Editing Sievert

{{Short description|Derived SI unit of equivalent dose of ionizing radiation}}
{{Other uses}}
{{Use dmy dates|date=June 2020}}
{{Infobox Unit
| bgcolour      = 
| name          = sievert
| image         = File:展望の宿 天神 2016 (26182596995).jpg
| caption       = Display of [[background radiation]] in a hotel at [[Naraha, Fukushima|Naraha]], Japan, showing dose rate in microsieverts per hour, five years after the [[Fukushima Daiichi nuclear disaster|Fukushima disaster]]
| standard      = [[SI]]
| quantity      = Stochastic health effect of ionizing radiation ([[equivalent dose]])
| symbol        = Sv
| dimension     = 
| namedafter    = [[Rolf Maximilian Sievert]]
| units1        = [[SI base unit]]s
| inunits1      = [[metre|m]]<sup>2</sup>⋅[[second|s]]<sup>−2</sup>
| units2        = Sv indicates absorbed dose modified by weighting factors.
| inunits2      = [[joule|J]]⋅[[kilogram|kg]]<sup>−1</sup>
| units3        = [[CGS]] units (non-SI)
| inunits3      = 100 [[Roentgen equivalent man|rem]]
}}
The '''sievert''' (symbol: '''Sv'''<ref group="note">Please note there are two non-SI units that use the same Sv abbreviation: the [[sverdrup]] and [[svedberg]].</ref>) is a derived unit in the [[International System of Units]] (SI) intended to represent the [[stochastic]] health risk of [[ionizing radiation]], which is defined as the probability of causing radiation-induced cancer and genetic damage. The sievert is important in [[dosimetry]] and [[radiation protection]]. It 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 unit is used for radiation dose quantities such as [[equivalent dose]] and [[effective dose (radiation)|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. According to the [[International Commission on Radiological Protection]] (ICRP), one sievert results in a 5.5% [[probability]] of eventually developing fatal cancer based on the disputed [[linear no-threshold model]] of ionizing radiation exposure.<ref name="ICRP103" /><ref>Based on the linear no-threshold model, the ICRP says, "In the low dose range, below about 100 mSv, it is scientifically plausible to assume that the incidence of cancer or heritable effects will rise in direct proportion to an increase in the equivalent dose in the relevant organs and tissues." ICRP publication 103 paragraph 64.</ref>

To calculate the value of stochastic health risk in sieverts, the physical quantity [[absorbed dose]] is converted into equivalent dose and effective dose by applying factors for radiation type and biological context, published by the ICRP and the [[International Commission on Radiation Units and Measurements]] (ICRU).  One sievert equals 100 [[Roentgen equivalent man|rem]], which is an older, [[Centimetre–gram–second system of units|CGS]] radiation unit. 

Conventionally, deterministic health effects due to acute tissue damage that is certain to happen, produced by high dose rates of radiation, are compared to the physical quantity absorbed dose measured by the unit [[gray (unit)|gray]] (Gy).<ref>ICRP report 103 para 104 and 105.</ref>

==Definition==

===CIPM definition of the sievert===

The SI definition given by the [[CIPM|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 [[International Commission on Radiation Units and Measurements|ICRU]]"

:''H'' = ''Q'' × ''D''<ref name="CIPM, 2002: Recommendation 2">{{citation |title=CIPM, 2002: Recommendation 2 |url=http://www.bipm.org/en/CIPM/db/2002/2/ |year=2000 |publisher=BIPM}}</ref>

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''".<ref name="CIPM, 2002: Recommendation 2"/>

In summary:

:'''gray''': quantity ''D''—absorbed dose
::1&nbsp;Gy = 1&nbsp;joule/kilogram—a physical quantity. 1&nbsp;Gy is the deposit of a joule of radiation energy per kilogram of matter or tissue.

:'''sievert''': quantity ''H''—equivalent dose
::1&nbsp;Sv = 1&nbsp;joule/kilogram—a biological effect. The sievert represents the equivalent biological effect of the deposit of a joule of radiation energy in a kilogram of human tissue. The ratio to absorbed dose is denoted by ''Q''.

===ICRP definition of the sievert===
The ICRP definition of the sievert is:<ref name="ICRP publication 103 - Glossary">ICRP publication 103 - Glossary.</ref>
: "The sievert is the special name for the SI unit of equivalent dose, effective dose, and operational dose quantities. The unit is joule per kilogram."

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.

==External dose quantities==
[[File:Dose quantities and units.png|thumb|upright=1.8|External radiation dose quantities used in radiological protection]]
When the sievert is used to represent the stochastic effects of external ionizing radiation on human tissue, the radiation doses received are measured in practice by radiometric instruments and [[dosimeters]] and are called operational quantities. To relate these actual received doses to likely health effects, protection quantities have been developed to predict the likely health effects using the results of large epidemiological studies. Consequently, this 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.

===Naming conventions===
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<ref>ICRP publication 60 published in 1991</ref> 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''.<ref name="endo" />

In the [[United States|USA]] there are differently named dose quantities which are not part of the ICRP nomenclature.<ref>[http://www.wmsym.org/archives/2009/pdfs/9444.pdf "The confusing world of radiation dosimetry"] - M.A. Boyd, U.S. Environmental Protection Agency 2009. An account of chronological differences between US and ICRP dosimetry systems.</ref>

===Physical quantities===
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 (physics)|kerma]] is the ionising effect on air of [[gamma rays]] and [[X-rays]] and is used for instrument calibration, and absorbed dose is the amount of radiation energy deposited per unit mass in the matter or tissue under consideration.

===Operational quantities===
Operational quantities are measured in practice, and are the means of directly measuring dose uptake due to exposure, or predicting dose uptake in a measured environment. 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 also used in practical regulations and guidance.<ref>ICRP publication 103, paragraph B147</ref>

The calibration of individual and area dosimeters 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.<ref>''Measurement of H*(10) and Hp(10) in Mixed High-Energy Electron and Photon Fields.'' E. Gargioni, L. Büermann and H.-M. Kramer Physikalisch-Technische Bundesanstalt (PTB), D-38116 Braunschweig, Germany</ref>

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.<ref>"Operational Quantities for External Radiation Exposure, Actual Shortcomings and Alternative Options", G. Dietze, D.T. Bartlett, N.E. Hertel, given at IRPA 2012, Glasgow, Scotland. May 2012</ref> The ICRU sphere is a theoretical 30&nbsp;cm diameter "tissue equivalent" sphere consisting of a material with a density of 1 g·cm<sup>−3</sup> 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.<ref>ICRP publication 103, paragraph B159</ref> 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.<ref name="IAEACalibration" />

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 {{nowrap|300 mm × 300 mm × 150 mm}} depth to represent the human torso.<ref name="IAEACalibration" />

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.<ref name="endo" />

===Protection quantities===
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".<ref>ICRP publication 103, paragraph 112</ref><ref>ICRP publication 103, paragraph B50</ref><ref name="IAEACalibration">{{citation |title=Calibration of Radiation Protection Monitoring Instruments |series=Safety Reports Series 16 |quote=In 1991, the International Commission on Radiological Protection (ICRP) [7] recommended a revised system of dose limitation, including specification of primary ''limiting quantities'' for radiation protection purposes. These protection quantities are essentially unmeasurable |url=http://www-pub.iaea.org/MTCD/Publications/PDF/P074_scr.pdf |year=2000 |publisher=IAEA |isbn=978-92-0-100100-9}}</ref> 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 [[Computational human phantom|anthropomorphic phantom]]s. 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.<ref>ICRP publication 103, paragraph B64</ref>

As protection quantities cannot practically be measured, operational quantities must be used to relate them to practical radiation instrument and dosimeter responses.<ref>ICRP publication 103, paragraph B146</ref>

===Instrument and dosimetry response===
This is an actual reading obtained from such as an ambient dose [[gamma ray|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]].

