Application of radioactivity. Radioactivity

Introduction 3

1 Radioactivity 5

1.1 Types radioactive decay and radioactive radiation 5

1.2 Law of Radioactive Decay 7

radiation 8

1.4 Source classification radioactive radiation and radioactive isotopes 10

2 Analytical techniques based on radioactivity measurements 12

2.1 Use of naturally occurring radioactivity in analysis 12

2.2 Activation analysis 12

2.3 Isotope dilution method 14

2.4 Radiometric titration 14

3 Applications of radioactivity 18

3.1 Application of radioactive tracers in analytical chemistry 18

3.2 Application radioactive isotopes 22

Conclusion 25

List of sources used 26

Introduction

Analysis methods based on radioactivity arose during the era of the development of nuclear physics, radiochemistry, and nuclear technology and are now successfully used in conducting various analyzes, including in industry and the geological service.

The main advantages of analytical methods based on the measurement of radioactive radiation are the low detection threshold of the analyzed element and wide versatility. Radioactivation analysis has the absolutely lowest detection threshold among all other analytical methods (10 -15 g). The advantage of some radiometric methods is the analysis without destruction of the sample, and the advantage of methods based on the measurement of natural radioactivity is the speed of analysis. A valuable feature of the radiometric method of isotope dilution lies in the possibility of analyzing a mixture of elements with similar chemical and analytical properties, such as zirconium - hafnium, niobium - tantalum, etc.

Additional complications when working with radioactive drugs are caused by the toxic properties of radioactive radiation, which do not cause an immediate reaction in the body and thereby complicate the timely application of necessary measures. This reinforces the need for strict adherence to safety precautions when working with radioactive drugs. IN necessary cases work with radioactive substances occurs with the help of so-called manipulators in special chambers, and the analyst himself remains in another room, reliably protected from the effects of radioactive radiation.

Radioactive isotopes are used in the following analytical methods:

1. precipitation method in the presence radioactive element;
2. isotope dilution method;
3. radiometric titration;
4. activation analysis;
5. definitions based on measurements of the radioactivity of naturally occurring isotopes.

In laboratory practice, radiometric titration is used relatively rarely. The application of activation analysis is associated with the use of powerful sources of thermal neutrons, and therefore this method is still of limited use.

In this course work The theoretical foundations of analysis methods that use the phenomenon of radioactivity and their practical application are considered.

1 Radioactivity

1.1 Types of radioactive decay and radiation

Radioactivity is a spontaneous transformation (decay) of the nucleus of an atom of a chemical element, leading to a change in its atomic number or a change in mass number. With this transformation of the nucleus, radioactive radiation is emitted.

The discovery of radioactivity dates back to 1896, when A. Becquerel discovered that uranium spontaneously emits radiation, which he called radioactive (from radio - emit and activas - effective).

Radioactive radiation occurs during spontaneous decay atomic nucleus. Several types of radioactive decay and radioactive
radiation.

Ra → Rn + He;

U → Th + α (He).

In accordance with the law of radioactive displacement, α-decay produces an atom whose atomic number is two units and whose atomic mass is four units less than that of the original atom.

2) β-Decomposition. There are several types of β-decay: electronic β-decay; positron β decay; K-grab. In electronic β decay, for example,

Sn → Y + β - ;

P → S + β - .

a neutron inside a nucleus turns into a proton. When a negatively charged β particle is emitted, the atomic number of the element increases by one, and atomic mass practically does not change.

During positron β-decay, a positron (β + -particle) is released from the atomic nucleus, and then turns into a neutron inside the nucleus. For example:

Na → Ne + β +

The lifespan of a positron is short, since when it collides with an electron, annihilation occurs, accompanied by the emission of γ quanta.

In K-capture, the nucleus of an atom captures an electron from a nearby electron shell (from the K-shell) and one of the protons of the nucleus is converted into a neutron.
For example,

K + e - = Ar + hv

One of the outer shell electrons moves to a free space in the K-shell, which is accompanied by the emission of a hard x-ray radiation.

3) Spontaneous division. It is typical for elements periodic table D.I. Mendeleev with Z > 90. During spontaneous fission, heavy atoms are divided into fragments, which are usually the elements in the middle of L.I. Mendeleev’s table. Spontaneous fission and α-decay limit the production of new transuranium elements.

The flux of α and β particles is called α and β radiation, respectively. In addition, γ-radiation is known. These are electromagnetic oscillations with a very short wavelength. In principle, γ-radiation is close to hard X-rays and differs from it in its intranuclear origin. X-ray radiation occurs during transitions in the electron shell of an atom, and γ-radiation is emitted by excited atoms resulting from radioactive decay (α and β).

