Radioactive transformation of chemical elements. Radioactive transformations. Transformations of elements. Radioactive series

Radioactivity is the ability atomic nuclei transform into other nuclei emitting a spectrum of particles. If the transformation of nuclei occurs spontaneously (spontaneously), then the radioactivity is called natural.

If the decay is carried out artificially, then the radioactivity is artificial.

Radioactivity was discovered by the French physicist Becquerel in 1896, who first observed the emission of penetrating radiation from uranium.

In 1890 Rutherford and Soddy used natural radioactivity
(thorium), as well as the radioactivity of light elements, led to a number of patterns.

I. Natural radioactivity is accompanied by three types of radiation.

1.  -radiation represents a stream of positively charged  particles. Core stream
.

3. -radiation – electromagnetic radiation with a short wavelength ~ rent. rays
Å.

II. Radioactivity is due to internal structure nuclei and does not depend on external conditions

Moreover, the decay of each nucleus does not affect the decay of other nuclei.

III. Different radioactive substances vary greatly in the amount of radioactive radiation used.

Radioactive substances are usually characterized by the number of decays per unit time.

Activity of a radioactive substance

It turned out that the number of decays per second is ~ the total number of atoms of a radioactive substance, that is

- shows that the number of rad.at. decreases

- radioactivity constant and characterizes the decay activity of an element

After integration

- law of radioactive decay (Rutherford)

- the initial number of radioactive nuclei

- number of undecayed nuclei per m.v. t

The lifespan of radioactive nuclei is usually characterized by a half-life, that is, the period of time during which the number of radioactive nuclei will decrease by half.

Based on this definition, it is easy to find the relationship between half-life and decay constant

the average lifetime of radioactive nuclei is determined by the expression

after integration it is easy to obtain

, that is, the half-life of nuclei

In experiments, the activity of a substance is usually measured, that is, the number of nuclear decays in 1 second.

However, the non-systemic unit is most often used

There are nuclei with a very long half-life (Uranium 9500 years) and there are nuclei with a half-life of several seconds (
- 5730 years)

- decay – decay of atomic nuclei by emission  - particles. This type of radioactivity is characteristic of elements located at the end of the periodic table. Currently, there are about 40 natural and more than 100 artificially caused  - emitters. However, all elements  -decay for Pv

that is, as a result  -decay, the nuclear charge decreases by 2 units, and A - by 4

We get

- decay has 2 features

1. Decay constant and emitted energy  -particles turned out to be interconnected and obey Nettol’s Geiger law

IN 1 And IN 2 – empirical constants

The law shows that the shorter the life expectancy, the greater the energy of the emitted α-particle.

2. Energy  -particles during decay are confined within narrow limits from
, which is significantly less than the energy that  -the particle should receive after  -decay during acceleration in the electric field of the nucleus.

Energy  -particles turned out to be small compared to the potential barrier of the nucleus.

3. A fine structure of the emitted  -particles, that is, some distribution is observed  in energy close to some average value. Moreover, this distribution is discrete.

Electronic capture

Borrows energy from other nucleons.

-the collapse was explained only after construction was completed quantum mechanics and is explained from her position. It does not lend itself to classical interpretation.

- potential well depth, potential barrier height 30 M eV

According to classical mechanics
-particles ( E  ) cannot overcome the potential barrier.

There are already one in the kernels
-particles that move inside the nucleus with energy
.

If there were no potential barrier, then
-the particle would leave the nucleus with energy

- the energy that it would spend to overcome the forces of gravity in the core.

However, due to the fact that the core has a shell, which leads to an increase in the potential barrier by approximately 30 M eV (see diagram), then
-the particle can leave the nucleus. Only by leaking through a potential object. According to quantum mechanics, a particle with wave properties can leak through a potential barrier without expending energy. The phenomenon is called tunnel effect .

Application
-decay is due to the fact that the probability of leakage
-particles through the barrier depends on the size of the nuclei. You can estimate the size of the nucleus by knowing the energy
-particles E  .

What happens to matter during radioactive radiation? To answer this question at the beginning of the 20th century. it wasn't very easy. Already at the very beginning of radioactivity research, many strange and unusual things were discovered.

First, the amazing consistency with which the radioactive elements uranium, thorium and radium emit radiation. Over the course of days, months and years, the radiation intensity did not change noticeably. It was unaffected by ordinary influences such as heat or increased pressure.

