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Encyclopedia > Sievert

The sievert (symbol: Sv) is the SI derived unit of dose equivalent. It attempts to reflect the biological effects of radiation as opposed to the physical aspects, which are characterised by the absorbed dose, measured in grays. It is named after Rolf Sievert, a Swedish medical physicist famous for work on radiation dosage measurement and research into the biological effects of radiation. SI derived units are part of the SI system of measurement units and are derived from the seven SI base units. ... The equivalent dose is a measure of the radiation dose to tissue where an attempt has been made to allow for the different relative biological effect of different types of radiation. ... Radiation as used in physics, is energy in the form of waves or moving subatomic particles. ... Absorbed dose is a measure of the energy deposited in a medium by ionising radiation. ... The gray (symbol: Gy) is the SI unit of absorbed dose. ... Professor Rolf Maximilian Sievert (6 May 1896 - 3 October 1966) was a medical physicist whose major contribution was in the study of the biological effects of radiation. ...

## Contents

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, WR . For an organism composed of multiple tissue types a weighted sum or integral is often used. (In 2002, the CIPM decided that the distinction between Q and N causes too much confusion and therefore deleted the factor N from the definition of absorbed dose in the SI brochure. [1].) In the physical sciences, a dimensionless number (or more precisely, a number with the dimensions of 1) is a quantity which describes a certain physical system and which is a pure number without any physical units; it does not change if one alters ones system of units of measurement... A weight function is a mathematical device used when performing a sum, integral, or average in order to give some elements more of a weight than others. ... This article is about the concept of integrals in calculus. ... The Comité international des poids et mesures or The International Committee for Weights and Measures (CIPM) consists of eighteen persons from Member States of the Metre Convention. ...

In terms of SI base units: The SI system of units defines seven SI base units: physical units defined by an operational definition. ...

1 Sv = 1 J/kg = 1 m2/s2 = 1 m2·s–2

## SI multiples and conversions

Frequently used SI multiples are the millisievert (1 mSv = 10–3 Sv) and microsievert (1 μSv = 10–6 Sv). An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol) to form a decimal multiple or submultiple. ...

An older unit of the equivalent dose is the rem (Roentgen equivalent man); 1 Sv is equal to 100 rem. In some fields and countries, 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). The Röntgen equivalent man or rem (symbol rem) is an obsolete unit of radiation dose. ...

## Explanation

Various terms are used with this unit:

• Dose equivalent
• Ambient dose equivalent
• Directional dose equivalent
• Personal dose equivalent
• Organ equivalent dose

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 varies considerably from place to place, but typically is around 2.4 mSv/year [2] (pdf). In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... Shown above is the bone scintigraphy of a young woman. ... Image of a typical positron emission tomography (PET) facility Positron emission tomography (PET) is a nuclear medicine medical imaging technique which produces a three-dimensional image or map of functional processes in the body. ... It has been suggested that Synchrotron X-ray tomographic microscopy, X-ray tomography be merged into this article or section. ... Background radiation is the ionizing radiation emitted from a variety of natural and artificial radiation sources: sources in the Earth and from those sources that are incorporated in our food and water, which are incorporated in our body, and in building materials and other products that incorporate those radioactive sources...

For acute 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 3 Sv will lead to death in 50% of cases within 30 days, and over 6 Sv survival is unlikely. See radiation poisoning for a more complete analysis of effects of various dosage levels. For other uses, see Nausea (disambiguation). ... Baldness (formally alopecia) is the state of lacking hair where it usually would grow, especially on the head. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Radiation poisoning, also called radiation sickness, is a form of damage to organ tissue due to excessive exposure to ionizing radiation. ...

Given the linear no-threshold model of radiation response , the collective dose that a population is exposed to is measured in "man-sieverts" (man.Sv). The linear no-threshold model or LNTM is a model of the damage cased by ionizing radiation, and particularly the increased risk of cancer. ...

## Q values

Here are some quality factor values:

• Photons, all energies : Q = 1
• Electrons and muons, all energies : Q = 1
• Neutrons,
• energy < 10 keV : 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
• Protons, energy > 2 MeV : Q = 5
• Alpha particles and other atomic nuclei : Q = 20

In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... For other uses, see Electron (disambiguation). ... The muon (from the letter mu (Î¼)--used to represent it) is an elementary particle with negative electric charge and a spin of 1/2. ... This article or section does not adequately cite its references or sources. ... An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. ... For other uses, see Proton (disambiguation). ... An alpha particle is deflected by a magnetic field Alpha radiation consists of helium-4 nuclei and is readily stopped by a sheet of paper. ...

## N values

Here are some N values for organs and tissues:

 This SI unit is named after Rolf Maximilian Sievert. As for all SI units whose names are derived from the proper name of a person, the first letter of its symbol is uppercase (Sv). But when an SI unit is spelled out, it should always be written in lowercase (sievert), unless it begins a sentence or is the name "degree Celsius". — Based on The International System of Units, section 5.2.

The sverdrup, named in honour of the pioneering oceanographers Harald and Otto Sverdrup, is an unit of measure of volume transport. ...

## References

• Comité international des poids et mesures (CIPM) 1984, Recommendation 1 (PV, 52, 31 and Metrologia, 1985, 21, 90)
• Abdeljelil Bakri, Neil Heather, Jorge Hendrichs, and Ian Ferris; Fifty Years of Radiation Biology in Entomology: Lessons Learned from IDIDAS, Annals of the Entomological Society of America, 98(1): 1-12 (2005)
• Introduction to Quantities and Units for Ionising Radiation National Physical Laboratory

Results from FactBites:

 Sievert - definition of Sievert in Encyclopedia (284 words) The sievert (symbol Sv) is an SI derived unit of equivalent dose or effective dose (of radiation), and so is dependent upon the biological effects of radiation as opposed to the physical aspects, characterised by the absorbed dose (measured in grays). The equivalent dose to a tissue is found by multiplying the absorbed dose by a "quality factor", dependent upon radiation type. The unit is named after Rolf Sievert, a Swedish medical physicist who was well-known for his work on radiation dosage measurement together with his research into the biological effects of radiation.
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