As a result of radioactive decay, elements are obtained that, according to their nuclear charge (ordinal number), must be placed in the already occupied cells of the periodic table by elements with the same serial number, but with a different atomic mass. These are so-called isotopes. By chemical properties they are generally considered to be indistinguishable, so a mixture of isotopes is usually treated as a single element. Invariance of isotopic composition in the overwhelming majority chemical reactions sometimes called the law of constancy of isotopic composition. For example, potassium in natural compounds is a mixture of isotopes, 93.259% from 39 K, 6.729% from 41 K and 0.0119% from 40 K (K-capture and β-decay). Calcium has six stable isotopes with mass numbers 40, 42, 43, 44, 46 and 48. In chemical analytical and many other reactions this ratio remains practically unchanged, therefore chemical reactions are not usually used to separate isotopes. Most often, various physical processes are used for this purpose - diffusion, distillation or electrolysis.

The unit of isotope activity is the becquerel (Bq), equal to the activity of the nuclide in a radioactive source in which one decay event occurs in 1 s.

1.2 Law of radioactive decay

Radioactivity observed in nuclei existing in natural conditions, is called natural, the radioactivity of nuclei obtained through nuclear reactions is called artificial.

Between artificial and natural radioactivity there is no fundamental difference. The process of radioactive transformation in both cases obeys the same laws - the law of radioactive transformation:

If t = 0, then const = -lg N 0. Finally

where A is activity at time t; A 0 – activity at t = 0.

Equations (1.3) and (1.4) characterize the law of radioactive decay. In kinetics, these are known as first-order reaction equations. The half-life T 1/2 is usually indicated as a characteristic of the rate of radioactive decay, which, like λ, is a fundamental characteristic of the process that does not depend on the amount of substance.

The half-life is the period of time during which a given amount of radioactive substance is reduced by half.

The half-lives of different isotopes vary significantly. It is located approximately from 10 10 years to insignificant shares seconds. Of course, substances with a half-life of 10 - 15 minutes. and smaller ones are difficult to use in the laboratory. Isotopes with very long half-lives are also undesirable in the laboratory, since in case of accidental contamination of surrounding objects with these substances, special work will be required to decontaminate the room and instruments.

1.3 Interaction of radioactive radiation with matter and counters

radiation

As a result of the interaction of radioactive radiation with matter, ionization and excitation of atoms and molecules of the substance through which it passes occurs. Radiation also produces light, photographic, chemical and biological effects. Radioactive radiation causes a large number of chemical reactions in gases, solutions, and solids. They are usually combined into a group of radiation-chemical reactions. This includes, for example, the decomposition (radiolysis) of water with the formation of hydrogen, hydrogen peroxide and various radicals that enter into redox reactions with dissolved substances.

Radioactive radiation causes various radiochemical transformations of various organic compounds - amino acids, acids, alcohols, ethers, etc. Intense radioactive radiation causes glass tubes to glow and a number of other effects in solids. Based on the study of the interaction of radioactive radiation with matter various ways detecting and measuring radioactivity.

Depending on the operating principle, radioactive radiation counters are divided into several groups.

Ionization counters. Their action is based on the occurrence of ionization or gas discharge, caused by ionization when radioactive particles or γ-quanta enter the counter. Among dozens of devices using ionization, typical are the ionization chamber and the Geiger-Muller counter, which is most widespread in chemical analytical and radiochemical laboratories.

For radiochemical and other laboratories, industry produces special counting units.

Scintillation counters. The operation of these counters is based on the excitation of scintillator atoms by γ quanta or a radioactive particle passing through the counter. Excited atoms, returning to a normal state, give off a flash of light.

In the initial period of studying nuclear processes, visual scintillation counting played an important role, but later it was supplanted by the more advanced Geiger-Müller counter. Currently, the scintillation method has again become widely used using a photomultiplier.

Cherenkov counters. The operation of these counters is based on the use of the Cherenkov effect, which consists in the emission of light when a charged particle moves in a transparent substance, if the speed of the particles exceeds the speed of light in this medium. The fact of superluminal speed of a particle in a given medium, of course, does not contradict the theory of relativity, since the speed of light in any medium is always less than in vacuum. The speed of movement of a particle in a substance can be greater than the speed of light in this substance, while remaining at the same time less than the speed of light in a vacuum, in full accordance with the theory of relativity. Cherenkov counters are used for research with very fast particles, for research in space, etc., since with their help a number of other important characteristics of particles can be determined (their energy, direction of movement, etc.).

1.4 Classification of sources of radioactive radiation and

radioactive isotopes

Sources of radioactive radiation are divided into closed and open. Closed - must be airtight. Open - any leaky radiation sources that can create radioactive contamination of air, equipment, table surfaces, walls, etc.

When working with sealed sources, the necessary precautions are limited to protection from external radiation.

Closed radiation sources with activity above 0.2 g-eq. radium should be placed in protective devices with remote control and installed in specially equipped rooms.

Short description

Additional complications when working with radioactive drugs are caused by the toxic properties of radioactive radiation, which do not cause an immediate reaction in the body and thereby complicate the timely application of necessary measures. This reinforces the need for strict adherence to safety precautions when working with radioactive drugs. If necessary, work with radioactive substances occurs with the help of so-called manipulators in special chambers, and the analyst himself remains in another room, reliably protected from the effects of radioactive radiation.

