Radiation Units
Measuring:
Measuring radioactivity
The nuclei of certain atoms are unstable and spontaneously disintegrate emitting radiation (alpha-particles, beta-particles or gamma rays). This changes the nature of the nucleus, and so the atom transforms (decays) into a different type of atom.
The radioactivity of a given amount of material is the number of nuclear decays that take place per unit of time.
Radioactivity units used:
- becquerel (Bq) is the SI unit of radioactivity equal to one nuclear decay per second. 1 Bq = 1 / s
- Therefore, an amount of material that produces one nuclear decay per second, is said to have a radioactivity of 1
- Bq exabecquerel (Ebq) = 1018 Bq
Measuring exposure to radioactivity
Ionizing radiation (such as alpha, beta and gamma radiation) is a very high-energy form of electromagnetic radiation, and can strip electrons from the atoms in the material through which it passes. This may damage human cells, causing death to some cells and modifying others.
Dose is a measure of the amount of energy from ionizing radiation deposited in a specified material.
Absorbed dose is the absorbed energy per unit mass.
Unit of absorbed dose used:
- gray (Gy) is the SI unit of absorbed dose, which is a joule per kilogram (J kg–1)
Effective dose is the absorbed dose multiplied by a factor that takes into consideration the type of radiation and the susceptibility of various organs and tissues to development of a severe radiation-induced cancer or genetic effect. Moreover, it applies equally to external and internal exposure and to uniform or non-uniform irradiation.
Units of effective dose used:
- sievert (Sv) is the SI unit of effective dose. Its units are J kg–1.
- millisievert (mSv) 1 mSv = 0.001 Sv
Source & © Further information on the International System of Units (SI) is provided by the International Bureau of Weights and Measures (BIPM)
www.bipm.fr/en/si/derived_units/2-2-2.html 
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