In 1895, Roentgen discovered that if through a glass tube with two soldered electrodes, from which air is pumped out to a pressure of 103 mm Hg. Art., skip an electric current, then the anode emits special, hitherto unknown, invisible to the eye rays. He called them X-rays. In Russia and in many other countries they began to be called x-rays. Roentgen, examining their properties, found the following:

1. They have a strong penetrating power, which depends on the nature of the substance and its thickness. Due to this property, they are widely used in medicine and industry.

2. They cause the glow (luminescence) of some bodies. With the help of screens of such substances, they can be observed.

3. Have an effect on the film (photochemical effect).

4. Able to actively ionize air and other substances.

5. They have a biological effect on body tissues, which has been used in the treatment of malignant tumors.

However, Roentgen himself did not reveal the nature of X-rays. Many researchers found similarities between X-rays and light - they propagated in a straight line and did not deviate in either an electric or magnetic field. But, if we assume the same nature of light and X-rays, then X-rays would have to have wave and quantum properties. However, X-ray diffraction could not be obtained for a long time. In 1910, P.N. Lebedev suggested using natural crystals as a diffraction grating for X-rays, and in 1912 the German physicist Laue performed this experiment. The flow of X-ray light was directed through the diaphragm onto the crystal, while on the screen or photographic film around the central bright spot (non-diffracted rays) a series of bright points appeared, arranged in a certain order.

The distance between the atoms of the crystal lattice, on the order of 1A°, is commensurate with the wavelength, and these gaps are the centers of secondary waves, which, when diffracted, give maxima in the form of white spots. But since Since the atoms are not strictly located one next to the other like the slits of a diffraction grating, then the maxima are arranged in a complex order than in a diffraction grating. Such a picture is called a Lauegram. This experiment showed that X-rays are of a wave nature.

Laue's experience allowed the use of X-ray diffraction:

1. To determine the wavelength, knowing the distance between atoms.

2. To determine the structure of substances according to the Lauegram, knowing the wavelength of X-rays.

A method for studying molecular structures, i.e. determination of the position of atoms in a molecule and their nature using x-rays, called x-ray diffraction analysis. To study biological structures, various phenomena of the interaction of X-rays with matter can be used: absorption, scattering and diffraction, inactivation (changes in the structure of molecules and the functions of their constituent parts under the action of X-rays). The method of scattering and diffraction of X-rays uses their wave properties. X-rays scattered by the atoms that make up the molecules interfere and give a picture - a Lauegram, in which the position and intensity of the maxima depend on the position of the atoms in the molecule and on the relative position of the molecules. If the molecules are arranged randomly, for example, in solutions, then the scattering does not depend on the internal structure of the molecules, but mainly on their size and shape.

Later, other properties of X-rays were studied:

1. Interference.

2. Refraction.

3. Total internal reflection.

4. Polarization.

5. Spectral composition.

6. Interaction with matter.

Get x-rays with an x-ray tube.

It consists of a glass container with as high a vacuum as possible (10 -6 - 10 -7 mm Hg), in which there are two electrodes.

Cathode - is a source of electrons and is made in the form of a spiral. The anode consists of a massive copper rod, on the end section of which there is a tungsten plate (anode mirror). The electrons are accelerated in the electric field and interact with the anode mirror. As a result of the interaction, an X-ray flux is formed. The whole tube is surrounded by a lead casing, there is only a small window for the radiation to exit. Because the anode during operation is very hot, it is cooled with water or oil. In some tubes, the anode is made to rotate. The wavelength of X-rays is from 0.001 to 2 nm. X-ray radiation is characterized by intensity and rigidity.

Intensity is the amount of energy carried by x-rays through an area of 1 cm 2 in 1 s.

The hardness of X-ray radiation is determined by its ability to pass through a substance, and the penetrating power depends on the wavelength. X-ray radiation arises as a result of the interaction of the electron flow with the atoms of the anode mirror.

An electron moving in a direction can be represented electric shock. Getting into the electric field of the atom, the movement of the electron slows down, which corresponds to a decrease in current. Current reduction

will cause a changing magnetic field around the electron, and a changing magnetic field will induce a changing electric field at adjacent points, etc., thus. When an electron is decelerated by an atom, an electromagnetic wave is produced. There is also quantum theory explaining the origin of bremsstrahlung X-rays. In addition to circular or elliptical stationary orbits, called periodic, there are also non-closed orbits of electrons (parabolic, hyperbolic), along which an electron can move without emitting or absorbing energy. Approaching the atom with a speed υ 1, the electron moves along a stationary non-closed orbit with energy E 1, slowing down, it moves to another stationary orbit with energy E 2, while a quantum of energy is emitted. The initial kinetic energy of an electron depends only on the accelerating voltage mυ 1 2 /2=eU and is a constant value. The final energy, depending on the braking conditions, can take any values from mυ 1 2 /2 to 0. Therefore, the energy of the emitted quantum can be any in the range from 0 to mυ 1 2 /2 . The emission spectrum is continuous, limited from the side

short wavelengths.

hv \u003d (mυ 1 2) / 2 - (mυ 2 2) / 2

The minimum quantum energy is determined from this equation,

If (mυ 2 2)/2= 0 , then or hv min \u003d (mυ 1 2) / 2

hc/λ max =eU, where λmax = (hc)/(eU)

An electron, interacting with an anode atom, can remove an orbital electron from the K, L, M orbit closest to the nucleus to a more distant one or even beyond the atom. An electron from a more distant orbit will move to the vacated place. In this case, an X-ray quantum is emitted, the wavelength of which is determined by the difference between the allowed energy states of the atom (hv = E 2 - E 1). Therefore, radiation can only be of certain wavelengths, the spectrum of such radiation will be line, and radiation is called characteristic.

