yanLaw of conservation of mass - The mass of substances entering into a chemical reaction is equal to the mass of substances formed as a result of the reaction

Atomic-molecular theory was developed by M.V. Lomonosov in 1741. Main provisions of the law:

1) all substances consist of “corpuscles” (molecules);

2) molecules consist of “elements” (atoms);

3) particles - molecules and atoms - are in continuous motion. The thermal state of bodies is the result of the movement of their particles;

4) molecules of simple substances consist of identical atoms, and molecules complex substances– from different atoms. The atomic-molecular theory was finally established in 1860.

Pgrowth substances- substances consisting exclusively of atoms of one chemical element, as opposed to complex substances. Depending on type chemical bond between atoms simple substances can be metals(Na, Mg, Al, Bi, etc.) and non-metals(H 2, N 2, Br 2, Si, etc.)

Chemical element- a collection of atoms with the same nuclear charge and the number of protons, coinciding with the serial (atomic) number in the periodic table. Each chemical element has its own name and symbol, which are given in Mendeleev's Periodic Table of Elements.

The law of constancy of composition - any specific chemically pure compound, regardless of the method of its preparation, consists of the same chemical elements

The law of multiple ratios is one of the stoichiometric laws of chemistry: if two elements form more than one compound with each other, then the masses of one of the elements per the same mass of the other element

are treated as integers, usually small.

The law of volumetric ratios: the volumes of reacting gases under the same conditions (temperature and pressure) relate to each other as whole numbers.

Atomic mass of the element- is the ratio of the mass of its atom to 1/12 of the mass of a 12C atom

Atoms in molecules are connected to each other in a certain sequence according to their valences. The sequence of interatomic bonds in a molecule is called its chemical structure and is reflected by one structural formula (structure formula). Molecular mass the mass of a molecule, expressed in atomic mass units. Numerically equal to molar mass.

A mole is a unit of quantity of a substance. This is the amount of a substance (or its portion) that contains 6.02 1023 particles (molecules, atoms or other particles)

Avagadro's law: equal volumes of different gases taken at the same temperature and pressure contain the same number of molecules

A mole is a unit of quantity of a substance. This is the amount of a substance (or its portion) that contains 6.02 1023 particles (molecules, atoms or other particles)

Equivalent- is a real or fictitious particle that can attach, release, or otherwise be equivalent to a hydrogen cation in ion exchange reactions or an electron in redox reactions

law of equivalents: all substances react in equivalent ratios. Valence is the property of atoms of a given element to add or replace a certain number of atoms of another element in a compound.

Avogadro's law allows us to determine the number of atoms that make up the molecules of simple gases. By studying the volumetric ratios in reactions involving hydrogen, oxygen, nitrogen and chlorine, it was found that the molecules of these gases are diatomic. Therefore, by determining the relative molecular mass of any of these gases and dividing it in half, one could immediately find the relative atomic mass of the corresponding element. For example, it was found that molecular mass chlorine is 70.90; from here atomic mass chlorine is equal to or 35.45.

Valence the ability of atoms of chemical elements to form a certain number of chemical bonds with atoms of other elements.

Internal e is the sum of the energies of molecular interactions and thermal movements of the molecule. Internal energy is a unique function of the state of the system

A covalent bond is formed by two electrons with opposite spins, and this electron pair belongs to two atoms.

energy state of electrons in an atom.

Mainquantum number - an integer indicating the energy level number. Characterizes electron energy occupying a given energy level. Is the first in a series of quantum numbers, which includes the principal, orbital and magnetic quantum numbers, as well as spin

Orbital quantum number- in quantum physics, the quantum number ℓ, which determines the shape of the amplitude distribution of the electron wave function in an atom, that is, the shape of the electron cloud. Defines the sublevel of the energy level specified by the main (radial) quantum number n and can take values

Is the eigenvalue of the operator orbital moment electron, different from the angular momentum of the electron j only on the spin operator s:

Ionization energy- represents the lowest energy required to remove an electron from a free atom. The following factors have the most significant influence on the ionization energy of an atom:

effective nuclear charge, which is a function of the number of electrons in the atom that shield the nucleus and are located in deeper internal orbitals;

radial distance from the nucleus to the maximum charge density of the outer electron, most weakly bound to the atom and leaving it during ionization;

a measure of the penetrating power of that electron;

interelectron repulsion among outer (valence) electrons.