Content

Introduction 3
1 Radioactivity 5
1.1 Types of radioactive decay and radiation 5
1.2 Law of Radioactive Decay 7
1.3 Interaction of radioactive radiation with matter and counters
radiation 8
1.4 Classification of sources of radioactive radiation and radioactive isotopes 10
2 Analytical techniques based on radioactivity measurements 12
2.1 Use of naturally occurring radioactivity in analysis 12
2.2 Activation analysis 12
2.3 Isotope dilution method 14
2.4 Radiometric titration 14
3 Applications of radioactivity 18
3.1 Use of radioactive tracers in analytical chemistry 18
3.2 Application of radioactive isotopes 22
Conclusion 25
List of sources used 26

The effect of radioactive radiation on humans

Radioactive radiation of all types (alpha, beta, gamma, neutrons), as well as electromagnetic radiation (X-rays) have a very strong biological effect on living organisms, which consists in the processes of excitation and ionization of atoms and molecules that make up living cells. Under the influence of ionizing radiation, complex molecules and cellular structures are destroyed, which leads to radiation damage to the body. Therefore, when working with any source of radiation, it is necessary to take all measures to radiation protection people who may be exposed to radiation.

However, a person can be exposed to ionizing radiation and living conditions. The inert, colorless, radioactive gas radon can pose a serious danger to human health. It is a decay product of radium and has a half-life T = 3.82 days. Radium is found in small quantities in soil, stones, and various building structures. Despite the relatively short lifetime, the radon concentration is continuously replenished due to new decays of radium nuclei, so radon can accumulate in indoors. Once in the lungs, radon emits -particles and turns into polonium, which is not a chemically inert substance. What follows is a chain of radioactive transformations of the uranium series. According to the American Commission radiation safety and control, a person on average receives 55% of ionizing radiation due to radon and only 11% due to medical services. The contribution of cosmic rays is approximately 8%. The total radiation dose a person receives during his life is many times less maximum permissible dose(SDA), which is established for people in certain professions who are subject to additional exposure to ionizing radiation.

Application of radioactive isotopes

One of the most outstanding studies carried out using “tagged atoms” was the study of metabolism in organisms. It has been proven that in a relatively short time the body undergoes almost complete renewal. The atoms that make it up are replaced by new ones. Only iron, as experiments on isotope studies of blood have shown, is an exception to this rule. Iron is part of the hemoglobin of red blood cells. When radioactive iron atoms were introduced into food, it was found that the free oxygen released during photosynthesis was originally part of the water, and not carbon dioxide. Radioactive isotopes are used in medicine both for diagnosis and for therapeutic purposes. Radioactive sodium, injected in small quantities into the blood, is used to study blood circulation; iodine is intensively deposited in the thyroid gland, especially in Graves' disease. By observing radioactive iodine deposition using a meter, a diagnosis can be made quickly. Large doses of radioactive iodine cause partial destruction of abnormally developing tissues, and therefore radioactive iodine is used to treat Graves' disease. Intense cobalt gamma radiation is used in treatment cancer diseases(cobalt gun).

No less extensive are the applications of radioactive isotopes in industry. One example of this is the following method for monitoring piston ring wear in engines internal combustion. By irradiating the piston ring with neutrons, they cause nuclear reactions in it and make it radioactive. When the engine operates, particles of ring material enter the lubricating oil. By examining the level of radioactivity in the oil after a certain time of engine operation, ring wear is determined. Radioactive isotopes make it possible to judge the diffusion of metals, processes in blast furnaces, etc.

Powerful gamma radiation radioactive drugs used for research internal structure metal castings in order to detect defects in them.

Radioactive isotopes are becoming increasingly used in agriculture. Irradiation of plant seeds (cotton, cabbage, radish, etc.) in small doses gamma rays from radioactive drugs leads to a noticeable increase in yield. Large doses of radiation cause mutations in plants and microorganisms, which in some cases leads to the emergence of mutants with new valuable properties (radio selection). This is how valuable varieties of wheat, beans and other crops were developed, and highly productive microorganisms used in the production of antibiotics were obtained. Gamma radiation from radioactive isotopes is also used to combat harmful insects and for conservation food products. “Tagged atoms” are widely used in agricultural technology. For example, to find out which phosphorus fertilizer is better absorbed by the plant, various fertilizers are labeled with radioactive phosphorus 15 32P. By then examining the plants for radioactivity, it is possible to determine the amount of phosphorus they have absorbed from different types of fertilizer. Interesting application radioactivity is a method of dating archaeological and geological finds by the concentration of radioactive isotopes. Most commonly used radiocarbon dating dating. An unstable isotope of carbon arises in the atmosphere due to nuclear reactions caused by cosmic rays. A small percentage of this isotope is found in the air along with the regular stable isotope. Plants and other organisms take up carbon from the air and accumulate both isotopes in the same proportions as in the air. Once plants die, they stop consuming carbon and unstable isotope as a result of decay, it gradually turns into nitrogen with a half-life of 5730 years. By accurately measuring the relative concentration of radioactive carbon in the remains of ancient organisms, the time of their death can be determined.

