ISOTOPS(Greek, isos equal, identical + topos place) - varieties of one chemical element that occupy the same place in the periodic system of Mendeleev's elements, that is, having the same nuclear charge, but differing in atomic masses. At the mention of I., be sure to indicate which isotope of which chemical. element he is. The term "isotope" is sometimes used in a broader sense - to describe the atoms of various elements. However, to designate any of the atoms, regardless of its belonging to a particular element, it is customary to use the term "nuclide".

I.'s belonging to a certain element and the main chem. properties are determined by its serial number Z or the number of protons contained in the nucleus (respectively, and the same number of electrons in the shell of an atom), and its nuclear-physical. properties are determined by the totality and ratio of the number of protons and neutrons included in it. Each nucleus consists of Z protons and N neutrons, and the total number of these particles, or nucleons, is the mass number A = Z + N, which determines the mass of the nucleus. It is equal to the value of the mass of the given nuclide rounded to the nearest whole number. Any nuclide, thus, is determined by the values ​​of Z and N, although some radioactive nuclides with the same Z and N can be in different nuclear energy states and differ in their nuclear physical. properties; such nuclides are called isomers. Nuclides with the same number of protons are called isotopes.

And. are designated by the symbol of the corresponding chemical. element with the index A located at the top left - mass number; sometimes the number of protons (Z) is also given at the bottom left. For example, radioactive I. phosphorus with mass numbers 32 and 33 denote: 32 P and 33 P or 32 P and 33 P, respectively. When designating I. without indicating the symbol of the element, the mass number is given after the designation of the element, for example. phosphorus-32, phosphorus-33.

I. different elements can have the same mass number. Atoms with different numbers of protons Z and neutrons N, but with the same mass number A, are called isobars (eg 14 32 Si, 15 32 P, 16 32 S, 17 32 Cl-isobars).

The name "isotope" was proposed by the English. scientists Soddy (F. Soddy). The existence of I. was first discovered in 1906 while studying the radioactive decay of heavy natural radioactive elements; in 1913, they were also found in the non-radioactive element neon, and then, using mass spectrometry, the isotopic composition of all elements of the periodic system was determined. In 1934, I. Joliot-Curie and F. Joliot-Curie were the first to obtain artificially radioactive radiation of nitrogen, silicon, and phosphorus, and subsequently, using various nuclear reactions on neutrons, charged particles, and high-energy photons, radioactive radiation of all known elements and synthesized radioactive I. 13 superheavy - transuranium elements (with Z≥ 93). There are 280 known stable, characterized by stability, and more than 1,500 radioactive, i.e., unstable, I., which undergo radioactive transformations at one rate or another. The duration of the existence of radioactive I. is characterized by a half-life (see) - a period of time T 1/2, during which the number of radioactive nuclei is halved.

In a natural mixture I. chem. different I. elements are contained in different quantities. Percentage And. in this chemical. element is called their relative abundance. So, for example, natural oxygen contains three stable oxygens: 16O (99.759%), 17O (0.037%), and 18O (0.204%). Many chem. elements have only one stable I. (9 Be, 19 F, 23 Na, 31 P, 89 Y, 127 I, etc.), and some (Tc, Pm, Lu and all elements with Z greater than 82) do not have any one stable I.

The isotopic composition of natural elements on our planet (and within the solar system) is basically constant, but there are small fluctuations in the abundance of atoms of light elements. This is explained by the fact that the differences in their masses are relatively large, and therefore the isotopic composition of these elements changes under the influence of various natural processes, as a result of isotope effects (i.e., differences in the properties of chemical substances that contain these isotopes). Thus, the isotopic composition of a number of biologically important elements (H, C, N, O, S) is associated, in particular, with the presence of the biosphere and the vital activity of plant and animal organisms.

The difference in the composition and structure of atomic nuclei I. of the same chemical. element (a different number of neutrons) determines the difference between their nuclear and physical. properties, in particular, the fact that some of its I. can be stable, while others can be radioactive.

radioactive transformations. The following types of radioactive transformations are known.

Alpha decay is a spontaneous transformation of nuclei, accompanied by the emission of alpha particles, i.e., two protons and two neutrons that form a helium nucleus 2 4 He. As a result, the charge Z of the original nucleus is reduced by 2, and the total number of nuclides or mass number is reduced by 4 units, for example:

88 226 Ra -> 86 222 Ra + 2 4 He

In this case, the kinetic energy of the emitted alpha particle is determined by the masses of the initial and final nuclei (taking into account the mass of the alpha particle itself) and their energy state. If the final nucleus is formed in an excited state, then the kinetic energy of the alpha particle decreases somewhat, and if the excited nucleus decays, then the energy of the alpha particle increases accordingly (in this case, the so-called long-range alpha particles are formed). The energy spectrum of alpha particles is discrete and lies in the range of 4-9 MeV for about 200 I. heavy elements and 2-4.5 MeV for almost 20 alpha radioactive I. rare-earth elements.

Beta decay is a spontaneous transformation of nuclei, in which the charge Z of the original nucleus changes by one, while the mass number A remains the same. beta decay is the interconversion of protons (p) and neutrons (n) that make up the nucleus, accompanied by the emission or absorption of electrons (e -) or positrons (e +), as well as neutrinos (v) and antineutrinos (v -). There are three types of beta decay:

1) electronic beta decay n -> p + e - + v - , accompanied by an increase in the charge Z by 1 unit, with the transformation of one of the neutrons of the nucleus into a proton, for example.

2) positron beta decay p -> n + e + + v , accompanied by a decrease in the charge Z by 1 unit, with the transformation of one of the protons of the nucleus into a neutron, for example.

3) electronic capture p + e - -> n + v with the simultaneous transformation of one of the protons of the nucleus into a neutron, as in the case of decay with the emission of a positron, also accompanied by a decrease in charge by 1 unit, for example.

In this case, the capture of an electron occurs from one of the electron shells of the atom, most often from the K-shell closest to the nucleus (K-capture).

