Thesievert (symbol:Sv[note 1]) is a unit in theInternational System of Units (SI) intended to represent thestochastic health risk ofionizing radiation, which is defined as the probability of causing radiation-induced cancer and genetic damage. The sievert is important indosimetry andradiation protection. It is named afterRolf Maximilian Sievert, a Swedish medical physicist renowned for work on radiation dose measurement and research into the biological effects of radiation.
To calculate the value of stochastic health risk in sieverts, the physical quantityabsorbed dose is converted into equivalent dose and effective dose by applying factors for radiation type and biological context, published by the ICRP and theInternational Commission on Radiation Units and Measurements (ICRU). One sievert equals 100rem, which is an older,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 unitgray (Gy).[3]
"The quantity dose equivalentH is the product of the absorbed doseD of ionizing radiation and the dimensionless factorQ (quality factor) defined as a function oflinear energy transfer by theICRU"
The value ofQ 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 doseD and the dose equivalentH, 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 doseD and the name sievert instead of joules per kilogram for the unit of dose equivalentH".[4]
In summary:
gray: quantityD—absorbed dose
1 Gy = 1 joule/kilogram—a physical quantity. 1 Gy is the deposit of a joule of radiation energy per kilogram of matter or tissue.
sievert: quantityH—equivalent dose
1 Sv = 1 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 byQ.
"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 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 anddosimeters 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.
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 anddose 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[6] developed the "protection" dose quantitieseffective andequivalent dose which are calculated from more complex computational models and are distinguished by not having the phrasedose equivalent in their name. Only the operational dose quantities which still use Q for calculation retain the phrasedose 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" asequivalent doses.[7]
In theUSA there are differently named dose quantities which are not part of the ICRP nomenclature.[8]
These are directly measurable physical quantities in which no allowance has been made for biological effects. Radiationfluence is the number of radiation particles impinging per unit area per unit time,kerma is the ionising effect on air ofgamma rays andX-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 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.[9]
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.[10]
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.[11] 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.[12] 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.[13]
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 is300 mm × 300 mm × 150 mm depth to represent the human torso.[13]
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.[7]
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".[14][15][13] These quantities cannot be measured in practice but their values are derived using models of external dose to internal organs of the human body, usinganthropomorphic 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.[16]
As protection quantities cannot practically be measured, operational quantities must be used to relate them to practical radiation instrument and dosimeter responses.[17]
This is an actual reading obtained from such as an ambient dosegamma monitor, or a personaldosimeter. 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 theUK, theIonising Radiations Regulations 1999.
Graphic showing relationship of "protection dose" quantities inSI units
The sievert is used in external radiation protection forequivalent dose (the external-source, whole-body exposure effects, in a uniform field), andeffective dose (which depends on the body parts irradiated).
These dose quantities are weighted averages of absorbed dose designed to be representative of thestochastic health effects of radiation, and use of the sievert implies that appropriateweighting factors have been applied to the absorbed dose measurement or calculation (expressed in grays).[1]
The ICRP calculation provides two weighting factors to enable the calculation of protection quantities.
1. The radiation factorWR, which is specific for radiation typeR – This is used in calculating the equivalent doseHT which can be for the whole body or for individual organs.
2. The tissue weighting factorWT, which is specific for tissue type T being irradiated. This is used withWR to calculate the contributory organ doses to arrive at an effective doseE for non-uniform irradiation.
When a whole body is irradiated uniformly only the radiation weighting factorWR 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 factorWT 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 correctiveradiation weighting factorWR, 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.
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.[1]
where
HT is the equivalent dose absorbed by tissueT,
DT,R is the absorbed dose in tissueT by radiation typeR and
WR is the radiation weighting factor defined by regulation.
Thus for example, an absorbed dose of 1 Gy by alpha particles will lead to an equivalent dose of 20 Sv.
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 injoules has increased by a factor of 20, thereby violating the laws ofconservation 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 factorWT, 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 factorWR 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 forWT are given in the table shown here.
The article oneffective 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.[5] 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 quantityH*(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.[20] An example of penetrating radiation isgamma rays.
