A radioactive source is a certain amount of a radionuclide that emits ionizing radiation. The latter usually includes gamma rays, alpha and beta particles, neutron radiation.
The role of sources
They can be used for irradiation when the radiation has an ionizing function, or as a source of metrological radiation for calibrating the radiometric process and instrumentation. They are also used to monitor industrial processes, such as thickness measurements in the paper and steel industries. Sources can be sealed in a container (high-penetrating radiation) or deposited on the surface (low-penetrating radiation), or are in the liquid.
Meaning and Application
They are used as a source of radiation in medicine for radiation therapy and in industry for radiography, food irradiation, sterilization, parasite disinsection and crosslinking with PVC irradiation.
Radionuclides
Radionuclides are selected in accordance with the type and nature of the radiation, its intensity and half-life. Common sources of radionuclides include cobalt-60, iridium-192, and strontium-90. Beckerel is a measure of the amount of SI activity of the source, although the historical Curie unit is still in partial use, for example, in the USA, despite the fact that the US NIST strongly recommends the use of the SI unit. For health purposes, it is mandatory in the EU.
Lifetime
The radiation source usually lives between 5 and 15 years before its activity drops to a safe level. However, in the presence of radionuclides with a long half-life, when used as means of calibration, they can be used much longer.
Closed and hidden
Many radioactive sources are closed. This means that they are constantly or completely contained in the capsule, or firmly bound by a solid substance to the surface. Capsules are usually made of stainless steel, titanium, platinum or other inert metal. The use of sealed sources eliminates almost the entire risk of dispersion of radioactive material into the environment due to improper handling, but the container is not designed to attenuate radiation, therefore, additional shielding is required for radiation protection. Closed ones are also used in almost all cases when chemical or physical incorporation into a liquid or gas is not required.
Sealed sources are classified by the IAEA according to their activities in relation to a minimally hazardous radioactive facility (which could cause significant harm to people). The ratio used is A / D, where A is the source activity and D is the minimum hazardous activity.
Please note that sources with a sufficiently low radioactive output (for example, used in smoke detectors), so as not to harm people, are not classified.
Capsule
Capsule sources, where radiation emanates efficiently from a point, are used to calibrate beta, gamma, and X-ray devices. Recently, they are unpopular both as industrial objects and as objects for study.
Lamellar sources
They are widely used for calibrating radioactive contamination instruments. That is, in fact, perform the role of a kind of miraculous counters.
Unlike a capsular source, the background that emits the plate should be on the surface to prevent the container from attenuating or self-shielding due to the specifics of the material. This is especially important for alpha particles that are easily stopped by a small mass. The Bragg curve shows the effect of attenuation in atmospheric air.
Unopened
Unopened sources are those that are not in a permanently sealed container and are widely used for medical purposes. They are used in cases where the source must be dissolved in a liquid for injection to the patient or oral administration. They are also used in industry in a similar manner for leak detection as a radioactive indicator.
Disposal and environmental aspects
Disposal of expired radioactive sources creates similar problems for the disposal of other nuclear waste, although to a lesser extent. Used low-level sources will sometimes be inactive enough to be disposed of using conventional waste disposal methods, usually in landfills. Other disposal methods are similar to those used for higher level radioactive waste, using different well depths depending on the activity of the waste.
A well-known case of careless handling of such an object was the accident in Goiania, which led to the deaths of several people.
Background radiation
Background radiation is always present on Earth. Most of the background radiation comes naturally from minerals, and a small part comes from artificial elements. Natural radioactive minerals in the earth, soil and water produce background radiation. The human body even contains some of these naturally occurring radioactive minerals. Cosmic radiation also contributes to the appearance of a radiation background around us. There may be large differences in the levels of natural background radiation from place to place, as well as changes in the same location over time. Natural radioisotopes are very strong background emitters.
Cosmic radiation
Cosmic radiation comes from the extremely energetic particles of the Sun and stars that enter the Earth’s atmosphere. That is, these celestial bodies can be called sources of radioactive radiation. Some particles fall on the ground, while others interact with the atmosphere, creating various types of radiation. Levels increase as you approach a radioactive object, so the amount of cosmic radiation usually increases in proportion to the climb. The higher the height, the higher the dose. This is why those living in Denver, Colorado (altitude 5,280 feet) receive a higher annual dose of cosmic radiation than anyone living at sea level (altitude 0 feet).
Uranium mining in Russia remains a controversial and “hot” topic, because this work is extremely dangerous. Naturally, uranium and thorium found in the earth are called primary radionuclides and are a source of terrestrial radiation. Traces of uranium, thorium, and their decay products can be found everywhere. Learn more about radioactive decay. Terrestrial radiation levels vary by location, but higher dose levels are usually observed in areas with higher concentrations of uranium and thorium in surface soils. Therefore, people involved in uranium mining in Russia are at great risk.