Applications of radioactivity.

1. Biological actions. Radioactive radiation has a detrimental effect on living cells. The mechanism of this action is associated with the ionization of atoms and the decomposition of molecules inside cells during the passage of fast charged particles. Cells in a state of rapid growth and reproduction are especially sensitive to the effects of radiation. This circumstance is used to treat cancer tumors.

For therapeutic purposes, radioactive drugs that emit g-radiation are used, since the latter penetrate into the body without noticeable weakening. When radiation doses are not too high, cancer cells die, while no significant damage is caused to the patient’s body. It should be noted that cancer radiotherapy, like x-ray therapy, is by no means universal remedy which always leads to a cure.

Excessively large doses of radioactive radiation cause serious illnesses animals and humans (so-called radiation sickness) can lead to death. In very small doses, radioactive radiation, mainly a-radiation, has, on the contrary, a stimulating effect on the body. This is associated with the healing effect of radioactive mineral waters containing small amounts of radium or radon.

2. Luminous compounds. Luminescent substances glow under the influence of radioactive radiation (cf. § 213). By adding to a luminescent substance (for example, zinc sulfide) very a small amount of Radium salts are used to prepare permanently glowing paints. These paints, when applied to watch dials and hands, sights, etc., make them visible in the dark.

3. Determining the age of the Earth. The atomic mass of ordinary lead, mined from ores that do not contain radioactive elements, is 207.2, the atomic mass of lead resulting from the decay of uranium is 206. The atomic mass of lead contained in some uranium minerals turns out to be very close to 206. This follows that these minerals at the time of formation (crystallization from a melt or solution) did not contain lead; all the lead present in such minerals accumulated as a result of the decay of uranium. Using the law of radioactive decay, it is possible to determine its age based on the ratio of the amounts of lead and uranium in a mineral.

The age of minerals determined by this method of various origins containing uranium is measured in hundreds of millions of years. The oldest minerals are over 1.5 billion years old.

Radioactive (or ionizing) radiation is energy that is released by atoms in the form of particles or waves electromagnetic nature. Humans are exposed to such exposure through both natural and anthropogenic sources.

The beneficial properties of radiation have made it possible to successfully use it in industry, medicine, scientific experiments and research, agriculture and other fields. However, with the spread of the use of this phenomenon, a threat to human health has arisen. A small dose of radioactive radiation can increase the risk of acquiring serious diseases.

The difference between radiation and radioactivity

Radiation, in in a broad sense, means radiation, that is, the propagation of energy in the form of waves or particles. Radioactive radiation is divided into three types:

• alpha radiation – flux of helium-4 nuclei;
• beta radiation – flow of electrons;
• Gamma radiation is a stream of high-energy photons.

The characteristics of radioactive radiation are based on their energy, transmission properties and the type of emitted particles.

Alpha radiation, which is a stream of corpuscles with positive charge, can be delayed by air or clothing. This species practically does not penetrate the skin, but when it enters the body, for example, through cuts, it is very dangerous and has a detrimental effect on internal organs.

Beta radiation has more energy - electrons move with high speed, and their sizes are small. That's why this type radiation penetrates through thin clothing and skin deep into tissue. Beta radiation can be shielded using an aluminum sheet a few millimeters thick or a thick wooden board.

Gamma radiation is high-energy radiation of an electromagnetic nature that has a strong penetrating ability. To protect against it, you need to use a thick layer of concrete or a plate of heavy metals such as platinum and lead.

The phenomenon of radioactivity was discovered in 1896. The discovery was made French physicist Becquerel. Radioactivity is the ability of objects, compounds, elements to emit ionizing radiation, that is, radiation. The reason for the phenomenon is the instability of the atomic nucleus, which releases energy during decay. There are three types of radioactivity:

• natural – characteristic of heavy elements, the serial number of which is greater than 82;
• artificial - initiated specifically with the help of nuclear reactions;
• induced - characteristic of objects that themselves become a source of radiation if they are heavily irradiated.

Elements that are radioactive are called radionuclides. Each of them is characterized by:

• half-life;
• type of radiation emitted;
• radiation energy;
• and other properties.

Sources of radiation

The human body is regularly exposed to radioactive radiation. Approximately 80% of the amount received annually comes from cosmic rays. Air, water and soil contain 60 radioactive elements that are sources natural radiation. Main natural source radiation is considered inert gas radon released from the ground and rocks. Radionuclides also enter the human body through food. Some of the ionizing radiation to which people are exposed comes from man-made sources, ranging from nuclear power generators and nuclear reactors to radiation used for treatment and diagnosis. Today, common artificial sources radiations are:

• medical equipment (basic anthropogenic source radiation);
• radiochemical industry (extraction, enrichment of nuclear fuel, processing of nuclear waste and its recovery);
• radionuclides used in agriculture and light industry;
• accidents at radiochemical plants, nuclear explosions, radiation emissions
• Construction Materials.