This is used for monitoring of low penetrating radiation and is usually expressed as the quantityH'(0.07). This means the radiation is equivalent to that found at a depth of 0.07 mm in the ICRU sphere phantom.[21] 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.[22] 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 quantityHp(10).[23]
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 thatH∗(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 calledEmax.
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 quantitiesHlens andHskin.
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.[7]
A final draft report was issued in July 2017 by ICRU/ICRP for consultation.[24]
The sievert is used for human internal dose quantities in calculatingcommitted 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, as the sum of the products of the committed organ or tissue equivalent doses and the appropriate tissue weighting factors, where 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.[5]
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".[25]
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 hasdeterministic andstochastic 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 inherentlyrandom, with most individuals in a group failing to ever exhibit anycausal negative health effects after exposure, while an indeterministic random minority do, often with the resulting subtle negative health effects being observable only after large detailedepidemiology 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 asradiation-induced cancer. The consensus of nuclear regulators, governments and theUNSCEAR is that the incidence of cancers due to ionizing radiation can be modeled as increasing linearly witheffective dose at a rate of 5.5% per sievert.[1] This is known as thelinear 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.[26][27] 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.[28][29]
This is a graph depicting the effect ofdose fractionation on the ability ofgamma 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 conferringradioresistance.
The deterministic (acute tissue damage) effects that can lead toacute 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:[30]
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 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.[1]
For comparison, natural radiation levels inside theUnited States Capitol 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 thegranite structure.[31] 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 naturalEpidemiology of cancer andcancer rates).
US Department of Energy 2010 dose chart in sieverts for a variety of situations and applications[32]Various doses of radiation in sieverts, ranging from trivial to lethal, expressed as comparative areasComparison of radiation doses – includes the amount detected on the trip from Earth to Mars by theRAD on theMSL (2011–2013).[33][34][35][36]
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.
Average accumulated exposure of residents over a period of 9–20 years, who suffered no ill effects, in apartments in Taiwan constructed with rebar containingCobalt-60[51]
500
mSv:
The U.S. 10 C.F.R. § 20.1201(a)(2)(ii) occupational dose limit, shallow-dose equivalent to skin, per annum[47]
670
mSv:
Highest dose received by a worker responding to the Fukushima emergency[52][a]
1
Sv:
Maximum allowed radiation exposure for NASA astronauts over their career[33]
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[53][32]
Fatal acute dose toLouis Slotin in 1946 criticality accident[56]
36
Sv:
Fatal acute dose toCecil Kelley in 1958, death occurred within 35 hours.[58]
54
Sv:
Fatal acute dose toBoris Korchilov in 1961 after a reactor cooling system failed on theSoviet submarine K-19 which required work in the reactor with no shielding[59]
All conversions between hours and years have assumed continuous presence in a steady field, disregarding known fluctuations, intermittent exposure andradioactive decay. Converted values are shown in parentheses. "/a" is "per annum", which means per year. "/h" means "per hour".
<1
mSv/a
<100
nSv/h
Steady dose rates below 100 nSv/h are difficult to measure.[citation needed]
1
mSv/a
(100
nSv/h avg)
ICRP recommended maximum for external irradiation of the human body, excluding medical and occupational exposures.
NRC definition of a high radiation area in a nuclear power plant, warranting a chain-link fence[68]
(17–173
Sv/a)
2–20
mSv/h
Typical dose rate for activatedreactor wall in possible futurefusion reactors after 100 years.[69] After approximately 300 years of decay the fusion waste would produce the same dose rate as exposure tocoal ash, with the volume of fusion waste naturally being orders of magnitude less than from coal ash.[70] Immediate predicted activation is 90 MGy/a.[citation needed]
TypicalPWR spent fuel waste, after 10-year cooldown, no shielding and no distance.[72]
(4.6–5.6
MSv/a)
530–650
Sv/h
The radiation level inside the primary containment vessel of the secondBWR-reactor of theFukushima power station, in February 2017, six years after a suspectedmeltdown.[73][74][75][76][77] In this environment, it takes between 22 and 34 seconds to accumulate amedian lethal dose (LD50/30).
