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ISOTOPS-varieties of the same chemical element, similar in their physicochemical properties, but having different atomic masses. The name "isotopes" was proposed in 1912 by the English radiochemist Frederick Soddy, who formed it from two Greek words: isos - the same and topos - place. Isotopes occupy the same place in the cell of Mendeleev's periodic system of elements.

An atom of any chemical element consists of a positively charged nucleus and a cloud of negatively charged electrons surrounding it. The position of a chemical element in the periodic system of Mendeleev (its serial number) is determined by the charge of the nucleus of its atoms. isotopes are called therefore varieties of the same chemical element whose atoms have the same nuclear charge (and, therefore, almost the same electron shells), but differ in the values ​​of the mass of the nucleus. According to the figurative expression of F. Soddy, the atoms of isotopes are the same "outside", but different "inside".

The neutron was discovered in 1932 – a particle that has no charge, with a mass close to the mass of the nucleus of a hydrogen atom - a proton , and created proton-neutron model of the nucleus. As a result in science, the final modern definition of the concept of isotopes has been established: isotopes are substances whose atomic nuclei consist of the same number of protons and differ only in the number of neutrons in the nucleus . Each isotope is usually denoted by a set of symbols , where X is the symbol of a chemical element, Z is the charge of the atomic nucleus (the number of protons), A is the mass number of the isotope (the total number of nucleons - protons and neutrons in the nucleus, A = Z + N). Since the charge of the nucleus is unambiguously associated with the symbol of the chemical element, often the notation A X is simply used for abbreviation.

Of all the isotopes known to us, only the isotopes of hydrogen have their own names. Thus, the 2 H and 3 H isotopes are called deuterium and tritium and are designated D and T, respectively (the 1 H isotope is sometimes called protium).

They occur naturally as stable isotopes. , and unstable - radioactive, the nuclei of atoms of which are subject to spontaneous transformation into other nuclei with the emission of various particles (or the processes of the so-called radioactive decay). Now about 270 stable isotopes are known, and stable isotopes are found only in elements with atomic number Z Ј 83. The number of unstable isotopes exceeds 2000, the vast majority of them were obtained artificially as a result of various nuclear reactions. The number of radioactive isotopes in many elements is very large and can exceed two dozen. The number of stable isotopes is much less. Some chemical elements consist of only one stable isotope (beryllium, fluorine, sodium, aluminum, phosphorus, manganese, gold and a number of other elements). The largest number of stable isotopes - 10 - was found in tin, in iron, for example, there are 4 of them, and in mercury - 7.

Discovery of isotopes, historical background.

In 1808, the English naturalist John Dalton first introduced the definition of a chemical element as a substance consisting of atoms of one kind. In 1869, the chemist DIMendeleev discovered the periodic law of chemical elements. One of the difficulties in substantiating the concept of an element as a substance that occupies a certain place in the cell of the periodic system was the experimentally observed non-integer atomic weights of elements. In 1866, the English physicist and chemist, Sir William Crookes, put forward the hypothesis that each natural chemical element is a mixture of substances that are identical in their properties, but have different atomic masses, but at that time such an assumption had not yet been experimentally confirmed and therefore little seen.

An important step towards the discovery of isotopes was the discovery of the phenomenon of radioactivity and the hypothesis of radioactive decay formulated by Ernst Rutherford and Frederick Soddy: radioactivity is nothing more than the decay of an atom into a charged particle and an atom of another element, which differs in its chemical properties from the original one. As a result, the concept of radioactive series or radioactive families arose. , at the beginning of which there is the first parent element, which is radioactive, and at the end - the last stable element. An analysis of the chains of transformations showed that in their course one and the same radioactive elements, differing only in atomic masses, can appear in one cell of the periodic system. In fact, this meant the introduction of the concept of isotopes.

Independent confirmation of the existence of stable isotopes of chemical elements was then obtained in the experiments of J. J. Thomson and Aston in 1912-1920 with beams of positively charged particles (or so-called canal rays ) emerging from the discharge tube.

In 1919 Aston designed an instrument called the mass spectrograph. (or mass spectrometer) . The discharge tube was still used as an ion source, but Aston found a way in which the successive deflection of a beam of particles in electric and magnetic fields led to the focusing of particles with the same charge-to-mass ratio (regardless of their speed) at the same point on the screen. Along with Aston, a mass spectrometer of a slightly different design was created in the same years by the American Dempster. As a result of the subsequent use and improvement of mass spectrometers by the efforts of many researchers, by 1935 an almost complete table of the isotopic compositions of all chemical elements known by that time was compiled.

