Roentgen equivalent in man

Rem. Ancient unit of measurement, which measures the radiation dose absorbed by a living being. Its name comes from the acronym in English “Roentgen equivalent for man”.


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  • 1 Origin
  • 2 Definition
  • 3 Formulation
  • 4 Equivalence in the International System
  • 5 Submultiples
  • 6 Note on terminology
  • 7 See also
  • 8 Reference
  • 9 Source


Between 1953 and 1962 the International Commission on Radiological Measurements and Units (ICRU) defined the radiological magnitudes: exposure, absorbed dose and equivalent dose and established its units (Röentgen, rad and rem). These units have been replaced by new ones, since in 1975 the International Bureau of Weights and Measures (BIPM) adopted new units for the International System (SI): Coulomb / Kg for exposure, for the absorbed dose of Gray and in 1979 for the equivalent dose the Sievert. The daily and frequent use of the milliSievert (mSv) in routine practice has made it the modern and international unit of biological equivalence and, as a consequence, the unit most used in Radiological Protection .


Roentgen 2 is the unit of radiation dose equivalent to the irradiation necessary for the ions produced in a cubic centimeter of dry air to transport an amount of electricity (negative or positive) equal to three ten millionths of coulomb . The rem unit reflects the response biological to ionizing radiation , so it can be used to compare the effects of different radiation. It takes into account different biological responses to different types of radiation, equivalent to the dose causing the same biological damage a Roentgen of X – ray or rays ganma. Not all radiation has the same biological effect, even with the same amount of absorbed dose. To get an idea of ​​what the rem represents under the law, a worker exposed to radiation cannot receive more than 5 rem in a year.


To determine the equivalent dose -rem – the absorbed dose (Da) in rads must be multiplied by a quality factor q, characteristic of each type of radiation . For electromagnetic radiation , the rad and the rem coincide in their value, since they are assigned a q value of 1.

Rem = Da.q

Equivalence in the International System

Unit of measurement Symbol Equivalence
Sievert 1 Sv 100 rem


The most common are the following:

Value Symbol Name
10 -6 rem μrem microremrem
10 -3 rem mrem milirrem

Terminology Note

This unit is known by Rem (Roentgen equivalent for man), it does not come from the proper name of a person, its symbol is properly these initials (rem). You can also write rem or REM.


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