The chemical reactions into which radioactive substances entered also did not affect the intensity of the radiation.

Secondly, very soon after the discovery of radioactivity it became clear that radioactivity is accompanied by the release of energy. Pierre Curie placed an ampoule of radium chloride in a calorimeter. α-, β- and γ-rays were absorbed in it, and due to their energy the calorimeter was heated. Curie determined that 1 g of radium releases 582 J of energy in 1 hour. And this energy is released continuously over a number of years.

Where does the energy come from, the release of which is not affected by all known influences? Apparently, during radioactivity, a substance experiences some profound changes, completely different from ordinary chemical transformations. It was assumed that the atoms themselves undergo transformations!

Now this idea may not cause much surprise, since a child can hear about it even before he learns to read. But at the beginning of the 20th century. it seemed fantastic and it took great courage to decide to express it. At that time, indisputable evidence for the existence of atoms had just been obtained. The centuries-old idea of ​​Democritus about the atomic structure of matter finally triumphed. And almost immediately after this, the immutability of atoms is called into question.

We will not go into detail about the experiments that ultimately led to full confidence is that during radioactive decay a chain of successive transformations of atoms occurs. Let us dwell only on the very first experiments begun by Rutherford and continued by him together with the English chemist F. Soddy (1877-1956).

Rutherford discovered that thorium activity, defined as the number of decays per unit time, remains unchanged in a closed ampoule. If the preparation is blown with even very weak air currents, then the activity of thorium is greatly reduced. Rutherford suggested that, simultaneously with the alpha particles, thorium emits some kind of gas, which is also radioactive. He called this gas emanation. By sucking air from an ampoule containing thorium, Rutherford isolated the radioactive gas and examined its ionizing ability. It turned out that the activity of this gas decreases rapidly with time. Every minute the activity decreases by half, and after ten minutes it is practically equal to zero. Soddy studied the chemical properties of this gas and found that it does not enter into any reactions, i.e., it is an inert gas. Subsequently, the gas was named radon and placed in the periodic table under serial number 86. Other radioactive elements also experienced transformations: uranium, actinium, radium. General conclusion, which scientists came to, was precisely formulated by Rutherford: “The atoms of a radioactive substance are subject to spontaneous modifications. At every moment a small part total number atoms becomes unstable and disintegrates explosively. In the overwhelming majority of cases, a fragment of an atom - an α-particle - is ejected at enormous speed. In some other cases, the explosion is accompanied by the ejection of a fast electron and the appearance of rays that, like X-rays, have high penetrating power and are called γ-radiation. It was discovered that as a result of an atomic transformation, a completely new type of substance is formed, completely different in its physical and chemical properties from the original substance. This new substance, however, is itself also unstable and undergoes a transformation with the emission of a characteristic radioactive radiation.

Thus, it is precisely established that the atoms of certain elements are subject to spontaneous disintegration, accompanied by the emission of energy in quantities enormous in comparison with the energy released during ordinary molecular modifications.”

After the atomic nucleus was discovered, it immediately became clear that it was this nucleus that underwent changes during radioactive transformations. After all, there are no os-particles in the electron shell at all, and a decrease in the number of shell electrons by one turns the atom into an ion, and not into a new chemical element. The ejection of an electron from the nucleus changes the charge of the nucleus (increases it) by one. The charge of the nucleus determines the atomic number of the element in the periodic table and all its chemical properties.

Note

Literature

Myakishev G.Ya. Physics: Optics. The quantum physics. 11th grade: Educational. For in-depth study physics. - M.: Bustard, 2002. - P. 351-353.

The main characteristic of an atom are 2 numbers:

1. mass number (A) – equal to the sum of protons and neutrons of the nucleus

2. atomic number (Z) in periodic table Mendeleev's elements – equal to the number protons in the nucleus, i.e. corresponds to the charge of the nucleus.

The type of radioactive transformation is determined Type of particles emitted during decay. The process of radioactive decay is always exothermic, that is, it releases energy. The initial nucleus is called the mother nucleus (in the diagrams below, indicated by the symbol X), and the resulting nucleus after decay is called the daughter nucleus (in the diagrams, symbol Y).