Isotope separation methods.

To study the properties of isotopes, and especially to use them for scientific and applied purposes, it is necessary to obtain them in more or less noticeable quantities. In conventional mass spectrometers, almost complete separation of isotopes is achieved, but their number is negligible. Therefore, the efforts of scientists and engineers were directed to the search for other possible methods of isotope separation. First of all, physical and chemical separation methods were mastered, based on differences in such properties of isotopes of the same element as evaporation rates, equilibrium constants, rates of chemical reactions, etc. The most effective among them were the methods of rectification and isotope exchange, which are widely used in the industrial production of isotopes of light elements: hydrogen, lithium, boron, carbon, oxygen and nitrogen.

Another group of methods is formed by the so-called molecular-kinetic methods: gaseous diffusion, thermal diffusion, mass diffusion (diffusion in a vapor stream), and centrifugation. Gas diffusion methods based on different diffusion rates of isotopic components in highly dispersed porous media were used during the Second World War in the organization of industrial production of uranium isotope separation in the United States as part of the so-called Manhattan project to create an atomic bomb. To obtain the necessary quantities of uranium, enriched up to 90% with the light isotope 235 U, the main "combustible" component of the atomic bomb, plants were built that occupied an area of ​​about four thousand hectares. More than 2 billion dollars were allocated for the creation of an atomic center with plants for the production of enriched uranium. After the war, plants for the production of enriched uranium for military purposes, also based on the diffusion method of separation, were developed and built in the USSR. In recent years, this method has given way to a more efficient and less costly centrifugation method. In this method, the effect of separating the isotope mixture is achieved due to the different action of centrifugal forces on the components of the isotope mixture that fills the centrifuge rotor, which is a thin-walled cylinder limited from above and below, rotating at a very high speed in a vacuum chamber. Hundreds of thousands of centrifuges connected in cascades, the rotor of each of which makes more than a thousand revolutions per second, are currently used in modern separation plants both in Russia and in other developed countries of the world. Centrifuges are used not only to produce the enriched uranium needed to power the nuclear reactors of nuclear power plants, but also to produce isotopes of about thirty chemical elements in the middle part of the Periodic Table. For the separation of various isotopes, electromagnetic separation installations with powerful ion sources are also used; in recent years, laser separation methods have also become widespread.

The use of isotopes.

Various isotopes of chemical elements are widely used in scientific research, in various fields of industry and agriculture, in nuclear energy, modern biology and medicine, in environmental studies and other areas. In scientific research (for example, in chemical analysis), as a rule, small amounts of rare isotopes of various elements are required, calculated in grams and even milligrams per year. At the same time, for a number of isotopes widely used in nuclear power engineering, medicine, and other industries, the need for their production can be many kilograms and even tons. Thus, in connection with the use of heavy water D 2 O in nuclear reactors, its global production by the beginning of the 1990s of the last century was about 5000 tons per year. The hydrogen isotope deuterium, which is part of heavy water, the concentration of which in the natural mixture of hydrogen is only 0.015%, along with tritium, in the future, according to scientists, will become the main fuel component of power thermonuclear reactors operating on the basis of nuclear fusion reactions. In this case, the need for the production of hydrogen isotopes will be enormous.

In scientific research, stable and radioactive isotopes are widely used as isotope indicators (labels) in the study of various processes occurring in nature.

In agriculture, isotopes ("labeled" atoms) are used, for example, to study the processes of photosynthesis, the digestibility of fertilizers, and to determine the efficiency of the use of nitrogen, phosphorus, potassium, trace elements, and other substances by plants.

Isotope technologies are widely used in medicine. So in the US, according to statistics, more than 36 thousand medical procedures are performed per day and about 100 million laboratory tests using isotopes. The most common procedures associated with computed tomography. The carbon isotope C 13 enriched up to 99% (natural content about 1%) is actively used in the so-called "diagnostic control of breathing". The essence of the test is very simple. The enriched isotope is introduced into the patient's food and, after participating in the metabolic process in various organs of the body, is released as carbon dioxide CO 2 exhaled by the patient, which is collected and analyzed using a spectrometer. The difference in the rates of processes associated with the release of various amounts of carbon dioxide labeled with the isotope C 13 makes it possible to judge the state of various organs of the patient. In the US, the number of patients who will undergo this test is estimated at 5 million people a year. Laser separation methods are now used to produce the highly enriched C 13 isotope on an industrial scale.

