The sievert (symbol: Sv[note 1]) is a derived unit of ionizing radiation dose in the International System of Units (SI) and is a measure of the health effect of low levels of ionizing radiation on the human body. The sievert is of importance in dosimetry and radiation protection, and is named after Rolf Maximilian Sievert, a Swedish medical physicist renowned for work on radiation dose measurement and research into the biological effects of radiation.
The sievert is used for radiation dose quantities such as equivalent dose and effective dose, which represent the risk of external radiation from sources outside the body, and committed dose which represents the risk of internal irradiation due to inhaled or ingested radioactive substances. The sievert is intended to represent the stochastic health risk, which for radiation dose assessment is defined as the probability of radiation-induced cancer and genetic damage. One sievert carries with it a 5.5% chance of eventually developing cancer based on the linear no-threshold model.
To enable consideration of stochastic health risk, calculations are performed to convert the physical quantity absorbed dose into equivalent dose and effective dose, the details of which depend on the radiation type and biological context. For applications in radiation protection and dosimetry assessment the International Commission on Radiological Protection (ICRP) and International Commission on Radiation Units and Measurements (ICRU) have published recommendations and data which are used to calculate these. These are under continual review, and changes are advised in the formal "Reports" of those bodies.
Conventionally, the sievert is not used for high dose rates of radiation that produce deterministic effects, which is the severity of acute tissue damage that is certain to happen, such as acute radiation syndrome; these effects are compared to the physical quantity absorbed dose measured by the unit gray (Gy).
One sievert equals 100 rem. The rem is an older, non-SI unit of measurement.
|Unit system||SI derived unit|
|Unit of||Health effect of ionizing radiation (Equivalent dose)|
|Named after||Rolf Maximilian Sievert|
|1 Sv in ...||... is equal to ...|
|SI base units||m2⋅s−2|
|Energy absorbed by mass||J⋅kg−1|
|CGS units (non-SI)||100 rem|
The SI definition given by the International Committee for Weights and Measures (CIPM) says:
"The quantity dose equivalent H is the product of the absorbed dose D of ionizing radiation and the dimensionless factor Q (quality factor) defined as a function of linear energy transfer by the ICRU"
The value of Q is not defined further by CIPM, but it requires the use of the relevant ICRU recommendations to provide this value.
The CIPM also says that "in order to avoid any risk of confusion between the absorbed dose D and the dose equivalent H, the special names for the respective units should be used, that is, the name gray should be used instead of joules per kilogram for the unit of absorbed dose D and the name sievert instead of joules per kilogram for the unit of dose equivalent H".
The gray – quantity D
The sievert – quantity H
The ICRP definition of the sievert is:
The sievert is used for a number of dose quantities which are described in this article and are part of the international radiological protection system devised and defined by the ICRP and ICRU.
The ICRU/ICRP dose quantities have specific purposes and meanings, but some use common words in a different order. There can be confusion between, for instance, equivalent dose and dose equivalent.
Although the CIPM definition states that the linear energy transfer function (Q) of the ICRU is used in calculating the biological effect, the ICRP in 1990 developed the "protection" dose quantities effective and equivalent dose which are calculated from more complex computational models and are distinguished by not having the phrase dose equivalent in their name. Only the operational dose quantities which still use Q for calculation retain the phrase dose equivalent. However, there are joint ICRU/ICRP proposals to simplify this system by changes to the operational dose definitions to harmonise with those of protection quantities. These were outlined at the 3rd International Symposium on Radiological Protection in October 2015, and if implemented would make the naming of operational quantities more logical by introducing "dose to lens of eye" and "dose to local skin" as equivalent doses.
The sievert is used to represent the biological effects of different forms of external ionizing radiation on various types of human tissue. Some quantities cannot be practically measured, but they must be related to actual instrumentation and dosimetry measurements. The resultant complexity has required the creation of a number of different dose quantities within a coherent system developed by the ICRU working with the ICRP.
The external dose quantities and their relationships are shown in the accompanying diagram. The ICRU is primarily responsible for the operational dose quantities, based upon the application of ionising radiation metrology, and the ICRP is primarily responsible for the protection quantities, based upon modelling of dose uptake and biological sensitivity of the human body.
These are directly measurable physical quantities in which no allowance has been made for biological effects. Radiation fluence is the number of radiation particles impinging per unit area per unit time, kerma is the ionising effect of the radiation field, and absorbed dose is the amount of radiation energy deposited per unit mass.
Protection quantities are calculated models, and are used as "limiting quantities" to specify exposure limits to ensure, in the words of ICRP, "that the occurrence of stochastic health effects is kept below unacceptable levels and that tissue reactions are avoided". These quantities cannot be measured in practice but their values are derived using models of external dose to internal organs of the human body, using anthropomorphic phantoms. These are 3D computational models of the body which take into account a number of complex effects such as body self-shielding and internal scattering of radiation. The calculation starts with organ absorbed dose, and then applies radiation and tissue weighting factors.
As protection quantities cannot practically be measured, operational quantities must be used to relate them to practical radiation instrument and dosimeter responses.
Operational quantities can be measured in practice, and are the means of measuring dose uptake due to exposure or predicting dose uptake in a measured environment, in relation to protection dose values. In this way they are used for practical dose control, by providing an estimate or upper limit for the value of the protection quantities related to an exposure. They are used in practical regulations and guidance.