Unstable nuclei undergo 4 main types of radioactive transformations:

A) Alpha decay- consists in the fact that a heavy nucleus spontaneously emits an alpha particle, i.e. this is a purely nuclear phenomenon. More than 200 alpha-active nuclei are known, almost all of them have a serial number greater than 83 (Am-241; Ra-226; Rn-222; U-238 and 235; Th-232; Pu-239 and 240). The energy of alpha particles from heavy nuclei is most often in the range from 4 to 9 MeV.

Examples of alpha decay:

B) Beta transformation– this is an intranucleon process; In the nucleus, a single nucleon decays, during which an internal restructuring of the nucleus occurs and b-particles (electron, positron, neutrino, antineutrino) appear. Examples of radionuclides that undergo beta transformation: tritium (H-3); C-14; sodium radionuclides (Na-22, Na-24); phosphorus radionuclides (P-30, P-32); sulfur radionuclides (S-35, S-37); potassium radionuclides (K-40, K-44, K-45); Rb-87; strontium radionuclides (Sr-89, Sr-90); iodine radionuclides (I-125, I-129, I-131, I-134); cesium radionuclides (Cs-134, Cs-137).

The energy of beta particles varies over a wide range: from 0 to Emax (total energy released during decay) and is measured in keV, MeV. For identical nuclei, the energy distribution of emitted electrons is regular and is called Electron spectrumB-decay, or beta spectrum; The energy spectrum of beta particles can be used to identify the decaying element.

One example of the beta transformation of a single nucleon is Free neutron decay(half-life 11.7 min):

Types of beta transformation of nuclei:

1) electron decay: .

Examples of electron decay: ,

2) Positron decay:

Examples of positron decay: ,

3) Electronic capture(K-capture, because the nucleus absorbs one of the electrons of the atomic shell, usually from the K-shell):

Examples of electronic capture: ,

IN) Gamma transformation (isomeric transition)– an intranuclear phenomenon in which, due to excitation energy, the nucleus emits a gamma quantum, passing into a more stable state; in this case, the mass number and atomic number do not change. The gamma radiation spectrum is always discrete. Gamma rays emitted by nuclei usually have energies from tens of keV to several MeV. Examples of radionuclides undergoing gamma transformation: Rb-81m; Cs-134m; Cs-135m; In-113m; Y-90m.

, where the index “m” means the metastable state of the nucleus.

Example of gamma transformation:

G) Spontaneous nuclear fission– possible for nuclei starting with mass number 232. The nucleus is divided into 2 fragments of comparable masses. It is the spontaneous fission of nuclei that limits the possibilities of obtaining new transuranium elements. Nuclear energy uses the process of fission of heavy nuclei when they capture neutrons:

As a result of fission, fragments with an excess number of neutrons are formed, which then undergo several successive transformations (usually beta decay).

• exposure dose
• absorbed dose
• equivalent dose
• effective equivalent dose

Radioactivity

This is the ability of the nuclei of different atoms chemical elements collapse, change with the emission of atomic and subatomic particles of high energies. During radioactive transformations, in the overwhelming majority of cases, the atomic nuclei (and therefore the atoms themselves) of some chemical elements are transformed into the atomic nuclei (atoms) of other chemical elements, or one isotope of a chemical element is transformed into another isotope of the same element.

Atoms whose nuclei are subject to radioactive decay or other radioactive transformations are called radioactive.

Isotopes

(from Greek wordsisos – “equal, identical” andtopos - "place")

These are nuclides of one chemical element, i.e. varieties of atoms of a particular element that have same atomic number but different mass numbers.

Isotopes have nuclei with the same number of protons and different number neutrons and occupy the same place in the periodic table of chemical elements. There are stable isotopes, which exist unchanged indefinitely, and unstable (radioisotopes), which decay over time.

Knownabout 280 stable Andmore than 2000 radioactive isotopes116 natural and artificially obtained elements .

Nuclide (from Latinnucleus – “nucleus”) is a collection of atoms with certain values ​​of nuclear charge and mass number.

Nuclide symbols:, WhereX – letter designation of the element,Z – number of protons (atomic number ), A – sum of the number of protons and neutrons (mass number ).

Even the very first and lightest atom in the periodic table, hydrogen, which has only one proton in its nucleus (and one electron revolves around it), has three isotopes.

Radioactive transformations

They can be natural, spontaneous (spontaneous) and artificial. Spontaneous radioactive transformations are a random, statistical process.

All radioactive transformations are usually accompanied by the release of excess energy from the nucleus of the atom in the form electromagnetic radiation.

Gamma radiation is a stream of gamma quanta with high energy and penetrating ability.

