Sievert

Definition

Le sievert (symbol: Sv ) is the unit derived from equivalent of amount of the international Système (IF). It is a Gray (Joule by Kilogram) qualified. See also Rolf Sievert, Swedish physicist who gave his name to this unit.

Radium of 1 Mg surrounded by a layer of Platine a thickness of 0,5 Misters.

It makes it possible to know over the duration the received amounts, it makes it possible to more easily give an account of the dangerosity of a medium.

It is about equivalent to 8,4 Röntgen S by Kilogram or to 21,6 Curie S by Kilogram. ” --->

the size equivalent Amount, H , is the product of the absorptive amount D of ionizing rays and of the factor without dimension: Q (factor loading due to the radiation).
the effective size Amount, E , is the sum of the products of the equivalent amount H and the factor without dimension: NR (factor loading due to Fabric).

These two sizes have as a unit Sievert, however they do not represent the same thing.

These two factor loadings are prescribed by the International Commission one Radiological Protection (ICRP). Thus, for a given radiation, the numerical value of H in joules per kilogram can be different from the numerical value of D in joules per kilogram, since it is function of the value of Q and NR . In order to avoid any risk of confusion between the absorptive amount D and the equivalent of amount H , it is necessary to employ the special names for the corresponding units, i.e. it is necessary to use the name " gray" instead of " joule by kilogram" for the unit of absorptive amount D and the name " sievert" instead of " joule by kilogram" for the unit of equivalent of amount H .

The sievert makes it possible to quantify a risk, the stochastic effect induced by weak radiations (the risk to contract in 20 years a cancer following an exposure). Thus, 1 mSv corresponds to the reduction in the life expectancy of 0,005% (value to be confirmed). Nevertheless to use the sievert to quantify the effect of an important radiation (typically about Gy) is tendentious, because for such a radiation the effect is not stochastic (I increase the risk to contract a cancer in 20 years) but deterministic: for an amount of 8 Gy (amount known as lethal) I know that I will die. The mechanisms with stochastic work in the case of effect (thus measured by sieverts) and in the case of deterministic effect (the Gy is enough) do not have anything to see.

stochastic effect: have for the moment emphasized only by the study of populations subjected to radiations (typically Hiroshima or the workers of the nuclear power) for one long period.
deterministic effect: are observable directly after (or shortly after irradiation). These effects were discovered at the beginning of the study of the radioactivity. This discovery led to the creation of the ancestor of the CIPR or ICRP in English.

Thus the factors Q and NR are proposed by CIPR but they are arbitrary, it already sometimes happened to them to vary notably (with the rise or the fall) according to the idea that the specialists in the question had risk. Typically the factor 0,20 which applies to the gonades takes account of the risk to transmit the consequences of the irradiation to his/her children, it is a risk which is regarded as inadmissible, it does not have for the moment clearly not measured yet, but as one must wait within the framework of the follow-up which the descendants are sufficiently old to validate or not the incidence of the irradiation of the gonades, by precaution one applies this factor of 0,20. The factor of quality Q reflects the relative biological effectiveness of radiation. Here are some values:

Photon S, all energies: Q = 1
Electron S and Muon S, all energies: Q = 1
Neutron S,

energy < 10 K eV: Q = 5
10 keV < energy < 100 keV: Q = 10
100 keV < energy < 2 MeV: Q = 20
2 MeV < energy < 20 MeV: Q = 10
energy > 20 MeV: Q = 5

Proton S, energy > 2 MeV: Q = 5
Particles alpha and other atomic nuclei: Q = 20

The factor NR , as for him, can represent inter alia the irradiated species (the Insecte S are much more resistant to radiations than the Mammifère S, for example), the susceptibility of the irradiated body, or correct the amount received according to its rate/rhythm of accumulation (two equivalent amounts in terms of energy deposited are not it if they are received over different periods) or of its voluminal concentration (a concentrated amount will be different from a diffuse amount). Here some values of NR for the bodies and fabrics:

Gonade S: NR = 0,20
Stomach, Large intestine, osseous Marrow, Lung: NR = 0,12
Brain, esophagus, Liver, Muscle S, Pancreas, Small intestine, Spleen, Kidney, Center, Thyroid, Uterus, Bladder: NR = 0,05
Skin, surface of the Os: NR = 0,01

And here some values of NR (relative to human) for various organizations:

Virus, Bacterium S, Protozoon S: NR ≈ 0,03 - 0,0003
Insects: NR ≈ 0,1 - 0,002
Mollusc S: NR ≈ 0,06 - 0,006
Plant S: NR ≈ 2 - 0,02
Poisson S: NR ≈ 0,75 - 0,03
Amphibian S: NR ≈ 0,4 - 0,14
Reptile S: NR ≈ 1 - 0,075
Bird X: NR ≈ 0,6 - 0,15
Human: NR = 1

If one supposes Q and NR equal to the unit, then 1 Sv ≈ 107,185 R.

