Radiation—Units of measurement (conventional or SI)
The radiation level displayed on the LCD may be provided in conventional units mR/hr (one-second survey meter mode) and uR/hr (one-minute background radiation mode) or Systems International (SI) units of mSv/hr or uSv/hr. Both the time range and units are user selectable using jumpers on the front of the printed circuit board (pcb). This is explained later under “Use”.
A Little on the Measurement of Radiation
There are a few scales that one can use to measure radiation. Depending upon your application, one scale is may be better than the others.
Radiation Measurements
Roentgen: Is the measurement of energy produced by Gamma or Beta 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 ionizing radiation (alpha, beta, gamma, neutrons, etc) into any medium. One rad is equivalent to the absorption 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 biological 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 that a person receiving the same dosage from alpha particles, by a factor of three. So alpha particles 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
Radiation
Beta, Gamma and X-rays
Thermal Neutrons
Fast n, a, and protons
Heavy and recoil nuclei
Quality Factor (Q)
1
3
10
20
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 ab sorbed dose and equivalent dose respectively.
The conversion from one system to another is simple:
1 Sv = 100 rem
1 mSv = 100 mR (mrem)
1 Gy = 100 rad
1mGy = 100 mrad
1 rem = .01 Sv
1 mR = .01 mSv
1 rad = .01 Gy
1 mrad = .01 mGy
