Ionizing radiation 202522 224788295 2008-07-10T12:31:05Z WikiBotas 4901395 robot Adding: [[lt:Jonizuojančioji spinduliuotė]] [[Image:Radioactive.svg|thumb|Radiation hazard symbol.]] <!-- Do not remove the text in the footnote for the following image; it is required by ISO. See [[Image talk:New_radiation_symbol_ISO_21482.svg]] for details. --> [[Image:New_radiation_symbol_ISO_21482.svg|thumb|Ionizing radiation hazard symbol (recently introduced).<ref><em>This symbol is included in ISO 21482:2007. ISO International Standards are protected by copyright and may be purchased from ISO or its members (please visit www.iso.org for more information). ISO has not reviewed the accuracy or veracity of this information.</em></ref>]] '''Ionizing radiation''' consists of highly-energetic [[particle radiation|particles]] or [[electromagnetic radiation|waves]] that can detach ([[ionize]]) at least one electron from an [[atom]] or [[molecule]]. Ionizing ability depends on the energy of individual particles or waves, and not on their number. A large flood of particles or waves will not, in the most common situations, cause ionization if the individual particles or waves are not by themselves ionizing. Examples of ionizing radiation are energetic [[beta particles]], [[neutrons]], and [[alpha particles]]. The ability of light waves ([[photons]]) to ionize an atom or molecule varies across the [[electromagnetic spectrum]]. [[X-ray]]s and [[gamma ray]]s can ionize almost any molecule or atom; far [[ultraviolet]] light can ionize many atoms and molecules; near ultraviolet and [[visible light]] are ionizing to very few molecules; [[microwave]]s and [[radio wave]]s are [[non-ionizing radiation]]. [[Visible light]] is so ubiquitous that [[photosensitivity|molecules that are ionized by it]] often react nearly spontaneously unless protected by materials that block the visible spectrum. Examples include photographic film and some molecules involved in [[photosynthesis]]. Ionizing radiation has many practical uses in medicine, research, construction, and other areas, but presents a health hazard if used improperly. If enough ionizations occur in a biological system, they can be destructive, by such means as causing [[DNA damage]] in individual cells. Extensive doses of ionizing radiation have been shown to have a [[mutation|mutating]] effect on the victim's descendants. Both helpful and harmful aspects of ionizing radiation are discussed below. == Types of radiation == [[Image:Alfa_beta_gamma_radiation.svg|250px|thumb|Alpha ('''α''') radiation consists of [[Helium-4|Helium-4]] ([[Helium-4|{{SimpleNuclide|Helium|4}}]]) nuclei and is stopped by a sheet of paper. Beta ('''β''') radiation, consisting of [[electron]]s, is halted by an aluminium plate. Gamma ('''γ''') radiation, consisting of energetic [[photon]]s, is eventually absorbed as it penetrates a dense material.]] Ionizing radiation is produced by [[radioactive decay]], [[nuclear fission]] and [[nuclear fusion]], by extremely hot objects (e.g., the Sun produces far-ultraviolet light), and by [[particle accelerator]]s that may produce, for example, fast electrons or protons or [[bremsstrahlung]] or [[synchrotron radiation]]. In order for a particle to be ionizing, it must both have a high enough energy and interact with the atoms of a target. Photons interact strongly with charged particles, so photons of sufficiently high energy also are ionizing. The energy at which this begins to happen with photons (light) is in the [[ultraviolet]] region of the electromagnetic spectrum; [[sunburn]] is one of the effects of ionization. Charged particles such as [[electron]]s, [[positron]]s, and [[alpha particle]]s also interact strongly with electrons of an atom or molecule. [[Neutron]]s, on the other hand, do not interact strongly with electrons, and so they cannot directly cause ionization by this mechanism. However, fast neutrons will interact with the protons in hydrogen (in the manner of a billiard ball hitting another, sending it away with all of the first ball's energy of motion), and this mechanism produces proton radiation ([[fast protons]]). These protons are ionizing because of their strong interaction with electrons in matter. A neutron can also interact with an atomic nucleus, depending on the nucleus and the neutron's velocity; these reactions happen with [[fast neutron]]s and [[slow neutron]]s, depending on the situation. Neutron interactions in this manner often produce [[radioactive]] nuclei, which produce ionizing radiation when they decay. [[Image:Types_of_radiation.png|350px|left]] In the picture at left, gamma rays are represented by wavy lines, charged particles and neutrons by straight lines. The little circles show where ionization processes occur. An ionization event normally produces a positive atomic ion and an electron. High-energy beta particles may produce [[bremsstrahlung]] when passing through matter, or secondary electrons (δ-electrons); both can ionize in turn. Unlike alpha or beta particles (see [[particle radiation]]), gamma rays do not ionize all along their path, but rather interact with matter in one of three ways: the [[photoelectric effect]], the [[Compton effect]], and [[pair production]]. By way of example, the figure shows Compton effect: two Compton scatterings that happen sequentially. In every scattering event, the gamma ray transfers energy to an electron, and it continues on its path in a different direction and with reduced energy. In the same figure, the neutron collides with a proton of the target material, and then becomes a fast recoil proton that ionizes in turn. At the end of its path, the neutron is captured by a nucleus in an (n,γ)-reaction that leads to a [[neutron capture]] photon. The negatively-charged electrons and positively charged [[ion]]s created by ionizing radiation may cause damage in living tissue. If the dose is sufficient, the effect may be seen almost immediately, in the form of [[radiation poisoning]]. Lower doses may cause [[cancer]] or other long-term problems. The effect of the very low doses encountered in normal circumstances (from both natural and artificial sources, like cosmic rays, medical X-rays and nuclear power plants) is a subject of current debate. A [[2005]] report released by the National Research Council (the BEIR VII report, summarized in [http://www.nap.edu/execsumm_pdf/11340.pdf]) indicated that the overall cancer risk associated with background sources of radiation was relatively low. Radioactive materials usually release [[alpha particle]]s, which are the nuclei of [[helium]], [[beta particle]]s, which are quickly moving [[electron]]s or [[positron]]s, or [[gamma ray]]s. Alpha and beta particles can often be stopped by a piece of [[paper]] or a [[aluminium foil|sheet of aluminium]], respectively. They cause most damage when they are emitted inside the human body. Gamma rays are less [[ion]]izing than either alpha or beta particles, and protection against gammas requires thicker shielding. The damage they produce is similar to that caused by [[X-ray]]s, and include burns and also [[cancer]], through [[mutation]]s. [[Human biology]] resists [[germline mutation]] by either correcting the changes in the [[DNA]] or inducing [[apoptosis]] in the mutated cell. Non-ionizing radiation is thought to be essentially harmless below the levels that cause heating. Ionizing radiation is dangerous in direct exposure, although the degree of danger is a subject of debate. Humans and animals can also be exposed to ionizing radiation internally: if radioactive isotopes are present in the environment, they may be taken into the body. For example, radioactive [[iodine]] is treated as normal iodine by the body and used by the [[thyroid]]; its accumulation there often leads to thyroid [[cancer]]. Some radioactive elements also [[bioaccumulate]]. == Uses of ionizing radiation == Ionizing radiation has many uses, such as to kill cancerous cells. However, although ionizing radiation has many applications, overuse can be hazardous to human health. For example, at one time, assistants in shoe shops [[Shoe-fitting_fluoroscope|used X-rays to check a child's shoe size]], but this practice was halted when it was discovered that ionizing radiation was dangerous. === Technical uses of ionizing radiation === Since ionizing radiations can penetrate matter, they are used for a variety of measuring methods. ;Radiography by means of gamma or X rays :This is a method used in industrial production. The piece to be radiographed is placed between the source and a photographic film in a cassette. After a certain exposure time, the film is developed and it shows internal defects of the material if there are any. ;Gauges :Gauges use the exponential absorption law of gamma rays :*Level indicators: Source and detector are placed at opposite sides of a container, indicating the presence or absence of material in the horizontal radiation path. Beta or gamma sources are used, depending on the thickness and the density of the material to be measured. The method is used for containers of liquids or of grainy substances :*Thickness gauges: if the material is of constant density, the signal measured by the radiation detector depends on the thickness of the material. This is useful for continuous production, like of paper, rubber, etc. ;Applications using ionization of gases by radiation :*To avoid the build-up of static electricity in production of paper, plastics, synthetic textiles, etc., a ribbon-shaped source of the alpha emitter <sup>241</sup>Am can be placed close to the material at the end of the production line. The source ionizes the air to remove electric charges on the material. :*[[Smoke detector]]: Two ionisation chambers are placed next to each other. Both contain a small source of <sup>241</sup>Am that gives rise to a small constant current. One is closed and serves for comparison, the other is open to ambient air; it has a gridded electrode. When smoke enters the open chamber, the current is disrupted as the smoke particles attach to the charged ions and restore them to a neutral electrical state. This reduces the current in the open chamber. When the current drops below a certain threshold, the alarm is triggered. :*[[Radioactive tracer]]s for industry: Since radioactive isotopes behave, chemically, mostly like the inactive element, the behavior of a certain chemical substance can be followed by ''tracing'' the radioactivity. Examples: :**Adding a gamma tracer to a gas or liquid in a closed system makes it possible to find a hole in a tube. :**Adding a tracer to the surface of the component of a motor makes it possible to measure wear by measuring the activity of the lubricating oil. === Biological and medical applications of ionizing radiation === In [[biology]], radiation is mainly used for [[Sterilization (microbiology)|sterilization]], and enhancing [[mutation]]s. For example, mutations may be induced by radiation to produce new or improved species. A very promising field is the [[sterile insect technique]], where male insects are sterilized and liberated in the chosen field, so that they have no descendants, and the population is reduced. Radiation is also useful in sterilizing medical hardware or [[food irradiation|food]]. The advantage for medical hardware is that the object may be sealed in plastic before sterilization. For food, there are strict regulations to prevent the occurrence of [[induced radioactivity]]. The growth of a seedling may be enhanced by radiation, but excessive radiation will hinder growth. Electrons, x rays, gamma rays or atomic [[ion]]s may be used in [[radiation therapy]] to treat malignant tumors ([[cancer]]). Tracer methods are used in [[nuclear medicine]] in a way analogous to the technical uses mentioned above. === Natural background radiation === Natural [[background radiation]] comes from four primary sources: cosmic radiation, solar radiation, external terrestrial sources, and [[radon]]. ====Cosmic radiation==== {{details|Cosmic ray|cosmic radiation}} The Earth, and all living things on it, are constantly bombarded by radiation from outside our solar system. This cosmic radiation consists of positively-charged ions from [[proton]]s to [[iron]] [[atomic nucleus|nuclei]]. The energy of this radiation can far exceed that which humans can create even in the largest particle accelerators. This radiation interacts in the atmosphere to create secondary radiation that rains down, including [[x-rays]], [[muon]]s, protons, [[alpha particle]]s, [[pion]]s, [[electron]]s, and [[neutron]]s. The [[dose]] from cosmic radiation is largely from muons, neutrons, and electrons, with a dose rate that varies in different parts of the world and based largely on the geomagnetic field, altitude, and solar cycle. The cosmic-radiation dose rate on airplanes is so high that, according to the United Nations UNSCEAR 2000 Report (see links at bottom), airline flight crew workers receive more dose on average than any other worker, including those in nuclear power plants. ====Solar radiation==== While most of the Sun's output consists of light ([[solar radiation]]), particle radiation is also produced and varies with the [[solar cycle]]. These particles are mostly [[proton]]s with relatively low energies (10-100 keV). Their average composition is similar to that of the Sun itself. This represents significantly lower energy particles than come from cosmic rays. Solar particles vary widely in their intensity and spectrum, increasing in strength after some solar events such as [[solar flare]]s. Further, an increase in the intensity of solar cosmic rays is often followed by a ''decrease'' in the galactic cosmic rays, called a [[Forbush decrease]] after their discoverer, the physicist Scott Forbush. These decreases are due to the [[solar wind]] which carries the Sun's magnetic field out further to shield the earth more thoroughly from cosmic radiation. The ionizing component of solar radiation is negligible relative to other forms of radiation on Earth's surface. ====External terrestrial sources==== Most materials on Earth contain some radioactive atoms, even if in small quantities. Most of the terrestrial non-radon-dose one receives from these sources is from gamma-ray emitters in the walls and floors when inside a house, or rocks and soil when outside. The major [[radionuclide]]s of concern for '''terrestrial radiation''' are [[potassium]], [[uranium]], and [[thorium]]. Each of these sources has been decreasing in activity since the birth of the Earth so that our present dose from potassium-40 is about ½ what it would have been at the dawn of [[life on Earth]]. ====Radon==== [[Radon]]-222 is produced by the decay of [[radium]]-226 which is present wherever uranium is found. Since radon is a gas, it seeps out of uranium-containing soils found across most of the world and may accumulate in well-sealed homes. It is often the single largest contributor to an individual's background radiation dose and is certainly the most variable from location to location. Radon gas could be the second largest cause of lung cancer in America, after [[smoking]].