The gray (symbol: Gy) is the SI unit of absorbed radiation dose. Absorbed dose (also known as total ionizing dose, TID is a measure of the energy deposited in a medium by Ionizing radiation.
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Definition
One gray is the absorption of one joule of radiation energy by one kilogram of matter. The joule (written in lower case ˈdʒuːl or /ˈdʒaʊl/ (symbol J) is the SI unit of Energy measuring heat, Electricity In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Matter is commonly defined as being anything that has mass and that takes up space.
Note that, for x and gamma rays, these are the same units as the sievert (Sv). The sievert (symbol Sv is the SI derived unit of dose equivalent. 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. Absorbed dose (also known as total ionizing dose, TID is a measure of the energy deposited in a medium by Ionizing radiation. The equivalent dose ( H T) is a measure of the Radiation dose to tissue where an attempt has been made to allow for the different relative biological
| This SI unit is named after Louis Harold Gray. awaiting copyright information --> Louis Harold Gray ( 10 November 1905 - 9 July 1965 As with every SI unit whose name is derived from the proper name of a person, the first letter of its symbol is uppercase (Gy). The musical instrument is spelled Cymbal. A symbol is something --- such as an object, Picture, written word a sound a piece Capital letters or majuscules pronunciation /məˈdʒʌskyuls ˈmædʒəˌskyuls/ in the Roman alphabet A, B, C, D, When an SI unit is spelled out in English, it should always begin with a lowercase letter (gray), except where any word would be capitalized, such as at the beginning of a sentence or in capitalized material such as a title. Lower case (also lower-case or lowercase) minuscule, or small letters are the smaller form of letters as opposed to upper Note that "degree Celsius" conforms to this rule because the "d" is lowercase. The Celsius Temperature scale was previously known as the centigrade scale.
— Based on The International System of Units, section 5. 2.
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Origin
The gray was defined in 1975 in honour of Louis Harold Gray (1905-1965), who used a similar concept, “that amount of neutron radiation which produces an increment of energy in unit volume of tissue equal to the increment of energy produced in unit volume of water by one röntgen of radiation,” in 1940. awaiting copyright information --> Louis Harold Gray ( 10 November 1905 - 9 July 1965 For other uses of röntgen or roentgen, see Roentgen The röntgen or roentgen (symbol R) is a unit
Explanation
The gray measures the deposited energy of radiation. The biological effects vary by the type and energy of the radiation and the organism and tissues involved. The sievert attempts to account for these variations. The sievert (symbol Sv is the SI derived unit of dose equivalent. A whole-body dose of 10-20 grays of high-energy radiation, delivered at one time, can be fatal to humans[1]. This dosage represents 750-1500 joules for a 75kg adult (equivalent to the chemical energy in a few grams of sugar). Since grays are such large amounts of radiation, medical use of radiation is typically measured in milligrays (mGy).
The average radiation dose from an abdominal x-ray is 1. 4 mGy, that from an abdominal CT scan is 8. 0 mGy, that from a pelvic CT scan is 25 mGy, and that from a selective spiral CT scan of the abdomen and the pelvis is 30 mGy. [2]
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Conversions
One gray is equivalent to 100 rad. The rad is a largely obsolete unit of absorbed Radiation dose with symbol rad.
The röntgen is defined as the radiation exposure equal to the quantity of ionizing radiation that will produce one esu of electricity in one cubic centimetre of dry air at 0 °C and a standard atmosphere , and is conventionally taken to be worth 0. For other uses of röntgen or roentgen, see Roentgen The röntgen or roentgen (symbol R) is a unit The statcoulomb ( statC) or franklin ( Fr) or electrostatic unit of charge ( esu) is the physical unit for Electrical A cubic centimetre or cubic centimeter (symbol cm3 —the abbreviation cc, though widely used is deprecated is a commonly used unit of Volume The Celsius Temperature scale was previously known as the centigrade scale. 258 mC/kg (using a conventional air density of about 1. 293 kg/m³). Using an air ionisation energy of about 36. 161 J/C, we have 1 Gy ≈ 107. 185 R.
| Submultiples | Multiples | |||||
|---|---|---|---|---|---|---|
| Value | Symbol | Name | Value | Symbol | Name | |
| 10–1 Gy | dGy | decigray | 101 Gy | daGy | decagray | |
| 10–2 Gy | cGy | centigray | 102 Gy | hGy | hectogray | |
| 10–3 Gy | mGy | milligray | 103 Gy | kGy | kilogray | |
| 10–6 Gy | µGy | microgray | 106 Gy | MGy | megagray | |
| 10–9 Gy | nGy | nanogray | 109 Gy | GGy | gigagray | |
| 10–12 Gy | pGy | picogray | 1012 Gy | TGy | teragray | |
| 10–15 Gy | fGy | femtogray | 1015 Gy | PGy | petagray | |
| 10–18 Gy | aGy | attogray | 1018 Gy | EGy | exagray | |
| 10–21 Gy | zGy | zeptogray | 1021 Gy | ZGy | zettagray | |
| 10–24 Gy | yGy | yoctogray | 1024 Gy | YGy | yottagray | |
| Common multiples are in bold face. | ||||||
References
- ^ Fred Solomon and Robert Q. Marston, Editors, The Medical Implications of Nuclear War (1986), National Academies Press, p. 235-236, http://www.nap.edu/catalog/940.html
- ^ Parungo C, The Pregnant Surgical Patient, ACS Surgery, http://www.acssurgery.com
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