Roentgen equivalent man

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roentgen equivalent man
Unit system CGS units
Unit of Health effect of ionizing radiation
Symbolrem
Named after roentgen
Conversions
1 rem in ...... is equal to ...
    SI base units     m 2⋅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.

Contents

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. 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  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, which was named after Wilhelm Röntgen, a German scientist who discovered X-rays. 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. [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 radiation-induced cancer. The consensus of the nuclear industry, nuclear regulators, and governments, is that the incidence of cancers caused by ionizing radiation can be modeled as increasing linearly with effective dose at a rate of 0.055% per rem (5.5%/Sv). [10] Individual studies, alternate models, and earlier versions of the industry consensus have produced other risk estimates scattered around this consensus model. There is general agreement that the risk is much higher for infants and fetuses than adults, higher for the middle-aged than for seniors, and higher for women than for men, though there is no quantitative consensus about this. [11] [12] There is much less data, and much more controversy, regarding the possibility of cardiac and teratogenic effects, and the modelling of internal dose. [13]

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 International Committee for Weights and Measures (CIPM) adopted the sievert in 1980 but never accepted the use of the rem. The NIST recognizes that this unit is outside the SI but temporarily accepts its use in the U.S. with the SI. [8] The rem remains in widespread use as an industry standard in the U.S. [23] The United States Nuclear Regulatory Commission still permits the use of the units curie, rad, and rem alongside SI units. [24]

The following table shows radiation quantities in SI and non-SI units:

Ionizing radiation related quantities
QuantityUnitSymbolDerivationYear SI equivalent
Activity (A) becquerel Bqs−11974SI unit
curie Ci3.7 × 1010 s−119533.7×1010 Bq
rutherford Rd106 s−119461,000,000 Bq
Exposure (X) coulomb per kilogram C/kgC⋅kg−1 of air1974SI unit
röntgen R esu / 0.001293 g of air19282.58 × 10−4 C/kg
Absorbed dose (D) gray Gy J⋅kg−11974SI unit
erg per gramerg/gerg⋅g−119501.0 × 10−4 Gy
rad rad100 erg⋅g−119530.010 Gy
Equivalent dose (H) sievert SvJ⋅kg−1 × WR 1977SI unit
röntgen equivalent man rem100 erg⋅g−1 × WR 19710.010 Sv
Effective dose (E) sievert SvJ⋅kg−1 × WR × WT 1977SI unit
röntgen equivalent man rem100 erg⋅g−1 × WR × WT 19710.010 Sv

See also

Related Research Articles

<span class="mw-page-title-main">Sievert</span> SI unit of equivalent dose of ionizing radiation

The sievert is a unit in the International System of Units (SI) intended to represent the stochastic health risk of ionizing radiation, which is defined as the probability of causing radiation-induced cancer and genetic damage. The sievert is important in dosimetry and radiation protection. It is named after Rolf Maximilian Sievert, a Swedish medical physicist renowned for work on radiation dose measurement and research into the biological effects of radiation.

The gray is the unit of ionizing radiation dose in the International System of Units (SI), defined as the absorption of one joule of radiation energy per kilogram of matter.

Radiation dosimetry in the fields of health physics and radiation protection is the measurement, calculation and assessment of the ionizing radiation dose absorbed by an object, usually the human body. This applies both internally, due to ingested or inhaled radioactive substances, or externally due to irradiation by sources of radiation.

Equivalent dose is a dose quantity H representing the stochastic health effects of low levels of ionizing radiation on the human body which represents the probability of radiation-induced cancer and genetic damage. It is derived from the physical quantity absorbed dose, but also takes into account the biological effectiveness of the radiation, which is dependent on the radiation type and energy. In the SI system of units, the unit of measure is the sievert (Sv).

<span class="mw-page-title-main">Health physics</span>

Health physics, also referred to as the science of radiation protection, is the profession devoted to protecting people and their environment from potential radiation hazards, while making it possible to enjoy the beneficial uses of radiation. Health physicists normally require a four-year bachelor’s degree and qualifying experience that demonstrates a professional knowledge of the theory and application of radiation protection principles and closely related sciences. Health physicists principally work at facilities where radionuclides or other sources of ionizing radiation are used or produced; these include research, industry, education, medical facilities, nuclear power, military, environmental protection, enforcement of government regulations, and decontamination and decommissioning—the combination of education and experience for health physicists depends on the specific field in which the health physicist is engaged.

Absorbed dose is a dose quantity which is the measure of the energy deposited in matter by ionizing radiation per unit mass. Absorbed dose is used in the calculation of dose uptake in living tissue in both radiation protection, and radiology. It is also used to directly compare the effect of radiation on inanimate matter such as in radiation hardening.

In radiation physics, kerma is an acronym for "kinetic energy released per unit mass", defined as the sum of the initial kinetic energies of all the charged particles liberated by uncharged ionizing radiation in a sample of matter, divided by the mass of the sample. It is defined by the quotient .

<span class="mw-page-title-main">Rolf Maximilian Sievert</span> Swedish medical physicist, professor

Rolf Maximilian Sievert was a Swedish medical physicist whose major contribution was in the study of the biological effects of ionizing radiation.

