Sievert
Encyclopedia : S : SI : SIE : 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.
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 composed 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
SI multiples and conversions
Frequently used SI multiples 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:- Dose equivalent
- Ambient dose equivalent
- Directional dose equivalent
- Personal dose equivalent
- Organ equivalent dose
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 less than two months in more than 80% of cases, and much over 4 Sv 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:
- 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:
- Gonads: N = 0.20
- Bone marrow, colon, lung, stomach: N = 0.12
- Bladder, brain, breast, kidney, liver, muscles, oesophagus, pancreas, small intestine, spleen, thyroid, uterus: N = 0.05
- Bone surface, skin: N = 0.01
- Viruses, bacteria, protozoans: N ≈ 0.03 – 0.0003
- Insects: N ≈ 0.1 – 0.002
- Molluscs: N ≈ 0.06 – 0.006
- Plants: N ≈ 2 – 0.02
- Fish: N ≈ 0.75 – 0.03
- Amphibians: N ≈ 0.4 – 0.14
- Reptiles: N ≈ 1 – 0.075
- Birds: N ≈ 0.6 – 0.15
- Humans: N = 1
|
| 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.
|
Sources
- 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] UK National Physical Laboratory
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.