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Radiation Terminology

International events can be confusing as a result of differences in terminology and units used when communicating event status. The two primary terms that are important to understanding ionizing radiation are activity and dose. Simple explanations of these terms are provided below.

Activity or radioactivity, describes the amount of radioactive material present. This term may be used to indicate a total amount of radioactivity present, as in the total amount of radioactive material contained in a location. It may also be used to indicate the amount of radioactivity spread across a surface area (e.g., surface contamination level), or in a volume (e.g., contaminant concentration). Scientifically, it is the measure of radioactive disintegrations per unit of time.

Units:

The traditional system used in the United States is curies. The international system used in most of the world is becquerel.

Example:

Activity is often expressed as becquerels per liter. This is similar to a recipe calling for a teaspoon of salt per gallon of water. It is the amount of material present in the volume you have.

Units of Activity	Units
37	giga becquerel	}per volume or area or total
37,000	mega becquerel
37,000,000,000	becquerel (Bq)
1	curie (Ci)
1000	millicurie
1,000,000	microcurie
1,000,000,000,000	picocurie

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Describes the amount of energy deposited in tissue as a result of exposure to ionizing radiation. This term may be used to indicate the total dose received as the result of an exposure to radiation. It may also be expressed as a dose rate, indicating the amount of dose received in a unit of time (e.g., per minute or hour). Scientifically, dose is expressed as a total effective dose equivalent for evaluating radiation doses to people.

Units:

The traditional system used in the United States is rem. The international system used in most of the world is Sievert (Sv)

Example:

The average dose to a US citizen from radiation that occurs in our natural environment is 340 millrem (0.340 rem) per year. This is equivalent to 3.4 millisieverts or 0.0034 Sieverts.

Equivalent Quantities	Units of Radiation Dose
0.001	rem	}per hour or total
1	milli rem
1000	micro rem
0.00001	Sv
0.01	milli Sv
10	micro Sv

Click here to use our pop-up conversion tool

For more details please visit: http://hps.org/public information/radterms/