Based on the method of penetration into the body, radiation exposure is divided into two types: internal and external. The latter is typical for radionuclides dispersed in the air (aerosol, dust). They get on your skin or clothing. In this case, radiation sources can be removed by washing them away. External radiation causes burns to the mucous membranes and skin. At internal type The radionuclide enters the bloodstream, for example by injection into a vein or through a wound, and is removed by excretion or therapy. Such radiation provokes malignant tumors.

The radioactive background depends significantly on geographical location– in some regions, radiation levels can be hundreds of times higher than average.

The effect of radiation on human health

Radioactive radiation, due to its ionizing effect, leads to the formation of free radicals in the human body - chemically active aggressive molecules that cause cell damage and death.

Cells of the gastrointestinal tract, reproductive and hematopoietic systems. Radioactive exposure disrupts their work and causes nausea, vomiting, bowel dysfunction, and fever. By affecting the tissues of the eye, it can lead to radiation cataracts. To the consequences ionizing radiation also include damage such as vascular sclerosis, deterioration of immunity, and disruption of the genetic apparatus.

The system of transmission of hereditary data has a fine organization. Free radicals and their derivatives are capable of disrupting the structure of the DNA carrier genetic information. This leads to mutations that affect the health of subsequent generations.

The nature of the effects of radioactive radiation on the body is determined by a number of factors:

• type of radiation;
• radiation intensity;
• individual characteristics of the body.

The effects of radioactive radiation may not appear immediately. Sometimes its consequences become noticeable after a significant period of time. Moreover, a large single dose of radiation is more dangerous than long-term exposure to small doses.

The amount of radiation absorbed is characterized by a value called Sievert (Sv).

• Normal background radiation does not exceed 0.2 mSv/h, which corresponds to 20 microroentgens per hour. When X-raying a tooth, a person receives 0.1 mSv.

• The lethal single dose is 6-7 Sv.

Application of ionizing radiation

Radioactive radiation is widely used in technology, medicine, science, military and nuclear industries and other fields human activity. The phenomenon underlies devices such as smoke detectors, power generators, icing alarms, and air ionizers.

In medicine, radioactive radiation is used in radiation therapy to treat cancer. Ionizing radiation allowed the creation of radiopharmaceuticals. With their help they carry out diagnostic examinations. Instruments for analyzing the composition of compounds and sterilization are built on the basis of ionizing radiation.

The discovery of radioactive radiation was, without exaggeration, revolutionary - the use of this phenomenon brought humanity to new level development. However, this also caused a threat to the environment and human health. In this regard, maintaining radiation safety is important task modernity.

Introduction 3
1 Radioactivity 5
1.1 Types of radioactive decay and radiation 5
1.2 Law of Radioactive Decay 7
1.3 Interaction of radioactive radiation with matter and counters
radiation 8
1.4 Classification of sources of radioactive radiation and radioactive isotopes 10
2 Analytical techniques based on radioactivity measurements 12
2.1 Use of naturally occurring radioactivity in analysis 12
2.2 Activation analysis 12
2.3 Isotope dilution method 14
2.4 Radiometric titration 14
3 Applications of radioactivity 18
3.1 Application of radioactive tracers in analytical chemistry 18
3.2 Application of radioactive isotopes 22
Conclusion 25
List of sources used 26

Introduction

deposition method in the presence of a radioactive element;
isotope dilution method;
radiometric titration;
activation analysis;
definitions based on measurements of the radioactivity of naturally occurring isotopes.

1 Radioactivity

1.1 Types of radioactive decay and radiation

In accordance with the law of radioactive displacement, during ?-decay an atom is obtained whose atomic number is two units, and whose atomic mass is four units less than that of the original atom.
2) ?-Decomposition. There are several types of?-decay: electronic?-decay; positron?-decay; K-grab. During electronic?-decay, for example,

Sn > Y + ? - ;
P > S + ? - .

A neutron inside a nucleus turns into a proton. When a negatively charged particle is emitted, the element's atomic number increases by one, but the atomic mass remains virtually unchanged.
During positron?-decay, a positron (? + -particle) is released from the atomic nucleus, and then turns into a neutron inside the nucleus. For example:

The lifespan of a positron is short, since when it collides with an electron, annihilation occurs, accompanied by the emission of ?-quanta.
In K-capture, the nucleus of an atom captures an electron from a nearby electron shell (from the K-shell) and one of the protons of the nucleus is converted into a neutron.
For example,
Cu >Ni+n
K + e - = Ar + hv