Orders of magnitude and regulation

By convenience, one usually uses the millisievert (mSv).

average annual Amount received in France: ~2,4 mSv/an/personne
Limit authorized for the population, in France: 5 mSv/an/personne
Limit authorized for the exposed personnel, in France: 20 mSv/an/personne
the man presents clinical signs due to the irradiations starting from a single amount equivalent to 1000 mSv. The individual is then systematically hospitalized.
lethal Amount: 8 Gy (beyond a sievert, measurement is not legitimate any more because the sievert gives an account of a stochastic risk due to a weak radiation (about 1 mGy rather), beyond a radiation of 1 Gy it does not have there more the stochastic one, it is a deterministic effect).
One defines the total acute irradiation as being the amount killing 50% of the subjects exposed to the ionizing ray. This value admits an interval from 3 to 4,5 Sv. It is accompanied by a hematologic syndrome being spread out over about thirty days. No treatment is managed.

(Which are the normative sources?)

Proportion received and clinical signs

The excessive irradiation is revealed by the presence of Prodrome S like nausea, the diarrhea, a feeling of tiredness and faintness.

For an amount from 2 to 4 Sv: one observes in practice clinical a syndrome hematopoietic. The populations of lymphocytes and globules white decrease considerably. One speaks about lymphopenia, leucopenia and the irradiation can lead to an anemia (deprives of red globules)
For an amount higher than 8 Sv: One observes a syndrome gastrointestinal with acute diarrheas, digestive hemorrhage leading to death.
For an amount higher than 20 Sv: A nervous syndrome with convulsions, coma and instantaneous death are observed.

However, these accidents being extremely rare, clinical descriptions cannot be established completely by epidemiology.

In addition, it was observed that the lymphocytary déplétion resulting from the exposure to an ionizing ray was directly proportional to the effective Dose. During a probable irradiation at a subject, one then carries out two blood tests at three hours of interval to evaluate the possible variations of the lymphocytary population.

Equivalent and close units

The physical units measuring the radioactivity are numerous.

{OUTLINE. To describe by specifying the relationship or equivalence with the unit IF):

Röntgen (symbol: R, with 1 R = 258 µC/kg ~ 9,330 mGy) the amount of ionizing radiation which produces a unit electrostatic CGS of electricity (a Franklin or Statcoulomb) in a Cubic centimeter of dry air with 0 °C under a atmosphere of pressure.
Roentgen is equivalent man (symbol: Rem, with 1 rem = 10 mSv)
Roentgen is equivalent physical (symbol: Reference mark) amount of radiation absorptive by a fabric mass which deposits same energy there as Röntgen in the same mass of air (~8,4– 9,3 mGy). The unit is used for radiations other than X or gamma.
radioactive Rate dose or, by abuse, “Amount” (shortened ddd, expressed in mSv/h)
Becquerel (symbol: Bq), unit of activity.
Rutherford (symbol: Rd, with 1 Rd = 1 MBq)
Curie (symbol: Ci, with 1 Ci ~ 37 GBq)
Coulomb per kilogram (or C/kg)
Gray (symbol: Gy)
Rad (symbol: rd, with 1 Gy = 100 rd)
DLxx (xx % of the lethal amount without hospitalization, estimated at 10 Sv)}
Unité Chews (symbol: ME (of German Corn salad-Einheit ), with 1 ME ~ 13,468 kBq/m ³) the quantity of Radon per liter of air which ionizes a D.C. current of 0,001 electrostatic unit CGS a second (Statampère), that is to say 0,364 nCi/L.
Sunshine Links or Strontium Links (symbol: S.U., with 1 S.U. ~ 1,065 pGy/s) biological contamination with the Strontium-90 which associates 1 NCV of ⁹⁰Sr per gram of body Calcium; the permissible load is of 1000 S.U

Sources

International committee of the weights and measures (CIPM) 1984, Recommendation 1 (statement, 52,31 and Metrologia, 1985, 21,90)
Abdeljelil Bakri, Neil Heather, Jorge Hendrichs, and Ian Ferris; '' Fifty Years off Biology Radiation in Entomology: Let us injure Learned from IDIDAS '', Annals off the Entomological Society off America, 98 (1): 1-12 (2005)
Article on the measurement of the radioactivity and civil protection on the site Luxorion .

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