The calibration of individual and area dosemeters in photon fields is performed by measuring the collision "air kerma free in air" under conditions of secondary electron equilibrium. Then the appropriate operational quantity is derived applying a conversion coefficient that relates the air kerma to the appropriate operational quantity. The conversion coefficients for photon radiation are published by the ICRU.
Simple (non-anthropomorphic) "phantoms" are used to relate operational quantities to measured free-air irradiation. The ICRU sphere phantom is based on the definition of an ICRU 4-element tissue-equivalent material which does not really exist and cannot be fabricated. The ICRU sphere is a theoretical 30 cm diameter "tissue equivalent" sphere consisting of a material with a density of 1 g·cm−3 and a mass composition of 76.2% oxygen, 11.1% carbon, 10.1% hydrogen and 2.6% nitrogen. This material is specified to most closely approximate human tissue in its absorption properties. According to the ICRP, the ICRU "sphere phantom" in most cases adequately approximates the human body as regards the scattering and attenuation of penetrating radiation fields under consideration. Thus radiation of a particular energy fluence will have roughly the same energy deposition within the sphere as it would in the equivalent mass of human tissue.
To allow for back-scattering and absorption of the human body, the "slab phantom" is used to represent the human torso for practical calibration of whole body dosimeters. The slab phantom is 300 mm × 300 mm × 150 mm depth to represent the human torso.
The joint ICRU/ICRP proposals outlined at the 3rd International Symposium on Radiological Protection in October 2015 to change the definition of operational quantities would not change the present use of calibration phantoms or reference radiation fields.
This is an actual reading obtained from such as an ambient dose gamma monitor, or a personal dosimeter. Such instruments are calibrated using radiation metrology techniques which will trace them to a national radiation standard, and thereby relate them to an operational quantity. The readings of instruments and dosimeters are used to prevent the uptake of excessive dose and to provide records of dose uptake to satisfy radiation safety legislation; such as in the UK, the Ionising Radiations Regulations 1999.
The sievert is used in external radiation protection for equivalent dose (the external-source, whole-body exposure effects, in a uniform field), and effective dose (which depends on the body parts irradiated).
These dose quantities are weighted averages of absorbed dose designed to be representative of the stochastic health effects of radiation, and use of the sievert implies that appropriate weighting factors have been applied to the absorbed dose measurement or calculation (expressed in grays).
The ICRP calculation provides two weighting factors to enable the calculation of protection quantities.
When a whole body is irradiated uniformly only the radiation weighting factor WR is used, and the effective dose equals the whole body equivalent dose. But if the irradiation of a body is partial or non-uniform the tissue factor WT is used to calculate dose to each organ or tissue. These are then summed to obtain the effective dose. In the case of uniform irradiation of the human body, these summate to 1, but in the case of partial or non-uniform irradiation, they will summate to a lower value depending on the organs concerned; reflecting the lower overall health effect. The calculation process is shown on the accompanying diagram. This approach calculates the biological risk contribution to the whole body, taking into account complete or partial irradiation, and the radiation type or types. The values of these weighting factors are conservatively chosen to be greater than the bulk of experimental values observed for the most sensitive cell types, based on averages of those obtained for the human population.
Since different radiation types have different biological effects for the same deposited energy, a corrective radiation weighting factor WR, which is dependent on the radiation type and on the target tissue, is applied to convert the absorbed dose measured in the unit gray to determine the equivalent dose. The result is given the unit sievert.
|Radiation||Energy (E)||WR (formerly Q)|
|x-rays, gamma rays,
beta particles, muons
|neutrons||< 1 MeV||2.5 + 18.2·e−[ln(E)]²/6|
|1 MeV - 50 MeV||5.0 + 17.0·e−[ln(2·E)]²/6|
|> 50 MeV||2.5 + 3.25·e−[ln(0.04·E)]²/6|
|protons, charged pions||2|
Nuclear fission products,
The equivalent dose is calculated by multiplying the absorbed energy, averaged by mass over an organ or tissue of interest, by a radiation weighting factor appropriate to the type and energy of radiation. To obtain the equivalent dose for a mix of radiation types and energies, a sum is taken over all types of radiation energy dose.
Thus for example, an absorbed dose of 1 Gy by alpha particles will lead to an equivalent dose of 20 Sv.
This may seem to be a paradox. It implies that the energy of the incident radiation field in joules has increased by a factor of 20, thereby violating the laws of Conservation of energy. However, this is not the case. The sievert is used only to convey the fact that a gray of absorbed alpha particles would cause twenty times the biological effect of a gray of absorbed x-rays. It is this biological component that is being expressed when using sieverts rather than the actual energy delivered by the incident absorbed radiation.
The second weighting factor is the tissue factor WT, but it is used only if there has been non-uniform irradiation of a body. If the body has been subject to uniform irradiation, the effective dose equals the whole body equivalent dose, and only the radiation weighting factor WR is used. But if there is partial or non-uniform body irradiation the calculation must take account of the individual organ doses received, because the sensitivity of each organ to irradiation depends on their tissue type. This summed dose from only those organs concerned gives the effective dose for the whole body. The tissue weighting factor is used to calculate those individual organ dose contributions.