Electron affinity- the amount of energy released when an electron attaches to an atom, molecule or radical. Electron affinity is usually expressed in electron volts. The value of Electron Affinity is important for understanding the nature of chemical bonds and the processes of formation of negative ions. The greater the Electron Affinity, the more easily the atom attaches an electron. The electron affinity of metal atoms is zero; for non-metal atoms, the electron affinity is greater, the closer the element (non-metal) is to the inert gas in D. I. Mendeleev’s periodic table. Therefore, within the period they intensify non-metallic properties as we approach the end of the period.

An atom consists of a nucleus and an electron “cloud” surrounding it. Located in the electronic cloud electrons carry negative electric charge. Protons included in core composition, carry positive charge. In any atom, the number of protons in the nucleus is exactly equal to the number of electrons in the electron cloud, so the atom as a whole is a neutral particle that does not carry a charge. An atom can lose one or more electrons or, conversely, capture someone else’s electrons. In this case, the atom acquires a positive or negative charge and is called ion.

Isotopes(from ancient Greek ισος - "equal", "same", and τόπος - "place") - varieties of atoms (and nuclei) of a chemical element that have the same atomic number, but at the same time different mass numbers. The name is due to the fact that all isotopes of one atom are placed in the same place (in one cell) of the periodic table: 16 8 O, 17 8 O, 18 8 O - three stable isotopes of oxygen.

Radioactive elements and their decay.

Radioactive decay- spontaneous change in the composition of unstable atomic nuclei through the emission of elementary particles or nuclear fragments. There are alpha, beta and gamma decays. Accordingly, they emit alpha, beta and gamma particles. The decay with the strongest penetrating ability is gamma decay (not rejected by a magnetic field). Alphas are positively charged particles. Beta are negatively charged particles.

Nuclei of radioactive elements or isotopes can decay in three main ways, and the corresponding nuclear decay reactions are named by the first three letters of the Greek alphabet. At alpha decay A helium atom consisting of two protons and two neutrons is released - it is usually called an alpha particle. Since alpha decay entails a decrease in the number of positively charged protons in an atom by two, the nucleus that emitted the alpha particle turns into the nucleus of an element two positions lower from it in the periodic table. At beta decay the nucleus emits an electron and the element moves one position forward according to the periodic table (in this case, essentially, a neutron turns into a proton with the radiation of this very electron). Finally, gamma decay - This decay of nuclei with the emission of high-energy photons, which are commonly called gamma rays. In this case, the nucleus loses energy, but the chemical element does not change. Radioactive element- a chemical element, all isotopes of which are radioactive.

1. 37. Artificial radioactivity.

Artificial radioactivity- spontaneous decay of nuclei of elements obtained artificially through appropriate nuclear reactions. All three types of radiation - a, b and g, characteristic of natural radioactivity, - are also emitted by artificially radioactive substances. However, among artificially radioactive substances there is often another type of decay that is not characteristic of naturally radioactive elements. This is a decay with the emission of positrons - particles that have the mass of an electron, but carry a positive charge. By absolute value The charges of the positron and electron are equal. Artificially- radioactive substances can be obtained with very different nuclear reactions. An example is the reaction of neutron capture by silver. To carry out such a reaction, it is enough to place a silver plate near a neutron source surrounded by paraffin.

1. 38. Nuclear reactions.

Nuclear reaction- the process of formation of new nuclei or particles during their collisions. The nuclear reaction was first observed by Rutherford in 1919, bombarding the nuclei of nitrogen atoms with α-particles; it was detected by the appearance of secondary ionizing particles that had a range in the gas greater than that of the α-particles and were identified as protons. Subsequently, photographs of this process were obtained using a cloud chamber.