<ref>See [http://www.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=35420 this web site].</ref> === Human-made radiation sources === Natural and artificial radiation sources are similar in their effects on matter. Above the background level of radiation exposure, the U.S. [[Nuclear Regulatory Commission]] (NRC) requires that its licensees limit human-made radiation exposure for individual members of the public to 100 [[roentgen equivalent man|mrem]] (1 [[sievert|mSv]]) per year, and limit occupational radiation exposure to adults working with radioactive material to 5,000 mrem (50 mSv) per year. The average exposure for Americans is about 360 mrem (3.6 mSv) per year, 81 percent of which comes from natural sources of radiation. The remaining 19 percent results from exposure to human-made radiation sources such as medical X-rays, most of which is deposited in people who have [[CAT scans]]. This compares with the average dose received by people in the UK of about 2.2 mSv. As already mentioned, an important source of natural radiation is [[radon]] gas, which seeps continuously from bedrock but can, because of its high density, accumulate in poorly ventilated houses. The background rate for radiation varies considerably with location, being as low as 1.5 mSv/a (1.5 mSv per year) in some areas and over 100 mSv/a in others. People in some parts of [[Ramsar]], a city in northern [[Iran]], receive an annual absorbed dose from background radiation that is up to 260 mSv/a. Despite having lived for many generations in these high background areas, inhabitants of Ramsar show no significant cytogenetic differences compared to people in normal background areas. This has led to the suggestion that high but steady levels of radiation are easier for humans to sustain than sudden radiation bursts. Some human-made radiation sources affect the body through direct radiation, while others take the form of [[radioactive contamination]] and [[irradiate]] the body from within. Medical procedures, such as diagnostic [[X-ray]]s, [[nuclear medicine]], and [[radiation therapy]] are by far the most significant source of human-made radiation exposure to the general public. Some of the major [[radionuclide]]s used are [[iodine|I-131]], [[technetium|Tc-99]], [[cobalt|Co-60]], [[iridium|Ir-192]], and [[caesium|Cs-137]]. These are rarely released into the environment. The public also is exposed to radiation from consumer products, such as [[tobacco]] ([[polonium]]-210), building materials, combustible fuels (gas, [[coal]], etc.), ophthalmic [[glass]], [[television]]s, luminous [[watch]]es and dials ([[tritium]]), airport [[X-ray]] systems, [[smoke detector]]s ([[americium]]), road construction materials, electron tubes, [[fluorescent lamp]] starters, and [[lantern]] mantles ([[thorium]]). Of lesser magnitude, members of the public are exposed to radiation from the [[nuclear fuel]] cycle, which includes the entire sequence from mining and milling of [[uranium]] to the disposal of the spent fuel. The effects of such exposure have not been reliably measured due to the extremely low doses involved. Estimates of exposure are low enough that proponents of nuclear power liken them to the mutagenic power of wearing trousers for two extra minutes per year (because heat causes mutation). Opponents use a cancer per dose model to assert that such activities cause several hundred cases of cancer per year. In a [[Nuclear warfare|nuclear war]], [[gamma ray]]s from [[Nuclear fallout|fallout]] of [[nuclear weapon]]s would probably cause the largest number of casualties. Immediately downwind of targets, doses would exceed 300 [[Gray (unit)|Gy]] per hour. As a reference, 4.5 Gy (around 15,000 times the average annual background rate) is fatal to half of a normal population, without medical treatment. Occupationally exposed individuals are exposed according to the sources with which they work. The radiation exposure of these individuals is carefully monitored with the use of pocket-pen-sized instruments called [[dosimeter]]s. Some of the radionuclides of concern include [[cobalt]]-60, [[caesium]]-137, [[americium]]-241, and [[iodine]]-131. Examples of industries where occupational exposure is a concern include: *Airline crew (the most exposed population) *Fuel cycle *Industrial radiography *Nuclear medicine and medical radiology