==Calculating protection dose quantities==
[[File:SI Radiation dose units.png|thumb|upright=2.2|Graphic showing relationship of "protection dose" quantities in [[SI]] units]]
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 (radiation)|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 [[Relative biological effectiveness|weighting factors]] have been applied to the absorbed dose measurement or calculation (expressed in grays).<ref name="ICRP103">{{cite journal |title=The 2007 Recommendations of the International Commission on Radiological Protection |journal=Annals of the ICRP |year=2007 |volume=37 |series=ICRP Publication 103 |issue=2–4 |url=http://www.icrp.org/publication.asp?id=ICRP%20Publication%20103 |access-date=17 May 2012 |isbn=978-0-7020-3048-2 |author1=ICRP }}</ref>

The ICRP calculation provides two weighting factors to enable the calculation of protection quantities.
:&nbsp;1. The radiation factor ''W''<sub>''R''</sub>, which is specific for radiation type ''R'' – This is used in calculating the equivalent dose ''H''<sub>''T''</sub> which can be for the whole body or for individual organs.
:&nbsp;2. The tissue weighting factor ''W''<sub>''T''</sub>, which is specific for tissue type T being irradiated. This is used with ''W''<sub>''R''</sub> to calculate the contributory organ doses to arrive at an effective dose ''E'' for non-uniform irradiation.

When a whole body is irradiated uniformly only the radiation weighting factor ''W''<sub>''R''</sub> 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 ''W''<sub>''T''</sub> 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.

===Radiation type weighting factor ''W''<sub>''R''</sub>===
{{Main|Equivalent dose}}

Since different radiation types have different biological effects for the same deposited energy, a corrective [[radiation weighting factor]] ''W<sub>R</sub>'', 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.

{| class="wikitable" style="float:right;"
|+Radiation weighting factors ''W''<sub>''R''</sub> <br/> used to represent [[relative biological effectiveness]]<br/> according to ICRP report 103<ref name=ICRP103 />
|-
! Radiation !! Energy (''E'') !! ''W''<sub>''R''</sub> (formerly ''Q'')
|-
| colspan="2"| [[x-ray]]s, [[gamma ray]]s,<br/>[[beta particle]]s, [[muon]]s || 1
|-
| rowspan=3 |[[neutron]]s || < 1 MeV || 2.5 + 18.2e<sup>−[ln(''E'')]<sup>2</sup>/6</sup>
|-
| 1 – 50 MeV || 5.0 + 17.0e<sup>−[ln(2''E'')]<sup>2</sup>/6</sup>
|-
| > 50 MeV || 2.5 + 3.25e<sup>−[ln(0.04''E'')]<sup>2</sup>/6</sup>
|-
| colspan="2"| [[proton]]s, charged [[pion]]s || 2
|-
| colspan="2"| [[alpha particle]]s,<br/>[[nuclear fission product]]s,<br/>heavy [[atomic nucleus|nuclei]] || 20
|}

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.<ref name="ICRP103" />

<math display=block>H_T = \sum_R W_R \cdot D_{T,R},</math>
where
:{{math|''H<sub>T</sub>''}} is the equivalent dose absorbed by tissue ''T'',
:{{math|''D''<sub>''T'',''R''</sub>}} is the absorbed dose in tissue ''T'' by radiation type ''R'' and
:{{math|''W<sub>R</sub>''}} is the radiation weighting factor defined by regulation.
Thus for example, an absorbed dose of 1&nbsp;Gy by alpha particles will lead to an equivalent dose of 20&nbsp;Sv.

[[File:Neutron radiation weighting factor as a function of kinetic energy.gif|thumb|upright=1.5|The radiation weighting factor for neutrons has been revised over time and remains controversial.]]

This may seem to be a paradox. It implies that the energy of the incident radiation field in [[joule]]s 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.

===Tissue type weighting factor ''W''<sub>''T''</sub>===

{{Main|effective dose (radiation)}}
The second weighting factor is the tissue factor ''W''<sub>''T''</sub>, 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 ''W''<sub>''R''</sub> 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 ''W''<sub>''T''</sub> are given in the table shown here.

{| class="wikitable"
|+Weighting factors for different organs<ref>UNSCEAR-2008 [http://www.unscear.org/docs/reports/2008/09-86753_Report_2008_Annex_A.pdf Annex A] page 40, table A1, retrieved 2011-7-20</ref>
|-
! rowspan=2 |Organs !! colspan=3 |Tissue weighting factors
|-
! ICRP26<br />1977 !! ICRP60<br />1990<ref name="ICRP60_Ch2">{{cite journal|title=1990 Recommendations of the International Commission on Radiological Protection: Quantities used in radiological protection|journal=Annals of the ICRP|year=1991|volume=21|series=ICRP publication 60|issue=1–3|pages=8|url=https://www.icrp.org/publication.asp?id=ICRP%20Publication%2060|isbn=978-0-08-041144-6|author1=ICRP|bibcode=1991JRP....11..199V|doi=10.1016/0146-6453(91)90066-P|doi-access=}}</ref> !! ICRP103<br />2007<ref name="ICRP103" />
|-
| [[Gonads]] || 0.25 || 0.20 || 0.08
|-
| Red [[bone marrow]] || 0.12 || 0.12 || 0.12
|-
| [[Colon (anatomy)|Colon]] || — || 0.12 || 0.12
|-
| [[Lung]] || 0.12 || 0.12 || 0.12
|-
| [[Stomach]] || — || 0.12 || 0.12
|-
| [[Breast]]s || 0.15 || 0.05 || 0.12
|-
| [[Bladder]] || — || 0.05 || 0.04
|-
| [[Liver]] || — || 0.05 || 0.04
|-
| [[Oesophagus]] || — || 0.05 || 0.04
|-
| [[Thyroid]] || 0.03 || 0.05 || 0.04
|-
| [[Skin]] || — || 0.01 || 0.01
|-
| [[Bone]] surface || 0.03 || 0.01 || 0.01
|-
| [[Salivary glands]] || — || — || 0.01
|-
| [[Brain]] || — || — || 0.01
|-
| Remainder of body || 0.30 || 0.05 || 0.12
|-
! Total !! 1.00 !! 1.00 !! 1.00
|}
The article on [[effective dose (radiation)|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.

==Operational quantities==
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.<ref name="ICRP publication 103 - Glossary"/> 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.

===Ambient dose equivalent===
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&nbsp;mm within the ICRU sphere phantom in the direction of origin of the field.<ref>ICRP report 103 paragraphs B163 - B164</ref> An example of penetrating radiation is [[gamma ray]]s.

