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The sievert is the International System of Units (SI) SI derived unit

SI derived unit

The International System of Units specifies a set of seven base units from which all other units of measurement are formed, by products of the powers of base units. These other units are called SI derived units, for example, the SI derived unit of area is square metre , and of density is...

of dose equivalent

Equivalent dose

The equivalent absorbed radiation dose, usually shortened to equivalent dose, is a computed average measure of the radiation absorbed by a fixed mass of biological tissue, that attempts to account for the different biological damage potential of different types of ionizing radiation...

radiation. It attempts to quantitatively evaluate the biological effects of ionizing radiation

Ionizing radiation

Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...

as opposed to just the absorbed dose

Absorbed dose

Absorbed dose is a measure of the energy deposited in a medium by ionizing radiation per unit mass...

of radiation energy, which is measured in gray

Gray (unit)

The gray is the SI unit of absorbed radiation dose of ionizing radiation , and is defined as the absorption of one joule of ionizing radiation by one kilogram of matter ....

. It is named after Rolf Maximilian Sievert

Rolf Maximilian Sievert

Professor Rolf Maximilian Sievert was a medical physicist whose major contribution was in the study of the biological effects of radiation.Professor Sievert was born in Stockholm, Sweden...

, a Swedish

Sweden

Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

medical physicist renowned for work on radiation dosage measurement and research into the biological effects of radiation.

Definition

The unit gray measures the absorbed dose of radiation (D), absorbed by any material. The unit sievert measures the equivalent dose of radiation (H), having the same damaging effect as an equal dose of gamma rays.

Both the gray, with symbol Gy and the sievert, with symbol Sv are SI derived unit

SI derived unit

s, defined as a unit of energy (joule) per unit of mass (kilogram):

1 Gy = 1 Sv = 1 J

Joule

The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...

/ kg

Kilogram

The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...

Dose equivalent

The equivalent dose to a tissue is found by multiplying the absorbed dose, in gray, by a weighting factor (W_R). The relation between absorbed dose D and equivalent dose H is thus:

.
The weighting factor (sometimes referred to as a quality factor) is determined by the radiation type and energy range.

where

H_T is the equivalent dose absorbed by tissue T

D_T,R is the absorbed dose in tissue T by radiation type R

W_R is the weighting factor defined by the following table

Radiation type and energy		W_R
electron Electron The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton... s, muon Muon The muon \|mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton... s, photon Photon In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force... s (all energies)
proton Proton The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number.... s and charged pion Pion In particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force.... s
alpha particle Alpha particle Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name... s, fission fragments, heavy ions
neutron Neutron The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of... s (function of linear energy transfer Linear energy transfer Linear energy transfer is a measure of the energy transferred to material as an ionizing particle travels through it. Typically, this measure is used to quantify the effects of ionizing radiation on biological specimens or electronic devices.... L in keV/μm)	L < 10
	10 ≤ L ≤ 100	0.32·L − 2.2
	L > 100	300 / sqrt(L)

Thus for example, an absorbed dose of 1 Gy by alpha particles will lead to an equivalent dose of 20 Sv. The maximum weight of 30 is obtained for neutrons with L = 100 keV/μm.

Effective dose

The effective dose of radiation (E), absorbed by a person is obtained by averaging over all irradiated tissues with weighting factors adding up to 1:

Tissue type	W_T (each)	W_T (group)
Bone marrow Bone marrow Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg... , colon Colon (anatomy) The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a... , lung Lung The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart... , stomach Stomach The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is... , breast Breast The breast is the upper ventral region of the torso of a primate, in left and right sides, which in a female contains the mammary gland that secretes milk used to feed infants.Both men and women develop breasts from the same embryological tissues... , remaining tissues
Gonad Gonad The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes... s
Bladder Urinary bladder The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow muscular, and distensible organ, the bladder sits on the pelvic floor... , oesophagus, liver Liver The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion... , thyroid Thyroid The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...
Bone Bone Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue... surface, brain Brain The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,... , salivary glands, skin Skin -Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
total

For other organisms, weighting factors have been defined, relative to the effect on humans:

Organism	relative weight
Virus Virus A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea... es, bacteria Bacteria Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals... , protozoans	0.03 – 0.0003
Insect Insect Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae... s	0.1 – 0.002
Molluscs	0.06 – 0.006
Plant Plant Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or... s	2 – 0.02
Fish Fish Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...	0.75 – 0.03
Amphibian Amphibian Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods... s	0.4 – 0.14
Reptile Reptile Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors... s	1 – 0.075
Bird Bird Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from... s	0.6 – 0.15

SI multiples and conversions

Frequently used SI multiples are the millisievert (1 mSv = 0.001 Sv) and microsievert (1 μSv = 0.000001 Sv).

An older unit for the equivalent dose, is the rem, still often used in the United States. One sievert is equal to 100 rem:

1 rem = 0.01 Sv = 10 mSv
1 mrem = 0.01 mSv = 10 μSv
1 Sv = 100 rem
1 mSv = 100 mrem = 0.1 rem
1 μSv = 0.1 mrem

The conventional units for its time derivative

Time derivative

A time derivative is a derivative of a function with respect to time, usually interpreted as the rate of change of the value of the function. The variable denoting time is usually written as t\,.-Notation:...

is mSv/h.

Single dose examples

Dental radiography: 0.005 mSv
Average dose to people living within 16 km of Three Mile Island accident
Three Mile Island accident
The Three Mile Island accident was a core meltdown in Unit 2 of the Three Mile Island Nuclear Generating Station in Dauphin County, Pennsylvania near Harrisburg, United States in 1979....

