Background radiation
Encyclopedia
Background radiation is the ionizing radiation
constantly present in the natural environment of the Earth, which is emitted by natural and artificial sources.
The background radiation of the human environment is a combination of:
Natural sources of background radiation account for most occurrences of human exposure to ionizing radiation
; excluding 3.0 per cent for medical exposure, e.g. radiological imaging and radiation therapy
, and other artificial sources of background radiation such as:
for a human being is about 2.4 millisievert
(mSv) per year. This exposure is mostly from cosmic radiation and natural radionuclides in the environment (including those within the body). This is far greater than human-caused background radiation exposure, which in the year 2000 amounted to an average of about 5 μSv per year from historical nuclear weapons testing, nuclear power accidents and nuclear industry operation combined, and is greater than the average exposure from medical tests, which ranges from 0.04 to 1 mSv per year. Older coal-fired power plants without effective fly ash capture are one of the largest sources of human-caused background radiation exposure.
The level of natural background radiation varies depending on location, and in some areas the level is significantly higher than average. Such areas include Ramsar in Iran, Guarapari
in Brazil, Kerala
in India, the northern Flinders Ranges
in Australia and Yangjiang
in China. In Ramsar a peak yearly dose of 260 mGy (not mSv) has been reported (compared with 0.06 mSv of a chest radiograph or up to 20 mSv of a CT scan). The highest levels of natural background radiation recorded in the world is from areas around Ramsar, particularly at Talesh-Mahalleh which is a very high background radiation area (VHBRA) having an effective dose equivalent several times in excess of ICRP-recommended radiation dose limits for radiation workers and up to 200 times greater than normal background levels. Most of the radiation in the area is due to dissolved radium
-226 in water of hot springs along with smaller amounts of uranium
and thorium
due to travertine
deposits. There are more than nine hot springs in the area with different concentrations of radioisotopes, and these are used as spas by locals and tourists. This high level of radiation does not seem to have caused ill effects on the residents of the area and even possibly has made them slightly more radioresistant
, which is puzzling and has been called "radiation paradox". It has also been reported that residents have healthier and longer lives. On the basis of this and other evidence including the fact that life had originated in a much more irradiated environment, some scientists have questioned the validity of linear no-threshold model
, on which all radiation regulations currently depend. Others point out that some level of radiation might actually be good for health and have a positive effect on population based on the controversial radiation hormesis
model, by jump starting DNA repair
mechanisms inside the cell. Background radiation doses in the immediate vicinities of particles of high atomic number materials, within the human body, have a small enhancement due to the photoelectric effect.
s to iron
and larger nuclei
derived sources outside our solar system
. This radiation interacts with atoms in the atmosphere to create secondary radiation, including X-ray
s, muon
s, proton
s, alpha particle
s, pion
s, electron
s, and neutron
s. The immediate dose from cosmic radiation is largely from muons, neutrons, and electrons, and this dose varies in different parts of the world based largely on the geomagnetic field and altitude. This radiation is much more intense in the upper troposphere
, around 10 km altitude, and is thus of particular concern for airline
crews and frequent passengers, who spend many hours per year in this environment. During their flights airline crews typically get an extra dose on the order of 2.2mSv (220 mrem) per year.
Similarly, cosmic rays cause higher background exposure in astronaut
s than in humans on the surface of Earth. Astronauts in low orbit
s, such as in the International Space Station
or the Space Shuttle
, are partially shielded by the magnetic field
of the Earth, but also suffer from the Van Allen radiation belt
which accumulates cosmic rays and results from the earths magnetic field. Outside low Earth orbit, as experienced by the Apollo astronauts who traveled to the Moon
, this background radiation is much more intense, and represents a considerable obstacle to potential future long term human exploration of the moon or Mars
.
Cosmic rays also cause elemental transmutation
in the atmosphere, in which secondary radiation generated by the cosmic rays combines with atomic nuclei in the atmosphere to generate different nuclides. Many so-called cosmogenic nuclides can be produced, but probably the most notable is carbon-14
, which is produced by interactions 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 with short-term variations in solar cosmic ray flux, but is considered practically constant over long scales of thousands to millions of years. The constant production, incorporation into organisms 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.
, rocks, water, air, and vegetation. The major radionuclide
s of concern for terrestrial radiation are common elements with low-abundance radioactive isotopes, like potassium
and carbon
, or the long-lived elements uranium
and thorium
and their decay products, some of which, like radium
and radon
are intensely radioactive but occur in low concentrations. Most of these sources have been decreasing, due to radioactive decay
since the formation of the Earth, because there is no significant amount currently transported to the Earth. Thus, the present activity on earth from uranium-238
is only half as much as it originally was because of its 4.5 billion
year half-life, and potassium
-40 (half-life 1.25 billion years) is only at about 8% of original activity. The effects on humans of the actual diminishment (due to decay) of these isotopes is minimal however. This is because humans evolved too recently for the difference in activity over a fraction of a half-life to be significant. Put another way, human history is so short in comparison to a half-life of a billion years, that the activity of these long-lived isotopes has been effectively constant throughout our time on this planet.