Radiation and people
Traces of radioactive substances can be found in the human body (mainly natural potassium-40). The element is found in the food, soil and water that we take. Our bodies contain a small amount of radiation, because the body metabolizes non-radioactive and radioactive forms of potassium and other elements in the same way.
A small fraction of the background radiation comes from human activity. Traces of radioactive elements dispersed in the environment as a result of nuclear weapons tests and accidents like the one that occurred at the Chernobyl nuclear power plant in Ukraine. Nuclear reactors emit a small amount of radioactive elements. Radioactive materials used in industry and even in some consumer products are also a source of small amounts of background radiation.
We are all exposed to radiation every day from natural sources, such as minerals in the earth, and artificial ones, such as medical x-rays. According to the National Council on Radiation Protection and Measurement (NCRP), the average annual dose per person in the United States is 620 millibar (6.2 millisievert).
In nature
Radioactive substances are often found in nature. Some of their quantities are found in soil, stones, water, air and vegetation, from which they are inhaled and enter the body. In addition to this internal exposure, people also receive external - from radioactive materials that remain outside the body, and from cosmic radiation from space. The average daily natural dose for humans is about 2.4 mSv (240 mber) per year.
This is four times the global average exposure to artificial radiation in the world, which in 2008 was about 0.6 mbar (60 Rem) per year. In some affluent countries, such as the United States and Japan, artificial irradiation is on average higher than natural due to wider access to specific medical instrumental research. In Europe, the average natural background exposure across countries ranges from 2 mSv (200 mbar) per year in the United Kingdom to more than 7 mSv (700 mbar) for some groups of people in Finland.
Daily exposure
Irradiation from natural sources is an integral part of everyday life both at work and in public places. Such exposure in most cases has little or no concern for society, but in certain situations it is necessary to take health protection measures into account, for example, when working with uranium and thorium ores and other naturally occurring radioactive materials (NORM). These situations have been the subject of increased Agency attention in recent years. And this, if not to mention examples of accidents involving the release of radioactive substances, such as the disaster at the Chernobyl nuclear power plant and at Fukushima, which forced scientists and politicians around the world to reconsider their attitude to the “peaceful atom”.
Earth radiation
Terrestrial radiation includes only sources that remain external to the body. But at the same time they continue to be dangerous radioactive sources of radiation. The main radionuclides of concern are potassium, uranium and thorium, their decomposition products. Moreover, some, such as radium and radon, are highly radioactive, but are found in low concentrations. The number of these objects is inexorably reduced since the formation of the Earth. The current radiation activity associated with the presence of uranium-238 is half that of the beginning of the existence of our planet. This is due to its half-life of 4.5 billion years, and for potassium-40 (half-life of 1.25 billion years) is only about 8% of the original. But during the existence of mankind, the amount of radiation has decreased very slightly.
Many isotopes with a shorter half-life (and therefore high radioactivity) did not decay due to their constant natural production. Examples of this are radium-226 (decay product of thorium-230 in the decay chain of uranium-238) and radon-222 (decay product of radium-226 in this chain).
Thorium and uranium
The radioactive chemical elements of thorium and uranium are mainly subjected to alpha and beta decay, and are not easy to detect. This makes them very dangerous. However, the same can be said of proton radiation. However, many of their secondary derivatives of these elements are also strong gamma emitters. Thorium-232 is detected using a peak of 239 keV from lead-212, 511, 583 and 2614 keV from thallium-208 and 911 and 969 keV from actinium-228. The radioactive chemical element Uranium-238 appears as peaks of bismuth-214 at 609, 1120 and 1764 keV (see. The same peak for atmospheric radon). Potassium-40 is detected directly through the gamma peak of 1461 keV.
The level above the sea and other large bodies of water tends to be about a tenth of the earth's background. Conversely, coastal areas (and regions near fresh water) may have an additional contribution from dispersed sediment.
Radon
The largest source of radioactive radiation in nature is radon in the air - a radioactive gas that is released from the earth. Radon and its isotopes, initial radionuclides and decay products contribute to an average respirable dose of 1.26 mSv / year (millisievert per year). Radon is not evenly distributed and varies with the weather, so much higher doses are used in many parts of the world where it poses a significant health hazard. Concentrations 500 times the global average were found inside buildings in Scandinavia, the USA, Iran and the Czech Republic. Radon is a decay product of uranium, which is relatively common in the earth's crust, but more concentrated in ore-bearing rocks scattered around the world. Radon seeps from these ores into the atmosphere or into groundwater, and also penetrates buildings. It can be inhaled into the lungs along with the decay products, where they will remain for some time after exposure. For this reason, radon is a natural source of radiation.