Vladimir Zhdanov

Probably, there is no such person on earth who would not have heard about isotopes. But not everyone knows what it is. The phrase "radioactive isotopes" sounds especially frightening. These obscure chemical elements terrify humanity, but in fact they are not as scary as it might seem at first glance.

Definition

To understand the concept of radioactive elements, it is first necessary to say that isotopes are samples of the same chemical element, but with different masses. What does it mean? Questions will disappear if we first remember the structure of the atom. It consists of electrons, protons and neutrons. The number of the first two elementary particles in the nucleus of an atom is always constant, while neutrons, which have their own mass, can occur in the same substance in different quantities. This circumstance gives rise to a variety of chemical elements with different physical properties.

Now we can give a scientific definition of the concept under study. So, isotopes are a cumulative set of chemical elements similar in properties, but having different masses and physical properties. According to more modern terminology, they are called a galaxy of nucleotides of a chemical element.

A bit of history

At the beginning of the last century, scientists discovered that the same chemical compound under different conditions can have different masses of electron nuclei. From a purely theoretical point of view, such elements could be considered new and they could begin to fill empty cells in the periodic table of D. Mendeleev. But there are only nine free cells in it, and scientists discovered dozens of new elements. In addition, mathematical calculations showed that the discovered compounds cannot be considered previously unknown, because their chemical properties fully corresponded to the characteristics of existing ones.

After lengthy discussions, it was decided to call these elements isotopes and place them in the same cell as those whose nuclei contain the same number of electrons with them. Scientists have been able to determine that isotopes are just some variations of chemical elements. However, the causes of their occurrence and the duration of life were studied for almost a century. Even at the beginning of the 21st century, it is impossible to assert that humanity knows absolutely everything about isotopes.

Persistent and non-persistent variations

Each chemical element has several isotopes. Due to the fact that there are free neutrons in their nuclei, they do not always enter into stable bonds with the rest of the atom. After some time, free particles leave the core, which changes its mass and physical properties. This is how other isotopes are formed, which eventually leads to the formation of a substance with an equal number of protons, neutrons and electrons.

Those substances that decay very quickly are called radioactive isotopes. They release a large number of neutrons into space, forming powerful ionizing gamma radiation, known for its strong penetrating ability, which negatively affects living organisms.

More stable isotopes are not radioactive, since the number of free neutrons they release is not capable of producing radiation and significantly affecting other atoms.

Quite a long time ago, scientists established one important pattern: each chemical element has its own isotopes, persistent or radioactive. Interestingly, many of them were obtained in the laboratory, and their presence in their natural form is small and not always recorded by instruments.

Distribution in nature

Under natural conditions, most often there are substances whose isotope mass is directly determined by its ordinal number in the D. Mendeleev table. For example, hydrogen, denoted by the symbol H, has serial number 1, and its mass is equal to one. Its isotopes, 2H and 3H, are extremely rare in nature.

Even the human body has a certain amount of radioactive isotopes. They get inside through food in the form of carbon isotopes, which, in turn, are absorbed by plants from the soil or air and pass into the composition of organic matter during photosynthesis. Therefore, both humans, animals, and plants emit a certain radiation background. Only it is so low that it does not interfere with normal functioning and growth.

The sources that contribute to the formation of isotopes are the inner layers of the earth's core and radiation from outer space.

As you know, the temperature on the planet largely depends on its hot core. But only recently it became clear that the source of this heat is a complex thermonuclear reaction, in which radioactive isotopes participate.

Isotope decay

Since isotopes are unstable formations, it can be assumed that, over time, they always decay into more permanent nuclei of chemical elements. This statement is true, because scientists have not been able to detect a huge number of radioactive isotopes in nature. And most of those that were mined in laboratories lasted from a couple of minutes to several days, and then turned back into ordinary chemical elements.

But there are also isotopes in nature that are very resistant to decay. They can exist for billions of years. Such elements were formed in those distant times, when the earth was still being formed, and there was not even a solid crust on its surface.

Radioactive isotopes decay and are re-formed very quickly. Therefore, in order to facilitate the assessment of the stability of the isotope, scientists decided to consider the category of its half-life.

Half life

It may not be immediately clear to all readers what is meant by this concept. Let's define it. The half-life of an isotope is the time during which the conditional half of the substance taken ceases to exist.