In addition, many shorter half-life and thus more intensely radioactive isotopes have not decayed out of the terrestrial environment, however, because of natural on-going production of them. Examples of these are carbon-14 (cosmogenic), radium
-226 (decay product of uranium-238) and radon-222 (a decay product of radium
-226).
(40K) and about 10 nanograms (10−8 g) of carbon-14
(14C), which has a decay half-life of 5,730 years. Excluding internal contamination by external radioactive material, the largest component of internal radiation exposure from biologically functional components of the human body is from potassium-40. The decay of about 4,000 nuclei of 40K per second makes potassium the largest source of radiation in terms of number of decaying atoms. The energy of beta particle
s produced by 40K is also about 10 times more powerful than the beta particles from 14C decay.
14C is present in the human body at a level of 3700 Bq with a biological half-life
of 40 days. There are about 1,200 beta particles per second produced by the decay of 14C. However, a 14C atom is in the genetic information of about half the cells, while potassium is not a component of DNA
. The decay of a 14C atom inside DNA in one person happens about 50 times per second, changing a carbon atom to one of nitrogen
.
is a terrestrial source of ionizing radiation that is of particular concern because, although on average it is very rare, this intensely radioactive element can be found in high concentrations in many areas of the world, where it represents a significant health hazard. Radon is a decay product of uranium, which is relatively common in the Earth's crust, but generally concentrated in ore-bearing rocks scattered around the world. Radon seeps out of these ores into the atmosphere or into ground water, and in these localities it can accumulate within dwellings and expose humans to high concentrations. The widespread construction of well insulated and sealed homes in the northern industrialized world has led to radon becoming the primary source of background radiation in some localities in northern North America and Europe. Some of these areas, including Cornwall
and Aberdeenshire
in the United Kingdom
have high enough natural radiation levels that nuclear licensed sites cannot be built there — the sites would already exceed legal radiation limits before they opened, and the natural topsoil and rock would all have to be disposed of as low-level nuclear waste.
Radiation exposure from radon is indirect. Radon has a short half-life (4 days) and decays into other solid particulate radium-series radioactive nuclides. These radioactive particles are inhaled and remain lodged in the lungs, causing continued exposure. People in affected localities can receive up to 10 mSv per year background radiation. Radon is thus the second leading cause of lung cancer
after smoking
, and accounts for 15,000 to 22,000 cancer deaths per year in the US alone.
Frequent above-ground nuclear explosions between the 1940s and 1960s scattered a substantial amount of radioactive contamination
. Some of this contamination is local, rendering the immediate surroundings highly radioactive, while some of it is carried longer distances as nuclear fallout
; some of this material is dispersed worldwide. The increase in background radiation due to these tests peaked in 1963 at about 0.15 mSv per year worldwide, or about 7% of average background dose from all sources. The Limited Test Ban Treaty of 1963 prohibited above-ground tests, thus by the year 2000 the worldwide dose from these tests has decreased to only 0.005 mSv per year.
Older coal-fired power plants without effective fly ash
capture are a large source of human-caused background radiation exposure. When coal is burned, uranium, thorium and all the uranium daughters accumulated by disintegration — radium, radon, polonium — are released. According to a 1978 article in Science magazine, "coal-fired power plants throughout the world are the major sources of radioactive materials released to the environment". Radioactive materials previously buried underground in coal deposits are released as fly ash or, if fly ash is captured, may be incorporated into concrete manufactured with fly ash. Radioactive materials are also released in gaseous emissions. The United Nations Scientific Committee on the Effects of Atomic Radiation estimates that per gigawatt-year (GWea) of electrical energy produced by coal, using the current mix of technology throughout the world, the population impact is approximately 0.8 lethal cancers per plant-year distributed over the affected population. With 400 GW of coal-fired power plants in the world, this amounts to some 320 deaths per year.
Under normal circumstances, a modern nuclear reactor releases minuscule amounts of radioactive contamination. While the radiation released in minor accidents varies, major accidents like Windscale fire
(Sellafield
accident), the Chernobyl accident, and the Fukushima I nuclear accidents release massive radioactive contamination into the environment.