departments (including nuclear oncology) *Nuclear power plants (during maintenance work near the reactor core) *Research laboratories (government, university and private) ==Biological effects of ionizing radiation== The biological effects of radiation are thought of in terms of their effects on living [[cell (biology)|cells]]. For low levels of radiation, the biological effects are so small they may not be detected in epidemiological studies. The body repairs many types of radiation and chemical damage. Biological effects of radiation on living cells may result in a variety of outcomes, including: #Cells experience DNA damage and are able to detect and repair the damage. #Cells experience DNA damage and are unable to repair the damage. These cells may go through the process of programmed cell death, or [[apoptosis]], thus eliminating the potential genetic damage from the larger tissue. #Cells experience a nonlethal DNA mutation that is passed on to subsequent cell divisions. This mutation may contribute to the formation of a cancer. Other observations at the tissue level are more complicated. These include: #In some cases, a small radiation dose reduces the impact of a subsequent, larger radiation dose. This has been termed an 'adaptive response' and is related to hypothetical mechanisms of [[Radiation hormesis|hormesis]]. === Hormesis === {{main|Radiation hormesis}} Radiation hormesis is the unproven theory that a low level of ionizing radiation (i.e. near the level of Earth's natural background radiation) helps "immunize" cells against DNA damage from other causes (such as free radicals or larger doses of ionizing radiation), and decreases the risk of cancer. The theory proposes that such low levels activate the body's DNA repair mechanisms, causing higher levels of cellular DNA-repair proteins to be present in the body, improving the body's ability to repair DNA damage. This assertion is very difficult to prove (using, for example, statistical cancer studies) because the effects of very low ionizing radiation levels are too small to be statistically measured amid the "noise" of normal cancer rates. Therefore, the idea of radiation hormesis is considered unproven by regulatory bodies, which generally use the standard "[[Linear_no-threshold_model|linear, no threshold]]" (LNT) model, which states that risk of cancer is directly proportional to the dose level of ionizing radiation. The LNT model is safer for regulatory purposes because it assumes worst-case damage due to ionizing radiation; therefore, if regulations are based on it, workers might be over-protected, but they will never be under-protected. At high ionizing radiation levels, such as the acute doses received near the Hiroshima and Nagasaki bomb blasts, the risk of cancer does increase roughly linearly with dose, which is the origin of the LNT model. Thus, there is a consensus that the LNT method should continue to be used because it is safer from a regulatory perspective and because the effects of very low radiation doses are too small to be measured statistically. See the National Academies Press book.<ref> {{cite book | title = Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 | isbn = -309-09156-X}} </ref>. === Chronic radiation exposure === Exposure to ionizing radiation over an extended period of time is called chronic exposure. The natural background radiation is chronic exposure, but a normal level is difficult to determine due to variations. Geographic location and occupation often affect chronic exposure. === Acute radiation exposure === Acute radiation exposure is an exposure to ionizing radiation which occurs during a short period of time. There are routine brief exposures, and the boundary at which it becomes significant is difficult to identify. Extreme examples include * Instantaneous flashes from nuclear explosions. * Exposures of minutes to hours during handling of highly radioactive sources. * Laboratory and manufacturing accidents. * Intentional and accidental high medical doses. The effects of acute events are more easily studied than those of chronic exposure. Chronic exposure is reactant. === Radiation levels === The associations between ionizing radiation exposure and the development of [[cancer]] are mostly based on populations exposed to relatively high levels of ionizing radiation, such as Japanese atomic bomb survivors, and recipients of selected diagnostic or therapeutic medical procedures. Cancers associated with high dose exposure include [[leukemia]], thyroid, breast, bladder, colon, liver, lung, esophagus, ovarian, multiple myeloma, and stomach cancers. [[United States Department of Health and Human Services]] literature also suggests a possible association between ionizing radiation exposure and prostate, nasal cavity/sinuses, pharyngeal and laryngeal, and pancreatic cancer. The period of time between