Roentgen equivalent man

Named after Wilhelm Röntgen (German scientist, 1845-1923), the roentgen equivalent in man (or mammal[1]) or rem (symbol rem) is a unit of radiation dose equivalent. It is the product of the absorbed dose in rads and a weighting factor, WR, which accounts for the effectiveness of the radiation to cause biological damage.

An acute whole-body dose of under 50 rem is typically subclinical and will produce nothing other than blood changes. 50 to 200 rem may cause illness but will rarely be fatal. Doses of 200 to 1,000 rem will probably cause serious illness with poor outlook at the upper end of the range. Doses of more than 1,000 rems are almost invariably fatal.[2] See radiation poisoning for a more complete analysis of effects of various dosage levels.

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.

Unit conversion

The rem and millirem are variant metric units in widest use among the American public, industry, and government.[3]

However, SI units are increasingly encountered beyond academic, scientific, and engineering environments. The SI unit of dose equivalent is the sievert (Sv); conversion is straightforward, as 1 Sv = 100 rem:

1.0000 rem = 1000.0 mrem = 1 rem = 0.010000 Sv = 10.000 mSv = 10000 µSv
0.0010 rem = 1.0 mrem = 1 mrem = 0.000010 Sv = 0.010 mSv = 10 µSv
100.0000 rem = 100000.0 mrem = 1 Sv = 1.000000 Sv = 1000.000 mSv = 1000000 µSv
0.1000 rem = 100.0 mrem = 1 mSv = 0.001000 Sv = 1.000 mSv = 1000 µSv
0.0001 rem = 0.1 mrem = 1 µSv = 0.000001 Sv = 0.001 mSv = 1 µSv

The style guide of the U.S. National Institute of Standards and Technology strongly discourages the authors of NIST publications from expressing doses in rem, in favor of recommending the SI unit.[4] For industries and firms that do not require the sole use of SI, however, the unit rem is often preferred.

See also

References

  1. ^ The Effects of Nuclear Weapons, Revised ed., US DOD 1962, p. 579
  2. ^ The Effects of Nuclear Weapons, Revised ed., US DOD 1962, pp. 592–593
  3. ^ Office of Air and Radiation; Office of Radiation and Indoor Air (May 2007). "Radiation: Risks and Realities" (in English) (PDF). Radiation: Risks and Realities. U.S. Environmental Protection Agency. p. 2. http://www.epa.gov/rpdweb00/docs/402-k-07-006.pdf. Retrieved 19 March 2011. "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." 
  4. ^ Guide for the Use of the International System of Units (SI), U.S. National Institute of Standards and technology.