Radiation levels at the stricken Fukushima I power plant have varied spiking up to 1,000 mSv/h (millisievert per hour), which is a level that can cause radiation sickness
to occur at a later time following a one hour exposure. Significant release in emissions of radioactive particles took place following hydrogen explosions at three reactors, as technicians tried to pump in seawater to keep the uranium fuel rods cool, and bled radioactive gas from the reactors in order to make room for the seawater. Concerns about the possibility of a large scale radiation leak resulted in 20 km exclusion zone being set up around the power plant and people within the 20–30 km zone being advised to stay indoors. Later, the UK, France and some other countries told their nationals to consider leaving Tokyo, in response to fears of spreading nuclear contamination. New Scientist has reported that emissions of radioactive iodine and cesium from the crippled Fukushima I nuclear plant have approached levels evident after the Chernobyl disaster
in 1986. On March 24, 2011, Japanese officials announced that "radioactive iodine-131 exceeding safety limits for infants had been detected at 18 water-purification plants in Tokyo and five other prefectures". See Radiation effects from Fukushima Daiichi nuclear disaster.
, the United States Environmental Protection Agency
, and other U.S. and international agencies, require that licensees limit radiation exposure to individual members of the public to 1 mSv
(100 mrem) per year, and limit occupational radiation exposure to adults working with radioactive material to 50 mSv (5 rem) per year, and 100 mSv (10 rem) in 5 years.
The exposure for an average person is about 3.6 mSv/year, 80 percent of which comes from natural sources of radiation. The remaining 20 percent results from exposure to artificial radiation sources, such as medical x-ray
s, industrial sources like smoke detectors and a small fraction from nuclear weapon
s tests. For average persons who have had no medical x-rays, only 3% of their annual radiation dose comes from artificial sources.
A standard medical x-ray's strength is about 2 mrem or 0.02 mSv but can be over ten times that, depending on the equipment used. A dental x-ray optimally has a dose as low as 0.0033 mSv but poor machines and technique can give doses as high as 0.11 mSv. The average American and European receives about 0.5 mSv of diagnostic medical dose per year; countries with lower levels of health care receive about one fifth of this dose.
Radiation treatment for various diseases also accounts for some dose, both in individuals and in those around them.
, a nearly uniform glow that fills the sky in the microwave part of the spectrum; stars, galaxies and other objects of interest in radio astronomy
stand out against this background.
In a laboratory, background radiation refers to the measured value from any sources that affect an instrument when a radiation source sample is not being measured. This background rate, which must be established as a stable value by multiple measurements, usually before and after sample measurement, is subtracted from the rate measured when the sample is being measured.
Background radiation for occupational doses measured for workers is all radiation dose that is not measured by radiation dose measurement instruments in potential occupational exposure conditions. This includes both "natural background radiation" and any medical radiation doses. This value is not typically measured or known from surveys, such that variations in the total dose to individual workers is not known. This can be a significant confounding factor in assessing radiation exposure effects in a population of workers who may have significantly different natural background and medical radiation doses. This is most significant when the occupational doses are very low.
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
constantly present in the natural environment of the Earth, which is emitted by natural and artificial sources.
Overview
Both Natural and human-made background radiation varies by location.| Radiation | UNSCEAR | Princeton | Wa State | MEXT | |||
|---|---|---|---|---|---|---|---|
| Type | Source | World average | Typical range | USA | USA | Japan | remark |
| Natural | Air | 1.26 | 0.2-10.0a | 2.29 | 2.00 | 0.40 | mainly from Radon, (a)depend on indoor accumulation of radon gas |
| Internal | 0.29 | 0.2-1.0b | 0.16 | 0.40 | 0.40 | mainly from food (K-40, C-14, etc.) (b)Depend on diets | |
| Terrestrial | 0.48 | 0.3-1.0c | 0.19 | 0.29 | 0.40 | (c)depend on soil and building material | |
| Cosmic | 0.39 | 0.3-1.0d | 0.31 | 0.26 | 0.30 | (d)from sea level to high elevation | |
| sub total | 2.40 | 1.0-13.0 | 2.95 | 2.95 | 1.50 | ||
| Man made | Medical | 0.60 | 0.03-2.0 | 3.00 | 0.53 | 2.30 | |
| Fallout | 0.007 | 0 - 1+ | - | - | 0.01 | peak at 1963 and spike at 1986. still high near test and accident sites. US; Fallout is included in others | |
| others | 0.0052 | 0-20 | 0.25 | 0.13 | 0.001 | average occupational exposure 0.7mSv, mining workers are high, population near Nuclear plant 0.02mSv | |
| sub total | 0.6 | 0 to tens | 3.25 | 0.66 | 2.311 | ||
| Total | 3.00 | 0 to tens | 6.20 | 3.61 | 3.81 | ||
- figures are pre "2011 Fukushima Nuclear Plant Accident"
- Human-made values at UNCEAR are from Japan NIRS which summarized UNCEAR data.
The background radiation of the human environment is a combination of:
- Sources in the EarthEarthEarth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. These include sources in water and food (banana equivalent doseBanana equivalent doseA banana equivalent dose is a whimsical unit of radiation exposure, informally defined as the additional dose a person will absorb from eating one banana...
), which are incorporated to the humanHumanHumans are the only living species in the Homo genus...
body, to building materials, and to products that incorporate radioactive sources from nature; - Sources from outer spaceOuter spaceOuter space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....
, such as cosmic rayCosmic rayCosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...
s; - Sources in the atmosphere, such as the radonRadonRadon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Its most stable isotope, 222Rn, has a half-life of 3.8 days...
gas released from the Earth's crust, which then decays into radioactive atoms that attach to airborne dust, and other particulate (granular, powder) materials, that human beings might ingest and inhale. Another factor is the radiation produced by the atomic bombardment of the upper atmosphere by high-energy cosmic rays.
Natural sources of background radiation account for most occurrences of human exposure to ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
; excluding 3.0 per cent for medical exposure, e.g. radiological imaging and radiation therapy
Radiation therapy
Radiation therapy , radiation oncology, or radiotherapy , sometimes abbreviated to XRT or DXT, is the medical use of ionizing radiation, generally as part of cancer treatment to control malignant cells.Radiation therapy is commonly applied to the cancerous tumor because of its ability to control...
, and other artificial sources of background radiation such as:
- Self-luminous dials and signs
- Global radioactive contaminationRadioactive contaminationRadioactive contamination, also called radiological contamination, is radioactive substances on surfaces, or within solids, liquids or gases , where their presence is unintended or undesirable, or the process giving rise to their presence in such places...
consequent to nuclear weapons testingNuclear testingNuclear weapons tests are experiments carried out to determine the effectiveness, yield and explosive capability of nuclear weapons. Throughout the twentieth century, most nations that have developed nuclear weapons have tested them... - Nuclear power station and nuclear fuel reprocessing accidents
- Normal operation of nuclear powerNuclear powerNuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...
facilities and like scientific research - Emissions from burning fossil fuelFossil fuelFossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...
s, such as those of coal-fueled power plantsFossil fuel power plantA fossil-fuel power station is a power station that burns fossil fuels such as coal, natural gas or petroleum to produce electricity. Central station fossil-fuel power plants are designed on a large scale for continuous operation... - Emissions from nuclear medicineNuclear medicineIn nuclear medicine procedures, elemental radionuclides are combined with other elements to form chemical compounds, or else combined with existing pharmaceutical compounds, to form radiopharmaceuticals. These radiopharmaceuticals, once administered to the patient, can localize to specific organs...
facilities and irradiated patients
Natural background radiation
Natural background radiation comes from two primary sources: cosmic radiation and terrestrial sources. The worldwide average background doseAbsorbed dose
Absorbed dose is a measure of the energy deposited in a medium by ionizing radiation per unit mass...
for a human being is about 2.4 millisievert
Sievert
The sievert is the International System of Units SI derived unit of dose equivalent radiation. It attempts to quantitatively evaluate the biological effects of ionizing radiation as opposed to just the absorbed dose of radiation energy, which is measured in gray...
(mSv) per year. This exposure is mostly from cosmic radiation and natural radionuclides in the environment (including those within the body). This is far greater than human-caused background radiation exposure, which in the year 2000 amounted to an average of about 5 μSv per year from historical nuclear weapons testing, nuclear power accidents and nuclear industry operation combined, and is greater than the average exposure from medical tests, which ranges from 0.04 to 1 mSv per year. Older coal-fired power plants without effective fly ash capture are one of the largest sources of human-caused background radiation exposure.
The level of natural background radiation varies depending on location, and in some areas the level is significantly higher than average. Such areas include Ramsar in Iran, Guarapari
Guarapari
Guarapari is a coastal town on the coast of Espírito Santo, Brazil. It is a part of Greater Vitoria. A municipal capital , it is located 47 km south of Vitória, of the state capital. Its population is 105,116 and its area is 592 km²....
in Brazil, Kerala
Kerala
or Keralam is an Indian state located on the Malabar coast of south-west India. It was created on 1 November 1956 by the States Reorganisation Act by combining various Malayalam speaking regions....
in India, the northern Flinders Ranges
Flinders Ranges
Flinders Ranges is the largest mountain range in South Australia, which starts approximately north west of Adelaide. The discontinuous ranges stretch for over from Port Pirie to Lake Callabonna...