===Directional dose equivalent===
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&nbsp;mm in the ICRU sphere phantom.<ref>ICRP report 103 paragraphs B165- B167</ref> 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.<ref>{{citation |last1=Mattsson |first1=Sören |last2=Söderberg |first2=Marcus |title=Radiation Protection in Nuclear Medicine |chapter=Dose Quantities and Units for Radiation Protection |chapter-url=https://www.springer.com/cda/content/document/cda_downloaddocument/9783642311666-c2.pdf |publisher=Springer Verlag |year=2013 |doi=10.1007/978-3-642-31167-3 |isbn=978-3-642-31166-6}}</ref> In radiological protection practice value of omega is usually not specified as the dose is usually at a maximum at the point of interest.

===Personal dose equivalent===
This is used for individual dose monitoring, such as with a personal dosimeter worn on the body. The recommended depth for assessment is 10&nbsp;mm which gives the quantity ''H''<sub>p</sub>(10).<ref>ICRP report 103 paragraphs B168 - B170</ref>

==Proposals for changing the definition of protection dose quantities==
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.

Specifically;

1. For area monitoring of effective dose of whole body it would be:

:''H'' = Φ × conversion coefficient

The driver for this is that ''H''<sup>∗</sup>(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 ''E''<sub>max</sub>.

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 ''H''<sub>lens</sub> and ''H''<sub>skin</sub>.

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.<ref name="endo">"Operational Quantities and new approach by ICRU" – Akira Endo. The 3rd International Symposium on the System of Radiological Protection, Seoul, Korea – October 20–22, 2015 [http://www.icrp.org/docs/icrp2015/18%20Akira%20Endo%202015.pdf]</ref>

A final draft report was issued in July 2017 by ICRU/ICRP for consultation.<ref>{{cite web|url=http://www.icrp.org/docs/ICRU%20and%20ICRP%20Draft%20Joint%20Report%20Operational%20Quantities%20for%20External%20Radiation%20Exposure.pdf|title=ICRP draft "Operational Quantities for External Radiation Exposure"}}</ref>

==Internal dose quantities==
{{Main|Committed dose}}
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, <math>E(t)</math> as the sum of the products of the committed organ or tissue equivalent doses and the appropriate tissue weighting factors <math>W_t</math>, where <math>t</math> 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.<ref name="ICRP publication 103 - Glossary"/>

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".<ref>ICRP publication 103 - Paragraph 144.</ref>

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.

==Health effects==
{{Further|Radiobiology}}
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===
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 (radiation)|effective dose]] at a rate of 5.5% per sievert.<ref name="ICRP103" /> This is known as the [[linear no-threshold model]] (LNT model). Some 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.<ref>{{cite journal | last=Tubiana | first=Maurice | title=Dose–effect relationship and estimation of the carcinogenic effects of low doses of ionizing radiation: The joint report of the Académie des Sciences (Paris) and of the Académie Nationale de Médecine | journal=International Journal of Radiation Oncology, Biology, Physics | publisher=Elsevier BV | volume=63 | issue=2 | year=2005 | issn=0360-3016 | doi=10.1016/j.ijrobp.2005.06.013 | pages=317–319| pmid=16168825 | doi-access=free }}</ref><ref>{{cite book | last=Allison | first=Wade | title=Nuclear is for life: a cultural revolution | publisher=Wade Allison Publishing | publication-place=Aylesbury | year=2015 | isbn=978-0-9562756-4-6 | oclc=945569856}}</ref> 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.<ref name="peck">{{cite web |last1=Peck |first1=Donald J. |title=How to Understand and Communicate Radiation Risk |url=http://www.imagewisely.org/Imaging-Professionals/Medical-Physicists/Articles/How-to-Understand-and-Communicate-Radiation-Risk.aspx |archive-url=https://web.archive.org/web/20101208060102/http://www.imagewisely.org/Imaging-Professionals/Medical-Physicists/Articles/How-to-Understand-and-Communicate-Radiation-Risk.aspx |url-status=dead |archive-date=8 December 2010 |publisher=Image Wisely |access-date=18 May 2012 |last2=Samei |first2=Ehsan }}</ref><ref name="UNSCEAR">{{cite book |author=United Nations Scientific Committee on the Effects of Atomic Radiation |title=Effects of ionizing radiation: UNSCEAR 2006 report to the General Assembly, with scientific annexes |year=2008 |publisher=United Nations |location=New York |isbn=978-92-1-142263-4 |url=http://www.unscear.org/unscear/en/publications.html |access-date=18 May 2012 }}</ref>

===Deterministic effects===
[[File:Effectofselfrepair.svg|thumb| This is a graph depicting the effect of [[dose fractionation]] on the ability of [[gamma rays]] to cause cell death. The blue line is for cells which were not given a chance to recover; the radiation was delivered in one session. The red line is for cells which were allowed to stand for a time and recover with the pause in delivery conferring [[radioresistance]].]]
The deterministic (acute tissue damage) effects that can lead to [[acute radiation syndrome]] only occur in the case of acute high doses (≳&nbsp;0.1&nbsp;Gy) and high dose rates (≳&nbsp;0.1&nbsp;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.

===ICRP dose limits===

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:<ref>{{cite journal|last1=ICRP|title=Report 103|pages=Table 8, section 6.5}}</ref>

* Planned exposure – limits given for occupational, medical and public 
* Emergency exposure – limits given for occupational and public exposure 
* Existing exposure – All persons exposed

For occupational exposure, the limit is 50&nbsp;mSv in a single year with a maximum of 100&nbsp;mSv in a consecutive five-year period, and for the public to an average of 1&nbsp;mSv (0.001&nbsp;Sv) of effective dose per year, not including medical and occupational exposures.<ref name="ICRP103" />

For comparison, natural radiation levels inside the [[United States Capitol]] are such that a human body would receive an additional dose rate of 0.85&nbsp;mSv/a, close to the regulatory limit, because of the uranium content of the [[granite]] structure.<ref name="FUSRAP">{{cite web |last=Formerly Utilized Sites Remedial Action Program |title=Radiation in the Environment |url=http://www.lrb.usace.army.mil/fusrap/docs/fusrap-fs-radenvironment-2008-09.pdf |publisher=US Army Corps of Engineers |access-date=18 May 2012 |archive-url=https://web.archive.org/web/20120211162419/http://www.lrb.usace.army.mil/fusrap/docs/fusrap-fs-radenvironment-2008-09.pdf |archive-date=11 February 2012 |url-status=dead}}</ref> 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&nbsp;a·0.85&nbsp;mSv/a·0.001&nbsp;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]]).