The ICRP values for WT are given in the table shown here.
|Organs||Tissue weighting factors|
|Red bone marrow||0.12||0.12||0.12|
|Remainder of body||0.30||0.05||0.12|
The article on effective dose gives the method of calculation. The absorbed dose is first corrected for the radiation type to give the equivalent dose, and then corrected for the tissue receiving the radiation. Some tissues like bone marrow are particularly sensitive to radiation, so they are given a weighting factor that is disproportionally large relative to the fraction of body mass they represent. Other tissues like the hard bone surface are particularly insensitive to radiation and are assigned a disproportionally low weighting factor.
In summary, the sum of tissue-weighted doses to each irradiated organ or tissue of the body adds up to the effective dose for the body. The use of effective dose enables comparisons of overall dose received regardless of the extent of body irradiation.
The operational quantities are used in practical applications for monitoring and investigating external exposure situations. They are defined for practical operational measurements and assessment of doses in the body. Three external operational dose quantities were devised to relate operational dosimeter and instrument measurements to the calculated protection quantities. Also devised were two phantoms, The ICRU "slab" and "sphere" phantoms which relate these quantities to incident radiation quantities using the Q(L) calculation.
This is used for area monitoring of penetrating radiation and is usually expressed as the quantity H*(10). This means the radiation is equivalent to that found 10 mm within the ICRU sphere phantom in the direction of origin of the field. An example of penetrating radiation is gamma rays.
This is used for monitoring of low penetrating radiation and is usually expressed as the quantity H'(0.07). This means the radiation is equivalent to that found at a depth of 0.07 mm in the ICRU sphere phantom. Examples of low penetrating radiation are alpha particles, beta particles and low-energy photons. This dose quantity is used for the determination of equivalent dose to such as the skin, lens of the eye. In radiological protection practice value of omega is usually not specified as the dose is usually at a maximum at the point of interest.
This is used for individual dose monitoring, such as with a personal dosimeter worn on the body. The recommended depth for assessment is 10 mm which gives the quantity Hp(10).
In order to simplify the means of calculating operational quantities, and assist in the comprehension of radiation dose protection quantities, ICRP Committee 2 & ICRU Report Committee 26 started in 2010 an examination of different means of achieving this by dose coefficients related to Effective Dose or Absorbed Dose.
1. For area monitoring of effective dose of whole body it would be:
H = Φ × conversion coefficient
The driver for this is that H∗(10) is not a reasonable estimate of effective dose due to high energy photons, as a result of the extension of particle types and energy ranges to be considered in ICRP report 116. This change would remove the need for the ICRU sphere and introduce a new quantity called Emax
2. For individual monitoring, to measure deterministic effects on eye lens and skin, it would be:
D = Φ × conversion coefficient for absorbed dose.
The driver for this is the need to measure the deterministic effect, which it is suggested, is more appropriate than stochastic effect. This would calculate equivalent dose quantities Hlens and Hskin.
This would remove the need for the ICRU Sphere and the Q-L function. Any changes would replace ICRU report 51, and part of report 57.
A final draft report was issued in July 2017 by ICRU/ICRP for consultation.
The sievert is used for human internal dose quantities in calculating committed dose. This is dose from radionuclides which have been ingested or inhaled into the human body, and thereby "committed" to irradiate the body for a period of time. The concepts of calculating protection quantities as described for external radiation applies, but as the source of radiation is within the tissue of the body, the calculation of absorbed organ dose uses different coefficients and irradiation mechanisms.
The ICRP defines Committed effective dose, E(t) as the sum of the products of the committed organ or tissue equivalent doses and the appropriate tissue weighting factors WT, where t is the integration time in years following the intake. The commitment period is taken to be 50 years for adults, and to age 70 years for children.
The ICRP further states "For internal exposure, committed effective doses are generally determined from an assessment of the intakes of radionuclides from bioassay measurements or other quantities (e.g., activity retained in the body or in daily excreta). The radiation dose is determined from the intake using recommended dose coefficients".
A committed dose from an internal source is intended to carry the same effective risk as the same amount of equivalent dose applied uniformly to the whole body from an external source, or the same amount of effective dose applied to part of the body.
Ionizing radiation has deterministic and stochastic effects on human health. Deterministic (acute tissue effect) events happen with certainty, with the resulting health conditions occurring in every individual who received the same high dose. Stochastic (cancer induction and genetic) events are inherently random, with most individuals in a group failing to ever exhibit any causal negative health effects after exposure, while an indeterministic random minority do, often with the resulting subtle negative health effects being observable only after large detailed epidemiology studies.
The use of the sievert implies that only stochastic effects are being considered, and to avoid confusion deterministic effects are conventionally compared to values of absorbed dose expressed by the SI unit gray (Gy).
Stochastic effects are those that occur randomly, such as radiation-induced cancer. The consensus of nuclear regulators, governments and the UNSCEAR is that the incidence of cancers due to ionizing radiation can be modeled as increasing linearly with effective dose at a rate of 5.5% per sievert. This is known as the Linear no-threshold model (LNT model). Some commentators such as the French Academy of Sciences (2005, Dose-effect relationships and...Tubiana, M. and Aurengo, A. Académie des Sciences & Académie Nationale de Médecine. (2005) www.researchgate.net/publication/277289357) and Oxford University (Wade Allison, 2015, Nuclear is for Life, pp79–80, ISBN 978-0-9562756-4-6) argue that this LNT model is now outdated and should be replaced with a threshold below which the body's natural cell processes repair damage and/or replace damaged cells. There is general agreement that the risk is much higher for infants and fetuses than adults, higher for the middle-aged than for seniors, and higher for women than for men, though there is no quantitative consensus about this.
