Types of radiation with the highest penetrating ability. The benefits and harms of radioactive radiation. Corpuscular emission. Alpha particles

The concept of “radiation” includes the entire range of electromagnetic waves, as well as electric current, radio waves, and ionizing radiation. With the latter, the physical state of atoms and their nuclei changes, turning them into charged ions or products of nuclear reactions. The smallest particles have energy, which is gradually lost when interacting with structural units. As a result of the movement, the substance through which the elements penetrate becomes ionized. The penetration depth is different for each particle. Because of its ability to change substances, radioactive light is harmful to the body. What types of radiation exist?

Corpuscular emission. Alpha particles

This type is a flow of radioactive elements whose mass is different from zero. An example is alpha and beta radiation, as well as electron, neutron, proton and meson. Alpha particles are atomic nuclei that are emitted when certain radioactive atoms decay. They consist of two neutrons and two protons. Alpha radiation comes from the nuclei of helium atoms, which are positively charged. Natural emission is typical for unstable radionuclides of the thorium and uranium series. Alpha particles exit the nucleus at speeds of up to 20 thousand km/sec. Along the path of movement, they form a strong ionization of the medium, tearing electrons from the orbits of atoms. Ionization by rays leads to chemical changes in the substance, as well as to disruption of its crystal structure.

Characteristics of alpha radiation

Rays of this type are alpha particles with a mass of 4.0015 atomic units. The magnetic moment and spin are zero, and the particle charge is double the elementary charge. The energy of alpha rays is in the range of 4-9 MeV. Ionizing alpha radiation occurs when an atom loses its electron and becomes an ion. The electron is knocked out due to the large weight of alpha particles, which are almost seven thousand times larger than it. As the particles pass through an atom and break off each negatively charged element, they lose their energy and speed. The ability to ionize matter is lost when all the energy is spent and the alpha particle is converted into a helium atom.

Beta radiation

It is a process in which electrons and positrons are produced by beta decay of elements ranging from the lightest to the heaviest. Beta particles cooperate with the electrons of atomic shells, transfer some of the energy to them and tear them out of orbit. In this case, a positive ion and a free electron are formed. Alpha and beta radiation have different speeds of movement. So, for the second type of rays it approaches the speed of light. Beta particles can be absorbed using a 1 mm thick layer of aluminum.

Gamma rays

They are formed during the decomposition of radioactive nuclei, as well as elementary particles. This is a short-wave type of electromagnetic radiation. It is formed when a nucleus transitions from a more excited energy state to a less excited one. It has a short wavelength and therefore has high penetrating power, which can cause serious harm to human health.

Properties

Particles that are formed during the decay of elemental nuclei can interact with the environment in different ways. This connection depends on the mass, charge, and energy of the particles. The properties of radioactive radiation include the following parameters:

1. Penetrating ability.

2. Ionization of the medium.

3. Exothermic reaction.

4. Impact on photographic emulsion.

5. The ability to cause the glow of luminescent substances.

6. With prolonged exposure, chemical reactions and breakdown of molecules are possible. For example, the color of an object changes.

The listed properties are used in detecting radiation due to the inability of humans to detect them with their senses.

Radiation sources

There are several reasons for particle emissions. These can be terrestrial or space objects that contain radioactive substances, technical devices that emit ionizing radiation. Also, the causes of the appearance of radioactive particles can be nuclear installations, control and measuring devices, medical supplies, and the destruction of radiation waste storage facilities. Hazardous sources are divided into two groups:

1. Closed. When working with them, radiation does not penetrate into the environment. An example would be radiation technology at nuclear power plants, as well as equipment in the X-ray room.
2. Open. In this case, the environment is exposed to radiation. Sources can be gases, aerosols, radioactive waste.

The elements of the series uranium, actinium and thorium are naturally occurring radioactive elements. When they decay, alpha and beta particles are emitted. The sources of alpha rays are polonium with atomic weights 214 and 218. The latter is a decay product of radon. This is a poisonous gas in large quantities that penetrates from the soil and accumulates in the basements of houses.

Sources of high-energy alpha radiation are a variety of charged particle accelerators. One such device is a phasotron. It is a cyclic resonant accelerator with a constant control magnetic field. The frequency of the accelerating electric field will vary slowly with period. The particles move in an unwinding spiral and are accelerated to an energy of 1 GeV.

