x-ray radiation- a type of high-energy electromagnetic radiation. It is actively used in various branches of medicine.
X-rays are electromagnetic waves, whose photon energy on the scale of electromagnetic waves is between ultraviolet radiation and gamma radiation (from ~10 eV to ~1 MeV), which corresponds to wavelengths from ~10^3 to ~10^−2 angstroms (from ~10^−7 up to ~10^−12 m). That is, it is incomparably harder radiation than visible light, which is on this scale between ultraviolet and infrared (“thermal”) rays.
The boundary between X-rays and gamma radiation is distinguished conditionally: their ranges intersect, gamma rays can have an energy of 1 keV. They differ in origin: gamma rays are emitted during processes occurring in atomic nuclei, while X-rays are emitted during processes involving electrons (both free and those in the electron shells of atoms). At the same time, it is impossible to determine from the photon itself during which process it arose, that is, the division into the X-ray and gamma ranges is largely arbitrary.
The X-ray range is divided into “soft X-ray” and “hard”. The boundary between them lies at the wavelength level of 2 angstroms and 6 keV of energy.
The X-ray generator is a tube in which a vacuum is created. There are electrodes - a cathode, to which a negative charge is applied, and a positively charged anode. The voltage between them is tens to hundreds of kilovolts. The generation of X-ray photons occurs when electrons “break off” from the cathode and crash into the anode surface at high speed. The resulting X-ray radiation is called “bremsstrahlung”, its photons have different wavelengths.
At the same time, photons of the characteristic spectrum are generated. Part of the electrons in the atoms of the anode substance is excited, that is, it goes to higher orbits, and then returns to its normal state, emitting photons of a certain wavelength. Both types of X-rays are produced in a standard generator.
Discovery history
On November 8, 1895, the German scientist Wilhelm Konrad Roentgen discovered that some substances, under the influence of "cathode rays", that is, the flow of electrons generated by a cathode ray tube, begin to glow. He explained this phenomenon by the influence of certain X-rays - so (“X-rays”) this radiation is now called in many languages. Later V.K. Roentgen studied the phenomenon he had discovered. On December 22, 1895, he gave a lecture on this topic at the University of Würzburg.
Later it turned out that X-ray radiation had been observed before, but then the phenomena associated with it were not given much importance. The cathode ray tube was invented a long time ago, but before V.K. X-ray, no one paid much attention to the blackening of photographic plates near it, etc. phenomena. The danger posed by penetrating radiation was also unknown.
Types and their effect on the body
“X-ray” is the mildest type of penetrating radiation. Overexposure to soft x-rays is similar to ultraviolet exposure, but in a more severe form. A burn forms on the skin, but the lesion is deeper, and it heals much more slowly.
Hard X-ray is a full-fledged ionizing radiation that can lead to radiation sickness. X-ray quanta can break the protein molecules that make up the tissues of the human body, as well as the DNA molecules of the genome. But even if an X-ray quantum breaks a water molecule, it doesn't matter: in this case, chemically active free radicals H and OH are formed, which themselves are able to act on proteins and DNA. Radiation sickness proceeds in a more severe form, the more the hematopoietic organs are affected.
X-rays have mutagenic and carcinogenic activity. This means that the probability of spontaneous mutations in cells during irradiation increases, and sometimes healthy cells can degenerate into cancerous ones. Increasing the likelihood of malignant tumors is a standard consequence of any exposure, including x-rays. X-ray is the least dangerous view penetrating radiation, but it can still be dangerous.
X-ray radiation: application and how it works
X-ray radiation is used in medicine, as well as in other areas of human activity.
Fluoroscopy and computed tomography
The most common application of X-rays is fluoroscopy. "Transillumination" of the human body allows you to get a detailed image of both bones (they are most clearly visible) and images internal organs.
Different transparency of body tissues in x-rays is associated with their chemical composition. Features of the structure of bones is that they contain a lot of calcium and phosphorus. Other tissues are composed mainly of carbon, hydrogen, oxygen and nitrogen. The phosphorus atom exceeds the weight of the oxygen atom almost twice, and the calcium atom - 2.5 times (carbon, nitrogen and hydrogen are even lighter than oxygen). In this regard, the absorption of X-ray photons in the bones is much higher.
In addition to two-dimensional “pictures”, radiography makes it possible to create a three-dimensional image of an organ: this type of radiography is called computed tomography. For these purposes, soft x-rays are used. The amount of exposure received in a single image is small: it is approximately equal to the exposure received during a 2-hour flight in an airplane at an altitude of 10 km.
X-ray flaw detection allows you to detect small internal defects in products. Hard x-rays are used for it, since many materials (metal, for example) are poorly “translucent” due to the high atomic mass of their constituent substance.
X-ray diffraction and X-ray fluorescence analysis
X-rays have properties that allow them to examine individual atoms in detail. X-ray diffraction analysis is actively used in chemistry (including biochemistry) and crystallography. The principle of its operation is the diffraction scattering of X-rays by atoms of crystals or complex molecules. Using X-ray diffraction analysis, the structure of the DNA molecule was determined.
X-ray fluorescence analysis allows you to quickly determine chemical composition substances.
There are many forms of radiotherapy, but they all involve the use of ionizing radiation. Radiotherapy is divided into 2 types: corpuscular and wave. Corpuscular uses flows of alpha particles (nuclei of helium atoms), beta particles (electrons), neutrons, protons, heavy ions. Wave uses rays of the electromagnetic spectrum - x-rays and gamma.
Radiotherapy methods are used primarily for the treatment of oncological diseases. The fact is that radiation primarily affects actively dividing cells, which is why the hematopoietic organs suffer this way (their cells are constantly dividing, producing more and more new red blood cells). Cancer cells are also constantly dividing and are more vulnerable to radiation than healthy tissue.
A level of radiation is used that suppresses the activity of cancer cells, while moderately affecting healthy ones. Under the influence of radiation, it is not the destruction of cells as such, but the damage to their genome - DNA molecules. A cell with a destroyed genome may exist for some time, but can no longer divide, that is, tumor growth stops.
Radiation therapy is the mildest form of radiotherapy. Wave radiation is softer than corpuscular radiation, and X-rays are softer than gamma radiation.