One of the electrons of the outer shell passes to a free place in the K-shell, which is accompanied by the emission of hard X-rays.
3) Spontaneous division. It is typical for elements of D.I. Mendeleev’s periodic table with Z > 90. During spontaneous fission, heavy atoms are divided into fragments, which are usually the elements in the middle of L.I. Mendeleev’s table. Spontaneous fission and β-decay limit the production of new transuranium elements.
Flow? and?-particles are called accordingly? and?-radiation. In addition, ?-radiation is known. These are electromagnetic oscillations with a very short wavelength. In principle, γ radiation is close to hard X-rays and differs from it in its intranuclear origin. X-ray radiation occurs during transitions in the electron shell of an atom, and α radiation is emitted by excited atoms resulting from radioactive decay (? and?).
As a result of radioactive decay, elements are obtained that, according to the charge of the nuclei (serial number), must be placed in the already occupied cells of the periodic table by elements with the same atomic number, but a different atomic mass. These are so-called isotopes. Their chemical properties are considered to be indistinguishable, so a mixture of isotopes is usually considered as one element. The constancy of the isotopic composition in the vast majority of chemical reactions is sometimes called the law of constancy of the isotopic composition. For example, potassium in natural compounds is a mixture of isotopes, 93.259% from 39 K, 6.729% from 41 K and 0.0119% from 40 K (K-capture and?-decay). Calcium has six stable isotopes with mass numbers 40, 42, 43, 44, 46 and 48. In chemical analytical and many other reactions this ratio remains practically unchanged, therefore chemical reactions are not usually used to separate isotopes. Most often, various physical processes are used for this purpose - diffusion, distillation or electrolysis.
The unit of isotope activity is the becquerel (Bq), equal to the activity of the nuclide in a radioactive source in which one decay event occurs in 1 s.

1.2 Law of radioactive decay

If t = 0, then const = -lg N 0. Finally

Where A is activity at time t; A 0 – activity at t = 0.
Equations (1.3) and (1.4) characterize the law of radioactive decay. In kinetics, these are known as first-order reaction equations. The half-life T1/2 is usually indicated as a characteristic of the rate of radioactive decay, which, like ?, is a fundamental characteristic of the process that does not depend on the amount of substance.
The half-life is the period of time during which a given amount of radioactive substance is reduced by half.
The half-lives of different isotopes vary significantly. It ranges from about 10 10 years to tiny fractions of a second. Of course, substances with a half-life of 10 - 15 minutes. and smaller ones are difficult to use in the laboratory. Isotopes with very long half-lives are also undesirable in the laboratory, since in case of accidental contamination of surrounding objects with these substances, special work will be required to decontaminate the room and instruments.

1.3 Interaction of radioactive radiation with matter and counters

radiation

1.4 Classification of sources of radioactive radiation and

radioactive isotopes

2 Analytical techniques based on radioactivity measurements

2.1 Use of naturally occurring radioactivity in analysis

2.2 Activation analysis

Neutrons enter into a nuclear reaction with the components of the analyzed sample, for example:
55 Mn + n = 56 Mn or Mn (n,?) 56 Mn
Radioactive 56 Mn decays with a half-life of 2.6 hours:

56 Mn > 56 Fe +

To obtain information about the composition of the sample, its radioactivity is measured for some time and the resulting curve is analyzed (Figure 2.1). When carrying out such an analysis, it is necessary to have reliable data on the half-lives of various isotopes in order to decipher the summary curve.

Figure 2.1 - Decrease in radioactivity over time

Another option for activation analysis is the method of ?-spectroscopy, based on measuring the ?-radiation spectrum of a sample. The energy of?-radiation is qualitative, and the counting rate is a quantitative characteristic of the isotope. Measurements are made using multichannel spectrometers with scintillation or semiconductor counters. This is a much faster and more specific, although somewhat less sensitive, method of analysis than radiochemical analysis.
An important advantage of activation analysis is its low detection limit. With its help, up to 10 -13 - 10 -15 g of substance can be detected under favorable conditions. In some special cases it was possible to achieve even lower detection limits. For example, it is used to monitor the purity of silicon and germanium in the semiconductor industry, detecting impurity content up to 10 -8 - 10 -9%. Such contents cannot be determined by any method other than activation analysis. When obtaining heavy elements of the periodic table, such as mendelevium and kurchatovium, researchers were able to count almost every atom of the resulting element.
The main disadvantage of activation analysis is the bulkiness of the neutron source, as well as the often long duration of the process of obtaining results.

2.3 Isotope dilution method

2.4 Radiometric titration

The change in activity during this titration can be seen in Figure 2.2a. A graphical definition of the equivalence point is also shown here. Before the equivalence point, the activity of the solution will decrease sharply, since the radioactive substance will pass from the solution into a precipitate. After the equivalence point, the activity of the solution will remain almost constant and very small.
As can be seen from Figure 2.2, b, adding hydrogen phosphate to the solution to the equivalence point will practically not cause an increase in the activity of the solution, since the radioactive isotope will precipitate. After the equivalence point, the activity of the solution begins to increase in proportion to the concentration of hydrogen phosphate.