Beta-minus decay is typical for neutron-rich nuclei, in which the number of neutrons is greater than in stable nuclei, and beta-plus decay and, accordingly, electron capture, for neutron-deficient nuclei, in which the number of neutrons is less than in stable nuclei, or so called beta-stable, nuclei. The decay energy is distributed between a beta particle and a neutrino, and therefore the beta spectrum is not discrete, like that of alpha particles, but continuous and contains beta particles with energies from close to zero to a certain Emax, characteristic of each radioactive radiation. Beta-radioactive radiations are found in all elements of the periodic system.

Spontaneous fission is the spontaneous decay of heavy nuclei into two (sometimes 3-4) fragments, which are the nuclei of the middle elements of the periodic system (the phenomenon was discovered in 1940 by Soviet scientists G. N. Flerov and K. A. Petrzhak).

Gamma radiation - photon radiation with a discrete energy spectrum, occurs during nuclear transformations, changes in the energy state of atomic nuclei, or during particle annihilation. The emission of gamma quanta accompanies radioactive transformation when a new nucleus is formed in an excited energy state. The lifetime of such nuclei is determined by nuclear physics. properties of the parent and daughter nuclei, in particular, increases with a decrease in the energy of gamma transitions and can reach relatively large values ​​for cases of a metastable excited state. The energy of gamma radiation emitted by different P. ranges from tens of keV to several MeV.

Nuclear stability. During beta decay, mutual transformations of protons and neutrons occur until the most energetically favorable ratio of p and n is reached, which corresponds to the stable state of the nucleus. All nuclides are divided in relation to beta decay into beta-radioactive and beta-stable nuclei. Beta-stable refers to either stable or alpha-radioactive nuclides for which beta decay is energetically impossible. All beta-resistant I. in chem. elements with atomic numbers Z up to 83 are stable (with a few exceptions), while heavy elements do not have stable I., and all of their beta-stable I. are alpha-radioactive.

During radioactive transformation, energy is released, corresponding to the ratio of the masses of the initial and final nuclei, the mass and energy of the emitted radiation. The possibility of p-decay occurring without changing the mass number A depends on the ratio of the masses of the corresponding isobars. Isobars with a larger mass as a result of beta decay turn into isobars with a smaller mass; the smaller the isobar mass, the closer it is to the P-stable state. The reverse process, by virtue of the law of conservation of energy, cannot proceed. So, for example, for the isobars mentioned above, the transformations proceed in the following directions with the formation of a stable isotope of sulfur-32:

The nuclei of nuclides resistant to beta decay contain at least one neutron per proton (exceptions are 1 1 H and 2 3 He), and as the atomic number increases, the N/Z ratio increases and reaches a value of 1.6 for uranium.

With an increase in the number N, the nucleus of this element becomes unstable with respect to electronic beta-minus decay (with the transformation n->p), therefore neutron-enriched nuclei are beta-active. Correspondingly, neutron-deficient nuclei are unstable to positron beta+ decay or electron capture (with p->n transformation), while alpha decay and spontaneous fission are also observed in heavy nuclei.

Separation of stable and production of artificially radioactive isotopes. The separation of I. is the enrichment of the natural mixture of I. of this chemical. element by individual constituents of I. and the isolation of pure I. from this mixture. All separation methods are based on isotope effects, i.e., on differences in physical and chemical. properties of different And. and the chemical containing them. compounds (strength of chemical bonds, density, viscosity, heat capacity, melting temperature, evaporation, diffusion rate, etc.). Ways of division also are based on distinctions in behavior And. and the connections containing them in fiz.-chem. processes. Practically used are electrolysis, centrifugation, gas and thermal diffusion, diffusion in a vapor stream, rectification, chemical. and isotope exchanges, electromagnetic separation, laser separation, etc. If a single process gives a low effect, i.e., a small separation factor I., it is repeated many times until a sufficient degree of enrichment is obtained. I. separation of light elements is most effective due to the large relative differences in the masses of their isotopes. For example, "heavy water", i.e., water enriched with heavy I. hydrogen - deuterium, the mass of which is twice as large, is obtained on an industrial scale in electrolysis plants; The extraction of deuterium by low-temperature distillation is also highly efficient. Separation of I. uranium (to obtain nuclear fuel - 235 U) is carried out at gas diffusion plants. A wide range of enriched stable I. is obtained on electromagnetic separation plants. In some cases, separation and enrichment of a mixture of radioactive radiation is used, for example, to obtain radioactive radiation of iron-55 with high specific activity and radionuclide purity.

Artificially radioactive radiations are obtained as a result of nuclear reactions—the interactions of nuclides with each other and with nuclear particles or photons, which result in the formation of other nuclides and particles. A nuclear reaction is conventionally denoted as follows: first, the symbol of the initial isotope is indicated, and then the symbol of the isotope formed as a result of this nuclear reaction. In parentheses between them, the acting particle or radiation quantum is indicated first, followed by the emitted particle or radiation quantum (see Table, column 2).

The probability of the implementation of nuclear reactions is quantitatively characterized by the so-called effective cross section (or cross section) of the reaction, denoted by the Greek letter o and expressed in barns (10 -24 cm 2). To obtain artificially radioactive nuclides, nuclear reactors are used (see. Nuclear reactors) and charged particle accelerators (see). Many radionuclides used in biology and medicine are obtained in a nuclear reactor by nuclear reactions of radiative capture, i.e. capture by the nucleus of a neutron with the emission of a gamma quantum (n, gamma), resulting in the formation of an isotope of the same element with a mass number of unit greater than the original, for example. 23 Na (n, γ) 24 Na, 31 P(n, γ) 32 P; according to the reaction (n, γ) followed by the decay of the resulting radionuclide and the formation of a "daughter", for example. 130 Te (n, γ) 131 Te -> 131 I; for reactions with emission of charged particles (n, p), (n, 2n), (n, α); e.g. 14 N (n, p) 14 C; by secondary reactions with tritons (t, p) and (t, n), for example. 7 Li (n, α) 3 H and then 16O (t, n) 18 F; according to the fission reaction U (n, f), for example. 90 Sr, 133 Xe, etc. (see Nuclear reactions).

