behavior of light rays under conditions approaching vacuum. The experiment involved a cathode gas discharge tube with reduced pressure and a fluorescent screen, which each time began to glow at the moment when the tube began to act.

Interested in a strange effect, Roentgen conducted a series of studies showing that the resulting radiation, invisible to the eye, is able to penetrate various obstacles: paper, wood, glass, some metals, and even through the human body. Despite the lack of understanding of the very nature of what is happening, whether such a phenomenon is caused by the generation of a stream of unknown particles or waves, the following pattern was noted - radiation easily passes through the soft tissues of the body, and much harder through solid living tissues and inanimate substances.

Roentgen was not the first to study this phenomenon. In the middle of the 19th century, Frenchman Antoine Mason and Englishman William Crookes studied similar possibilities. However, it was Roentgen who first invented the cathode tube and an indicator that could be used in medicine. He was the first to publish a scientific work, which brought him the title of the first Nobel laureate among physicists.

In 1901, a fruitful collaboration began between the three scientists, who became the founding fathers of radiology and radiology.

X-ray properties

X-rays are an integral part of the general spectrum of electromagnetic radiation. The wavelength is between gamma and ultraviolet rays. X-rays have all the usual wave properties:

  • diffraction;
  • refraction;
  • interference;
  • propagation speed (it is equal to light).

To artificially generate an X-ray flux, special devices are used - X-ray tubes. X-ray radiation arises from the contact of fast tungsten electrons with substances evaporating from a hot anode. Against the background of interaction, short-length electromagnetic waves arise, which are in the spectrum from 100 to 0.01 nm and in the energy range of 100-0.1 MeV. If the wavelength of the rays is less than 0.2 nm - this is hard radiation, if the wavelength is greater than the specified value, they are called soft x-rays.

It is significant that the kinetic energy arising from the contact of electrons and the anode substance is 99% converted into heat energy and only 1% is X-rays.

X-ray radiation - bremsstrahlung and characteristic

X-radiation is a superposition of two types of rays - bremsstrahlung and characteristic. They are generated in the handset simultaneously. Therefore, X-ray irradiation and the characteristic of each specific X-ray tube - the spectrum of its radiation, depends on these indicators, and represents their superposition.

Bremsstrahlung or continuous X-rays are the result of deceleration of electrons evaporating from a tungsten filament.

Characteristic or line X-rays are formed at the moment of rearrangement of the atoms of the substance of the anode of the X-ray tube. The wavelength of the characteristic rays directly depends on the atomic number of the chemical element used to make the anode of the tube.

The listed properties of X-rays allow them to be used in practice:

  • invisible to the ordinary eye;
  • high penetrating ability through living tissues and inanimate materials that do not transmit visible light;
  • ionization effect on molecular structures.

Principles of X-ray Imaging

The property of x-rays on which imaging is based is the ability to either decompose or cause some substances to glow.

X-ray irradiation causes a fluorescent glow in cadmium and zinc sulfides - green, and in calcium tungstate - blue. This property is used in the technique of medical X-ray transillumination, and also increases the functionality of X-ray screens.

The photochemical effect of X-rays on light-sensitive silver halide materials (illumination) makes it possible to carry out diagnostics - to take X-ray images. This property is also used in measuring the amount of the total dose that laboratory assistants receive in X-ray rooms. Wearable dosimeters have special sensitive tapes and indicators. The ionizing effect of X-ray radiation makes it possible to determine the qualitative characteristics of the obtained X-rays.

A single exposure to conventional X-rays increases the risk of cancer by only 0.001%.

Areas where X-rays are used

The use of X-rays is acceptable in the following industries:

  1. Safety. Fixed and portable devices for detecting dangerous and prohibited items at airports, customs or in crowded places.
  2. Chemical industry, metallurgy, archeology, architecture, construction, restoration work - to detect defects and conduct chemical analysis of substances.
  3. Astronomy. It helps to observe cosmic bodies and phenomena with the help of X-ray telescopes.
  4. military industry. For the development of laser weapons.

The main application of X-rays is in the medical field. Today, the section of medical radiology includes: radiodiagnostics, radiotherapy (X-ray therapy), radiosurgery. Medical universities produce highly specialized specialists - radiologists.

