- published: 08 Nov 2014
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The gray (symbol: Gy) is the SI derived unit of absorbed dose, specific energy (imparted) and of kerma. Such energies are typically associated with ionising radiation such as X-rays or gamma particles or with other nuclear particles. It is defined as the absorption of one joule of such energy by one kilogram of matter (usually human tissue).
The gray was named after the British physicist Louis Harold Gray, a pioneer in the field of measurement of radium radiation and X-rays and their effects on living tissue, and was adopted as part of SI by the 15th CGPM in 1975. The SI unit replaces the traditional cgs unit, the rad (equivalent to 0.01 Gy), which remains common in industry in the United States, while "strongly discouraged" in the style guide for U.S. National Institute of Standards and Technology authors.
One gray is the absorption of one joule of energy, in the form of ionizing radiation, per kilogram of matter.
For xrays and gamma rays, these are the same units as the sievert (Sv). For alpha particles one gray is twenty sievert. To avoid any risk of confusion between the absorbed dose (by matter) and the equivalent dose (by biological tissues), one must use the corresponding special units, gray is used instead of the joule per kilogram for absorbed dose and the sievert instead of the joule per kilogram for the dose equivalent. The word "gray" is both the singular and plural spelling.
Grey or gray is an achromatic or neutral color.
Complementary colors are defined to mix to grey, either additively or subtractively, and many color models place complements opposite each other in a color wheel. To produce grey in RGB displays, the R, G, and B primary light sources are combined in proportions equal to that of the white point. In four-color printing, greys are produced either by the black channel, or by an approximately equal combination of CMY primaries. Images which consist wholly of neutral colors are called monochrome, black-and-white or greyscale.
The first recorded use of grey as a color name in the English language was in AD 700.Grey is the British, Canadian, Australian, Irish, New Zealand and South African spelling, although gray remained in common usage in the UK until the second half of the 20th century.Gray is the preferred American spelling, although grey is an accepted variant.Gray became the preferred spelling in American English around 1825.
Most grey pigments have a cool or warm cast to them, as the human eye can detect even a minute amount of saturation.[citation needed]Yellow, orange, and red create a "warm grey". Green, blue, and violet create a "cool grey". When there is no cast at all, it is referred to as "neutral grey", "achromatic grey" or simply "grey".
Unit may refer to: