Editing Roentgen equivalent man (section)

{{Short description|Radiation unit}}
{{About|the [[Centimetre–gram–second system of units|CGS]] unit of [[equivalent dose]]|the historical equivalent of modern [[kerma (physics)|kerma]]|roentgen (unit)}}{{For|the light metro system of Montreal|Réseau express métropolitain}}
{{Use dmy dates|date=April 2022}}
{{Infobox Unit
| bgcolour =
| name = roentgen equivalent man
| image = 
| caption = 
| standard = [[CGS]] units
| quantity = [[Equivalent dose|Health effect of ionizing radiation]]
| symbol = rem
| dimension = 
| namedafter = [[Roentgen (unit)|roentgen]]
| units1 = [[SI base unit]]s
| inunits1 = [[metre|m]]<sup>2</sup>⋅[[second|s]]<sup>−2</sup>
| units2 = [[SI derived unit]]
| inunits2 = 0.01 [[Sievert|Sv]]
}}
The '''roentgen equivalent man''' ('''rem''')<ref name=EPA2>{{cite web|title=RADInfo Glossary of Radiation Terms|publisher=United States Environmental Protection Agency|website=EPA.gov|url=https://www.epa.gov/enviro/radinfo-glossary-radiation-terms|access-date=18 December 2016|date=31 August 2015}}</ref><ref name=Slate>{{citation|date=11 December 2015|title=The First Line of Defense|first1=Jim|last1=Morris|first2=Jamie Smith|last2=Hopkins|work=Slate|url=http://www.slate.com/articles/news_and_politics/politics/2015/12/nuclear_weapons_plants_are_killing_the_people_who_once_guarded_them_a_center.html|access-date=18 December 2016}}</ref> is a [[Centimetre–gram–second system of units|CGS unit]] of [[equivalent dose]], [[effective dose (radiation)|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.

Quantities measured in rem are designed to represent the [[stochastic]] biological risk of ionizing radiation, which is primarily [[radiation-induced cancer]]. These quantities are derived from [[absorbed dose]], which in the CGS system has the unit [[rad (unit)|rad]]. There is no universally applicable conversion constant from rad to rem; the conversion depends on [[relative biological effectiveness]] (RBE).

The rem has been defined since 1976 as equal to 0.01&nbsp;[[sievert]], which is the more commonly used [[SI unit]] outside the United States. Earlier definitions going back to 1945 were derived from the [[Roentgen (unit)|roentgen unit]], which was named after [[Wilhelm Röntgen]], a German scientist who discovered [[X-ray]]s. The unit name is misleading, since 1 roentgen actually deposits about 0.96 rem in soft biological tissue, when all weighting factors equal unity. Older units of rem following other definitions are up to 17% smaller than the modern rem.

Doses 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. Note that the quantities that are measured in rem were not designed to be correlated to ARS symptoms. The [[absorbed dose]], measured in rad, is a better indicator of ARS.<ref name="remdef">''The Effects of Nuclear Weapons'', Revised ed., US DOD 1962</ref>{{rp|592–593}}

A 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 radiation|background]] sources.