radiation exposure and the detection of cancer is known as the [[latent period]]. Those cancers that may develop as a result of radiation exposure are indistinguishable from those that occur naturally or as a result of exposure to other chemical [[carcinogen]]s. Furthermore, [[National Cancer Institute]] literature indicates that other chemical and physical hazards and lifestyle factors, such as smoking, [[alcohol]] consumption, and diet, significantly contribute to many of these same diseases. Although radiation may cause cancer at high doses and high dose rates, [[public health]] data regarding lower levels of exposure, below about 1,000 mrem (10 mSv), are harder to interpret. To assess the health impacts of lower radiation doses, researchers rely on models of the process by which radiation causes cancer; several models have emerged which predict differing levels of risk. Studies of occupational workers exposed to chronic low levels of radiation, above normal background, have provided mixed evidence regarding cancer and transgenerational effects. Cancer results, although uncertain, are consistent with estimates of risk based on atomic bomb survivors and suggest that these workers do face a small increase in the probability of developing leukemia and other cancers. One of the most recent and extensive studies of workers was published by Cardis et al. in 2005 [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15987704&query_hl=1&itool=pubmed_docsum]. The linear dose-response model suggests that any increase in dose, no matter how small, results in an incremental increase in risk. The [[linear no-threshold model]] (LNT) hypothesis is accepted by the [[Nuclear Regulatory Commission]] (NRC) and the EPA and its validity has been reaffirmed by a National Academy of Sciences Committee. (See the BEIR VII report, summarized in [http://www.nap.edu/execsumm_pdf/11340.pdf].) Under this model, about 1% of a population would develop cancer in their lifetime as a result of ionizing radiation from background levels of natural and man-made sources. <!-- Is there a source for the "low doses alter DNA"? --> <!-- Well, here's an explanation, but we still need a good source on this contentious topic --> Ionizing radiation damages tissue by causing ionization, which disrupts molecules directly and also produces highly reactive [[Radical (chemistry)|free radicals]], which attack nearby cells. The net effect is that biological molecules suffer local disruption; this may exceed the body's capacity to repair the damage and may also cause mutations in cells currently undergoing replication. Two widely studied instances of large-scale exposure to high doses of ionizing radiation are: [[nuclear weapon|atomic bomb]] survivors in [[1945]]; and emergency workers responding to the [[1986]] [[Chernobyl accident]]. Approximately 134 plant workers and fire fighters engaged at the Chernobyl power plant received high radiation doses (70,000 to 1,340,000 mrem or 700 to 13,400 mSv) and suffered from acute radiation sickness. Of these, 28 died from their radiation injuries. Longer term effects of the Chernobyl accident have also been studied. There is a clear link (see the [http://www.unscear.org/unscear/en/publications/2000_2.html UNSCEAR 2000 Report, Volume 2: Effects]) between the Chernobyl accident and the unusually large number, approximately 1,800, of thyroid cancers reported in contaminated areas, mostly in children. These were fatal in some cases. Other health effects of the Chernobyl accident are subject to current debate. ==== Ionizing radiation level examples ==== Recognized effects of acute radiation exposure are described in the article on [[radiation poisoning]]. The exact units of measurement vary, but light radiation sickness begins at about 50&ndash;100 [[rad (unit)|rad]] (0.5&ndash;1 [[gray (unit)|gray (Gy)]], 0.5&ndash;1 [[Sievert|Sv]], 50&ndash;100 [[Roentgen equivalent man|rem]], 50,000&ndash;100,000 mrem). Although the SI unit of radiation dose equivalent is the sievert, chronic radiation levels and standards are still often given in millirems, 1/1000th of a rem (1 mrem = 0.01 mSv). The following table includes some short-term dosages for comparison purposes. {| ! Level (mSv) !! Duration !! Description |- | 0.001-0.01 || Hourly || Cosmic ray dose on high-altitude flight, depends on position and solar sunspot phase.