When the anode material is bombarded with electrons, both types of radiation exist. Consider the scheme of the x-ray machine.

The X-ray apparatus includes the following components:

1. X-ray tube (RT)

2. Step-up transformer (TP2).

3. Step-down transformer (TR,).

4. Autotransformer (ATR).

5. High voltage rectifier (B).

The primary winding of the step-up transformer is fed from the AC mains through an autotransformer. The autotransformer serves to regulate the voltage between the anode and cathode. Changing the voltage changes the wavelength λ min \u003d l,24 / U , and the wavelength characterizes the radiation hardness, i.e. The autotransformer is used to adjust the X-ray hardness. The voltage between the anode and cathode of an x-ray tube in medical x-ray machines is up to 60 kV, in industrial ones - 200 - 250 kV. The tube is powered by direct current. As a rectifier, high-voltage diodes or kenotrons are used, one-half-wave and two-half-wave circuits are used. To power the glow of the tube, a step-down transformer TR 1 is used. A rheostat R is placed in the primary circuit of this transformer. By changing the resistance, we change the cathode filament current, and, consequently, its temperature and the number of emitted electrons. The number of electrons characterizes the intensity of X-ray radiation, thus. Rheostat R serves to change the radiation intensity, which is determined by the following formula:

Ф = kJU 2 Z",

where J is the anode current, U is the voltage between the cathode and the anode of the tube, Z is the ordinal number of the substance of the anode mirror. Protection against exposure to x-ray radiation given by medical and diagnostic devices is as follows:

1. Screening of the radiation source. The X-ray tube is self-protective. The chamber is covered with lead sheets.

2.Individual protection of service personnel (apron, gloves, screen glass is made of leaded material).

3. Protected by law (shorter working hours, additional leave, special meals, etc.)

When X-rays interact with a substance, some of them are reflected from the surface, some pass through the substance without interaction, and some pass inside the substance, interacting with atoms.

In this case, three cases of interaction can arise.

1. If the photon does not have sufficient energy to transfer the orbital electron to a higher energy level, then the interaction occurs by elastic collision, the direction of the photon changes, and the energy and wavelength remain the same hv 1 = hv 2 This interaction is called coherent or classical scattering.

2. If the quantum energy is equal to or slightly exceeds the work function of the electron from the metal, then the interaction occurs photoelectric effect, the energy of a photon is expended on the work of getting an electron out of an atom and imparting kinetic energy to it.

hv 1 \u003d A out + (mυ 2) / 2

If the energy is less than the work function, but sufficient to transfer an electron from one orbit to another (with a higher energy level), then radiation in the visible part of the spectrum can occur, x-ray luminescence or activation of molecules. Both types of interaction are combined common name - true absorption.

3. If the energy of a photon significantly exceeds the work of an electron, which is more typical for hard short-wave radiation and external electrons of an atom, then during the interaction the photon gives up part of the energy. A photon with a lower energy and a recoil photoelectron appear. This phenomenon is called incoherent scattering or Compton effect.

The resulting new photon and electron are called secondary radiation. Secondary radiation can cause new reactions (coherent scattering, true absorption, Compton effect) with the formation of tertiary electrons, quanta, etc. As a result of all these processes, ionization of the substance and radiation with a longer wavelength occurs, which is scattered in all directions.

The parallel flow of X-rays is weakened when passing through a substance. The weakening obeys Bouguer's law: Ф \u003d Ф 0 e - μd

Fo is the flow incident on the substance, F is the flow passing through the substance, μ is the linear attenuation coefficient, d is the thickness of the substance layer.

For X-ray radiation used in medicine with a photon energy of 150-200 keV for deep therapy; 60-100 keV for diagnostics; attenuation coefficient is determined by the formula:

μ = kpZ 3 λ 3 ,

k is the coefficient of proportionality, depending on the choice of units of measurement, p is the density of the substance, Z is the ordinal number of the element, λ is the radiation wavelength.

If an inhomogeneous substance is placed in the path of X-ray radiation, then on a fluorescent screen we will get shadows of individual details

substances. Such a heterogeneous substance is the human body. Translucent with X-rays, according to the shape and size, as well as the intensity of the shadow image, they judge the normal or pathological state of the organs. This method of diagnosing diseases is called X-ray diagnostics. There are two main methods of X-ray diagnostics: fluoroscopy and radiography. During fluoroscopy, the shadow image of organs is observed on a fluorescent screen. On the screen, denser tissues (heart, blood vessels) are seen as dark, little absorbing tissues (lung fields) as light. During radiography, the shadow image is photographed on film. The image is obtained negative (reverse) in relation to the image on the screen.

In addition to the basic methods, special methods of X-ray diagnostics are used.

1. Contrast radiography. To obtain a more contrasting image, special substances are used that are injected into tissues - negative contrast agents (air, oxygen) are used in dense tissues (brain), positive contrast agents (barium salts, iodine-based colloids) for low-absorbing tissues.

2. Fluorography. Photographing an x-ray image from a screen onto a small format film. The screen, optics and camera film are combined into a large light-tight system, which allows you to shoot in a dark room. This method is used for mass survey of the population.