The deterministic (acute tissue damage) effects that can lead to acute radiation syndrome only occur in the case of acute high doses (≳ 0.1 Gy) and high dose rates (≳ 0.1 Gy/h) and are conventionally not measured using the unit sievert, but use the unit gray (Gy). A model of deterministic risk would require different weighting factors (not yet established) than are used in the calculation of equivalent and effective dose.
The ICRP recommends a number of limits for dose uptake in table 8 of report 103. These limits are "situational", for planned, emergency and existing situations. Within these situations, limits are given for the following groups;
For occupational exposure, the limit is 50 mSv in a single year with a maximum of 100 mSv in a consecutive five-year period, and for the public to an average of 1 mSv (0.001 Sv) of effective dose per year, not including medical and occupational exposures.
For comparison, natural radiation levels inside the US capitol building are such that a human body would receive an additional dose rate of 0.85 mSv/a, close to the regulatory limit, because of the uranium content of the granite structure. According to the conservative ICRP model, someone who spent 20 years inside the capitol building would have an extra one in a thousand chance of getting cancer, over and above any other existing risk (calculated as: 20 a·0.85 mSv/a·0.001 Sv/mSv·5.5%/Sv ≈ 0.1%). However, that "existing risk" is much higher; an average American would have a 10% chance of getting cancer during this same 20-year period, even without any exposure to artificial radiation (see natural Epidemiology of cancer and cancer rates). These estimates are, however, unmindful of every living cell's natural repair mechanisms, evolved over a few billion years of exposure to environmental chemical and radiation threats that were higher in the past, and exaggerated by the evolution of oxygen metabolism.
Significant radiation doses are not frequently encountered in everyday life. The following examples can help illustrate relative magnitudes; these are meant to be examples only, not a comprehensive list of possible radiation doses. An "acute dose" is one that occurs over a short and finite period of time, while a "chronic dose" is a dose that continues for an extended period of time so that it is better described by a dose rate.
|98||nSv:||banana equivalent dose, an illustrative unit of radiation dose representing the measure of radiation from a typical banana[a]|
|250||nSv:||U.S. limit on effective dose from a single airport security screening|
|5–10||μSv:||one set of dental radiographs|
|80||μSv:||average dose to people living within 10 mi (16 km) of Three Mile Island accident|
|400–600||μSv:||two-view mammogram, using weighting factors updated in 2007|
|1||mSv:||U.S. 10 CFR § 20.1301(a)(1) dose limit for individual members of the public, total effective dose equivalent, per annum|
|1.5–1.7||mSv:||annual dose for flight attendants|
|2–7||mSv:||barium fluoroscopy, e.g. Barium meal, up to 2 minutes, 4–24 spot images|
|10–30||mSv:||single full-body CT scan|
|50||mSv:||U.S. 10 C.F.R. § 20.1201(a)(1)(i) occupational dose limit, total effective dose equivalent, per annum|
|68||mSv:||estimated maximum dose to evacuees who lived closest to the Fukushima I nuclear accidents|
|80||mSv:||6-month stay on the International Space Station|
|160||mSv:||chronic dose to lungs over one year smoking 1.5 packs of cigarettes per day, mostly due to inhalation of Polonium-210 and Lead-210|
|250||mSv:||6-month trip to Mars — radiation due to cosmic rays, which are very difficult to shield against|
|500||mSv:||the U.S. 10 C.F.R. § 20.1201(a)(2)(ii) occupational dose limit, shallow-dose equivalent to skin, per annum|
|670||mSv:||highest dose received by a worker responding to the Fukushima emergency[a]|
|1||Sv:||maximum allowed radiation exposure for NASA astronauts over their career|
|4–5||Sv:||dose required to kill a human with a 50% risk within 30 days (LD50/30), if the dose is received over a very short duration|
|4.5–6||Sv:||fatal acute doses during Goiânia accident|
|5.1||Sv:||fatal acute dose to Harry Daghlian in 1945 criticality accident|
|10 to 17||Sv:||fatal acute doses during Tokaimura nuclear accident. Hisashi Ouchi who received 17 Sv was kept alive for 83 days after the accident.|
|21||Sv:||fatal acute dose to Louis Slotin in 1946 criticality accident|
|36||Sv:||fatal acute dose to Cecil Kelley in 1958, death occurred within 35 hours.|
|54||Sv:||fatal acute dose to Boris Korchilov in 1961 after a reactor cooling system failed on the Soviet submarine K-19 which required work in the reactor with no shielding|
|64||Sv:||nonfatal dose to Albert Stevens spread over ≈21 years, due to a 1945 plutonium injection experiment by doctors working on the secret Manhattan Project.[a]|
All conversions between hours and years have assumed continuous presence in a steady field, disregarding known fluctuations, intermittent exposure and radioactive decay. Converted values are shown in parentheses.