This does not mean that the rest of the connection will be destroyed in the same amount of time. With regard to this half, it is necessary to consider a different category - the period of time during which its second part, that is, a quarter of the original amount of the substance, will disappear. And this consideration continues ad infinitum. It can be assumed that it is simply impossible to calculate the time of complete decay of the initial amount of matter, since this process is practically endless.

However, scientists, knowing the half-life, can determine how much of the substance existed in the beginning. These data are successfully used in related sciences.

In the modern scientific world, the concept of complete decay is practically not used. For each isotope, it is customary to indicate its half-life, which varies from a few seconds to many billions of years. The lower the half-life, the more radiation comes from the substance and the higher its radioactivity.

Enrichment of minerals

In some branches of science and technology, the use of a relatively large amount of radioactive substances is considered mandatory. But at the same time, in natural conditions, there are very few such compounds.

It is known that isotopes are uncommon variants of chemical elements. Their number is measured by a few percent of the most resistant variety. That is why scientists need to carry out artificial enrichment of fossil materials.

Over the years of research, it was possible to find out that the decay of an isotope is accompanied by a chain reaction. The released neutrons of one substance begin to influence another. As a result of this, heavy nuclei break up into lighter ones and new chemical elements are obtained.

This phenomenon is called a chain reaction, as a result of which more stable, but less common isotopes can be obtained, which are later used in the national economy.

Application of decay energy

Scientists also found that during the decay of a radioactive isotope, a huge amount of free energy is released. Its quantity is usually measured by the Curie unit, equal to the fission time of 1 g of radon-222 in 1 second. The higher this indicator, the more energy is released.

This was the reason for the development of ways to use free energy. This is how nuclear reactors appeared, in which a radioactive isotope is placed. Most of the energy it gives off is collected and converted into electricity. Based on these reactors, nuclear power plants are created, which provide the cheapest electricity. Reduced versions of such reactors are put on self-propelled mechanisms. Considering the danger of accidents, most often such machines are submarines. In the event of a reactor failure, the number of victims on the submarine will be easier to minimize.

Another very scary option for using half-life energy is atomic bombs. During World War II, they were tested on humanity in the Japanese cities of Hiroshima and Nagasaki. The consequences were very sad. Therefore, the world has an agreement on the non-use of these dangerous weapons. At the same time, large states with a focus on militarization continue research in this industry today. In addition, many of them, secretly from the world community, are making atomic bombs, which are thousands of times more dangerous than those used in Japan.

Isotopes in medicine

For peaceful purposes, the decay of radioactive isotopes has learned to use in medicine. By directing radiation to the affected area of ​​the body, it is possible to stop the course of the disease or help the patient to recover completely.

But more often radioactive isotopes are used for diagnostics. The thing is that their movement and the nature of the cluster is easiest to fix by the radiation that they produce. So, a certain non-dangerous amount of a radioactive substance is introduced into the human body, and doctors use instruments to observe how and where it gets.

Thus, the diagnosis of the work of the brain, the nature of cancerous tumors, the features of the work of the endocrine and external secretion glands are carried out.

Application in archeology

It is known that in living organisms there is always radioactive carbon-14, the half-life of which isotope is 5570 years. In addition, scientists know how much of this element is contained in the body until the moment of his death. This means that all cut trees emit the same amount of radiation. Over time, the intensity of radiation decreases.

This helps archaeologists determine how long ago the tree from which the galley or any other ship was built died, and therefore the very time of construction. This research method is called radioactive carbon analysis. Thanks to him, it is easier for scientists to establish the chronology of historical events.

isotopes- varieties of atoms (and nuclei) of a chemical element that have the same atomic (ordinal) number, but different mass numbers.

The term isotope is formed from the Greek roots isos (ἴσος "equal") and topos (τόπος "place"), meaning "same place"; Thus, the meaning of the name is that different isotopes of the same element occupy the same position in the periodic table.

Three natural isotopes of hydrogen. The fact that each isotope has one proton has variants of hydrogen: the isotope identity is determined by the number of neutrons. From left to right, the isotopes are protium (1H) with zero neutrons, deuterium (2H) with one neutron, and tritium (3H) with two neutrons.

The number of protons in the nucleus of an atom is called the atomic number and is equal to the number of electrons in a neutral (non-ionized) atom. Each atomic number identifies a particular element, but not an isotope; An atom of a given element can have a wide range in the number of neutrons. The number of nucleons (both protons and neutrons) in a nucleus is the mass number of an atom, and each isotope of a given element has a different mass number.

