A radioactive source is a certain amount of a radionuclide that emits ionizing radiation. The latter usually includes gamma rays, alpha and beta particles, and neutron radiation.
Role of sources
They can be used for irradiation, when the radiation performs an ionizing function, or as a source of metrological radiation for the calibration of the radiometric process and instrumentation. They are also used to monitor industrial processes such as thickness measurement in the paper and steel industries. Sources can be sealed in a container (high-penetrating radiation) or deposited on a surface (low-penetrating radiation), or in a liquid.
Meaning and application
As a source of radiation, they are used in medicine for radiation therapy and in industry for radiography, irradiationfood, sterilization, pest control and PVC irradiation cross-linking.
Radionuclides are selected according to the type and nature of radiation, its intensity and half-life. Common sources of radionuclides include cob alt-60, iridium-192 and strontium-90. The measurement of the amount of SI source activity is the Becquerel, although the historical Curie unit is still in partial use, for example in the US, despite the US NIST strongly recommending the use of the SI unit. For he alth purposes, it is mandatory in the EU.
A source of radiation typically lives 5 to 15 years before its activity drops to a safe level. However, when radionuclides with long half-lives are available, they can be used as calibration tools for much longer.
Closed and hidden
Many radioactive sources are closed. This means that they are permanently either completely contained in the capsule or firmly bound by a solid to the surface. Capsules are usually made of stainless steel, titanium, platinum or other inert metal. The use of sealed sources eliminates virtually all risk of dispersing radioactive material to the environment due to improper handling, but the container is not designed to attenuate radiation, so additional shielding is required for radiation protection. Closed ones are also used in almost all cases where notchemical or physical incorporation into a liquid or gas is required.
Sealed sources are classified by the IAEA according to their activities in relation to a minimally dangerous radioactive object (which can 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 low enough radioactive yield (such as those used in smoke detectors) not to harm humans are not classified.
Capsule sources, where radiation effectively comes from a point, are used to calibrate beta, gamma and X-ray instruments. Recently, they have been unpopular both as industrial objects and as objects for study.
They are widely used for calibration of radioactive contamination instruments. That is, in fact, they play the role of a kind of miraculous counters.
Unlike a capsule source, the background emitted by a plate source must be on the surface to prevent container fading or self-shielding due to the nature of the material. This is especially important for alpha particles, which are easily stopped by a small mass. The Bragg curve shows the effect of damping in atmospheric air.
Unopened sources are those that are not in a permanently sealed container and are widely used for medical purposes. They apply in caseswhen the source needs to be dissolved in a liquid for injection into a patient or ingestion. They are also used in industry in a similar way for leak detection as a radioactive tracer.
Recycling and environmental aspects
The disposal of expired radioactive sources poses similar problems to the disposal of other nuclear waste, although to a lesser extent. Spent low-level sources will sometimes be inactive enough to be disposed of using normal waste disposal methods, usually in landfills. Other disposal methods are similar to those used for higher level radioactive waste, using different borehole depths depending on the activity of the waste.
A well-known case of careless handling of such an object was an accident in Goiania, which led to the death of several people.
Background radiation is always present on Earth. Most of the background radiation comes naturally from minerals, while a small part comes from man-made elements. Natural radioactive minerals in earth, soil and water produce background radiation. The human body even contains some of these natural radioactive minerals. Cosmic radiation also contributes to the radiation background around us. There can be large variations in natural background radiation levels from place to place, as well as changes in the same location over time. Natural radioisotopes are very strong backgroundemitters.
Cosmic radiation comes from extremely energetic particles from the Sun and stars that enter the Earth's atmosphere. That is, these celestial bodies can be called sources of radioactive radiation. Some particles hit the ground, while others interact with the atmosphere, creating various types of radiation. Levels increase as you get closer to a radioactive object, so the amount of cosmic radiation usually increases in proportion to the climb. The higher the altitude, the higher the dose. This is why those living in Denver, Colorado (5,280 feet) receive a higher annual dose of radiation from cosmic radiation than anyone living at sea level (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. Trace amounts of uranium, thorium and their decay products can be found everywhere. Learn more about radioactive decay. Terrestrial radiation levels vary by location, but areas with higher concentrations of uranium and thorium in surface soils typically experience higher dose levels. 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 food, soil and water, which weaccept. Our bodies contain small amounts of radiation because the body metabolizes non-radioactive and radioactive forms of potassium and other elements in the same way.
A small fraction of background radiation comes from human activities. Trace amounts of radioactive elements have been dispersed into the environment as a result of nuclear weapons testing and accidents like the one that occurred at the Chernobyl nuclear power plant in Ukraine. Nuclear reactors release small amounts of radioactive elements. Radioactive materials used in industry and even in some consumer products also emit small amounts of background radiation.
We are all exposed to radiation every day from natural sources, such as minerals in the earth, and man-made sources, such as medical x-rays. According to the National Council on Radiation Protection and Measurement (NCRP), the average annual human exposure to radiation in the United States is 620 millirems (6.2 millisieverts).
Radioactive substances are often found in nature. Some of them are found in soil, rocks, water, air and vegetation, from which they are inhaled and ingested. In addition to this internal exposure, humans also receive external exposure from radioactive materials that remain outside the body and from cosmic radiation from outer space. The average daily natural dose for humans is about 2.4 mSv (240 mrem) per year.
This is four times thethe global average exposure to artificial radiation in the world, which in 2008 was about 0.6 mrem (60 Rem) per year. In some we althy countries, such as the US and Japan, artificial exposure exceeds natural exposure on average due to greater access to specific medical instrumentation. In Europe, the average natural background exposure across countries ranges from 2 mSv (200 mrem) per year in the United Kingdom to over 7 mSv (700 mrem) for some groups of people in Finland.
