Glossary & Units

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video 'Measuring Radiation'

Radioactivity, Radiation & Irradiation

​Units of radi​oactivity:

The Becquerel (Bq) is the SI unit of radioactivity.  One Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays per second.  The Curie (Ci) is the non-SI unit of radioactivity that is most commonly used by the industrial irradiation industry.  The Ci is defined as 1Ci = 3.7 x 10,000,000,000 decays per second.

1Ci = 37GBq       1GBq = 27mCi
1kCi = 37TBq      1TBq = 27Ci
1MCi = 37PBq     1PBq = 27kCi

Specific activity:

This is the level of radioactivity (Bq or Ci) per unit mass, normally expressed as Ci/g within the manufacture and specification of industrial Cobalt-60 sources. 


Ionising radiation:

Ionising radiation is radiation that has enough energy to liberate an electron from an atom or molecule, ionising it.  Gamma radiation produced by Cobalt-60 sources is ionizing radiation and it is therefore suitable for sterilisation and material modification.


The process of exposing a material or articles to a source of ionising radiation.  One method of industrial irradiation is the exposure of product to irradiation generated by a Cobalt-60 source.  Click here to find out more about Cobalt-60 and Gamma Irradiation.


Dose & Dosimetry


Dose is a general term applied to quantify the level of ionising radiation received or absorbed by a body with which it interacts.    

Absorbed dose:

The gray (Gy) is the SI unit of absorbed radiation dose.  One gray is defined as the absorption of one joule of energy, in the form of ionizing radiation, per kilogram of matter.  The rad is a non-SI unit of absorbed radiation dose and is less commonly used by the industrial irradiation industry.

1kGy =100krad        1rad = 10mGy
10kGy = 1Mrad        1krad = 10Gy
25kGy = 2.5Mrad     1Mrad = 10kGy

Equivalent dose:

Equivalent dose is a measure of adsorbed radiation that attempts to account for the biological damage to living tissue by ionizing radiation.  It is therefore used for assessing the health risk of radiation exposure.  The sievert (Sv) is the SI unit of equivalent radiation dose.  The rem is a less widely used unit and conversion is simply 1Sv = 100rem 

Dose rate:

This is the rate at which ionising radiation is being absorbed.  It is expressed as dose received per unit time and usually measured in millisieverts per hour (mSv/hr) or millirem per hour (mrem/hr). 


Dosimetry is the measurement of absorbed dose to a product using dosimeters.  This process is necessary within industrial irradiation to confirm that all parts of a treated product have received sufficient dose to achieve the desired effect.


A dosimeter is a device used to measure absorbed dose to a product.  Common types used within industrial irradiation include perspex, film, alanine and cericcerous dosimeters each of which have a measurable and reproducible response to radiation.

Dose uniformity ratio (DUR):

This is the ratio of the maximum dose divided by the minimum dose, sometimes called the overdose ratio.  Within industrial irradiation it is usually desirable to operate with the lowest possible DUR as any unnecessary dose to product is inefficient and potentially damaging to some products.