For example, carbon-12, carbon-13, and carbon-14 are three isotopes of elemental carbon with mass numbers 12, 13, and 14, respectively. The atomic number of carbon is 6, which means that each carbon atom has 6 protons, so the neutron numbers of these isotopes are 6, 7, and 8, respectively.

Huclides and isotopes

The nuclide belongs to the nucleus, not to the atom. Identical nuclei belong to the same nuclide, for example, each carbon-13 nuclide nucleus consists of 6 protons and 7 neutrons. The concept of nuclides (referring to individual nuclear species) emphasizes nuclear properties over chemical properties, while the isotope concept (grouping all the atoms of each element) emphasizes chemical reaction over nuclear. The neutron number has a great influence on the properties of nuclei, but its influence on the chemical properties is negligible for most elements. Even in the case of the lightest elements, where the ratio of neutrons to atomic number varies the most between isotopes, it usually has only a minor effect, although it does matter in some cases (for hydrogen, the lightest element, the isotope effect is large. To greatly affect to biology). Because isotope is an older term, it is better known than nuclide and is still occasionally used in contexts where nuclide might be more appropriate, such as nuclear technology and nuclear medicine.

Notation

An isotope or nuclide is identified by the name of a particular element (this indicates the atom number) followed by a hyphen and a mass number (for example, helium-3, helium-4, carbon-12, carbon-14, uranium-235, and uranium-239). When a chemical symbol is used, e.g. "C" for carbon, standard notation (now known as "AZE notation" because A is the mass number, Z is the atomic number, and E for the element) is to indicate the mass number (number of nucleons) with a superscript at the top left of chemical symbol and indicate the atomic number with a subscript in the lower left corner). Since the atomic number is given by the symbol of the element, usually only the mass number in the superscript is given, and the atom index is not given. The letter m is sometimes appended after the mass number to indicate a nuclear isomer, a metastable or energetically excited nuclear state (as opposed to the lowest energy ground state), such as 180m 73Ta (tantalum-180m).

Radioactive, primary and stable isotopes

Some isotopes are radioactive and are therefore called radioisotopes or radionuclides, while others have never been observed to decay radioactively and are called stable isotopes or stable nuclides. For example, 14 C is a radioactive form of carbon, while 12 C and 13 C are stable isotopes. There are about 339 naturally occurring nuclides on Earth, of which 286 are primordial nuclides, meaning they have been around since the formation of the solar system.

The original nuclides include 32 nuclides with very long half-lives (over 100 million years) and 254 that are formally considered "stable nuclides" because they have not been observed to decay. In most cases, for obvious reasons, if an element has stable isotopes then those isotopes dominate the elemental abundance found on Earth and in the solar system. However, in the case of three elements (tellurium, indium, and rhenium), the most abundant isotope found in nature is actually one (or two) extremely long-lived radioisotope(s) of the element, despite the fact that these elements have one or more stable isotopes.

The theory predicts that many apparently "stable" isotopes/nuclides are radioactive, with extremely long half-lives (not considering the possibility of proton decay, which would make all nuclides eventually unstable). Of the 254 nuclides that have never been observed, only 90 of them (all of the first 40 elements) are theoretically resistant to all known decay forms. Element 41 (niobium) is theoretically unstable by spontaneous fission, but this has never been discovered. Many other stable nuclides are in theory energetically susceptible to other known forms of decay, such as alpha decay or double beta decay, but decay products have not yet been observed, and thus these isotopes are considered to be "observationally stable". The predicted half-lives for these nuclides often greatly exceed the estimated age of the universe, and in fact there are also 27 known radionuclides with half-lives longer than the age of the universe.

Radioactive nuclides, artificially created, currently 3339 nuclides are known. These include 905 nuclides that are either stable or have half-lives greater than 60 minutes.

Isotope Properties

Chemical and molecular properties

A neutral atom has the same number of electrons as protons. Thus, different isotopes of a given element have the same number of electrons and have a similar electronic structure. Since the chemical behavior of an atom is largely determined by its electronic structure, different isotopes exhibit almost identical chemical behavior.

An exception to this is the kinetic isotope effect: due to their large masses, heavier isotopes tend to react somewhat more slowly than lighter isotopes of the same element. This is most pronounced for protium (1 H), deuterium (2 H), and tritium (3 H), since deuterium has twice the mass of protium and tritium has three times the mass of protium. These differences in mass also affect the behavior of their respective chemical bonds by changing the center of gravity (reduced mass) of atomic systems. However, for heavier elements, the relative mass difference between isotopes is much smaller, so that the effects of mass difference in chemistry are usually negligible. (Heavy elements also have relatively more neutrons than lighter elements, so the ratio of nuclear mass to total electron mass is somewhat larger.)