3. Electroradiography differs from conventional radiography in the manner in which the image is acquired; with this method, a beam of x-rays that have passed through the patient's body is directed to a pre-infected selenium plate. X-rays that have passed through the body change the potential of the plate in its different sections, respectively, the intensity of the radiation falling on these areas - a “latent electrical image” appears on the plate. To "develop" the image, the selenium plate is sprayed with graphite powder, which is attracted to those places where the charge has been preserved and does not linger in those places that have lost their charge under the action of X-rays. This image is easily transferred to plain paper. After erasing the powder, the plate can be used again. More than 1000 shots can be taken on one plate. The main advantages of electroroentgenography are that it allows you to quickly obtain images without the cost of film, without a wet photo process, without darkening, and has a higher resolution.

4. X-ray computed tomography. This method consists in moving the X-ray tube along a certain trajectory in order to photograph the object from various positions. At the same time, the image on the film also moves. However, the shooting is done in such a way that the x-ray beam always passes the same point O. If you move this point, then you can get a layered shadow image in the image (tomography - layered recording). Reading such images is quite difficult. Computer technology helps the doctor in this matter, so the word computed tomography is added. X-ray computed tomography makes it possible to obtain an image with details of about 1 mm, two formations differ in contrast with a difference in absorption of about 0.1%.

5. X-ray television. With the help of special X-ray image photoamplifiers (URI), a weak image on the screen is recorded and enhanced, and using television transmission equipment, an image is obtained on the TV screen. The image on the TV screen of considerable brightness, provides the identification of relatively small details of the object, allows you to take photos and films.

X-rays are used to "treat" malignant neoplasms - X-ray therapy. When living tissues are irradiated with X-rays, the functional state of cells changes. The primary effect of X-rays on matter is ionization. It was found that at lethal doses, about 1 million ions are formed in the cell (there are 10 14 atoms in the cell). During the primary exchange of energy, no visible structural changes occur in atoms and molecules. Modern physiology considers the primary effects of the interaction of ionizing radiation with matter (including X-rays) in two aspects: interaction with water molecules in aqueous solutions and action on organic compounds. In aqueous solutions, radicals (OH -, H +), hydroperoxide and peroxide compounds (H 2 O 2) are formed, which have high chemical activity. When exposed to organic compounds, excited molecules, radicals, ions, peroxides are formed, which are also very active chemically. That. The primary interaction is physical laws excitation and ionization of molecules. The ionization of atoms and molecules causes secondary processes that develop according to biological laws. Active peroxide compounds oxidize and change cellular enzymes, which causes a disruption in the normal course of biochemical processes - cells lose the ability to synthesize certain types of proteins, without which cell division is impossible. Mutations occur, the course of protein, carbohydrate, peptide and cholesterol metabolism changes. In such reactions, protein molecules can be destroyed and decomposed into amino acids, up to the formation of very toxic histamine-like compounds, under the influence of which dystrophic and necrotic changes develop. X-rays have a particularly strong effect on fast-growing, poorly differentiated cells - hematopoietic organs, skin, gonads, which makes it possible to use x-rays to irradiate cancerous tumors of these formations. It should be remembered that radiation acts not only on a biological object subjected to radiation, but also on subsequent generations, through the hereditary apparatus of cells.

In the study and practical use of atomic phenomena, one of critical roles playing x-rays. Thanks to their research, many discoveries were made and methods for analyzing substances were developed, which are used in various fields. Here we will consider one of the types of X-rays - characteristic X-rays.

Nature and properties of X-rays

X-ray radiation is a high-frequency change in the state of an electrical magnetic field propagating in space at a speed of about 300,000 km / s, that is, electromagnetic waves. On the scale of the range of electromagnetic radiation, X-rays are located in the wavelength range from approximately 10 -8 to 5∙10 -12 meters, which is several orders of magnitude shorter than optical waves. This corresponds to frequencies from 3∙10 16 to 6∙10 19 Hz and energies from 10 eV to 250 keV, or 1.6∙10 -18 to 4∙10 -14 J. It should be noted that the boundaries of the frequency ranges of electromagnetic radiation are rather conventional due to their overlap.

Is the interaction of accelerated charged particles (high-energy electrons) with electric and magnetic fields and with atoms of matter.

X-ray photons are characterized by high energies and high penetrating and ionizing power, especially for hard X-rays with wavelengths less than 1 nanometer (10 -9 m).

X-rays interact with matter, ionizing its atoms, in the processes of the photoelectric effect (photoabsorption) and incoherent (Compton) scattering. In photoabsorption, an X-ray photon, being absorbed by an electron of an atom, transfers energy to it. If its value exceeds the binding energy of an electron in an atom, then it leaves the atom. Compton scattering is characteristic of harder (energetic) X-ray photons. Part of the energy of the absorbed photon is spent on ionization; in this case, at a certain angle to the direction of the primary photon, a secondary one is emitted, with a lower frequency.

Types of X-ray radiation. Bremsstrahlung

To obtain rays, glass vacuum bottles with electrodes located inside are used. The potential difference across the electrodes needs to be very high - up to hundreds of kilovolts. On a tungsten cathode heated by current, thermionic emission occurs, that is, electrons are emitted from it, which, accelerated by the potential difference, bombard the anode. As a result of their interaction with the atoms of the anode (sometimes called the anticathode), X-ray photons are born.

Depending on what process leads to the birth of a photon, there are such types of X-ray radiation as bremsstrahlung and characteristic.

Electrons can, meeting with the anode, slow down, that is, lose energy in the electric fields of its atoms. This energy is emitted in the form of X-ray photons. Such radiation is called bremsstrahlung.