1. 39. Theory of chemical structure.

This theory has four provisions: 1) The atoms in the molecule are connected in a certain sequence in accordance with their valency. This sequence is called chemical structure. 2) The properties of a substance depend not only on the qualitative and quantitative composition of the molecule, but also on its chemical structure. Substances that have the same composition but different structures are called isomers, and their very existence isomerism. 3) Atoms and groups of atoms in a molecule mutually influence each other directly or through other atoms. 4) The structure of matter is knowable; synthesis of substances with a given structure is possible. Butlerov.1861

1. 40. Covalent bond.

Covalent bond- a chemical bond formed by the overlap of a pair of valence electron clouds. Electronic clouds that provide communication are called shared electron pair. It can be polar or non-polar. An important characteristic of a covalent bond is its polarity. If a molecule consists of 2 atoms that are connected by a polar bond, then such a molecule is a polar molecule. It is a dipole. A dipole is an electrically neutral system in which the centers of positive and negative charge are located at a certain distance from each other. The polarity of a molecule is quantified by the dipole moment, which is equal to the product of the length of the dipole and the value of the effective charge. Effective charge = 1.6 * 10 -19 C. The ability of molecules and individual bonds to be polyrized under the influence of an external electric field is called polyrizability. The ability of an atom to participate in the formation of a limited number covalent bonds, is called the saturation of a covalent bond. The direction of the covalent bond determines the spatial structure of the molecules, i.e. overlap of electron clouds. Occurs only at a certain mutual orientation of the orbitals, which provides the highest electron density in the overlap region.

Radioactivity - This is the property of the atomic nuclei of certain chemical elements to spontaneously transform into the nuclei of other elements with the emission of a special kind of radiation called radioactive. You cannot influence the course of the process radioactive decay, without changing the state atomic nucleus. To the speed of the current radioactive transformations do not have any effect on changes in temperature and pressure, the presence of electric and magnetic fields, type chemical compound of a given radioactive element and its state of aggregation.

Radioactive phenomena occurring in nature are called natural radioactivity(cosmic radiation and radiation from natural radionuclides scattered in earth rocks, soil, water, air, building and other materials, living organisms). For example, the 40 K isotope is widely dispersed in soils and is firmly retained by clays due to sorption processes. Clay soils are almost everywhere richer in radioactive elements than sandy and limestone soils. Radioactive heavy elements (U, Th, Ra) are found mainly in granite rocks. Radioactive elements are common in nature in minute quantities. IN earth's crust Naturally radioactive elements are found mainly in uranium ores, and almost all of them are isotopes heavy elements With atomic number more than 83. Radioactive decay chains begin with uranium - radium (- Ra), thorium () or actinium ().

Similar processes occurring in artificially produced substances (through corresponding nuclear reactions) are called artificial radioactivity(coal combustion, development of radioactive ore deposits, use of radionuclides in various sectors of the economy, operation of nuclear technical installations, nuclear explosions in for peaceful purposes(construction of underground storage facilities, oil production, canal construction), accidents at facilities containing radioactive substances, nuclear waste from nuclear power plants, industry, navy, testing nuclear weapons(at nuclear explosions About 250 isotopes of 35 elements (225 of them radioactive) are formed, both direct fission fragments of the nuclei of heavy elements (235 U, 239 Pu, 233 U, 238 U) and their decay products.

The amount of radioactive fission products (RFP) increases according to the power of the nuclear charge. Some of the resulting RPDs disintegrate in the next seconds and minutes after the explosion, while the other part has a half-life of about several hours.

Radionuclides such as 86 Rb, 89 Sr, 91 Y, 95 Cd, 125 Sn. l25 Te, l31 I, 133 Xe, l36 Cs, 140 Ba, 141 Ce, 156 Eu, 161 Yb, have a half-life of several days, a 85 Kr, 90 Sr, 106 Ru, 125 Sb, 137 Cs, l47 Pm, l5l Sm, l55 Eu - from one year to several tens of years. The group consisting of 87 Rb, 93 Zr, l29 I, 135 Cs, 144 Nd, 137 Sm is characterized by extremely slow decay, lasting millions of years)).