X-rays are also a stream of photons - usually with lower energy. Only the “birthplace” of X-ray radiation is not the nucleus, but the electron shells. The main flux of X-ray radiation occurs in a substance when “radioactive particles” (“radioactive radiation” or “radioactive radiation”) pass through it. ionizing radiation»).

The main types of radioactive transformations:

• radioactive decay;
• fission of atomic nuclei.

This is the emission, the ejection at enormous speeds from the nuclei of atoms of “elementary” (atomic, subatomic) particles, which are commonly called radioactive (ionizing) radiation.

When one isotope of a given chemical element decays, it turns into another isotope of the same element.

For natural of (natural) radionuclides, the main types of radioactive decay are alpha and beta minus decay.

Titles " alpha" And " beta” were given by Ernest Rutherford in 1900 while studying radioactive radiation.

For artificial(man-made) radionuclides, in addition, neutron, proton, positron (beta-plus) and rarer types of decay and nuclear transformations(mesonic, K-capture, isomeric transition, etc.).

Alpha decay

This is the emission of an alpha particle from the nucleus of an atom, which consists of 2 protons and 2 neutrons.

An alpha particle has a mass of 4 units, a charge of +2 and is the nucleus of a helium atom (4He).

As a result of the emission of an alpha particle, new element, which is located in the periodic table 2 cells to the left, since the number of protons in the nucleus, and therefore the charge of the nucleus and the element number, became two units less. And the mass of the resulting isotope turns out to be 4 units less.

A alpha – decay- this is a characteristic type of radioactive decay for natural radioactive elements of the sixth and seventh periods of the table of D.I. Mendeleev (uranium, thorium and their decay products up to and including bismuth) and especially for artificial - transuranium - elements.

That is, individual isotopes of all are susceptible to this type of decay. heavy elements, starting with bismuth.

So, for example, the alpha decay of uranium always produces thorium, the alpha decay of thorium always produces radium, the decay of radium always produces radon, then polonium, and finally lead. In this case, from a specific isotope of uranium-238, thorium-234 is formed, then radium-230, radon-226, etc.

The speed of an alpha particle when leaving the nucleus is from 12 to 20 thousand km/sec.

Beta decay

Beta decay- the most common type of radioactive decay (and radioactive transformations in general), especially among artificial radionuclides.

Each chemical element there is at least one beta-active isotope, that is, subject to beta decay.

An example of a natural beta-active radionuclide is potassium-40 (T1/2=1.3×109 years), the natural mixture of potassium isotopes contains only 0.0119%.

In addition to K-40, significant natural beta-active radionuclides are also all decay products of uranium and thorium, i.e. all elements from thallium to uranium.

Beta decay includes such types of radioactive transformations as:

– beta minus decay;

– beta plus decay;

– K-capture (electronic capture).

Beta minus decay– this is the emission of a beta minus particle from the nucleus – electron , which was formed as a result of the spontaneous transformation of one of the neutrons into a proton and an electron.

At the same time, the beta particle at speeds up to 270 thousand km/sec(9/10 the speed of light) flies out of the core. And since there are one more protons in the nucleus, the nucleus of this element turns into the nucleus of the neighboring element on the right - with a higher number.

During beta-minus decay, radioactive potassium-40 is converted into stable calcium-40 (in the next cell to the right). And radioactive calcium-47 turns into scandium-47 (also radioactive) to the right of it, which, in turn, also turns into stable titanium-47 through beta-minus decay.

Beta plus decay– emission of beta-plus particles from the nucleus – positron (a positively charged “electron”), which was formed as a result of the spontaneous transformation of one of the protons into a neutron and a positron.

As a result of this (since there are fewer protons), this element turns into the one next to it on the left in the periodic table.

For example, during beta-plus decay, the radioactive isotope of magnesium, magnesium-23, turns into the stable isotope of sodium (on the left), sodium-23, and the radioactive isotope of europium, europium-150, turns into the stable isotope of samarium, samarium-150.

– emission of a neutron from the nucleus of an atom. Characteristic of nuclides of artificial origin.

When a neutron is emitted, one isotope of a given chemical element transforms into another, with less weight. For example, during neutron decay, the radioactive isotope of lithium, lithium-9, turns into lithium-8, radioactive helium-5 into stable helium-4.

