Which indicates the amount of radioactive substance in a sample or source?

The amount of radioactive substance in a sample or source is indicated by activity. Activity refers to the rate at which a radioactive material decays and is measured in terms of disintegrations per second, typically expressed in units such as becquerels (Bq) or curies (Ci). This concept is fundamental in nuclear medicine and radiology, as it helps determine how much radiation is being emitted from a source and influences the effectiveness and safety of diagnostic and therapeutic procedures.

In contrast, half-life is the time it takes for half of the radioactive atoms in a sample to decay, which provides information about the stability and longevity of the radioactive material but does not indicate the current amount present at a given moment. Dosage refers to the total amount of radioactive material administered to a patient, reflecting exposure for therapeutic or diagnostic purposes, but it does not encompass the concept of activity itself. Exposure typically pertains to the amount of radiation that a material or person is subjected to rather than the rate of decay of the radioactive substance.