Artificial radionuclides various reasons fall into environment, thereby increasing background radiation. In addition, they are included in biological systems and enter directly into the body of animals and humans. All this creates a danger for the normal functioning of a living organism.

External and internal sources, acting continuously, inform the body of a certain absorbed dose. Most exposure from sources of natural radiation a person receives due to earthly sources-- on average more than 5/6 of the annual effective equivalent dose received by the population (mainly internal exposure). The remainder comes from cosmic radiation (mainly external radiation). The effective equivalent dose from exposure to cosmic radiation is about 300 μSv/year (for those living at sea level); for those living above 2 thousand m above sea level, this value is several times higher. The average annual safe dose for humans is about 1.2 mGy to the gonads and 1.3 mGy to the skeleton.

Artificial radioactivity was discovered by the couple Irène (1897–1956) and Frédéric (1900–1958) Joliot-Curie. On January 15, 1934, their note was presented by J. Perrin at a meeting of the Paris Academy of Sciences. Irene and Frederick were able to establish that after bombardment by alpha particles, some light elements - magnesium, boron, aluminum - emit positrons. Next, they tried to establish the mechanism of this emission, which differed in nature from all cases of nuclear transformations known at that time. Scientists placed a source of alpha particles (polonium) at a distance of one millimeter from aluminum foil. They then exposed her to radiation for about ten minutes. A Geiger-Muller counter showed that the foil emits radiation, the intensity of which decreases exponentially with time, with a half-life of 3 minutes 15 seconds. In experiments with boron and magnesium, the half-lives were 14 and 2.5 minutes, respectively. But in experiments with hydrogen, lithium, carbon, beryllium, nitrogen, oxygen, fluorine, sodium, calcium, nickel and silver, no such phenomena were found. However, the Joliot-Curies concluded that the radiation caused by the bombardment of aluminum, magnesium and boron atoms could not be explained by the presence of any impurity in the polonium preparation. “An analysis of the radiation of boron and aluminum in a cloud chamber showed,” K. Manolov and V. Tyutyunnik write in their book “Biography of the Atom,” that it is a stream of positrons. It became clear that scientists were dealing with a new phenomenon that was significantly different from all known cases of nuclear transformations. Nuclear reactions known up to that time were of an explosive nature, while the emission of positive electrons by some light elements irradiated with the alpha rays of polonium continued for some more or less long time after the source of the alpha rays had been removed. In the case of boron, for example, this time reaches half an hour.” The Joliot-Curies came to the conclusion that here we're talking about about real radioactivity, manifested in the emission of a positron. New evidence was needed, and, first of all, it was necessary to isolate the corresponding radioactive isotope. Based on the research of Rutherford and Cockroft, Irene and Frederic Joliot-Curie were able to establish what happens to aluminum atoms when they are bombarded with polonium alpha particles. First, alpha particles are captured by the nucleus of an aluminum atom, the positive charge of which increases by two units, as a result of which it turns into the nucleus of a radioactive phosphorus atom, called “radiophosphorus” by scientists. This process is accompanied by the emission of one neutron, which is why the mass of the resulting isotope increases not by four, but by three units and becomes equal to 30. A stable isotope of phosphorus has a mass of 31. “Radiophosphorus” with a charge of 15 and a mass of 30 decays with a half-life of 3 minutes 15 seconds , emitting one positron and turning into a stable isotope of silicon. The only and indisputable proof that aluminum turns into phosphorus and then into silicon with a charge of 14 and a mass of 30 could only be the isolation of these elements and their identification using their characteristic qualitative chemical reactions. For any chemist working with stable compounds, this was a simple task, but for Irene and Frederic the situation was completely different: the phosphorus atoms they produced lasted just over three minutes. Chemists have many methods for detecting this element, but they all require lengthy determinations. Therefore, the opinion of chemists was unanimous: to identify phosphorus as such a short time