<ref>UNSCEAR 2000 report, Volume 1, Annex B, ``Exposures from natural radiation sources'', pp 88. See figure 3. available online at [http://www.unscear.org/unscear/en/publications/2000_1.html]</ref> |- | 0.01 || Annual || USA dose from nuclear fuel and nuclear power plants <ref name="ORNLappa">Oak Ridge National Laboratory (http://www.ornl.gov/sci/env_rpt/aser95/appa.htm)</ref> |- | 0.01 || Daily || Natural background radiation, including radon <ref name="ORNLtb"> Oak Ridge National Laboratory (http://www.ornl.gov/sci/env_rpt/aser95/tb-a-2.pdf)</ref> |- | 0.1 || Annual ||Average USA dose from consumer products <ref name="ORNLappa"/> |- | 0.15 || Annual ||USA EPA cleanup standard {{Fact|date=March 2007}} |- | 0.25 || Annual || USA NRC cleanup standard for individual sites/sources {{Fact|date=March 2007}} |- | 0.27 || Annual || USA dose from natural cosmic radiation (0.16 coastal plain, 0.63 eastern Rocky Mountains) <ref name="ORNLappa"/> |- | 0.28 || Annual || USA dose from natural terrestrial sources <ref name="ORNLappa"/> |- | 0.39 || Annual || Global level of human internal radiation due to radioactive potassium{{Fact|date=March 2007}} |- | 0.46 || Acute || Estimated largest off-site dose possible from [[March 28]] [[1979]] Three Mile Island accident{{Fact|date=March 2007}} |- | 0.48 || Day || USA NRC public area exposure limit{{Fact|date=March 2007}} |- | 0.66 || Annual || Average USA dose from human-made sources <ref name="ORNLtb"/> |- | 1 || Annual || Limit of dose from all DOE facilities to a member of the public who is not a radiation worker <ref name="ORNLtb"/> |- | 1.1 || Annual ||1980 average USA radiation worker occupational dose <ref name="ORNLtb"/> |- | 2 || Annual || USA average medical and natural background [http://www.ornl.gov/sci/env_rpt/aser95/tb-a-2.pdf]<br/> Human internal radiation due to radon, varies with radon levels <ref name="ORNLappa"/> |- | 2.2 || Acute ||Average dose from upper gastrointestinal diagnostic X-ray series{{Fact|date=March 2007}} |- | 3 || Annual ||USA average dose from all natural sources <ref name="ORNLtb"/> |- | 3.66 || Annual ||USA average from all sources, including medical diagnostic radiation doses{{Fact|date=March 2007}} |- | few || Annual ||Estimate of cobalt-60 contamination within about 0.5 mile of [[dirty bomb]]{{Fact|date=March 2007}} |- | 5 || Annual ||USA NRC occupational limit for minors (10% of adult limit)<br/>USA NRC limit for visitors<br/>Orvieto town, Italy, natural [http://www.unscear.org/docs/reports/annexb.pdf] <!--if this link breaks again, look for the 2000 UNSCEAR Report Vol 1: Sources and Effects of Ionizing Radiation, Annex B: Exposures from natural radiation sources (74 pages)--> |- | 5 ||Pregnancy|| USA NRC occupational limit for pregnant women{{Fact|date=March 2007}} |- | 6.4 || Annual || High Background Radiation Area (HBRA) of Yangjiang, China [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11715418&dopt=Citation] |- | 7.6 || Annual || Fountainhead Rock Place, Santa Fe, NM natural{{Fact|date=March 2007}} |- | 10&ndash;50 || Acute || USA EPA nuclear accident emergency action level <ref name="ORNLtb"/> |- | 50 || Annual || USA NRC occupational limit ([http://www.nrc.gov/reading-rm/doc-collections/cfr/part020/ 10 CFR 20]) |- | 100 || Acute || USA EPA acute dose level estimated to increase cancer risk 0.8% <ref name="ORNLtb"/> |- | 120 || 30 years || Exposure, long duration, [[Ural mountains]], lower limit, lower cancer mortality rate[http://cnts.wpi.edu/RSH/Docs/Pollycove2000_Symp_on_Med_Ben.htm] |- | 150 || Annual || USA NRC occupational eye lens exposure limit {{Fact|date=March 2007}} |- | 175 || Annual || Guarapari, Brazil natural radiation sources [http://www.lewrockwell.com/miller/miller12.html] |- | 250 || Acute || USA EPA voluntary maximum dose for emergency non-life-saving work <ref name="ORNLtb"/> |- | 260 || Annual ||Ramsar, Iran, natural background peak dose [http://www.sciencemag.org/cgi/content/full/309/5736/883] |- | 500 || Annual || USA NRC occupational whole skin, limb skin, or single organ exposure limit<br/> |- | 500 || 30 years || Exposure, long duration, [[Ural mountains]], upper limit (exposed population lower cancer mortality rate) [http://cnts.wpi.edu/RSH/Docs/Pollycove2000_Symp_on_Med_Ben.htm] |- | 750 || Acute || USA EPA voluntary maximum dose for emergency life-saving work <ref name="ORNLtb"/> |- | 500-1000|| Acute || Low-level radiation sickness due to short-term exposure<br/> |- | 500-1000|| Detonation || World War II nuclear bomb victims{{Fact|date=March 2007}} |- | 4500-5000 || Acute || [[LD50|LD<sub>50</sub>]] in humans (from [[radiation poisoning]]), with medical treatment. <ref>[http://web.princeton.edu/sites/ehs/osradtraining/biologicaleffects/page.htm Biological Effects of Ionizing Radiation<!