Information AboutMsv |
| CATEGORIES ABOUT SIEVERT | |
| si derived units | |
| units of radiation dose | |
| radiation health effects | |
| radiobiology | |
| radioactivity | |
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DEFINITION The equivalent dose to a tissue is found by multiplying the absorbed dose, in grays, by a Dimensionless "quality factor" ''Q'', dependent upon radiation type, and by another dimensionless factor ''N'', dependent on all other pertinent factors. ''N'' depends upon the part of the body irradiated, the time and volume over which the dose was spread, even the species of the subject. Together, ''Q'' and ''N'' constitute the Radiation Weighting Factor , ''rW''. For an organism comprised of multiple tissue types a Weighted Sum or Integral is often used. In terms of SI Base Unit s: :1 Sv = 1 J/kg = 1 m2·s–2 Although the sievert has the same dimensions as the gray (i.e. joules per kilogram), it measures a different thing. To avoid any risk of confusion between the absorbed dose and the equivalent dose, one must use the corresponding special units, namely the ''gray'' instead of the ''joule per kilogram'' for absorbed dose and the ''sievert'' instead of the ''joule per kilogram'' for the dose equivalent. For a given amount of radiation (measured in grays), the biological effect (measured in sieverts) can vary considerably as a result of the radiation weighting factor ''rW''. SI MULTIPLES AND CONVERSIONS Frequently used SI Multiple s are the millisievert (1mSv = 10-3Sv) and microsievert (1μSv = 10-6Sv). An older unit of the equivalent dose is the Rem (Roentgen equivalent man); 1 Sv is equal to 100 rem. In some fields, rem and mrem continue to be used along with Sv and mSv, unavoidably causing confusion (1 Sv = 100 rem, 10 mSv = 1 rem: it is hard to memorize when to use which conversion factor). EXPLANATION Various terms are used with this unit:
The millisievert (mSv) is commonly used to measure the effective dose in diagnostic medical procedures (e.g. X-rays , Nuclear Medicine , Positron Emission Tomography and Computed Tomography ). The Natural Background effective dose rate varies considerably from place to place, but typically is around 3.5 mSv/year. For a full body equivalent dose, 1 Sv causes slight blood changes, 2-5 Sv causes nausea, hair loss, hemorrhage and will cause death in many cases. More than 6 Sv will lead to death in less than two months in more than 80% of cases, and much over 4 is more likely than not to cause death. See Radiation Poisoning for a more complete analysis of effects of various dosage levels. The Collective Dose that a population is exposed to is measured in "man-sieverts" (man.Sv). ''Q'' VALUES Here are some quality factor values:
N VALUES Here are some N values for organs and tissues:
And for other organisms, relative to humans:
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