impossible. However, the Joliot-Curie spouses did not recognize the word “impossible.” And although this “unsolvable” task required backbreaking labor, tension, masterly dexterity and endless patience, it was solved. Despite the extremely low yield of products of nuclear transformations and the completely insignificant mass of the substance that underwent the transformation - only a few million atoms, it was possible to establish Chemical properties the resulting radioactive phosphorus. The discovery of artificial radioactivity was immediately rated as one of the largest discoveries of the century. Before this, the radioactivity that was inherent in some elements could not be caused, destroyed, or changed in any way by man. The Joliot-Curie couple were the first to artificially cause radioactivity by obtaining new radioactive isotopes. Scientists foresaw the great theoretical significance of this discovery and the possibility of its practical applications in the field of biology and medicine. Already in next year The discoverers of artificial radioactivity, Irène and Frédéric Joliot-Curie, were awarded the Nobel Prize in Chemistry. Continuing these studies, the Italian scientist Fermi showed that bombardment with neutrons causes artificial radioactivity in heavy metals. Enrico Fermi (1901–1954) was born in Rome. Even as a child, Enrico showed great aptitude for mathematics and physics. His outstanding knowledge of these sciences, acquired mainly as a result of self-education, allowed him to receive a scholarship in 1918 and enter the École Normale Supérieure at the University of Pisa. Enrico then received a temporary position as lecturer in mathematics for chemists at the University of Rome. In 1923, he went on a business trip to Germany, to Göttingen, to see Max Born. Upon returning to Italy, Fermi worked at the University of Florence from January 1925 until the fall of 1926. Here he gets his first academic degree“free associate professor” and, most importantly, creates his famous work on quantum statistics. In December 1926, he took up the position of professor in the newly established department of theoretical physics at the University of Rome. Here he organized a team of young physicists: Rasetti, Amaldi, Segre, Pontecorvo and others, who made up the Italian school modern physics. When the first department of theoretical physics was established at the University of Rome in 1927, Fermi, who had gained international authority, was elected its head. Here in the capital of Italy, Fermi rallied several outstanding scientists around him and founded the country's first school of modern physics. In international scientific circles it began to be called the Fermi group. Two years later, Fermi was appointed by Benito Mussolini to the honorary position of member of the newly created Royal Academy of Italy. In 1938 Fermi was awarded Nobel Prize in physics. The Nobel Committee's decision stated that the prize was awarded to Fermi "for his evidence of the existence of new radioactive elements obtained by irradiation with neutrons and the related discovery of nuclear reactions caused by slow neutrons." Enrico Fermi learned about artificial radioactivity immediately, in the spring of 1934, as soon as the Joliot-Curie spouses published their results. Fermi decided to repeat the Joliot-Curie experiments, but took a completely different path, using neutrons as bombarding particles. Fermi later explained the reasons for the distrust of neutrons on the part of other physicists and his own lucky guess: “The use of neutrons as bombarding particles suffers from the disadvantage that the number of neutrons that can be practically disposed of is immeasurable.” less number alpha particles received from radioactive sources, or the number of protons and deuterons accelerated in high-voltage devices. But this disadvantage is partially compensated by the greater efficiency of neutrons in carrying out artificial nuclear transformations. Neutrons also have another advantage. They are highly capable of causing nuclear transformations. The number of elements that can be activated by neutrons greatly exceeds the number of elements that can be activated by other types of particles." In the spring of 1934, Fermi began irradiating elements with neutrons. Fermi's "neutron guns" were small tubes several centimeters long. They were filled with a “mixture” of fine beryllium powder and radium emanation. This is how Fermi described one of these neutron sources: “It was a glass tube only 1.5 cm in size ... in which there were grains of beryllium; Before soldering the tube, it was necessary to introduce a certain amount of radium emanation into it. Alpha particles