Ability to penetrate substances

Alpha, beta, and gamma radiation have a certain range. Thus, the movement of alpha particles in the air is several centimeters, while beta particles can travel several meters, and gamma rays can travel up to hundreds of meters. If a person has experienced external alpha radiation, the penetration power of which is equal to the surface layer of the skin, then he will be in danger only in the case of open wounds on the body. Eating food irradiated with these elements causes severe harm.

Beta particles can penetrate the body only to a depth of no more than 2 cm, but gamma particles can cause irradiation of the entire body. The rays of the last particles can only be stopped by concrete or lead slabs.

Alpha radiation. Impact on humans

The energy of these particles formed during radioactive decay is not enough to overcome the initial layer of skin, so external irradiation does not harm the body. But if the source of the formation of alpha particles is an accelerator and their energy reaches above tens of MeV, then a threat to the normal functioning of the body is present. Direct penetration of a radioactive substance into the body causes enormous harm. For example, through inhalation of poisoned air or through the digestive tract. Alpha radiation can, in minimal doses, cause a person to develop radiation sickness, which often ends in the death of the victim.

Alpha rays cannot be detected using a dosimeter. Once in the body, they begin to irradiate nearby cells. The body forces cells to divide faster to fill the gap, but those born again are again exposed to harmful effects. This leads to loss of genetic information, mutations, and the formation of malignant tumors.

Permissible exposure limits

The standard of ionizing radiation in Russia is regulated by the “Radiation Safety Standards” and the “Basic Sanitary Rules for Working with Radioactive Substances and Other Sources of Ionizing Radiation.” According to these documents, exposure limits are developed for the following categories:

1. "A". This includes employees who work with a radiation source on a permanent basis or temporarily. The permissible limit is calculated as an individual equivalent dose of external and internal radiation per year. This is the so-called maximum permissible dose.

2. "B". The category includes the portion of the population that may be exposed to radiation sources because they live or work near them. In this case, the permissible dose per year is also calculated, at which health problems will not occur for 70 years.

3. "B". This type includes the population of a region, region or country exposed to radiation. Limitation of exposure occurs through the introduction of standards and control of radioactivity of objects in the environment, harmful emissions from nuclear power plants, taking into account dose limits for the previous categories. The impact of radiation on the population is not subject to regulation, since exposure levels are very low. In cases of radiation accidents in the regions, all necessary safety measures are applied.

Security measures

Alpha radiation protection is not a problem. Radiation rays are completely blocked by a thick sheet of paper and even human clothing. The danger arises only from internal exposure. To avoid it, personal protective equipment is used. These include overalls (overalls, moleskin helmets), plastic aprons, oversleeves, rubber gloves, and special shoes. To protect the eyes, plexiglass shields are used, dermatological products (pastes, ointments, creams), and respirators are also used. Enterprises are resorting to collective protection measures. As for protection from radon gas, which can accumulate in basements and bathrooms, in this case it is necessary to frequently ventilate the premises and insulate the basements from the inside.

The characteristics of alpha radiation lead us to the conclusion that this type has a low throughput and does not require serious protective measures during external exposure. These radioactive particles cause great harm when they penetrate into the body. Elements of this type extend over minimal distances. Alpha, beta, and gamma radiation differ from each other in their properties, penetrating ability, and impact on the environment.

Passing through matter, radiation microparticles waste their energy in collisions with orbital electrons, as well as in interactions with powerful electric and magnetic fields when particles fly near the nucleus. Most of the collisions and interactions occur not with nuclei, but with electrons on the shells of the atom. Knocking an electron out of an atom leads to the formation of an ion, i.e., ionization.
The energy of particles emitted during radioactive decay is of the order of mega- or kiloelectronvolts, and in a single collision an average of about 33-35 eV of energy is absorbed (transferred to atoms of the medium), from which it follows that the waste of all the energy will require a large number of ionization events. For example, with an average energy of β-radiation 90Y equal to 930 keV, its complete absorption will occur in ~10.4 collisions.
The total path length of a particle depends on the density of the medium. In table 2.5 shows approximate values ​​of the penetrating ability of various types of radiation on various materials. In general, the ratio of the penetrating power of different types of radiation can be represented as γ > β > α.