Similarly, two molecules that differ only in the isotopes of their atoms (isotopologues) have the same electronic structure and hence almost indistinguishable physical and chemical properties (again, with deuterium and tritium being the primary exceptions). The vibrational modes of a molecule are determined by its shape and the masses of its constituent atoms; Therefore, different isotopologues have different sets of vibrational modes. Because vibrational modes allow a molecule to absorb photons of the appropriate energies, isotopologues have different optical properties in the infrared.

Nuclear properties and stability

Atomic nuclei are made up of protons and neutrons bound together by a residual strong force. Because the protons are positively charged, they repel each other. Neutrons, which are electrically neutral, stabilize the nucleus in two ways. Their contact pushes the protons back a little, reducing the electrostatic repulsion between the protons, and they exert an attractive nuclear force on each other and on the protons. For this reason, one or more neutrons are required for two or more protons to bind to the nucleus. As the number of protons increases, so does the ratio of neutrons to protons needed to provide a stable nucleus (see graph on the right). For example, although the ratio neutron: proton 3 2 He is 1:2, the ratio neutron: proton 238 92 U
Over 3:2. A number of lighter elements have stable nuclides with a ratio of 1:1 (Z = N). The nuclide 40 20 Ca (calcium-40) is the observable heaviest stable nuclide with the same number of neutrons and protons; (Theoretically, the heaviest stable is sulfur-32). All stable nuclides heavier than calcium-40 contain more neutrons than protons.

Number of isotopes per element

Of the 81 elements with stable isotopes, the largest number of stable isotopes observable for any element is ten (for the element tin). No element has nine stable isotopes. Xenon is the only element with eight stable isotopes. Four elements have seven stable isotopes, eight of which have six stable isotopes, ten have five stable isotopes, nine have four stable isotopes, five have three stable isotopes, 16 have two stable isotopes, and 26 elements have only one (of which 19 are the so-called mononuclide elements, which have a single primordial stable isotope that dominates and fixes the atomic weight of the natural element with high precision, 3 radioactive mononuclide elements are also present). In total, there are 254 nuclides that have not been observed to decay. For 80 elements that have one or more stable isotopes, the average number of stable isotopes is 254/80 = 3.2 isotopes per element.

Even and odd numbers of nucleons

Protons: The ratio of neutrons is not the only factor affecting nuclear stability. It depends also on the parity or oddness of its atomic number Z, the number of neutrons N, hence the sum of their mass number A. Odd both Z and N tends to lower the nuclear binding energy, creating odd nuclei that are generally less stable. This significant difference in nuclear binding energy between neighboring nuclei, especially odd isobars, has important consequences: unstable isotopes with suboptimal numbers of neutrons or protons decay by beta decay (including positron decay), electron capture, or other exotic means such as spontaneous fission and decay. clusters.

Most stable nuclides are an even number of protons and an even number of neutrons, where Z, N, and A are all even. Odd stable nuclides are divided (approximately evenly) into odd ones.

atomic number

The 148 even proton, even neutron (EE) nuclides make up ~58% of all stable nuclides. There are also 22 primordial long-lived even nuclides. As a result, each of the 41 even elements from 2 to 82 has at least one stable isotope, and most of these elements have multiple primary isotopes. Half of these even elements have six or more stable isotopes. The extreme stability of helium-4, due to the binary bonding of two protons and two neutrons, prevents any nuclides containing five or eight nucleons from existing long enough to serve as platforms for the accumulation of heavier elements through nuclear fusion.

These 53 stable nuclides have an even number of protons and an odd number of neutrons. They are a minority compared to the even isotopes, which are about 3 times as numerous. Among the 41 even-Z elements that have a stable nuclide, only two elements (argon and cerium) do not have even-odd stable nuclides. One element (tin) has three. There are 24 elements that have one odd-even nuclide and 13 that have two odd-even nuclides.

