There is no exact conversion from hours to years because of leap years, but approximate conversions are:ġ mrem/h = 8,766 mrem/yr 0.1141 mrem/h = 1,000 mrem/yr In many occupational scenarios, the hourly dose rate might fluctuate to levels thousands of times higher for a brief period of time, without infringing on the annual total exposure limits. Regulatory limits and chronic doses are often given in units of mrem/yr or rem/yr, where they are understood to represent the total amount of radiation allowed (or received) over the entire year. The conventional units for dose rate is mrem/h. However, the SI unit the sievert (Sv) is the normal unit outside the United States, and is increasingly encountered within the US in academic, scientific, and engineering environments. The rem and millirem are CGS units in widest use among the U.S. : 592–593Ī rem is a large dose of radiation, so the millirem ( mrem), which is one thousandth of a rem, is often used for the dosages commonly encountered, such as the amount of radiation received from medical x-rays and background sources. The absorbed dose, measured in rad, is a better indicator of ARS. Note that the quantities that are measured in rem were not designed to be correlated to ARS symptoms. Older units of rem following other definitions are up to 17% smaller than the modern rem.ĭoses greater than 100 rem received over a short time period are likely to cause acute radiation syndrome (ARS), possibly leading to death within weeks if left untreated. The unit name is misleading, since 1 roentgen actually deposits about 0.96 rem in soft biological tissue, when all weighting factors equal unity. Earlier definitions going back to 1945 were derived from the roentgen unit, which was named after Wilhelm Röntgen, a German scientist who discovered X-rays. The rem has been defined since 1976 as equal to 0.01 sievert, which is the more commonly used SI unit outside the United States. There is no universally applicable conversion constant from rad to rem the conversion depends on relative biological effectiveness (RBE).
These quantities are derived from absorbed dose, which in the CGS system has the unit rad. Quantities measured in rem are designed to represent the stochastic biological risk of ionizing radiation, which is primarily radiation-induced cancer. The roentgen equivalent man ( rem) 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.
For the historical equivalent of modern kerma, see roentgen (unit). This article is about the CGS unit of equivalent dose.
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