in Australia and Yangjiang
Yangjiang
Yangjiang , historically known as Yeungkong, is a prefecture-level city in southwestern Guangdong province, People's Republic of China. It borders Maoming to the west, Yunfu to the north, Jiangmen to the east, and looks out to the South China Sea to the south. It is famous for being the base of...
in China. In Ramsar a peak yearly dose of 260 mGy (not mSv) has been reported (compared with 0.06 mSv of a chest radiograph or up to 20 mSv of a CT scan). The highest levels of natural background radiation recorded in the world is from areas around Ramsar, particularly at Talesh-Mahalleh which is a very high background radiation area (VHBRA) having an effective dose equivalent several times in excess of ICRP-recommended radiation dose limits for radiation workers and up to 200 times greater than normal background levels. Most of the radiation in the area is due to dissolved radium
Radium
Radium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226,...
-226 in water of hot springs along with smaller amounts of uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
and thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
due to travertine
Travertine
Travertine is a form of limestone deposited by mineral springs, especially hot springs. Travertine often has a fibrous or concentric appearance and exists in white, tan, and cream-colored varieties. It is formed by a process of rapid precipitation of calcium carbonate, often at the mouth of a hot...
deposits. There are more than nine hot springs in the area with different concentrations of radioisotopes, and these are used as spas by locals and tourists. This high level of radiation does not seem to have caused ill effects on the residents of the area and even possibly has made them slightly more radioresistant
Radioresistance
Radioresistance is the property of organisms that are capable of living in environments with very high levels of ionizing radiation.Radioresistance is surprisingly high in many organisms, in contrast to previously held views...
, which is puzzling and has been called "radiation paradox". It has also been reported that residents have healthier and longer lives. On the basis of this and other evidence including the fact that life had originated in a much more irradiated environment, some scientists have questioned the validity of linear no-threshold model
Linear no-threshold model
The linear no-threshold model is a method for predicting the long term, biological damage caused by ionizing radiation and is based on the assumption that the risk is directly proportional to the dose at all dose levels....
, on which all radiation regulations currently depend. Others point out that some level of radiation might actually be good for health and have a positive effect on population based on the controversial radiation hormesis
Radiation hormesis
Radiation hormesis is the hypothesis that low doses of ionizing radiation are beneficial, stimulating the activation of repair mechanisms that protect against disease, that are not activated in absence of ionizing radiation...
model, by jump starting DNA repair
DNA repair
DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as UV light and radiation can cause DNA damage, resulting in as many as 1...
mechanisms inside the cell. Background radiation doses in the immediate vicinities of particles of high atomic number materials, within the human body, have a small enhancement due to the photoelectric effect.
Cosmic radiation
The Earth, and all living things on it, are constantly bombarded by radiation from outer space. This radiation primarily consists of positively charged ions from protonProton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s to iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
and larger nuclei
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
derived sources outside our solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
. This radiation interacts with atoms in the atmosphere to create secondary radiation, including X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s, muon
Muon
The muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...
s, proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s, alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
s, pion
Pion
In particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force....
s, electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s, and neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s. The immediate dose from cosmic radiation is largely from muons, neutrons, and electrons, and this dose varies in different parts of the world based largely on the geomagnetic field and altitude. This radiation is much more intense in the upper troposphere
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....
, around 10 km altitude, and is thus of particular concern for airline
Airline
An airline provides air transport services for traveling passengers and freight. Airlines lease or own their aircraft with which to supply these services and may form partnerships or alliances with other airlines for mutual benefit...
crews and frequent passengers, who spend many hours per year in this environment. During their flights airline crews typically get an extra dose on the order of 2.2mSv (220 mrem) per year.
Similarly, cosmic rays cause higher background exposure in astronaut
Astronaut
An astronaut or cosmonaut is a person trained by a human spaceflight program to command, pilot, or serve as a crew member of a spacecraft....
s than in humans on the surface of Earth. Astronauts in low orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
s, such as in the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
or the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
, are partially shielded by the magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
of the Earth, but also suffer from the Van Allen radiation belt
Van Allen radiation belt
The Van Allen radiation belt is a torus of energetic charged particles around Earth, which is held in place by Earth's magnetic field. It is believed that most of the particles that form the belts come from solar wind, and other particles by cosmic rays. It is named after its discoverer, James...
which accumulates cosmic rays and results from the earths magnetic field. Outside low Earth orbit, as experienced by the Apollo astronauts who traveled to the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
, this background radiation is much more intense, and represents a considerable obstacle to potential future long term human exploration of the moon or Mars
Manned mission to Mars
A manned mission to Mars has been the subject of science fiction, engineering, and scientific proposals throughout the 20th century and into the 21st century...