|<1||mSv/a||<100||nSv/h||Steady dose rates below 100 nSv/h are difficult to measure.|
|1||mSv/a||(100||nSv/h avg)||ICRP recommended maximum for external irradiation of the human body, excluding medical and occupational exposures.|
|2.4||mSv/a||(270||nSv/h avg)||Human exposure to natural background radiation, global average[a]|
|24||mSv/a||(2.7||μSv/h avg)||Natural background radiation at airline cruise altitude[b]|
|130||mSv/a||(15||μSv/h avg)||Ambient field inside most radioactive house in Ramsar, Iran[c]|
|(800||mSv/a)||90||μSv/h||Natural radiation on a monazite beach near Guarapari, Brazil.|
|(9||Sv/a)||1||mSv/h||NRC definition of a high radiation area in a nuclear power plant, warranting a chain-link fence|
|2–20||mSv/h||Typical dose rate for activated reactor wall in possible future fusion reactors after 100 years. After approximately 300 years of decay the fusion waste would produce the same dose rate as exposure to coal ash, with the volume of fusion waste naturally being orders of magnitude less than from coal ash. Immediate predicted activation is 90 MGy/a.|
|(1.7||kSv/a)||190||mSv/h||Highest reading from fallout of the Trinity bomb, 20 mi (32 km) away, 3 hours after detonation.[c]|
|(2.3||MSv/a)||270||Sv/h||typical PWR spent fuel bundle, after 10-year cooldown, no shielding|
|(4.6–5.6||MSv/a)||530–650||Sv/h||The radiation level inside the primary containment vessel of the second BWR-reactor of the Fukushima power station, as of February 2017, six years after a suspected meltdown. In this environment, it takes between 22 to 34 seconds to accumulate a median lethal dose (LD50/30).|
Notes on examples:
The sievert has its origin in the röntgen equivalent man (rem) which was derived from CGS units. The International Commission on Radiation Units and Measurements (ICRU) promoted a switch to coherent SI units in the 1970s, and announced in 1976 that it planned to formulate a suitable unit for equivalent dose. The ICRP pre-empted the ICRU by introducing the sievert in 1977.
The sievert was adopted by the International Committee for Weights and Measures (CIPM) in 1980, five years after adopting the gray. The CIPM then issued an explanation in 1984, recommending when the sievert should be used as opposed to the gray. That explanation was updated in 2002 to bring it closer to the ICRP's definition of equivalent dose, which had changed in 1990. Specifically, the ICRP had introduced equivalent dose, renamed the quality factor (Q) to radiation weighting factor (WR), and dropped another weighting factor 'N' in 1990. In 2002, the CIPM similarly dropped the weighting factor 'N' from their explanation but otherwise kept other old terminology and symbols. This explanation only appears in the appendix to the SI brochure and is not part of the definition of the sievert.
This SI unit is named after Rolf Maximilian Sievert. As with every International System of Units (SI) unit named for a person, the first letter of its symbol is upper case (Sv). However, when an SI unit is spelled out in English, it is treated as a common noun and should always begin with a lower case letter (sievert)—except in a situation where any word in that position would be capitalized, such as at the beginning of a sentence or in material using title case.
Frequently used SI prefixes are the millisievert (1 mSv = 0.001 Sv) and microsievert (1 μSv = 0.000001 Sv) and commonly used units for time derivative or "dose rate" indications on instruments and warnings for radiological protection are μSv/h and mSv/h. Regulatory limits and chronic doses are often given in units of mSv/a or Sv/a, where they are understood to represent an average over the entire year. In many occupational scenarios, the hourly dose rate might fluctuate to levels thousands of times higher for a brief period of time, without infringing on the annual limits. The conversion from hours to years varies because of leap years and exposure schedules, but approximate conversions are:
Conversion from hourly rates to annual rates is further complicated by seasonal fluctuations in natural radiation, decay of artificial sources, and intermittent proximity between humans and sources. The ICRP once adopted fixed conversion for occupational exposure, although these have not appeared in recent documents:
Therefore, for occupation exposures of that time period,
The following table shows radiation quantities in SI and non-SI units:
|Activity (A)||curie||Ci||3.7 × 1010 s−1||1953||3.7×1010 Bq|
|rutherford||Rd||106 s−1||1946||1,000,000 Bq|
|Exposure (X)||röntgen||R||esu / 0.001293 g of air||1928||2.58 × 10−4 C/kg|
|Fluence (Φ)||(reciprocal area)||m−2||1962||m−2|
|Absorbed dose (D)||erg||erg⋅g−1||1950||1.0 × 10−4 Gy|
|rad||rad||100 erg⋅g−1||1953||0.010 Gy|
|Dose equivalent (H)||röntgen equivalent man||rem||100 erg⋅g−1||1971||0.010 Sv|
|sievert||Sv||J⋅kg−1 × WR||1977||SI|
Although the United States Nuclear Regulatory Commission permits the use of the units curie, rad, and rem alongside SI units, the European Union European units of measurement directives required that their use for "public health ... purposes" be phased out by 31 December 1985.