==Dose examples==
{{main|Orders of magnitude (radiation)}}
[[File:027 dose-ranges-sievert.jpg|thumb|US Department of Energy 2010 dose chart in sieverts for a variety of situations and applications<ref name="NRC chart">{{cite web|url=https://www.nrc.gov/docs/ML1209/ML120970113.pdf |title=Ionizing Radiation Dose Ranges (Rem and Sievert charts) |work=[[United States Department of Energy|US Department of Energy]] |date=June 2010 |access-date=2018-05-28}}</ref>]]
[[File:Exposure chart-XKCD.svg|thumb|Various doses of radiation in sieverts, ranging from trivial to lethal, expressed as comparative areas]]
[[File:PIA17601-Comparisons-RadiationExposure-MarsTrip-20131209.png|thumb|right|Comparison of radiation doses – includes the amount detected on the trip from Earth to Mars by the [[Radiation assessment detector|RAD]] on the [[Mars Science Laboratory|MSL]] (2011–2013).<ref name="SCI-20130531a">{{cite journal |last1=Kerr |first1=R. A. |title=Radiation Will Make Astronauts' Trip to Mars Even Riskier |journal=[[Science (journal)|Science]] |volume=340 |issue=6136 |date=31 May 2013 |page=1031 |issn=0036-8075 |doi=10.1126/science.340.6136.1031 |pmid=23723213|bibcode=2013Sci...340.1031K }}</ref><ref name="ZeitlinHassler2013">{{cite journal |last1=Zeitlin |first1=C. |last2=Hassler |first2=D. M. |last3=Cucinotta |first3=F. A. |last4=Ehresmann |first4=B. |last5=Wimmer-Schweingruber |first5=R. F. |last6=Brinza |first6=D. E. |last7=Kang |first7=S. |last8=Weigle |first8=G. |last9=Bottcher |first9=S. |last10=Bohm |first10=E. |last11=Burmeister |first11=S. |last12=Guo |first12=J. |last13=Kohler |first13=J. |last14=Martin |first14=C. |last15=Posner |first15=A. |last16=Rafkin |first16=S. |last17=Reitz |first17=G. |title=Measurements of Energetic Particle Radiation in Transit to Mars on the Mars Science Laboratory |journal=[[Science (journal)|Science]] |volume=340 |issue=6136 |date=31 May 2013 |pages=1080–1084 |issn=0036-8075 |doi=10.1126/science.1235989 |pmid=23723233 |display-authors=1|bibcode = 2013Sci...340.1080Z |s2cid=604569 }}</ref><ref name="NYT-20130530">{{cite news|last=Chang |first=Kenneth |title=Data Point to Radiation Risk for Travelers to Mars|url=https://www.nytimes.com/2013/05/31/science/space/data-show-higher-cancer-risk-for-mars-astronauts.html |date=30 May 2013 |newspaper=The New York Times|access-date=31 May 2013 }}</ref><ref name="SN-20130629">{{cite journal |last=Gelling |first=Cristy|title=Mars trip would deliver big radiation dose; Curiosity instrument confirms expectation of major exposures|url=http://www.sciencenews.org/view/generic/id/350728/description/Mars_trip_would_deliver_big_radiation_dose|volume=183|issue=13|page=8|journal=[[Science News]] |date=29 June 2013 |access-date=8 July 2013 |doi=10.1002/scin.5591831304}}</ref> ]]
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.

