Thursday, March 17, 2011

Radiation Levels - FAQ

What's the Difference Between Roentgen, Rad and Rem Radiation Measurements?

A: Since nuclear radiation affects people, we must be able to measure its presence. We also need to relate the amount of radiation received by the body to its physiological effects. Two terms used to relate the amount of radiation received by the body are exposure and dose. When you are exposed to radiation, your body absorbs a dose of radiation.

As in most measurement quantities, certain units are used to properly express the measurement. For radiation measurements they are:


* Roentgen: The roentgen measures the energy produced by gamma radiation in a cubic centimeter of air. It is usually abbreviated with the capital letter "R". A milliroentgen, or "mR", is equal to one one-thousandth of a roentgen. An exposure of 50 roentgens would be written "50 R".

* Rad: Or, Radiation Absorbed Dose recognizes that different materials that receive the same exposure may not absorb the same amount of energy. A rad measures the amount of radiation energy transferred to some mass of material, typically humans. One roentgen of gamma radiation exposure results in about one rad of absorbed dose.

* Rem: Or, Roentgen Equivalent Man is a unit that relates the dose of any radiation to the biological effect of that dose. To relate the absorbed dose of specific types of radiation to their biological effect, a "quality factor" must be multiplied by the dose in rad, which then shows the dose in rems. For gamma rays and beta particles, 1 rad of exposure results in 1 rem of dose.

Other measurement terms: Standard International (SI) units which may be used in place of the rem and the rad are the sievert (Sv) and the gray (Gy). These units are related as follows: 1Sv = 100 rem, 1Gy = 100 rad. Two other terms which refer to the rate of radioactive decay of a radioactive material are curie (Ci) and becquerel (Bq).

Bottom Line: Fortunately, cutting through the above confusion, for purposes of practical radiation protection in humans, most experts agree (including FEMA Emergency Management Institute) that Roentgen, Rad and Rem can all be considered equivalent. The exposure rates you'll usually see will be expressed simply in terms of roentgen (R) or milliroentgen (mR).

Source: http://www.radmeters4u.com/#1b


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The radiation levels at Fukushima is about 36,000 microSieverts per hour.That works out to


0.030168  Roentgen/hour (numerical equivalent)


Now compare to Chernobyl
Location Radiation (roentgens per hour) Sieverts per hour (SI Unit)
Vicinity of the reactor core 30,000 300
Fuel fragments 15,000–20,000 150-200
Debris heap at the place of circulation pumps 10,000 100
Debris near the electrolyzers 5,000–15,000 50-150
Water in the Level +25 feedwater room 5,000 50
Level 0 of the turbine hall 500–15,000 5-150
Area of the affected unit 1,000–1,500 10-15
Water in Room 712 1,000 10
Control room, shortly after explosion 3–5 .03-.05
Gidroelektromontazh depot 30 .3
Nearby concrete mixing unit 10–15 .10-.15

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