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There are a few scales that one can use to measure radiation. Depending upon your application, one scale
may be better than the others.
Radiation Measurements
Roentgen: Is the measurement of energy produced by Gamma or X-Ray radiation in a cubic centimeter of
air. It is abbreviated with the capital "R". One milliroentgen, abbreviated "mR" is one-thousandth of a
roentgen. One microroentgen, abbreviated "uR" is one-millionth of a roentgen.
RAD: Radiation Absorbed Dose. Original measuring unit for expressing the absorption of all types of ion-
izing radiation (alpha, beta, gamma, neutrons, etc) into any medium. One rad is equivalent to the absorp-
tion of 100 ergs of energy per gram of absorbing tissue.
REM: Roentgen Equivalent Man is a measurement that correlates the dose of any radiation to the biologi-
cal effect of that radiation. Since not all radiation has the same biological effect, the dosage is multiplied by
a "quality factor" (Q). For example, a person receiving a dosage of gamma radiation will suffer much less
damage than a person receiving the same dosage from alpha particles, by a factor of three. So alpha parti-
cles will cause three times more damage than gamma rays. Therefore, alpha radiation has a quality factor
of three. Following is the Q factor for a few radiation types.
The difference between the rad and rem is that the rad is a measurement of the radiation absorbed by the
material or tissue. The rem is a measurement of the biological effect of that absorbed radiation.
For general purposes most physicists agree that the Roentgen, Rad and Rem may be considered equivalent.
System International (SI) of Units
The System International of unit for radiation measurements is now the official system of measurements.
This system uses the "gray" (Gy) and "sivert" (Sv) for absorbed dose and equivalent dose respectively.
The conversion from one system to another is simple:
14
Me asu reme nt of Ra di a tion
Radiation:
Beta, Gamma and X-rays
Thermal Neutrons
Fast n, a, and protons
Heavy and recoil nuclei
1 Sv = 100 rem
1 mSv = 100 mR (mrem)
1 Gy = 100 rad
1mGy = 100 mrad
Quality Factor (Q)
1
3
10
20
1 rem = .01 Sv
1 mR = .01 mSv
1 rad = .01 Gy
1 mrad = .01 mGy
Images SI, Inc.
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