===Dose examples===
{|
| style="text-align:right;" | 98 || nSv: || [[Banana equivalent dose]], an illustrative unit of radiation dose representing the measure of radiation from a typical banana<ref>[[RadSafe]] mailing list: [http://health.phys.iit.edu/extended_archive/9503/msg00074.html original posting] and [http://health.phys.iit.edu/archives/2011-March/031395.html follow up thread]. FGR11 discussed.</ref><ref group=lower-alpha name="internal">Noted figures are dominated by a [[committed dose]] which gradually turned into effective dose over an extended period of time. Therefore the true acute dose must be lower, but standard dosimetry practice is to account committed doses as acute in the year the radioisotopes are taken into the body.</ref>
|-
| style="text-align:right;"| 250 || nSv: || U.S. limit on effective dose for general-use x-ray security screening systems such as those previously used in airport security screening<ref>{{cite book |last=American National Standards Institute |title=Radiation Safety for Personnel Security Screening Systems Using X-Rays or Gamma Radiation |year=2009 |url=http://hps.org/documents/securityscreening_ps017-1.pdf |id=ANSI/HPS N43.17 |access-date=31 May 2012 }}</ref>
|-
| style="text-align:right;"| 5–10 || μSv: || One set of [[dental radiograph]]s<ref>{{cite book |last1=Hart |first1=D. |title=Radiation Exposure of the UK Population from Medical and Dental X-ray Examinations |year=2002 |publisher=National Radiological Protection Board |isbn=0-85951-468-4 |url=http://cloud.medicalphysicist.co.uk/nrpb_w4.pdf |last2=Wall |first2=B. F. |access-date=18 May 2012 |page=9 }}</ref>
|-
| style="text-align:right;"| 80 || μSv: || Average (one time) dose to people living within {{cvt|10|mi|km|0}} of the plant during the [[Three Mile Island accident]]<ref name="ANS-tmi">{{cite web |url=http://www.nuclearconnect.org/what-happened-and-what-didnt-in-the-tmi-2-accident |access-date=2018-12-28 |title=What Happened and What Didn't in the TMI-2 Accident |publisher=[[American Nuclear Society]] |url-status=dead |archive-url=https://web.archive.org/web/20041030210238/http://www.ans.org/pi/resources/sptopics/tmi/whathappened.html |archive-date=30 October 2004}}</ref>
|-
| style="text-align:right;"| 400–600 || μSv: || Two-view [[mammogram]], using weighting factors updated in 2007<ref>{{cite journal |last=Hendrick |first=R. Edward |title=Radiation Doses and Cancer Risks from Breast Imaging Studies |journal=Radiology |date=October 2010 |volume=257 |pages=246–253 |doi=10.1148/radiol.10100570 |pmid=20736332 |issue=1 |doi-access= }}</ref>
|-
| style="text-align:right;"| 1 || mSv: || U.S. 10 [[Code of Federal Regulations|CFR]] § 20.1301(a)(1) dose limit for individual members of the public, total [[Effective dose (radiation)|effective dose]] equivalent, [[wikt:per annum|per annum]]<ref name="CFR-20.1301">{{cite web |url=https://www.nrc.gov/reading-rm/doc-collections/cfr/part020/part020-1301.html |title=NRC: 10 CFR 20.1301 Dose limits for individual members of the public |publisher=NRC |access-date=2014-02-07}}</ref>
|-
| style="text-align:right;"| 1.5–1.7 || mSv: || Annual [[Occupational exposure limit|occupational dose]] for [[flight attendant]]s<ref name="GrajewskiWaters2002">{{cite journal |last1=Grajewski |first1=Barbara |last2=Waters |first2=Martha A. |last3=Whelan |first3=Elizabeth A. |last4=Bloom |first4=Thomas F. |title=Radiation dose estimation for epidemiologic studies of flight attendants |journal=American Journal of Industrial Medicine |volume=41 |issue=1 |year=2002 |pages=27–37 |issn=0271-3586 |doi=10.1002/ajim.10018|pmid=11757053 |url=https://zenodo.org/record/1229076 }}</ref>
|-
| style="text-align:right;"| 2–7 || mSv: || Barium fluoroscopy, e.g. [[Barium meal]], up to 2 minutes, 4–24 spot images<ref name="wall97">{{cite journal |last1=Wall |first1=B. F. |last2=Hart |first2=D. |title=Revised Radiation Doses for Typical X-Ray Examinations |journal=The British Journal of Radiology |year=1997 |volume=70 |pages=437–439 |pmid=9227222 |issue=833 |doi=10.1259/bjr.70.833.9227222 }} (5,000 patient dose measurements from 375 hospitals)</ref>
|-
| style="text-align:right;"| 10–30 || mSv: || Single full-body [[CT scan]]<ref name="NEJM-radiation">{{cite journal |pages=2277–2284 |doi=10.1056/NEJMra072149 |title=Computed Tomography — an Increasing Source of Radiation Exposure |year=2007 |last1=Brenner |first1=David J. |last2=Hall |first2=Eric J. |journal=New England Journal of Medicine |volume=357 |issue=22 |pmid=18046031|s2cid=2760372 |url=https://repositorio.unal.edu.co/handle/unal/79492 }}</ref><ref name="ctscan">{{cite journal |pmid=9166072 |year=1997 |last1=Van Unnik |first1=J. G. |last2=Broerse |first2=J. J. |last3=Geleijns |first3=J. |last4=Jansen |first4=J. T. |last5=Zoetelief |first5=J. |last6=Zweers |first6=D. |title=Survey of CT techniques and absorbed dose in various Dutch hospitals |volume=70 |issue=832 |pages=367–71 |journal=The British Journal of Radiology|doi=10.1259/bjr.70.832.9166072 }} (3000 examinations from 18 hospitals)</ref>
|-
| style="text-align:right;"| 50 || mSv: || U.S. 10 C.F.R. § 20.1201(a)(1)(i) occupational dose limit, total effective dose equivalent, per annum<ref name="CFR-20.1201">{{cite web |url=https://www.nrc.gov/reading-rm/doc-collections/cfr/part020/part020-1201.html |title=NRC: 10 CFR 20.1201 Occupational dose limits for adults |publisher=NRC |access-date=2014-02-07}}</ref>
|-
| style="text-align:right;"| 68 || mSv: || Estimated maximum dose to evacuees who lived closest to the [[Fukushima I nuclear accidents]]<ref>{{cite journal |last1=Hosoda |first1=Masahiro |title=The time variation of dose rate artificially increased by the Fukushima nuclear crisis |journal=Scientific Reports |year=2011 |volume=1 |doi=10.1038/srep00087 |last2=Tokonami |first2=Shinji |last3=Sorimachi |first3=Atsuyuki |last4=Monzen |first4=Satoru |last5=Osanai |first5=Minoru |last6=Yamada |first6=Masatoshi |last7=Kashiwakura |first7=Ikuo |last8=Akiba |first8=Suminori |bibcode = 2011NatSR...1E..87H |page=87 |pmid=22355606 |pmc=3216573 }}</ref>
|-