Because of their odd neutron numbers, even-odd nuclides tend to have large neutron capture cross sections due to the energy that comes from neutron coupling effects. These stable nuclides may be unusually abundant in nature, mainly because in order to form and enter into primordial abundance, they must escape neutron capture in order to form yet other stable even-odd isotopes over the course of how s is the process and r is the neutron capture process. during nucleosynthesis.

odd atomic number

The 48 stable odd-proton and even-neutron nuclides, stabilized by their even number of paired neutrons, form the majority of the stable isotopes of the odd elements; Very few odd-proton-odd neutron nuclides make up others. There are 41 odd elements from Z = 1 to 81, of which 39 have stable isotopes (the elements technetium (43 Tc) and promethium (61 Pm) have no stable isotopes). Of these 39 odd Z elements, 30 elements (including hydrogen-1, where 0 neutrons is even) have one stable odd-even isotope, and nine elements: chlorine (17 Cl), potassium (19K), copper (29 Cu), gallium ( 31 Ga), Bromine (35 Br), silver (47 Ag), antimony (51 Sb), iridium (77 Ir) and thallium (81 Tl) each have two odd-even stable isotopes. Thus, 30 + 2 (9) = 48 stable even-even isotopes are obtained.

Only five stable nuclides contain both an odd number of protons and an odd number of neutrons. The first four "odd-odd" nuclides occur in low molecular weight nuclides, for which changing from a proton to a neutron or vice versa will result in a very lopsided proton-neutron ratio.

The only completely "stable", odd-odd nuclide is 180m 73 Ta, which is considered the rarest of the 254 stable isotopes and is the only primordial nuclear isomer that has not yet been observed to decay, despite experimental attempts.

Odd number of neutrons

Actinides with an odd number of neutrons tend to fissile (with thermal neutrons), while those with an even neutron number tend not to, although they do fission into fast neutrons. All observationally stable odd-odd nuclides have a non-zero integer spin. This is because a single unpaired neutron and an unpaired proton have more nuclear force attraction to each other if their spins are aligned (producing a total spin of at least 1 unit) rather than aligned.

Occurrence in nature

Elements are made up of one or more naturally occurring isotopes. Unstable (radioactive) isotopes are either primary or post-example. The original isotopes were the product of stellar nucleosynthesis, or another type of nucleosynthesis such as cosmic ray splitting, and have persisted up to the present because their decay rate is so slow (eg uranium-238 and potassium-40). Post-natural isotopes have been created by cosmic ray bombardment as cosmogenic nuclides (eg tritium, carbon-14) or the decay of a radioactive primordial isotope into the daughter of a radioactive radiogenic nuclide (eg uranium to radium). Several isotopes are naturally synthesized as nucleogenic nuclides by other natural nuclear reactions, such as when neutrons from natural nuclear fission are absorbed by another atom.

As discussed above, only 80 elements have stable isotopes, and 26 of them have only one stable isotope. Thus, about two-thirds of the stable elements occur naturally on Earth in a few stable isotopes, with the highest number of stable isotopes for an element being ten, for tin (50Sn). About 94 elements exist on Earth (up to and including plutonium), although some are only found in very small amounts, such as plutonium-244. Scientists believe that elements that occur naturally on Earth (some only as radioisotopes) occur as 339 isotopes (nuclides) in total. Only 254 of these naturally occurring isotopes are stable in the sense that they have not been observed to date. An additional 35 primordial nuclides (a total of 289 primordial nuclides) are radioactive with known half-lives, but have half-lives in excess of 80 million years, allowing them to exist since the beginning of the solar system.

All known stable isotopes naturally occur on Earth; Other natural isotopes are radioactive, but because of their relatively long half-lives, or because of other continuous natural production methods. These include the cosmogenic nuclides mentioned above, nucleogenic nuclides, and any radiogenic isotopes resulting from the continued decay of a primary radioactive isotope such as radon and radium from uranium.

Another ~3000 radioactive isotopes not found in nature have been created in nuclear reactors and particle accelerators. Many short-lived isotopes not found naturally on Earth have also been observed by spectroscopic analysis naturally created in stars or supernovae. An example is aluminum-26, which does not naturally occur on Earth, but is found in abundance on an astronomical scale.

The tabulated atomic masses of the elements are averages that explain the presence of multiple isotopes with different masses. Prior to the discovery of isotopes, empirically determined non-integrated values ​​for atomic mass confused scientists. For example, a sample of chlorine contains 75.8% chlorine-35 and 24.2% chlorine-37, giving an average atomic mass of 35.5 atomic mass units.