emitted by radon in large number collide with beryllium atoms and produce neutrons... The experiment is performed as follows. IN close proximity A plate of aluminum, or iron, or in general the element that it is desirable to study, is placed from the neutron source and left for several minutes, hours or days (depending on the specific case). Neutrons emitted from a source collide with the nuclei of matter. In this case, many nuclear reactions occur various types..." What did all this look like in practice? The sample under study was specified time under intense neutron irradiation, then one of Fermi's employees literally ran the sample to a Geiger-Muller counter located in another laboratory and recorded the counter pulses. After all, many new artificial radioisotopes were short-lived. In the first message, dated March 25, 1934, Fermi reported that by bombarding aluminum and fluorine, he obtained isotopes of sodium and nitrogen that emitted electrons (and not positrons, as in Joliot-Curie). The neutron bombardment method proved to be very effective, and Fermi wrote that this high efficiency in achieving fission “completely compensates for the weakness of existing neutron sources compared to sources of alpha particles and protons.” In fact, much was known. Neutrons entered the nucleus of the fired atom, turning it into an unstable isotope, which spontaneously decayed and emitted. In this radiation lay the unknown: some of the artificially produced isotopes emitted beta rays, others gamma rays, and still others alpha particles. Every day the number of artificially obtained radioactive isotopes increased. Each new nuclear reaction had to be comprehended in order to understand the complex transformations of atoms. For each reaction it was necessary to establish the nature of the radiation, because only by knowing it can one imagine the pattern of radioactive decay and predict the element that will be obtained in the final result. Then it was the chemists' turn. They had to identify the resulting atoms. This also took time. Using his "neutron gun", Fermi bombarded fluorine, aluminum, silicon, phosphorus, chlorine, iron, cobalt, silver and iodine. All these elements were activated, and in many cases Fermi could indicate chemical nature the resulting radioactive element. He managed to activate 47 of the 68 elements studied by this method. Inspired by the success, he, in collaboration with F. Rasetti and O. Dagostino, undertook neutron bombardment of heavy elements: thorium and uranium. “Experiments have shown that both elements, previously purified from ordinary active impurities, can be strongly activated when bombarded by neutrons.” On October 22, 1934, Fermi made a fundamental discovery. By placing a paraffin wedge between the neutron source and the activated silver cylinder, Fermi noticed that the wedge did not reduce neutron activity, but slightly increased it. Fermi concluded that this effect was likely due to the presence of hydrogen in the paraffin, and decided to test how it would affect the fission activity a large number of hydrogen containing elements. Having carried out the experiment first with paraffin, then with water, Fermi noted an increase in activity hundreds of times. Fermi's experiments revealed enormous efficiency slow neutrons. But, in addition to remarkable experimental results, in the same year Fermi achieved remarkable theoretical achievements. Already in the December 1933 issue in Italian scientific journal His preliminary thoughts on beta decay were published. In early 1934, his classic article “Towards the Theory of Beta Rays” was published. The author's summary of the article reads: “It is proposed quantity theory beta decay, based on the existence of neutrinos: in this case, the emission of electrons and neutrinos is considered by analogy with the emission of a light quantum by an excited atom in the theory of radiation. Formulas are derived from the lifetime of the nucleus and for the shape of the continuous spectrum of beta rays; the resulting formulas are compared with experiment.” Fermi in this theory gave birth to the neutrino hypothesis and the proton-neutron model of the nucleus, also accepting the isotonic spin hypothesis proposed by Heisenberg for this model. Based on the ideas expressed by Fermi, Hideki Yukawa predicted in 1935 the existence of a new elementary particle, now known as the pi meson, or pion. Commenting on Fermi’s theory, F Rasetti wrote: “The theory he built on this basis turned out to be able to withstand almost without change two and a half decades of revolutionary development nuclear physics. It might be noted that physical theory rarely is born in such a final form.”