|100.0000 rem||=||100,000.0 mrem||=||1 Sv||=||1.000000 Sv||=||1000.000 mSv||=||1,000,000 µSv|
|1.0000 rem||=||1000.0 mrem||=||1 rem||=||0.010000 Sv||=||10.000 mSv||=||10000 µSv|
|0.1000 rem||=||100.0 mrem||=||1 mSv||=||0.001000 Sv||=||1.000 mSv||=||1000 µSv|
|0.0010 rem||=||1.0 mrem||=||1 mrem||=||0.000010 Sv||=||0.010 mSv||=||10 µSv|
|0.0001 rem||=||0.1 mrem||=||1 µSv||=||0.000001 Sv||=||0.001 mSv||=||1 µSv|
In 1991, the International Commission on Radiological Protection (ICRP)  recommended a revised system of dose limitation, including specification of primary limiting quantities for radiation protection purposes. These protection quantities are essentially unmeasurable
dose rates of 2-20 mSv/h, typical of plasma facing components after intermediate storage for up to 100 years
The men's decathlon event at the 1932 Olympic Games took place between August 5 & August 6. Points are listed by the scoring table from 1912 which were used to determine the winner. Adjusted points are points using the 1985 scoring table. The official Olympic results shows both results, but medal winners were determined by the 1912 scoring table.Carl Richard Nyberg
Carl Richard Nyberg (May 28, 1858, – 1939) was the founder of Max Sieverts Lödlampfabrik, then one of the largest industries in Sundbyberg, Sweden. Nyberg was born in Arboga. After school he started working for a jeweller and later he moved to Stockholm and worked with various metalworks. He later got work at J. E. Eriksons mekaniska verkstad (later renamed to "Mekanikus").It was while working there that he formulated the idea of the blowtorch. He later worked on the idea and created a blowtorch with strong, directed heat and also with several safety measures built in. He quit his work at Mekanikus in 1882 and set up a workshop at Luntmakargatan in Stockholm making blowtorches. However the business didn't work well because it took too long to both manufacture and sell them. For a time he made a living selling rings supposedly for curing gout. In 1884 he moved his workshop to Sundbyberg. In 1886, he met Max Sievert at a country fair and Sievert became interested in Nyberg's blowtorch and started selling it. After encouragement by the owner of Sundbyberg gård he started AB Alpha and after encouragement from L. M. Ericsson he started producing wire.After Primus started producing blowtorches he also decided to make paraffin oil/kerosene cookers. The first model, called Viktoria, wasn't very successful, but the later Svea did better. He delivered many to Russia and soon he produced 3000 per week. In 1906 the company was changed into a stock company. He was quite generous towards his workers and often gave them stock in the company. The workers became known as "Nybergs snobbar" (Nyberg's snobs) because they were generally better off than those who worked in other places. In 1922 the company was sold to Max Sievert who continued to own it until 1964 when it was bought by Esso.
Nyberg also worked on many other inventions, for instance steam engines, aeroplanes, boat propellers and various other machines. He was most famous as an aviation pioneer and he became known as "Flyg-Nyberg" (Flying-Nyberg). From 1897 and onward until around 1910, outside his home in Lidingö he built and tested his Flugan (The Fly) on a circular wood track in his garden and on the ice during the wintertime. However, due the lack of small effective gasoline engines at that time, he only managed a few short jumps. He worked hard with the help of professor J.E. Cederblom at KTH in the development of wing profiles but did not succeed to get The Fly in the air. He also designed and built his own wind tunnel to be able to make test of small wing models. The Fly had a wingspan of 5 meters, and the surface area of the wings was 13 m². The engine was a steam engine of his own design, with a boiler heated by four of his blowtorches. It produced a maximum of 10 hp (7 kW) at 2000 rpm. The total weight of the plane was 80 kg.Committed dose
The committed dose in radiological protection is a measure of the stochastic health risk due to an intake of radioactive material into the human body. Stochastic in this context is defined as the probability of cancer induction and genetic damage, due to low levels of radiation. The SI unit of measure is the sievert.
A committed dose from an internal source represents the same effective risk as the same amount of effective dose applied uniformly to the whole body from an external source, or the same amount of equivalent dose applied to part of the body. The committed dose is not intended as a measure for deterministic effects such as radiation sickness which is defined as the severity of a health effect which is certain to happen.
The radiation risk proposed by the International Commission on Radiological Protection (ICRP) predicts that an effective dose of one sievert carries a 5.5% chance of developing cancer. Such a risk is the sum of both internal and external radiation dose.Counts per minute
The measurement of ionizing radiation is sometimes expressed as being a rate of counts per unit time as registered by a radiation monitoring instrument, for which counts per minute (cpm) and counts per second (cps) are commonly used quantities.
Count rate measurements are associated with the detection of particles, such as alpha particles and beta particles. However, for gamma ray and X-ray dose measurements a unit such as the sievert is normally used.
Both cpm and cps are the rate of detection events registered by the measuring instrument, not the rate of emission from the source of radiation. For radioactive decay measurements it must not be confused with disintegrations per unit time (dpm), which represents the rate of atomic disintegration events at the source of the radiation.Equivalent dose
Equivalent dose is a dose quantity H representing the stochastic health effects of low levels of ionizing radiation on the human body which represents the probability of radiation-induced cancer and genetic damage. It is derived from the physical quantity absorbed dose, but also takes into account the biological effectiveness of the radiation, which is dependent on the radiation type and energy. In the SI system of units, the unit of measure is the sievert (Sv).Gray (unit)
The gray (symbol: Gy) is a derived unit of ionizing radiation dose in the International System of Units (SI). It is defined as the absorption of one joule of radiation energy per kilogram of matter.It is used as a unit of the radiation quantity absorbed dose which measures the energy deposited by ionizing radiation in a unit mass of matter being irradiated, and is used for measuring the delivered dose of ionising radiation in applications such as radiotherapy, food irradiation and radiation sterilization. As a measure of low levels of absorbed dose, it also forms the basis for the calculation of the radiation protection unit the sievert, which is a measure of the health effect of low levels of ionizing radiation on the human body.