-- Bot generated title -->]</ref> |} == Monitoring and controlling exposure to ionizing radiation == Radiation has always been present in the environment and in our bodies. The human body cannot sense ionizing radiation, but a range of instruments exists which are capable of detecting even very low levels of radiation from natural and man-made sources. [[Dosimeter]]s measure an absolute dose received over a period of time. Ion-chamber dosimeters resemble pens, and can be clipped to one's clothing. Film-badge dosimeters enclose a piece of [[photographic film]], which will become exposed as radiation passes through it. Ion-chamber dosimeters must be periodically recharged, and the result logged. Film-badge dosimeters must be developed as photographic emulsion so the exposures can be counted and logged; once developed, they are discarded. [[Geiger counter]]s and [[scintillation counter]]s measure the dose rate of ionizing radiation directly. There are four standard ways to limit exposure: Time: For people who are exposed to radiation in addition to natural background radiation, limiting or minimizing the exposure time will reduce the dose from the radiation source. Distance: Radiation intensity decreases sharply with distance, according to an [[inverse square law]]. Shielding: Barriers of [[lead]], [[concrete]], or water give effective protection from radiation formed of energetic particles such as [[gamma ray]]s and [[neutron]]s. Some radioactive materials are stored or handled underwater or by [[remote control]] in rooms constructed of thick concrete or lined with lead. There are special [[plastic]] shields which stop beta particles and air will stop alpha particles. Shielding can be designed using ''halving thicknesses'', the thickness of material that reduces the radiation by half. Halving thicknesses for gamma rays are discussed in the article [[gamma ray]]s. Containment: Radioactive materials are confined in the smallest possible space and kept out of the environment. [[Radioactive isotope]]s for medical use, for example, are dispensed in closed handling facilities, while [[nuclear reactor]]s operate within closed systems with multiple barriers which keep the radioactive materials contained. Rooms have a reduced air pressure so that any leaks occur into the room and not out of it. In a [[nuclear warfare|nuclear war]], an effective [[fallout shelter]] reduces human exposure at least 1,000 times. Most people can accept doses as high as 1 Gy{{Fact|date=February 2007}}, distributed over several months, although with increased risk of cancer later in life. Other [[civil defense]] measures can help reduce exposure of populations by reducing ingestion of isotopes and occupational exposure during war time. One of these available measures could be the use of [[potassium iodide]] (KI) tablets which effectively block the uptake of dangerous radioactive iodine into the human [[thyroid]] gland. ==See also== <div style="-moz-column-count:4; column-count:4;"> *[[Civil defense]] *[[Electromagnetic radiation]] *[[Fallout shelter]] *[[Gamma ray]] *[[Hormesis]] *[[Irradiated mail]] *[[Kearny Fallout Meter]] *[[Non-ionizing radiation]] *[[Nuclear warfare]] *[[Nuclear weapon]] *[[Particle radiation]] *[[Petkau effect]] *[[Radiant energy]] *[[Radiation poisoning]] *[[Radiation therapy]] *[[Radioactive contamination]] *[[Radioactivity]] *[[Radiobiology]] *[[Radioresistance]] *[[Radiosensitivity]] </div> == References == {{reflist}} == External links == *[http://www.nrc.gov The Nuclear Regulatory Commission] regulates most commercial radiation sources and non-medical exposures in the US: *[http://www.belleonline.com/ Biological Effects of Low Level Exposures: Radiation Hormesis] *[http://books.nap.edu/catalog/11340.html?onpi_newsdoc062905 Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2] *[http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+@rel+ionizing+radiation NLM Hazardous Substances Databank &ndash; Ionizing Radiation] *[http://www.riscrad.org RISC-RAD] is a European research project on assessment of low dose cancer risk *[http://www.unscear.org/unscear/en/publications/2000_1.html UNSCEAR 2000 Report, Volume 1: Sources] *[http://www.unscear.org/unscear/en/publications/2000_2.html UNSCEAR 2000 Report, Volume 2: Effects] *[http://www.npl.co.uk/publications/ionising_radiation/ Beginners Guide to Ionising Radiation Measurement] *[http://www.npl.co.uk/ionrad/quantities.html Quantities, units and their relationships] *[http://www.ki4u.com/free_book/s60p792.htm Plans for homemade ionizing radiation meter] *[http://www.pocketrad.com/articles/householdsources.html List of common household radioactive items] * [http://www.wikimindmap.org/viewmap.php?wiki=en.wikipedia.org&topic=Ionizing_radiation WikiMindMap] {{Nuclear Technology}} <!--Categories--> [[Category:Radioactivity]] [[Category:Radiobiology]] [[Category:Radiation health effects]] <!--Interwiki--> [[af:Ioniserende straling]] [[bg:Радиация]] [[cs:Ionizující záření]] [[da:Ioniserende stråling]] [[de:Ionisierende Strahlung]] [[es:Radiación ionizante]] [[eo:Joniga radiado]] [[fr:Rayonnement ionisant]] [[ko:이온화 방사선]] [[is:Jónandi geislun]] [[lt:Jonizuojančioji spinduliuotė]] [[hu:Ionizáló sugárzás]] [[nl:Ioniserende straling]] [[ja:放射線]] [[no:Ioniserende stråling]] [[nn:Ioniserande stråling]] [[pl:Promieniowanie jonizujące]] [[pt:Radiação ionizante]] [[ru:Ионизирующие излучения]] [[simple:Ionizing radiation]] [[fi:Ionisoiva säteily]] [[sv:Joniserande strålning]]