During pregnancy
It is dangerous to use ionizing radiation during pregnancy. X-rays are mutagenic and can cause abnormalities in the fetus. X-ray therapy is incompatible with pregnancy: it can only be used if it has already been decided to have an abortion. Restrictions on fluoroscopy are softer, but in the first months it is also strictly prohibited.
In case of emergency, X-ray examination is replaced by magnetic resonance imaging. But in the first trimester they try to avoid it too (this method has appeared recently, and with absolute certainty to speak about the absence of harmful consequences).
An unequivocal danger arises when exposed to a total dose of at least 1 mSv (in old units - 100 mR). With a simple x-ray (for example, when undergoing fluorography), the patient receives about 50 times less. In order to receive such a dose at a time, you need to undergo a detailed computed tomography.
That is, the mere fact of a 1-2-fold “X-ray” at an early stage of pregnancy does not threaten with serious consequences (but it’s better not to risk it).
Treatment with it
X-rays are used primarily in the fight against malignant tumors. This method is good because it is highly effective: it kills the tumor. It is bad because healthy tissues are not much better, there are numerous side effects. The organs of hematopoiesis are at particular risk.
In practice, various methods are used to reduce the effect of x-rays on healthy tissues. The beams are directed at an angle in such a way that a tumor appears in the zone of their intersection (due to this, the main absorption of energy occurs just there). Sometimes the procedure is performed in motion: the patient's body rotates relative to the radiation source around an axis passing through the tumor. At the same time, healthy tissues are in the irradiation zone only sometimes, and the sick - all the time.
X-rays are used in the treatment of certain arthrosis and similar diseases, as well as skin diseases. In this case, the pain syndrome is reduced by 50-90%. Since the radiation used is softer, side effects, similar to those that occur in the treatment of tumors, is not observed.
FEDERAL AGENCY FOR EDUCATION OF THE RUSSIAN FEDERATION
STATE EDUCATIONAL INSTITUTION
HIGHER PROFESSIONAL EDUCATION
MOSCOW STATE INSTITUTE OF STEEL AND ALLOYS
(UNIVERSITY OF TECHNOLOGY)
NOVOTROITSKY BRANCH
Department of OEND
COURSE WORK
Discipline: Physics
Topic: X-RAY
Student: Nedorezova N.A.
Group: EiU-2004-25, No. З.К.: 04Н036
Checked by: Ozhegova S.M.
Introduction
Chapter 1
1.1 Biography of Roentgen Wilhelm Conrad
1.2 Discovery of X-rays
Chapter 2
2.1 X-ray sources
2.2 Properties of X-rays
2.3 Registration of X-rays
2.4 Use of X-rays
Chapter 3
3.1 Analysis of crystal structure imperfections
3.2 Spectrum analysis
Conclusion
List of sources used
Applications
Introduction
A rare person has not gone through an x-ray room. Pictures taken in x-rays are familiar to everyone. In 1995, this discovery was 100 years old. It is hard to imagine what great interest it aroused a century ago. In the hands of a man turned out to be an apparatus with which it was possible to see the invisible.
This invisible radiation, capable of penetrating, albeit to varying degrees, into all substances, which is electromagnetic radiation with a wavelength of about 10 -8 cm, was called X-ray radiation, in honor of Wilhelm Roentgen, who discovered it.
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 less 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, in chemistry to analyze compounds, and in physics to study the structure of crystals.
Roentgen's discovery was followed by experiments by other researchers who discovered many new properties and possibilities for using this radiation. A major contribution was made by M. Laue, W. Friedrich, and P. Knipping, who in 1912 demonstrated the diffraction of X-rays as they pass 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.
This term paper is to study the phenomenon of x-ray radiation, the history of discovery, properties and identify the scope of its application.
Chapter 1
1.1 Biography of Roentgen Wilhelm Conrad
Wilhelm Conrad Roentgen was born on March 17, 1845 in the border region of Germany with Holland, in the city of Lenepe. He received his technical education in Zurich at the same Higher Technical School (Polytechnic) where Einstein later studied. Passion for physics forced him after leaving school in 1866 to continue physical education.
In 1868 he defended his dissertation for the degree of Doctor of Philosophy, he worked as an assistant at the Department of Physics, first in Zurich, then in Giessen, and then in Strasbourg (1874-1879) with Kundt. Here Roentgen went through a good experimental school and became a first-class experimenter. Roentgen performed part of the important research with his student, one of the founders of Soviet physics, A.F. Ioffe.
Scientific research relates to electromagnetism, crystal physics, optics, molecular physics.
In 1895, he discovered radiation with a wavelength shorter than the wavelength of ultraviolet rays (X-rays), later called x-rays, and investigated their properties: the ability to reflect, absorb, ionize air, etc. He proposed the correct design of the tube for obtaining X-rays - an inclined platinum anticathode and a concave cathode: he was the first to take photographs using X-rays. Discovered in 1885 the magnetic field of a dielectric moving in electric field(the so-called "X-ray current"). His experience clearly showed that the magnetic field is created by moving charges, and was important for the creation of X. Lorentz electronic theory. A significant number of Roentgen's works are devoted to the study of the properties of liquids, gases, crystals, electromagnetic phenomena, discovered the relationship of electrical and optical phenomena in crystals For the discovery of the rays that bear his name, Roentgen in 1901 was the first among physicists to be awarded the Nobel Prize.
From 1900 until the last days of his life (he died on February 10, 1923) he worked at the University of Munich.
1.2 Discovery of X-rays
End of the 19th century was marked by increased interest in the phenomena of the passage of electricity through gases. Even Faraday seriously studied these phenomena, described various forms of discharge, discovered a dark space in a luminous column of rarefied gas. Faraday dark space separates the bluish, cathode glow from the pinkish, anode glow.
A further increase in the rarefaction of the gas significantly changes the nature of the glow. The mathematician Plücker (1801-1868) discovered in 1859, at sufficiently strong rarefaction, a weakly bluish beam of rays emanating from the cathode, reaching the anode and causing the glass of the tube to glow. Plücker's student Gittorf (1824-1914) in 1869 continued his teacher's research and showed that a distinct shadow appears on the fluorescent surface of the tube if a solid body is placed between the cathode and this surface.