The gray is also used in radiation metrology as a unit of the radiation quantity kerma; defined as the sum of the initial kinetic energies of all the charged particles liberated by uncharged ionizing radiation in a sample of matter per unit mass. The gray is an important unit in ionising radiation measurement and was named after British physicist Louis Harold Gray, a pioneer in the measurement of X-ray and radium radiation and their effects on living tissue.The gray was adopted as part of the International System of Units in 1975. The corresponding cgs unit to the gray is the rad (equivalent to 0.01 Gy), which remains common largely in the United States, though "strongly discouraged" in the style guide for U.S. National Institute of Standards and Technology authors.Hans-Heinrich Sievert
Hans Heinrich Sievert (1909–1963) was a German Olympic decathlete. He competed at the 1932 Summer Olympics and the 1936 Summer Olympics.In 1934 he became the last decathlon world record holder under the 1915 method of scoring, with 8790.46 points, and won the gold medal at the 1934 European Championships. In the Nazi period in Germany, Sievert was seen as a symbolic hope of the German "master race" in the 1936 Summer Olympics. However, he was injured during the games and the gold medal was won by American Glenn Morris, who also beat Sievert's record. Sievert was recommended to leave the sport after his injury.In World War II, Sievert became an officer of the German armed forces. In Hungary in 1944, he lost his left foot to a land mine. After the war, Sievert became the chairman of Hamburg's track-and-field event federation and a sport advisor to the German government. He became ill in 1957 and quit his work, moving into the home of his father in Eutin. He married Ruth Hagemann, a fellow athlete that Sievert met while training in the 1930s, and had two daughters who also became athletes.José Joaquín Chaverri Sievert
José Joaquín Chaverri Sievert (born August 30, 1949) is a Costa Rican diplomat. In 2005 he was appointed Director of Foreign Policy of the Ministry of Foreign Affairs. He has also served as Costa Rican ambassador to Germany, Denmark and Czechoslovakia.Orders of magnitude (radiation)
Recognized effects of higher acute radiation doses are described in more detail in the article on radiation poisoning. Although the International System of Units (SI) defines the sievert (Sv) as the unit of radiation dose equivalent, chronic radiation levels and standards are still often given in units of millirems (mrem), where 1 mrem equals 1/1000 of a rem and 1 rem equals 0.01 Sv. Light radiation sickness begins at about 50–100 rad (0.5–1 gray (Gy), 0.5–1 Sv, 50–100 rem, 50,000–100,000 mrem).
The following table includes some dosages for comparison purposes, using millisieverts (mSv) (one thousandth of a sievert). The concept of radiation hormesis is relevant to this table – radiation hormesis is a hypothesis stating that the effects of a given acute dose may differ from the effects of an equal fractionated dose. Thus 100 mSv is considered twice in the table below – once as received over a 5-year period, and once as an acute dose, received over a short period of time, with differing predicted effects. The table describes doses and their official limits, rather than effects.Roentgen (unit)
The roentgen or röntgen () (symbol R) is a legacy unit of measurement for the exposure of X-rays and gamma rays. It is defined as the electric charge freed by such radiation in a specified volume of air divided by the mass of that air.
In 1928 it was the first international measurement quantity for ionising radiation to be defined for radiation protection, and was an easily replicated method of measuring air ionization directly by using an ion chamber. It is named after the German physicist Wilhelm Röntgen, who discovered X-rays.
Although relatively easy to measure, the roentgen had the disadvantage that it was only a measure of air ionisation and not a direct measure of radiation absorption in other materials. As the science of radiation dosimetry developed, it was realised that the ionising effect, and hence tissue damage, was linked to energy absorbed, not just radiation exposure. Consequently new radiometric units for radiation protection were defined which took this into account. In 1953 the International Commission on Radiation Units and Measurements (ICRU) recommended the rad, equal to 100 erg/g, as the unit of measure of the new radiation quantity absorbed dose. The rad was expressed in coherent cgs units.
In 1975 the unit gray was named as the SI unit of absorbed dose. The gray was equal to 100 rad, the cgs unit.
Additonally, a new quantity Kerma was defined for air ionisation, and is the modern metrological, but not radiation protection, successor to the roengten, and from this the absorbed dose can be calculated using known coefficients for specific target materials. In radiation protection the absorbed dose is the energy absorption which is an indication of likely acute tissue effects occurring at high dose rates, and from low levels of absorbed dose the equivalent dose, representing the stochastic health risk, can be calculated; for which the current SI units used are the gray (Gy) and the sievert (Sv) respectively.
The roengten has been redefined over the years. It was last defined by the US National Institute of Standards and Technology (NIST) in 1998 as 2.58×10−4 C/kg, with a recommendation that the definition be given in every document where the roentgen is used. One roentgen deposits 0.00877 grays (0.877 rads) of absorbed dose in dry air, or 0.0096 Gy (0.96 rad) in soft tissue. One roentgen of X-rays may deposit anywhere from 0.01 to 0.04 Gy (1.0 to 4.0 rad) in bone depending on the beam energy. This tissue-dependent conversion from kerma to absorbed dose is called the F-factor in radiotherapy contexts. The conversion depends on the ionizing energy of a reference medium, which is ambiguous in the latest NIST definition.Roentgen equivalent man
The roentgen equivalent man (or rem) is an older, CGS unit of equivalent dose, effective dose, and committed dose which are measures of the health effect of low levels of ionizing radiation on the human body.
