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Measurement units

The SI unit of radioactivity is the Becquerel (Bq) - equivalent to an average disintegration rate of one per second.
Since the Becquerel is such a small unit, multiples such as kBq (103), MBq (106) and GBq (109) are normally used.
The older unit of radioactivity, still commonly used, is the Curie (Ci) - equivalent to the radioactivity of one gram of radium and is equal to 3.7 x 1010 disintegrations per second.

Because the Curie is such a large unit, fractions such as milliCurie (mCi, 10-3Ci) and microCurie (µCi, 10-6Ci) are normally used.


Equivalence of Bequerel and Curie units of radioactivity

1μCi = 37kBq
1mCi = 37MBq
1Ci = 37GBq
1kBq = 27nCi
1MBq = 27μCi
1GBq = 27mCi

Radioactivity measurement

The radioactivity of a radiopharmaceutical is most commonly described in terms of the Radioactivity Concentration, for example MBq per ml of solution.

So as well as knowing the amount of radioactivity in a sample it is often also necessary to know its volume. This is normally measured either by weighing, by using graduated vials, or by drawing the sample into a syringe.

Measurement of low levels of radioactivity

Measurement of intermediate-high levels of radioactivity