Radioactivity is the ability of some chemical elements (uranium, thorium, radium, californium) to spontaneously decay and emit invisible radiation.

Radioactive substances (RS) decay at a strictly defined rate, measured by half-life, i.e. the time during which half of all atoms decay. Radioactive decay cannot be stopped or accelerated by any means.

A beam of radiation in a magnetic field is divided into three types of radiation:

b-radiation is a stream of positively charged particles representing a helium nucleus, moving at a speed of about 20,000 km/s, i.e. 35,000 times faster than modern aircraft. An alpha particle is a heavy particle; it is 7300 times heavier than an electron. In animal tissues, its penetrating ability is even less and is measured in microns. Alpha particles are part of cosmic rays near the Earth (6%).

Alpha decay is a spontaneous transformation of nuclei, accompanied by the emission of two protons and two neutrons forming the He 4 2 nucleus.

As a result of alpha decay, the nuclear charge decreases by 2, and mass number by 4 units. For example: kinetic energy the emitted b-particle is determined by the masses of the initial and final core of the b-particle. More than 200 b-active nuclei are known, located mainly at the end periodic table. There are also about 20 known b-radioactive isotopes rare earth elements. Here, b-decay is most typical for nuclei with the number of neutrons N = 84, which, when emitting b-particles, turn into nuclei with a filled nuclear envelope(N=82). The lifetime of b-active nuclei varies widely: from 3*10 -7 sec (for Po 212) to (2-5)*10 15 years ( natural isotopes Ce 142, 144, 176) The energy of the observed b-decay lies in the range of 4-9 MeV (with the exception of long-range b-particles) for all heavy nuclei and 2-4.5 MeV for rare earth elements.

c- radiation - a flow of charged negatively charged particles (electrons). Their speed of 200,000-300,000 km/s approaches the speed of light. The mass of beta particles is 1/1840 of the mass of hydrogen. Beta particles are light particles.

g-radiation - is short-wave electromagnetic radiation. In properties it is close to x-ray radiation, but has significantly greater speed and energy, but propagates at the speed of light. On the spectrum electromagnetic waves these rays occupy almost the position on the far right. They are followed only cosmic rays. The energy of gamma rays averages about 1.3 MeV (megaelectronvolts). This is very high energy. The oscillation frequency of gamma ray waves is 10 20 times/sec, that is, gamma rays are very hard rays, and their penetrating power is high. They pass through the human body unhindered.

Some nuclear reactions produce highly penetrating radiation that is not deflected by electrical and magnetic fields. These rays penetrate a layer of lead several meters thick. This radiation is a stream of neutrally charged particles. These particles are called neutrons.

The mass of a neutron is equal to the mass of a proton. Neutrons have at different speeds, on average less than the speed of light. Fast neutrons develop energies of the order of 0.5 MeV and higher, slow ones - from fractions to several thousand electron volts. Neutrons, being electrically neutral particles, have, like gamma rays, high penetrating power. The weakening of the neutron flux mainly occurs due to collisions with the nuclei of other atoms and due to the capture of neutrons by the nuclei of atoms. So, when colliding with light nuclei, neutrons in to a greater extent lose their energy, but light hydrogen-containing substances such as water, paraffin, human body tissue, wet concrete, soil are the best moderators and absorbers of neutrons.

In nature, many chemical elements emit radiation. These elements are called radioactive elements, and the process itself is called natural radioactivity. Neither enormous pressures and temperatures, nor magnetic and electric fields. Radioactive radiation is associated with the transformation of the nuclei of an element. There are two types of natural radioactive decay.

Alpha decay, in which a nucleus emits an alpha particle. With this type of decay, one nucleus always produces a nucleus of another element, which has a charge of two units less and a mass of four units less. So, for example, radium decays, turning into radon:

Ra 88 226 > He 2 4 + Rn 86 222

Beta decay, in which a beta particle is emitted from the nucleus. Since a beta particle can be differently charged, beta decay can be either electron or positron.

Electronic decay produces an element with the same mass, but with a charge greater than one. This is how thorium turns into protactinium:

Th 90 233 >Pa 91 233 + e -1 + g - quantum.

During positron decay, a radioactive element loses a positive particle and turns into an element with the same mass, but with a charge less by one. So the isotope of magnesium turns into sodium:

Mg 12 23 > Na 11 23 + e +1 + g- quantum.