According to the generally accepted theory of cosmology, only the isotopes of hydrogen and helium, traces of some isotopes of lithium and beryllium, and possibly some boron, were created in the Big Bang, while all other isotopes were synthesized later, in stars and supernovae, as well as in the interactions between energetic particles , such as cosmic rays, and previously obtained isotopes. The corresponding isotopic abundance of isotopes on Earth is due to the quantities produced by these processes, their propagation through the galaxy, and the rate of decay of the isotopes, which are unstable. After the initial merger of the solar system, isotopes were redistributed according to mass, and the isotopic composition of the elements varies slightly from planet to planet. This sometimes makes it possible to trace the origin of meteorites.

Atomic mass of isotopes

The atomic mass (mr) of an isotope is determined mainly by its mass number (i.e., the number of nucleons in its nucleus). Small corrections are due to the binding energy of the nucleus, the small difference in mass between the proton and neutron, and the mass of the electrons associated with the atom.

Mass number is a dimensionless quantity. Atomic mass, on the other hand, is measured using the unit of atomic mass, based on the mass of the carbon-12 atom. It is denoted by the symbols "u" (for the unified atomic mass unit) or "Da" (for the dalton).

The atomic masses of an element's natural isotopes determine the element's atomic mass. When an element contains N isotopes, the expression below applies to the average atomic mass:

Where m 1 , m 2 , …, mN are the atomic masses of each individual isotope, and x 1 , …, xN is the relative abundance of these isotopes.

Application of isotopes

There are several applications that exploit the properties of the various isotopes of a given element. Isotope separation is an important technological issue, especially with heavy elements such as uranium or plutonium. Lighter elements such as lithium, carbon, nitrogen and oxygen are usually separated by gaseous diffusion of their compounds such as CO and NO. The separation of hydrogen and deuterium is unusual because it is based on chemical rather than physical properties, such as in the Girdler sulfide process. Uranium isotopes have been separated by volume by gaseous diffusion, gas centrifugation, laser ionization separation and (in the Manhattan Project) by type of mass spectrometry production.

Use of chemical and biological properties

• Isotope analysis is the determination of the isotopic signature, the relative abundance of the isotopes of a given element in a particular sample. For nutrients in particular, significant variations in C, N and O isotopes can occur. The analysis of such variations has a wide range of applications, such as the detection of adulteration in foods or the geographic origin of foods using isoscapes. The identification of some meteorites originating on Mars is based in part on the isotopic signature of the trace gases they contain.
• Isotopic substitution can be used to determine the mechanism of a chemical reaction through the kinetic isotope effect.
• Another common application is isotopic labeling, the use of unusual isotopes as tracers or markers in chemical reactions. Usually the atoms of a given element are indistinguishable from each other. However, by using isotopes of different masses, even different non-radioactive stable isotopes can be distinguished using mass spectrometry or infrared spectroscopy. For example, in "Stable Isotope Labeling of Amino Acids in Cell Culture" (SILAC), stable isotopes are used to quantify proteins. If radioactive isotopes are used, they can be detected by the radiation they emit (this is called radioisotope marking).
• Isotopes are commonly used to determine the concentration of various elements or substances using the isotopic dilution method, in which known amounts of isotopically substituted compounds are mixed with samples and the isotopic characteristics of the resulting mixtures are determined using mass spectrometry.

Using nuclear properties

• A method similar to radioisotope tagging is radiometric dating: using the known half-life of an unstable element, one can calculate the time elapsed since the existence of a known isotope concentration. The most widely known example is radiocarbon dating, which is used to determine the age of carbonaceous materials.
• Some forms of spectroscopy are based on the unique nuclear properties of specific isotopes, both radioactive and stable. For example, nuclear magnetic resonance (NMR) spectroscopy can only be used for isotopes with a non-zero nuclear spin. The most common isotopes used in NMR spectroscopy are 1 H, 2 D, 15 N, 13 C, and 31 P.
• Mössbauer spectroscopy also relies on the nuclear transitions of specific isotopes such as 57 Fe.

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.

TheDifference.ru 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.

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, forming 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 particle. 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 for each 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 isotopic 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 study the distribution, ways and nature of the movement of labeled substances in various media 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) is the ability to follow biol, the behavior of chemical labeled radionuclides. 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. compounds, 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 allow you 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 separation of 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 determine not only various patol, conditions, but also very small changes reflecting the initial stages of the 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. In this case, for control, color indicators of the received dose are used, 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 (MACs) 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; To and m e N of M. Radioactive indicators in biology, the lane with English. 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 K and at-shansky D. A. Radiation sterilization, M., 1974, bibliogr.; Fateeva M. N. Essays on radioisotope diagnostics, M., 1960, bibliogr.; Xeveshi 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 (current), compiler of the table. V.V. Bochkarev.