X-ray sources. Is the X-ray tube the source of ionizing radiation?

Throughout the entire history of life on Earth, organisms have been constantly exposed to cosmic rays and the radionuclides formed by them in the atmosphere, as well as the radiation of substances that are ubiquitous in nature. Modern life is adjusted to all the features and limitations of the environment, including natural sources of X-ray radiation.

Despite the fact that a high level of radiation is certainly harmful to organisms, some types of radioactive radiation are important for life. For example, the radiation background contributed to the fundamental processes of chemical and biological evolution. Also obvious is the fact that the heat of the core of the Earth is provided and maintained due to the heat dissipation of primary, natural radionuclides.

Cosmic rays

Radiation of extraterrestrial origin, which continuously bombards the Earth, is called cosmic.

The fact that this penetrating radiation hits our planet from space, rather than terrestrial origin, was detected in experiments to measure ionization at various altitudes, from sea level to 9000 m. It was found that the intensity of ionizing radiation was reduced to an altitude of 700 m, And then increased rapidly with the climb. The initial decrease can be explained by the decrease in the intensity of terrestrial gamma rays, and the increase by the action of cosmic rays.

The sources of X-ray radiation in space are as follows:

• Groups of galaxies;
• Seyfert galaxies;
• The sun;
• stars;
• Quasars;
• black holes;
• Supernova remnants;
• White dwarfs;
• Dark stars, etc.

Evidence of such radiation, for example, is the increase in the intensity of cosmic rays observed on Earth after flares on the Sun. But our luminary does not make the main contribution to the overall flow, since its diurnal variations are very small.

Two types of rays

Cosmic rays are divided into primary and secondary. Radiation that does not interact with matter in the atmosphere, lithosphere or hydrosphere of the Earth is called primary. It consists of protons (≈ 85%) and alpha particles (≈ 14%), with much smaller fluxes (<1%) of heavier nuclei. Secondary cosmic X-rays, whose radiation sources are primary radiation and atmosphere, consist of subatomic particles, such as pions, muons and electrons. At sea level, almost all of the observed radiation consists of secondary cosmic rays, 68% of which are muons and 30% are electrons. Less than 1% of the flux at sea level consists of protons.

Primary cosmic rays, as a rule, have a huge kinetic energy. They are positively charged and receive energy due to acceleration in magnetic fields. In a vacuum of outer space, charged particles can exist for a long time and travel millions of light years. During this flight they acquire a high kinetic energy, on the order of 2-30 GeV (1 GeV = 10 ⁹ eV). Individual particles have energies up to 10 ¹⁰ GeV.

The high energies of primary cosmic rays allow them, literally, to split atoms in a terrestrial atmosphere during a collision. Along with neutrons, protons and subatomic particles, light elements such as hydrogen, helium and beryllium can form. The muons are always charged, and also decay rapidly into electrons or positrons.

Magnetic Shield

The intensity of cosmic rays with a rise sharply increases to a maximum at an altitude of about 20 km. From 20 km to the boundary of the atmosphere (up to 50 km), the intensity decreases.

This regularity is explained by the increase in the production of secondary radiation as a result of the increase in air density. At an altitude of 20 km, most of the primary radiation has already interacted, and a decrease in intensity from 20 km to sea level reflects the absorption of secondary rays by the atmosphere, which is equivalent to approximately a 10-meter layer of water.

The intensity of radiation is also related to latitude. At one height, the cosmic flux increases from the equator to a latitude of 50-60 ° and remains constant to the poles. This is explained by the shape of the Earth's magnetic field and the distribution of the energy of the primary radiation. The magnetic lines of force that extend beyond the atmosphere are, as a rule, parallel to the earth's surface at the equator and perpendicular to the poles. Charged particles easily move along the lines of the magnetic field, but with difficulty cross it in the transverse direction. From poles to 60 °, virtually all primary radiation reaches the Earth's atmosphere, and at the equator only particles with energies exceeding 15 GeV can penetrate through the magnetic shield.