Notes on examples:
^abcdNoted figures are dominated by acommitted 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.
^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.
^abNoted figures exclude any committed dose from radioisotopes taken into the body. Therefore the total radiation dose would be higher unless respiratory protection was used.
The sievert was adopted by theInternational 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.[81]
The sievert is named afterRolf Maximilian Sievert. As with everySI unit named for a person, its symbol starts with anupper case letter (Sv), but when written in full, it follows the rules for capitalisation of acommon noun; i.e.,sievert becomes capitalised at the beginning of a sentence and in titles but is otherwise in lower case.
Frequently usedSI prefixes are the millisievert (1 mSv = 0.001 Sv) and microsievert (1 μSv = 0.000 001 Sv) and commonly used units fortime 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 mSv/h = 8.766 Sv/a
114.1 μSv/h = 1 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:[82]
8 h = 1 day
40 h = 1 week
50 weeks = 1 year
Therefore, for occupation exposures of that time period,
^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.
^abc"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[1]
^"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.
^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
^"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
^abcCalibration of Radiation Protection Monitoring Instruments(PDF), Safety Reports Series 16, IAEA, 2000,ISBN978-92-0-100100-9,In 1991, the International Commission on Radiological Protection (ICRP) [7] recommended a revised system of dose limitation, including specification of primarylimiting quantities for radiation protection purposes. These protection quantities are essentially unmeasurable
^Formerly Utilized Sites Remedial Action Program."Radiation in the Environment"(PDF). US Army Corps of Engineers. Archived fromthe original(PDF) on 11 February 2012. Retrieved18 May 2012.
^Hendrick, R. Edward (October 2010). "Radiation Doses and Cancer Risks from Breast Imaging Studies".Radiology.257 (1):246–253.doi:10.1148/radiol.10100570.PMID20736332.
^Wall, B. F.; Hart, D. (1997). "Revised Radiation Doses for Typical X-Ray Examinations".The British Journal of Radiology.70 (833):437–439.doi:10.1259/bjr.70.833.9227222.PMID9227222. (5,000 patient dose measurements from 375 hospitals)
^Van Unnik, J. G.; Broerse, J. J.; Geleijns, J.; Jansen, J. T.; Zoetelief, J.; Zweers, D. (1997). "Survey of CT techniques and absorbed dose in various Dutch hospitals".The British Journal of Radiology.70 (832):367–71.doi:10.1259/bjr.70.832.9166072.PMID9166072. (3000 examinations from 18 hospitals)
^American Nuclear Society (March 2012)."Appendix B"(PDF). In Klein, Dale; Corradini, Michael (eds.).Fukushima Daiichi: ANS Committee Report. Retrieved19 May 2012.
^Glasstone, Dolan (1962),The Effects of Nuclear Weapons, Defense Atomic Support Agency, Dept. of Defense, Chapter VIII, Initial nuclear radiation
^abMcLaughlin, Thomas P.; Monahan, Shean P.; Pruvost, Norman L.; Frolov, Vladimir V.; Ryazanov, Boris G.; Sviridov, Victor I. (May 2000).A Review of Criticality Accidents(PDF). Los Alamos, NM: Los Alamos National Laboratory. pp. 74–75. LA-13638. Retrieved21 April 2010.
^Dolgodvorov, Vladimir (November 2002)."K-19, the Forgotten Sub" (in Russian). trud.ru. Retrieved2 July 2015.
^Moss, William; Eckhardt, Roger (1995)."The Human Plutonium Injection Experiments"(PDF).Los Alamos Science. Radiation Protection and the Human Radiation Experiments (23):177–223. Retrieved13 November 2012.
^Wyckoff, H. O. (April 1977).Round table on SI units: ICRU Activities(PDF). International Congress of the International Radiation Protection Association. Paris, France. Retrieved18 May 2012.
^Office of Air and Radiation; Office of Radiation and Indoor Air (May 2007)."Radiation: Risks and Realities"(PDF). U.S. Environmental Protection Agency. p. 2. Retrieved19 March 2011.
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