: 0.08 mSv during the accident
Mammogram — Single Exposure, Equipment Mean: 2 mSv
Mammogram — Procedural Mean, Equipment Variation: 4–5 mSv
Brain CT scan: 0.8–5 mSv
Chest CT scan: 6–18 mSv
Gastrointestinal series
Gastrointestinal series
A gastrointestinal series, also called a GI series, is a radiologic examination of the upper and/or lower gastrointestinal tract.*Upper GI series*Lower GI series...

X-ray investigation: 14 mSv
International Commission on Radiological Protection
International Commission on Radiological Protection
The International Commission on Radiological Protection is an advisory body providing recommendations and guidance on radiation protection; It was founded in 1928 by the International Society of Radiology and was then called the ‘International X-ray and Radium Protection Committee’...

recommended limit for volunteers averting major nuclear escalation: 500 mSv
International Commission on Radiological Protection
International Commission on Radiological Protection
The International Commission on Radiological Protection is an advisory body providing recommendations and guidance on radiation protection; It was founded in 1928 by the International Society of Radiology and was then called the ‘International X-ray and Radium Protection Committee’...

recommended limit for volunteers rescuing lives or preventing serious injuries: 1000 mSv

Hourly dose examples

Average individual background radiation dose: 0.23 μSv/h (0.00023 mSv/h); 0.17 μSv/h for Australians, 0.34 μSv/h for Americans
The hourly doses are 1.6 μSv/h (14 mSv/year) in the city of Fukushima
Fukushima
may refer to:*Fukushima City – the capital city of Fukushima Prefecture, Japan*Fukushima Prefecture – a Japanese prefecture*Two nuclear power plants located in Fukushima Prefecture:**Fukushima Daiichi Nuclear Power Plant...

and 0.062 μSv/h (0.54 mSv/year) in Tokyo
Tokyo
, ; officially , is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family...

as of May 25, 2011.
Highest reported level during Fukushima accident: 433 Sv/h for the gas/steam inside the primary containment (drywell) of reactor unit 1 on August 19, 2011 (note the reading is not micro or milli Sv, but Sv/h).
Highest dose rate measured in Finland during the Chernobyl disaster
Chernobyl disaster
The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine , which was under the direct jurisdiction of the central authorities in Moscow...

: 5 µSv/h
Measurements taken after Fukushima accident: Greater than 10 Sv/h for the Ventilation shaft between reactors I and II(equipment used could only read up to 10 Sv/h)

Yearly dose examples

Maximum acceptable dose for the public from any man made facility: 1 mSv/year
Dose from living near a nuclear power station: 0.0001–0.01 mSv/year
Dose from living near a coal-fired power station: 0.0003 mSv/year
Dose from sleeping next to a human for 8 hours every night: 0.02 mSv/year
Dose from cosmic radiation (from sky) at sea level: 0.24 mSv/year
Dose from terrestrial radiation (from ground): 0.28 mSv/year
Dose from natural radiation in the human body: 0.40 mSv/year
Dose from standing in front of the granite of the United States Capitol
United States Capitol
The United States Capitol is the meeting place of the United States Congress, the legislature of the federal government of the United States. Located in Washington, D.C., it sits atop Capitol Hill at the eastern end of the National Mall...

building: 0.85 mSv/year
Average individual background radiation
Background radiation
Background radiation is the ionizing radiation constantly present in the natural environment of the Earth, which is emitted by natural and artificial sources.-Overview:Both Natural and human-made background radiation varies by location....

dose: 2 mSv/year; 1.5 mSv/year for Australians, 3.0 mSv/year for Americans
Dose from atmospheric sources (mostly radon): 2 mSv/year
Total average radiation dose for Americans: 6.2 mSv/year
New York-Tokyo flights for airline crew: 9 mSv/year
Current average dose limit for nuclear workers: 20 mSv/year
Dose from background radiation in parts of Iran, India and Europe: 50 mSv/year
Dose from smoking 30 cigarettes a day: 60–160 mSv/year

Dose limit examples

Criterion for relocation after Chernobyl disaster
Chernobyl disaster
The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine , which was under the direct jurisdiction of the central authorities in Moscow...

: 350 mSv/lifetime
In most countries, the current maximum permissible dose to radiation workers is 20 mSv per year averaged over five years, with a maximum of 50 mSv in any one year. This is over and above background exposure, and excludes medical exposure. The value originates from the International Commission on Radiological Protection (ICRP), and is coupled with the requirement to keep exposure as low as reasonably achievable (ALARA
ALARP
ALARP stands for "as low as reasonably practicable", and is a term often used in the milieu of safety-critical and safety-involved systems. The ALARP principle is that the residual risk shall be as low as reasonably practicable...

) — taking into account social and economic factors.
Public dose limits for exposure from uranium mining or nuclear plants are usually set at 1 mSv/yr above background.
Dose limit applied to workers during Fukushima emergency: 250 mSv.

History

Historically, the weighting factors for radiation type and tissue type were separated out as Q and N respectively. In 2002, the CIPM decided that the distinction between Q and N caused too much confusion and therefore deleted the factor N from the definition of absorbed dose in the SI brochure.

The older version of the definitions contained Q and N factors, corresponding to the current W_R and W_T, with values:

Radiation type and energy	Q
electron Electron The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton... s, positron Positron The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron... s, muon Muon The muon \|mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton... s, or photons (gamma Gamma ray Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei... , X-ray X-ray X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma... )
neutron Neutron The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of... s <10 keV
neutrons 10–100 keV
neutrons 100 keV – 2 MeV
neutrons 2 MeV – 20 MeV
neutrons >20 MeV
protons other than recoil protons and energy >2 MeV
alpha particle Alpha particle Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name... s, fission fragments, nonrelativistic heavy nuclei

Tissue type	N (each)	N (group)
bone surface, skin
bladder, breast, liver, esophagus, thyroid, other
bone marrow, colon, lung, stomach
gonads
total