Sievert

From Freepedia

The sievert (symbol: Sv) is the SI 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.

Contents

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 units:

1 Sv = 1 J/kg = 1 m2·s–2

Note that these are the same units as the gray. 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.

SI multiples

Multiple Name Symbol Multiple Name Symbol
100 sievert Sv      
101 decasievert daSv 10–1 decisievert dSv
102 hectosievert hSv 10–2 centisievert cSv
103 kilosievert kSv 10–3 millisievert mSv
106 megasievert MSv 10–6 microsievert µSv
109 gigasievert GSv 10–9 nanosievert nSv
1012 terasievert TSv 10–12 picosievert pSv
1015 petasievert PSv 10–15 femtosievert fSv
1018 exasievert ESv 10–18 attosievert aSv
1021 zettasievert ZSv 10–21 zeptosievert zSv
1024 yottasievert YSv 10–24 yoctosievert ySv

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 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).

Conversions

1 Sv is equal to 100 rems. If you assume Q and N equal to 1, then 1 Sv ≈ 107.185 röntgens (R).

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

N values

Here are some N values for organs and tissues:

And for other organisms, relative to humans:

Sources

Retrieved from "http://en.freepedia.org/Sievert.html"


Views
Personal tools
In other languages
Similar Links