Goldstein (1850-1931), studying the properties of rays, called them cathode rays (1876). Three years later, William Crookes (1832-1919) proved the material nature of cathode rays and called them "radiant matter" - a substance in a special fourth state. His evidence was convincing and clear. Experiments with the "Crookes tube" were demonstrated later in all physical classrooms . The deflection of the cathode beam by a magnetic field in a Crookes tube has become a classic school demonstration.
However, experiments on the electrical deflection of cathode rays were not so convincing. Hertz did not detect such a deviation and came to the conclusion that the cathode ray is an oscillatory process in the ether. Hertz's student F. Lenard, experimenting with cathode rays, showed in 1893 that they pass through a window covered with aluminum foil and cause a glow in the space behind the window. Hertz devoted his last article, published in 1892, to the phenomenon of the passage of cathode rays through thin metal bodies. It began with the words:
"Cathode rays differ from light in a significant way in terms of their ability to penetrate solids." Describing the results of experiments on the passage of cathode rays through gold, silver, platinum, aluminum, etc. leaves, Hertz notes that he did not observe any special differences in the phenomena The rays do not pass through the leaves in a straight line, but are scattered by diffraction.The nature of the cathode rays was still unclear.
It was with such tubes of Crookes, Lenard and others that the Würzburg professor Wilhelm Konrad Roentgen experimented at the end of 1895. Once, after the end of the experiment, he closed the tube with a black cardboard cover, turned off the light, but did not turn off the inductor that fed the tube, he noticed a glow of the screen from barium cyanogen located near the tube. Struck by this circumstance, Roentgen began to experiment with the screen. In his first report "On a new kind of rays", dated December 28, 1895, he wrote about these first experiments: "A piece of paper coated with barium platinum-cyanide, when approaching a tube, closed with a thin black cardboard cover that fits snugly enough to it, with each discharge it flashes with a bright light: it begins to fluoresce. Fluorescence is visible with sufficient darkening and does not depend on whether we bring the paper with the side coated with barium synerogen or not coated with barium synerogen. The fluorescence is noticeable even at a distance of two meters from the tube.”
Careful examination showed Roentgen "that black cardboard, transparent neither to the visible and ultraviolet rays of the sun, nor to the rays of an electric arc, is permeated with some kind of fluorescent agent." Roentgen investigated the penetrating power of this "agent", which he called for brevity "X-rays", for various substances. He found that the rays pass freely through paper, wood, ebonite, thin layers of metal, but are strongly delayed by lead.
He then describes the sensational experience:
“If you hold your hand between the discharge tube and the screen, you can see the dark shadows of the bones in the faint outlines of the shadow of the hand itself.” This was the first X-ray examination of the human body.
These shots made a huge impression; the discovery had not yet been completed, and X-ray diagnostics had already begun its journey. "My lab was flooded with doctors bringing in patients who suspected they had needles in their different parts body,” wrote the English physicist Schuster.
Already after the first experiments, Roentgen firmly established that X-rays differ from cathode ones, they do not carry a charge and are not deflected by a magnetic field, but they are excited by cathode rays. "X-rays are not identical with cathode rays, but they are excited by them in the glass walls of the discharge tube ”, wrote Roentgen.
He also established that they are excited not only in glass, but also in metals.
Mentioning the Hertz-Lenard hypothesis that cathode rays “are a phenomenon occurring in the ether,” Roentgen points out that “we can say something similar about our rays.” However, he failed to detect the wave properties of the rays, they "behave differently than hitherto known ultraviolet, visible, infrared rays." In their chemical and luminescent actions, they, according to Roentgen, are similar to ultraviolet rays. In the first message, he expressed the assumption left later that they can be longitudinal waves in the ether.
Roentgen's discovery aroused great interest in the scientific world. His experiments were repeated in almost all laboratories in the world. In Moscow they were repeated by P.N. Lebedev. In St. Petersburg, the inventor of radio A.S. Popov experimented with X-rays, demonstrated them at public lectures, receiving various X-rays. In Cambridge D.D. Thomson immediately applied the ionizing effect of X-rays to study the passage of electricity through gases. His research led to the discovery of the electron.
Chapter 2
X-ray radiation - electromagnetic ionizing radiation, occupying the spectral region between gamma and ultraviolet radiation within wavelengths from 10 -4 to 10 3 (from 10 -12 to 10 -5 cm).R. l. with wavelength λ< 2 условно называются жёсткими, с λ >2 - soft.
2.1 X-ray sources
The most common source of X-rays is the X-ray tube.
X-ray tubes are used in X-ray structural analysis
The main characteristics of X-ray tubes are the maximum permissible accelerating voltage (1-500 kV), electronic current (0.01 mA - 1A), specific power dissipated by the anode (10-10 4 W / mm 2), total power consumption (0.002 W - 60 kW) and focus sizes (1 µm - 10 mm). The efficiency of the x-ray tube is 0.1-3%.
Some radioactive isotopes can also serve as sources of X-rays.
Synchrotrons and electron storage rings with energies of several GeV can serve as sources of soft X-rays with λ on the order of tens and hundreds. In intensity, the X-ray radiation of synchrotrons exceeds the radiation of an X-ray tube in the specified region of the spectrum by 2-3 orders of magnitude.
Natural sources of X-rays - the Sun and other space objects.
2.2 Properties of X-rays
Depending on the mechanism of origin of X-rays, their spectra can be continuous (bremsstrahlung) or line (characteristic). A continuous X-ray spectrum is emitted by fast charged particles as a result of their deceleration when interacting with target atoms; this spectrum reaches a significant intensity only when the target is bombarded with electrons. The intensity of bremsstrahlung X-rays is distributed over all frequencies up to the high-frequency boundary 0 , at which the photon energy h 0 (h is Planck's constant
Line radiation occurs after the ionization of an atom with the ejection of an electron from one of its inner shells. Such ionization can be the result of an atom colliding with a fast particle, such as an electron (primary x-rays), or the absorption of a photon by an atom (fluorescent x-rays). The ionized atom finds itself in the initial quantum state at one of the high energy levels and after 10 -16 -10 -15 seconds passes into the final state with a lower energy. In this case, an atom can emit an excess of energy in the form of a photon of a certain frequency. The frequencies of the lines of the spectrum of such radiation are characteristic of the atoms of each element, therefore the line X-ray spectrum is called characteristic. The dependence of the line frequency of this spectrum on the atomic number Z is determined by the Moseley law.