.
Cosmic rays also cause elemental transmutation
Nuclear transmutation
Nuclear transmutation is the conversion of one chemical element or isotope into another. In other words, atoms of one element can be changed into atoms of other element by 'transmutation'...
in the atmosphere, in which secondary radiation generated by the cosmic rays combines with atomic nuclei in the atmosphere to generate different nuclides. Many so-called cosmogenic nuclides can be produced, but probably the most notable is carbon-14
Carbon-14
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues , to date archaeological, geological, and hydrogeological...
, which is produced by interactions with nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
atoms. These cosmogenic nuclides eventually reach the Earth's surface and can be incorporated into living organisms. The production of these nuclides varies slightly with short-term variations in solar cosmic ray flux, but is considered practically constant over long scales of thousands to millions of years. The constant production, incorporation into organisms and relatively short half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of carbon-14 are the principles used in radiocarbon dating
Radiocarbon dating
Radiocarbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" ,...
of ancient biological materials such as wooden artifacts or human remains.
Terrestrial sources
Radioactive material is found throughout nature. It occurs naturally in the soilSoil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
, rocks, water, air, and vegetation. The major radionuclide
Radionuclide
A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...
s of concern for terrestrial radiation are common elements with low-abundance radioactive isotopes, like potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
and carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
, or the long-lived elements uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
and thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
and their decay products, some of which, like radium
Radium
Radium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226,...
and radon
Radon
Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Its most stable isotope, 222Rn, has a half-life of 3.8 days...
are intensely radioactive but occur in low concentrations. Most of these sources have been decreasing, due to radioactive decay
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
since the formation of the Earth, because there is no significant amount currently transported to the Earth. Thus, the present activity on earth from uranium-238
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...
is only half as much as it originally was because of its 4.5 billion
1000000000 (number)
1,000,000,000 is the natural number following 999,999,999 and preceding 1,000,000,001.In scientific notation, it is written as 109....
year half-life, and potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
-40 (half-life 1.25 billion years) is only at about 8% of original activity. The effects on humans of the actual diminishment (due to decay) of these isotopes is minimal however. This is because humans evolved too recently for the difference in activity over a fraction of a half-life to be significant. Put another way, human history is so short in comparison to a half-life of a billion years, that the activity of these long-lived isotopes has been effectively constant throughout our time on this planet.
In addition, many shorter half-life and thus more intensely radioactive isotopes have not decayed out of the terrestrial environment, however, because of natural on-going production of them. Examples of these are carbon-14 (cosmogenic), radium
Radium
Radium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226,...
-226 (decay product of uranium-238) and radon-222 (a decay product of radium
Radium
Radium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226,...
-226).
Radiation inside the human body
Some of the essential elements that make up the human body, mainly potassium and carbon, have radioactive isotopes that add significantly to our background radiation dose. An average human contains about 30 milligrams of potassium-40Potassium-40
Potassium-40 is a radioactive isotope of potassium which has a very long half-life of 1.248 years, or about 39.38 seconds.Potassium-40 is a rare example of an isotope which undergoes all three types of beta decay. About 89.28% of the time, it decays to calcium-40 with emission of a beta particle...
(40K) and about 10 nanograms (10−8 g) of carbon-14
Carbon-14
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues , to date archaeological, geological, and hydrogeological...
(14C), which has a decay half-life of 5,730 years. Excluding internal contamination by external radioactive material, the largest component of internal radiation exposure from biologically functional components of the human body is from potassium-40. The decay of about 4,000 nuclei of 40K per second makes potassium the largest source of radiation in terms of number of decaying atoms. The energy of beta particle
Beta particle
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...
s produced by 40K is also about 10 times more powerful than the beta particles from 14C decay.
14C is present in the human body at a level of 3700 Bq with a biological half-life
Biological half-life
The biological half-life or elimination half-life of a substance is the time it takes for a substance to lose half of its pharmacologic, physiologic, or radiologic activity, as per the MeSH definition...
of 40 days. There are about 1,200 beta particles per second produced by the decay of 14C. However, a 14C atom is in the genetic information of about half the cells, while potassium is not a component of DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
. The decay of a 14C atom inside DNA in one person happens about 50 times per second, changing a carbon atom to one of nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
.
