Specific activity Specific activity Specific activity is the activity per quantity of a radionuclide and is a physical property of that radionuclide. Activity is a quantity related to radioactivity. The SI unit of activity is the becquerel (Bq), equal to one reciprocal second. The becquerel is defined as the number of radioactive transformations per second that occur in a particular radioactive isotope. Its related non-SI unit equivalent is the Curie (Ci) which is transformations per second. Since the probability of radioactive decay for a given radionuclide is a fixed physical quantity (with some slight exceptions, see changing decay rates), the number of
Centimetre–gram–second system of units base units are therefore the same in both systems, and there is an unambiguous one-to-one correspondence of derived units: Thus, for example, the CGS unit of pressure, barye, is related to the CGS base units of length, mass, and time in the same way as the SI unit of pressure, pascal, is related to the SI base units of length, mass, and time: Expressing a CGS derived unit in terms of the SI base units, or vice versa, requires combining the scale factors that relate the two systems: The conversion factors relating electromagnetic units in the CGS and SI systems