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The roentgen equivalent man (rem) [1] [2] is a CGS unit of equivalent dose, effective dose, and committed dose, which are dose measures used to estimate potential health effects of low levels of ionizing radiation on the human body.
Recognized effects of higher acute radiation doses are described in more detail in the article on radiation poisoning.Although the International System of Units (SI) defines the sievert (Sv) as the unit of radiation dose equivalent, chronic radiation levels and standards are still often given in units of millirems (mrem), where 1 mrem equals 1/1,000 of a rem and 1 rem equals 0.01 Sv.
The gray was adopted as part of the International System of Units in 1975. The corresponding cgs unit to the gray is the rad (equivalent to 0.01 Gy), which remains common largely in the United States, though "strongly discouraged" in the style guide for U.S. National Institute of Standards and Technology. [3]
The CIPM also says that "in order to avoid any risk of confusion between the absorbed dose D and the dose equivalent H, the special names for the respective units should be used, that is, the name gray should be used instead of joules per kilogram for the unit of absorbed dose D and the name sievert instead of joules per kilogram for the unit ...
The roentgen or röntgen (/ ˈ r ɛ n t ɡ ə n,-dʒ ə n, ˈ r ʌ n t-/; [2] symbol R) is a legacy unit of measurement for the exposure of X-rays and gamma rays, and is defined as the electric charge freed by such radiation in a specified volume of air divided by the mass of that air (statcoulomb per kilogram).
The SI unit of measure for equivalent dose is the sievert, defined as one Joule per kg. [11] In the United States the roentgen equivalent man (rem), equal to 0.01 sievert, is still in common use, although regulatory and advisory bodies are encouraging transition to sievert. [12]
gray: Gy J⋅kg −1: 1974 SI unit erg per gram erg/g erg⋅g −1: 1950 1.0 × 10 −4 Gy: rad: rad 100 erg⋅g −1: 1953 0.010 Gy Equivalent dose (H) sievert: Sv J⋅kg −1 × W R: 1977 SI unit röntgen equivalent man: rem 100 erg⋅g −1 × W R: 1971 0.010 Sv Effective dose (E) sievert: Sv J⋅kg −1 × W R × W T: 1977 SI unit röntgen ...
To represent stochastic risk the dose quantities equivalent dose H T and effective dose E are used, and appropriate dose factors and coefficients are used to calculate these from the absorbed dose. [8] Equivalent and effective dose quantities are expressed in units of the sievert or rem which implies that biological effects have been taken into ...