It is clear that the braking conditions will differ for individual electrons. This means that X-rays are converted into different quantities their kinetic energy. As a result, bremsstrahlung includes photons of different frequencies and, accordingly, wavelengths. Therefore, its spectrum is continuous (continuous). Sometimes for this reason it is also called "white" X-rays.

The energy of the bremsstrahlung photon cannot exceed the kinetic energy of the electron that generates it, so that the maximum frequency (and smallest wavelength) of bremsstrahlung corresponds to highest value kinetic energy of electrons incident on the anode. The latter depends on the potential difference applied to the electrodes.

There is another type of X-ray that comes from a different process. This radiation is called characteristic, and we will dwell on it in more detail.

How characteristic X-rays are produced

Having reached the anticathode, a fast electron can penetrate inside the atom and knock out any electron from one of the lower orbitals, that is, transfer to it energy sufficient to overcome the potential barrier. However, if there are higher energy levels occupied by electrons in the atom, the vacated place will not remain empty.

It must be remembered that the electronic structure of the atom, like any energy system, seeks to minimize energy. The vacancy formed as a result of the knockout is filled with an electron from one of the higher levels. Its energy is higher, and, occupying a lower level, it radiates a surplus in the form of a quantum of characteristic X-ray radiation.

The electronic structure of an atom is a discrete set of possible energy states of electrons. Therefore, X-ray photons emitted during the replacement of electron vacancies can also have only strictly defined energy values, reflecting the level difference. As a result, the characteristic X-ray radiation has a spectrum not of a continuous, but of a line type. Such a spectrum makes it possible to characterize the substance of the anode - hence the name of these rays. It is precisely because of the spectral differences that it is clear what is meant by bremsstrahlung and characteristic X-rays.

Sometimes the excess energy is not emitted by the atom, but is spent on knocking out the third electron. This process - the so-called Auger effect - is more likely to occur when the electron binding energy does not exceed 1 keV. The energy of the released Auger electron depends on the structure of the energy levels of the atom, so the spectra of such electrons are also discrete.

General view of the characteristic spectrum

Narrow characteristic lines are present in the X-ray spectral pattern along with a continuous bremsstrahlung spectrum. If we represent the spectrum as a plot of intensity versus wavelength (frequency), we will see sharp peaks at the locations of the lines. Their position depends on the anode material. These maxima are present at any potential difference - if there are X-rays, there are always peaks too. With increasing voltage at the electrodes of the tube, the intensity of both continuous and characteristic X-ray radiation increases, but the location of the peaks and the ratio of their intensities does not change.

The peaks in the X-ray spectra have the same shape regardless of the material of the anti-cathode irradiated by electrons, but for different materials they are located at different frequencies, uniting in series according to the proximity of the frequency values. Between the series themselves, the difference in frequencies is much more significant. The shape of the maxima does not depend in any way on whether the anode material represents a pure chemical element or whether it is a complex substance. In the latter case, the characteristic X-ray spectra of its constituent elements are simply superimposed on each other.

With increasing serial number chemical element all lines of its x-ray spectrum are shifted towards higher frequency. The spectrum retains its form.

Moseley's law

The phenomenon of spectral shift of characteristic lines was experimentally discovered by the English physicist Henry Moseley in 1913. This allowed him to associate the frequencies of the maxima of the spectrum with the ordinal numbers of the chemical elements. Thus, the wavelength of the characteristic X-ray radiation, as it turned out, can be clearly correlated with a specific element. IN general view Moseley's law can be written as follows: √f = (Z - S n)/n√R, where f is the frequency, Z is the ordinal number of the element, S n is the screening constant, n is the principal quantum number and R is the Rydberg constant. This relationship is linear and appears on the Moseley diagram as a series of straight lines for each value of n.

The values of n correspond to individual series of characteristic X-ray peaks. Moseley's law allows one to determine the serial number of a chemical element irradiated by hard electrons from the measured wavelengths (they are uniquely related to the frequencies) of the X-ray spectrum maxima.

The structure of the electron shells of chemical elements is identical. This is indicated by the monotonicity of the shift change in the characteristic spectrum of X-ray radiation. The frequency shift reflects not structural, but energy differences between electron shells, unique for each element.

The role of Moseley's law in atomic physics

There are slight deviations from the strict linear dependence expressed by Moseley's law. They are connected, firstly, with the peculiarities of the filling order of the electron shells in some elements, and, secondly, with the relativistic effects of the motion of electrons in heavy atoms. In addition, when the number of neutrons in the nucleus changes (the so-called isotopic shift), the position of the lines can change slightly. This effect made it possible to study the atomic structure in detail.

The significance of Moseley's law is extremely great. Sequentially applying it to elements periodic system Mendeleev established a pattern of increasing the serial number according to each small shift in the characteristic maxima. This helped clarify the issue of physical sense the ordinal number of the elements. The Z value is not just a number: it is the positive electric charge of the nucleus, which is the sum of the unit positive charges of the particles that make up it. The correct placement of elements in the table and the presence of empty positions in it (then they still existed) received powerful confirmation. The validity of the periodic law was proved.

Moseley's law, in addition, became the basis on which a whole direction arose experimental studies- X-ray spectrometry.

The structure of the electron shells of the atom

Let us briefly recall how the electronic structure is arranged. It consists of shells, denoted by the letters K, L, M, N, O, P, Q, or numbers from 1 to 7. Electrons within the shell are characterized by the same main quantum number n, which determines the possible energy values. In outer shells, the energy of electrons is higher, and the ionization potential for outer electrons is correspondingly lower.

The shell includes one or more sublevels: s, p, d, f, g, h, i. In each shell, the number of sublevels increases by one compared to the previous one. The number of electrons in each sublevel and in each shell cannot exceed a certain value. They are characterized, in addition to the main quantum number, by the same value of the orbital electron cloud that determines the shape. Sublevels are labeled with the shell they belong to, such as 2s, 4d, and so on.

The sublevel contains which are set, in addition to the main and orbital, by one more quantum number - magnetic, which determines the projection of the electron's orbital momentum onto the direction of the magnetic field. One orbital can have no more than two electrons, differing in the value of the fourth quantum number - spin.

Let us consider in more detail how characteristic X-ray radiation arises. Since the origin of this type of electromagnetic emission is associated with phenomena occurring inside the atom, it is most convenient to describe it precisely in the approximation of electronic configurations.

The mechanism of generation of characteristic X-rays

So, the cause of this radiation is the formation of electron vacancies in the inner shells, due to the penetration of high-energy electrons deep into the atom. The probability that a hard electron will interact increases with the density of the electron clouds. Therefore, collisions are most likely within densely packed inner shells, such as the lowest K-shell. Here the atom is ionized, and a vacancy is formed in the 1s shell.

This vacancy is filled by an electron from the shell with a higher energy, the excess of which is carried away by the X-ray photon. This electron can "fall" from the second shell L, from the third shell M and so on. This is how the characteristic series is formed, in this example, the K-series. An indication of where the electron filling the vacancy comes from is given in the form of a Greek index when designating the series. "Alpha" means that it comes from the L-shell, "beta" - from the M-shell. At present, there is a tendency to replace the Greek letter indices with the Latin ones adopted to designate shells.

The intensity of the alpha line in the series is always the highest, which means that the probability of filling a vacancy from a neighboring shell is the highest.

Now we can answer the question, what is the maximum energy of the characteristic x-ray quantum. It is determined by the difference in the energy values of the levels between which the electron transition occurs, according to the formula E \u003d E n 2 - E n 1, where E n 2 and E n 1 are the energies of the electronic states between which the transition occurred. The highest value of this parameter is given by K-series transitions with maximum high levels atoms heavy elements. But the intensity of these lines (peak heights) is the smallest, since they are the least likely.

If, due to insufficient voltage on the electrodes, a hard electron cannot reach the K-level, it forms a vacancy at the L-level, and a less energetic L-series with longer wavelengths is formed. Subsequent series are born in a similar way.

In addition, when a vacancy is filled, a new vacancy appears in the overlying shell as a result of an electronic transition. This creates the conditions for generating the next series. Electronic vacancies move higher from level to level, and the atom emits a cascade of characteristic spectral series, while remaining ionized.

Fine structure of characteristic spectra

Atomic X-ray spectra of characteristic X-ray radiation are characterized by a fine structure, which is expressed, as in optical spectra, in line splitting.

The fine structure is due to the fact that the energy level - the electron shell - is a set of closely spaced components - subshells. To characterize the subshells, one more, internal quantum number j is introduced, which reflects the interaction of the intrinsic and orbital magnetic moments of the electron.

In connection with the influence of the spin-orbit interaction energy structure the atom becomes more complex, and as a result, the characteristic X-ray radiation has a spectrum, which is characterized by split lines with very closely spaced elements.

Fine structure elements are usually denoted by additional digital indices.

The characteristic X-ray radiation has a feature that is reflected only in the fine structure of the spectrum. The transition of an electron to the lowest energy level does not occur from the lower subshell of the overlying level. Such an event has a negligible probability.

The use of X-rays in spectrometry

This radiation, due to its features described by Moseley's law, underlies various X-ray spectral methods for the analysis of substances. When analyzing the X-ray spectrum, either diffraction of radiation by crystals (wave-dispersive method) or detectors sensitive to the energy of absorbed X-ray photons (energy-dispersive method) are used. Majority electron microscopes equipped with some kind of X-ray spectrometry attachments.

Wave-dispersive spectrometry is characterized by especially high accuracy. With the help of special filters, the most intense peaks in the spectrum are selected, thanks to which it is possible to obtain almost monochromatic radiation with a precisely known frequency. The anode material is chosen very carefully to ensure that a monochromatic beam of the desired frequency is obtained. Its diffraction on the crystal lattice of the studied substance makes it possible to study the structure of the lattice with great accuracy. This method is also used in the study of DNA and other complex molecules.

One of the features of the characteristic X-ray radiation is also taken into account in gamma spectrometry. This is the high intensity of the characteristic peaks. Gamma spectrometers use lead shielding against external background radiation that interferes with measurements. But lead, absorbing gamma quanta, experiences internal ionization, as a result of which it actively emits in the X-ray range. Additional cadmium shielding is used to absorb the intense peaks of the characteristic x-ray radiation from lead. It, in turn, is ionized and also emits X-rays. To neutralize the characteristic peaks of cadmium, a third shielding layer is used - copper, the X-ray maxima of which lie outside the operating frequency range of the gamma spectrometer.

Spectrometry uses both bremsstrahlung and characteristic X-rays. Thus, in the analysis of substances, the absorption spectra of continuous X-rays by various substances are studied.

a brief description of x-ray radiation

X-rays are electromagnetic waves (flux of quanta, photons), the energy of which is located on the energy scale between ultraviolet radiation and gamma radiation (Fig. 2-1). X-ray photons have energies from 100 eV to 250 keV, which corresponds to radiation with a frequency of 3×10 16 Hz to 6×10 19 Hz and a wavelength of 0.005–10 nm. The electromagnetic spectra of x-rays and gamma rays overlap to a large extent.

Rice. 2-1. Electromagnetic radiation scale

The main difference between these two types of radiation is the way they occur. X-rays are obtained with the participation of electrons (for example, during the deceleration of their flow), and gamma rays - with the radioactive decay of the nuclei of some elements.

X-rays can be generated during deceleration of an accelerated stream of charged particles (the so-called bremsstrahlung) or when high-energy transitions occur in the electron shells of atoms (characteristic radiation). Medical devices use X-ray tubes to generate X-rays (Figure 2-2). Their main components are a cathode and a massive anode. The electrons emitted due to the difference in electrical potential between the anode and the cathode are accelerated, reach the anode, upon collision with the material of which they are decelerated. As a result, bremsstrahlung X-rays are produced. During the collision of electrons with the anode, the second process also occurs - electrons are knocked out of the electron shells of the anode atoms. Their places are occupied by electrons from other shells of the atom. During this process, a second type of X-ray radiation is generated - the so-called characteristic X-ray radiation, the spectrum of which largely depends on the anode material. Anodes are most often made of molybdenum or tungsten. There are special devices for focusing and filtering X-rays in order to improve the resulting images.

Rice. 2-2. Scheme of the X-ray tube device:

The properties of X-rays that determine their use in medicine are penetrating power, fluorescent and photochemical effects. Penetrating power of X-rays and their absorption by tissues human body and artificial materials are the most important properties that determine their use in radiation diagnostics. The shorter the wavelength, the greater the penetrating power of X-rays.

There are "soft" X-rays with low energy and radiation frequency (respectively, with the largest wavelength) and "hard" X-rays with high photon energy and radiation frequency, which have a short wavelength. The wavelength of X-ray radiation (respectively, its "hardness" and penetrating power) depends on the magnitude of the voltage applied to the X-ray tube. The higher the voltage on the tube, the greater the speed and energy of the electron flow and the shorter the wavelength of the x-rays.

During the interaction of X-ray radiation penetrating through the substance, qualitative and quantitative changes occur in it. The degree of absorption of X-rays by tissues is different and is determined by the density and atomic weight of the elements that make up the object. The higher the density and atomic weight of the substance of which the object (organ) under study consists, the more X-rays are absorbed. The human body contains tissues and organs of different densities (lungs, bones, soft tissues, etc.), which explains the different absorption of X-rays. The visualization of internal organs and structures is based on the artificial or natural difference in the absorption of X-rays by various organs and tissues.

To register the radiation that has passed through the body, its ability to cause fluorescence of certain compounds and to have a photochemical effect on the film is used. For this purpose, special screens for fluoroscopy and photographic films for radiography are used. In modern X-ray machines, special systems of digital electronic detectors - digital electronic panels - are used to register attenuated radiation. In this case, X-ray methods are called digital.

Due to the biological effect of X-rays, it is necessary to protect patients during the examination. This is achieved

the shortest possible exposure time, the replacement of fluoroscopy with radiography, the strictly justified use of ionizing methods, protection by shielding the patient and staff from exposure to radiation.

LECTURE 32 X-RAY RADIATION

1. X-ray sources.

2. Bremsstrahlung X-rays.

3. Characteristic x-ray radiation. Moseley's law.

4. Interaction of X-ray radiation with matter. The law of weakening.

5. Physical foundations use of x-rays in medicine.

6. Basic concepts and formulas.

7. Tasks.

X-ray radiation - electromagnetic waves with a wavelength from 100 to 10 -3 nm. On the scale of electromagnetic waves, X-ray radiation occupies the region between UV radiation and γ -radiation. X-rays (X-rays) were discovered in 1895 by K. Roentgen, who in 1901 became the first Nobel Laureate in physics.

32.1. X-ray sources

Natural sources of X-rays are some radioactive isotopes (for example, 55 Fe). Artificial sources of powerful X-rays are x-ray tubes(Fig. 32.1).

Rice. 32.1. X-ray tube device

The X-ray tube is an evacuated glass flask with two electrodes: the anode A and the cathode K, between which a high voltage U (1-500 kV) is created. The cathode is a coil heated by electric current. Electrons emitted by a heated cathode (thermionic emission) are accelerated by an electric field to big speeds (for this you need high voltage) and fall on the anode of the tube. When these electrons interact with the anode material, two types of X-ray radiation arise: brake And characteristic.

The working surface of the anode is located at some angle to the direction of the electron beam in order to create the desired direction of the x-rays.

Approximately 1% of the kinetic energy of electrons is converted into X-rays. The rest of the energy is released as heat. Therefore, the working surface of the anode is made of a refractory material.

32.2. Bremsstrahlung X-ray

An electron moving in some medium loses its speed. This creates a negative acceleration. According to Maxwell's theory, any accelerated the movement of a charged particle is accompanied by electromagnetic radiation. The radiation that occurs when an electron decelerates in the anode material is called bremsstrahlung X-rays.

The properties of bremsstrahlung are determined by the following factors.

1. Radiation is emitted by individual quanta, the energies of which are related to the frequency by the formula (26.10)

where ν is the frequency, λ is the wavelength.

2. All electrons reaching the anode have the same kinetic energy equal to work electric field between anode and cathode:

where e is the electron charge, U is the accelerating voltage.

