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The rad (radiation absorbed dose) is a unit of absorbed radiation dose, with symbol rad. The rad was first proposed in 1918 as "that quantity of X rays which when absorbed will cause the destruction of the [malignant mammalian] cells in question..."^[1] It was defined in CGS units in 1953 as the dose causing 100 ergs of energy to be absorbed by one gram of matter. It was restated in SI units in 1970 as the dose causing 0.01 joule of energy to be absorbed per kilogram of matter.

The United States Nuclear Regulatory Commission requires the use of the units curie, rad, and rem as part of the Code of Federal Regulations 10CFR20.

However, it is now superseded in the SI by the gray; 100 rad are equal to 1 gray. The continued use of the rad is "strongly discouraged" by the author style guide of the U.S. National Institute of Standards and Technology.^[2]

To gauge biological effects the dose in rads is multiplied by a 'quality factor' which is dependent on the type of ionising radiation. The modified dose is now measured in rems (roentgen equivalent mammal, or man)^[3]. 100 rem = 1 sievert (Sv). A dose of under 100 rems is subclinical and will produce nothing other than blood changes. 100 to 200 rems will cause illness but will rarely be fatal. Doses of 200 to 1000 rems will likely cause serious illness with poor outlook at the upper end of the range. Doses of more than 1000 rems are almost invariably fatal^[4].

[edit] See also

• Radiation poisoning
• Röntgen
• Röntgen equivalent man (rem)
• Sievert
• Ionizing radiation

[edit] References

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