Moseley's law, the law relating the frequency of the spectral lines of the characteristic X-ray radiation chemical element with its serial number. G. Moseley experimentally installed
where R is the Rydberg constant
Moseley's law was irrefutable proof of the correct placement of elements in the periodic table of elements
In accordance with Moseley's law, X-ray characteristic spectra do not exhibit the periodic patterns inherent in optical spectra. This indicates that the inner electron shells of atoms of all elements that appear in the characteristic X-ray spectra have a similar structure.
Later experiments revealed some deviations from the linear dependence for the transition groups of elements, associated with a change in the order of filling of the outer electron shells, as well as for heavy atoms, appearing as a result of relativistic effects (conditionally explained by the fact that the speeds of the inner ones are comparable to the speed of light).
Depending on a number of factors - on the number of nucleons in the nucleus (isotonic shift), the state of the outer electron shells (chemical shift), etc. - the position of the spectral lines on the Moseley diagram may change somewhat. The study of these shifts allows one to obtain detailed information about the atom.
Bremsstrahlung X-rays emitted by very thin targets are completely polarized near 0; as 0 decreases, the degree of polarization decreases. Characteristic radiation, as a rule, is not polarized.
When X-rays interact with matter, the photoelectric effect can occur.
When X-rays pass through a layer of substance with thickness x, their initial intensity I 0 decreases to the value I = I 0 e - μ x where μ is the attenuation coefficient. The attenuation of I occurs due to two processes: the absorption of X-ray photons by matter and the change in their direction upon scattering. In the long-wavelength region of the spectrum, the absorption of X-rays predominates, in the short-wavelength region, their scattering. The degree of absorption increases rapidly with increasing Z and λ. For example, hard X-rays freely penetrate through a layer of air ~ 10 cm; an aluminum plate 3 cm thick attenuates X-rays with λ = 0.027 by half; soft x-rays are significantly absorbed in air and their use and study is possible only in a vacuum or in a weakly absorbing gas (for example, He). When X-rays are absorbed, the atoms of a substance are ionized.
The effect of X-rays on living organisms can be beneficial or harmful, depending on the ionization they cause in the tissues. Since the absorption of X-rays depends on λ, their intensity cannot serve as a measure of the biological effect of X-rays. X-ray measurements are used to measure the effect of X-rays on matter.
Scattering of X-rays in the region of large Z and λ occurs mainly without a change in λ and is called coherent scattering, while in the region of small Z and λ, as a rule, it increases (incoherent scattering). There are 2 types of incoherent X-ray scattering - Compton and Raman. In Compton scattering, which has the character of inelastic corpuscular scattering, a recoil electron flies out of the atomic shell due to the energy partially lost by the X-ray photon. In this case, the energy of the photon decreases and its direction changes; the change in λ depends on the scattering angle. During Raman scattering of a high-energy X-ray photon by a light atom, a small part of its energy is spent on ionization of the atom and the direction of the photon's motion changes. The change of such photons does not depend on the scattering angle.
The refractive index n for x-rays differs from 1 by a very small amount δ = 1-n ≈ 10 -6 -10 -5 . The phase velocity of X-rays in a medium is greater than the speed of light in a vacuum. The deviation of X-rays during the transition from one medium to another is very small (a few arc minutes). When X-rays fall from a vacuum onto the surface of a body at a very small angle, their total external reflection occurs.
2.3 Registration of X-rays
The human eye is not sensitive to x-rays. X-ray
rays are recorded using a special x-ray film containing an increased amount of Ag, Br. In the region λ<0,5 чувствительность этих плёнок быстро падает и может быть
искусственно повышена плотно прижатым к плёнке флуоресцирующим экраном. В
области λ>5, the sensitivity of ordinary positive film is quite high, and its grains are much smaller than the grains of X-ray film, which increases the resolution. At λ of the order of tens and hundreds, X-rays act only on the thinnest surface layer of the photographic emulsion; to increase the sensitivity of the film, it is sensitized with luminescent oils. In X-ray diagnostics and flaw detection, electrophotography is sometimes used to record X-rays.
X-rays of high intensity can be recorded using an ionization chamber
2.4 Use of X-rays
X-rays are most widely used in medicine for X-ray diagnostics.
X-ray structural analysis
X-ray microscopy
X-rays coming from space carry information about the chemical composition of cosmic bodies and about the physical processes taking place in space. X-ray astronomy deals with the study of cosmic x-rays
Chapter 3
One of the main tasks of X-ray diffraction analysis is the determination of the real or phase composition of a material. The X-ray diffraction method is direct and is characterized by high reliability, rapidity and relative cheapness. The method does not require a large amount of substance, the analysis can be carried out without destroying the part. The areas of application of qualitative phase analysis are very diverse both for scientific research and for control in production. You can check the composition of the raw materials of metallurgical production, synthesis products, processing, the result of phase changes during thermal and chemical-thermal treatment, analyze various coatings, thin films, etc.
Each phase, having its own crystal structure, is characterized by a certain set of discrete values of interplanar distances d/n from the maximum and below, inherent only to this phase. As follows from the Wulf-Bragg equation, each value of the interplanar distance corresponds to a line on the x-ray pattern from a polycrystalline sample at a certain angle θ (at a given value of the wavelength λ). Thus, a certain system of lines (diffraction maxima) will correspond to a certain set of interplanar distances for each phase in the X-ray diffraction pattern. The relative intensity of these lines in the X-ray pattern depends primarily on the structure of the phase. Therefore, by determining the location of the lines on the radiograph (its angle θ) and knowing the wavelength of the radiation at which the radiograph was taken, it is possible to determine the values of the interplanar distances d/n using the Wulf-Bragg formula:
/n = λ/ (2sin θ). (1)
Having determined the set of d/n for the material under study and comparing it with the previously known d/n data for pure substances, their various compounds, it is possible to establish which phase the given material comprises. It should be emphasized that it is the phases that are determined, and not the chemical composition, but the latter can sometimes be deduced if there are additional data on the elemental composition of a particular phase. The task of qualitative phase analysis is greatly facilitated if the chemical composition of the material under study is known, because then it is possible to make preliminary assumptions about the possible phases in this case.
