Roentgen equivalent man
roentgen equivalent man | |
---|---|
CGS units | |
Unit of | Health effect of ionizing radiation |
Symbol | rem |
Named after | roentgen |
Conversions | |
1 rem in ... | ... is equal to ... |
SI base units | m2⋅s−2 |
SI derived unit | 0.01 Sv |
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.
Quantities measured in rem are designed to represent the
The rem has been defined since 1976 as equal to 0.01
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.[3]: 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 sources.
Usage
The rem and millirem are CGS units in widest use among the U.S. public, industry, and government.[4] 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, and have now virtually replaced the rem.[5]
The conventional units for dose rate is mrem/h. 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. 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. The annual conversions to a Julian year are:
- 1 mrem/h = 8,766 mrem/yr
- 0.1141 mrem/h = 1,000 mrem/yr
The International Commission on Radiological Protection (ICRP) once adopted fixed conversion for occupational exposure, although these have not appeared in recent documents:[6]
- 8 h = 1 day
- 40 h = 1 week
- 50 week = 1 yr
Therefore, for occupation exposures of that time period,
- 1 mrem/h = 2,000 mrem/yr
- 0.5 mrem/h = 1,000 mrem/yr
The U.S. National Institute of Standards and Technology (NIST) strongly discourages Americans from expressing doses in rem, in favor of recommending the SI unit.[7] The NIST recommends defining the rem in relation to the SI in every document where this unit is used.[8]
Health effects
Ionizing radiation has deterministic and stochastic effects on human health. The deterministic effects that can lead to acute radiation syndrome only occur in the case of high doses (> ~10 rad or > 0.1 Gy) and high dose rates (> ~10 rad/h or > 0.1 Gy/h). A model of deterministic risk would require different weighting factors (not yet established) than are used in the calculation of equivalent and effective dose. To avoid confusion, deterministic effects are normally compared to absorbed dose in units of rad, not rem.[9]
Stochastic effects are those that occur randomly, such as
The ICRP recommends limiting artificial irradiation of the public to an average of 100 mrem (1 mSv) of effective dose per year, not including medical and occupational exposures.[10] For comparison, radiation levels inside the United States Capitol are 85 mrem/yr (0.85 mSv/yr), close to the regulatory limit, because of the uranium content of the granite structure.[14] The NRC sets the annual total effective dose of full body radiation, or total body radiation (TBR), allowed for radiation workers 5,000 mrem (5 rem).[15][16]
History
The concept of the rem first appeared in literature in 1945[17] and was given its first definition in 1947.[18] The definition was refined in 1950 as "that dose of any ionizing radiation which produces a relevant biological effect equal to that produced by one roentgen of high-voltage x-radiation."[19] Using data available at the time, the rem was variously evaluated as 83, 93, or 95 erg/gram.[20] Along with the introduction of the rad in 1953, the ICRP decided to continue the use of the rem. The US National Committee on Radiation Protection and Measurements noted in 1954 that this effectively implied an increase in the magnitude of the rem to match the rad (100 erg/gram).[21] The ICRP introduced and then officially adopted the rem in 1962 as the unit of equivalent dose to measure the way different types of radiation distribute energy in tissue and began recommending values of relative biological effectiveness (RBE) for various types of radiation.[22] In practice, the unit of rem was used to denote that an RBE factor had been applied to a number which was originally in units of rad or roentgen.
