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specific activity[spə′sif·ik ak′tiv·əd·ē]
The activity of a radioisotope of an element per unit weight of element present in the sample.
The activity per unit mass of a pure radionuclide.
The activity per unit weight of a sample of radioactive material. In these three cases, specific activity can be expressed in such units as millicuries per gram, disintegrations per second per milligram, or counts per minute per milligram.