The key to phase analysis is to accurately measure d/n and line intensity. Although this is in principle easier to achieve using a diffractometer, the photomethod for qualitative analysis has some advantages, primarily in terms of sensitivity (the ability to detect the presence of a small amount of phase in the sample), as well as the simplicity of the experimental technique.
The calculation of d/n from the X-ray pattern is carried out using the Wulf-Bragg equation.
As the value of λ in this equation, λ α cf K-series is usually used:
λ α cf = (2λ α1 + λ α2) /3 (2)
Sometimes the K α1 line is used. Determining the diffraction angles θ for all X-ray lines allows you to calculate d / n according to equation (1) and separate the β-lines (if there was no filter for (β-rays).
3.1 Analysis of crystal structure imperfections
All real single-crystal and even more so polycrystalline materials contain certain structural imperfections (point defects, dislocations, various types of interfaces, micro- and macrostresses), which have a very strong effect on all structure-sensitive properties and processes.
Structural imperfections cause distortions of the crystal lattice of various nature and, as a result, different type changes in the diffraction pattern: a change in the interatomic and interplanar distances causes a shift in the diffraction maxima, microstresses and dispersion of the substructure lead to a broadening of the diffraction maxima, lattice microdistortions lead to a change in the intensity of these maxima, the presence of dislocations causes anomalous phenomena during the passage of X-rays and, consequently, local inhomogeneities of the contrast on x-ray topograms, etc.
As a result, X-ray diffraction analysis is one of the most informative methods for studying structural imperfections, their type and concentration, and the nature of their distribution.
The traditional direct method of X-ray diffraction, which is implemented on stationary diffractometers, due to their design features, allows quantitative determination of stresses and strains only on small samples cut from parts or objects.
Therefore, at present, there is a transition from stationary to portable small-sized X-ray diffractometers, which provide an assessment of stresses in the material of parts or objects without destruction at the stages of their manufacture and operation.
Portable X-ray diffractometers of the DRP * 1 series make it possible to control residual and effective stresses in large-sized parts, products and structures without destruction
The program in the Windows environment allows not only to determine the stresses using the "sin 2 ψ" method in real time, but also to monitor the change in the phase composition and texture. The linear coordinate detector provides simultaneous registration at diffraction angles 2θ = 43°. small-sized X-ray tubes of the "Fox" type with high luminosity and low power (5 W) ensure the radiological safety of the device, in which at a distance of 25 cm from the irradiated area, the radiation level is equal to the natural background level. Devices of the DRP series are used in determining stresses at various stages of metal forming, cutting, grinding, heat treatment, welding, surface hardening in order to optimize these technological operations. Control over the drop in the level of induced residual compressive stresses in especially critical products and structures during their operation makes it possible to take the product out of service before its destruction, preventing possible accidents and catastrophes.
3.2 Spectrum analysis
Along with the determination of the atomic crystal structure and phase composition of the material for its complete characteristics it is mandatory to determine its chemical composition.
Increasingly, various so-called instrumental methods of spectral analysis are used in practice for these purposes. Each of them has its own advantages and applications.
One of the important requirements in many cases is that the method used ensures the safety of the analyzed object; It is these methods of analysis that are discussed in this section. The next criterion according to which the methods of analysis described in this section were chosen is their locality.
The method of fluorescence X-ray spectral analysis is based on the penetration of rather hard X-ray radiation (from an X-ray tube) into the analyzed object, penetrating into a layer with a thickness of the order of several micrometers. The characteristic X-ray radiation arising in this case in the object makes it possible to obtain averaged data on its chemical composition.
To determine the elemental composition of a substance, one can use the analysis of the characteristic X-ray spectrum of a sample placed on the anode of an X-ray tube and subjected to electron bombardment - the emission method, or the analysis of the spectrum of secondary (fluorescent) X-ray radiation of a sample subjected to irradiation with hard X-rays from an X-ray tube or other source - fluorescent method.
The disadvantage of the emission method is, firstly, the need to place the sample on the anode of the x-ray tube, followed by pumping vacuum pumps; obviously, this method is unsuitable for fusible and volatile substances. The second drawback is related to the fact that even refractory objects are damaged by electron bombardment. The fluorescent method is free from these shortcomings and therefore has a much wider application. The advantage of the fluorescence method is also the absence of bremsstrahlung, which improves the sensitivity of the analysis. Comparison of the measured wavelengths with tables of spectral lines of chemical elements is the basis of a qualitative analysis, and the relative intensities of the spectral lines of different elements that form the sample substance form the basis of a quantitative analysis. From a consideration of the mechanism of excitation of characteristic X-ray radiation, it is clear that the radiations of one or another series (K or L, M, etc.) arise simultaneously, and the ratio of line intensities within the series is always constant. Therefore, the presence of this or that element is established not by individual lines, but by a series of lines as a whole (except for the weakest ones, taking into account the content of this element). For relatively light elements, the analysis of the K-series lines is used, for heavy elements, the L-series lines; under different conditions (depending on the equipment used and on the analyzed elements), different regions of the characteristic spectrum may be most convenient.
The main features of X-ray spectral analysis are as follows.
Simplicity of X-ray characteristic spectra even for heavy elements (compared to optical spectra), which simplifies the analysis (small number of lines; similarity in their mutual arrangement; with an increase in the serial number, a regular shift of the spectrum to the short-wavelength region occurs; comparative simplicity of quantitative analysis).
Independence of wavelengths from the state of atoms of the analyzed element (free or in chemical compound). This is due to the fact that the occurrence of characteristic X-ray radiation is associated with the excitation of internal electronic levels, which in most cases practically do not change with the degree of ionization of atoms.
The possibility of separation in the analysis of rare earth and some other elements that have small differences in the spectra in the optical range due to the similarity of the electronic structure of the outer shells and differ very little in their chemical properties.