Radon exposure
Although radon is found in nature, its effect can be enhanced or reduced as a result of human activities, in particular, the construction of a house. A poorly sealed basement in a house with good insulation can lead to the accumulation of radon in the living room, putting its residents at risk. The widespread construction of well-insulated and sealed houses in the industrialized countries of the north has made radon the main source of background radiation in some communities in northern North America and Europe. Some building materials, such as lightweight concrete with shale alum, phosphogypsum and Italian tuff, can emit radon if they contain radium and gas poros.
Radiation exposure from radon is indirect. Radon has a short half-life (4 days) and decays into other solid particles of radioactive nuclides of the radium series. These radioactive elements are inhaled and remain in the lungs, causing prolonged exposure. Thus, it is believed that radon is the second leading cause of lung cancer after smoking, and accounts for between 15,000 and 22,000 cancer deaths per year in the United States alone. However, discussions about opposing experimental results are still ongoing.
Most of the atmospheric background is caused by radon and its decay products. The gamma spectrum shows noticeable peaks at 609, 1120 and 1764 keV, belonging to bismuth-214, the decay product of radon. The atmospheric background is highly dependent on the direction of the wind and meteorological conditions. Radon can also be released from the ground by bursts and then form “radon clouds” that can travel tens of kilometers.
Space background
Earth and all life on it is constantly bombarded by radiation from space. This radiation mainly consists of positively charged ions: from protons to iron, and larger nuclei obtained outside our solar system. This radiation interacts with atoms in the atmosphere, creating a secondary air stream, including x-rays, muons, protons, alpha particles, pions, electrons and neutrons.
The direct dose of cosmic radiation mainly comes from muons, neutrons and electrons, and it varies in different parts of the world depending on the geomagnetic field and altitude. For example, the city of Denver in the United States (at an altitude of 1,650 meters) receives a dose of cosmic rays approximately two times greater than at a point at sea level.
This radiation is much more intense in the upper troposphere at an altitude of about 10 km and, therefore, is of particular concern to crew members and regular passengers who spend many hours a year in this environment. During their flights, airline crews usually receive an additional professional dose from 2.2 mSv (220 mbar) per year to 2.19 mSv / year, according to various studies.
Radiation in orbit
In the same way, cosmic rays cause a higher background exposure for astronauts than for people on the surface of the Earth. Cosmonauts operating in low orbits, such as employees of international space stations or shuttles, are partially protected by the Earth’s magnetic field, but also suffer from the so-called Van Allen belt, which is the result of the influence of the Earth’s magnetic field. Outside the low Earth orbit, as Apollo astronauts traveling to the Moon experienced, this background radiation is much more intense and represents a significant obstacle to the potential future long-term human exploration of the Moon or Mars.
Cosmic influences also cause elemental transmutation in the atmosphere, in which the secondary radiation generated by them is combined with atomic nuclei in the atmosphere, forming various nuclides. Many so-called cosmogenic nuclides can be obtained, but carbon-14, which is formed upon interaction with nitrogen atoms, is probably the most noticeable. These cosmogenic nuclides ultimately reach the Earth's surface and can be incorporated into living organisms. The production of these nuclides varies insignificantly during short-term metamorphoses of the solar ray flux, but is considered to be practically constant on large scales - from thousands to millions of years. Continuous production, incorporation into organisms, and the relatively short half-life of carbon-14 are principles used in radiocarbon dating of ancient biological materials such as wood artifacts or human remains.
Gamma radiation
Cosmic radiation at sea level is usually manifested as gamma radiation with an energy of 511 keV as a result of the annihilation of positrons created by nuclear reactions of high-energy particles and gamma rays. At high altitudes, there is also the contribution of the continuous spectrum of bremsstrahlung. Therefore, among scientists, the issue of solar radiation and radiation balance is considered very important.
Radiation inside the body
The two most important elements that make up the human body, namely potassium and carbon, contain isotopes that significantly increase our background radiation dose. This means that they can also be sources of radiation.
Hazardous chemical elements and compounds tend to accumulate. The average person’s body contains about 17 milligrams of potassium-40 (40K) and about 24 nanograms (10–8 g) of carbon-14 (14C) (half-life - 5,730 years). Excluding internal contamination by external radioactive materials, these two elements are the largest components of the internal exposure of the biologically functional components of the human body. About 4,000 cores with a frequency of 40K per second decay and the same number at 14C. The energy of beta particles formed at 40K is about 10 times greater than that of beta particles formed at 14C.
14C is present in the human body at a level of about 3,700 Bq (0.1 μCi) with a biological half-life of 40 days. This means that as a result of the decay of 14C, about 3,700 beta particles per second are formed. About half of human cells contain a 14C atom.
The average global internal dose of radionuclides other than radon and its decay products is 0.29 mSv / year, of which 0.17 mSv / year falls on 40K, 0.12 mSv / year comes from a series of uranium and thorium, and 12 μSv / year - from 14C. It is also worth noting that medical x-ray machines are also often radioactive, but their radiation is not dangerous to humans.