Radon
RadonRadon
Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Its most stable isotope, 222Rn, has a half-life of 3.8 days...
is a terrestrial source of ionizing radiation that is of particular concern because, although on average it is very rare, this intensely radioactive element can be found in high concentrations in many areas of the world, where it represents a significant health hazard. Radon is a decay product of uranium, which is relatively common in the Earth's crust, but generally concentrated in ore-bearing rocks scattered around the world. Radon seeps out of these ores into the atmosphere or into ground water, and in these localities it can accumulate within dwellings and expose humans to high concentrations. The widespread construction of well insulated and sealed homes in the northern industrialized world has led to radon becoming the primary source of background radiation in some localities in northern North America and Europe. Some of these areas, including Cornwall
Cornwall
Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...
and Aberdeenshire
Aberdeenshire
Aberdeenshire is one of the 32 unitary council areas in Scotland and a lieutenancy area.The present day Aberdeenshire council area does not include the City of Aberdeen, now a separate council area, from which its name derives. Together, the modern council area and the city formed historic...
in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
have high enough natural radiation levels that nuclear licensed sites cannot be built there — the sites would already exceed legal radiation limits before they opened, and the natural topsoil and rock would all have to be disposed of as low-level nuclear waste.
Radiation exposure from radon is indirect. Radon has a short half-life (4 days) and decays into other solid particulate radium-series radioactive nuclides. These radioactive particles are inhaled and remain lodged in the lungs, causing continued exposure. People in affected localities can receive up to 10 mSv per year background radiation. Radon is thus the second leading cause of lung cancer
Lung cancer
Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue and, eventually, into other parts of the body. Most cancers that start in lung, known as primary...
after smoking
Tobacco smoking
Tobacco smoking is the practice where tobacco is burned and the resulting smoke is inhaled. The practice may have begun as early as 5000–3000 BCE. Tobacco was introduced to Eurasia in the late 16th century where it followed common trade routes...
, and accounts for 15,000 to 22,000 cancer deaths per year in the US alone.
Human-caused background radiation
Radioactive contamination
Radioactive contamination, also called radiological contamination, is radioactive substances on surfaces, or within solids, liquids or gases , where their presence is unintended or undesirable, or the process giving rise to their presence in such places...
. Some of this contamination is local, rendering the immediate surroundings highly radioactive, while some of it is carried longer distances as nuclear fallout
Nuclear fallout
Fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes...
; some of this material is dispersed worldwide. The increase in background radiation due to these tests peaked in 1963 at about 0.15 mSv per year worldwide, or about 7% of average background dose from all sources. The Limited Test Ban Treaty of 1963 prohibited above-ground tests, thus by the year 2000 the worldwide dose from these tests has decreased to only 0.005 mSv per year.
Older coal-fired power plants without effective fly ash
Fly ash
Fly ash is one of the residues generated in combustion, and comprises the fine particles that rise with the flue gases. Ash which does not rise is termed bottom ash. In an industrial context, fly ash usually refers to ash produced during combustion of coal...
capture are a large source of human-caused background radiation exposure. When coal is burned, uranium, thorium and all the uranium daughters accumulated by disintegration — radium, radon, polonium — are released. According to a 1978 article in Science magazine, "coal-fired power plants throughout the world are the major sources of radioactive materials released to the environment". Radioactive materials previously buried underground in coal deposits are released as fly ash or, if fly ash is captured, may be incorporated into concrete manufactured with fly ash. Radioactive materials are also released in gaseous emissions. The United Nations Scientific Committee on the Effects of Atomic Radiation estimates that per gigawatt-year (GWea) of electrical energy produced by coal, using the current mix of technology throughout the world, the population impact is approximately 0.8 lethal cancers per plant-year distributed over the affected population. With 400 GW of coal-fired power plants in the world, this amounts to some 320 deaths per year.
Under normal circumstances, a modern nuclear reactor releases minuscule amounts of radioactive contamination. While the radiation released in minor accidents varies, major accidents like Windscale fire
Windscale fire
The Windscale fire of 10 October 1957 was the worst nuclear accident in Great Britain's history, ranked in severity at level 5 on the 7-point International Nuclear Event Scale. The two piles had been hurriedly built as part of the British atomic bomb project. Windscale Pile No. 1 was operational in...
(Sellafield
Sellafield
Sellafield is a nuclear reprocessing site, close to the village of Seascale on the coast of the Irish Sea in Cumbria, England. The site is served by Sellafield railway station. Sellafield is an off-shoot from the original nuclear reactor site at Windscale which is currently undergoing...
accident), the Chernobyl accident, and the Fukushima I nuclear accidents release massive radioactive contamination into the environment.