X-ray fluorescence spectroscopy is "non-destructive", so it has an advantage over conventional optical spectroscopy when analyzing thin samples - thin metal sheet, foil, etc.
X-ray fluorescence spectrometers, among them multichannel spectrometers or quantometers, providing express quantitative analysis of elements (from Na or Mg to U) with an error of less than 1% of the determined value, a sensitivity threshold of 10 -3 ... 10 -4% .
x-ray beam
Methods for determining the spectral composition of x-rays
Spectrometers are divided into two types: crystal-diffraction and crystalless.
The decomposition of X-rays into a spectrum using a natural diffraction grating - a crystal - is essentially similar to obtaining a spectrum of ordinary light rays using an artificial diffraction grating in the form of periodic strokes on glass. The condition for the formation of a diffraction maximum can be written as the condition of "reflection" from a system of parallel atomic planes separated by a distance d hkl .
When conducting a qualitative analysis, one can judge the presence of an element in a sample by one line - usually the most intense line of the spectral series suitable for a given analyzer crystal. The resolution of crystal diffraction spectrometers is sufficient to separate the characteristic lines even of elements adjacent in position in the periodic table. However, it is also necessary to take into account the imposition of different lines of different elements, as well as the imposition of reflections of different orders. This circumstance should be taken into account when choosing analytical lines. At the same time, it is necessary to use the possibilities of improving the resolution of the instrument.
Conclusion
Thus, x-rays are invisible electromagnetic radiation with a wavelength of 10 5 - 10 2 nm. X-rays can penetrate some materials that are opaque to visible light. They are emitted during the deceleration of fast electrons in matter (continuous spectrum) and during transitions of electrons from the outer electron shells of the atom to the inner ones (linear spectrum). Sources of X-ray radiation are: X-ray tube, some radioactive isotopes, accelerators and accumulators of electrons (synchrotron radiation). Receivers - film, luminescent screens, nuclear radiation detectors. X-rays are used in X-ray diffraction analysis, medicine, flaw detection, X-ray spectral analysis, etc.
Having considered the positive aspects of V. Roentgen's discovery, it is necessary to note its harmful biological effect. It turned out that X-rays can cause something like a severe sunburn (erythema), accompanied, however, by deeper and more permanent damage to the skin. Appearing ulcers often turn into cancer. In many cases, fingers or hands had to be amputated. There were also deaths.
It has been found that skin damage can be avoided by reducing exposure time and dose, using shielding (eg lead) and remote controls. But gradually other, more long-term effects of X-ray exposure were revealed, which were then confirmed and studied in experimental animals. Effects due to X-rays and other ionizing radiations (such as gamma rays emitted by radioactive materials) include:
) temporary changes in the composition of the blood after a relatively small excess exposure;
) irreversible changes in the composition of the blood (hemolytic anemia) after prolonged excessive exposure;
) an increase in the incidence of cancer (including leukemia);
) faster aging and early death;
) the occurrence of cataracts.
The biological impact of X-rays on the human body is determined by the level of radiation dose, as well as by which particular organ of the body was exposed to radiation.
The accumulation of knowledge about the effects of X-ray radiation on the human body has led to the development of national and international standards for permissible radiation doses, published in various reference books.
To avoid the harmful effects of X-rays, control methods are used:
) availability of adequate equipment,
) monitoring compliance with safety regulations,
) correct use equipment.
List of sources used
1) Blokhin M.A., Physics of X-rays, 2nd ed., M., 1957;
) Blokhin M.A., Methods of X-ray spectral studies, M., 1959;
) X-rays. Sat. ed. M.A. Blokhin, trans. with him. and English, M., 1960;
) Kharaja F., General course of X-ray engineering, 3rd ed., M. - L., 1966;
) Mirkin L.I., Handbook of X-ray diffraction analysis of polycrystals, M., 1961;
) Weinstein E.E., Kakhana M.M., Reference tables on X-ray spectroscopy, M., 1953.
) X-ray and electron-optical analysis. Gorelik S.S., Skakov Yu.A., Rastorguev L.N.: Proc. Allowance for universities. - 4th ed. Add. And a reworker. - M.: "MISiS", 2002. - 360 p.
Applications
Annex 1
General view of X-ray tubes
Appendix 2
Scheme of X-ray tube for structural analysis
Scheme of an X-ray tube for structural analysis: 1 - metal anode glass (usually grounded); 2 - windows made of beryllium for x-ray output; 3 - thermionic cathode; 4 - glass bulb, isolating the anode part of the tube from the cathode; 5 - cathode terminals, to which the filament voltage is applied, as well as high (relative to the anode) voltage; 6 - electrostatic system for focusing electrons; 7 - anode (anticathode); 8 - branch pipes for input and output of running water cooling the anode glass.
Annex 3
Moseley diagram
Moseley diagram for K-, L- and M-series of characteristic X-rays. The abscissa shows the serial number of the element Z, the ordinate - ( With is the speed of light).
Appendix 4
Ionization chamber.
Fig.1. Section of a cylindrical ionization chamber: 1 - cylindrical body of the chamber, which serves as a negative electrode; 2 - cylindrical rod serving as a positive electrode; 3 - insulators.
Rice. 2. Scheme of switching on the current ionization chamber: V - voltage on the electrodes of the chamber; G is a galvanometer that measures the ionization current.
Rice. 3. Current-voltage characteristic of the ionization chamber.
Rice. 4. Scheme of switching on the pulsed ionization chamber: C - capacitance of the collecting electrode; R is resistance.
Annex 5
Scintillation counter.
Scheme of a scintillation counter: light quanta (photons) "knock out" electrons from the photocathode; moving from dynode to dynode, the electron avalanche multiplies.
Appendix 6
Geiger-Muller counter.
Rice. 1. Scheme of a glass Geiger-Muller counter: 1 - hermetically sealed glass tube; 2 - cathode (a thin layer of copper on a stainless steel tube); 3 - output of the cathode; 4 - anode (thin stretched thread).
Rice. 2. Scheme of switching on the Geiger-Muller counter.
Rice. 3. The counting characteristic of the Geiger-Muller counter.
Annex 7
proportional counter.
Scheme of a proportional counter: a - electron drift region; b - area of gas amplification.