In addition to penetrating ability, another important indicator of radiation is ionization density, which is defined as the average number of ion pairs formed per unit path length of a particle. Naturally, both of these indicators are interrelated in an inverse relationship. The ionization density depends, among other things, on the size of the radiation particles: the larger the particles, the greater the probability of collisions when passing through the atoms of the medium and the higher the ionization density. The highest value of this indicator is for α- and n-radiations, much lower for β-radiations (flows of electrons and positrons), and very small for γ-photons, especially since the latter do not yet have an electric charge, and therefore cannot deflect in magnetic and electric fields in an atom. But the order of magnitude of the ionization density of α-, β- and γ-radiation in the same type of media differs in the ratio of approximately 10:4:10:2:1.
The trace of particle movement in a medium is called a track. From a collision with orbital electrons, the direction of motion of such a large particle as α (its mass is approximately 7400 times greater than the mass of an electron) practically does not change, but the trajectories of light particles (free electrons or positrons) turn out to be strongly broken and zigzag. Let us consider the features of the passage of different types of radiation through matter.
α-radiation. In accordance with the highest ionization density of α-particles, their range in all media is very small: even in air, α-radiation propagates over a distance not exceeding 3-7 cm, and in dense media the range is even shorter. In biological tissues, the range of an α particle rarely exceeds 40-60 µm, i.e. its effect is usually limited by the size of one cell. The low penetrating ability of α-radiation makes any protection from unclosed sources of α-radiation practically unnecessary.
β-radiation. The ranges of beta particles vary markedly depending on their energy. There are soft radiations with energies less than 0.5 MeV and hard radiations with energies greater than 1 MeV. The range of β-particles from hard emitters (for example, 32P or 90Y) reaches 10 m or more in air, but in dense media it is only a few mm. The actual range (according to the thickness of the material that completely absorbs radiation) is even less due to the zigzag trajectories of β-particles. Therefore, with surface soil contamination, external radiation from β-emitting isotopes (from radiostrontium, for example) does not pose a serious danger, since the radiation does not reach the soil surface when the radionuclide is already at a depth of more than 1 cm.
In the laboratory, organic glass screens up to 10 mm thick are used to protect against β-radiation. To work with soft β-emitters, even such protection is not required, since the maximum range of β-radiation in air from 14C (maximum energy 0.156 MeV) is only 15 cm, from tritium (2H, maximum energy 0.019 MeV) - less than 5 mm.
γ-radiation. In comparative terms, the penetrating power of γ-radiation is the greatest, however, taking into account the geometric scattering factor, which is proportional to the square of the distance, the real range of γ-sources in open areas is 200-300 m. With the help of airplanes or helicopters equipped with sensitive equipment, γ-radiation can identify and map the levels of radioactive contamination of an area; in cartography, this is done using the aerial gamma survey method. However, we must remember that the most reliable and accurate results are when flying at an altitude of 25-50 to 200-254) m, but not higher.
In dense media, γ-radiation can pass through tens and even hundreds of centimeters of thickness. To shield γ-radiation, materials with high density, such as lead, are chosen. The thickness of the shielding protection is determined by the overall activity of the source; for reliable protection, a lead thickness of up to 5-30 cm (or even more) may be required.
Neutron radiation. The absorption of neutrons in dense media occurs with a relatively high ionization density, so their penetrating ability is low. In the input, fast neutrons are slowed down to low energies at distances of the order of 8 cm, in soils or building structures - up to 20-40 cm. The mechanisms of neutron absorption are very specific, so it is necessary to select special materials to protect against fast or slow neutrons.

Different types of radiation are accompanied by the release of different amounts of energy and have different penetrating abilities, so they have different effects on the tissues of a living organism.

The greater the radiation energy and the depth of penetration of the rays, the more severe the radiation injury.

Thus, the penetrating power of g-radiation, which travels at the speed of light, is very high: only a thick lead or concrete slab can stop it.

In case of external irradiation of a person:

alpha particles are completely retained by the surface layer of the skin;

beta particles cannot penetrate deeper into the human body than a few millimeters;

Gamma rays can cause irradiation of the entire body.

Half life

The number of decays per second in a radioactive source is called activity. Activity unit – becquerel (Bq,Bq): 1 Bq is equal to one decay per second.