Some radionuclides either cannot be obtained in a nuclear reactor at all, or their production is irrational for medical purposes. According to the reaction (n, γ), in most cases it is impossible to obtain isotopes without a carrier; some reactions have a too small cross section a, and the irradiated targets have a low relative content of the initial isotope in the natural mixture, which leads to low reaction yields and insufficient specific activity of the preparations. Therefore, many important radionuclides used in clinical radiodiagnostics, are obtained with sufficient specific activity using isotopically enriched targets. For example, to obtain calcium-47, a target enriched in calcium-46 from 0.003 to 10-20% is irradiated; to obtain iron-59, a target with iron-58 enriched from 0.31 to 80% is irradiated to obtain mercury-197 - target with mercury-196 enriched from 0.15 to 40%, etc.

In the reactor arr. receive radionuclides with an excess of neutrons, decaying with beta-mirus_radiation. Neutron-deficient radionuclides, which are formed in nuclear reactions on charged particles (p, d, alpha) and photons and decay with the emission of positrons or by capturing electrons, in most cases are obtained at cyclotrons, linear accelerators of protons and electrons (in the latter case, bremsstrahlung is used) at energies of accelerated particles of the order of tens and hundreds of MeV. So get for honey. radionuclides by reactions: 51 V (р, n) 51 Cr, 67 Zn (р, n) 67 Ga, 109 Ag (α, 2n) 111 In, 44 Ca (γ, p) 43 K, 68 Zn (γ, p) 67 Cu, etc. An important advantage of this method of obtaining radionuclides is that they, having, as a rule, a different chemical. nature than the material of the irradiated target can be isolated from the latter without a carrier. This allows you to receive the necessary radiofarms. drugs with high specific activity and radionuclide purity.

To obtain many short-lived radionuclides directly in clinical institutions, the so-called. isotope generators containing a long-lived parent radionuclide, during the decay of which the desired short-lived daughter radionuclide is formed, for example. 99m Tc, 87m Sr, 113m In, 132 I. The latter can be repeatedly extracted from the generator during the lifetime of the parent nuclide (see Radioactive Isotope Generators).

Application of isotopes in biology and medicine. Radioactive and stable radiations are widely used in scientific research. As a label, they are used for the preparation of isotope indicators (see Labeled compounds) - substances and compounds that have an isotopic composition different from the natural one. The method of isotope indicators is used to investigate the distribution, ways and nature of the movement of labeled substances in various environments and systems, carry out their quantitative analysis, study the structure of chemical. compounds and biologically active substances, the mechanisms of various dynamic processes, including their metabolism in the body of plants, animals and humans (see Radioisotope study). By means of a method of isotope indicators carry out researches in biochemistry (study of a metabolism, a structure and the mechanism of biosynthesis of proteins, nucleinic to - t, fats and carbohydrates in a live organism, flow rate biochemical, reactions, etc.); in physiology (migration of ions and various substances, absorption processes from the gastrointestinal tract of fats and carbohydrates, excretion, circulation, behavior and role of microelements, etc.); in pharmacology and toxicology (study of the behavior of drugs and toxic substances, their absorption, ways and speed of accumulation, distribution, excretion, mechanism of action, etc.); in microbiology, immunology, virology (the study of the biochemistry of microorganisms, the mechanisms of enzymatic and immunochemical reactions, the interaction of viruses and cells, the mechanisms of action of antibiotics, etc.); in hygiene and ecology (the study of contamination with harmful substances and decontamination of industries and the environment, the ecological chain of various substances, their migration, etc.). And. apply also in other medico-biol. research (to study the pathogenesis of various diseases, the study of early changes in metabolism, etc.).

In honey. In practice, radionuclides are used to diagnose and treat various diseases, as well as for radiation sterilization of honey. materials, products and medicines. Clinics use more than 130 radiodiagnostic and 20 radiotherapeutic techniques using open radiopharmaceuticals. preparations (RFP) and sealed isotope sources of radiation. For this purpose, St. 60 radionuclides, approx. 30 of them are the most widespread (table). Radiodiagnostic preparations make it possible to obtain information about the func- tions and anatomical state of organs and systems of the human body. At the heart of radioisotope diagnostics (see) the possibility to follow biol, behavior of the chemical marked by radionuclides lies. substances and compounds in a living organism without violating its integrity and changing functions. The introduction of the desired radioisotope of the corresponding element into the structure of the chemical. The use of a compound, practically without changing its properties, makes it possible to monitor its behavior in a living organism by external detection of radiation radiation, which is one of the very important advantages of the method of radioisotope diagnostics.

Dynamic indicators of the behavior of the labeled compound make it possible to evaluate the function, the state of the organ or system under study. So, according to the degree of dilution of the radiopharmaceutical with 24 Na, 42 K, 51 Cr, 52 Fe, 131 I, etc. in liquid media, the volume of circulating blood, erythrocytes, the exchange of albumin, iron, water exchange of electrolytes, etc. are determined. and excretion of radiopharmaceuticals in organs, body systems or in the lesion, it is possible to assess the state of central and peripheral hemodynamics, determine the function of the liver, kidneys, lungs, study iodine metabolism, etc. Radiopharmaceuticals with radioisotopes of iodine and technetium make it possible to study all the functions of the thyroid gland. With the help of 99m Tc, 113m In, 123 I, 131 I, 133 Xe, you can conduct a comprehensive study of the lungs - to study the distribution of blood flow, the state of ventilation of the lungs and bronchi. Radiopharmaceuticals with 43 K, 86 Rb, 99m Tc, 67 Ga, 131 I, 113m In, 197 Hg, etc. make it possible to determine the blood flow and blood supply to the brain, heart, liver, kidneys and other organs. Radioactive colloidal solutions and some iodine-organic preparations make it possible to assess the state of polygonal cells and hepatocytes (Kupffer cells) and the antitoxic function of the liver. With the help of radioisotope scanning, an anatomical and topographic study and determination of the presence, size, shape and position of volumetric lesions of the liver, kidneys, bone marrow, thyroid, parathyroid and salivary glands, lungs, lymph nodes, are carried out; radionuclides 18 F, 67 Ga, 85 Sr, 87M Sr, 99M Tc make it possible to investigate diseases of the skeleton, etc.