3. The kinetic energy of an electron is partially transferred to the substance and goes to heat it (Q), and is partially spent on the creation of an X-ray quantum:

4. Relationship between Q and hv accidentally.

Due to the last property (4), the quanta generated by various electrons, have various frequencies and wavelengths. Therefore, the bremsstrahlung spectrum is solid. typical view spectral density the X-ray flux (Φ λ = άΦ/άλ) is shown in fig. 32.2.

Rice. 32.2. Bremsstrahlung spectrum

From the side of long waves, the spectrum is limited by a wavelength of 100 nm, which is the boundary of X-ray radiation. From the side of short waves, the spectrum is limited by the wavelength λ min . According to formula (32.2) minimum wavelength corresponds to the case Q = 0 (the kinetic energy of the electron is completely converted into the energy of the quantum):

Calculations show that the bremsstrahlung flux (Φ) is directly proportional to the square of the voltage U between

anode and cathode, current I in the tube and atomic number Z of the anode substance:

The X-ray bremsstrahlung spectra at various voltages, various cathode temperatures, and various anode materials are shown in Figs. 32.3.

Rice. 32.3. Bremsstrahlung spectrum (Φ λ):

a - at different voltages U in the tube; b - at different temperatures T

cathode; c - with different anode substances differing in parameter Z

With an increase in the anode voltage, the value λmin shifts towards shorter wavelengths. At the same time, the height of the spectral curve also increases (Fig. 32.3, A).

As the cathode temperature increases, the electron emission increases. Correspondingly, the current I in the tube also increases. The height of the spectral curve increases, but the spectral composition of the radiation does not change (Fig. 32.3, b).

When the anode material changes, the height of the spectral curve changes in proportion to the atomic number Z (Fig. 32.3, c).

32.3. Characteristic x-ray radiation. Moseley's law

When cathode electrons interact with anode atoms, along with X-ray bremsstrahlung, X-ray radiation arises, the spectrum of which consists of individual lines. This radiation

has the following origin. Some cathodic electrons penetrate deep into the atom and knock electrons out of it. inner shells. The vacancies thus formed are filled with electrons with top shells, resulting in the emission of radiation quanta. This radiation contains a discrete set of frequencies determined by the anode material and is called characteristic radiation. The full spectrum of an x-ray tube is a superposition of the characteristic spectrum on the bremsstrahlung spectrum (Fig. 32.4).

Rice. 32.4. X-ray tube emission spectrum

The existence of characteristic X-ray spectra has been discovered using X-ray tubes. Later it was found that such spectra arise during any ionization of the inner orbits of chemical elements. Having studied the characteristic spectra of various chemical elements, G. Moseley (1913) established the following law, which bears his name.

The square root of the characteristic radiation frequency is linear function element's serial number:

where ν is the frequency of the spectral line, Z is the atomic number of the emitting element, A, B are constants.

Moseley's law makes it possible to determine the atomic number of a chemical element from the observed spectrum of characteristic radiation. This played a big role in the placement of elements in the periodic system.

32.4. Interaction of X-ray radiation with matter. law of weakening

There are two main types of interaction of X-ray radiation with matter: scattering and photoelectric effect. When scattered, the direction of motion of a photon changes. In the photoelectric effect, a photon absorbed.

1. Coherent (elastic) scattering occurs when the energy of an X-ray photon is insufficient for the internal ionization of an atom (knocking out an electron from one of the inner shells). In this case, the direction of motion of the photon changes, and its energy and wavelength do not change (therefore, this scattering is called elastic).

2. Incoherent (Compton) scattering occurs when the photon energy is much greater than the internal ionization energy A u: hv >> A u.

In this case, the electron breaks away from the atom and acquires some kinetic energy E k. The direction of the photon during Compton scattering changes, and its energy decreases:

Compton scattering is associated with the ionization of the atoms of matter.

3. photoelectric effect occurs when the photon energy hv is sufficient to ionize the atom: hv > A u. At the same time, the X-ray quantum absorbed and its energy is spent on the ionization of the atom and the communication of kinetic energy to the ejected electron E k \u003d hv - AI.

Compton scattering and the photoelectric effect are accompanied by characteristic X-ray radiation, since after the knocking out of internal electrons, the vacancies are filled with electrons from the outer shells.

X-ray luminescence. In some substances, electrons and quanta of Compton scattering, as well as photoelectric effect electrons, cause excitation of molecules, which is accompanied by radiative transitions to the ground state. This produces a glow called X-ray luminescence. The luminescence of barium platinum-cyanogen allowed X-rays to be discovered by Roentgen.

law of weakening

The scattering of X-rays and the photoelectric effect lead to the fact that as the X-ray radiation penetrates deep into the primary beam of radiation is weakened (Fig. 32.5). The easing is exponential:

The value of μ depends on the absorbing material and the radiation spectrum. For practical calculations, as a characteristic of the weakened

Rice. 32.5. Attenuation of the X-ray flux in the direction of the incident rays

Where λ - wavelength; Z is the atomic number of the element; k is some constant.

32.5. Physical bases of use

x-ray radiation in medicine

In medicine, X-rays are used for diagnostic and therapeutic purposes.

X-ray diagnostics- Methods for obtaining images of internal organs using x-rays.

The physical basis of these methods is the law of X-ray attenuation in matter (32.10). Cross-sectional uniform X-ray flux after passing through inhomogeneous tissue will become inhomogeneous. This inhomogeneity can be recorded on photographic film, a fluorescent screen, or using a matrix photodetector. For example, the mass weakening coefficients of bone tissue - Ca 3 (PO 4) 2 - and soft tissues - mainly H 2 O - differ by 68 times (μ m bone /μ m water = 68). Bone density is also higher than soft tissue density. Therefore, an x-ray image produces a light image of the bone against a darker background of soft tissues.