The rad is a unit of absorbed radiation dose, defined as 1 rad = 0.01 Gy = 0.01 J/kg. It was originally defined in CGS units in 1953 as the dose causing 100 ergs of energy to be absorbed by one gram of matter. The material absorbing the radiation can be human tissue, air, water, or any other substance.

The International Commission on Radiological Protection (ICRP) is an independent, international, non-governmental organization, with the mission to protect people, animals, and the environment from the harmful effects of ionising radiation. Its recommendations form the basis of radiological protection policy, regulations, guidelines and practice worldwide.

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Radiobiology is a field of clinical and basic medical sciences that involves the study of the effects of ionizing radiation on living things, in particular health effects of radiation. Ionizing radiation is generally harmful and potentially lethal to living things but can have health benefits in radiation therapy for the treatment of cancer and thyrotoxicosis. Its most common impact is the induction of cancer with a latent period of years or decades after exposure. High doses can cause visually dramatic radiation burns, and/or rapid fatality through acute radiation syndrome. Controlled doses are used for medical imaging and radiotherapy.

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<span class="mw-page-title-main">Roentgen (unit)</span> Measurement of radiation exposure

The roentgen or röntgen 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 . In 1928, it was adopted as the first international measurement quantity for ionizing radiation to be defined for radiation protection, as it was then the most easily replicated method of measuring air ionization by using ion chambers. It is named after the German physicist Wilhelm Röntgen, who discovered X-rays and was awarded the first Nobel Prize in Physics for the discovery.

<span class="mw-page-title-main">Orders of magnitude (radiation)</span>

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<span class="mw-page-title-main">Radiation exposure</span> Measure of ionization of air by ionizing radiation

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References

  1. ↑ "RADInfo Glossary of Radiation Terms". EPA.gov. United States Environmental Protection Agency. 31 August 2015. Retrieved 18 December 2016.
  2. ↑ Morris, Jim; Hopkins, Jamie Smith (11 December 2015), "The First Line of Defense", Slate, retrieved 18 December 2016
  3. ↑ The Effects of Nuclear Weapons, Revised ed., US DOD 1962
  4. ↑ 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.
  5. ↑ Pradhan, A. S. (2007). "Evolution of dosimetric quantities of International Commission on Radiological Protection (ICRP): Impact of the forthcoming recommendations". Journal of Medical Physics / Association of Medical Physicists of India. 32 (3): 89–91. doi: 10.4103/0971-6203.35719 . ISSN   0971-6203. PMC   3000504 . PMID   21157526.
  6. ↑ 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.
  7. ↑ 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.
  8. 1 2 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.
  9. ↑ "§ 20.1004 Units of radiation dose". NRC Web. Retrieved 29 January 2024.
  10. 1 2 Icrp (2007). The 2007 Recommendations of the International Commission on Radiological Protection. ICRP publication 103. Vol. 37. ISBN   978-0-7020-3048-2 . Retrieved 17 May 2012.{{cite book}}: |journal= ignored (help)
  11. ↑ Peck, Donald J.; Samei, Ehsan. "How to Understand and Communicate Radiation Risk". Image Wisely. Retrieved 18 May 2012.
  12. ↑ United Nations Scientific Committee on the Effects of Atomic Radiation (2008). Effects of ionizing radiation : UNSCEAR 2006 report to the General Assembly, with scientific annexes. New York: United Nations. ISBN   978-92-1-142263-4 . Retrieved 18 May 2012.
  13. ↑ European Committee on Radiation Risk (2010). Busby, Chris; et al. (eds.). 2010 recommendations of the ECRR : the health effects of exposure to low doses of ionizing radiation (PDF) (Regulators' ed.). Aberystwyth: Green Audit. ISBN   978-1-897761-16-8. Archived from the original (PDF) on 21 July 2012. Retrieved 18 May 2012.
  14. ↑ Formerly Utilized Sites Remedial Action Program. "Radiation in the Environment". US Army Corps of Engineers. Retrieved 10 September 2017.
  15. ↑ "Information for Radiation Workers". NRC Web. Retrieved 29 January 2024.
  16. ↑ "Total Body Irradiation » Radiation Oncology » College of Medicine » University of Florida" . Retrieved 29 January 2024.
  17. ↑ 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.
  18. ↑ Nucleonics. 1 (2). 1947.{{cite journal}}: Missing or empty |title= (help)
  19. ↑ Parker, H.M. (1950). "Tentative Dose Units for Mixed Radiations". Radiology. 54 (2): 257–262. doi:10.1148/54.2.257. PMID   15403708.
  20. ↑ Anderson, Elda E. (March 1952). "Units of Radiation and Radioactivity". Public Health Reports. 67 (3): 293–297. doi:10.2307/4588064. JSTOR   4588064. PMC   2030726 . PMID   14900367.
  21. ↑ 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.
  22. ↑ Pradhan, A. S. (2007). "Evolution of dosimetric quantities of International Commission on Radiological Protection (ICRP): Impact of the forthcoming recommendations". Journal of Medical Physics / Association of Medical Physicists of India. 32 (3): 89–91. doi: 10.4103/0971-6203.35719 . ISSN   0971-6203. PMC   3000504 . PMID   21157526.
  23. ↑ Handbook of Radiation Effects, 2nd edition, 2002, Andrew Holmes-Siedle and Len Adams
  24. ↑ 10 CFR 20.1003. US Nuclear Regulatory Commission. 2009.
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