In the USSR, radiation safety standards have been developed and put into effect for patients using radioactive substances for diagnostic purposes, which strictly regulate these procedures in terms of permissible exposure levels. Due to this, as well as the rational choice of methods and equipment for various types of examinations and the use in radiopharmaceuticals, if possible, of short-lived radionuclides that have favorable radiation characteristics in terms of the efficiency of their registration with minimal radiation exposure, the radiation exposure to the patient's body during radioisotope diagnostic procedures is much lower than doses. received at rentgenol, inspections, and in most cases do not exceed hundredths and tenths of a glad.

In the 70s. 20th century radioisotope preparations have become more widely used for in vitro studies, mainly for immunochem. analysis. Radioimmunochem. methods are based on highly specific immunochemical. reactions antigen - an antibody, as a result a cut the stable complex from an antibody and an antigen is formed. After separating the resulting complex from unreacted antibodies or antigens, a quantitative determination is carried out by measuring their radioactivity. The use of antigens or antibodies labeled with radioisotopes, e.g. 125 I, increases the sensitivity of immunochem. tests tens and hundreds of times. Using these tests, it is possible to determine the content of hormones, antibodies, antigens, enzymes, enzymes, vitamins and other biologically active substances in the body at concentrations up to 0.1 mg/ml. Thus it is possible to define not only various patol, states, but also very small changes reflecting initial stages of a disease. For example, these techniques are successfully used for early in vitro diagnosis of diabetes mellitus, infectious hepatitis, carbohydrate metabolism disorders, some allergic and a number of other diseases. Such radioisotope tests are not only more sensitive, simpler, but also allow for mass research and are completely safe for patients (see Radioisotope Diagnostics).

With to lay down. the purpose of radiopharmaceuticals and radionuclide sources of radiation are applied by Ch. arr. in oncology, as well as in the treatment of inflammatory diseases, eczema, etc. (see Radiation therapy). For these purposes, both open radiopharmaceuticals injected into the body, into tissues, serous cavities, joint cavities, intravenously, intraarterially and into the lymph system, as well as closed sources of radiation for external, intracavitary and interstitial therapy are used. With the help of the appropriate radiopharmaceuticals, Ch. arr. colloids and suspensions containing 32 P, 90 Y, 131 I, 198 Au and other radionuclides treat diseases of the hematopoietic system and various tumors, acting locally on patol, focus. With contact irradiation (dermatol, and ophthalmic beta-applicators), 32 P, 90 Sr, 90 Y, 147 Pm, 204 Tl are used, in remote gamma therapeutic devices - sources of 60 Co or 137 Cs of high activity (hundreds and thousands of curies) . For interstitial and intracavitary irradiation, needles, granules, wire and other special types of sealed sources with 60 Co, 137 Cs, 182 Ta, 192 Ir, 198 Au are used (see Radioactive drugs).

Radioactive nuclides are also used to sterilize materials, medical products. prescriptions and medicines. The practical application of radiation sterilization has become possible since the 50s, when powerful sources of ionizing radiation appeared. In comparison with traditional methods of sterilization (see), the radiation method has a number of advantages. Since at the usual sterilizing dose of radiation (2-3 Mrad) there is no significant increase in the temperature of the irradiated object, radiation sterilization of thermolabile objects, including biol, preparations and products from some types of plastics, becomes possible. The effect of radiation on the irradiated sample occurs simultaneously in its entire volume, and sterilization is carried out with a high degree of reliability. At the same time, color indicators of the received dose are used for control, placed on the surface of the package of the sterilized object. Honey. products and means are sterilized at the end of the technol. cycle already in finished form and in hermetic packaging, including from polymeric materials, which eliminates the need to create strictly aseptic production conditions and guarantees sterility after the release of products by the enterprise. Radiation sterilization is especially effective for honey. disposable products (syringes, needles, catheters, gloves, sutures and dressings, blood collection and transfusion systems, biological products, surgical instruments, etc.), non-injectable medicines, tablets and ointments. During radiation sterilization of medicinal solutions, one should take into account the possibility of their radiation decomposition, leading to a change in composition and properties (see Sterilization, cold).

Toxicology of radioactive isotopes - a branch of toxicology that studies the effect of incorporated radioactive substances on living organisms. Its main tasks are: establishment of admissible levels of maintenance and receipt of radionuclides in a human body with air, water and food stuffs, and also degree of harmlessness of RV entered into an organism at a wedge, radiodiagnostic researches; clarification of the specifics of damage by radionuclides depending on the nature of their distribution, energy and type of radiation, half-life, dose, routes and rhythm of intake and the search for effective means for preventing damage.

The influence of radionuclides on the human body, widely used in industry, scientific and honey, is studied most deeply. research, as well as resulting from the fission of nuclear fuel.

The toxicology of radioactive isotopes is organically connected with radiobiology (see), radiation hygiene (see) and medical radiology (see).

Radioactive substances can get into a human body through respiratory ways, went. - kish. tract, skin, wound surfaces, and with injections - through blood vessels, muscle tissue, articular surfaces. The nature of the distribution of radionuclides in the body depends on the main chemical. properties of the element, the form of the administered compound, the route of entry and fiziol, the state of the body.

Quite significant differences were found in the distribution and routes of excretion of individual radionuclides. Soluble compounds Ca, Sr, Ba, Ra, Y, Zr selectively accumulate in bone tissue; La, Ce, Pr, Pu, Am, Cm, Cf, Np - in the liver and bone tissue; K, Cs, Rb - in muscle tissue; Nb, Ru, Te, Po are distributed relatively evenly, although they tend to accumulate in the reticuloendothelial tissue of the spleen, bone marrow, adrenal glands and lymph nodes; I and At - in the thyroid gland.