A) - change in the activity of the phosphate solution containing during titration with the solution; b) - change in the activity of the solution when titrated with phosphate containing.
Figure 2.2 - Types of radiometric titration curves

Radiometric titration reactions must meet the requirements usually applied to titrimetric analysis reactions (speed and completeness of the reaction, constancy of the composition of the reaction product, etc.). An obvious condition for the applicability of the reaction in this method is also the transition of the reaction product from the analyzed solution to another phase in order to eliminate interference in determining the activity of the solution. This second phase is often a precipitate that forms. There are known methods where the reaction product is extracted with an organic solvent. For example, when titrating many cations with dithizone, chloroform or carbon tetrachloride is used as an extractant. The use of an extractant allows one to more accurately establish the equivalence point, since in this case its determination allows one to measure the activity of both phases.

2.5 Mössbauer effect

The effect was discovered in 1958 by R. P. Mossbauer. Under this name, the phenomena of emission, absorption and scattering of ?-quanta by atomic nuclei are often combined without the expenditure of energy on the recoil of the nuclei. The absorption of?-radiation is usually studied, therefore the Mössbauer effect is often also called?-resonance spectroscopy (GRS).
When ?-quanta are emitted, the atomic nucleus returns to its normal state. However, the energy of the emitted radiation will be determined not only by the difference in the energy states of the nucleus in the excited and normal conditions. Due to the law of conservation of momentum, the nucleus experiences so-called recoil. This leads to the fact that in the case of a gaseous atom, the energy of the emitted radiation will be less than in the case when the emitter is located in a solid body. In the latter case, energy losses due to recoil are reduced to a negligible value. Thus, γ-quanta of radiation emitted without recoil can be absorbed by unexcited atoms of the same element. However, the difference in the chemical environment of the emitter nucleus and the absorber nucleus causes some difference in the energy states of the nuclei, sufficient to prevent resonant absorption of γ quanta from occurring. The difference in the energy states of nuclei is quantitatively compensated using the Doppler effect, according to which the radiation frequency (in in this case energy?-quanta) depends on the speed of movement. At a certain speed of movement of the emitter (or absorber, since only their relative speed displacement) resonant absorption occurs. The dependence of the intensity of absorption of ?-quanta on the speed of movement is called the Mössbauer spectrum. A typical Mössbauer spectrum is presented in Figure 2.3, where the count rate, inversely proportional to it, is plotted as a measure of absorption intensity.

Figure 2.3 - Mössbauer absorption spectrum

The speed of movement of the sample or emitter usually does not exceed several centimeters per second. The Mössbauer spectrum is a very important characteristic of a substance. It allows one to judge the nature of the chemical bond in the compounds under study, their electronic structure and other features and properties.

3 Applications of radioactivity

3.1 Application of radioactive tracers in analytical chemistry

Where is the radioactivity of the sample, expressed in becquerels, and is the mass of the sample of the analyte, in which the radionuclide is evenly distributed, remains constant both for the entire sample and for any part of it.
Let's consider an experiment to determine the vapor pressure of such an extremely difficult-to-volatile and refractory metal as tungsten. Artificially produced?-radioactive tungsten-185 can be used as a tag. Let's prepare metal tungsten containing this mark and determine its specific activity. Next, we will collect metal vapors that evaporated from the tungsten surface at a selected temperature and were contained in a certain volume of vapor. Under the same conditions in which they were determined, we will find the activity of these vapors. It is obvious that the mass of vapors

Next, knowing the volume of vapor, you can find its density at the temperature of the experiment, and then, using information about the composition of the vapor, and its pressure.
Similarly, using a radioactive label, you can find the concentration of a substance in a solution and determine, for example, its concentration in a saturated solution. In a similar way, one can find the mass of a substance remaining after extraction into aquatic environment, and passed into the organic phase. Next, it is possible to calculate the distribution coefficients between the phases of the extracted substance (here the use of radioactive tracers is important when the distribution coefficients are very high and there are no other analytical methods for determining ultra-low quantities of the extracted substance remaining in the aqueous phase).
The use of radioactive tracers in the isotope dilution method is original. Suppose you need to determine the content of any amino acid in a mixture of amino acids with similar properties, and it is impossible to perform a complete (quantitative) separation of amino acids using chemical methods, but there is a method that allows you to isolate a small fraction of this amino acid from a mixture in its pure form (for example, using chromatography). A similar problem arises when determining the content of any lanthanide in a mixture of lanthanides and when determining in which chemical forms this or that element is found in nature, for example, in river or sea water.
We will use it to determine the total iodine content in sea ​​water portion of iodide ions by mass and activity. Let's introduce these labeled iodide ions into the analyzed sample and heat it so that the radioactive label is evenly distributed over all iodine-containing samples. chemical forms, located in sea water (such forms in this case are iodide, iodate, and periodate ions). Next, using silver nitrate, we will isolate a small part of the iodide ions in the form of an AgI precipitate and determine its mass and radioactivity. If general content iodine in the sample is equal, it turns out that

Using a slightly different technique, it is possible to find the iodine content of seawater in the form of iodide ions. To do this, after introducing a radioactive label into the sample, conditions should be created under which isotope exchange (exchange of iodine atoms) between iodide ions and other forms containing iodine (iodate and periodate ions) does not occur (for this you need to use a cold solution with a neutral environment). By further isolating a small portion of iodide ions from sea water using a precipitant - silver nitrate in the form of AgI (portion weight) and measuring its radioactivity, using formula (3.5) one can find the content of iodide ions in the sample.