The
The following table shows radiation quantities in SI and non-SI units:
Quantity | Unit | Symbol | Derivation | Year | SI equivalent |
---|---|---|---|---|---|
Activity (A) | becquerel | Bq | s−1 | 1974 | SI unit |
curie | Ci | 3.7 × 1010 s−1 | 1953 | 3.7×1010 Bq | |
rutherford | Rd | 106 s−1 | 1946 | 1,000,000 Bq | |
Exposure (X) | coulomb per kilogram | C/kg | C⋅kg−1 of air | 1974 | SI unit |
röntgen | R | esu / 0.001293 g of air | 1928 | 2.58 × 10−4 C/kg | |
Absorbed dose (D) | 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 × WR | 1977 | SI unit |
röntgen equivalent man | rem | 100 erg⋅g−1 × WR | 1971 | 0.010 Sv | |
Effective dose (E) | sievert | Sv | J⋅kg−1 × WR × WT | 1977 | SI unit |
röntgen equivalent man | rem | 100 erg⋅g−1 × WR × WT | 1971 | 0.010 Sv |
See also
- Roentgen equivalent physical
- Banana equivalent dose
- Health threat from cosmic rays
- Orders of magnitude (radiation)
References
- ^ "RADInfo Glossary of Radiation Terms". EPA.gov. United States Environmental Protection Agency. 31 August 2015. Retrieved 18 December 2016.
- ^ Morris, Jim; Hopkins, Jamie Smith (11 December 2015), "The First Line of Defense", Slate, retrieved 18 December 2016
- ^ The Effects of Nuclear Weapons, Revised ed., US DOD 1962
- ^ Office of Air and Radiation; Office of Radiation and Indoor Air (May 2007). "Radiation: Risks and Realities". U.S. Environmental Protection Agency. p. 2. Retrieved 23 May 2012.
In the United States, we measure radiation doses in units called rem. Under the metric system, dose is measured in units called sieverts. One sievert is equal to 100 rem.
- PMID 21157526.
- ^ Recommendations of the International Commission on Radiological Protection and of the International Commission on Radiological Units (PDF). National Bureau of Standards Handbook. Vol. 47. US Department of Commerce. 1950. Retrieved 14 November 2012.
- ^ Thompson, Ambler; Taylor, Barry N. (2008). Guide for the Use of the International System of Units (SI) (2008 ed.). Gaithersburg, MD: National Institute of Standards and Technology. p. 10. SP811. Archived from the original on 16 May 2008. Retrieved 28 November 2012.
- ^ a b Hebner, Robert E. (28 July 1998). "Metric System of Measurement: Interpretation of the International System of Units for the United States" (PDF). Federal Register. 63 (144): 40339. Retrieved 9 May 2012.
- ^ "§ 20.1004 Units of radiation dose". NRC Web. Retrieved 29 January 2024.
- ^ )
- ^ Peck, Donald J.; Samei, Ehsan. "How to Understand and Communicate Radiation Risk". Image Wisely. Retrieved 18 May 2012.
- ISBN 978-92-1-142263-4. Retrieved 18 May 2012.
- ISBN 978-1-897761-16-8. Archived from the original(PDF) on 21 July 2012. Retrieved 18 May 2012.
- ^ Formerly Utilized Sites Remedial Action Program. "Radiation in the Environment". US Army Corps of Engineers. Retrieved 10 September 2017.
- ^ "Information for Radiation Workers". NRC Web. Retrieved 29 January 2024.
- ^ "Total Body Irradiation » Radiation Oncology » College of Medicine » University of Florida". Retrieved 29 January 2024.
- ^ Cantrill, S.T; H.M. Parker (5 January 1945). "The Tolerance Dose". Argonne National Laboratory: US Atomic Energy Commission. Archived from the original on 30 November 2012. Retrieved 14 May 2012.
- ^ Nucleonics. 1 (2). 1947.
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(help) - PMID 15403708.
- PMID 14900367.
- ^ Permissible Doses from External Sources of Radiation (PDF). National Bureau of Standards Handbook. Vol. 59. US Department of Commerce. 24 September 1954. p. 31. Retrieved 14 November 2012.
- PMID 21157526.
- ^ Handbook of Radiation Effects, 2nd edition, 2002, Andrew Holmes-Siedle and Len Adams
- ^ 10 CFR 20.1003. US Nuclear Regulatory Commission. 2009.