The distribution in the body of elements belonging to a certain group of the periodic system of Mendeleev has much in common. Elements of the first main group (Li, Na, K, Rb, Cs) are completely absorbed from the intestine, relatively evenly distributed throughout the organs and excreted mainly in the urine. Elements of the second main group (Ca, Sr, Ba, Ra) are well absorbed from the intestines, are selectively deposited in the skeleton, and are excreted in somewhat large quantities with feces. Elements of the third main and fourth side groups, including light lanthanides, actinides and transuranium elements, are practically not absorbed from the intestine, as a rule, they are selectively deposited in the liver and, to a lesser extent, in the skeleton, and are excreted mainly with feces. Elements of the fifth and sixth main groups of the periodic system, with the exception of Po, are relatively well absorbed from the intestines and excreted almost exclusively in the urine during the first day, due to which they are found in organs in relatively small quantities.

The deposition of radionuclides in the lung tissue during inhalation depends on the size of the inhaled particles and their solubility. The larger the aerosols, the greater their proportion is retained in the nasopharynx and the smaller one penetrates into the lungs. Light, poorly soluble compounds slowly leave. High concentration of such radionuclides is often found in limf, nodes of roots of lungs. Very quickly absorbed in the lungs tritium oxide, soluble compounds of alkaline and alkaline earth elements. Pu, Am, Ce, Cm and other heavy metals are slowly absorbed into the lungs.

Radiation safety standards (RSRs) regulate the intake and content of radionuclides in the body of persons whose work is associated with occupational hazards, and individuals from the population, as well as the population as a whole, the permissible concentrations of radionuclides in the atmospheric air and water, food products. These norms are based on the values ​​​​of the maximum permissible doses (MPD) of exposure established for four groups of critical organs and tissues (see Critical Organ, Maximum Permissible Doses).

For persons working in conditions of occupational hazards, the accepted value of the SDA for irradiation of the whole body, gonads and red bone marrow is 5 rem / year, muscle and adipose tissue, liver, kidneys, spleen, zhel.-kish. tract, lungs, eye lens - 15 rem / year, bone tissue, thyroid gland and skin - 30 rem / year, hands, forearms, ankles and feet - 75 rem / year.

The norms for individuals from the population are recommended 10 times lower than for persons working in conditions of occupational hazards. Irradiation of the entire population is regulated by a genetically significant dose, which should not exceed 5 rem in 30 years. This dose does not include possible radiation doses due to honey. procedures and natural background radiation.

The value of the annual maximum allowable intake of soluble and insoluble compounds (μCi/year) through the respiratory organs for personnel, the limit of the annual intake of radionuclides through the respiratory and digestive organs for individuals from the population, the average annual allowable concentrations (MAC) of radionuclides in the atmospheric air and water (curie / k) for individuals from the population, as well as the content of radionuclides in a critical organ corresponding to the maximum allowable intake level (mCi) for personnel, are given in the regulations.

When calculating the allowable levels of radionuclide intake into the body, the often occurring uneven nature of the distribution of radionuclides in individual organs and tissues is also taken into account. The uneven distribution of radionuclides, leading to the creation of high local doses, underlies the high toxicity of alpha emitters, which is largely facilitated by the absence of recovery processes and the almost complete summation of the damage caused by this type of radiation.

Designations: β- - beta radiation; β+ - positron radiation; n - neutron; p - proton; d - deuteron; t - triton; α - alpha particle; E.Z. - decay by electron capture; γ - gamma radiation (as a rule, only the main lines of the γ spectrum are given); I. P. - isomeric transition; U (n, f) - uranium fission reaction. The specified isotope is isolated from a mixture of fission products; 90 Sr-> 90 Y - obtaining a daughter isotope (90 Y) as a result of the decay of the parent isotope (90 Sr), including using an isotope generator.

Bibliography: Ivanov I. I. et al. Radioactive isotopes in medicine and biology, M., 1955; Kamen M. Radioactive tracers in biology, trans. from English, M., 1948, bibliography; Levin V. I. Obtaining radioactive isotopes, M., 1972; Radiation safety standards (NRB-69), M., 1972; Obtaining in the reactor and the use of short-lived isotopes, trans. from in., ed. V. V. Bochkareva and B. V. Kurchatov. Moscow, 1965. Isotope Production, ed. V. V. Bochkareva. Moscow, 1973. Selinov I. P. Atomic nuclei and nuclear transformations, t. 1, M.-L., 1951, bibliogr.; Tumanyan M. A. and Kaushansky D. A. Radiation sterilization, M., 1974, bibliogr.; Fateeva M. N. Essays on radioisotope diagnostics, M., 1960, bibliogr.; Heveshi G. Radioactive tracers, trans. from English, M., 1950, bibliography; Dynamic studies with radioisotopes in medicine 1974, Proc, symp., v. 1-2, Vienna, IAEA, 1975; L e d e g e g Ch. M., Hollander J. M. a. P e g 1 m and n I. Tables of isotopes, N. Y., 1967; Silver S. Radioactive isotopes in clinical medicine, New Engl. J. Med., v. 272, p. 569, 1965, bibliogr.

V. V. Bochkarev; Yu. I. Moskalev (toks.), Compiler of the table. V.V. Bochkarev.

Repeat the main provisions of the topic "Basic concepts of chemistry" and solve the proposed tasks. Use ##6-17.

Basic provisions

1. Substance(simple and complex) is any combination of atoms and molecules that is in a certain state of aggregation.

The transformation of substances, accompanied by a change in their composition and (or) structure, is called chemical reactions .

2. Structural units substances:

· Atom- the smallest electrically neutral particle of a chemical element and a simple substance, which has all its chemical properties and is further physically and chemically indivisible.

· Molecule- the smallest electrically neutral particle of a substance that has all its chemical properties, physically indivisible, but divisible chemically.