The use of radioactive atoms is also the basis for such a universal, extremely sensitive method of analytical chemistry as activation analysis. When performing an activation analysis, it is necessary to use a suitable nuclear reaction activate the atoms of the element being determined in the sample, that is, make them radioactive. Most often, activation analysis is performed using a neutron source. If, for example, it is necessary to find the content of the rare earth element dysprosium Dy in solid rock, proceed as follows.
First, a series of samples is prepared containing known varying amounts of Dy (taken, for example, in the form of DyF 3 or Dy 2 O 3 - oxygen and fluorine atoms are not activated by neutrons). These samples are irradiated under the same conditions with the same neutron flux. The neutron source required for these experiments is a small (pen-sized) ampoule containing a neutron-emitting material (for example, a mixture of americium-241 and beryllium). Such a neutron source can be safely stored by placing it in a hole made in the center of a paraffin block the size of a water bucket.
For irradiation, samples with a known dysprosium content are placed in wells located in a paraffin block and located at the same distance from the source (Figure 3.1).

1 – paraffin block, 2 – ampoule neutron source,
3 – irradiated samples.
Figure 3.1 – Scheme of neutron activation analysis

Samples of the analyzed rock are placed in the same wells. Under the influence of neutrons, the nuclear reaction 164 Dy(n, g) 165 Dy occurs in the samples. After a certain time (for example, after 6 hours), all samples are removed from the wells and their activities are measured under the same conditions. Based on the measurement data of the activity of the drugs, a calibration graph is constructed in the coordinates “dysprosium content in the sample - drug activity”, and from it the dysprosium content in the analyzed material is found (Figure 3.2).

Figure 3.2 – Graph of the dependence of the recorded activity/neutron-activated samples on the mass m of dysprosium in the samples. The analyzed sample contains about 3 µg of dysprosium

The activation analysis method is good not only because of its high sensitivity. Since the radiation of radionuclides formed during activation differs in type and energy, when using spectrometric radiometric equipment it becomes possible to simultaneously determine up to 10-15 elements in a sample after its activation.
And one more important advantage of activation analysis: radionuclides often formed as a result of activation by neutrons decay quite quickly, so that after some time the analyzed object turns out to be non-radioactive. Thus, in many cases, activation analysis is an analysis that is not associated with the destruction of the analyzed object. This is especially important when we're talking about on determining the composition archaeological finds, meteorites and other unique samples.

3.2 Use of radioactive isotopes

radiation particle irradiation radon

People have learned to use radiation in for peaceful purposes, With high level security, which allowed us to raise almost all industries to a new level.

Producing energy using nuclear power plants. From all industries economic activity human energy has the most big influence for our lives. Heat and light in homes, traffic flows and the operation of industry - all this requires energy. This industry is one of the fastest growing. Over 30 years, the total capacity of nuclear power units has increased from 5 thousand to 23 million kilowatts.

Few people doubt that nuclear power has taken a strong place in the energy balance of humanity.

Let's consider the use of radiation in flaw detection. X-ray and gamma flaw detection are one of the most common uses of radiation in industry to control the quality of materials. The X-ray method is non-destructive, so that the material being tested can then be used for its intended purpose. Both X-ray and gamma flaw detection are based on the penetrating ability of X-ray radiation and the characteristics of its absorption in materials.

Gamma radiation is used for chemical transformations, for example, in polymerization processes.

Perhaps one of the most important emerging industries is nuclear medicine. Nuclear medicine is a branch of medicine associated with the use of advances nuclear physics, in particular, radioisotopes, etc.

Today, nuclear medicine makes it possible to study almost all human organ systems and is used in neurology, cardiology, oncology, endocrinology, pulmonology and other areas of medicine.

Using methods nuclear medicine study the blood supply to organs, bile metabolism, kidney, bladder, and thyroid function.

It is possible not only to obtain static images, but also to overlay images obtained at different points in time to study dynamics. This technique is used, for example, in assessing heart function.

In Russia, two types of diagnostics using radioisotopes are already actively used - scintigraphy and positron emission tomography. They allow you to create complete models of organ function.

Doctors believe that at low doses, radiation has a stimulating effect, training the system biological protection person.

Many resorts use radon baths, where the level of radiation is slightly higher than in natural conditions.

It was noticed that those who take these baths have improved performance and calmed down. nervous system, injuries heal faster.

Research by foreign scientists suggests that the incidence and mortality from all types of cancer are lower in areas with higher natural background radiation(most sunny countries can be classified as such).