The time during which on average half of all radionuclides of a given type in any radioactive source decay is called the half-life. The decrease in the concentration of radionuclides in the body by half is called the half-life. For example, on the territory of Ukraine, as a result of the Chernobyl accident, the following radionuclides with half-life and half-life periods fell: carbon 14 - 5730 years and 200 days, respectively; cesium 137, 30 years and 100 days, respectively; strontium 90 – 29 and 20 years, respectively; iodine 131 – 8 and 138 days, respectively. The area becomes safe for living and use after approximately 10 half-lives.

Natural radioactive background

The world's population is constantly exposed to natural background radiation. This is cosmic radiation (protons, alpha particles, gamma rays), radiation from natural radioactive substances present in the soil, and radiation from those radioactive substances (also natural) that enter the human body with air, food, and water. The total dose generated by natural radiation varies greatly in different areas of the Earth. In Ukraine it ranges from 70 to 200 mrem/year.

Natural background provides approximately one third of the so-called population dose of the general background. Another third of people receive it during medical diagnostic procedures - x-rays, fluorography, x-rays, etc. The rest of the population dose comes from human stay in modern buildings. Coal-fired thermal power plants also contribute to increased background radiation, since coal contains dispersed radioactive elements. When flying on airplanes, a person also receives a small dose of ionizing radiation. But all these are very small quantities that do not have a harmful effect on human health.

Effect of ionizing radiation

In the organs and tissues of biological objects, as in any environment, during irradiation, as a result of energy absorption, processes of ionization and excitation of atoms occur.

The effect of ionizing radiation is the radiolysis of water molecules. As you know, water makes up about 80% of the mass of all organs and tissues of the human body.

When water ionizes, radicals are formed that have both oxidizing and reducing properties.

FREE RADICALS - particles with unpaired electrons in outer atomic or molecular orbitals

Peroxide substances (or free radicals) have strong oxidizing and toxic properties. Combining with organic substances, they cause significant chemical changes in cells and tissues, denaturation of protein and other organic structures with the formation of toxic histamine-like substances.

Beta radiation is a stream of electrons or positrons emitted by the nuclei of atoms of radioactive substances during radioactive decay. The maximum range in air is 1800 cm, and in living tissues - 2.5 cm. The ionizing ability of p-particles is lower, and the penetrating ability is higher than that of oc-particles, since they have a significantly smaller mass and have the same energy as a-particles have less charge.

Neutron radiation is a stream of neutrons that convert their energy in elastic and non-elastic interactions with atomic nuclei. During inelastic interactions, secondary radiation arises, which can consist of both charged particles and gamma quanta (gamma radiation). In elastic interactions, ordinary ionization of a substance is possible. The penetrating power of neutrons is high.

Water is the most widely used extinguishing agent. It has a significant heat capacity and a very high heat of evaporation (-2.22 kJ/g), due to which it has a strong cooling effect on the fire. The most significant disadvantages of water include its insufficient wetting (and, therefore, penetrating) ability when extinguishing fibrous materials (wood, cotton, etc.) and high mobility, leading to large losses of water and damage to surrounding objects. To overcome these disadvantages, surfactants (wetting agents) and viscosity-increasing substances (sodium carboxymethylcellulose) are added to water.

In explosive areas, radioisotope neutralizers are used, the action of which is based on the ionization of air by the alpha radiation of plutonium-239 and beta radiation of promethium-147. The penetrating ability of alpha particles in the air is several centimeters, so the use of an alpha source is safe for personnel.

Depending on the size of the droplets, the jets are droplet (droplet diameter > 0.4 mm), atomized (droplet diameter 0.2-0.4 mm) and finely atomized (fog-like, droplet diameter
When extinguishing with water jets, their penetrating ability is essential, which is determined by the pressure

The pressure of the water jet is determined experimentally by the speed of movement of the drops and the air flow they entrain. Penetration ability decreases with decreasing jet pressure and droplet size. When the droplet diameter is more than 0.8 mm, the penetrating ability does not depend on the jet pressure.

Radioactive isotopes emit various types of radiation invisible to the eye: a-rays (alpha rays), 3-rays (beta rays), rays (gamma rays) and neutrons. They are able to penetrate solid, liquid and gaseous bodies, and for different types of radiation the penetrating ability is not the same: rays have the greatest penetrating ability. In order to detain them, a layer of lead approximately 15 cm thick is needed.)