3. Chemical element A type of atom with a certain nuclear charge.

4. Compound atom :

Particle	How to determine?	Charge		Weight
		Cl	conventional units		a.u.m.
Electron	Ordinal Number (N)	1.6 ∙ 10 -19		9.10 ∙ 10 -28	0.00055
Proton	Ordinal number (N)	1.6 ∙ 10 -19		1.67 ∙ 10 -24	1.00728
Neutron	Ar-N			1.67 ∙ 10 -24	1.00866

5. Compound atomic nucleus :

The nucleus consists of elementary particles ( nucleons) –

protons(1 1 p ) and neutrons(10n).

· Because Almost all the mass of an atom is concentrated in the nucleus m p ≈ m n≈ 1 amu, then rounded valueA rof a chemical element is equal to the total number of nucleons in the nucleus.

7. isotopes- a variety of atoms of the same chemical element, differing from each other only in their mass.

· Designation of isotopes: to the left of the symbol of the element indicate the mass number (top) and the serial number of the element (bottom)

Why do isotopes have different masses?

Task: Determine the atomic composition of chlorine isotopes: 35 17Cland 37 17Cl?

Isotopes have different masses due to the different number of neutrons in their nuclei.

8. In nature, chemical elements exist as mixtures of isotopes.

The isotopic composition of the same chemical element is expressed in terms of atomic fractions(ω at.), which indicate what part is the number of atoms of a given isotope from the total number of atoms of all isotopes of a given element, taken as one or 100%.

For example:

ω at (35 17 Cl) = 0.754

ω at (37 17 Cl) = 0.246

9. The periodic table shows the average values ​​of the relative atomic masses of chemical elements, taking into account their isotopic composition. Therefore A r indicated in the table are fractional.

A rWed= ω at.(1) ∙ Ar (1) + … + ω at.(n ) ∙ Ar ( n )

For example:

A rWed(Cl) \u003d 0.754 ∙ 35 + 0.246 ∙ 37 \u003d 35.453

10. Task to solve:

No. 1. Determine the relative atomic mass of boron if it is known that the mole fraction of the 10 B isotope is 19.6%, and the 11 B isotope is 80.4%.

11. The masses of atoms and molecules are very small. At present, a unified measurement system has been adopted in physics and chemistry.

1 amu =m(a.m.u.) = 1/12 m(12C) = 1.66057 ∙ 10 -27 kg \u003d 1.66057 ∙ 10 -24 g.

Absolute masses of some atoms:

m( C) \u003d 1.99268 ∙ 10 -23 g

m( H) \u003d 1.67375 ∙ 10 -24 g

m( O) \u003d 2.656812 ∙ 10 -23 g

A r- shows how many times a given atom is heavier than 1/12 of a 12 C atom. M r∙ 1.66 ∙ 10 -27 kg

13. The number of atoms and molecules in ordinary samples of substances is very large, therefore, when characterizing the amount of a substance, a unit of measurement is used -mole .

· Mole (ν)- a unit of the amount of a substance that contains as many particles (molecules, atoms, ions, electrons) as there are atoms in 12 g of an isotope 12 C

Mass of 1 atom 12 C is 12 amu, so the number of atoms in 12 g of the isotope 12 C equals:

N A= 12 g / 12 ∙ 1.66057 ∙ 10 -24 g = 6.0221 ∙ 10 23

· Physical quantity N A called constant Avogadro (Avogadro's number) and has the dimension [ N A ] = mol -1 .

14. Basic formulas:

M = M r = ρ ∙ Vm(ρ – density; V m – volume at n.c.)

Tasks for independent solution

No. 1. Calculate the number of nitrogen atoms in 100 g of ammonium carbonate containing 10% non-nitrogen impurities.

No. 2. Under normal conditions, 12 liters of a gas mixture consisting of ammonia and carbon dioxide has a mass of 18 g. How many liters of each of the gases does the mixture contain?

No. 3. Under the action of an excess of hydrochloric acid on 8.24 g of a mixture of manganese oxide (IV) with an unknown oxide MO 2 that does not react with hydrochloric acid, 1.344 l of gas at n.o. In another experiment, it was found that the molar ratio of manganese oxide (IV) to the unknown oxide is 3:1. Set the formula for the unknown oxide and calculate its mass fraction in the mixture.

It has been established that every chemical element found in nature is a mixture of isotopes (hence they have fractional atomic masses). To understand how isotopes differ from one another, it is necessary to consider in detail the structure of the atom. An atom forms a nucleus and an electron cloud. The mass of an atom is influenced by the electrons moving at a staggering speed in orbits in the electron cloud, the neutrons and protons that make up the nucleus.

What are isotopes

isotopes A type of atom of a chemical element. There are always equal numbers of electrons and protons in any atom. Since they have opposite charges (electrons are negative, and protons are positive), the atom is always neutral (this elementary particle does not carry a charge, it is equal to zero). When an electron is lost or captured, the atom loses its neutrality, becoming either a negative or a positive ion.
Neutrons have no charge, but their number in the atomic nucleus of the same element can be different. This does not affect the neutrality of the atom, but it does affect its mass and properties. For example, each isotope of a hydrogen atom has one electron and one proton each. And the number of neutrons is different. Protium has only 1 neutron, deuterium has 2 neutrons, and tritium has 3 neutrons. These three isotopes differ markedly from each other in properties.

Comparison of isotopes

How are isotopes different? They have a different number of neutrons, different masses and different properties. Isotopes have an identical structure of electron shells. This means that they are quite similar in chemical properties. Therefore, they are assigned one place in the periodic system.
Stable and radioactive (unstable) isotopes have been found in nature. The nuclei of atoms of radioactive isotopes are able to spontaneously transform into other nuclei. In the process of radioactive decay, they emit various particles.
Most elements have over two dozen radioactive isotopes. In addition, radioactive isotopes are artificially synthesized for absolutely all elements. In a natural mixture of isotopes, their content fluctuates slightly.
The existence of isotopes made it possible to understand why, in some cases, elements with a lower atomic mass have a higher serial number than elements with a larger atomic mass. For example, in an argon-potassium pair, argon includes heavy isotopes, and potassium includes light isotopes. Therefore, the mass of argon is greater than that of potassium.

