Absorbed dose is a measurable, physical quantity.
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It is expressed in grays (Gy), or, more frequently milligrays (mGy), which are 1/1000th of a gray.
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1 gray = 1 joule of energy deposited in 1 kilogram of material i.e. 1 Gy = 1 J/kg.
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Equivalent dose = absorbed Dose multiplied the appropriate radiation weighting factor.
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The radiation weighting factors are needed because different types of radiation (like alpha, beta, gamma, and neutrons) can have different effects even if the absorbed dose is the same.
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Equivalent dose is expressed in sieverts (Sv), or, more frequently, millisieverts (mSv) which are 1/1000th of a sievert, and the organ should always be specified (for example "25 mSv to the skin").
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In the simplest cases, for gamma (photon) and beta (electron) radiation, the radiation weighting factor is 1, and therefore, for example, an absorbed dose of 1 mGy in an organ equals an equivalent dose of 1 mSv to that organ.
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Effective dose = sum for all organs of (equivalent dose to the organ times the appropriate tissue weighting factor)
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The tissue weighting factors are needed because different organs have different levels of sensitivity to radiation, even if the equivalent dose is the same.
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Effective dose is expressed in sieverts (Sv), or, more frequently, millisieverts (mSv) which are 1/1000th of a sievert. This is the most frequently used dose in radiological protection. Unless you see mention of a specific organ, a "dose" in Sv or mSv is the effective dose.
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In the simplest cases, for uniform whole-body exposure to gamma (photon) or beta (electron) radiation, the radiation weighting factor is 1, and the tissue weighting factors add up to 1, and therefore, for example, an absorbed dose of 1 mGy equals an effective dose of 1 mSv.
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