Annex 8
Semiconductor detectors
Semiconductor detectors; the sensitive area is highlighted by hatching; n - region of a semiconductor with electronic conductivity, p - with hole, i - with intrinsic conduction; a - silicon surface-barrier detector; b - drift germanium-lithium planar detector; c - germanium-lithium coaxial detector.
The German scientist Wilhelm Conrad Roentgen can rightly be considered the founder of radiography and the discoverer of the key features of X-rays.
Then back in 1895, he did not even suspect the breadth of application and popularity of X-radiation discovered by him, although even then they raised a wide resonance in the world of science.
It is unlikely that the inventor could have guessed what benefit or harm the fruit of his activity would bring. But today we will try to find out what effect this kind of radiation has on the human body.
- X-radiation is endowed with a huge penetrating power, but it depends on the wavelength and density of the material that is irradiated;
- under the influence of radiation, some objects begin to glow;
- the x-ray affects living beings;
- thanks to X-rays, some biochemical reactions begin to occur;
- An x-ray beam can take electrons from some atoms and thereby ionize them.
Even the inventor himself was primarily concerned with the question of what exactly the rays he discovered were.
After conducting a series of experimental studies, the scientist found out that X-rays are intermediate waves between ultraviolet and gamma radiation, the length of which is 10 -8 cm.
The properties of the X-ray beam, which are listed above, have destructive properties, but this does not prevent them from being used for useful purposes.
So where in the modern world can X-rays be used?
- They can be used to study the properties of many molecules and crystalline formations.
- For flaw detection, that is, to check industrial parts and devices for defects.
- In the medical industry and therapeutic research.
Due to the short lengths of the entire range of these waves and their unique properties, the most important application of the radiation discovered by Wilhelm Roentgen became possible.
Since the topic of our article is limited to the impact of X-rays on the human body, which encounters them only when going to the hospital, then we will consider only this branch of application.
The scientist who invented X-rays made them an invaluable gift for the entire population of the Earth, because he did not patent his offspring for further use.
Since World War I, portable X-ray machines have saved hundreds of wounded lives. Today, X-rays have two main applications:
- Diagnosis with it.
X-ray diagnostics is used in various options:
- X-ray or transillumination;
- x-ray or photograph;
- fluorographic study;
- tomography using x-rays.
Now we need to understand how these methods differ from each other:
- The first method assumes that the subject is located between a special screen with a fluorescent property and an X-ray tube. The doctor, based on individual characteristics, selects the required strength of the rays and receives an image of the bones and internal organs on the screen.
- In the second method, the patient is placed on a special x-ray film in a cassette. In this case, the equipment is placed above the person. This technique allows you to get an image in the negative, but with finer details than with fluoroscopy.
- Mass examinations of the population for lung disease allows for fluorography. At the time of the procedure, the image is transferred from a large monitor to a special film.
- Tomography allows you to get images of internal organs in several sections. A whole series of images are taken, which are hereinafter referred to as a tomogram.
- If you connect the help of a computer to the previous method, then specialized programs will create a complete image made using an x-ray scanner.
All these methods of diagnosing health problems are based on the unique property of X-rays to light up photographic film. At the same time, the penetrating ability of inert and other tissues of our body is different, which is displayed in the picture.
After another property of X-rays to influence tissues from a biological point of view was discovered, this feature began to be actively used in tumor therapy.
Cells, especially malignant ones, divide very quickly, and the ionizing property of radiation has a positive effect on therapeutic therapy and slows down tumor growth.
But the other side of the coin is the negative effect of x-rays on the cells of the hematopoietic, endocrine and immune system, which also rapidly divide. As a result of the negative influence of the X-ray, radiation sickness manifests itself.
The effect of x-rays on the human body
Literally immediately after such a loud discovery in the scientific world, it became known that X-rays can affect the human body:
- In the course of research on the properties of X-rays, it turned out that they are capable of causing burns on the skin. Very similar to thermal. However, the depth of the lesion was much greater than domestic injuries, and they healed worse. Many scientists dealing with these insidious radiations have lost their fingers.
- By trial and error, it was found that if you reduce the time and vine of endowment, then burns can be avoided. Later, lead screens and the remote method of irradiating patients began to be used.
- The long-term perspective of the harmfulness of rays shows that changes in the composition of the blood after irradiation leads to leukemia and early aging.
- The degree of severity of the impact of X-rays on the human body directly depends on the irradiated organ. So, with X-rays of the small pelvis, infertility can occur, and with the diagnosis of hematopoietic organs - blood diseases.
- Even the most insignificant exposures, but over a long period of time, can lead to changes at the genetic level.
Of course, all studies were conducted on animals, but scientists have proven that pathological changes will also apply to humans.
IMPORTANT! Based on the obtained data, X-ray exposure standards were developed, which are uniform throughout the world.
Doses of x-rays for diagnosis
Probably, everyone who leaves the doctor's office after an x-ray is wondering how this procedure will affect their future health?
Radiation exposure in nature also exists and we encounter it daily. To make it easier to understand how x-rays affect our body, we compare this procedure with the natural radiation received:
- on a chest x-ray, a person receives a dose of radiation equivalent to 10 days of background exposure, and the stomach or intestines - 3 years;
- tomogram on the computer of the abdominal cavity or the whole body - the equivalent of 3 years of radiation;
- examination on chest x-ray - 3 months;
- limbs are irradiated, practically without harming health;
- dental x-ray due to the precise direction of the beam beam and the minimum exposure time is also not dangerous.
IMPORTANT! Despite the fact that the given data, no matter how frightening they may sound, meet international requirements. However, the patient has every right to ask additional funds protection in case of strong fear for their well-being.
All of us are faced with x-ray examination, and more than once. However, one category of people outside of the prescribed procedures are pregnant women.
The fact is that X-rays extremely affect the health of the unborn child. These waves can cause vices prenatal development as a result of the effect on chromosomes.
IMPORTANT! The most dangerous period for x-rays is pregnancy before 16 weeks. During this period, the most vulnerable are the pelvic, abdominal and vertebral regions of the baby.
Knowing about this negative property of x-rays, doctors all over the world are trying to avoid prescribing it for pregnant women.
But there are other sources of radiation that a pregnant woman may encounter:
- microscopes powered by electricity;
- color TV monitors.
Those who are preparing to become a mother must be aware of the danger that awaits them. During lactation, X-rays do not pose a threat to the body of the nursing and the baby.
What about after the x-ray?
Even the most minor effects of X-ray exposure can be minimized by following a few simple recommendations:
- drink milk immediately after the procedure. As you know, it is able to remove radiation;
- dry white wine or grape juice has the same properties;
- it is desirable at first to eat more foods containing iodine.
IMPORTANT! You should not resort to any medical procedures or use medical methods after visiting the x-ray room.
No matter how negative the properties of the once discovered X-rays, the benefits of their use far outweigh the harm. In medical institutions, the transillumination procedure is carried out quickly and with minimal doses.
The nature of X-rays
Bremsstrahlung X-ray, its spectral properties.
Characteristic x-ray radiation (for review).
Interaction of X-ray radiation with matter.
Physical basis for the use of X-rays in medicine.
X-rays (X - rays) were discovered by K. Roentgen, who in 1895 became the first Nobel laureate in physics.
The nature of X-rays
x-ray radiation - electromagnetic waves with a length of 80 to 10 -5 nm. Long-wave X-ray radiation is covered by short-wave UV radiation, short-wave - by long-wave -radiation.
X-rays are produced in x-ray tubes. fig.1.
K - cathode
1 - electron beam
2 - X-ray radiation
Rice. 1. X-ray tube device.
The tube is a glass flask (with a possibly high vacuum: the pressure in it is about 10–6 mm Hg) with two electrodes: anode A and cathode K, to which a high voltage U (several thousand volts) is applied. The cathode is a source of electrons (due to the phenomenon of thermionic emission). The anode is a metal rod that has an inclined surface in order to direct the resulting X-ray radiation at an angle to the axis of the tube. It is made of a highly heat-conducting material to remove the heat generated during electron bombardment. On the beveled end there is a plate made of refractory metal (for example, tungsten).
The strong heating of the anode is due to the fact that the main number of electrons in the cathode beam, having hit the anode, experience numerous collisions with the atoms of the substance and transfer a large amount of energy to them.
Under the action of high voltage, the electrons emitted by the hot cathode filament are accelerated to high energies. The kinetic energy of an electron is equal to mv 2 /2. It is equal to the energy that it acquires by moving in the electrostatic field of the tube:
mv 2 /2 = eU(1)
where m, e are the electron mass and charge, U is the accelerating voltage.
The processes leading to the appearance of bremsstrahlung X-rays are due to the intense deceleration of electrons in the anode material by the electrostatic field of the atomic nucleus and atomic electrons.
The origin mechanism can be represented as follows. Moving electrons are some kind of current that forms its own magnetic field. Electron deceleration - a decrease in current strength and, accordingly, a change in induction magnetic field, which will cause the occurrence of an alternating electric field, i.e. appearance of an electromagnetic wave.
Thus, when a charged particle flies into matter, it slows down, loses its energy and speed, and emits electromagnetic waves.
Spectral properties of X-ray bremsstrahlung.
So, in the case of electron deceleration in the anode material, bremsstrahlung radiation.
The bremsstrahlung spectrum is continuous. The reason for this is as follows.
When electrons decelerate, each of them has part of the energy used to heat the anode (E 1 \u003d Q), the other part to create an X-ray photon (E 2 \u003d hv), otherwise, eU \u003d hv + Q. The ratio between these parts is random.
Thus, the continuous spectrum of X-ray bremsstrahlung is formed due to the deceleration of many electrons, each of which emits one X-ray quantum hv (h) of a strictly defined value. The value of this quantum different for different electrons. Dependence of the X-ray energy flux on the wavelength , i.e. the X-ray spectrum is shown in Fig.2.
Fig.2. Bremsstrahlung spectrum: a) at different voltages U in the tube; b) at different temperatures T of the cathode.
Short-wave (hard) radiation has a greater penetrating power than long-wave (soft) radiation. Soft radiation is more strongly absorbed by matter.
From the side of short wavelengths, the spectrum ends abruptly at a certain wavelength m i n . Such short-wavelength bremsstrahlung occurs when the energy acquired by an electron in an accelerating field is completely converted into photon energy (Q = 0):
eU = hv max = hc/ min , min = hc/(eU), (2)
min (nm) = 1.23/UkV
The spectral composition of the radiation depends on the voltage on the X-ray tube; with increasing voltage, the value of m i n shifts towards short wavelengths (Fig. 2a).
When the temperature T of the cathode incandescence changes, the electron emission increases. Consequently, the current I in the tube increases, but the spectral composition of the radiation does not change (Fig. 2b).
The energy flux Ф of bremsstrahlung is directly proportional to the square of the voltage U between the anode and the cathode, the current strength I in the tube and the atomic number Z of the anode substance:
Ф = kZU 2 I. (3)
where k \u003d 10 -9 W / (V 2 A).
They are emitted with the participation of electrons, in contrast to gamma radiation, which is nuclear. Artificial X-rays are created by strongly accelerating charged particles and by moving electrons from one energy level to another, releasing a large amount of energy. Devices that can be obtained are X-ray tubes and particle accelerators. Its natural sources are radioactively unstable atoms and space objects.
Discovery history
It was made in November 1895 by Roentgen, a German scientist who discovered the fluorescence effect of barium platinum cyanide during the operation of a cathode ray tube. He described the characteristics of these rays in some detail, including the ability to penetrate living tissue. They were called X-rays by the scientist, the name "X-ray" took root in Russia later.
What characterizes this type of radiation
It is logical that the features of this radiation are due to its nature. An electromagnetic wave is what X-rays are. Its properties are the following:
X-ray radiation - harm
Of course, at the time of opening and long years after that, no one realized how dangerous it was.
Where are x-rays used?
- Medicine. X-ray diagnostics - "transmission" of living organisms. X-ray therapy - the effect on tumor cells.
- The science. Crystallography, chemistry and biochemistry use them to reveal the structure of matter.
- Industry. Detection of defects in metal parts.
- Safety. X-ray equipment is used to detect dangerous items in luggage at airports and other places.
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