ImGist determined that the difference between isotopes from each other is as follows:

They have different numbers of neutrons.
Isotopes have different masses of atoms.
The value of the mass of atoms of ions affects their total energy and properties.

When studying the properties of radioactive elements, it was found that atoms with different nuclear masses can be found in the same chemical element. At the same time, they have the same nuclear charge, that is, these are not impurities of third-party substances, but the same substance.

What are isotopes and why do they exist

In Mendeleev's periodic system, both a given element and atoms of a substance with a different mass of the nucleus occupy one cell. Based on the above, such varieties of the same substance were given the name "isotopes" (from the Greek isos - the same and topos - place). So, isotopes- these are varieties of a given chemical element, differing in the mass of atomic nuclei.

According to the accepted neutron roton model of the nucleus It was possible to explain the existence of isotopes as follows: the nuclei of some atoms of a substance contain a different number of neutrons, but the same number of protons. In fact, the nuclear charge of the isotopes of one element is the same, therefore, the number of protons in the nucleus is the same. Nuclei differ in mass, respectively, they contain a different number of neutrons.

Stable and unstable isotopes

Isotopes are either stable or unstable. To date, about 270 stable isotopes and more than 2000 unstable ones are known. stable isotopes- These are varieties of chemical elements that can independently exist for a long time.

Most of unstable isotopes was obtained artificially. Unstable isotopes are radioactive, their nuclei are subject to the process of radioactive decay, that is, spontaneous transformation into other nuclei, accompanied by the emission of particles and / or radiation. Almost all radioactive artificial isotopes have very short half-lives, measured in seconds and even fractions of seconds.

How many isotopes can a nucleus contain

The nucleus cannot contain an arbitrary number of neutrons. Accordingly, the number of isotopes is limited. Even in the number of protons elements, the number of stable isotopes can reach ten. For example, tin has 10 isotopes, xenon has 9, mercury has 7, and so on.

Those elements the number of protons is odd, can only have two stable isotopes. Some elements have only one stable isotope. These are substances such as gold, aluminum, phosphorus, sodium, manganese and others. Such variations in the number of stable isotopes for different elements are associated with a complex dependence of the number of protons and neutrons on the binding energy of the nucleus.

Almost all substances in nature exist as a mixture of isotopes. The number of isotopes in the composition of a substance depends on the type of substance, atomic mass and the number of stable isotopes of a given chemical element.

Even ancient philosophers suggested that matter is built from atoms. However, the fact that the “bricks” of the universe themselves consist of the smallest particles, scientists began to guess only at the turn of the 19th and 20th centuries. Experiments proving this made a real revolution in science in its time. It is the quantitative ratio of the constituent parts that distinguishes one chemical element from another. Each of them has its own place in according to the serial number. But there are varieties of atoms that occupy the same cells in the table, despite the difference in mass and properties. Why this is so and what isotopes are in chemistry will be discussed later.

Atom and its particles

Exploring the structure of matter through bombardment with alpha particles, E. Rutherford proved in 1910 that the main space of the atom is filled with emptiness. And only in the center is the core. Negative electrons move in orbits around it, making up the shell of this system. This is how the planetary model of the “bricks” of matter was created.

What are isotopes? Remember from a chemistry course that the nucleus also has a complex structure. It consists of positive protons and uncharged neutrons. The number of the former determines the qualitative characteristics of the chemical element. It is the number of protons that distinguishes substances from each other, endowing their nuclei with a certain charge. And on this basis, they are assigned a serial number in the periodic table. But the number of neutrons in the same chemical element differentiates them into isotopes. The definition in chemistry of this concept can therefore be given as follows. These are varieties of atoms that differ in the composition of the nucleus, have the same charge and serial numbers, but have different mass numbers due to differences in the number of neutrons.

Notation

Studying chemistry in grade 9 and isotopes, students will learn about accepted conventions. The letter Z marks the charge of the nucleus. This figure coincides with the number of protons and therefore is their indicator. The sum of these elements with neutrons, marked with the sign N, is A - the mass number. The family of isotopes of one substance, as a rule, is indicated by the icon of that chemical element, which in the periodic table is endowed with a serial number coinciding with the number of protons in it. The left superscript added to the specified icon corresponds to the mass number. For example, 238 U. The charge of an element (in this case, uranium, marked with serial number 92) is indicated by a similar index below.

Knowing these data, one can easily calculate the number of neutrons in a given isotope. It is equal to the mass number minus the serial number: 238 - 92 \u003d 146. The number of neutrons could be less, from this this chemical element would not cease to be uranium. It should be noted that most often in other, simpler substances, the number of protons and neutrons is approximately the same. Such information helps to understand what an isotope is in chemistry.

Nucleons

It is the number of protons that gives individuality to a certain element, and the number of neutrons does not affect it in any way. But the atomic mass is made up of these two indicated elements, which have the common name "nucleons", representing their sum. However, this indicator does not depend on those forming the negatively charged shell of the atom. Why? It's worth just comparing.

The mass fraction of a proton in an atom is large and is approximately 1 AU. u m or 1.672 621 898 (21) 10 -27 kg. The neutron is close to the parameters of this particle (1.674 927 471(21) 10 -27 kg). But the mass of an electron is thousands of times smaller, it is considered negligible and is not taken into account. That is why, knowing the superscript of an element in chemistry, it is not difficult to find out the composition of the nucleus of isotopes.

Isotopes of hydrogen

The isotopes of certain elements are so well known and common in nature that they have received their own names. The clearest and simplest example of this is hydrogen. Under natural conditions, it is found in its most common form of protium. This element has a mass number of 1, and its nucleus consists of one proton.

So what are hydrogen isotopes in chemistry? As you know, the atoms of this substance have the first number in the periodic table and, accordingly, are endowed in nature with a charge number of 1. But the number of neutrons in the nucleus of an atom is different for them. Deuterium, being heavy hydrogen, in addition to the proton, has one more particle in the nucleus, that is, the neutron. As a result, this substance exhibits its own physical properties, unlike protium, having its own weight, melting point and boiling point.