Radiation levels at the stricken Fukushima I power plant have varied spiking up to 1,000 mSv/h (millisievert per hour), which is a level that can cause radiation sickness
Radiation Sickness
Radiation Sickness is a VHS by the thrash metal band Nuclear Assault. The video is a recording of a concert at the Hammersmith Odeon, London in 1988. It was released in 1991...
to occur at a later time following a one hour exposure. Significant release in emissions of radioactive particles took place following hydrogen explosions at three reactors, as technicians tried to pump in seawater to keep the uranium fuel rods cool, and bled radioactive gas from the reactors in order to make room for the seawater. Concerns about the possibility of a large scale radiation leak resulted in 20 km exclusion zone being set up around the power plant and people within the 20–30 km zone being advised to stay indoors. Later, the UK, France and some other countries told their nationals to consider leaving Tokyo, in response to fears of spreading nuclear contamination. New Scientist has reported that emissions of radioactive iodine and cesium from the crippled Fukushima I nuclear plant have approached levels evident after the Chernobyl disaster
Chernobyl disaster
The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine , which was under the direct jurisdiction of the central authorities in Moscow...
in 1986. On March 24, 2011, Japanese officials announced that "radioactive iodine-131 exceeding safety limits for infants had been detected at 18 water-purification plants in Tokyo and five other prefectures". See Radiation effects from Fukushima Daiichi nuclear disaster.
Artificial radiation sources
The radiation from natural and artificial radiation sources are identical in their nature and their effects. These materials are distributed in the environment, and in our bodies, according to the chemical properties of the elements. The Nuclear Regulatory CommissionNuclear Regulatory Commission
The Nuclear Regulatory Commission is an independent agency of the United States government that was established by the Energy Reorganization Act of 1974 from the United States Atomic Energy Commission, and was first opened January 19, 1975...
, the United States Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
, and other U.S. and international agencies, require that licensees limit radiation exposure to individual members of the public to 1 mSv
Sievert
The sievert is the International System of Units SI derived unit of dose equivalent radiation. It attempts to quantitatively evaluate the biological effects of ionizing radiation as opposed to just the absorbed dose of radiation energy, which is measured in gray...
(100 mrem) per year, and limit occupational radiation exposure to adults working with radioactive material to 50 mSv (5 rem) per year, and 100 mSv (10 rem) in 5 years.
The exposure for an average person is about 3.6 mSv/year, 80 percent of which comes from natural sources of radiation. The remaining 20 percent results from exposure to artificial radiation sources, such as medical x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s, industrial sources like smoke detectors and a small fraction from nuclear weapon
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
s tests. For average persons who have had no medical x-rays, only 3% of their annual radiation dose comes from artificial sources.
A standard medical x-ray's strength is about 2 mrem or 0.02 mSv but can be over ten times that, depending on the equipment used. A dental x-ray optimally has a dose as low as 0.0033 mSv but poor machines and technique can give doses as high as 0.11 mSv. The average American and European receives about 0.5 mSv of diagnostic medical dose per year; countries with lower levels of health care receive about one fifth of this dose.
Radiation treatment for various diseases also accounts for some dose, both in individuals and in those around them.
Other usage
In other contexts, background radiation may simply be any radiation that is pervasive, whether ionizing or not. A particular example of this is the cosmic microwave background radiationCosmic microwave background radiation
In cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....
, a nearly uniform glow that fills the sky in the microwave part of the spectrum; stars, galaxies and other objects of interest in radio astronomy
Radio astronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
stand out against this background.
In a laboratory, background radiation refers to the measured value from any sources that affect an instrument when a radiation source sample is not being measured. This background rate, which must be established as a stable value by multiple measurements, usually before and after sample measurement, is subtracted from the rate measured when the sample is being measured.
Background radiation for occupational doses measured for workers is all radiation dose that is not measured by radiation dose measurement instruments in potential occupational exposure conditions. This includes both "natural background radiation" and any medical radiation doses. This value is not typically measured or known from surveys, such that variations in the total dose to individual workers is not known. This can be a significant confounding factor in assessing radiation exposure effects in a population of workers who may have significantly different natural background and medical radiation doses. This is most significant when the occupational doses are very low.
See also
- Background radiation equivalent timeBackground Radiation Equivalent TimeBackground Radiation Equivalent Time, or BRET, is a unit of measurement of ionizing radiation dosage. One BRET is the equivalent of one day worth of average human exposure to background radiation. The unit is also referred to as BERT .BRET units are used as a measure of low level radiation...
(BRET) - Environmental radioactivityEnvironmental radioactivityEnvironmental radioactivity is produced by radioactive materials in the human environment. While some radioisotopes, such as strontium-90 and technetium-99 , are only found on Earth as a result of human activity, and some, like potassium-40 , are only present due to natural processes, a few...
- Banana equivalent doseBanana equivalent doseA banana equivalent dose is a whimsical unit of radiation exposure, informally defined as the additional dose a person will absorb from eating one banana...