Exposure from natural sources is an integral part of everyday life both at work and in public places. Such exposures are in most cases of little or no public concern, but in certain situations he alth protection measures must be taken into account, for example when working with uranium and thorium ores and other naturally occurring radioactive materials (NORM). These situations have become the focus of the Agency's attention in recent years. And this, without mentioning the examples of accidents with the release of radioactive substances, such as the disaster at the Chernobyl nuclear power plant and Fukushima, which forced scientists and politicians around the world to reconsider their attitude towards the "peaceful atom".
Earth 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 decay products. Andsome, such as radium and radon, are highly radioactive but occur in low concentrations. The number of these objects has been inexorably reduced since the formation of the Earth. The current radiation activity associated with the presence of uranium-238 is half as much as at 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 shorter half-lives (and therefore high radioactivity) have not decayed due to their constant natural production. Examples of this are radium-226 (the decay product of thorium-230 in the decay chain of uranium-238) and radon-222 (the decay product of radium-226 in that chain).
Thorium and uranium
The radioactive chemical elements thorium and uranium mostly undergo alpha and beta decay and are not easy to detect. This makes them very dangerous. However, the same can be said about proton radiation. However, many of their side derivatives of these elements are also strong gamma emitters. Thorium-232 is detected with the 239 keV peak 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 bismuth-214 peaks at 609, 1120 and 1764 keV (see same peak for atmospheric radon). Potassium-40 is detected directly through the 1461 gamma peakkeV.
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 scattered sediment.
The largest source of radioactive radiation in nature is airborne radon, a radioactive gas released from the earth. Radon and its isotopes, parent radionuclides and decay products contribute to the average respirable dose of 1.26 mSv/year (millisievert per year). Radon is unevenly distributed and varies with the weather, so that much higher doses are used in many parts of the world where it poses a significant he alth hazard. Concentrations up to 500 times the world average have been found inside buildings in Scandinavia, the US, Iran and the Czech Republic. Radon is a decay product of uranium that is relatively common in the earth's crust, but more concentrated in ore-bearing rocks scattered around the world. Radon leaks from these ores into the atmosphere or groundwater, and also seeps into 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 classified as a natural source of radiation.
Although radon occurs naturally, exposure can be increased or decreased by human activities, such as building a house. Poorly sealed cellarA well-insulated home can lead to radon buildup in the home, putting its occupants at risk. The widespread construction of well-insulated and sealed homes in the industrialized countries of the north has resulted in radon becoming a major 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 release radon if they contain radium and are porous to gas.
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, radon is thought to be the second leading cause of lung cancer after smoking, and is responsible for between 15,000 and 22,000 cancer deaths per year in the US alone. However, the discussion about the opposite experimental results is 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, a decay product of radon. The atmospheric background strongly depends on the direction of the wind and meteorological conditions. Radon can also be released from the ground in bursts and then form "radon clouds" that can travel tens of kilometers.
The earth and all living things on it are constantlybombarded by radiation from space. This radiation mainly consists of positively charged ions, from protons to iron, and larger nuclei produced outside our solar system. This radiation interacts with atoms in the atmosphere, creating secondary airflow, 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 about twice the dose of cosmic rays than at a point at sea level.
This radiation is much stronger in the upper troposphere at about 10 km and thus is of particular concern to crew members and regular passengers who spend many hours a year in this environment. During their flights, airline crews typically receive an additional occupational dose ranging from 2.2 mSv (220 mrem) per year to 2.19 mSv/year, according to various studies.
Radiation in orbit
Similarly, cosmic rays cause higher background exposure for astronauts than for humans on the Earth's surface. Astronauts working 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 Earth's magnetic field. Outside of low Earth orbit, likeexperienced by Apollo astronauts traveling to the Moon, this background radiation is much more intense and represents a significant barrier to 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 combines with atomic nuclei in the atmosphere, forming various nuclides. Many so-called cosmogenic nuclides can be produced, but probably the most notable is carbon-14, which is formed by interaction with nitrogen atoms. These cosmogenic nuclides eventually reach the Earth's surface and can be incorporated into living organisms. The production of these nuclides varies slightly during short-term solar flux metamorphoses, but is considered to be practically constant over large scales - from thousands to millions of years. The constant production, incorporation and relatively short half-life of carbon-14 are the principles used in radiocarbon dating of ancient biological materials such as wooden artifacts or human remains.
Cosmic radiation at sea level typically appears as 511 keV gamma radiation from positron annihilation created by nuclear reactions of high-energy particles and gamma rays. At high altitudes, there is also a contribution from 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 greatly increase our background radiation dose. This means that they can also be sources of radioactive radiation.
Hazardous chemical elements and compounds tend to accumulate. The average human 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 internal exposure to the biologically functional components of the human body. About 4,000 nuclei decay at 40K per second and the same number at 14C. The energy of beta particles formed at 40K is approximately 10 times greater than that of beta particles formed at 14C.
14C is present in the human body at around 3,700 Bq (0.1 µCi) with a biological half-life of 40 days. This means that the decay of 14C produces about 3,700 beta particles per second. Approximately half of human cells contain a 14C atom.
Global average internal dose of radionuclides other than radon and its decay products is 0.29 mSv/yr, of which 0.17 mSv/yr is at 40K, 0.12 mSv/yr comes from the uranium series and thorium, and 12 μSv / year - from 14C. It is also worth noting that medical X-ray machines are also oftenradioactive, but their radiation is not dangerous to humans.