If a stable isotope of iodine - iodine-127 - is irradiated with gamma rays, then it becomes radioactive, emits a neutron and turns into another, also radioactive isotope - iodine-126. That's an example artificial neutron decay .

As a result of radioactive transformations, they can form isotopes of other chemical elements or the same element, which may themselves be radioactive elements.

Those. disintegration of some original radioactive isotope can lead to a certain number of successive radioactive transformations of various isotopes of different chemical elements, forming the so-called. "decay chains".

For example, thorium-234, formed during the alpha decay of uranium-238, turns into protactinium-234, which in turn turns back into uranium, but into a different isotope - uranium-234.

All these alpha and beta minus transitions end with the formation of stable lead-206. And uranium-234 undergoes alpha decay - again into thorium (thorium-230). Further, thorium-230 by alpha decay - into radium-226, radium - into radon.

Fission of atomic nuclei

Is it spontaneous, or under the influence of neutrons, core splitting atom into 2 approximately equal parts, into two “shards”.

When dividing they fly out 2-3 extra neutrons and an excess of energy is released in the form of gamma quanta, much greater than during radioactive decay.

If for one act of radioactive decay there is usually one gamma ray, then for 1 act of fission there are 8 -10 gamma quanta!

In addition, flying fragments have a large kinetic energy(speed), which turns into heat.

Departed neutrons can cause fission two or three similar nuclei, if they are nearby and if neutrons hit them.

Thus, it becomes possible to implement a branching, accelerating fission chain reaction atomic nuclei releasing enormous amounts of energy.

Fission chain reaction

If the chain reaction is allowed to develop uncontrollably, an atomic (nuclear) explosion will occur.

If the chain reaction is kept under control, its development is controlled, not allowed to accelerate and constantly withdraw released energy(heat), then this energy (“ atomic energy") can be used to generate electricity. This is done in nuclear reactors and nuclear power plants.

Characteristics of radioactive transformations

Half life (T1/2 ) – the time during which half of the radioactive atoms decay and their the quantity is reduced by 2 times.

The half-lives of all radionuclides are different - from fractions of a second (short-lived radionuclides) to billions of years (long-lived).

Activity– this is the number of decay events (in general, acts of radioactive, nuclear transformations) per unit of time (usually per second). The units of activity are becquerel and curie.

Becquerel (Bq)– this is one decay event per second (1 disintegration/sec).

Curie (Ci)– 3.7×1010 Bq (disp./sec).

The unit arose historically: 1 gram of radium-226 in equilibrium with its daughter decay products has such activity. It was with radium-226 that the laureates worked for many years Nobel Prize French scientific couple Pierre Curie and Marie Skłodowska-Curie.

Law of Radioactive Decay

The change in the activity of a nuclide in a source over time depends on the half-life of a given nuclide according to an exponential law:

AAnd(t) = AAnd (0) × exp(-0.693t/T1/2 ),

Where AAnd(0) – initial activity of the nuclide;
AAnd(t) – activity after time t;

T1/2 – half-life of the nuclide.

Relationship between mass radionuclide(without taking into account the mass of the inactive isotope) and his activity is expressed by the following relationship:

Where mAnd– radionuclide mass, g;

T1/2 – half-life of the radionuclide, s;

AAnd– radionuclide activity, Bq;

A – atomic mass radionuclide.

Penetrating power of radioactive radiation.

Alpha particle range depends on the initial energy and usually ranges from 3 to 7 (rarely up to 13) cm in air, and in dense media it is hundredths of a mm (in glass - 0.04 mm).

Alpha radiation does not penetrate a sheet of paper or human skin. Due to their mass and charge, alpha particles have the greatest ionizing ability; they destroy everything in their path, therefore alpha-active radionuclides are the most dangerous for humans and animals when ingested.

Beta particle range in the substance due to its low mass (~ 7000 times

Less than the mass of the alpha particle), the charge and size are much larger. In this case, the path of a beta particle in matter is not linear. Penetration is also dependent on energy.

The penetrating ability of beta particles formed during radioactive decay is in the air reaches 2÷3 m, in water and other liquids is measured in centimeters, in solids– see in fractions

Beta radiation penetrates into body tissue to a depth of 1÷2 cm.

Attenuation factor for n- and gamma radiation.

The most penetrating types of radiation are neutron and gamma radiation. Their range in the air can reach tens and hundreds of meters(also depending on energy), but with less ionizing power.

