U.S. Armed Forces Nuclear, Biological and Chemical Survival Manual by Dick Capt. USN (ret) Couch

Author:Dick, Capt. USN (ret) Couch [DICK COUCH, CAPTAIN, USNR (RET.)]
Language: eng
Format: epub
Publisher: Basic Books
Published: 2011-12-26T05:00:00+00:00

Units of Radiation

The radiation absorbed dose (rad) is a measure of the energy deposited in matter by ionizing radiation. This terminology is being replaced by the International System skin dose unit for radiation absorbed dose, the gray (Gy): 1 Gy = 100 rad; 10 milligray (mGy) = 1 rad; 1 rad = 1 centigray (cGy). The dose in gray is a measure of absorbed dose in any material. The unit for dose, gray, is not restricted to any specific radiation, but can be used for all forms of ionizing radiation. Dose means the total amount of energy absorbed per gram of tissue. The exposure could be single or multiple and either short or long in duration.

Dose rate is the dose of radiation per unit of time.

Free-in-air dose refers to the radiation measured in air at a certain point. Free-in-air dose is easy to measure with current field instruments, and more meaningful doses, such as midline tissue dose or dose to the blood-forming organs, may be estimated by approximation. Military tactical dosimeters measure the free-in-air doses.

Different radiation types have more effects as their energy is absorbed in tissue. The difference is adjusted by use of the quality factor (QF). The dose in rads times the QF yields the rem, or radiation equivalent man. The international unit for this radiation equivalency is the sievert (Sv) and is appropriately utilized when estimating long-term risks of radiation injury.

Since the QF for X-ray or gamma radiation = 1, then for pure gamma radiation:

100 rad = 100 cGy = 1,000 mGy = 1 Gy = 1 Sv = 100 rem

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