Secondary X-ray sources

As a result of the interaction of cosmic rays with matter, a significant amount of radionuclides is continuously produced. Most of them are fragments, but some of them are formed by the activation of stable atoms by neutrons or muons. The natural production of radionuclides in the atmosphere corresponds to the intensity of cosmic radiation in height and latitude. About 70% of them occur in the stratosphere, and 30% in the troposphere.

With the exception of H-3 and C-14, radionuclides are usually found in very low concentrations. Tritium is diluted and mixed with water and H-2, and C-14 combines with oxygen to form CO ₂ , which is mixed with the carbon dioxide of the atmosphere. Carbon-14 penetrates into the plants in the process of photosynthesis.

Earth's radiation

Of the many radionuclides that formed with the Earth, only a few have a half-life, long enough to explain their current existence. If our planet was formed about 6 billion years ago, then in order to stay in measurable quantities, it would take a half-life of at least 100 million years. Of the primary radionuclides that are still found, three are of the greatest importance. The source of X-ray radiation is K-40, U-238 and Th-232. Uranium and thorium each form a chain of decay products, which are almost always in the presence of the initial isotope. Although many of the daughter radionuclides are short-lived, they are common in the environment, since they are constantly formed from long-lived starting materials.

Other primary long-lived sources of X-rays, in short, are at very low concentrations. These are Rb-87, La-138, Ce-142, Sm-147, Lu-176, etc. Naturally occurring neutrons form many other radionuclides, but their concentration is usually very low. In Oaklo's career in Gabon, Africa, there is evidence of the existence of a "natural reactor" in which nuclear reactions took place. The depletion of U-235 and the presence of fission products within the rich uranium deposit indicate that about 2 billion years ago a spontaneous chain reaction occurred here.

Despite the fact that the original radionuclides are ubiquitous, their concentration depends on the location. The main reservoir of natural radioactivity is the lithosphere. In addition, it varies considerably within the lithosphere. Sometimes this is due to certain types of compounds and minerals, sometimes - purely regionally, with a slight correlation with types of rocks and minerals.

The distribution of primary radionuclides and their daughter decay products in natural ecosystems depends on many factors, including the chemical properties of nuclides, the physical factors of the ecosystem, and the physiological and ecological attributes of flora and fauna. The weathering of rocks, their main reservoir, supplies U, Th and K to the soil. The decay products of Th and U also participate in this transmission. From soil K, Ra, a little U and very little Th are assimilated by plants. They use potassium-40 as well as stable K. Radium, the decay product of U-238, is used by the plant, not because it is an isotope, but because it is chemically close to calcium. The absorption of uranium and thorium by plants is usually insignificant, since these radionuclides are usually insoluble.

Radon

The most important of all sources of natural radiation is an element without taste and smell, an invisible gas that is 8 times heavier than air, radon. It consists of two main isotopes - radon-222, one of the decay products of U-238, and radon-220, formed during the decay of Th-232.

Rocks, soil, plants, animals emit radon into the atmosphere. Gas is a product of the decay of radium and is produced in any material that contains it. Since radon is an inert gas, it can be emitted by surfaces that come into contact with the atmosphere. The amount of radon that emanates from a given rock mass depends on the amount of radium and the surface area. The smaller the rock, the more radon it can release. The concentration of Rn in the air next to radium-containing materials also depends on the speed of air movement. In basements, caves and mines that have poor air circulation, radon concentrations can reach significant levels.

Rn decays sufficiently fast and forms a series of daughter radionuclides. After the formation in the atmosphere, the products of the decay of radon combine with fine particles of dust, which settles on the soil and plants, and is also inhaled by animals. Rains are particularly effective in purifying the air of radioactive elements, but the collision and subsidence of aerosol particles also contributes to their deposition.

In a moderate climate, the concentration of radon in the room is on the average about 5-10 times higher than in the open air.