By directing a beam of alpha particles onto an aluminum plate, for the first time they obtained an artificial radioactive isotope of phosphorus P 15 30:

Al 13 27 + He 2 4 > P 15 30 + n 0 1

The isotopes obtained in this way were called artificially radioactive, and their ability to decay was called artificial radioactivity. Currently, over 900 artificial radioactive isotopes have been obtained.

They are widely used in medicine and biology to study chemical transformations in organism. This method is called the tagged atom method.

Radioactivity is... the ability of the nuclei of atoms of some chemical elements to spontaneously transform into the nuclei of other chemical elements with the release of energy in the form of radiation. Substances that exist in nature are called naturally radioactive, while substances that have acquired this property artificially are called artificially radioactive. The phenomenon of radioactivity was discovered in 1896 by the French physicist A. Becquerel while studying the phosphorescence of uranium salts. During the spontaneous, independent of external causes, decay of uranium salts, rays similar to X-rays were emitted: they penetrated through opaque substances, illuminated photographic paper, ionized gases, and affected living tissue. In 1898 Marie Sklodowska-Curie discovered the radioactivity of thorium. She also showed that uranium ore has greater radioactivity compared to pure uranium. Marie and Pierre Curie suggested that uranium salts contain admixtures of other radioactive substances, which turned out to be polonium and radium.

Radiations from naturally radioactive elements, as shown by the English physicist E. Rutherford (1911), have different physical properties. Some of the rays in an electric field are deflected towards a negatively charged conductor, which indicates their positive charge; they were called ά-rays. Another part of the rays was deflected towards a positively charged conductor. These negatively charged rays are called β-rays. Electrically neutral rays that were not deflected by an electric field were called γ-rays.

Studying the essence of natural radioactive decay led E. Rutherford to the conclusion about the possibility of artificial fission of nuclei. In 1919, when bombarding the nucleus of a nitrogen atom with ά particles, he knocked out a positively charged particle - a proton. At the same time, a new chemical element was formed - oxygen.

In 1932, data appeared on the existence in the nucleus of atoms, along with protons, of neutrons similar in size to them. Soviet physicists D. D. Ianenko, E. G. Gapon and German physicist Goldhaber developed a theory about the proton-neutropic structure of the atomic nucleus. English physicist Chadwick discovered the neutron in 1933. Irene and Frederic Joliot-Curie, when bombarding ά-particles of aluminum, boron, and magnesium, received a positron along with neutrons. Moreover, positrons were emitted even after the irradiation of aluminum ceased, i.e., for the first time, radioactive elements were obtained artificially.

2713A1 +42 ά→10n + 3015P→ e+ + 3014Si

The first generator of neutrons, which were produced in an accelerator of heavy charged particles (cyclotron), was designed in 1936 by Laurence.

In 1940, Soviet physicists G.N. Flerov and K.A. Petrzhak discovered the phenomenon of spontaneous fission of uranium nuclei into large fragments with the release of 2-3 free neutrons, which, in turn, caused the fission of other nuclei with the release of new neutrons, etc. etc. The possibility of a chain reaction is shown, which could be used to irradiate stable chemical elements with neutrons and transform them into radioactive ones. In contrast to alpha particles, neutrons, being electrically neutral, easily penetrate into the nuclei of atoms, transferring them to an excited state.

In 1942, in the USA, the Italian physicist E. Fermi first obtained chain reaction in practice, creating a working nuclear reactor. The development of the first samples dates back to the Second World War atomic weapons. It was used by the USA in 1945 during the bombing Japanese cities Hiroshima and Nagasaki. In 1954, the USSR began commercial operation of the world's first nuclear power plant.

Thanks to the creation of atomic reactors and powerful charged particle accelerators, radioactive isotopes of all chemical elements have now been obtained that can be used for the needs of the national economy, including medicine.

Artificially radioactive isotopes are obtained by bombarding the nuclei of atoms of stable chemical elements with neutrons, protons, deuterons, as well as from fission products of uranium or plutonium in nuclear reactors.

An example is the reaction for producing radiophosphorus:

3115P + 10n → 3215Р or 3115P + 11H → 3215P + e+ + p.

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