| style="text-align:right;"| 80 || mSv: || 6-month stay on the [[International Space Station]]
|-
|style="text-align:right;"| 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<ref>{{cite web|archive-url=https://web.archive.org/web/20130613131654/http://www.ors.od.nih.gov/sr/drs/training/GRS/Pages/sectionf.aspx|title=F. Typical Sources of Radiation Exposure |archive-date=2013-06-13 |access-date=2019-06-20 |publisher=[[National Institute of Health]] |url-status=dead |url=http://www.ors.od.nih.gov/sr/drs/training/GRS/Pages/sectionf.aspx}}</ref><ref>{{cite web|url=http://www.aradnj.com/radiation2.html|archive-url=https://web.archive.org/web/20120426011721/http://www.aradnj.com/radiation2.html|archive-date=2012-04-26|title=Radiation Risk for Xray and CT exams - dosage chart|date=2012-04-26|access-date=2019-04-15}}</ref>
|-
| style="text-align:right;"| 250 || mSv: || 6-month [[trip to Mars]]—radiation due to [[cosmic ray]]s, which are very difficult to shield against
|-
| style="text-align:right;"| 400 || mSv: || Average accumulated exposure of residents over a period of 9–20 years, who suffered no ill effects, in apartments in Taiwan constructed with rebar containing [[Cobalt-60]]<ref>{{cite journal|title=Effects of Cobalt-60 Exposure on Health of Taiwan Residents Suggest New Approach Needed in Radiation Protection|date=2006-08-25|pmc=2477708|last1=Chen|first1=W. L.|last2=Luan|first2=Y. C.|last3=Shieh|first3=M. C.|last4=Chen|first4=S. T.|last5=Kung|first5=H. T.|last6=Soong|first6=K. L.|last7=Yeh|first7=Y. C.|last8=Chou|first8=T. S.|last9=Mong|first9=S. H.|last10=Wu|first10=J. T.|last11=Sun|first11=C. P.|last12=Deng|first12=W. P.|last13=Wu|first13=M. F.|last14=Shen|first14=M. L.|journal=Dose-Response |volume=5|issue=1|pages=63–75|doi=10.2203/dose-response.06-105.Chen|pmid=18648557}}</ref>
|-
| style="text-align:right;"| 500 || mSv: || The U.S. 10 C.F.R. § 20.1201(a)(2)(ii) occupational dose limit, shallow-dose equivalent to skin, per annum<ref name="CFR-20.1201"/>
|-
| style="text-align:right;"| 670 || mSv: || Highest dose received by a worker responding to the Fukushima emergency<ref>{{cite book |last=American Nuclear Society |title=Fukushima Daiichi: ANS Committee Report |date=March 2012 |chapter-url=http://fukushima.ans.org/report/Fukushima_report.pdf |editor1=Klein, Dale |editor2=Corradini, Michael |access-date=19 May 2012 |chapter=Appendix B}}</ref><ref group=lower-alpha name="internal" />
|-
| style="text-align:right;"| 1 || Sv: || Maximum allowed radiation exposure for NASA astronauts over their career<ref name="SCI-20130531a"/>
|-
| style="text-align:right;"| 4–5 || Sv: || Dose required to kill a human with a 50% risk within 30 days (LD<sub>50</sub>/30), if the dose is received over a very short duration<ref>{{cite web|url=https://www.nrc.gov/reading-rm/basic-ref/glossary/lethal-dose-ld.html|website=www.nrc.gov|access-date=2017-02-12|title=Lethal dose (LD)}}</ref><ref name="NRC chart"/> 
|-
| style="text-align:right;"| 5 || Sv: || Calculated dose from the [[prompt neutron|neutron]] and [[gamma ray]] flash, 1.2&nbsp;km from ground zero of the [[Little Boy]] fission bomb, air burst at 600 m.<ref>{{cite web |url=https://nuclearsecrecy.com/nukemap/ |title=NUKEMAP |last=Wellerstein |first=Alex |website=nuclearsecrecy.com |publisher=[[Alex Wellerstein]] |access-date=2021-04-15}}</ref><ref>{{citation|last1=Glasstone|first1=Dolan|date=1962|publisher=Defense Atomic Support Agency, Dept. of Defense|title=The Effects of Nuclear Weapons|at=Chapter VIII, Initial nuclear radiation|url=https://books.google.com/books?id=Ovu108BraNUC}}</ref>
|-
| style="text-align:right;"| 4.5–6 || Sv: || Fatal acute doses during [[Goiânia accident]]
|-
| style="text-align:right;"| 5.1 || Sv: || Fatal acute dose to [[Harry Daghlian]] in 1945 [[criticality accident]]<ref name=McLaughlin>{{cite book |last1=McLaughlin |first1=Thomas P. |last2=Monahan |first2=Shean P. |last3=Pruvost |first3=Norman L. |last4=Frolov |first4=Vladimir V. |last5=Ryazanov |first5=Boris G. |last6=Sviridov |first6=Victor I. |title=A Review of Criticality Accidents |date=May 2000 |publisher=Los Alamos National Laboratory |location=Los Alamos, NM |url=http://www.orau.org/ptp/Library/accidents/la-13638.pdf |access-date=21 April 2010 |pages=74–75 |id=LA-13638 }}</ref>
|-
| style="text-align:right;"| 10 to 17 || Sv: || Fatal acute doses during [[Tokaimura nuclear accident]]. [[Hisashi Ouchi]] who received 17 Sv lived for 83 days after the accident.<ref>{{cite news | url=http://www.japantimes.co.jp/news/1999/12/22/national/jco-worker-succumbs-after-83-days/ | title=JCO worker succumbs after 83 days|access-date=24 April 2016}}</ref>
|-
| style="text-align:right;"| 21 || Sv: || Fatal acute dose to [[Louis Slotin]] in 1946 criticality accident<ref name=McLaughlin/>
|-
| style="text-align:right;"| 36 || Sv: || Fatal acute dose to [[Cecil Kelley]] in 1958, death occurred within 35 hours.<ref>{{cite journal|title=The Cecil Kelley Criticality Accident: The Origin of the Los Alamos Human Tissue Analysis Program|journal=[[Los Alamos Science]]|volume=23|year=1995|pages=250–251|url=http://library.lanl.gov/cgi-bin/getfile?23-13.pdf}}</ref>
|-
| style="text-align:right;"| 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<ref>{{cite web |last=Dolgodvorov|first=Vladimir | title=K-19, the Forgotten Sub |date=November 2002 |publisher=trud.ru |url=http://www.trud.ru/article/21-11-2002/49488_submarina_sberegshaja_mir.html |access-date=2 July 2015|language=ru}}</ref>
|-
| style="text-align:right;"| 64 || Sv: || Nonfatal dose to [[Albert Stevens]] spread over ≈21 years, due to a 1945 [[Human radiation experiments|plutonium injection experiment]] by doctors working on the secret [[Manhattan Project]].<ref>{{cite journal |last1=Moss |first1=William |last2=Eckhardt |first2=Roger |title=The Human Plutonium Injection Experiments |journal=Los Alamos Science |year=1995 |series=Radiation Protection and the Human Radiation Experiments |issue=23 |pages=177–223 |url=https://fas.org/sgp/othergov/doe/lanl/pubs/00326640.pdf |access-date=13 November 2012 }}</ref><ref group=lower-alpha name="internal" />
|}