If the organ under study and the tissues surrounding it have similar attenuation coefficients, then special contrast agents. So, for example, during fluoroscopy of the stomach, the subject takes a mushy mass of barium sulfate (BaSO 4), in which the mass attenuation coefficient is 354 times greater than that of soft tissues.

For diagnostics, X-ray radiation with a photon energy of 60-120 keV is used. In medical practice, the following methods of X-ray diagnostics are used.

1. X-ray. The image is formed on a fluorescent screen. The image brightness is low and can only be viewed in a darkened room. The physician must be protected from exposure.

The advantage of fluoroscopy is that it is carried out in real time. The disadvantage is a large radiation load on the patient and the doctor (compared to other methods).

The modern version of fluoroscopy - X-ray television - uses X-ray image intensifiers. The amplifier perceives the weak glow of the X-ray screen, amplifies it and transmits it to the TV screen. As a result, the radiation load on the doctor has sharply decreased, the brightness of the image has increased, and it has become possible to record the results of the examination on video.

2. Radiography. The image is formed on a special film that is sensitive to x-rays. Pictures are taken in two mutually perpendicular projections (direct and lateral). The image becomes visible after photo processing. The finished dried image is viewed in transmitted light.

At the same time, details are satisfactorily visible, the contrast of which differs by 1-2%.

In some cases, before the examination, the patient is given a special contrast agent. For example, an iodine-containing solution (intravenously) in the study of the kidneys and urinary tract.

The advantages of radiography are a high resolution, short exposure time and almost complete safety for the doctor. The disadvantages include the static image (the object cannot be traced in dynamics).

3. Fluorography. In this examination, the image obtained on the screen is photographed on a sensitive small format film. Fluorography is widely used in the mass survey of the population. If pathological changes are found on the fluorogram, then the patient is prescribed a more detailed examination.

4. Electroroentgenography. This type of examination differs from conventional radiography in the way the image is captured. Use instead of film selenium plate, electrified by X-rays. The result is a latent image of electrical charges that can be made visible and transferred to paper.

5. Angiography. This method is used in the examination of blood vessels. A contrast agent is injected into the vein through a catheter, after which a powerful x-ray machine takes a series of images following each other in a fraction of a second. Figure 32.6 shows an angiogram in the region of the carotid artery.

6. X-ray computed tomography. This type of X-ray examination allows you to get an image of a flat section of the body with a thickness of several mm. In this case, the given cross section is repeatedly illuminated under different angles with the fixation of each individual image in the computer's memory. Then

Rice. 32.6. Angiogram showing a narrowing in the canal of the carotid artery

Rice. 32.7. Scanning scheme of tomography (a); tomogram of the head in cross section at eye level (b).

computer reconstruction is carried out, the result of which is the image of the scanned layer (Fig. 32.7).

Computed tomography makes it possible to distinguish elements with a density difference between them up to 1%. Conventional radiography allows you to capture a minimum difference in density between adjacent areas of 10-20%.

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

The biological effect of radiation is to disrupt the vital activity of especially rapidly multiplying cells. Very hard X-rays (with a photon energy of approximately 10 MeV) are used to destroy cancer cells deep within the body. To reduce damage to healthy surrounding tissues, the beam rotates around the patient in such a way that only the damaged area remains under its influence at all times.

32.6. Basic concepts and formulas

Table continuation

End of table

32.7. Tasks

1. Why does an electron beam in medical X-ray tubes strike one point of the anticathode, and does not fall on it in a wide beam?

Answer: to obtain a point source of x-rays, giving a sharp outline of translucent objects on the screen.

2. Find the boundary of bremsstrahlung X-rays (frequency and wavelength) for voltages U 1 = 2 kV and U 2 = 20 kV.

4. Lead screens are used to protect against x-rays. The linear absorption of X-rays in lead is 52 cm -1 . What should be the thickness of the shielding layer of lead in order for it to reduce the X-ray intensity by 30 times?

5. Find the X-ray tube radiation flux at U = 50 kV, I = 1 mA. The anode is made of tungsten (Z = 74). Find the efficiency of the tube.

6. For X-ray diagnostics of soft tissues, contrast agents are used. For example, the stomach and intestines are filled with a mass of barium sulfate (BaSO 4 ). Compare the mass attenuation coefficients of barium sulfate and soft tissues (water).

7. What will give a thicker shadow on the X-ray screen: aluminum (Z = 13, ρ = 2.7 g/cm 3) or the same layer of copper (Z = 29, ρ = 8.9 g/cm 3)?

8. How many times is the thickness of the aluminum layer greater than the thickness of the copper layer, if the layers attenuate x-rays in the same way?

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

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

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

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

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

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

Discovery history

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

Later it turned out that X-ray radiation had been observed before, but then the phenomena associated with it were not given of great importance. The cathode ray tube was invented a long time ago, but before V.K. No one took X-rays special attention on 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 use of X-rays is fluoroscopy. "Silence" 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 is almost twice as heavy as the oxygen atom, and the calcium atom is 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 identify small internal defects in products. Hard x-rays are used for it, since many materials (metal, for example) are poorly “translucent” due to the high atomic mass of their constituent substance.

X-ray diffraction and X-ray fluorescence analysis

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

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

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

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

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

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

During pregnancy

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

When 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.