Over the past few decades, man "artificially" produced several hundred radionuclides, concomitant X-ray radiation, sources, properties, the use of which is used in medicine, military science, energy production, instrumentation and mineral exploration.

The individual effect of man-made sources of radiation varies greatly. Most people receive a relatively small dose of artificial radiation, but some - many thousands of times the radiation of natural sources. Technogenic sources are better controlled than natural sources.

X-ray sources in medicine

In industry and medicine, as a rule, only pure radionuclides are used, which makes it easier to identify ways of leakage from storage sites and the utilization process.

The use of radiation in medicine is widespread and potentially can have a significant impact. It includes X-ray sources used in medicine for:

• Diagnostics;
• Therapy;
• Analytical procedures;
• Cardiostimulation.

For diagnosis use both closed sources, and a wide variety of radioactive indicators. Medical institutions, as a rule, distinguish these applications as radiology and nuclear medicine.

Is the X-ray tube the source of ionizing radiation? Computer tomography and fluorography are well-known diagnostic procedures that are performed with its help. In addition, in medical radiography, there are many uses of isotope sources, including gamma and beta, and experimental neutron sources for cases where X-ray machines are inconvenient, inappropriate or can be dangerous. In terms of ecology, radiographic radiation is not dangerous as long as its sources remain accountable and disposed of properly. In this respect, the history of radium elements, radon needles and radium-containing luminescent compounds is not encouraging.

Usually, x-ray sources are used based on ⁹⁰ Sr or ¹⁴⁷ Pm. The appearance of ²⁵² Cf as a portable neutron generator made neutron radiography widely available, although in general this method still strongly depends on the availability of nuclear reactors.

Nuclear medicine

The main danger to the environment is represented by radioisotope labels in nuclear medicine and X-ray sources. Examples of undesirable effects are:

• Irradiation of the patient;
• Exposure of hospital staff;
• Exposure to the transport of radioactive pharmaceuticals;
• Impact in the production process;
• Exposure to radioactive waste.

In recent years, there has been a tendency to reduce patient exposure due to the introduction of short-lived isotopes of more narrowly focused action and the use of more highly concentrated preparations.

A shorter half-life reduces the impact of radioactive waste, since most of the long-lived elements are excreted through the kidneys.

Apparently, the impact on the environment through the sewage system does not depend on whether the patient is in a hospital or is treated as an outpatient. Although most of the radioactive elements released are likely to be short-lived, the cumulative effect greatly exceeds the level of pollution of all nuclear power plants combined.

The most commonly used in medicine radionuclides are x-ray sources:

• ^99m Tc - scanning of the skull and brain, cerebral blood scanning, scanning of the heart, liver, lungs, thyroid gland, placental localization;
• ¹³¹ I - blood, liver scans, placental localization, scanning and treatment of the thyroid gland;
• ⁵¹ Cr - determination of the duration of the existence of red blood cells or sequestration, volume of blood;
• ⁵⁷ Shilling's case;
• ³² P - metastases in bone tissue.

Broad application of radioimmunoassay procedures, radiation analysis of urine and other research methods using labeled organic compounds has significantly increased the use of liquid-scintillation drugs. Organic solutions of phosphorus, usually based on toluene or xylene, constitute a rather large volume of liquid organic waste that must be disposed of. Processing in liquid form is potentially dangerous and environmentally unacceptable. For this reason, incineration is preferred.

Since long-lived ³ N or ¹⁴ C are readily soluble in the environment, their effect is within the normal range. But the cumulative effect can be significant.

Another medical application of radionuclides is the use of plutonium batteries to power pacemakers. Thousands of people are alive today because these devices help to function their hearts. Sealed sources of ²³⁸ Pu (150 GBq) are surgically implanted in patients.

Industrial X-ray radiation: sources, properties, applications

Medicine is not the only area in which this part of the electromagnetic spectrum has found application. A significant component of the technogenic radiation situation are the radioisotopes and sources of X-rays used in industry. Examples of such applications:

• Industrial radiography;
• Measurement of radiation;
• Smoke detectors;
• Self-luminous materials;
• X-ray crystallography;
• Scanners for baggage and hand luggage inspection;
• X-ray lasers;
• Synchrotrons;
• Cyclotrons.