===Dose rate examples===
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. "/a" is "per annum", which means per year. "/h" means "per hour".
{|
|-
| style="text-align:right;"| <1 || {{nowrap|mSv/a}} || style="text-align:right;"| <100 || {{nowrap|nSv/h}} || Steady dose rates below 100 nSv/h are difficult to measure.{{Citation needed|date=May 2013}}
|-
| style="text-align:right;"| 1 || {{nowrap|mSv/a}} || style="text-align:right;"| (100 || {{nowrap|nSv/h avg)}} || ICRP recommended maximum for external irradiation of the human body, excluding medical and occupational exposures.
|-
| style="text-align:right;"| 2.4 || {{nowrap|mSv/a}} || style="text-align:right;"| (270 || {{nowrap|nSv/h avg)}} || Human exposure to [[Background radiation#Natural background radiation|natural background radiation]], global average<ref group=lower-alpha name="internal" />
|-
| style="text-align:right;"| (8 || {{nowrap|mSv/a)}} || style="text-align:right;"| 810 || {{nowrap|nSv/h avg}} || Next to the [[Chernobyl New Safe Confinement]] (May 2019)<ref>{{cite web|url=https://www.google.com/maps/place/Sarkofag+Chornobyl%CA%B9s%CA%B9koyi+Aes/@51.3914528,30.0954923,-6a,15y,90t/data=!3m8!1e2!3m6!1sAF1QipMcTGNrPSWbatUzlM5df-Hj1iVuDftsFpHh65Z8!2e10!3e12!6shttps://lh5.googleusercontent.com/p/AF1QipMcTGNrPSWbatUzlM5df-Hj1iVuDftsFpHh65Z8=w203-h304-k-no!7i3648!8i5472!4m12!1m6!3m5!1s0x472a7d77be6d043b:0xfc14fe4e87c2f4bf!2sChernobyl+Power+Plant!8m2!3d51.381484!4d30.119319!3m4!1s0x472a7d08112a07a9:0x6f7f413c8c094933!8m2!3d51.3892859!4d30.0988302|title=Google Maps|website=Google Maps}}</ref>
|-
| style="text-align:right;"| ~8 || {{nowrap|mSv/a}} || style="text-align:right;"| (~900 || {{nowrap|nSv/h avg)}} || Average natural background radiation in Finland<ref>{{cite book |title=An introduction to nuclear waste immobilisation, second edition |date=13 November 2018 |publisher=Elsevier |isbn=978-0-08-099392-8 |edition=2nd}}</ref>
|-
| style="text-align:right;"| 24 || {{nowrap|mSv/a}} || style="text-align:right;"| (2.7 || {{nowrap|μSv/h avg)}} || Natural background radiation at airline cruise altitude<ref>{{cite news |last=Bailey |first=Susan |title=Air crew radiation exposure—An overview |url=https://www2.ans.org/pubs/magazines/nn/docs/2000-1-3.pdf |access-date=19 May 2012 |newspaper=Nuclear News |date=January 2000 }}</ref><ref group=lower-alpha>The dose rate received by air crews is highly dependent on the radiation weighting factors chosen for protons and neutrons, which have changed over time and remain controversial.</ref>
|-
| style="text-align:right;"| (46 || {{nowrap|mSv/a)}} || style="text-align:right;"| 5.19 || {{nowrap|μSv/h avg}} || Next to Chernobyl Nuclear Power Plant, before installing the [[Chernobyl New Safe Confinement|New Sarcophagus]] in November 2016<ref>{{cite web|url=https://www.youtube.com/watch?v=TRL7o2kPqw0| archive-url=https://ghostarchive.org/varchive/youtube/20211117/TRL7o2kPqw0| archive-date=2021-11-17 | url-status=live|title=The Most Radioactive Places on Earth|date=17 December 2014|via=YouTube}}{{cbignore}}</ref>
|-
| style="text-align:right;"| 130 || {{nowrap|mSv/a}} || style="text-align:right;"| (15 || {{nowrap|μSv/h avg)}} || Ambient field inside most radioactive house in [[Ramsar, Iran]]<ref name="HNBR2009">{{cite journal |last1=Hendry |first1=Jolyon H. |last2=Simon |first2=Steven L. |last3=Wojcik |first3=Andrzej |last4=Sohrabi |first4=Mehdi |last5=Burkart |first5=Werner |last6=Cardis |first6=Elisabeth |last7=Laurier |first7=Dominique |last8=Tirmarche |first8=Margot |last9=Hayata |first9=Isamu| display-authors= 3 |title=Human exposure to high natural background radiation: what can it teach us about radiation risks? |journal=Journal of Radiological Protection |date=1 June 2009 |volume=29 |issue=2A |pages=A29–A42 |doi=10.1088/0952-4746/29/2A/S03 |pmid=19454802 |pmc=4030667 |url=http://cricket.biol.sc.edu/papers/natural/Hendry%20et%20al%202009.pdf |access-date=1 December 2012 |bibcode=2009JRP....29...29H |archive-url=https://web.archive.org/web/20131021233519/http://cricket.biol.sc.edu/papers/natural/Hendry%20et%20al%202009.pdf |archive-date=21 October 2013 |url-status=dead}}</ref><ref group=lower-alpha name="external" />
|-
| style="text-align:right;"| (350 || {{nowrap|mSv/a)}} || style="text-align:right;"| 39.8 || {{nowrap|μSv/h avg}} || Inside "The Claw" of Chernobyl<ref>{{cite news| url= https://www.news.com.au/technology/environment/the-claw-of-chernobyl-most-dangerous-thing-in-the-exclusion-zone/news-story/533246f01b396bd8deb106c315aecf61| title= The Claw of Chernobyl: most dangerous thing in the exclusion zone| first= LJ |last= Charleston| date= July 7, 2019| website= news.com.au| publisher= | access-date= January 31, 2021}}</ref>
|-
| style="text-align:right;"| (800 || {{nowrap|mSv/a)}} || style="text-align:right;"| 90 || {{nowrap|μSv/h}} || Natural radiation on a [[monazite]] beach near [[Guarapari]], Brazil.<ref>{{cite book |last=| first= |title=Sources and Effects of Ionizing Radiation |year=2000 |publisher= [[United Nations Scientific Committee on the Effects of Atomic Radiation]], United Nations |chapter-url=http://www.unscear.org/unscear/publications/2000_1.html |access-date=11 November 2012 |page=121 |volume=1 |chapter=Annex B }}</ref><!--Not mentioned in UNSCEAR 2008, oddly enough.-->
|-
| style="text-align:right;"| (9 || {{nowrap|Sv/a)}} || style="text-align:right;"| 1 || {{nowrap|mSv/h}} || NRC definition of a high radiation area in a nuclear power plant, warranting a chain-link fence<ref>{{cite book |last= | first= | title=Regulatory Guide 8.38: Control of Access to High and Very High Radiation Areas in Nuclear Power Plants |year=2006| publisher= US Nuclear Regulatory Commission |url=http://www.orau.org/ptp/PTP%20Library/library/NRC/Reguide/08-038.PDF }}</ref>
|-
| style="text-align:right;"| {{nowrap|(17–173}} || {{nowrap|Sv/a)}} || style="text-align:right;"| {{nowrap|2–20}} || {{nowrap|mSv/h}} || Typical dose rate for activated [[plasma facing material|reactor wall]] in possible future [[fusion reactor]]s after 100 years.<ref name="FUS539">{{cite web |url=http://www.afs.enea.it/dipacel/Eudora%20Backup/copied%20from%20Mac%2015-7-2008/Spool%20Folder/481002814/ukaea-fus-539.pdf |title=Consideration of strategies, industry experience, processes and time scales for the recycling of fusion irradiated material |publisher=UKAEA |page=vi |quote=dose rates of 2-20 mSv/h, typical of plasma facing components after intermediate storage for up to 100 years |access-date=5 March 2013 |archive-url=https://web.archive.org/web/20131012025037/http://www.afs.enea.it/dipacel/Eudora%20Backup/copied%20from%20Mac%2015-7-2008/Spool%20Folder/481002814/ukaea-fus-539.pdf |archive-date=12 October 2013 |url-status=dead}}</ref> 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.<ref>''Energy Markets: The Challenges of the New Millennium'', 18th World Energy Congress, Buenos Aires, Argentina, 21–25 October 2001, [https://web.archive.org/web/20040506065141/http://www.worldenergy.org/wec-geis/publications/default/tech_papers/18th_Congress/downloads/ds/ds6/ds6_5.pdf Figure X page 13.]</ref> Immediate predicted activation is 90 M[[Gray (unit)|Gy]]/a.{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}}
|-
| style="text-align:right;"| (1.7 || {{nowrap|kSv/a)}} || style="text-align:right;"| 190 || {{nowrap|mSv/h}} || Highest reading from [[fallout]] of the [[Trinity bomb]], {{convert|20|mi|km|0|abbr=on}} away, 3 hours after detonation.<ref>{{cite book |last=Widner |first=Thomas |title=Draft Final Report of the Los Alamos Historical Document Retrieval and Assessment (LAHDRA) Project |date=June 2009 |publisher=Centers for Disease Control and Prevention |url=http://www.lahdra.org/pubs/reports/Entire%20report/LAHDRA%20Draft%20Final%20Report_vJy23p.pdf |access-date=12 November 2012}}</ref><ref group=lower-alpha name="external">Noted figures exclude any committed dose from radioisotopes taken into the body. Therefore the total radiation dose would be higher unless respiratory protection was used.</ref>
|-
| style="text-align:right;"| (2.3 || {{nowrap|MSv/a)}} || style="text-align:right;"| 270 || {{nowrap|Sv/h}} || Typical [[Pressurized water reactor|PWR]] spent fuel waste, after 10-year cooldown, no shielding and no distance.<ref>{{cite book |last=Su |first= S. |title= TAD Source Term and Dose Rate Evaluation |date= August 2006 |publisher= Bechtel Saic |url= http://pbadupws.nrc.gov/docs/ML0907/ML090770282.pdf |access-date=2021-09-17|id=000-30R-GGDE-00100-000-00A |page=19}}</ref>
|-
| style="text-align:right;"| {{nowrap|(4.6–5.6}} || {{nowrap|MSv/a)}} || style="text-align:right;"| {{nowrap|530–650}} || {{nowrap|Sv/h}} || The radiation level inside the primary containment vessel of the second [[Boiling water reactor|BWR]]-reactor of the [[Fukushima Daiichi nuclear disaster|Fukushima]] power station, in February 2017, six years after a suspected [[nuclear meltdown|meltdown]].<ref>{{cite news |date=10 February 2017 |title=High radiation readings at Fukushima's No. 2 reactor complicate robot-based probe |url=http://www.japantimes.co.jp/news/2017/02/10/national/high-radiation-readings-at-fukushima-no-2-reactor/#.WJ85W3-pmUl |url-status=dead |archive-url=https://web.archive.org/web/20170212074539/http://www.japantimes.co.jp/news/2017/02/10/national/high-radiation-readings-at-fukushima-no-2-reactor/#.WKASt2HP32e |archive-date=2017-02-12 |newspaper=The Japan Times Online}}</ref><ref>{{Cite news |url= https://www.theguardian.com/environment/2017/feb/03/fukushima-daiichi-radiation-levels-highest-since-2011-meltdown|title=Fukushima nuclear reactor radiation at highest level since 2011 meltdown|first=Justin|last=McCurry|date=3 February 2017|via= theguardian.com |newspaper= The Guardian}}</ref><ref>{{cite web| url= https://www.extremetech.com/extreme/243904-fukushimas-reactor-2-far-radioactive-previously-realized-no-sign-containment-breach| title=Fukushima's Reactor #2 is far more radioactive than previously realized | first= Joel| last= Hruska |date= February 3, 2017 |website= extremetech.com |access-date= January 31, 2021}}</ref><ref>{{cite web |url= https://gizmodo.com/excessive-radiation-inside-fukushima-fries-clean-up-rob-1792217866 |first= George| last= Dvorsky| date= February 10, 2018 |website= [[Gizmodo.com]] |title= Excessive Radiation Inside Fukushima Fries Clean-up Robot |access-date= January 31, 2021}}</ref><ref>{{cite news |url= https://www.washingtonpost.com/news/worldviews/wp/2017/02/08/japanese-nuclear-plant-just-recorded-an-astronomical-radiation-level-should-we-be-worried/|title=Japanese nuclear plant just recorded an astronomical radiation level. Should we be worried?| newspaper= [[The Washington Post]]| first1= Anna| last1= Fifield| first2= Yuki| last2= Oda| place= Tokyo| date= February 8, 2017 |access-date= January 31, 2021}}</ref> In this environment, it takes between 22 and 34 seconds to accumulate a [[median lethal dose]] (LD<sub>50</sub>/30).
|}