As protection against n- and gamma radiation, thick layers of concrete, lead, steel, etc. are used, and we are talking about the attenuation factor.

In relation to the cobalt-60 isotope (E = 1.17 and 1.33 MeV), for a 10-fold attenuation of gamma radiation, protection is required from:

• lead about 5 cm thick;
• concrete about 33 cm;
• water – 70 cm.

For 100-fold attenuation of gamma radiation, 9.5 cm thick lead shielding is required; concrete – 55 cm; water – 115 cm.

Units of measurement in dosimetry

Dose (from Greek - “share, portion”) irradiation.

Exposure dose(for X-ray and gamma radiation) – determined by air ionization.

SI unit of measurement – “coulomb per kg” (C/kg)- this is the exposure dose of x-ray or gamma radiation, when created in 1 kg dry air, a charge of ions of the same sign is formed, equal to 1 Cl.

The non-system unit of measurement is "x-ray".

1 R = 2.58× 10 -4 Kl/kg.

A-priory 1 roentgen (1P)– this is the exposure dose upon absorption of which 1 cm3 dry air is formed 2,08 × 10 9 ion pairs.

The relationship between these two units is as follows:

1 C/kg = 3.68 103 R.

Exposure dose 1Р corresponds to the absorbed dose in the air 0.88 rad.

Dose

Absorbed dose– the energy of ionizing radiation absorbed by a unit mass of matter.

The radiation energy transferred to a substance is understood as the difference between the total kinetic energy of all particles and photons entering the volume of matter under consideration and the total kinetic energy of all particles and photons leaving this volume. Therefore, the absorbed dose takes into account all the ionizing radiation energy left within that volume, regardless of how that energy is spent.

Absorbed dose units:

Gray (Gr)– unit of absorbed dose in the SI system of units. Corresponds to 1 J of radiation energy absorbed by 1 kg of substance.

Glad– extra-systemic unit of absorbed dose. Corresponds to a radiation energy of 100 erg absorbed by a substance weighing 1 gram.

1 rad = 100 erg/g = 0.01 J/kg = 0.01 Gy.

The biological effect at the same absorbed dose is different for different types radiation.

For example, with the same absorbed dose alpha radiation turns out much more dangerous than photon or beta radiation. This is due to the fact that alpha particles create denser ionization along their path in biological tissue, thus concentrating harmful effects on the body in a specific organ. In this case, the entire body experiences a much greater inhibitory effect of radiation.

Consequently, to create the same biological effect when irradiated with heavy charged particles, a lower absorbed dose is required than when irradiated with light particles or photons.

Equivalent dose– product of the absorbed dose and the radiation quality factor.

Equivalent dose units:

sievert(Sv) is a unit of measurement for dose equivalent, any type of radiation that produces the same biological effect as the absorbed dose in 1 Gy

Hence, 1 Sv = 1 J/kg.

Bare(non-systemic unit) is the amount of energy of ionizing radiation absorbed 1 kg biological tissue, in which the same biological effect is observed as with the absorbed dose 1 rad X-ray or gamma radiation.

1 rem = 0.01 Sv = 100 erg/g.

The name “rem” is formed from the first letters of the phrase “biological equivalent of an x-ray.”

Until recently, when calculating the equivalent dose, “ radiation quality factors » (K) – correction factors that take into account the different effects on biological objects (different abilities to damage body tissues) of different radiations at the same absorbed dose.

Now these coefficients in the Radiation Safety Standards (NRB-99) are called “weighting coefficients for individual types of radiation when calculating the equivalent dose (WR).”

Their values ​​are respectively:

• X-ray, gamma, beta radiation, electrons and positrons – 1 ;
• protons with E more than 2 MeV – 5 ;
• neutrons with E less than 10 keV) – 5 ;
• neutrons with E from 10 kev to 100 kev – 10 ;
• alpha particles, fission fragments, heavy nuclei – 20 etc.

Effective equivalent dose– equivalent dose, calculated taking into account the different sensitivity of different body tissues to radiation; equal to equivalent dose, obtained by a specific organ, tissue (taking into account their weight), multiplied by corresponding " radiation risk coefficient ».

These coefficients are used in radiation protection to take into account the different sensitivity of different organs and tissues in the occurrence of stochastic effects from exposure to radiation.

In NRB-99 they are called “weighing coefficients for tissues and organs when calculating the effective dose.”