Since most of these applications involve the use of encapsulated isotopes, radiation exposure occurs during transport, transmission, maintenance and disposal.

Is the X-ray tube the source of ionizing radiation in industry? Yes, it is used in the systems of nondestructive control of airports, in the study of crystals, materials and structures, industrial control. Over the past decades, doses of radiation exposure in science and industry have reached half the value of this indicator in medicine; Hence, the contribution is significant.

Encapsulated sources of X-rays themselves have little effect. But their transportation and disposal are alarming when they are lost or mistakenly thrown to the landfill. Such X-ray sources are usually supplied and installed in the form of double-sealed discs or cylinders. Capsules are made of stainless steel and require periodic leak testing. Their disposal can be a problem. Short-lived sources can be stored and decayed, but even then they must be properly accounted for, and residual active material must be disposed of in a licensed institution. Otherwise, the capsules must be sent to specialized institutions. Their power determines the material and size of the active part of the X-ray source.

X-ray source storage locations

A growing problem is the safe decommissioning and decontamination of industrial sites where radioactive materials were stored in the past. Basically, these are previously built enterprises for processing nuclear materials, but it is necessary to participate in other industries, such as factories for the production of self-luminous tritium-containing signs.

A particular problem is the long-lived low-level sources, which are widely distributed. For example, ²⁴¹ Am is used in smoke detectors. In addition to radon, these are the main sources of X-ray radiation in everyday life. Individually, they do not pose any danger, but a significant number of them can present a problem in the future.

Nuclear explosions

Over the past 50 years, everyone has been exposed to radiation from radioactive fallout caused by nuclear weapons tests. Their peak occurred in 1954-1958 and in 1961-1962.

In 1963, three countries (the USSR, the United States and Great Britain) signed an agreement on the partial prohibition of nuclear tests in the atmosphere, the ocean and outer space. Over the next two decades, France and China conducted a series of much smaller trials that ended in 1980. Underground testing is still underway, but they usually do not cause precipitation.

Radioactive contamination after atmospheric tests falls near the site of the explosion. Partly they remain in the troposphere and are carried by the wind around the world at the same latitude. As they move, they fall to the ground, remaining about a month in the air. But most of it is pushed into the stratosphere, where the pollution remains for many months, and slowly descend the entire planet.

Radioactive precipitation includes several hundred different radionuclides, but only a few of them are capable of affecting the human body, so their size is very small, and the decay occurs quickly. The most significant are C-14, Cs-137, Zr-95 and Sr-90.

Zr-95 has a half-life of 64 days, and Cs-137 and Sr-90 - about 30 years. Only carbon-14 with a half-life of 5730 will remain active in the distant future.

Atomic Energy

Nuclear power is the most controversial of all anthropogenic sources of radiation, but it has a very small contribution to the impact on human health. In normal operation, nuclear facilities emit a small amount of radiation into the environment. As of February 2016, there were 442 civilian operating nuclear reactors in 31 countries and another 66 were under construction. This is only part of the nuclear fuel cycle . It begins with the extraction and grinding of uranium ore and continues to produce nuclear fuel. After being used in power plants, fuel cells are sometimes recycled for the recovery of uranium and plutonium. In the end, the cycle ends with the disposal of nuclear waste. At each stage of this cycle, leakage of radioactive materials is possible.

About half of the world uranium ore production comes from open quarries, the other half from mines. Then it is crushed on nearby crushers, which produce a large amount of waste - hundreds of millions of tons. These wastes remain radioactive for millions of years after the company ceases its operation, although the radiation radiation constitutes a very small fraction of the natural background.

After that, uranium is converted into fuel by further processing and cleaning at the concentrating plants. These processes lead to air and water pollution, but they are much less than at other stages of the fuel cycle.