Tritium

Tritium is the most complex of all. This is superheavy hydrogen. In accordance with the definition of isotopes in chemistry, it has a charge number of 1, but a mass number of 3. It is often called a triton, because in addition to one proton, it has two neutrons in the nucleus, that is, it consists of three elements. The name of this element, discovered in 1934 by Rutherford, Oliphant and Harteck, was proposed even before its discovery.

It is an unstable substance exhibiting radioactive properties. Its nucleus has the ability to split with the release of a beta particle and an electron antineutrino. The decay energy of this substance is not very high and amounts to 18.59 keV. Therefore, such radiation is not too dangerous for humans. Ordinary clothing and surgical gloves can protect against it. And this radioactive element obtained with food is quickly excreted from the body.

Isotopes of uranium

Much more dangerous are the various types of uranium, of which 26 are known to science today. Therefore, when talking about what isotopes are in chemistry, it is impossible not to mention this element. Despite the variety of types of uranium, only three of its isotopes occur in nature. These include 234 U, 235 U, 238 U. The first of them, having suitable properties, is actively used as fuel in nuclear reactors. And the latter - for the production of plutonium-239, which itself, in turn, is indispensable as the most valuable fuel.

Each of the radioactive elements is characterized by its own. This is the length of time during which the substance splits in the ratio of ½. That is, as a result of this process, the amount of the preserved part of the substance is halved. This period of time for uranium is huge. For example, for the isotope-234, it is estimated at 270 millennia, and for the other two indicated varieties, it is much more significant. The record half-life is that of uranium-238, lasting billions of years.

Nuclides

Not every type of atom, characterized by its own and strictly defined number of protons and electrons, is so stable that there is at least some long period sufficient for its study. Those that are relatively stable are called nuclides. Stable formations of this kind do not undergo radioactive decay. Unstable are called radionuclides and, in turn, are also divided into short-lived and long-lived. As is known from grade 11 chemistry lessons about the structure of isotope atoms, osmium and platinum have the largest number of radionuclides. Cobalt and gold each have one stable nuclide, and tin has the largest number of stable nuclides.

Calculation of the serial number of the isotope

Now let's try to summarize the information described earlier. Having understood what isotopes are in chemistry, it's time to figure out how you can use the knowledge gained. Let's look at this with a specific example. Suppose it is known that a certain chemical element has a mass number of 181. At the same time, the shell of an atom of this substance contains 73 electrons. How can one, using the periodic table, find out the name of a given element, as well as the number of protons and neutrons in its nucleus?

Let's start solving the problem. You can determine the name of a substance by knowing its serial number, which corresponds to the number of protons. Since the number of positive and negative charges in an atom is equal, it is 73. So, this is tantalum. Moreover, the total number of nucleons in total is 181, which means that the protons of this element are 181 - 73 = 108. Quite simply.

Isotopes of gallium

The element gallium in has an atomic number of 71. In nature, this substance has two isotopes - 69 Ga and 71 Ga. How to determine the percentage of varieties of gallium?

Solving problems on isotopes in chemistry is almost always associated with information that can be obtained from the periodic table. This time, you should do the same. Let us determine the average atomic mass from the indicated source. It is equal to 69.72. Denoting for x and y the quantitative ratio of the first and second isotopes, we take their sum equal to 1. So, in the form of an equation, this will be written: x + y = 1. It follows that 69x + 71y = 69.72. Expressing y in terms of x and substituting the first equation into the second, we get that x = 0.64 and y = 0.36. This means that 69 Ga is contained in nature 64%, and the percentage of 71 Ga is 34%.

Isotope transformations

The radioactive fission of isotopes with their transformation into other elements is divided into three main types. The first of these is alpha decay. It occurs with the emission of a particle, which is the nucleus of a helium atom. That is, this formation, consisting of a set of pairs of neutrons and protons. Since the number of the latter determines the charge number and the number of an atom of a substance in the periodic system, as a result of this process, a qualitative transformation of one element into another occurs, and in the table it shifts to the left by two cells. In this case, the mass number of the element is reduced by 4 units. We know this from the structure of atoms of isotopes.

When the nucleus of an atom loses a beta particle, which is essentially an electron, its composition changes. One of the neutrons is transformed into a proton. This means that the qualitative characteristics of the substance change again, and the element is shifted in the table by one cell to the right, practically without losing mass. Typically, such a transformation is associated with electromagnetic gamma radiation.

Radium isotope conversion

The above information and knowledge from grade 11 chemistry about isotopes again helps to solve practical problems. For example, the following: 226 Ra during decay turns into a chemical element of group IV, which has a mass number of 206. How many alpha and beta particles should it lose in this case?

Given the changes in the mass and group of the daughter element, using the periodic table, it is easy to determine that the isotope formed during the fission will be lead with a charge of 82 and a mass number of 206. And given the charge number of this element and the original radium, it should be assumed that its nucleus lost five alpha -particles and four beta particles.

Use of radioactive isotopes

Everyone is well aware of the harm that radioactive radiation can cause to living organisms. However, the properties of radioactive isotopes are useful for humans. They are successfully used in many industries. With their help, it is possible to detect leaks in engineering and building structures, underground pipelines and oil pipelines, storage tanks, heat exchangers at power plants.

These properties are also actively used in scientific experiments. For example, the tsetse fly is a carrier of many serious diseases for humans, livestock and domestic animals. In order to prevent this, the males of these insects are sterilized by means of weak radioactive radiation. Isotopes are also indispensable in the study of the mechanisms of certain chemical reactions, because the atoms of these elements can label water and other substances.

In biological research, labeled isotopes are often also used. For example, it was in this way that it was established how phosphorus affects the soil, the growth and development of cultivated plants. The properties of isotopes are also successfully used in medicine, which made it possible to treat cancerous tumors and other serious diseases, and to determine the age of biological organisms.