For the body as a whole this coefficient is taken equal to 1 , and for some organs it has the following meanings:

• bone marrow (red) – 0.12; gonads (ovaries, testes) – 0.20;
• thyroid gland – 0.05; leather – 0.01, etc.
• lungs, stomach, large intestine – 0.12.

To evaluate the full effective equivalent dose received by a person, the indicated doses for all organs are calculated and summed up.

To measure equivalent and effective equivalent doses, the SI system uses the same unit - sievert(Sv).

1 Sv equal to the equivalent dose at which the product of the absorbed dose in Gr eyah (in biological tissue) by the weighting coefficients will be equal to 1 J/kg.

In other words, this is the absorbed dose at which 1 kg substances release energy into 1 J.

The non-systemic unit is the rem.

Relationship between units of measurement:

1 Sv = 1 Gy * K = 1 J/kg * K = 100 rad * K = 100 rem

At K=1(for x-rays, gamma, beta radiation, electrons and positrons) 1 Sv corresponds to the absorbed dose in 1 Gy:

1 Sv = 1 Gy = 1 J/kg = 100 rad = 100 rem.

Back in the 50s, it was established that with an exposure dose of 1 roentgen, air absorbs approximately the same amount of energy as biological tissue.

Therefore, it turns out that when estimating doses we can assume (with minimal error) that exposure dose of 1 roentgen for biological tissue corresponds(equivalent) absorbed dose of 1 rad And equivalent dose of 1 rem(at K=1), that is, roughly speaking, 1 R, 1 rad and 1 rem are the same thing.

With an exposure dose of 12 μR/hour per year, we receive a dose of 1 mSv.

In addition, to assess the impact of AI, the following concepts are used:

Dose rate– dose received per unit of time (second, hour).

Background– the exposure dose rate of ionizing radiation in a given location.

Natural background– the exposure dose rate of ionizing radiation created by all natural sources of radiation.

Sources of radionuclides entering the environment

1. Natural radionuclides , which have survived to our time from the moment of their formation (possibly from the time of the formation solar system or the Universe), since they have long half-lives, which means their lifetime is long.

2.Radionuclides of fragmentation origin, which are formed as a result of the fission of atomic nuclei. Formed in nuclear reactors in which controlled chain reaction, as well as during nuclear weapons testing (uncontrolled chain reaction).

3. Radionuclides of activation origin are formed from ordinary stable isotopes as a result of activation, that is, when a subatomic particle (usually a neutron) enters the nucleus of a stable atom, as a result of which the stable atom becomes radioactive. Obtained by activating stable isotopes by placing them in the reactor core, or by bombardment stable isotope in accelerators elementary particles protons, electrons, etc.

Areas of application of radionuclide sources

AI sources are used in industry, agriculture, scientific research and medicine. In medicine alone, approximately one hundred isotopes are used for various medical research, diagnosis, sterilization and radiotherapy.

Around the world, many laboratories use radioactive materials to scientific research. Thermoelectric generators based on radioisotopes are used to produce electricity for autonomous power supply of various equipment in remote and hard-to-reach areas (radio and light beacons, weather stations).

Everywhere in industry, instruments containing radioactive sources are used to monitor technological processes (density, level and thickness gauges), non-destructive testing instruments (gamma flaw detectors), and instruments for analyzing the composition of matter. Radiation is used to increase the size and quality of crops.

The influence of radiation on the human body. Effects of radiation

Radioactive particles, possessing enormous energy and speed, when passing through any substance they collide with atoms and molecules of this substance and lead to their destruction ionization, to the formation of “hot” ions and free radicals.

Since biological Human tissue is 70% water, then to a large extent It is water that undergoes ionization. Ions and free radicals form compounds harmful to the body, which trigger a whole chain of sequential biochemical reactions and gradually lead to the destruction of cell membranes (cell walls and other structures).

Radiation affects people differently depending on gender and age, the state of the body, its immune system, etc., but especially strongly on infants, children and adolescents. When exposed to radiation hidden (incubation, latent) period, that is, the delay time before the onset of a visible effect can last for years or even decades.

The impact of radiation on the human body and biological objects causes three different negative effects:

• genetic effect for hereditary (sex) cells of the body. It can and does manifest itself only in posterity;
• genetic-stochastic effect, manifested for the hereditary apparatus of somatic cells - body cells. It manifests itself during the life of a particular person in the form of various mutations and diseases (including cancer);
• somatic effect, or rather, immune. This is a weakening of the body’s defenses and immune system due to the destruction of cell membranes and other structures.