X-Radiation - harm and benefit, effects on the body

The high penetrating power and ionizing effect of X-rays can cause a change in the structure of the DNA of the cell, therefore it is dangerous for humans. The harm from X-ray radiation is directly proportional to the received radiation dose. Different organs respond to irradiation to varying degrees. The most susceptible include:

  • bone marrow and bone tissue;
  • lens of the eye;
  • thyroid;
  • mammary and sex glands;
  • lung tissue.

Uncontrolled use of X-ray radiation can cause reversible and irreversible pathologies.

Consequences of X-ray exposure:

  • damage to the bone marrow and the occurrence of pathologies of the hematopoietic system - erythrocytopenia, thrombocytopenia, leukemia;
  • damage to the lens, with the subsequent development of cataracts;
  • cellular mutations that are inherited;
  • development of oncological diseases;
  • getting radiation burns;
  • development of radiation sickness.

Important! Unlike radioactive substances, X-rays do not accumulate in the tissues of the body, which means that there is no need to remove X-rays from the body. The harmful effect of X-rays ends when the medical device is turned off.

The use of X-rays in medicine is permissible not only for diagnostic (traumatology, dentistry), but also for therapeutic purposes:

  • from x-rays in small doses, the metabolism in living cells and tissues is stimulated;
  • certain limiting doses are used for the treatment of oncological and benign neoplasms.

Methods for diagnosing pathologies using X-rays

Radiodiagnostics includes the following methods:

  1. Fluoroscopy is a study in which an image is obtained on a fluorescent screen in real time. Along with the classical real-time imaging of a body part, today there are X-ray television transillumination technologies - the image is transferred from a fluorescent screen to a television monitor located in another room. Several digital methods have been developed for processing the resulting image, followed by transferring it from the screen to paper.
  2. Fluorography is the cheapest method for examining the chest organs, which consists in making a small picture of 7x7 cm. Despite the possibility of error, it is the only way to conduct a mass annual examination of the population. The method is not dangerous and does not require the withdrawal of the received radiation dose from the body.
  3. Radiography - obtaining a summary image on film or paper to clarify the shape of an organ, its position or tone. Can be used to assess peristalsis and the condition of the mucous membranes. If there is a choice, then among modern X-ray devices, preference should be given neither to digital devices, where the x-ray flux can be higher than that of old devices, but to low-dose X-ray devices with direct flat semiconductor detectors. They allow you to reduce the load on the body by 4 times.
  4. Computed X-ray tomography is a technique that uses x-rays to obtain the required number of images of sections of a selected organ. Among the many varieties of modern CT devices, low-dose high-resolution CT scanners are used for a series of repeated studies.

Radiotherapy

X-ray therapy refers to local treatment methods. Most often, the method is used to destroy cancer cells. Since the effect of exposure is comparable to surgical removal, this treatment method is often called radiosurgery.

Today, x-ray treatment is carried out in the following ways:

  1. External (proton therapy) - the radiation beam enters the patient's body from the outside.
  2. Internal (brachytherapy) - the use of radioactive capsules by implanting them into the body, with the placement closer to the cancerous tumor. The disadvantage of this method of treatment is that until the capsule is removed from the body, the patient needs to be isolated.

These methods are gentle, and their use is preferable to chemotherapy in some cases. Such popularity is due to the fact that the rays do not accumulate and do not require removal from the body, they have a selective effect, without affecting other cells and tissues.

Safe X-ray exposure rate

This indicator of the norm of permissible annual exposure has its own name - a genetically significant equivalent dose (GED). There are no clear quantitative values ​​for this indicator.

  1. This indicator depends on the age and desire of the patient to have children in the future.
  2. It depends on which organs were examined or treated.
  3. The GZD is affected by the level of natural radioactive background of the region where a person lives.

Today, the following average GZD standards are in force:

  • the level of exposure from all sources, with the exception of medical ones, and without taking into account the natural radiation background - 167 mRem per year;
  • the norm for an annual medical examination is not more than 100 mRem per year;
  • the total safe value is 392 mRem per year.

X-ray radiation does not require excretion from the body, and is dangerous only in case of intense and prolonged exposure. Modern medical equipment uses low-energy radiation of short duration, so its use is considered relatively harmless.