Notes on examples:
{{Reflist|group=lower-alpha}}

==History==
The sievert has its origin in the [[roentgen equivalent man|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,<ref>{{cite conference |last=Wyckoff |first=H. O. |title=Round table on SI units: ICRU Activities |conference=International Congress of the International Radiation Protection Association |date=April 1977 |url=http://www.irpa.net/irpa4/cdrom/VOL.2/P2_101.PDF |access-date=18 May 2012 |location=Paris, France }}</ref> and announced in 1976 that it planned to formulate a suitable unit for equivalent dose.<ref>{{cite journal |last1=Wyckoff |first1=H. O. |title=The New Special Names of SI Units in the Field of Ionizing Radiations |journal=British Journal of Radiology |date=May 1976 |volume=49 |pages=476–477 |url=http://bjr.birjournals.org/content/49/581/476.2.full.pdf |access-date=18 May 2012 |issn=1748-880X |pmid=949584 |last2=Allisy |first2=A. |last3=Lidén |first3=K. |issue=581 |doi=10.1259/0007-1285-49-581-476-b}}</ref> The ICRP pre-empted the ICRU by introducing the sievert in 1977.<ref name="ICRP26">{{cite journal |title=Recommendations of the ICRP |journal=Annals of the ICRP |year=1977 |volume=1 |series=ICRP publication 26 |issue=3 |url=http://www.icrp.org/publication.asp?id=ICRP%20Publication%2026 |access-date=17 May 2012 }}</ref>

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 (W<sub>R</sub>), 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.<ref name="SI">{{SIbrochure}}</ref>

==Common SI usage==
{{SI unit lowercase|Rolf Maximilian Sievert|sievert|Sv}}

Frequently used [[SI prefixes]] are the millisievert (1&nbsp;mSv = 0.001&nbsp;Sv) and microsievert (1&nbsp;μSv = 0.000&nbsp;001&nbsp;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:

: 1&nbsp;mSv/h = 8.766&nbsp;Sv/a
: 114.1&nbsp;μSv/h = 1&nbsp;Sv/a

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:<ref>{{cite book |title=Recommendations of the International Commission on Radiological Protection and of the International Commission on Radiological Units |year=1950 |publisher=US Department of Commerce |url=http://www.orau.org/ptp/Library/NBS/NBS%2047.pdf |access-date=14 November 2012 |series=National Bureau of Standards Handbook |volume=47 }}</ref>

: 8&nbsp;h = 1&nbsp;day
: 40&nbsp;h = 1&nbsp;week
: 50&nbsp;weeks = 1&nbsp;year

Therefore, for occupation exposures of that time period,

: 1&nbsp;mSv/h = 2&nbsp;Sv/a
: 500&nbsp;μSv/h = 1&nbsp;Sv/a

==Ionizing radiation quantities==
[[File:Radioactivity and radiation.png|thumb|upright=1.8|Graphic showing relationships between radioactivity and detected ionizing radiation]]
The following table shows radiation quantities in SI and non-SI units:
{{Radiation related quantities}}

Although the United States Nuclear Regulatory Commission permits the use of the units [[Curie (unit)|curie]], [[rad (radiation unit)|rad]], and [[Roentgen equivalent man|rem]] alongside SI units,<ref>{{cite book|title=10 CFR 20.1004|year=2009|publisher=US Nuclear Regulatory Commission|url=https://www.nrc.gov/reading-rm/doc-collections/cfr/part020/part020-1004.html}}</ref> the [[European Union]] [[European units of measurement directives]] required that their use for "public health ... purposes" be phased out by 31 December 1985.<ref>{{cite web
| url = http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:31980L0181:EN:NOT
| author = The Council of the European Communities
| title = Council Directive 80/181/EEC of 20 December 1979 on the approximation of the laws of the Member States relating to Unit of measurement and on the repeal of Directive 71/354/EEC
| date=1979-12-21
| access-date=19 May 2012}}</ref>

===Rem equivalence===
An older unit for the dose equivalent is the [[Roentgen equivalent man|rem]],<ref name="EPA">{{cite web |title=Radiation: Risks and Realities |url=http://www.epa.gov/rpdweb00/docs/402-k-07-006.pdf |publisher=U.S. Environmental Protection Agency |access-date=19 March 2011 |author=Office of Air and Radiation |author2=Office of Radiation and Indoor Air |page=2 |date=May 2007 }}</ref> still often used in the United States. One sievert is equal to 100 rem:

{| class="wikitable" style="text-align: right;"
|-
| 100<span style="color:transparent">.0000</span> rem || = || 100,000<span style="color:transparent">.0</span> mrem || =
! 1 Sv
| = || 1<span style="color:transparent">.000000</span> Sv || = || 1000<span style="color:transparent">.000</span> mSv || = || 1,000,000 μSv
|-
| 1<span style="color:transparent">.0000</span> rem || = || 1000<span style="color:transparent">.0</span> mrem || =
! 1 rem
| = || 0.01<span style="color:transparent">0000</span> Sv || = || 10<span style="color:transparent">.000</span> mSv || = || 10000 μSv
|-
| 0.1<span style="color:transparent">000</span> rem || = || 100<span style="color:transparent">.0</span> mrem || =
! 1 mSv
| = || 0.001<span style="color:transparent">000</span> Sv || = || 1<span style="color:transparent">.000</span> mSv || = || 1000 μSv
|-
| 0.001<span style="color:transparent">0</span> rem || = || 1<span style="color:transparent">.0</span> mrem || =
! 1 mrem
| = || 0.00001<span style="color:transparent">0</span> Sv || = || 0.01<span style="color:transparent">0</span> mSv || = || 10 μSv
|-
| 0.0001 rem || = || 0.1 mrem || =
! 1 μSv
| = || 0.000001 Sv || = || 0.001 mSv || = || 1 μSv
|}

==See also==
* [[Acute radiation syndrome]]
* [[Becquerel]] (disintegrations per second)
* [[Counts per minute]]
* [[Radiation exposure]]
* [[Rutherford (unit)]]
* [[Sverdrup]] (a non-SI unit of volume transport with the same symbol Sv as sievert)

== Explanatory notes ==
{{Reflist|group="note"}}

==References==
{{Reflist}}
{{Refbegin}}
* {{citation |url=http://www.unscear.org/docs/reports/gareport.pdf |title=Report of the United Nations Scientific Committee on the Effects of Atomic Radiation to the General Assembly |publisher=[[United Nations Scientific Committee on the Effects of Atomic Radiation]]}}
{{Refend}}

==External links==
* {{cite web|last=Glover|first=Paul|title=Millisieverts and Radiation|url=http://www.sixtysymbols.com/videos/radiation.htm|work=Sixty Symbols|publisher=[[Brady Haran]] for the [[University of Nottingham]]}}
* [https://eurados.sckcen.be/ Eurados - The European radiation dosimetry group]
{{Radiation protection|state=uncollapsed}}
{{Radiation|state=uncollapsed}}
{{SI units}}
{{Ionising radiation related quantities}}

[[Category:Radiation health effects]]
[[Category:Radiobiology]]
[[Category:Radioactivity]]
[[Category:Units of radiation dose]]
[[Category:Units of radioactivity]]
[[Category:Radiation protection]]
[[Category:SI derived units]]