Related materials

It was one of the most important stages in the development of modern physical knowledge. Scientists did not immediately come to the correct conclusions regarding the structure of the smallest particles. And much later, other laws were discovered - for example, the laws of motion of microparticles, as well as features of the transformation of atomic nuclei that occur during radioactive decay.

Rutherford's experiments

The radioactive transformations of atomic nuclei were first studied by the English researcher Rutherford. Even then it was clear that the bulk of the mass of an atom lies in its nucleus, since electrons are many hundreds of times lighter than nucleons. In order to explore positive charge inside the nucleus, in 1906 Rutherford proposed studying the atom by probing with alpha particles. Such particles arose during the decay of radium, as well as some other substances. During his experiments, Rutherford gained an understanding of the structure of the atom, which was given the name “planetary model”.

First observations of radioactivity

Back in 1985, the English researcher W. Ramsay, who is known for his discovery of argon gas, made interesting discovery. He discovered helium gas in a mineral called kleveite. Subsequently, large amounts of helium were also found in other minerals, but only in those containing thorium and uranium.

This seemed very strange to the researcher: where could gas come from in minerals? But when Rutherford began to study the nature of radioactivity, it turned out that helium was a product of radioactive decay. Some chemical elements “give birth” to others, with completely new properties. And this fact contradicted all the previous experience of chemists of that time.

Frederick Soddy's observation

Together with Rutherford, scientist Frederick Soddy was directly involved in the research. He was a chemist, and therefore all his work was carried out in relation to the identification of chemical elements according to their properties. In fact, the radioactive transformations of atomic nuclei were first noticed by Soddy. He managed to find out what the alpha particles that Rutherford used in his experiments are. After making measurements, scientists found that the mass of one alpha particle is 4 atomic mass units. Having accumulated a certain number of such alpha particles, the researchers discovered that they turned into a new substance - helium. The properties of this gas were well known to Soddy. Therefore, he argued that alpha particles were able to capture electrons from outside and turn into neutral helium atoms.

Changes inside the nucleus of an atom

Subsequent studies were aimed at identifying the features of the atomic nucleus. Scientists realized that all transformations occur not with electrons or the electron shell, but directly with the nuclei themselves. It was the radioactive transformations of atomic nuclei that contributed to the transformation of some substances into others. At that time, the features of these transformations were still unknown to scientists. But one thing was clear: as a result, new chemical elements somehow appeared.

For the first time, scientists were able to trace such a chain of metamorphoses in the process of converting radium into radon. The reactions that resulted in such transformations, accompanied by special radiation, were called nuclear by researchers. Having made sure that all these processes take place precisely inside the nucleus of an atom, scientists began to study other substances, not just radium.

Open types of radiation

Core discipline that may require answers to similar questions- this is physics (9th grade). Radioactive transformations of atomic nuclei are included in her course. While conducting experiments on the penetrating power of uranium radiation, Rutherford discovered two types of radiation, or radioactive transformations. The less penetrating type was called alpha radiation. Later, beta radiation was also studied. Gamma radiation was first studied by Paul Villard in 1900. Scientists have shown that the phenomenon of radioactivity is associated with the decay of atomic nuclei. Thus, a crushing blow was dealt to the previously prevailing ideas about the atom as an indivisible particle.

Radioactive transformations of atomic nuclei: main types

It is now believed that during radioactive decay three types of transformations occur: alpha decay, beta decay, and electron capture, otherwise called K-capture. During alpha decay, an alpha particle is emitted from the nucleus, which is the nucleus of a helium atom. The radioactive nucleus itself is transformed into one that has less electric charge. Alpha decay is characteristic of substances that occupy the last places in the periodic table. Beta decay is also included in the radioactive transformations of atomic nuclei. The composition of the atomic nucleus with this type also changes: it loses neutrinos or antineutrinos, as well as electrons and positrons.

This type of decay is accompanied by short-wavelength electromagnetic radiation. In electron capture, the nucleus of an atom absorbs one of the nearby electrons. In this case, the beryllium nucleus can turn into a lithium nucleus. This type was discovered in 1938 by an American physicist named Alvarez, who also studied the radioactive transformations of atomic nuclei. The photographs in which the researchers tried to capture such processes contain images similar to a blurry cloud due to the small size of the particles being studied.