Specific activity several other biomedical applications. 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
2019 redefinition of SI base units values associated with the following constants of nature: The seven definitions above are rewritten below with the derived units (joule, coulomb, hertz, lumen and watt) expressed in terms of the seven base units (second, metre, kilogram, ampere, kelvin, mole and candela), according to the updated 9th edition of the SI Brochure (2018). In the list that follows, the symbol sr stands for the dimensionless unit steradian. As part of the redefinition, the international prototype kilogram was retired and definitions of the kilogram, the ampere, and the kelvin were replaced. The definition of the mole was revised. These changes have the