Quantities measured in rem are designed to represent the stochastic biological risk of ionizing radiation; primarily radiation-induced cancer. These quantities are derived from absorbed dose, which in the CGS system has the unit rad which is also an older unit. There is no universally applicable conversion constant from rad to rem; the conversion depends on relative biological effectiveness (RBE).
The rem has been defined since 1976 as equal to 0.01 sievert, which is the more commonly used SI unit outside the United States. A number of earlier definitions going back to 1945 were derived from the roentgen unit, which was named after Wilhelm Röntgen, a German scientist who discovered X-rays. The acronym is now a misleading historical artifact, since 1 roentgen actually deposits about 0.96 rem in soft biological tissue, when all weighting factors equal unity. Older units of rem following other definitions are up to 17% smaller than the modern rem.
One rem carries with it a 0.05% chance of eventually developing cancer. Doses greater than 100 rem received over a short time period are likely to cause acute radiation syndrome (ARS), possibly leading to death within weeks if left untreated. Note that the quantities that are measured in rem were not designed to be correlated to ARS symptoms. The absorbed dose, measured in rad, is the best indicator of ARS.A rem is a large dose of radiation, so the millirem (mrem), which is one thousandth of a rem, is often used for the dosages commonly encountered, such as the amount of radiation received from medical x-rays and background sources.Rolf Maximilian Sievert
Rolf Maximilian Sievert (Swedish: [ˈrɔlf maksɪˈmiːlɪan ˈsiːvɛʈ]; 6 May 1896 – 3 October 1966) was a Swedish medical physicist whose major contribution was in the study of the biological effects of ionizing radiation.
Sievert was born in Stockholm, Sweden. He served as head of the physics laboratory at Sweden's Radiumhemmet from 1924 to 1937, when he became head of the department of radiation physics at the Karolinska Institute. He played a pioneering role in the measurement of doses of radiation especially in its use in the diagnosis and treatment of cancer. In later years, he focused his research on the biological effects of repeated exposure to low doses of radiation. In 1964, he founded the International Radiation Protection Association, serving for a time as its chairman. He also chaired the United Nations Scientific Committee on the Effects of Atomic Radiation.
He invented a number of instruments for measuring radiation doses, the most widely known being the Sievert chamber.
In 1979, at the Conférence Générale des Poids et Mesures (General Conference on Weights and Measures or CGPM), the SI unit for ionizing radiation dose equivalent was named after him and given the name sievert (Sv).Ruth Siewert
Ruth Siewert (also Sievert-Schnaudt, Sievert; 1915 – July 2002) was a German contralto and voice teacher. She performed roles by Richard Wagner at major opera houses in Europe and at the Bayreuth Festival, and was known as a singer of oratorio and Lied.Sievert Allen Rohwer
Sievert Allen Rohwer (22 December 1887 in Telluride – 12 February 1951) was an American entomologist who specialized in Hymenoptera. He was a graduate of the University of Colorado. At the time of his death, Rohwer was serving as the Coordinator Defense Activities for the Agricultural Research Administration within the U.S. Department of Agriculture. Rohwer worked for the USDA from 1909 until his death.Rohwer wrote Technical papers on miscellaneous forest insects. II. The genotypes of the sawflies or woodwasps, or the superfamily Tenthredinoidea. Technical series US Department of Agriculture, Bureau of Entomology, Washington, DC 20: 69–109 (1911) and very many papers describing new species of Hymenoptera. His collection is held by the Smithsonian Institution Washington D. C.Sievert chamber
A Sievert chamber is a type of ionization chamber used in radiation dose measurements. It was invented by Professor Rolf Maximilian Sievert in Sweden in the years 1920-40.Sievert integral
The Sievert integral, named after Swedish medical physicist Rolf Sievert, is a special function commonly encountered in radiation transport calculations.
It plays a role in the sievert (symbol: Sv) unit of ionizing radiation dose in the International System of Units (SI).Svedberg
A Svedberg unit (symbol S, sometimes Sv) is a non-metric unit for sedimentation coefficient. The Svedberg unit (S) offers a measure of a particle's size based on its sedimentation rate, i.e. how fast a particle of given size and shape 'settles' to the bottom of a solution. The Svedberg is a measure of time, defined as exactly 10−13 seconds (100 fs).
For biological molecules, sedimentation rate is typically measured as the rate of travel in a centrifuge tube subjected to high g-force.The Svedberg (S) is distinct from the SI unit sievert or the non-SI unit sverdrup, which also use the symbol Sv.Sverdrup
In oceanography, a sverdrup (symbol: Sv) is a non-SI unit of flow, with 1 Sv equal to 1,000,000 cubic metres per second (264,000,000 USgal/s); it is equivalent to the SI derived unit cubic hectometer per second (symbol: hm³/s or hm³⋅s⁻¹). It is used almost exclusively in oceanography to measure the volumetric rate of transport of ocean currents. It is named after Harald Sverdrup. It is distinct from the SI unit sievert or the non-SI svedberg, which use the same symbol.
In the context of ocean currents, one million cubic meters per second may be most easily imagined as a "slice" of ocean, 1 km wide x 1 km deep x 1 m thick. At this scale, these units can be more easily compared in terms of width of the current (several km), depth (hundreds of meters), and current speed (as meters per second). Thus, a hypothetical current 50 km wide, 500 m (0.5 km) deep, and moving at 2 m/s would transport 50 Sv of water.
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Radiation (physics and health)
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